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Copolymers of isotactic polypropylene (iPP) with 4-methyl-1-pentene (iPP4MP) were prepared with a highly isoselective homogeneous organometallic catalyst in a range of 4-methyl-1-pentene (4MP) concentrations between about 1.7 and 14 mol %. Crystallization from the melt at different crystallizations temperatures have been performed to study the effect of 4MP comonomeric units excluded from the crystals on the crystallization of α and γforms. All samples crystallize in mixtures of α and γforms, and for each sample, the fraction of γform increases with increasing crystallization temperature to achieve a maximum value fγ(max), which depends on the 4MP concentration. Compared to the homopolymer, the maximum fractional amount of γform fγ(max) rapidly increases with increasing 4MP content achieving the highest value of 92% at low 4MP concentration of 2.2 mol %, and decreases with a further increase of 4MP concentration. These data are compared with analogous data of the maximum amount of γform that develops in copolymers of iPP with ethylene and butene. This allows comparing the different effects of rejection of defects from the crystals, which produces interruption of the regular propene sequences and shortening of the length of the crystallizable sequences, the inclusion of defects into crystals of α and γforms, and the effect of the crystallization kinetics. Since 4MP comonomeric units are excluded from the crystals, the behavior of iPP4MP copolymers provides the sole interruption effect, which is highly efficient and produces the highest amount of γform of 92% at low 4MP concentration of nearly 2 mol %. The observed decrease of fγ(max) at higher 4MP concentrations is due to the too slow crystallization rate of the γform at these 4MP contents that induces the crystallization of the kinetically favored α form. In fact, crystals of γforms that develop in these copolymers are highly defective and show melting temperatures lower than those of the α form and, therefore, experience low undercooling at high crystallization temperatures. These results demonstrate that in metallocene iPP copolymers containing a significant amount of constitutional defects, the crystallization of the γform is favored because of the short regular propene sequences, whereas the crystallization of the α form is always kinetically favored.

The crystallization behavior of propene–ethylene (iPPC2), propene–butene (iPPC4), propene–pentene (iPPC5), and propene–hexene (iPPC6) isotactic copolymers, prepared with single center metallocene catalysis, is described. Thanks to the perfectly random distribution of comonomers along the macromolecules, these copolymers can be considered as model for the crystallization behavior of isotactic polypropylene (iPP) that is mainly defined by the average length of the regular propene sequences. A model of the crystallization behavior of iPP is described based on the definition of a double effect of defects (stereodefects and comonomers), the interruption effect of defects excluded from the crystals that shortens the length of the crystallizable propene sequences inducing crystallization of the γ form, and the effect of inclusion of defects in the crystals of α form, γ form or δ form that induces the crystallization of the form whose lattice is less disturbed by the defect.

A study of the structure and morphology of diblock copolymers composed of crystallizable blocks of polyethylene (PE) and syndiotactic polypropylene (sPP) having different lengths is reported. In both analyzed samples, the PE block crystallizes first by cooling from the melt (at 130 °C) and the sPP block crystallizes after at a lower temperature. Small angle X-ray scattering (SAXS) recorded during cooling showed three correlation peaks at values of the scattering vector, q1 = 0.12 nm−1, q2 = 0.24 nm−1 and q3 = 0.4 nm−1, indicating development of a lamellar morphology, where lamellar domains of PE and sPP alternate, each domain containing stacks of crystalline lamellae of PE or sPP sandwiched by their own amorphous phase of PE or sPP. At temperatures higher than 120 °C, when only PE crystals are formed, the morphology is defined by the formation of stacks of PE lamellae (17 nm thick) alternating with amorphous layers and with a long period of nearly 52 nm. At lower temperatures, when crystals of sPP are also well-formed, the morphology is more complex. A model of the morphology at room temperature is proposed based on the correlation distances determined from the self-correlation functions extracted from the SAXS data. Lamellar domains of PE (41.5 nm thick) and sPP (8.2 nm thick) alternate, each domain containing stacks of crystalline lamellae sandwiched by their own amorphous phase, forming a global morphology having a total lamellar periodicity of 49.7 nm, characterized by alternating amorphous and crystalline layers, where the crystalline layers are alternatively made of stacks of PE lamellae (22 nm thick) and thinner sPP lamellae (only 3.5 nm thick).

The crystallization from the melt in isothermal conditions of metallocene random propene-pentene isotactic copolymers (iPPC5) has been studied. All samples with pentene concentration between 0.5 and 10 mol % crystallize at any crystallization temperature in mixtures of α and γforms of isotactic polypropylene (iPP) and the amount of γform increases with increasing crystallization temperature up to a maximum (fγ(max)), which depends on pentene concentration. Pentene defects produce a shortening of the regular propene sequences that in turn induces crystallization of the γform. At concentrations higher than 6-7 mol %, pentene units are incorporated to a high extent in the crystals of α and trigonal forms, which are stabilized over the γform, and fγ(max) decreases. The maximum fraction of γform is, therefore, related to the average length of regular propene sequences and the degree of incorporation of defects in the crystals of α and γforms. The values of fγ(max) that develop in iPPC5 copolymers have been compared with those that develop in copolymers of iPP with ethylene (iPPC2), butene (iPPC4), and hexene (iPPC6) and in stereoirregular iPPs reported in the literature. Stereoirregular iPPs and iPPC2 copolymers give the same relationship between fγ(max) and the average length of regular propene sequences (LiPP), whereas iPPC4, iPPC5, and iPPC6 copolymers show different behaviors. In particular, iPPC5 copolymers exhibit a behavior intermediate between those of iPPC4 and iPPC6 copolymers. The relationship between fγ(max) and LiPP of iPPC5 copolymers fits perfectly between the relationships found for iPPC4 and iPPC6 copolymers, in agreement with the different types and sizes of comonomers and the different efficiencies of their interruption and inclusion effects. These data give evidence of the general view of the crystallization behavior of iPP, based on the definition of a double role exerted by defects, the interruption effect that shortens the regular propene sequences and favors crystallization of γform, and the effect of incorporation of defects into the crystalline unit cells of α and γforms, which favors crystallization of the form that better accommodates the defect into crystals. The relative efficiency of these two effects depends on the type and size of the defect. The different relationships between fγ(max) and LiPP are a result of the equilibrium between interruption and inclusion effects achieved by each defect and confirm that the crystallization of γform is a perfect indicator of the length of the regular propene sequences and may provide very detailed information on the molecular structure of iPP.

Isotactic polypropylene-block-polyethylene block copolymers (iPP-b-PE) composed of crystalline blocks of isotactic polypropylene (iPP) and linear polyethylene (PE) of different block lengths have been synthesized with a living and stereoselective pyridylamidohafnium catalyst. The structure and morphology of iPP-b-PE that develop upon crystallization from the melt are presented. Temperature and time resolved X-ray diffraction experiments in wide (WAXS) and small angles (SAXS) recorded during cooling from the melt indicate that PE blocks crystallize first upon cooling and the iPP block crystallizes at lower temperatures and nucleates over the crystals of PE formed before. The SAXS data indicate that PE lamellar stacks formed first at high temperature have higher periodicity of 30 nm, whereas iPP lamellar stacks formed after at lower temperature have lower periodicity of 11–12 nm. The crystallization of the iPP and PE blocks drives microphase separation and determines the final morphology leading to a lamellar morphology characterized by alternation of amorphous and crystalline layers. At nanoscale the morphology is characterized by alternating iPP and PE microdomains, each domain including stacks of lamellar crystals of iPP or PE of different periodicities, separated by the corresponding amorphous regions of iPP or PE. Polarized optical micrographs of the melt-crystallized samples show the presence of bundle-like crystals in samples with longer block of iPP and of small banded spherulites in samples with longer block of PE. The observation of banded spherulites typical of PE suggests that the crystallization of PE defines the global morphology and is not altered by the structure of the melt, confirming that crystallization of PE occurs first upon cooling from the melt.

We report the full characterization of a photocurable dimethacrylate-based formulation modified with small amounts (1 and 3 wt%) of a polystyrene-block-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP). The UV curable formulation is a mixture of bisphenol A bis(2-hydroxy-3-methacryloxypropyl)ether (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) and contains phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (Irgacure819) as photoinitiator. We demonstrate that the addition of a small amount of BCP in the uncured formulation is able to induce a phase separation at the nanometer scale. The nanoscale structure formed in the pre-cure stage is retained after the UV curing, so obtaining nanostructured solid cross-linked materials. The studied materials can be used in the manufacturing process of stereolithography and, therefore, in modern 3D printers. The ability to induce and control the formation of nanostructures in the material by adding BCPs in the formulations could open new opportunities to tailor and improve the properties of the 3D printed objects.

The crystallization behavior of butene-ethylene random isotactic copolymers prepared with a Ziegler-Natta catalyst, in particular the surprising crystallization of form II of isotactic polybutene in samples with a high ethylene concentration, provides novel evidence of the long-debated blocky molecular structure of these "random" copolymers.

The crystallization and thermal properties of copolymers of isotactic poly(1-butene) (iPB) with ethylene (iPBEt) synthesized with a Ziegler-Natta catalyst and ethylene (E) content between 7 and 45 mol % are presented. The crystallization properties provide evidence of a multiblock molecular structure of these copolymers. The samples have been separated in two or three fractions by standard fractionation in boiling solvents. Samples with ethylene concentration lower than 16 mol % surprisingly crystallize in form II of iPB, and crystallization of polyethylene also occurs for the maximum ethylene content of 45 mol %. Even more surprising is the result that the melting temperature of crystals of any polymorphic form of iPB that crystallize in these samples do not depend on the ethylene concentration. This suggests that long crystallizable butene sequences are present even at high ethylene concentration. In all fractions, the chains are composed of multiblocks where the comonomers are segregated, with blocks characterized by long crystallizable butene sequences and blocks with shorter butene sequences. In the different fractions, the average length of butene sequences is nearly the same. The different fractions are featured by different amounts of the constituting blocks.

Syndiotactic propene–hexene (sPPC6) and propene–octene (sPPC8) copolymers have been synthesized in a wide range of compositions with a syndiospecific metallocene catalyst. The samples are crystallized up to a comonomer content of nearly 20 mol% with crystallinity, melting and glass transition temperatures that decrease with increasing concentrations of comonomers. The copolymers show elastic properties that depend on the crystallization behavior. The as-prepared samples with a comonomer content lower than 2 mol% crystallize in mixtures of the helical form I and form II of syndiotactic polypropylene (sPP), the latter containing conformational kink band defects and the former containing a b/4 shift disorder. Both sPPC6 and sPPC8 copolymers crystallize from the melt in disordered modifications of form I characterized by disorder in the alternation of right- and left-handed two-fold helical chains along the axes of the orthorhombic unit cell of form I of sPP. At high crystallization temperatures, more ordered modifications of form I develop for samples with a low comonomer concentration and form II surprisingly crystallizes in samples with a high comonomer content. The crystallization of form II rather than the ordered form I in melt-crystallized samples is a valuable result because it indicates that it is possible to tune the polymorphic transformations and the elastic properties of these copolymers through tuning of the branches concentrations.

The mechanical properties of copolymers of syndiotactic polypropylene (sPP) with 1-hexene and 1-octene have been studied and correlated with the structural transformations occurring during stretching and relaxation. These copolymers crystallize in disordered modifications of form I of sPP, with crystallinity, melting, and glass-transition temperatures that decrease with increasing comonomer content. All copolymers show remarkable mechanical properties and elastic behavior, with great improvement of flexibility and ductility with respect to the sPP homopolymer already at small comonomer concentrations. For low comonomer content up to 4-5 mol %, the elastic recovery is associated to a reversible conformational phase transition between the trans-planar form III or the trans-planar mesophase and the helical form II, which gives an enthalpic contribution to the elasticity. As the comonomer content increases, the trans-planar conformation is progressively destabilized and the observed elastic properties are not associated with any conformational transformation during stretching and relaxation. In these cases, copolymers behave as conventional thermoplastic elastomers where elasticity is purely entropic and crystals only act as topological constraints of the elastomeric network. These copolymers represent an exemplary case of the possibility to combine in the same materials desired and apparently incompatible physical properties of elasticity, crystallinity, and strength by controlling the crystallization behavior, achieved by tailoring the chemical structure in the synthetic process.

The mechanical properties and elastic behavior of Ziegler-Natta isotactic 1-butene-ethylene (BuEt-ZN) copolymers, having a broad composition from 1.7 to 45.5 mol% of ethylene units, are studied. The multi-site nature of the catalytic system determines a non-uniform distribution of the comonomers along the polymer chains; the copolymers present a blocky microstructure and composed of fractions of chains made of long and short butene sequences, which can be separated by solvent fractionation procedures. Incorporation of ethylene induces improving of drawability and decrease of rigidity with respect to homopolymer, associated with the lower crystallinity, and outstanding elastomeric behavior when the ethylene amount exceeds 5.5 mol%. In these copolymers the presence of irregular fractions of chains with short butene sequences, showing crystallization of the defective and low-melting temperature form I′ upon aging of the amorphous at room temperature, is responsible for the good elasticity of the materials.

The mechanical properties and the structural transformations occurring during deformation of some commercial grades of ethylene/1-octene multiblock copolymers (OBCs) obtained from chain shuttling technology are analyzed. The samples are characterized by a statistical multiblock architecture, where soft and amorphous blocks with high octene concentration (approximate to 18.9 mol %) alternate with hard and crystalline blocks with low octene concentration (approximate to 0.5 mol %). The length of blocks (BL) and the number of blocks/chain (NB) change from chain to chain according to a statistical distribution. The selected samples have molecular mass in the range 85-130 kg/mol, percentage of hard segments in the range 15-27%, and a melting temperature of approximate to 120 degrees C. The average molecular masses of the hard blocks M-H and soft blocks M-S are in the ranges 2-3 kg/mol and 6-15 kg/mol, respectively, whereas the number of blocks/chain is in between 2 and 17. Even though the samples are characterized by similar octene concentration, small difference in molecular mass, and fractional content of hard blocks, they show remarkable differences of mechanical properties, depending on the average BL and NB values, encompassing from those of strong elastomers, in the case of samples with low block length and high number of blocks/chain, to those of soft elastomers, in the case of samples with high block length and low number of blocks/chain. The differences in the mechanical properties of OBC samples are amplified by stretching at high temperatures. Not previously stretched films obtained by compression molding show only partial recovery of the initial dimensions in mechanical cycles of stretching and releasing the tension, with values of recovered strain higher than 50% at 25 degrees C. However, the resultant specimens obtained by release of the tension show good elastomeric properties in a wide deformation range at 25 degrees C and, in the case of the samples with high strength, also at 60 degrees C. Fiber diffraction analysis reveals that by stretching at high deformation the orientation of the crystals is accomplished by mechanical melting and formation of an oriented amorphous phase, namely, involving the hard segments extracted from the crystals. Upon releasing the tension recrystallization occurs, and the high degree of orientation achieved by the crystals and amorphous phase is lost.

The mechanical behavior of propylene−pentene isotactic copolymers synthesized with a single-center organometallic catalyst in a broad interval of pentene (Pe) concentration, from 3 to 50 mol %, is analyzed. All copolymers show flexible behavior with very high deformation at breaking. The presence and entrance of Pe counits in α and δ forms of isotactic polypropylene (iPP) transform a strong and fragile iPP homopolymer into ductile and flexible materials. The stress at yield decreases as the Pe content increases, but a different behavior has been observed for samples in the α form or in the δ form. In samples in the α form, from 3 to 8.8 mol % of Pe, the stress at yield increases as the thickness of crystalline lamellae increases, while in samples in the δ form containing higher Pe counits, it decreases as the thickness of lamellae increases and Pe content increases. Phase transition of the α form in the mesophase and crystallization of the δ form, in samples with 8−11 mol % of Pe, occur upon deformation and are correlated to the strain-hardening observed at high strain.

The crystallographic micromechanical model (CMM) for prediction of yield stress of semicrystalline polymers, based on the thermally activated nucleation of screw dislocations at the boundary of lamellar crystals, is employed to interpret the yield behavior by effect of uniaxial drawing of some isotactic copolymers of propylene with different comonomeric units such as ethylene, 1-butene, 1-pentene, 1-hexene, and 1-octadecene (iPPEt, iPPBu, iPPPe, iPPHe and iPPOc, respectively). The samples are characterized by a random distribution of the comonomeric units. The CMM predicts that the values of stress at yield depend on the thickness of the lamellar crystals and relies on two parameters, i.e. the critical value of the free energy needed for nucleation and activation of a screw dislocation in crystallographic planes parallel to the chain axes, and the shear modulus relative to the planes of slip for the dislocations, whereas the role of the interlamellar amorphous phase is neglected. The aim of this study is to analyze to which extend the thickness of the lamellar crystals influences the yield stress for a series of propylene-based copolymers having a well-defined chain microstructure and crystallized in the α and/or γ forms, but possessing different degree of crystallinity, thickness of the lamellar crystals, stability of the crystals and also intrinsic flexibility of the portions of chains belonging to the amorphous regions, in relation with the degree of inclusion (exclusion) of the co-monomers in (from) the crystals. It is shown that, in the case of copolymers with a comonomer concentration lower than a threshold, the yield stress increases with increasing the lamellar thickness regardless of type of comonomer, the relative amount of the two polymorphs (α and γ forms), and the degree of inclusion, in good agreement with the predictions of the CMM approach. For copolymers with comonomer concentration higher than a threshold and bulky side groups, which are excluded from the crystals, the thickness of the lamellar crystals becomes low and the role of the chains in the amorphous regions becomes not negligible. In the case of copolymers with high butene concentration, instead, the stress at yield decreases with increasing the thickness of the lamellar crystals, because the high degree of inclusion of butene units in the crystals induces not only an increase in the thickness of the lamellar crystals, but also a decrease in the stability of the crystals, and the role of the chains located in the interlamellar amorphous layers acting as tie-molecules may not be disregarded.

Nanoporous/nanocomposite thin films with controlled morphology at nanoscale were prepared onto transparent and conductive indium tin oxide (ITO) supports by exploiting the self-assembly of a lamellar polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymer (BCP). A perpendicular orientation of PS and PMMA lamellar nanodomains was achieved by grafting a random PS-r-PMMA copolymer to the ITO supports and successive thermal annealing. Stable and reproducible nanoporous morphologies, characterized by PS lamellar nanodomains of width equal to ≈20 nm alternating to nanochannels of width equal to ≈8 nm, were obtained by irradiating the samples with an appropriate UV-C dose able to fix the relative arrangement of PS domains through activation of cross-linking reactions and selective removal of PMMA blocks. Nanoporous hybrid composites with a stable morphology were obtained either by applying the UV irradiation protocol to BCP nanocomposites characterized by selective inclusion of zinc oxide (ZnO) nanoparticles (NPs) in the PS domains (nanocomposite first/nanopores after) or by selective infiltration of cadmium selenide (CdSe) NPs in the nanochannels left free by PMMA removal through UV irradiation (nanopores first/nanocomposite after), demonstrating the strenght of the approach.

A study of the crystallization behavior and kinetics of form II-form I transition in isotactic butene-ethylene copolymers (iPBEt) prepared with Ziegler-Natta catalyst with ethylene concentration in the range 9–44 mol% is presented. The samples have been separated with boiling solvents in different fractions containing chains with different ethylene concentration. Crystallization of form II from the melt is observed in each fraction even at high ethylene concentration, up to nearly 16 mol%. For higher ethylene content the samples do not crystallize from the melt but still crystallize during aging at room temperature in form I′. The comparison with the crystallization behavior of iPBEt copolymers prepared with homogeneous metallocene catalysts, characterized by a random distribution of ethylene units, has shown that the form II-form I transformation in Ziegler-Natta copolymers is much slower than in metallocene copolymers having the same ethylene concentrations and for the metallocene copolymers a low concentration of ethylene units of nearly 6 mol% is sufficient to prevent crystallization from the melt of form II. This indicates that in the chains of Ziegler-Natta iPBEt copolymers the regular butene sequences interrupted by the ethylene units are much longer than those of the chains of copolymers prepared with metallocene catalysts of the same ethylene concentration, giving further evidence of the multiblock structure of Ziegler-Natta iPBEt copolymers.

Isotactic propylene-butene copolymers [i(P-co-B)] with precise and controlled molecular structures were synthesized with various organometallic catalysts having different stereoselectivities. Stereoregular and stereodefective samples of i(P-co-B) with 1-butene (B) content variable in the whole range of composition were synthesized. All samples crystallize regardless of composition, indicating cocrystallization of propene and 1-butene units, which are incorporated in the unit cells of polymorphic forms of isotactic poly(propylene) (iPP) and isotactic poly(1-butene) (iPB). The copolymers show a continuum change of crystal morphology with the composition, transforming from big spherulites to bundle-like and needle-like crystals, to granular crystals. The cocrystallization allows maintaining high crystallinity of copolymers for any composition and provides an opportunity to develop outstanding mechanical properties that can be tailored by changing the isotacticity and composition. This allows, ideally, combining in the same material the different properties of stiffness of iPP and flexibility of iPB. These copolymers show, indeed, mechanical properties intermediate between iPP and iPB, ranging from stiffness/brittleness and ductility/flexibility depending on the composition and isotacticity, with high strength and Young's modulus that may be regulated by the stereoregularity of the iPP and iPB sequences, which is, in turn, dictated by the catalyst structure.

In this review, the phenomenon of polymorphism in polymers is discussed on the basis of the thermodynamic stability of different polymorphs that defines the conformations of chains in the crystalline lattice and the packing mode. In particular, we show that the symmetry and energy stability of the chain conformation, the crystal density and entropy of packing, and the presence of defects and disorder in the crystals are the main factors that define the mode of crystallization of polymers and induce polymorphism. How specific polymorphs are selected and the effects of the molecular structure and processing conditions on polymorphism are analyzed. How crystallization of particular polymorphs affects the material's properties and ultimate applications is also discussed. The polymorphic behaviors of isotactic polypropylene and poly(1-butene) are described as examples of how processing and the controlled modification of the molecular structure of polyolefins using methods of controlled synthesis that allow controlled incorporation of configurational and constitutional defects may drive crystallization of a desired polymorph. The possibility to select a particular polymorph using these strategies results in a tool to tailor the physical and mechanical properties of polymers.

The crystalline morphology of ethylene/1-octene (EO-BC) statistical multiblock copolymers is investigated by transmission electron microscopy (TEM). EO-BCs are an important class of thermoplastic elastomers characterized by alternating crystalline, octene-poor, hard blocks and amorphous, octene-rich, soft blocks and statistical distribution of block length (BL) and number of blocks/chain (NB). Adopting similar crystallization conditions, samples with only subtle differences in the chain microstructure, are shown to display different solid-state morphology as probed by TEM and different melt rheology. In particular, the homogeneous or heterogeneous lamellar morphology which develops in the solid state reflects the tendency of the samples to show homogeneous or heterogeneous melt-rheology, respectively. As EO-BCs are a reactor blend of non-uniform chains, it is argued that the solid state and melt phase behavior of EO-BCs is controlled by differences in the relative abundance of chains including a prevalence of hard blocks of short and/or high length.

The phase behavior of ethylene/propylene(/diene) (EP(D)M) co- (and ter-)polymers characterized by ethylene content in the range 64–78 wt%, and comparatively low level of crystallinity, in the range 1–15%, is analyzed during stretching, through collection of wide angle X-ray scattering data. All samples experience crystallization by effect of stretching, but whereas for the samples with ethylene content ≥71% crystallinity starts increasing already after yielding, the nearly amorphous sample, with 64 wt% ethylene content, experiences crystallization only at strain above a threshold (≈170%). In all cases, a high degree of orientation of the amorphous phase is achieved already at low deformations. It is shown that for the samples with high ethylene content, the pre-existing crystals undergo initial fragmentation and/or mechanical melting at low deformations, and successive oriented recrystallization at higher deformations. The role of oriented amorphous phase, along with the role of pre-existing crystals as nuclei able to foster further crystallization is highlighted.

In this paper the morphologies and crystallization properties of crystalline block copolymers are reviewed. The equilibrium morphologies expected in crystalline-amorphous diblock copolymers and the different modes of crystallization, such as, breakout, templated crystallization, confined crystallization and pass through crystallization are described. The effects of confinement on crystallization mode and crystallization kinetics are also analyzed in detail. The paper is focused on the morphologies and nanostructures produced in crystalline block copolymers based on polyolefins. Early studies performed on block copolymers containing highly defective polyethylene block, synthesized by hydrogenation of block copolymers containing 1,4-polybutadiene blocks prepared by classic anionic living polymerization, are described in the first part of the paper. Then, the paper features recent advances in the synthesis and characterization of crystalline block copolymers containing stereoregular polyolefins, such as stereoregular polypropylene and linear polyethylene prepared using novel organometallic catalysts able to promote the living and stereoselective polymerization of α-olefins. Strategies for creating nanoscale patters exploiting the ability to induce desired orientations of the crystalline phase through epitaxial crystallization of the crystallizable blocks on crystalline substrates are described. According to this strategy, the desired orientations of the crystalline phase may be suitably designed and act as templates to create the desired final ordered nanostructure.

The adsorption of myoglobin (Mb) onto nanoporous thin films build up using block‐copolymers (BCPs) is analyzed. The nanoporous thin films, fabricated by exploiting self‐assembly of lamellar BCPs and the concept of sacrificial block, are characterized by a well‐defined morphology containing nanochannels of width ≈20 nm delimited by polystyrene (PS) domains, decorated with pendant poly(ethylene oxide) (PEO) chains. The adsorption of Mb onto the nanoporous material is studied by means of UV–visible spectroscopy, quartz crystal microbalance, and neutron reflectometry measurements. In order to determine the role of nanopores, experiments are also conducted by using supports made of nonporous PS thin films and nude glass slides. The results indicate that the BCP‐nanoporous material exhibits a remarkably higher adsorption capability than PS and glass. As PEO exhibits a low degree of protein adsorption, this result may be essentially attributed to the presence of the nanopores. The large surface area, the opened pore structure, and the trapping effect of the pores are the main factors determining the increased Mb adsorption capability of the BCP‐based support. Yet, the presence of PEO chains decorating the PS walls at porous surface does not prevent Mb biomolecules to establish good interactions with the support.

The development of a highly oriented fiber morphology by stretching low stereoregular isotactic polypropylene (iPP) samples is studied at two different temperatures. The structural and morphological transformations occurring during deformation are followed in real time by collecting in situ wide (WAXS) and small-angle (SAXS) X-ray scattering data. WAXS analysis reveals that the disordered γ form initially present in the samples gradually transforms by stretching into the oriented mesomorphic form of iPP at room temperature and in well-oriented crystals of α form at 60 °C. SAXS analysis indicates that regardless of the stretching temperature, a cascade of events occurs at mesoscale during deformation, consisting in interlamellar separation and lamellar reorientation at low deformations, followed by formation of chevron-like textures, lamellar fragmentation, and cavitation. Moreover, different fibrillary morphologies develop at the different temperatures. In fact, the fibrillary morphology that develops at room temperature is characterized by rod-like fibrillary entities containing mesomorphic aggregates separated by amorphous regions, placed at uncorrelated longitudinal and lateral distances. Instead, the morphology that develops at 60 °C consists of a fibrillary network for the more stereoregular sample and of rod-like fibrillary entities for the less stereoregular sample, and both morphologies include well-oriented crystals of α form alternating with amorphous regions which are periodically stacked along the stretching direction and are placed at uncorrelated lateral distance. We argue that the difference in structural arrangement of amorphous and crystalline regions at mesoscale in the stretched samples are mainly due to the increase of the mobility of the chains in the amorphous matrix at higher temperature, which facilitates the relaxation of the amorphous phase and the changes in the relative arrangement of the crystalline domains.

Highly ordered lamellar nanostructures with high orientation of lamellar microdomains have been obtained by epitaxial crystallization of crystalline diblock copolymers constituted by crystalline polyethylene (PE) linked to an amorphous block of a propene-ethene random copolymer (EP). The epitaxial crystallization onto crystals of p-chlorobenzoic acid induces formation of crystalline PE lamellae highly aligned along one direction, resulting in ordered lamellar nanostructures with perfectly aligned layers of crystalline PE alternating to amorphous layers of EP block. The periodicity of the lamellar structure can be modulated by modifying the molecular mass of the amorphous EP block. Epitaxy has been coupled with the technique of gold decoration so that the ordered nanostructures produced by epitaxy act as template for the formation of long, straight, and parallel rows of gold nanoparticles.

Ethylene-co-norbornene copolymers were synthesized by a dual catalyst system at three concentrations of norbornene in the feed and variable amounts of ZnEt2, as a possible chain transfer agent. The dual catalyst system consists of two ansa-metallocenes, isopropyliden(&eta, 5-cyclopentadienyl)(&eta, 5-indenyl)zirconium dichloride (1) and isopropyliden(&eta, 5-3-methylcyclopentadienyl)(&eta, 5-fluorenyl)zirconium dichloride (2), activated with dimethylanilinium tetrakis(pentafluorophenyl)borate, in presence of TIBA. Values of norbornene content, molecular mass, glass transition temperature, and reactivity ratios r11 and r21 of copolymers prepared in the presence of 1+2 are intermediate between those of reference copolymers. The study of tensile and elastic properties of ethylene-co-norbornene copolymers (poly(E-co-N)s) gave evidence that copolymers were obtained in part through transfer of polymer chains between different transition metal sites. Mechanical properties are clearly different from those expected from a blend of the parent samples and reveal that copolymers obtained in the presence of 1+2 and ZnEt2 consist of a reactor blend of segmented chains produced by exchange from 2 to 1 and 1 to 2 acting as the ideal compatibilizer of chains produced by the chain transfer from 1 to 1, and from 2 to 2.

Ethylene

The synthesis of a poly(3,5-tricyclo[2.2.1.0(2,6)]heptylene) [poly(norbornadiene) (PNBD)] mediated by the TiCl4/Et2AlCl catalytic system is reported. This polymer is characterized by a rigid nortricyclene repeating structure and unique 3,5-enchainment and is obtained through a transannular cationic polymerization of norbornadiene involving both double bonds. The new PNBD is crystalline with high glass transition and melting temperatures due to the rigid tricyclic repeating structure. C-13 NMR spectra indicate that the chains of PNBD contain only exo/exo (xx) and exo/endo (xn) nortricyclene repeating monomeric units. Models of the chain conformation and crystal structure of PNBD are also reported. Models of low conformational energy of isotactic and syndiotactic chains of PNBD have been obtained from the regular enchainment of xx and xn units. The model of the isotactic (xx)(m) chain with s(2/1) helical symmetry assumes a nearly trans-planar conformation, whereas the models of the syndiotactic (xn-xn)(m) and (nx-xn)(m) chains with tc and ti symmetries, respectively, assume the conformations (TG(-)G(-)TG(+)G(+))(n) and (G(-)TTTG(+)T)(n), respectively. Ideal limit ordered models of the crystal structure have been obtained from the X-ray powder diffraction data and the conformational energy analysis. A good agreement between experimental and calculated powder diffraction profiles has been obtained for a limit ordered model of packing of syndiotactic chains (nx-xn)(m) of PNBD with ti symmetry in an orthorhombic unit cell with axes a = 6.6 angstrom, b = 11.0 angstrom, and c = 6.84 angstrom according to the monoclinic space group P2(1)/c. The real crystal structure of PNBD is disordered because of the possible presence of configurational disorder in the chains due to possible random enchainment of nortricyclene monomeric units in the xx, xn and nx configurations that produces conformational and packing disorder.

The crystallization behavior and the morphology of blends obtained by mixing a highly crystalline and isotactic poly(1-butene) (iPB) and a copolymer of isotactic polypropylene (iPP) with 26 mol% of 1-hexene (C3C6 copolymer) have been studied. The C3C6 copolymer does not crystallize from the melt but the amorphous sample crystallizes into the trigonal form of iPP by aging at room temperature. All the blends crystallize from the melt in form II of iPB and the aging at room temperature induces transformation into form I and crystallization of the C3C6 copolymer. Both the melt crystallization of form II and its transformation into form I of iPB are retarded in the blends by the presence of the C3C6 component, whereas the crystallization from amorphous phase of the C3C6 copolymer is accelerated thanks to the nucleating effect of the preformed iPB crystals. A good inter-mixing of the two components occurs by solution blending. However, the initial state of the blend obtained by precipitation from solution is not at equilibrium and at 200 °C phase separation takes place by effect of spinodal decomposition, and the degree of demixing increases with increasing the residence time at 200 °C. The final morphology of the iPB/C3C6 blends depends on the composition and can be controlled and modulated by changing time and temperature of melt treatment.

The crystal structure and polymorphism of isotactic (iPP) and syndioactic polypropylene (sPP) are illustrated, highlighting the rich variety of phase behavior of these polymers, the conditions of obtainment of the different polymorphs and the disorder phenomena occurring in the crystals. After description of the concepts of packing and conformational polymorphism occurring in the case of iPP and sPP respectively, the crystal structure of the different polymorphs of iPP and sPP are described. In particular, the main structural features relative to the monoclinc α-, the trigonal β- and the orthorhombic γ-forms, of iPP including the mesomorphic form, and the trigonal form which develops in random isotactic copolymers of propylene with pentene or hexene units, are described at first, the chain conformation in all these polymorphs being the 3/1 helix. Then, the complex polymorphism of sPP and the crystal structure of the orthorhombic helical form I and II, the orthorhombic trans-planar form III, the monoclininc form IV, and the trans-planar and helical mesophases are illustrated. The implications of the crystal structure with the final properties are outlined for these polymers, the great fortune of which was the almost simultaneous discovery of the polymerization catalyst systems and the structural elucidation.

The crystal structures and the polymorphism of polymers are described on the basis of the main principles that define the conformation of polymer chains in the crystalline state and the modes of packing of macromolecules. We show that the presence of defects and disorder in the crystals influences the polymorphic behavior. The cases of polymorphism of isotactic poly(butene) (iPB) and syndiotactic poly(styrene) (sPS) are ilustrated as examples. In the case of iPB, the effect of the presence of defects of stereoregularity and of comonomeric units on the crystallization of form I and form II is described as an example of alteration of the crystallization behavior because of the modification of both thermodynamic stability and crystallization kinetics from the melt of the polymorphic forms. The case of sPS is taken as an example of a very complex polymorphic behavior arising from the presence and development of structural disorder.

Syndiotactic poly(3-methyl-1-butene) (sP3MB) has been obtained for the first time by hydrogenation of 3,4-dpoly(isoprene), which in turn has been synthesized with the catalyst FeCl2(2,2'-bipyridine)(2) activated with methylaluminoxane. The synthesized sample of sP3MB is amorphous but crystallizes by stretching and annealing of the oriented amorphous phase at 60-70 degrees C. The diffraction image of the annealed fibers shows only three equatorial reflections and a few weak reflections distributed on three nonequatorial layer lines. From these data a model of the conformation of the chains of sP3MB is proposed. The chains of sP3MB assume in the crystalline phase a 3/1 helical conformation, providing the first example of a syndiotactic polymer with 3-fold helical chains. A high degree of disorder is present in the crystals so that the structure can be described by an arrangement of parallel conformationally ordered 3/1 helical chains and disorder in the lateral correlations between the chains.

The chain-shuttling technology has emerged as a powerful tool for the efficient production of ethylene/1- octene multiblock copolymers (EOBCs) characterized by a statistical distribution in block length (BL) and numbers of blocks per chain (BN) (blockiness) and unique properties of elastomers with high melting temperature and low density. The crystallization properties and the morphology at nanometric length scales of some commercial grades of EOBC samples are analyzed. The samples are characterized by alternating soft and hard blocks and similar molecular characteristics, including the octene concentration in the hard and soft blocks, the fraction of hard blocks, and the melting temperature of ∼120 °C. Differences occur for the molecular mass of the hard (MH ≈ 2 or 3 kg/mol) and soft (MS, from 3 to 5 times MH) block and BN (in the range of 2−17). Small-angle X-ray scattering (SAXS) measurements, coupled with differential scanning calorimetry thermal analysis of isothermally crystallized samples, indicate that the hard blocks crystallize in separated domains forming chain-folded lamellae organized in stacks with little or no inclusion of soft segments in the interlamellar amorphous regions. The lamellar thickness, which develops at identical undercooling, varies from sample to sample and depends on the differences in the statistical distribution of block lengths, which generates a variety of environments for the crystallization. Two relevant length scales are identified for the description of the hierarchical structural organization of EOBCs in the solid state, the lamellar length scale, and the scale of domain spacing. The organization at lamellar length scale involves the stacking of the chain-folded lamellae at average separation distance L (long spacing), to form fringed lathlike entities having low thickness, wherein the lamellar entities lay down with the chain axes oriented parallel rather than perpendicular to the basal planes. The organization of the laths at higher length scale is also layered and involves the relative arrangement of the fringed laths in the compliant matrix populated by soft blocks bridging the laths, to form an interwoven elastomeric network characterized by an average layer periodicity D that is 4 to 5 times higher than the long spacing L. However, the contribution to the SAXS intensity at large length scale deriving from the presence of long hard blocks crystallizing as isolated lamellae passing through the soft matrix may not be excluded. The thickness of the laths is small (∼10 nm), as the lateral growth of the crystalline lamellae is hampered by the attached soft segment. This small size, and the parallel chain axis orientation to the basal plane of the laths, complies well with the need to accommodate the covalently bonded noncrystallizable soft blocks emerging as fringes from the laths at low cost of free energy, reducing to a minimum the loss of conformational entropy

The development of a highly oriented fiber morphology by effect of tensile deformation of stereodefective isotactic polypropylene (iPP) samples, starting from the unoriented form, is studied by following the transformation in real time during stretching through wide angle X-ray scattering (WAXS) measurements. In the stretching process, after yielding, the initial form transforms into the mesomorphic form of iPP through mechanical melting and re-crystallization. The analysis of the scattering invariant measured in theWAXS region highlights that the size of the mesomorphic domains included in the well oriented fiber morphology obtained at high deformations increases through a process which involves the coalescence of the small fragments formed by effect of tensile stress during lamellar destruction with the domain of higher dimensions. info:eu-repo/semantics/publishedVersion

A study of the mechanical behavior of isotactic 1,2-poly(E-3-methyl-1,3-pentadiene) (iP3MPD) and of the structural and morphological transformations that take place upon stretching is presented. Amorphous samples do not show viscous flow but show high ductility, strain hardening, and elastomeric behavior. An unusual double yielding appears in the stress- strain curves that may be correlated to occurrence of events typical of yielding at low deformation followed by stress-induced crystallization of a mesomorphic form at higher deformation (200-300%). The yielding stress and an endothermic hysteresis effect at the glass transition simultaneously increase upon aging of the amorphous glass due to a local densification or formation of local order in the amorphous glass upon physical aging. The elasticity is accompanied by the crystallization of the mesophase during deformation and its melting upon relaxation. During successive cycles of tensile deformation and elastic recovery the yielding peak is still observed during every stretching step. The elasticity of iP3MPD is an unusual case of a polymer that shows rubbery elastomeric properties below the glass-transition temperature.

A method for assessing the puzzling molecular architecture of ethylene/1-octene multi-block copolymers, synthesized via chain-shuttling technology, is proposed. They are commercial elastomers characterized by alternating segments with low (hard blocks) and high (soft blocks) octene concentration. Our molecular assessment allows determining plausible value for the average length of blocks and number of blocks/chain, setting the basis for a definitive elucidation of structure-properties relationships of these elusive systems. Namely, the molecular basis which explains the similar crystallization properties, and the large difference in mechanical properties of this class of copolymers is unveiled thanks to our approach. We demonstrate that at 25 °C we have similar values of Young modulus and deformation at break higher than 1400%, but large strain hardening before breaking or flat mechanical behavior up to the break, depending on the short or long average block length of the multiblock copolymers, respectively, coupled with a high or low number of blocks/chain, respectively. At 60 °C these differences are amplified entailing no strain hardening but preservation of high ductility for copolymers with short average block length and high number of blocks/chain, remarkable decrease of strain at break of about two orders of magnitude (from ≈2000 to ≈90%) for copolymers with long average block length and lower number of blocks/chain.

The structure and the mechanical properties of metallocene-made butene-pentene (iPBC5) and butene-hexene (iPBC6) isotactic copolymers are studied. The effect of the presence of pentene and hexene units on the crystallization behavior and the mechanical properties of isotactic polybutene (iPB) is analyzed. All iPBC5 copolymers crystallize from the melt in form II of iPB, which transforms into form I by aging at room temperature. On the contrary, in iPBC6 copolymers the presence of hexene units stabilizes the form II and, for hexene concentrations higher than 11 mol%, prevents the transformation of form II into form I at room temperature. Both iPBC5 and iPBC6 copolymers show mechanical behavior of highly flexible and ductile materials with enhanced ductility compared to iPB, with values of stress at yielding and of Young's modulus that decrease with increasing comonomer content. In all the iPBC5 copolymers, form II crystallized from the melt transforms into form I by stretching, whereas in iPBC6 copolymers form II is stabilized and the transformation of form II into form I by stretching is completely inhibited at high hexene concentrations.

We set up a facile approach for fabrication of supports with tailored nanoporosity for immobilization of enzymes. To this aim block copolymers (BCPs) self-assembly has been used to prepare nanostructured thin films with well-defined architecture containing pores of tailorable size delimited by walls with tailorable degree of hydrophilicity. In particular, we employed a mixture of polystyrene-block-poly(l-lactide) (PS-PLLA) and polystyrene-block-poly(ethylene oxide) (PS-PEO) diblock copolymers to generate thin films with a lamellar morphology consisting of PS lamellar domains alternating with mixed PEO/PLLA blocks lamellar domains. Selective basic hydrolysis of the PLLA blocks generates thin films, patterned with nanometric channels containing hydrophilic PEO chains pending from PS walls. The shape and size of the channels and the degree of hydrophilicity of the pores depend on the relative length of the blocks, the molecular mass of the BCPs, and the composition of the mixture. The strength of our approach is demonstrated in the case of physical adsorption of the hemoprotein peroxidase from horseradish (HRP) using 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) with H2O2 as substrate. The large surface area, the tailored pore sizes, and the functionalization with hydrophilic PEO blocks make the designed nanostructured materials suitable supports for the nanoconfinement of HRP biomolecules endowed with high catalytic performance, no mass-transfer limitations, and long-term stability.

In semi-crystalline polymers, polymorphic transitions between different crystalline forms can be triggered not only by thermal treatments but also by mechanical deformation. The transformations related to phase changes of the crystals, and those occurring at lamellar length scales by the effect of tensile deformation are studied in detail, focusing on a set of isotactic polypropylene samples, having a molecular mass in the range 100–200 kg/mol, polydispersity index close to two, and different concentration stereodefects along the chains with a uniform distribution. This enables the effect of the microstructure of the chains on the deformation behaviour to be illustrated. The transformations which occur by effect of deformation are followed in real time during stretching through wide and small angle X-ray scattering measurements, made using the high flux of X-rays available at a Synchrotron light sources. The stream of data obtained in the measurements performed in continuum are analysed in the framework of our current understanding of the deformation mechanism of semi-crystalline polymers. This study shows that, during the transformations of a spherulitic morphology into a fibrillar morphology, the stress-induced phase transitions which occur during plastic deformation are regulated by the same factors that govern the textural and morphological changes that is the ability of the entangled amorphous chains to transmit the stress and the intrinsic stability of the lamellar crystals. Since the relative stability of the different polymorphic forms involved in the structural transformations and the intrinsic flexibility of the chains depend on the stereoregularity, we are able to make precise correlations between the stereoregularity of the chains, and the deformation behaviour, paving the way for understanding the material properties at molecular level.

A study of the mechanical properties and of the crystallization behaviour of samples of isotactic polybutene (iPB) of different stereoregularity prepared with metallocene catalysts, is presented. Stereoregular samples with concentration of rr defetcs lower than 2 mol% crystallize from the melt by compression-molding and fast cooling to room temperature in form II, whereas more stereoirregular samples crystallize surprisingly mainly in form III. The stereodefective iPB samples show interesting mechanical properties of high ductility and flexibility that increase with increasing concentration of rr stereodefects, with values of deformation at break higher than 1000% for the most stereoirregular sample containing about 5 mol% of stereodefects. The aging at room temperature produces transformation of form II into form I in more stereoregular samples, whereas no phase transformation occurs in more stereoirregular samples crystallized mainly in form III. A strong increase of Young’s modulus and of stress at yield is observed after transformation of form II into form I. For more stereoirregular samples with concentration of rr defects higher than 2 mol% crystallized in form III, the mechanical properties do not change significantly upon aging at room temperature because no phase transformations occur during aging. Also for the aged samples a remarkable increase of ductility and flexibility with increasing concentration of rr stereodefects is observed. The mechanical deformation is associated with stress induced transformations of form II and form III into form I. These results indicate that mechanical properties of iPB can be modified by the controlled incorporation of stereodefects and improvement of ductility is easily obtained while maintaining high crystallinity by inclusion of small amounts of rr stereodefects.

A study of the morphology and the mechanical properties of the mesomorphic form of isotactic polypropylene (iPP) that crystallizes in samples of different stereoregularity prepared with metallocene catalysts is reported. Highly isotactic samples slowly crystallized from the melt in the α form show the typical lamellar morphology with organization in spherulites. Bundle-like elongated crystalline entities and needle-like crystals of γ form are instead observed for stereoirregular samples slowly crystallized from the melt in the γ form. All samples crystallize by fast quenching the melt at 0 °C in the mesomorphic form, regardless of stereoregularity. Crystals of the mesomorphic form always exhibit a nodular morphology and absence of lamellar spherulitic superstructures, independent of the stereoregularity. This morphology accounts for the similar good deformability of all the quenched samples, whatever the concentration of stereodefects. For all samples and any stereoregularity, the nodular morphology with absence of spherulites is preserved after annealing and transformation of the mesophase into α form. The formation of a nodular α form accounts for outstanding properties of high ductility and mechanical strength of the annealed samples crystallized in the α form. The most stereoirregular sample with rr concentration of 11% shows elastic behavior either when it is slowly crystallized in the γ form or when it is crystallized in the mesomorphic form and also after annealing and transformation of the mesophase into the nodular α form.

The resolution of the crystal structure and the physical properties of isotactic 1,2-poly(E-3-methyl-1,3-pentadiene) (iPE3MPD) are presented. This new polymer is one of the very few examples of known crystalline isotactic 1,2-polydienes. It does not crystallize by cooling from the melt but crystallizes by aging the amorphous samples at room temperature for several days and successive annealing. The stretching of amorphous or low crystalline compression-molded samples gives oriented fibers of a highly disordered mesomorphic form. Well-oriented fibers of the ordered crystalline form of iPE3MPD have been prepared by stretching amorphous or low crystalline compression-molded samples and successive annealing at 60-70 degrees C under tension. The crystalline structure of iPE3MPD is characterized by macromolecules in 7/2 helical conformation packed in an orthorhombic unit cell with parameters a = 17.4 angstrom, b = 16.5 angstrom, c = 15:3 angstrom according to the space group P2(1)ab. iPE3MPD has shown interesting mechanical properties of high deformability with elastic behavior associated with the crystallization during deformation of the mesophase that melts upon relaxation.

In recent years it has been introduced a new generation of complexes of transition metals and lanthanides with various ligands containing donor atoms such as P, N, and O (e.g., phosphines, imines, iminopyridines, and ketoimines) that, in combination with MAO, give highly stereoregular polymers (cis-1,4, iso- and syndiotactic; 1,2, iso- and syndiotactic) from various substituted butadienes (i.e., isoprene, 1,3-pentadiene, 1,3-hexadiene, 3-methyl-1,3-pentadiene, 1,3-heptadiene, 1,3-octadiene, and 5-methyl-1,3-hexadiene). The availability of all these stereoregular polymers has allowed us to have access, via hydrogenation reaction with p-toluenesulfonyl hydrazide, to a whole series of olefin homopolymers and perfectly alternating copolymers which, in some cases, were not obtainable through the simple stereospecific polymerization of the corresponding monomers. In this communication, we report on the synthesis and characterization (by NMR, DSC, GPC, and X-ray) of four perfectly alternating ethylene/2-butene copolymers having different stereoregularity degree, from completely isotactic to predominantly syndiotatctic; in particular, the racemo-di-isotactic ethylene/2-butene copolymer obtained by hydrogenation of diisotactic trans-1,4-poly(2,4-hexadiene) is a novel polymer which was never reported before.7

The yield behavior during uniaxial drawing of isotactic random copolymers of propene with ethylene (iPPEt), 1-butene (iPPBu), 1-pentene (iPPPe), 1-hexene (iPPHe), and 1-octadecene (iPPOc) is analyzed within the framework of our current understanding of deformation properties of semicrystalline polymers, that is, the intrinsic stability of lamellar crystals and related polymorphism phenomena, along with the ability of entangled amorphous chains to transmit stress. The samples selected for analysis were synthesized using single-site metalorganic catalysts, are highly stereoregular, and contain small amounts of regiodefects caused by secondary 2,1 erythro units. Moreover, the interchain and intrachain distribution of comonomeric units is uniform. In the case of iPPEt copolymers, samples containing ≈3.5 mol% stereodefects were also studied. The yield behavior of these samples depends on the kind and concentration of defects, and is directly related to the level of inclusion in and exclusion from crystals of the comonomeric units. Apart from iPPBu copolymer samples with high butene content, the yield stress of all samples increases with the thickness of lamellar crystals according to a common trend, regardless of comonomer. In the case of iPPBu copolymers containing a high concentration of butene units, the yield stress decreases with increasing lamellar thickness. The increase in yield stress with lamellar thickness is rationalized in terms of the micromechanical model of crystallographic slips, based on thermal activation of screw dislocations. The parameters of the model describing the yield behavior are the critical free energy required to form a screw dislocation and the shear modulus associated with the slip planes of the dislocations. These were set as identical to those deduced for isotactic polypropylene homopolymer samples (iPP) crystallized under different conditions. Study of the yield behavior of these copolymers extends the use of the dislocation model to a set of samples crystallized under similar conditions but characterized by differences in comonomeric unit, degree of crystallinity, lamellar thickness, polymorphism, and intrinsic flexibility of the chain backbone. The results indicate that for a homogeneous class of propene-based copolymers, namely crystallized in the α-form of iPP under similar conditions, lamellar thickness controls the level of plastic resistance provided that the concentration of structural irregularities in the crystals is not too high. iPPBu copolymers with high comonomer concentration do not obey this rule because of the high level of inclusion of comonomers in the crystals, which induces an increase in lamellar thickness but also a decrease in crystal stability.

The morphology and the electrical properties of hybrid nanocomposites characterized by the dispersion of ZnO nanoparticles (NPs), a n-type semiconductor, within an organic nanostructured matrix of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymer are presented. A selective inclusion of NPs only into the lamellar PS nanodomains of the block copolymer matrix has been achieved by synthetizing ZnO NPs coated with n-hexadecylamine (HDA) and tert-butylphosphonic acid (TBPA) molecules and subsequent thermal annealing of the nanocomposites ZnO NPs/PS-b-PMMA. Thermal treatments have allowed obtaining in one step the vertical orientation of the lamellar BCP nanodomains and the migration of the NPs to the PS domains, resulting in the formation of nanocomposites characterized by a precise control of the position of n-semiconductor ZnO NPs. Current-voltage measurements on the nanocomposites have indicated the presence of continuous path of charge carriers in the BCP films when the ZnO NPs content is above a threshold concentration. The experimental results have allowed the setup and validation of a theoretical protocol to study heterogeneous interfaces. In particular, the interaction of ZnO most stable nonpolar surface with prototypical capping agents has been analyzed by using density functional theory (DFT) calculations. © 2017 American Chemical Society.

A study of the nucleating effects of isotactic poly(trimethylallylsilane) (iPTMAS) and poly(vinylcyclohexane) (iPVCH) for isotactic polypropylene (iPP) and their influence on the mechanical behavior of iPP is reported. The particles of catalyst are covered by poly(trimethylallylsilane) or poly(vinylcyclohexane) by polymerization of the corresponding monomers before polymerization of propylene. The method guarantees that the nucleating agents are perfectly dispersed into the iPP samples, with their consequent high efficiency. Isotactic poly(vinylcyclohexane) and poly(trimethylallylsilane) favor crystallization from the melt of α and β forms, respectively. Both nucleating agents affect the morphology greatly reducing the size of shperulites. This in turn affects the mechanical properties improving ductility and flexibility. All nucleated samples crystallize by rapid cooling from the melt in the α form and not in the mesophase, as occurs in the pure iPP. The resulting α form presents nodular crystals and behaves as a stiff material with high deformability.

In this work, atomic force microscopy probes are functionalized by virtue of self-assembling monolayers of block copolymer (BCP) micelles loaded either with clusters of silver nanoparticles or bimetallic heterostructures consisting of mixed species of silver and gold nanoparticles. The resulting self-organized patterns allow coating the tips with a sort of nanometal skin made of geometrically confined nanoislands. This approach favors the reproducible engineering and tuning of the plasmonic properties of the resulting structured tip by varying the nanometal loading of the micelles. The newly conceived tips are applied for experiments of tip-enhanced Raman scattering (TERS) spectroscopy and scattering-type scanning near-field optical microscopy (s-SNOM). TERS and s-SNOM probe characterizations on several standard Raman analytes and patterned nanostructures demonstrate excellent enhancement factor with the possibility of fast scanning and spatial resolution

We report a method for the preparation of ordered patterns of Pd species on a substrate based on the use of polystyrene-block-poly(ethylene oxide) copolymer (PS-b-PEO) templates and selective inclusion of palladium (Pd) species in the PEO domains. PS-b-PEO samples of different total molecular masses self-assemble in a cylindrical microphase-separated morphology, in which vertically aligned PEO cylinders, with different diameters depending on the molecular mass, are organized in a hexagonal array of different lateral spacings. The cylindrical nanostructure is maintained after the selective inclusion of Pd species (Pd acetate and Pd nanoparticles (NPs) after reduction of Pd ions of the salt) in the PEO cylinders so that the characteristic sizes (diameters and lateral spacings) of the included Pd species are tuned by the characteristic sizes of the block copolymer (BCP) template, which are regulated by molecular mass. Treatment of nanocomposites at elevated temperatures in air removes the polymer matrix and leads to the formation of arrays of palladium oxide (PdO) NPs covering a solid support. The patterns of PdO NPs are characterized by different particle diameters and gap distances, mirroring the patterns and characteristic nanodimensions of the parent BCPs used as templates.

Many efforts are continuously devoted to the construction of hybrid biomaterials for specific applications, by immobilizing enzymes on different types of surfaces and/or nanomaterials. In addition, advances in computational, molecular and structural biology have led to a variety of strategies for designing and engineering artificial enzymes with defined catalytic properties. Here, we report the conjugation of an artificial heme enzyme (MIMO) with lipoic acid (LA) as a building block for the development of gold-based biomaterials. We show that the artificial MIMO@LA can be successfully conjugated to gold nanoparticles or immobilized onto gold electrode surfaces, displaying quasi-reversible redox properties and peroxidase activity. The results of this work open interesting perspectives toward the development of new totally-synthetic catalytic biomaterials for application in biotechnology and biomedicine, expanding the range of the biomolecular component aside from traditional native enzymes.