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Innovative hybrid nanocomposites based on a nanostructured block copolymer (BCP) matrix whose lamellar nanodomains are selectively loaded with metal nanoparticles, have been prepared. A symmetric poly(styrene-b-methylmethacrylate) (PS-b-PMMA) amorphous BCP showing a lamellar morphology has been employed. Thin films of PS-b-PMMA were deposited by spin-coating or drop casting on indium thin oxide (ITO) substrate in order to achieve orientation of lamellae with the lamellar surface perpendicular to the substrate. The perpendicular orientation is related to the use of ITO substrate, which shows a neutral surface with non-preferential interactions with the PS and PMMA domains. Hybrid nanocomposites have been then prepared by selective incorporation of gold nanoparticles into the PS lamellar domain by using a simple method based on the selective deposition of thermally evaporated gold nanoparticles. This innovative approach can be very useful for the realization of nanocomposites that could be used as active layer in non-volatile OFET memory devices or very efficient organic solar cells, depending on the appropriate guest molecules.

We report the synthesis and the crystal structure of isotactic poly((R,S)-3-methyl-1-pentene) (iP(R,S)3MP). A purely random achiral copolymer of two enantiomeric (R) and (S) 3-methyl-1-pentene monomers cannot be obtained by polymerization of the racemic mixture of the (R) and (S) monomers but has been obtained by stereospecific polymerization of 3-methyl-1,3-pentadiene to isotactic 1,2-poly(3-methyl-1,3-pentadiene) (iP3MPD12) and successive hydrogenation. The crystal structures of achiral iP(R,S)3MP and chiral poly((S)-3-methyl-1-pentene) (iP(S)3MP) are different, indicating that crystal structures of polymers may be driven by different entropic effects related to chirality and type of crystal disorder. The conformational disorder of the chiral lateral groups prevails in chiral iP(S)3MP, inducing crystallization of chains of one helical chirality, whereas the entropic effect due to the statistical substitution of chains of different helical chirality in the sites of the lattice prevails in achiral iP(R,S)3MP. [ABSTRACT FROM AUTHOR]

We report the cocrystallization of the regio- and stereoregular chiral copolymer poly(limonene carbonate). To the best of our knowledge, this marks the first example of an amorphous, enantiomerically pure polymer that becomes crystalline upon stereocomplexation with its complementary enantiomer. By analyzing X-ray powder diffraction data, we propose a packing model in which sheets of enantiopure chains interdigitate with layers of the opposite enantiomer, forming a 'steric zipper'. [ABSTRACT FROM AUTHOR]

A strategy to tailor the properties of isotactic polypropylene, based on the combination of the crystallization of the mesophase and the control of the molecular structure and concentration of stereodefects via polymerization with metallocene catalysts, is presented. The mechanical properties can be modulated through the conventional slow crystallization from the melt in the α and γ forms, depending on the concentration of stereodefects, or the crystallization of the mesophase by melt quenching. 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, but with remarkable differences in the values of the modulus and tensile strength. [ABSTRACT FROM AUTHOR]

Crystallization and phase separation in the melt in semicrystalline block copolymers (BCPs) compete in defining the final solid state structure and morphology. In crystalline–crystalline di-block copolymers the sequence of crystallization of the two blocks plays a definitive role. In this work we show that the use of epitaxial crystallization on selected crystalline substrates allows achieving of a control over the crystallization of the blocks by inducing crystal orientations of the different crystalline phases and a final control over the global morphology. A sample of polyethylene-block-syndiotactic polypropylene (PE-b-sPP) block copolymers has been synthesized with a stereoselective living organometallic catalyst and epitaxially crystallized onto crystals of two different crystalline substrates, p-terphenyl (3Ph) and benzoic acid (BA). The epitaxial crystallization on both substrates produces formation of highly ordered morphologies with crystalline lamellae of sPP and PE highly oriented along one direction. However, the epitaxial crystallization onto 3Ph should generate a single orientation of sPP crystalline lamellae highly aligned along one direction and a double orientation of PE lamellae, whereas BA crystals should induce high orientation of only PE crystalline lamellae. Thanks to the use of the two selective substrates, the final morphology reveals the sequence of crystallization events during cooling from the melt and what is the dominant event that drives the final morphology. The observed single orientation of both crystalline PE and sPP phases on both substrates, indeed, indicates that sPP crystallizes first onto 3Ph defining the overall morphology and PE crystallizes after sPP in the confined interlamellar sPP regions. Instead, PE crystallizes first onto BA defining the overall morphology and sPP crystallizes after PE in the confined interlamellar PE regions. This allows for discriminating between the different crystalline phases and defining the final morphology, which depends on which polymer block crystallizes first on the substrate. This work also shows that the use of epitaxial crystallization and the choice of suitable substrate offer a means to produce oriented nanostructures and morphologies of block copolymers depending on the composition and the substrates. [ABSTRACT FROM AUTHOR]

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. Image 1 • Living-stereoselective catalysts synthesize crystalline polyolefin block copolymers. • Equilibrium morphologies in crystalline block copolymers are described. • The segregation strength affects the crystallization mode and kinetics. • Crystallization of one block may be confined in crystalline lamellae of another block. • The presence of crystallinity may be exploited to create ordered nanostructures. [ABSTRACT FROM AUTHOR]

Thestructure and crystallization properties of a norbornene end-functionalizedsyndiotactic polypropylene (sPP) macromonomer (MMsPP) with [rrrr] = 80 mol % and molecular mass Mn= 3600 g/mol and corresponding comb-like poly(macromonomer)(pMMsPP) with Mn= 100000 g/mol have beeninvestigated using wide angle (WAXS) and small angle (SAXS) X-rayscattering, atomic force (AFM), transmission electron (TEM), and optical(OM) microscopy. The analysis reveals the tendency of the macromonomerand poly(macromonomer) to form structures characterized by layersof sPP chains alternated to layers occupied by the cyclic groups (norborneneor polynorbornene), and a small degree of interdigitation of sPP chainsbelonging to adjacent layers facing each other in an end-to-end arrangement.It is argued that this layering is dictated, upon crystallization,by nanophase separation of the flexible sPP chains in regions apartfrom those occupied by the cyclic groups coupled to formation of sPPcrystals organized in the lamellar morphology. SAXS measurements indicatethat in isothermally crystallized samples the layered structures areirregular and include sPP lamellar crystals of uniform thickness separatedby amorphous layers whose thickness values have a multimodal distribution.These properties are intrinsic to the chemical structure of our systemsand are only minimally influenced by the topological constrains ofthe covalent bonding of macromonomers in the corresponding comb-polymer. [ABSTRACT FROM AUTHOR]

A studyof the morphology and the mechanical properties of themesomorphic form of isotactic polypropylene (iPP) that crystallizesin samples of different stereoregularity prepared with metallocenecatalysts is reported. Highly isotactic samples slowly crystallizedfrom the melt in the α form show the typical lamellar morphologywith organization in spherulites. Bundle-like elongated crystallineentities and needle-like crystals of γ form are instead observedfor stereoirregular samples slowly crystallized from the melt in theγ form. All samples crystallize by fast quenching the melt at0 °C in the mesomorphic form, regardless of stereoregularity.Crystals of the mesomorphic form always exhibit a nodular morphologyand absence of lamellar spherulitic superstructures, independent ofthe stereoregularity. This morphology accounts for the similar gooddeformability of all the quenched samples, whatever the concentrationof stereodefects. For all samples and any stereoregularity, the nodularmorphology with absence of spherulites is preserved after annealingand transformation of the mesophase into α form. The formationof a nodular α form accounts for outstanding properties of highductility and mechanical strength of the annealed samples crystallizedin the α form. The most stereoirregular sample with rrconcentration of 11% shows elastic behavior either whenit is slowly crystallized in the γ form or when it is crystallizedin the mesomorphic form and also after annealing and transformationof the mesophase into the nodular α form. [ABSTRACT FROM AUTHOR]

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. Image 1 • The mechanical behavior of BuEt-ZN blocky copolymers is studied. • The BuEt-ZN copolymers show remarkable elastomeric properties. • The formation of form I′ by crystallization of amorphous is the key for the elasticity. [ABSTRACT FROM AUTHOR]

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. Image 1 [ABSTRACT FROM AUTHOR]

The correlations between the thermal behavior and the crystal morphology of isotactic propene-pentene copolymers were studied through wide-angle (WAXS) and small-angle (SAXS) X-ray diffraction. Copolymers with pentene concentration lower than 11 mol% crystallize in the α form of isotactic polypropylene (iPP) and a concomitant decrease of melting temperature and of the thickness of crystalline lamellae with increasing pentene concentration has been observed. At higher pentene concentrations the trigonal form of iPP crystallizes and a neat increase crystalline lamellar thickness and of the long period, with a slower decrease of melting temperature and crystallinity have been observed. These results have been treated in the general framework of copolymer crystallization theories, using a method proposed by Crist and correlated with the different level of inclusion of pentene co-units in the crystals of α and trigonal forms. For copolymers with pentene concentration lower than 11 mol% pentene co-units are in part incorporated in the crystals of α form. For higher pentene concentrations the decrease of melting temperature coupled with the increase of lamellae thickness with increasing comonomer content is the hallmark of the almost total inclusion of pentene co-units in the crystals of the trigonal form. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Binary blends of samples of syndiotactic polypropylene of different stereoregularity have been prepared by mixing a more stereoregular and crystalline sample sPP1 having [ rrrr ] = 78%, with low stereoregular and poorly crystalline samples sam PP1 and sam PP2 having [ rrrr ] = 54.6 and 45.8%, respectively, and a nearly atactic fully amorphous sample am PP1 with [ rrrr ] = 26.5%. The blends show separate melting of the two components with the more stereoregular component sPP1 melting at high temperature and the poorly syndiotactic component melting at lower temperature. Crystals of sPP1 are formed by cooling from the melt whereas more defective crystals of sam PP1 and sam PP2 are formed by cold crystallization during aging at room temperature. The presence of the strereoirregular component disturbs the melt crystallization of the stereoregular component sPP1 and depression of the crystallization and melting temperatures of sPP1 in the blends is observed. On the other hand, the cold crystallization at room temperature of the irregular component is accelerated and favored by the presence of the more stereoregular component sPP1, whose crystals act as crystallization nuclei. All data indicate interactions between the components in the melt and amorphous state, compatible with a good degree of mixing. [ABSTRACT FROM AUTHOR]

When in contact with water, poly(lactic acid), PLA, undergoes severe physical changes. Hydrolysis is obviously the most expected and studied one, and it is followed by weight loss. However, other phenomena occur such as opacification and crystallization. Although these phenomena are sometimes reported in the literature, apart from hydrolysis which has been thoroughly studied at several temperatures, the other ones have not been deeply analyzed and their timescales have not been so far determined. This work aims at studying the physical changes induced by water sorption to PLA, by analyzing the modifications taking place in solid samples immersed in water for different times (starting from a few hours) and at temperatures close to the glass transition. The obtained results allow determining the timescales of the different phenomena and thus the possible cause-effect relationship among them. In particular, it is shown that opacity is the first phenomenon to become evident, on a timescale consistent with water sorption, and seems to be due to crazes induced by water. The second phenomenon to become evident is the crystallinity evolution, which is shown to be consistent with a heterogeneous nucleation on the crazes. These two phenomena take place before hydrolysis becomes significant, thus raising doubts about the fact that hydrolysis can be their cause. [ABSTRACT FROM AUTHOR]

The crystallization behavior and the mechanical properties of random isotactic butene–octene copolymers (iPBC8) prepared with a metallocene catalyst are presented. Samples with low octene concentrations, up to nearly 6 mol%, crystallize from the melt in form II. In these samples octene units stabilize the tetragonal form II, decelerating or even preventing the transformation of form II into the trigonal form I. Octene concentrations higher than 7 mol% prevent crystallization of the samples from the melt and the obtained amorphous samples crystallize by aging at room temperature in mixtures of form II and form I'. The sample with the highest octene concentration of 11.5 mol% crystallizes surprisingly from the amorphous phase directly in the pure form I'. In these samples, form I' crystallized from the amorphous phase transforms into form II by stretching. Form II transforms back into form I' upon releasing the tension. Therefore, in samples where form I' is favored in powder samples, form II is favored in stretched fibers. The transformation of form I into form II by stretching and the back transformation of form II into form I after releasing the tension is unusual for isotactic polybutene (iPB) and rather unexpected. The presence of octene comonomer units also affects the mechanical behavior of iPB and produces increase of flexibility and ductility with increasing comonomer content, and samples with octene concentration higher than 6–7 mol% show unexpected remarkable elastomeric properties. The formation of crystals of form II or form I' during aging allows development of elastomeric properties and enhancement of mechanical strength. The elastic properties are associated to the reversible crystal–crystal phase transition between form II and form I occurring during stretching and when the tension is removed. [ABSTRACT FROM AUTHOR]

A studyof the crystallization behavior and mechanical propertiesof random isotactic butene–ethylene copolymers prepared witha metallocene catalyst is presented. The use of the metallocene catalysisensures a fine control over the molecular structure with low concentrationof rrstereodefects (0.8%), negligible amount ofregiodefects, and random and uniform distribution of ethylene constitutionaldefects. This molecular characteristic has allowed evidencing theonly effect of the presence of ethylene units on the polymorphic behaviorand mechanical properties of isotactic polybutene (iPB). The presenceof ethylene accelerates the transition of form II into form I at roomtemperature and at concentration of nearly 6 mol % favors the directcrystallization from the melt of the stable form I. The presence ofethylene also affects the mechanical behavior of iPB and producesincrease of flexibility and ductility with increasing ethylene content.A significant modification of the properties of iPB is observed forethylene concentration higher than 8 mol %, with development of elastomericproperties, never observed for the iPB homopolymer prepared with Ziegler–Nattacatalysts and not observed in the iPB homopolymer with similar contentof stereo defects. In these samples, elastomeric properties are dueto the low degree of crystallinity that develops upon aging at roomtemperature by direct crystallization of form I′ from the amorphousphase. [ABSTRACT FROM AUTHOR]

A studyof the mechanical properties and of the crystallizationbehavior of samples of isotactic polybutene (iPB) of different stereoregularityprepared with metallocene catalysts is presented. Stereoregular sampleswith concentration of rrdefects lower than 2 mol% crystallize from the melt by compression-molding and fast coolingto room temperature in form II, whereas more stereoirregular samplescrystallize surprisingly mainly in form III. The stereodefective iPBsamples show interesting mechanical properties of high ductility andflexibility that increase with increasing concentration of rrstereodefects, with values of deformation at break higherthan 1000% for the most stereoirregular sample containing about 5mol % of stereodefects. The aging at room temperature produces transformationof form II into form I in more stereoregular samples, whereas no phasetransformation occurs in more stereoirregular samples crystallizedmainly in form III. A strong increase of Young’s modulus andof stress at yield is observed after transformation of form II intoform I. For more stereoirregular samples with concentration of rrdefects higher than 2 mol % crystallized in form III,the mechanical properties do not change significantly upon aging atroom temperature because no phase transformations occur during aging.Also for the aged samples, a remarkable increase of ductility andflexibility with increasing concentration of rrstereodefectsis observed. The mechanical deformation is associated with stressinduced transformations of form II and form III into form I. Theseresults indicate that mechanical properties of iPB can be modifiedby the controlled incorporation of stereodefects and improvement ofductility is easily obtained while maintaining high crystallinityby inclusion of small amounts of rrstereodefects. [ABSTRACT FROM AUTHOR]

Highlights: [•] The mesomorphic form of iPP crystallizes also in stereoirregular samples. [•] The mesophase of stereoirregular samples transforms into α form at 25°C. [•] The mesophase always transforms into α form by annealing at T >60–70°C. [•] The transformation into α form occurs even in samples that crystallize into γ form. [•] Evidences supporting the structure model of the mesophase of iPP are given. [ABSTRACT FROM AUTHOR]

Abstract: The structure and properties of blends of poly(ethylene terephthalate) (PET) with poly(trimethylene terephthalate) (PTT) at PTT concentration ≤30 wt.%, obtained with three different methods: from solution, melt extrusion, and direct spinning, are investigated. Relationships between the method of preparation and properties of blends are established. All blends show glass transition temperature at values determined by composition, and crystallization properties also dependent on the preparation method. Blends obtained from solution show separated melting of components. For blends obtained from the melt only PET crystallizes. The melting temperature decreases with the residence time of the melt at high temperatures, due to occurrence of ester exchange reactions. It is shown that reactive blending of PET/PTT mixtures occurring during preparation is a versatile route for obtainment of engineering materials with good mechanical properties, high crystallinity, glass transition temperature lower than that of PET, and melting temperature that may be controlled by the processing conditions. [Copyright &y& Elsevier]

The tensile properties and the structural transformations occurring by effect of deformation of un-vulcanized ethylene/propylene(/diene) elastomers with ethylene contents ranging from 57 to 83 mol% are analyzed and interpreted in terms of the chain microstructure. It is shown that the samples with ethylene contents larger than or equal to 73 mol% experience a slight but significant increase of crystallinity upon stretching and partial melting of the new oriented crystals formed by stretching after releasing the tension. The degree of crystallinity, the tensile properties, the incremental crystallinity achieved upon stretching and the residual crystallinity left upon release of the tension all show well-defined correlations with the average ethylene content and the ethylene sequence length distribution. The tensile properties and the strain hardening behavior are correlated with the incremental crystallinity achieved upon stretching at high strain. [Display omitted] • The structure & properties of ethylene/propylene(/diene) rubbers are investigated. • The chain microstructure controls the strain induced crystallization (SIC). • For ethylene content >80 mol%: moderate SIC entails moderate strain hardening (SH). • For ethylene content <80 mol% and >70 mol%: high SIC entails high SH. • For ethylene content <70 mol%: low SIC entails low SH. [ABSTRACT FROM AUTHOR]

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. Image 1 • The crystallization behavior of iPBEt-ZN block copolymers is studied. • The comparison with metallocene iPBEt-Met random copolymers is presented. • Form II-Form I transition in iPBEt-ZN is slower than in iPBEt-Met copolymers. • The crystallization of Form I′ and Form II is driven by the average length of butene sequences. [ABSTRACT FROM AUTHOR]