Search

Brush block copolymers (BBCPs) exhibit attractive features for use as templates for functional hybrid nanomaterials including rapid ordering dynamics and access to broad ranges of domain sizes; however, there are relatively few studies of the morphology of the BBCPs as a function of their structural variables and fewer still studies of BBCP composite systems. Here we report the structural diversity and phase behavior of one class of BBCP nanocomposites as a function of the volume fractions of their components and the side chain symmetry of the BBCPs. We conducted a systematic investigation of gold nanoparticle (NP) (∼2 nm) assembly in a series of poly(tert-butyl acrylate)-block-poly(ethylene oxide) (PtBA-b-PEO) BBCPs with a fixed side chain length of PtBA (Mn = 8.2 kg/mol) but with different PEO brush lengths (Mn = 5.0, 2.0, or 0.75 kg/mol) as well as volume fractions (fPEO = 0.200–0.484). The gold NPs are selectively incorporated within the PEO domain via hydrogen bond interactions between the 4-mercapto...

The morphologies of sulfonated polystyrene-block-fluorinated polyisoprene (s-PS-b-f-PI) were studied as functions of different kinds of solvents and thermal annealing, using transmission electron microscope microscopy (TEM), small angle X-ray scattering (SAXS) and intermediate angle X-ray diffraction (IMAXD). The film of the block copolymer ionomer with an acid form [sulfonated PS-b-fluorinated PI (sH-PS-b-f-PI)], which was cast from anhydrous tetrahydrofuran (THF), developed a well-ordered cylindrical morphology of the f-PI domains in the sH-PS matrix. The morphology was explained by the solubility parameter and the Bjerrum length. The morphology changed to that of a no long-range ordered structure, through thermal annealing. The result was different from the usual behavior of uncharged diblock copolymers and could have been due to the ionic cluster formation. The solution casting films of the block copolymer ionomer with a cesium neutralized form (sCs-PS-b-f-PI) were obtained from the mixed solvent of THF/water (98/2, wt/wt) and DMSO. The ionic cluster formation in the film cast from the mixed solvent was hardly changed by annealing. The promotion of the ionic cluster formation by annealing was clearly observed in the film cast from DMSO. However, hindrance of microphase separation by the promotion of the ionic cluster formation was not confirmed in this study.

Concerted experimental and theoretical investigations have been carried out to understand the microphase separation in diblock copolymer melts containing poly (1,3-cyclohexadiene), PCHD, as one of the constituents. In particular, we have studied diblock copolymer melts containing polystyrene (PS), polybutadiene (PB), and polyisoprene (PI) as the second block. We have systematically varied the ratio of 1,2-/1,4-microstructures of poly (1,3-cyclohexadiene) to tune the conformational asymmetry between the two blocks and characterized the effects of these changes on the morphologies using transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). Our experimental investigations reveal that the melts of PCHD-b-PB, PCHD-b-PS and PCHD-b-PI containing nearly equal fractions of each component and high percentage of 1,4-microstructures in the PCHD block form cylindrical rather than lamellar morphologies as expected in symmetric diblock copolymers. In contrast, the morphologies of PCHD-b-PB, PCHD-b-PS and PCHD-b-PI containing PCHD block with higher 1,2-microstructure are found to be disordered at 110 � C. The change in the morphological behavior is in good agreement with our numerical calculations using the random phase approximation and self-consistent field theory for conformationally asymmetric diblock copolymer melts. Also, the effects of composition fluctuations are studied by extending the BrazovskiieLeiblereFredricksoneHelfand (J. Chem. Phys. 87, 697 (1987)) theory to conformationally asymmetric diblock copolymer melts. These results allow the understanding of the underlying self-assembly process that highlights the importance of the conformational asymmetry in tuning the morphologies in block copolymers.

In this study, block copolymer ionomers of the cesium salt (20 mol %) of fluorinated polyisoprene-block-sulfonated polystyrene were spin cast into membranes and annealed under an electric field of ∼40 V/μm at 130 °C for 24 h. The effect of this treatment was a 2.5 times increase in the ionic conductivity as measured by electrochemical impedance spectroscopy, under all humidity conditions measured. This can be attributed to the increased connectivity of the ionic domains of the block copolymers. This E-field alignment technique may thus find application in the fabrication of nanostructured polyelectrolytes with enhanced charge transport capacity.

Conventional transmission electron microscopy (TEM) was utilized to characterize vesicles formed by the spontaneous self-assembly of a novel zwitterionic block copolymer in the ionic liquid (2-hydroxyethyl)dimethylammonium methanesulfonate as well as in 0.1 M phosphate buffered saline (PBS). This block copolymer was synthesized via ring-opening metathesis polymerization (ROMP) of a norbornene-based sulfobetaine, followed by its end-functionalization with polystyrene to generate the necessary amphiphilic structure. The ionic liquid enabled the visualization of the vesicles in their swollen state by TEM, demonstrating a new method for improved characterization of polymer vesicles.

Well-ordered block copolymer nanocomposites with d-spacings as small as 15 nm and additive loadings greater than 70 mass % were formed upon blending functionalized polyhedral oligomeric silsesquioxanes (POSS) additives into disordered block copolymers containing poly(ethylene oxide) (PEO) as one of the blocks. The POSS additives were functionalized with maleamic acid or aminophenyl groups as ligands to enable selective hydrogen bonding with the PEO chains. The selective interaction of the additives with the PEO chains caused microphase separation of the block copolymer leading to formation of well-ordered morphologies as evidenced by small-angle X-ray scattering. Further addition of the additive induced transitions between cylindrical and spherical morphologies. While both ligands induced order, the maleamic acid ligand enabled higher levels of incorporation of POSS cages into the PEO phases of the composite. Differential scanning calorimetry and wide-angle X-ray diffraction were performed to confirm comp...

Small-angle neutron scattering (SANS) and ultra-small-angle X-ray scattering (USAXS) have been used to study the structural changes in fluorinated polyisoprene/sulfonated polystyrene (FISS) diblock copolymers as they evolved from the dry state to the water swollen state. A dilation of the nanometer-scale hydrophilic domains has been observed as hydration increased, with greater dilation occurring in the more highly sulfonated samples or upon hydration at higher temperatures. Furthermore, a decrease in the order in these phase separated structures is observed upon swelling. The glass transition temperatures of the fluorinated blocks have been observed to decrease upon hydration of these materials, and at the highest hydration levels, differential scanning calorimetry (DSC) has shown the presence of tightly bound water. A precipitous drop in the mechanical integrity of the 50% sulfonated materials is also observed upon exceeding the glass transition temperature (Tg), as measured by dynamic mechanical analysis (DMA).

With a view to optimizing morphology and ultimately properties, membranes have been cast from relatively inexpensive block copolymer ionomers of fluorinated polyisoprene -block- sulfonated polystyrene (FISS) with various sulfonation levels, in both the acid form and the cesium neutralized form. The morphology of these membranes was characterized by transmission electron microscopy and ultra-small angle X-ray scattering, as well as water uptake, proton conductivity and methanol permeability within the temperature range from 20 to 60 °C. Random phase separated morphologies were obtained for all samples except the cesium sample with 50 mol% sulfonation. The transport properties increased with increasing degree of sulfonation and temperature for all samples. The acid form samples absorbed more water than the cesium samples with a maximum swelling of 595% recorded at 60 °C for the acid sample having 50 mol% sulfonation. Methanol permeability for the latter sample was more than an order of magnitude less than for Nafion 112 but so was the proton conductivity within the plane of the membrane at 20 °C. Across the plane of the membrane this sample had half the conductivity of Nafion 112 at 60 °C.

We present the synthesis and characterization of a new class of high temperature thermoplastic elastomers composed of polybenzofulvene polyisoprene polybenzofulvene (FIF) triblock copolymers. All copolymers were prepared by living anionic polymerization in benzene at room temperature. Homopolymerization and effects of additives on the glass transition temperature (T-g) of polybenzofulvene (PBF) were also investigated. Among all triblock copolymers studied, FIF with 14 vol % of PBF exhibited a maximum stress of 14.3 +/- 1.3 MPa and strain at break of 1390 +/- 66% from tensile tests. The stress strain curves of FIF-10 and 14 were analyzed by a statistical molecular approach using a nonaffine tube model to estimate the thermoplastic elastomer behavior. Dynamic mechanical analysis that the softening temperature of PBF in FIF was 145 degrees C, much higher than that of thermoplastic elastomers with polystyrene hard blocks. Microphase separation of FIF triblock copolymers was observed by small-angle X-ray scattering, even though long-range order was not achieved under the annealing conditions employed. In addition, the microphase separation of the resulting triblock copolymers was examined by atomic force microscopy.

Commercial polypropylene pelvic mesh products were characterized in terms of their chemical compositions and molecular weight characteristics before and after implantation. These isotactic polypropylene mesh materials showed clear signs of oxidation by both Fourier-transform infrared spectroscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS). The oxidation was accompanied by a decrease in both weight-average and z-average molecular weights and narrowing of the polydispersity index relative to that of the non-implanted material. SEM revealed the formation of transverse cracking of the fibers which generally, but with some exceptions, increased with implantation time. Collectively these results, as well as the loss of flexibility and embrittlement of polypropylene upon implantation as reported by other workers, may only be explained by in vivo oxidative degradation of polypropylene.

To date the self-assembly of ordered metal nanoparticle (NP)/block copolymer hybrid materials has been limited to NPs with core diameters (D(core)) of less than 10 nm, which represents only a very small fraction of NPs with attractive size-dependent physical properties. Here this limitation has been circumvented using amphiphilic brush block copolymers as templates for the self-assembly of ordered, periodic hybrid materials containing large NPs beyond 10 nm. Gold NPs (D(core) = 15.8 ± 1.3 nm) bearing poly(4-vinylphenol) ligands were selectively incorporated within the hydrophilic domains of a phase-separated (polynorbornene-g-polystyrene)-b-(polynorbornene-g-poly(ethylene oxide)) copolymer via hydrogen bonding between the phenol groups on gold and the PEO side chains of the brush block copolymer. Well-ordered NP arrays with an inverse cylindrical morphology were readily generated through an NP-driven order-order transition of the brush block copolymer.

Characterization of pore structure and pore wall crystal structure was performed on porous high-density polyethylene (HDPE) material using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron diffraction (ED). The porous HDPE material was obtained through crystallization from swollen cross-linked polyethylene gels (CSX process1) in supercritical propane. SEM showed an open-pore structure of micron-sized pores, large void fraction, and surface area as well as thin yet rigid pore walls, making this material a good candidate for a variety of applications. TEM revealed oriented lamellar structure in the pore walls which was much different from structures found in typical bulk HDPE as well as that of the cross-linked HDPE before CSX processing. Electron diffraction results confirmed the presence of oriented lamellar stacking. On the basis of this oriented lamellar structure, possible mechanisms for crystallization and pore formation are suggested.

PS-PI multigraft copolymers with tri- tetra- and hexafunctional polystyrene branch points have been studied to investigate the influence of molecular architecture on morphological and tensile properties and to find novel material concepts. It was found that the morphological behaviour of these grafted copolymers can be predicted using theoretical approaches. The number of branch points, however, greatly influences the long-range order of microphase separation. Additionally, two new parameters for adjusting mechanical properties of multigraft copolymers are found in our investigations: 1) functionality of the graft copolymer: tri-, tetra- or hexafunctional and 2) number of branch points per molecule. Tetrafunctional multigraft copolymers show surprising high strain at break values up to 1550 %. With increasing number of branch points strain at break and tensile strength increase, where a linear dependence of mechanical properties on the number of branch points is obvious. Excellent elasticity of tetra and hexafunctional multigraft copolymers at high deformation was proved in hysteresis experiments.

Using a series of AnBn miktoarm star block copolymers with different numbers of arms (n = 1, 2, 4, and 16), the effect of molecular architecture on the grain growth kinetics was investigated by ann...

A novel bottom-up approach to obtain polymer nanocomposites using cubic silsesquioxanes (POSS) nanoparticles as building blocks is reported. The design is based on associative interaction between particles to form ordered nanostructure and limited crystal growth to render anisotropic shapes. Specifically, the affinity between POSS units causes these particles to aggregate and closely pack into a crystalline lattice. The organic polymer, covalently connected to each POSS unit, limits the crystallization into a two-dimensional lattice as demonstrated in random copolymers of polybutadiene and cubic silsesquioxanes. The copolymers were synthesized by ring-opening metathesis copolymerization of cyclooctadiene and POSS bearing a polymerizable norbornene group. The polymers were characterized using NMR, DSC, TEM, WAXD, and SAXS. The data from TEM and X-ray diffraction clearly show the formation of two-dimensional lamellar-like nanostructures of assembled cubic silsesquioxanes.

The living cationic sequential block copolymerization of isobutylene (IB) with tert-butyl vinyl ether (tBVE) was studied using a one-pot procedure in hexanes/CH2Cl2 and hexanes/CH3Cl solvent systems at −80 °C. It was carried out by the so-called capping-tuning technique, involving the capping of living PIB chain ends with 1,1-ditolylethylene (DTE) followed by addition of titanium(IV) isopropoxide (Ti(OIp)4) to lower the Lewis acidity before the introduction of tBVE. Homopolymerizations/model block copolymerizations of tBVE were carried out using 2-chloro-2,4,4-trimethylpentane (TMPCl) instead of living PIB. The living nature was exhibited by the linear plots of ln([M]0/[M]) vs time and number average molecular weight (Mn) vs conversion. 13C NMR spectroscopy indicated that the PtBVE is highly isotactic with close to 80% meso dyads. Well-defined PIB-b-PtBVE diblock copolymers were synthesized by the living cationic polymerization of IB followed by capping the living PIB ends with DTE and fine-tuning the Lew...

An electric field induced sphere-to-cylinder transition in thin films of asymmetric polystyrene-b-poly(methyl methacrylate) diblock copolymers was observed. In the absence of an applied electric field, thin films of the asymmetric diblock copolymer consisted of layers of spherical microdomains with poor in-plane long-range ordering. Under a ∼40V/μm applied electric field, hexagonally packed cylindrical microdomains normal to the surface were found. Cross-sectional transmission electron microscopy images of the intermediate stages of the alignment indicated that, under an electric field, the asymmetric diblock copolymer formed spherical microdomains that were deformed into ellipsoids and, with time, interconnected into cylindrical microdomains oriented in the direction of the applied electric field. Simulations suggest that improved long-range order of the cylindrical microdomains could be achieved by cycling the electrical field.

Multigraft copolymers with polyisoprene backbones and polystyrene branches, having multiple regularly spaced branch points, were synthesized by anionic polymerization high vacuum techniques and controlled chlorosilane linking chemistry. The functionality of the branch points (1, 2 and 4) can be controlled, through the choice of chlorosilane linking agent. The morphologies of the various graft copolymers were investigated by transmission electron microscopy and X-ray scattering. It was concluded that the morphology of these complex architectures is governed by the behavior of the corresponding miktoarm star copolymer associated with each branch point (constituting block copolymer), which follows Milner's theoretical treatment for miktoarm stars. By comparing samples having the same molecular weight backbone and branches but different number of branches it was found that the extent of long range order decreases with increasing number of branch points. The stress-strain properties in tension were investigated for some of these multigraft copolymers. For certain compositions thermoplastic elastomer (TPE) behavior was observed, and in many instances the elongation at break was much higher (2-3X) than that of conventional triblock TPEs.

The phase behavior of mixtures of polyisobutylene (PIB), polyethylene (PE), and a symmetric polyethylene-block-head-to-head polypropylene copolymer (PE−PP) was studied by transmission electron microscopy (TEM) and small-angle neutron and light scattering. The thermodynamic interactions between PE/PP and PE/PIB are repulsive (Flory−Huggins parameter χ > 0 and decreases with increasing temperature), while those between PP/PIB are attractive (χ < 0 and increases with increasing temperature). When the PE−PP copolymer is added to a 50/50 PE/PIB mixture, the resulting phase diagram in temperature−copolymer composition space exhibits many of the characteristics of “fish-shaped” phase diagrams found in oil/water mixtures stabilized by balanced surfactants. This is due to the interplay between the different χ parameters that characterize the system. Lamellar phases, single droplet microemulsions, and bicontinuous microemulsions were observed. The length scales of these structures and the locations of the phase tra...

To probe the effect of junction point functionality in miktoarm star block copolymer architecture on chain conformation and morphology, a series of AnBn miktoarm star copolymers where A arms are PS blocks and B arms are PI blocks were investigated. The overall series including a diblock and the star block copolymers can be represented by AnBn, where n = 1, 2, 4, and 16. These materials were produced by synthesizing a single batch of living PS arms and a single batch of living PI arms and then linking them together with chlorosilane coupling agents of different functionality. Thus, all PS arms are identical and all PI arms are identical across the entire series of materials. All stars in the series have equal numbers of PS and PI arms, and the volume fractions of all the samples in the series (nearly 0.50 PS by volume) are identical within experimental error. All the materials were found, via small-angle X-ray scattering and transmission electron microscopy, to form lamellar morphologies. A significant inc...

A series of five cyclic block copolymers of styrene and butadiene, having essentially the same molecular weight (52 ± 5 kg/mol) and PS volume fraction varying from 11 to 70%, were synthesized by cyclization of α,ω-dilithium polystyrene−polybutadiene−polystyrene triblock copolymers with bis(dimethylchlorosilyl)ethane. The cyclic block copolymers thus obtained have practically the same molecular weight and composition as their corresponding linear triblock copolymers. All materials were investigated via transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) techniques. In three cases where the cyclic and the corresponding linear block copolymer had the same morphology, the domain spacings of the cyclic block copolymers are found to be 84%−89% of those of their respective linear triblock copolymers. In the other two cases different morphologies are found in the cyclic and its corresponding triblock copolymer. Compared to their linear triblocks, the interfaces are curved away from the ...

Hybrid copolymers with dendritic−linear blocks are shown to exhibit many of the classic microphase-separated structures of linear−linear block copolymers. Transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS) were used to evaluate the morphology of a sixth generation (G6) poly(benzyl ether) dendron covalently bonded to linear polystyrene (PS) at the dendron focal point. Increasing the fraction of the linear block, φPS, through an increase in the molecular weight of the PS block revealed morphologies evolving from disordered to ordered lamellar to hexagonally close-packed dendron cylinders. Significantly, the observed morphologies are distinct from those expected for analogous linear−linear blocks at equivalent volume fraction, although the direction of progression follows expectation. Quantitative analysis suggests substantial molecular deformation or shape change in the dendritic phase. The possible role of conformational entropy in determi...

Aliphatic 22,12-polyurethane has been crystallized directly from the melt and isothermally at 105 °C from N,N-dimethylformamide to give chain-folded lamellae of thickness ≈ 14 nm. The crystals have been investigated using X-ray diffraction, electron microscopy (imaging and diffraction), and computer modeling. The diffraction data was used to establish that the chains crystallize in a single-chain, triclinic unit cell, and the structure bears a strong resemblance to chain-folded lamellar crystals of even−even nylons. The results show that, even for a molecule with relatively long alkane segments, the hydrogen bonds exercise a controlling influence on the crystallization process and crystalline structure. Two models were investigated: one based on an analogy with nylon 6 6 and the other derived using molecular dynamics; they both turned out to be closely related. The model generated using molecular dynamics predicted localized rotations at the termini of the ester−amide coupled units. The resolution of the...

A series of linear, aliphatic m,n-polyurethanes [O−(CH2)m−O−C(O)−NH−(CH2)n−NH−C(O)]x derived from long-chain aliphatic diols HO−(CH2)m−OH, where m = 12, 22, or 32, and much shorter diisocyanates OCN−(CH2)n−NCO, where n = 4, 6, 8, or 12, were previously characterized and shown to have physical and thermal properties similar to polyethylene. The current study shows, however, that hydrogen bonding still exercises a controlling influence on the crystallization process of these long-chain, aliphatic polyurethanes. X-ray diffraction, electron diffraction, and infrared spectroscopy indicate that these long alkane segment polyurethanes have interchain and intersheet distances similar to that seen for polyamides and polyurethanes of higher hydrogen bonding densities. Hydrogen bonding controls the crystallization, packing, and morphology of these polyurethanes, resulting in a crystal structure analogous to that of aliphatic, even−even (syncephlic) polyamides and unlike that of polyethylene. Additionally, high-tempe...

Morphological characteristics and mechanical properties of a series of block-double-graft (BDG) copolymers and terpolymers polystyrene−[1,2-polybutadiene-g-X2] (X = 1,4-polybutadiene, polyisoprene, polystyrene, and polystyrene-b-polyisoprene diblocks) were investigated by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and tensile testing. All BDG materials have linear polystyrene−1,2-polybutadiene (PS-b-1,2-PBD) diblock copolymer backbones. Two identical branches are grafted at every randomly distributed tetrafunctional junction point on the 1,2-PBD part of the backbone. Standard microstructures, such as body-center-cubic spheres, hexagonally packed cylinders, and lamellae, are obtained at different total PS volume fractions. It is found that when the branches are polydienes, the BDG molecules form the same morphologies as their linear diblock counterparts. In such cases, phase separation occurs between the polystyrene domain and a combined diene microdomain formed by the bac...

The crystallization behavior of functionalized polymethylene chains with carbamate esters placed periodically between alternating docosyl and octyl segments has been examined with infrared spectroscopy. Specific features of both the interactions and the chain conformation have been found. The crystallization kinetics, including the induction period, can be followed with time-resolved infrared spectroscopy (5 s time resolution) and occurs in three stages. The kinetics of local hydrogen-bonding rearrangement is quite different from the kinetics of methylene chain stem ordering. The interchain interactions are characterized by a broad distribution of states. The initial melt consists of highly interacting chains (75% hydrogen bonded). During crystallization, this broad asymmetric ensemble of interacting states changes continuously to one dominated by that characteristic of the ordered structure. Even with the time resolution achievable, the specific features of a crystallite nucleus could not be captured.

A morphological study of three I5S six-arm miktoarm star block copolymers is presented. These miktoarm stars are comprised of five arms of polyisoprene (PI) and one arm of polystyrene (PS) joined together at a single junction point. The strong segregation limit theory for the morphological behavior of miktoarm stars predicts that these materials should form spherical morphologies, but only lamellar and cylindrical morphologies were observed by TEM and SAXS. These results are similar to previously reported discrepancies between experimentally observed morphological behaviors of miktoarm stars and the predictions of the theory. Previous work has attributed the discrepancies to the neglect of the effect of the multifunctional junction points on calculated free energies. The current results suggest that, in addition to this, geometrical packing constraints prevent the formation of morphologies such as spheres and cylinders in highly asymmetric miktoarm stars in which the minor volume fraction component would ...

The bulk morphology of a crystalline/amorphous diblock copolymer under different thermal conditions was studied. The diblock copolymer, poly((ethylene oxide)-b-1,4-polybutadiene), forms a microphas...

Transmission electron microscopy (TEM) and electron diffraction (ED) are used to study the morphology of a semicrystalline polyolefin diblock copolymer polyethylene- b -atactic-polypropylene (PE- b -aPP) and its blend with polyethylene homopolymer. By using RuCl 3 /NaClO as the staining agent, both the contrast between amorphous PP and amorphous PE regions and the contrast between amorphous PE regions and crystalline PE regions can be obtained. As a result, both the larger lamellar structures due to microphase separation and the smaller crystalline PE lamellae can be resolved on TEM micrographs. Electron diffraction coupled with TEM imaging is used to elucidate the orientation of PE crystallites with respect to the interfaces of the microphase separated block copolymer lamellar domains. Fast quenching from a microphase separated melt-state was found to result in confinement of PE crystallization within the microphase separated PE domains of the block copolymer morphology. The orientation of the PE crystallites thus formed was found to be random.

This work is part of an extensive study of model nonlinear block copolymer/homopolymer blends. Effects of graft molecular architecture on the morphology of block copolymer/homopolymer blends have been examined. The single graft Y-shaped block copolymers used in the study are I2S block copolymers, which have two low polydispersity (PDI) polyisoprene arms and one low PDI polystyrene arm joint at a single junction point. Previously reported linear diblock copolymer/homopolymer blend systems showed that the order−order transitions (OOTs) occur at about the same volume fractions as in pure linear diblock copolymers. The OOT occurs at the same volume fraction regardless of the direction from which it is approached, i.e., blending homopolymer A with a diblock which forms A cylinders in a B matrix to push it toward lamella or blending B homopolymer with a lamellar diblock to push it back toward cylinders. This study shows that when a homopolymer is blended with an I2S block copolymer, the OOTs split so that they ...

Structure/property relationships of polystyrene–polyisobutylene–polystyrene (PS–PIB–PS) triblock copolymer made by different processes were studied using dynamic mechanical analysis (DMA). The PS–PIB–PS films were composed of approximately 30% polystyrene end-blocks. Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) confirm that a self-assembled, segregated cylindrical morphology forms in the copolymer. DMA was used as a tool to investigate the structure–property relationships in these polymers. Modified PS–PIB–PS copolymers were also characterized. Modifications of the copolymers were carried out by conversion of approximately 20 mol% of the polystyrene end-blocks to styrene sulfonic acid. The modified copolymers exhibited distinctly different thermal characteristics than the unmodified copolymers, which were most notable in the storage modulus and tan δ data. The presence of sulfonic acid groups disrupted the morphology and solvent sorption characteristics of the copolymers. Dynamic mechanical behavior is discussed as it relates to the morphology of the PS–PIB–PS copolymers formed via different processing methods and chemical modification.

T-junction grain boundaries were studied in a blend of polyisoprene homopolymer and a single graft block copolymer I2S with two equal length blocks of polyisoprene and one arm of polystyrene linked at a common junction point. The overall polyisoprene volume fraction in the blend was 0.52, and its equilibrium morphology was lamellar. While T-junctions were previously observed to be quite rare compared to other tilt grain boundary morphologies such as chevrons and omegas, they were found in abundance in the blend used in the current study. The T-junctions in the blend show a number of distinctive characteristics including enlarged semicylindrical end caps terminating polystyrene lamella and an increase in the spacing of the lamella as they near their termination at the T-junction. Simple free energy calculations show that the homopolymer present in the blend stabilizes the cylindrical curvature of the end caps, rendering the T-junction morphology more stable in blends than in neat block copolymers. This agr...

An investigation of the morphological behavior of a series of graft copolymers having multiple regularly spaced, tetrafunctional branch points has been carried out. The behavior of these materials, comprised of polyisoprene backbones with two polystyrene arms grafted to the backbone at each branch point, is shown to be effectively modeled by considering the behavior of smaller, architectural subunits based on the local environment of each junction point (constituting block copolymer). Morphological behavior was characterized using TEM and SAXS. Well-ordered cylindrical and lamellar morphologies were observed. Several samples appear to form cylindrical domains in disordered arrangements. Samples predicted to form spheres form instead a microphase-separated “mesh” morphology. Lamellar grain size and shape were also investigated, and lamellar grain orientation correlation lengths were determined. These measurements show a decrease in grain size with increasing number of branch points per molecule. They also ...

A series of A 2 B 2 four-arm, miktoarm stars of polystyrene and polyisoprene have been synthesized. The morphological behavior of these materials has been characterized using TEM, SAXS, and SANS, and was found to agree in general with the predictions of Milner's theory for miktoarm star morphological behavior. One sample was found to exhibit a cylindrical morphology where lamellae were predicted; this behavior is similar to other discrepancies observed in previous studies of miktoarm star morphological behavior. A second sample, predicted to form a bicontinuous morphology, was found to exhibit hexagonally packed cylinders. The tetrafunctional junction point also results in an increase in spacing for the lamellar sample in this series over that of an AB diblock, but not as great as the increase previously observed for A 8 B 8 16-arm star materials.

To understand the reversible gelation and subsequent aging of hydrogels prepared by freeze/thaw processing of poly(vinyl alcohol) (PVOH) solutions, the microstructures of gels prepared by different freeze/thaw protocols and aged to varying extents are studied by cryogenic transmission electron microscopy, solid-state nuclear magnetic resonance, X-ray scattering, and differential scanning calorimetry (DSC). As discussed in the literature, gelation by the freeze/thaw process occurs as a homogeneous aqueous poly(vinyl alcohol) solution is cycled, perhaps multiple times, between temperatures above 0 °C and well below 0 °C. The current investigation has determined that a few percent of chain segments crystallize during the first cycle, organizing themselves into 3-8 nm primary crystallite junctions separated on an irregular mesh by an average spacing of ∼ 30 nm. Aging or imposition of additional freeze/thaw cycles augments the level of crystallinity and transforms the as-formed liquid-like microstructure, characterized in the electron microscope by rounded ∼ 30 nm pores, into a fibrillar network. Observation that the transformation occurs at fixed mesh spacing and approximately constant average crystallite size suggests the formation of secondary crystallites that do not affect network connectivity. Dendritic ice crystallization and possibly spinodal decomposition superimpose on this nanoscale structure a matrix of much larger pores.

A morphological study of three A5B, six-arm miktoarm star block copolymers is presented. The miktoarm stars are comprised of five arms of polyisoprene and one arm of polystyrene joined together at a single junction point. The strong segregation limit theory for the morphological behavior of miktoarm stars predicts that these materials should form cylindrical (two samples) and lamellar (one sample) morphologies, but only lamellar morphologies were observed by TEM and SAXS. These results are similar to previously reported discrepancies between miktoarm star morphological behavior and the predictions of the theory. Combining the data of this study with that of previous morphological studies of miktoarm star materials, we can track the increasing discrepancy between the experimentally observed morphology and theoretical predictions as the molecular asymmetry parameter, e, increases. The A5B materials in this study were also observed to form exceptionally well-ordered morphologies.

A microphase-separated core−shell cylinder morphology has been observed, via transmission electron microscopy and small-angle X-ray scattering, in diblock copolymers of polystyrene (PS) and poly(1,3-cyclohexadiene) (PCHD). The structures consist of PS cylindrical cores surrounded by PCHD cylindrical annuli which are then hexagonally packed in a matrix of PS. The materials were produced by anionic polymerization of styrene followed by 1,3-cyclohexadiene. Characterization by size exclusion chromatography revealed a main peak due to diblock with a very narrow molecular weight distribution. However, a significant amount of PS homopolymer (about 30%) was present in the as-synthesized materials. The as-synthesized materials with homopolymer present produced core−shell morphologies, and these structures became much more regular when the homopolymer was removed by fractionation. After fractionation, the pure core−shell forming diblocks had PCHD volume fractions of around 0.37 and polydispersities well under 1.1.

Structural types of dendrimer nanocomposites have been studied and the respective formation mechanisms have been described, with illustration of nanocomposites formed from poly(amidoamine) PAMAM dendrimers and zerovalent metals, such as gold and silver. Structure of {(Au(0))n−PAMAM} and {(Ag(0))n−PAMAM} gold and silver dendrimer nanocomposites was found to be the function of the dendrimer structure and surface groups as well as the formation mechanism and the chemistry involved. Three different types of single nanocomposite architectures have been identified, such as internal (‘I’), external (‘E’) and mixed (‘M’) type nanocomposites. Both the organic and inorganic phase could form nanosized pseudo-continuous phases while the other components are dispersed at the molecular or atomic level either in the interior or on the surface of the template/container. Single units of these nanocomposites may be used as building blocks in the synthesis of nanostructured materials.

The morphologies of two series of model graft copolymers were studied using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). Both series of materials have monodisperse polybutadiene (PB) backbones and monodisperse polystyrene (PS) graft blocks. In one series there are on average five trifunctional junction points randomly distributed along the PB backbone. Each junction point grafts one PS block to the backbone. In the other series there are on average four tetrafunctional junction points randomly distributed along the PB backbone. Each junction point grafts two PS blocks to the backbone. A range of overall PB and PS volume fractions was investigated for both series. These materials simulate a controlled and known degree of architectural disorder. Current theory cannot rigorously predict the morphological behavior for these complex molecular architectures. However, it is found that an approximate extension of existing theory utilizing the constituting block copolymer (fundam...

The morphologies formed by block copolymers with a double-graft, π or (S,I)I′(S,I) architecture were investigated using transmission electron microscopy (TEM) and small angle neutron scattering (SANS). Here S and I represent blocks of polystyrene and polyisoprene, respectively. These materials were synthesized using anionic polymerization and chlorosilane linking, and they were characterized using size exclusion chromatography, membrane osmometry, and low-angle laser light scattering. This characterization work confirmed the desired molecular architectures and narrow molecular weight distributions. The results of morphological characterization indicate that one can understand complex grafting architectures by decomposing them into fundamental building blocks, which are taken as the component single-graft structures out of which the larger structure is constructed. We propose rules for dividing structures into these components, which we call constituting block copolymers . For the π double-graft architecture, the constituting block copolymer is an asymmetric single-graft block copolymer. The morphological behaviour of the more complex double-graft architecture is approximately equivalent to that of the constituting single-graft block copolymer. Through the use of the constituting block copolymers we map the experimentally determined morphological behaviour of eight materials with π architecture onto the morphology diagram calculated by Milner for mikto arm stars. As in our previous study of asymmetric single-graft block copolymers, the asymmetry of the graft location along the backbone requires a generalization of the molecular asymmetry parameter, e , used in the calculated morphology diagram.

The morphologies formed by block copolymers with a double‐graft, H or S2IS2 architecture were investigated using transmission electron microscopy (TEM) and small angle neutron scattering (SANS). Here S and I represent blocks of polystyrene and polyisoprene, respectively. These materials were synthesized using anionic polymerization and chlorosilane linking, and they were characterized using size exclusion chromatography, membrane osmometry, and low‐angle laser light scattering. This characterization work confirmed the desired molecular architectures and narrow molecular weight distributions. The results of morphological characterization indicate that one can understand complex grafting architectures by decomposing them into fundamental building blocks, which are taken as the component single graft structures out of which the larger structure is constructed. We propose rules for dividing structures into these components, which we call constituting block copolymers. The morphological behavior of the more co...

The relation between rheology and the time dependent morphology of a phase-separating binary blend of polystyrene and poly(vinyl methyl ether) was investigated by heating a sample from the single-phase (at 90 °C) into the two-phase regime (at 124 °C, 16 K above the LCST) and maintaining its temperature there while measuring the evolution of the dynamic moduli G‘ and G‘‘. Morphological changes occurred slowly so that there was sufficient time to cycle the dynamic mechanical measurements repeatedly over five decades in frequency. The morphology was observed on length scales from 1 mm down to 1 nm by conventional optical microscopy combined with digital image analysis, Hoffman modulation microscopy, TEM, and WISE NMR with spin diffusion. NMR shows that major compositional changes occur mostly in the first 20 min and then the composition remains constant at about 60:40 PS/PVME for the PS-rich matrix and 5:95 PS/PVME for the PVME-rich microdomains. The PVME-rich microdomains are separated by thin layers of the...

This paper reports on the synthesis and morphological characterization of graft block copolymers in which a single polystyrene (PS) arm was grafted at an asymmetric position along a polyisoprene (PI) backbone. These materials represent a model series of asymmetric simple graft (ASG) block copolymer structures. The synthesis of these materials was carried out with methods developed for three-arm “miktoarm” star copolymers using anionic polymerization high-vacuum techniques with cholorosilane linking agents. The three arms were two polyisoprene blocks with different degrees of polymerization and one deuterated polystyrene block, which formed an asymmetric simple graft structure (ASG). Molecular characterization was performed using size exclusion chromatography (SEC) with refractive index and UV detection, membrane osmometry, and low-angle laser light scattering. These techniques confirmed that the materials exhibited narrow molecular weight distributions and low compositional heterogeneity. The morphologies...

The morphological behavior of three well-defined miktoarm star block copolymers having 16 arms/molecule was characterized using transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS) techniques. The molecules, called Vergina stars, have 8 arms of polyisoprene and 8 arms of polystyrene radiating from a single junction point. The samples, with polystyrene volume fractions of 0.37, 0.44, and 0.47 and total molecular weights ranging from 330 000 to 894 000, were all found to microphase separate into lamellar morphologies. In this respect all three samples, in agreement with theory, behave in the same way as linear diblock copolymers of the same relative volume fractions. Incorporating results from previous studies in the literature of miktoarm block copolymers containing trifunctional and tetrafunctional branch points, as well as the new Vergina star data, the scaling behavior of the area per junction versus junction functionality was investigated.

Well-defined graft copolymers with polyisoprene backbones and polystyrene branches, having trifunctional branch points, of the type S2IS2 (H-shaped) and (SI)I(SI) (π-shaped) were synthesized by anionic polymerization high-vacuum techniques. The synthetic strategy involves the preparation of the outer parts of the molecules, carrying one reactive Si−Cl bond, followed by coupling with difunctional living poly(isoprenyllithium) chains. In this way, the number and placement of the branches can be precisely controlled. Molecular characterization of the fractionated samples by size exclusion chromatography with UV and RI detection, membrane osmometry, low-angle laser light scattering, and 1H-NMR spectroscopy confirmed that the materials exhibit narrow molecular weight distributions and low compositional heterogeneity. The strongly microphase-separated morphologies of these two samples were characterized using TEM and SAXS. The π architecture with a PS volume fraction of 0.21 was found to form body-centered cubi...

A new equilibrium morphology consisting of randomly oriented wormlike micelles dispersed in a continuous matrix is observed in a neat, strongly segregated I2S simple graft block copolymer. The equilibrium nature of the worm phase is determined via a set of selective solvent casting and prolonged annealing experiments. Transmission electron microscopy (TEM) experiments on quenched samples allow a unique opportunity to directly observe the transition of a kinetically trapped, nonequilibrium folded-layer morphology, formed by casting the sample with a solvent selective for polyisoprene (PI), into the equilibrium, randomly oriented worm phase through an intermediate folded-lace morphology. The folded-lace intermediate is similar to the “mesh” structure previously observed by Hashimoto et al. in starblock/homopolymer blends.1 The simple graft block copolymer, formed by grafting a single polystyrene (PS) chain onto the center of a polyisoprene backbone, introduces a 2:1 PI/PS arm number asymmetry in the microph...

The morphological behavior of a series of well-defined A2B simple graft or “Y” architecture block copolymers is characterized via small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). This model architecture is formed by grafting a polystyrene block onto the center of a polyisoprene backbone. The volume fraction windows in which specific strongly segregated microphase-separated morphologies are observed are shifted to higher volume fractions of the PS graft material than in the corresponding linear diblock copolymers. These findings are in good agreement with recently calculated theoretical phase behavior for simple graft, A2B, block copolymers. However, a new morphology, not found in neat linear diblock copolymers, is also observed. This A2B material is microphase separated into wormlike micelles but not ordered on a lattice. This morphology is found at high PS graft volume fraction (φs = 0.81), where the two PI chains per molecule are initially forced to the concave side of the...

We have synthesized linear ABC triblock terpolymers containing poly(1,3-cyclohexadiene), PCHD, as an end block and characterized their morphologies in the melt. Specifically, we have studied terpolymers containing polystyrene (PS), polybutadiene (PB), and polyisoprene (PI) as the other blocks. Systematically varying the ratio of 1,2- /1,4-microstructures of poly(1,3-cyclohexadiene), we have studied the effects of conformational asymmetry among the three blocks on the morphologies using transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and self-consistent field theory (SCFT) performed with PolySwift++. Our work reveals that the triblock terpolymer melts containing a high percentage of 1,2-microstructures in the PCHD block are disordered at 110 °C for all the samples, independent of sequence and volume fraction of the blocks. In contrast, the triblock terpolymer melts containing a high percentage of 1,4-microstructure form regular morphologies known from the literature. The accuracy of the SCFT calculations depends on calculating the χ parameters that quantify the repulsive interactions between different monomers. Simulations using χ values obtained from solubility parameters and group contribution methods are unable to reproduce the morphologies as seen in the experiments. However, SCFT calculations accounting for the enhancement of the χ parameter with an increase in the conformational asymmetry lead to an excellent agreement between theory and experiments. These results highlight the importance of conformational asymmetry in tuning the χ parameter and, in turn, morphologies in block copolymers.

No abstract available.

The bulk morphologies formed by a new class of charged block copolymers, 75 vol % fluorinated polyisoprene (FPI) – 25 vol% sulfonated polystyrene (PSS) with 50% sulfonation, are characterized, and the fundamental underlying forces that promote the self-assembly processes are elucidated. The results show how the bulk morphologies are substantially different from their uncharged diblock counterparts (PS-PI) and also how morphology can be tuned with volume fraction of the charged block and the casting solvent. A physical understanding based on the underlying strong electrostatic interactions between the charged block and counterions is obtained using Monte Carlo (MC) and Molecular Dynamics (MD) simulations. The 75/25 FPI-PSS shows hexagonal morphologies with the minority blocks (PSS) forming the continuous phase due to charge percolation and the FPI blocks arranged in hexagonal cylinders. Some long-range order can be sustained even if lipophobicity is increased (addition of water), albeit with lower dimensional structures. However, thermal annealing provides sufficient energy to disrupt the percolated charges and promotes aggregation of ionic sites which leads to a disordered system. Diverse and atypical morphologies are readily accessible by simply changing the number distribution of the charges on the PSS block.