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Multilayer thin films that consist of poly(vinyl alcohol) (PVA) and weak polyacids such as poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) were prepared by hydrogen bonding interactions. Both the degree of hydrolysis and molecular weight of PVA were investigated in terms of their influence on growth behavior and pH stability. Multilayer films containing PVA and PAA could be assembled successfully only by using partially hydrolyzed PVA and low-pH solutions. By comparing films containing PAA with those containing a more strongly interacting partner, PMAA, it was shown that the extent of PVA hydrolysis becomes significant only when weak hydrogen bonding pairs such as PVA and PAA were used. pH-triggered dissolution experiments demonstrated that the degree of hydrolysis can be used as an additional parameter by which to tune the pH stability of the film. Also, the presence of an abundance of free hydroxyl and carboxylic acid groups in the multilayer allowed enhanced pH stability to be obtained by th...

We investigate the effect of block copolymer (BCP) molecular weight and connectivity on the morphology and time–temperature dependent swelling of thin film hydrogels created through layer-by-layer (LbL) assembly of BCP micelles with poly(acrylic acid). BCPs of poly(N,N-dimethylaminoethyl methacrylate) (D) and poly(propylene oxide) (P), a P–D diblock, a long D–P–D triblock, and a short D–P–D triblock copolymer, were compared in terms of their temperature response in solution and within micelle–polyelectrolyte multilayers (mPEMs). The critical micellization concentration and micellization temperature of the BCPs in solution, as well as the swelling transition temperature, Tstt, of the mPEMs, decreased with increasing P block length. AFM imaging of dry mPEMs shows regular dimpled surface structures that arise from surface relaxation of micelles. When the mPEMs are cooled below Tstt in water, the thin ∼200 nm films can swell reversibly between 3 and 6 times their dry thicknesses within 2 min. The degree of sw...

A hybrid micro-/nanofluidic device which contains an array of parallel nanochannels has been employed to study polyelectrolyte multilayer (PEM) deposition in confined geometries. Layer-by-layer (LbL) assembly of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate) (PSS) at pH 4 and salt concentrations ranging from 0.1 to 1 M was used to conformally coat the nanochannel walls, systematically narrowing the channel width from 222 to 11 nm in the wet state. The thicknesses of confined multilayers were measured using SEM and these results were compared with those obtained on planar, unconfined surfaces. A procedure for direct measurement of the gap thickness using dc conductance was also developed. LbL assembly in the nanochannels resulted in lower bilayer thicknesses than those obtained on planar surfaces. This observation is attributed to the surface charge-induced depletion of unadsorbed polyelectrolytes within the channel. The ability to conformally coat the walls of the nanochannels with functi...

In this article, we seek to enable large-scale, fully reversible, thermally induced volumetric changes in layer-by-layer (LbL) electrostatically self-assembled thin films through the incorporation of A-B-A triblock copolymers. Poly(N,N-dimethylaminoethyl methacrylate)-b-poly(propylene oxide)-b-poly(N,N-dimethylaminoethyl methacrylate) (abbreviated “PD-PPO-PD”) was used as a dual pH and temperature-responsive component in the electrostatic self-assembly of multilayer thin films. In solutions of this triblock copolymer with poly(N,N-dimethylaminoethyl methacrylate) (PD) weak polyelectrolyte end blocks, the dehydration temperature of the central poly(propylene oxide) (PPO) block was strongly dependent on solution pH, as shown by microdifferential scanning calorimetry (micro-DSC) and dye solubilization techniques. Multilayer films were then assembled with poly(acrylic acid) (PAA) or poly(4-styrene sulfonate) (PSS) as anionic binding partners at various pH values, where the triblock copolymer was incorporated ...

We have measured the Young’s modulus and thickness of ultrathin polyelectrolyte multilayer (PEM), polystyrene (PS), and poly(methyl methacrylate) (PMMA) films as a function of relative humidity. We demonstrate that PEMs undergo substantial swelling and plasticization in the presence of ambient water and that both the choice of polyelectrolytes and the pH of the deposition baths influence the response of a PEM film to changes in humidity. These responses were roughly linear in two of the PEM systems tested; however, a third system demonstrated evidence of antiplasticization and an abrupt swelling transition at intermediate humidity. This behavior is attributed to an internal structure rich in hydrogen-bonding sites. Overall, our results suggest that the chemical composition and molecular architecture of PEMs are responsible for differences in the environmental responsiveness of these materials. Both PS and PMMA films exhibited comparatively small but measurable swelling and plasticization in the presence o...

The amphiphilic block copolymer polystyrene-block-poly(acrylic acid) (PS-b-PAA) forms micelles in toluene that can be cast onto a planar substrate to create quasi-hexagonal arrays of spherical PAA domains in a PS matrix. Treatment of these ultrathin films with an appropriate selective solvent swells the PAA domains and fractures open (cavitates) the PS matrix, thereby exposing the PAA chains to solution. Here we have investigated the conditions required for this cavitation process to occur and the end-state polymer morphology of close-packed films of PS-b-PAA micelles following treatment with a series of short alkyl chain alcohols or aqueous solutions of varying pH and ionic strength. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were employed to characterize the morphologies of the precursor and solvent-treated films. In addition to the effects of solvent conditions, we show that the cavitation process is influenced by the molecular weight of the PS block and is thermally rever...

We demonstrate the time- and concentration-dependent dissolution (etching) of polyelectrolyte multilayer (PEM) films comprised of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) immersed in NaCl solutions. PEM thickness decreases to a reproducible unchanging value that depends upon the initial film thickness and the concentration of NaCl. As opposed to a “top-down” removal of PEM chains from the film, the dissolution mechanism involves the diffusion and association of chains throughout the PEM that leave the film in the form of polyelectrolyte complexes (PECs). The PEC phase diagram is invoked to explain the observations presented in this paper and work by previous researchers. We demonstrate the straightforward application of PEM salt etching to pattern films where the spatial position and amount of dissolved material are controlled, resulting in a multicolor reflector and a gradient-thickness film. In addition to providing a more comprehensive picture of PEM stability, these results ma...

We present a modified version of a strain-induced buckling instability technique that relies on the analysis of a two-plate composite film deposited on an elastomeric poly(dimethylsiloxane) (PDMS) substrate. We have previously shown that the “strain-induced elastic buckling instability for mechanical measurements” (SIEBIMM) technique is suitable for testing polyelectrolyte multilayers (PEMs) that are amenable to deposition directly on the testing substrate. The method presented in this paper broadens the applicability of the SIEBIMM technique through the transfer of a thin layer of polystyrene (PS) to the PDMS surface prior to film deposition, which creates a deposition surface that can be treated to promote adhesion of films not amenable to transfer or assembly directly onto PDMS. Multilayers assembled onto the PS-coated PDMS substrates yield thin two-plate PS−PEM composite films on the surface of the PDMS substrates that buckle like their homogeneous counterparts. The mechanical contribution of the PS l...

Polymers are known to exhibit strong rate-dependent mechanical behavior. In different temperature and/or frequency regimes, the rate sensitivities of polymers change as various primary (α) and secondary (β) molecular mobility mechanisms are accessed. The incorporation of nanoparticles into the polymer matrix can potentially alter the local molecular level structure and thus offers an opportunity to tailor the rate-dependent mechanical deformation and failure behavior of the polymer. In this study, methacryl-POSS is incorporated into poly(vinyl chloride), producing a range in weight fraction of well-dispersed POSS. Dioctyl phthalate (DOP) plasticized PVC is also prepared with a range in DOP content using the same method. Both methacryl-POSS and DOP plasticize the PVC. Dynamic mechanical analysis (DMA) revealed that the incorporation of POSS in PVC introduced reductions in both the primary (α) and secondary (β) transition temperatures. DOP reduced the α-transition temperature in the blends, whereas a pronou...

We report several strategies for varying the diameter, the center-to-center spacing, and the areal density of block copolymer micelles, or inorganic nanoclusters synthesized in the cores of the micelles, on planar substrates. The amphiphilic block copolymer, poly(styrene-b-acrylic acid) (PS/PAA), forms micelles in toluene solution that can be spin-coated onto a substrate to create quasi-hexagonal arrays of spherical PAA domains within a PS matrix. The carboxylic acid groups within the PAA domains can be utilized in a nanoreactor synthesis scheme to create inorganic nanocluster arrays, or the PAA domains can be cavitated to expose the carboxylic acid groups to the surface for possible covalent coupling reactions. The strategies we use to vary the planar arrangements include variation of the molecular weight of PS/PAA, variation of the amount of metal loaded into the micellar solution, addition of PS homopolymer into the micellar solution, and the mixing of different micellar solutions. Through these routes...

Creation of an orientationally ordered hierarchical nanocomposite can be done by the preferential insertion of individual polymer-covered clay layers into block copolymer (BCP) microdomainsin the present instance, PS-functionalized silicate layers into the polystyrene (PS) domains of a styrene−butadiene−styrene triblock copolymer (SBS). We present here the method required to achieve such an ordered block copolymer−nanoparticle composite and report preliminary mechanical properties. PS is grafted-to or polymerized-from individual clay sheets in order to provide a neutral enthalpic interaction between the PS chains on the clay layers and the PS blocks in the SBS. The molecular weight of the PS chains tethered to the clay was varied, and we show that higher molecular weight is critical in obtaining individual clay sheets dispersed in the SBS matrix. When exfoliated, the clay sheets serve as a template for the lamellar domains. Because of their large areal dimensions and concentration, the clay particles like...

Polyelectrolyte multilayers with alternating porous and fully dense regions have been assembled from poly(acrylic acid) (PAA), poly(allylamine hydrochloride) (PAH), and poly(sodium 4-styrenesulfonate) (SPS) in appropriate combinations. The porous zones were developed postassembly via immersion of the heterostructure film into an aqueous acidic medium followed by rinsing in deionized water. Properly assembled PAH/PAA regions exhibit a reversible, pH-gated nanoporosity transition while PAH/SPS regions remain unchanged upon treatment at low pH. The application of these structures as one-dimensional dielectric mirrors and vapor sensors has been investigated. Organic liquid crystal molecules were also successfully loaded selectively into the nanoporous regions via a capillary force driven wicking action. Potential applications for drug delivery and as Bragg stacks with tunable refractive index layers are also discussed.

Polyelectrolyte multilayer (PEM) films comprised of the weak polyelectrolyte pair poly(allylamine hydrochloride)/poly(acrylic acid) were characterized in nanoindentation tests near 295 K. Film thickness in ambient air ranged from 80 to 6000 nm, and indentation depth varied from a few nanometers to 3000 nm for the thickest films tested. Elastic modulus and hardness of the films were independent of the contact depth over a range of penetration where artifacts arising from the free surface and the underlying glass substrate were insignificant. Moduli of the dry films were in the range of 10 GPa while the same films immersed in water showed modulus values about 2 orders of magnitude lower. Properties of the dry films were dependent on the selected assembly pH conditions but were insensitive to post-assembly cross-linking; both the modulus and the hardness of the hydrated films were affected significantly by the introduction of covalent cross-links into the PEM structure.

The grain structure in lamellar block copolymer samples undergoing a disorder-to-order transition was studied by a combination of depolarized light scattering (DPLS) and transmission electron microscopy (TEM). The 4-fold symmetry of the DPLS profiles indicated the presence of anisotropic grains. A pattern recognition algorithm for analyzing the TEM micrographs of samples partially filled with anisotropic, ordered grains was developed. The volume fractions of sample occupied by ordered grains determined from light scattering and electron microscopy are in reasonable agreement. Both methods indicate that, on average, the characteristic length of the grains in the direction perpendicular to the lamellar planes was a factor of 2 larger than that in the plane of the lamellae. The absolute magnitudes of grain sizes determined by light scattering are about 50% larger than those determined by microscopy.

We report the formation of novel self-assembled ultrathin (ca. 20 nm) films comprising in-plane arrays of nanoscale surface cavities. The original micellar thin films, formed by casting kinetically stable reverse micelles from a solution of a styrene (PS)−acrylic acid (PAA) diblock copolymer in toluene onto silicon nitride substrates, consist of lateral hexagonal arrays of spherical PAA microdomains in PS matrix. Upon aqueous treatment to load metal ions into the PAA domains, cavitation of the individual PAA micelle cores occurs, leading to the formation of cavities in the center of the micelles and exposing the PAA domains to the film's surface. Experimental evidence reveals that cavitation takes place as a result of hydration and swelling of the PAA micelle cores during sample treatment in an alkaline solution. The use of these cavitated, metal-loaded PAA domains as arrays of open nanoreactors for inorganic nanocluster synthesis is demonstrated.

A stretching device suitable for fitting within a deuterium nuclear magnetic resonance (NMR) probe was constructed to investigate the large strain uniaxial tensile deformation behavior of nylon 6 plasticized by 40 wt % of phenol-d5. The phenol-d5 molecules probe the environment of the amorphous regions in nylon 6; the phenol-d5 molecules do not exist in a “free” state, and they remain associated with the amide groups by hydrogen bonding during deformation. Deuterium NMR spectra show that the quadrupolar splitting varies linearly with strain throughout the experiment, indicating that the orientation of the phenol-d5 molecules in the amorphous phase is simply a function of strain and not of stress. The line width increases with strain at low-to-moderate strains but attains a constant value at large strains (in the strain-hardening regime). From low-to-moderate strains, the line width behavior arises from a decrease in the translational motion of the phenol-d5 molecules between amide groups in the amorphous ...

Simultaneous determination of the lamellar morphological length scale and the grain size of several low molecular weight heterogeneous styrene−butadiene block copolymers was accomplished through the use of ultra-small-angle X-ray scattering measurements. NIST's X23A3 Ultra SAXS beamline of the National Synchotron Light Source in the Brookhaven National Laboratory provided a scattering vector, q, from 0.0004 to 0.1 A-1. Many of the block copolymer specimens display a clearly resolvable peak in the Ultra SAXS region, and grain size was determined using the spherical form factor. Determination of Porod's law constant and the value of the scattering invariant provided a preliminary verification of the proposed scattering mechanism by solving for the contrast factor and the volume fraction of the grain boundaries in these specimens. Grain size in a given polymer was a function of annealing temperature and time. For the case of a block copolymer swollen with varying amounts of cumene, both the lamellar repeat d...

Deuterium nuclear magnetic resonance (NMR) studies of varying amounts of D2O absorbed in undrawn commercial polyamide 6 (PA6) rods at room temperature suggest the presence of only one type of water closely associated with amide sites via hydrogen bonding and that its motion can be modeled as both isotropic rotational and translational diffusion. Time constants for spin−lattice relaxation (T1) and spin−spin relaxation (T2) are used to obtain correlation times for the motions. The dependence of T1 on D2O content shows a minimum, indicating that the correlation time is on the order of ω0τc ∼ 1. Translational diffusion occurs on the time scale of less than 1 ms and describes the motion of D2O hopping between different solvated sites. The corresponding range of diffusivity of D2O in PA6, ∼10-10 cm2/s, agrees with values reported for macroscopic diffusion measurements. Within each solvated site the solvent molecules undergo isotropic reorientation diffusion on the order of nanoseconds. The correlation times of ...

A new carbazole-functionalized norbornene derivative, 5-[methylbis(N-carbazolyl)silyl]-2-norbornene, was polymerized via living ring-opening metathesis polymerization (ROMP) with RuCl2(CHPh)(PCy3)2...

Small-angle X-ray scattering was used to compare the morphology of extruded ultrahigh molecular weight polyethylene (UHMWPE) and melt-crystallized high-density polyethylene (HDPE). The crystalline morphology of UHMWPE has a low degree of order, rendering direct methods of analysis of the scattering curves unsuitable. We have demonstrated that the indirect transformation method, requiring no extrapolation of the scattering curve, can be used to obtain the one-dimensional correlation functions for these dense lamellar systems. The lamellar morphology of UHMWPE contained a large distribution of lamellar thicknesses, diffuse interfaces, and a large variation of interlamellar spacing as compared to those features in HDPE. The interlamellar spacing of extruded UHMWPE determined from the one-dimensional correlation function was 50 nm and that of melt-crystallized HDPE was 26 nm. The amorphous zone thickness of HDPE was 8 nm.

The molecular mobility at the interface of poly(dimethylsiloxane) [PDMS]/nylon-6 block copolymers was investigated using dynamic mechanical analysis (DMA) and solid-state deuterium NMR. Using DMA, T g depression of the nylon matrix was observed with increasing PDMS content, and the mechanical loss peaks were broadened to lower temperature. When the room-temperature line spectra of solid-state deuterium NMR were compared for nylon-6 homopolymer and PDMS/nylon-6 diblock copolymer, a clear difference was observed ; a peak associated with highly mobile nylon was observed in the block copolymer spectrum. This high mobility peak was observed even at -50°C. Using a selectively deuterated triblock copolymer, the origin of this peak was shown to arise from a shell of softened nylon in the vicinity of PDMS domains. This softening effect was lost at -80°C where PDMS domains can crystallize. This softened shell is not only from the compositionally mixed interfacial zone but also from a fraction of the pure nylon region surrounding the interfacial zone.

Sequential ring-opening metathesis polymerization of either norbornene or 9-methyltetracyclo-[6.2.1,1 3.6 .0 2,7 ]dodec-4-ene (MTD) and 7,8-bis(trifluoromethyl)tricyclo[4.2.2.0 2,5 ]deca-3,7,9-triene (TCDT) with Mo(CHCMe 3 )(NAr)(OCMe 3 ) 2 (Ar = 2,6-diisopropylphenyl) followed by linking termination with a conjugated dialdehyde results in highly soluble A-B-A triblock copolymers containing a precursor to Durham polyacetylene as the central block. A series of copolymers that contained from 10 to 200 equiv of TCDT was synthesized. The precursor copolymers were spin coated to give submicron thin films. In the case of the copolymers made with norbornene, higher spin speeds resulted in a red shift of the UV/vis spectra of the final polyacetylene-containing copolymer, indicative of longer average conjugation lengths within the film. A red shift was also observed in the UV/vis spectra of copolymers made with more equivalents of TCDT. The nonlinear optical susceptibility (X (3) ) of the copolymers was probed with third harmonic generation and degenerate four-wave mixing. X (3) increased with increasing equivalents ofTCDT. In all cases, the copolymers made with norbornene had larger X (3) values than the copolymers made with MTD.

A series of semicrystalline triblock copolymers E/EP/E, of poly(ethylene) (E) and poly(ethylenepropylene) (EP) were subjected to high levels of plane strain compression using a channel die. The processing was carried out at 150°, a temperature which lies well above both the E block melting points (99-103°) and the quiescent order-disorder transitions (ca. 106°) for these samples. The lamellar orientation relative to the specimen boundaries was determined using two dimensional SAXS. By using a 2.4 MPa applied stress on the channel die, the lamellae orient parallel to the plane of shear, while processing at an applied stress of 8.0 MPa causes the lamellae to orient perpendicular to the plane of shear. Gas permeability coefficients P for He and CO 2 were measured at 25° for E/EP/E 25/50/25 specimens and compared to modeling predictions. The upper bound (lamellae aligned in parallel with respect to the permeation direction) and lower bound (series lamellar alignment) models were compared to experimental permeation data on the corresponding oriented triblock specimens

Tracer diffusion of 3000 g/mol perdeuterated polybutadiene (dPB) into high molecular weight polystyrene (PB) was measured with forward recoil spectroscopy (FRED) in the temperature range from 90 to 110°C in the presence of argon and helium pressures up to 11.9 MPa. The diffusion coefficient for dPB in PB at 107°C increases from 1.2×10 -13 to 8.7×10 -13 cm 2 /s the argon pressure is increased from atmospheric pressure to 11.9 MPa. When helium is the pressurizing medium, the diffusion coefficient for dPB in PB at 107°C decreases from 1.2×10 -13 to 3.7×10 -14 cm 2 /s as the pressure is increased from atmospheric pressure to 11.3 MPa

A series of semicrystalline diblock copolymers of poly(ethylene)/poly(ethylene-propylene) (E/EP) were subjected to high levels of plane strain compression using a channel die. Deformations were imposed both below and above the melting point of the E block. The crystallographic and morphological textures were eramined using WAXD pole figure analysis and two-dimensional SAXS. The lattice unit cell orientation of the crystallized E chains with respect to the lamellar superstructure was determined, as well as the lamellar orientation relative to the specimen boundaries

Surface composition of solution-cast films of diblock copolymers of poly(dimethylsilorane) (PDMS) and nylon-6 was measured by using angle-dependent ESCA. Segregation of PDMS in the free surface region of the block copolymers was detected. The surface composition of these amorphous-semicrystalline block copolymers depends on both their polymer structure and the way the films are prepared. Mixed solvents can be used to control the competition between crystallization and microphase separation and, eventually, to adjust the surface composition of the solution-cast films. Annealing of the solution-cast films drives more PDMS into the surface region

The thermally-induced diffusion of low molecular weight perdeuterated polybutadiene (dPB) in polystyrene (PS) was measured with forward recoil spectroscopy (FRES). Diffusion coefficients were determined for 3000 g/mol dPB penetrating into a 350 000 g/mol PS matrix in the temperature range 97-115 o C. The diffusion coefficients vary from 10 -15 to 10 -12 cm 2 /s. The apparent activation energy is 99 kcal/mol. Solubility limits for dPB in PS at temperatures ranging from 105 to 160 o C were also determined with FRES. The results were used to construct a portion of the binodal curve for this polymer system

Numerous specimens of a single linear polyethylene sample were deformed by plane strain compression in a channel die to very large plastic strains. The mechanisms of deformation were elucidated by density measurements, polarized light microscopy, TEM and wide-angle and small-angle X-ray diffraction.

The plastic resistances for the three most important mechanisms actig in HDPE, i.e. the (100)[001] and (010)[001] chain slips and (100)[010] transverse slip was investigated and the ranges of crystal odrientation in which a single one of these mechanisms dominares the observed deviation behavior were explored. An attempt was also made to detect the (110)[001] chain slip, which according to theoretical predictions should also be an active mechanism in the deformation of polyethylene crystals

X-ray pole figure analysis and small angle x-ray scattering were used to determine the lattice unit cell orientation with respect to the lamellar microstructure for semicrystalline diblock copolymers of ethylene-co-butylene-b- ethylethylene (EBEE). The x-ray data indicate that the orientation of the crystallized EB chains is perpendicular to the lamellar normals, unlike the chain cry folding which has been observed in semicrystalline homopolymers and proposed for semicrystalline diblock copolymers where the crystallized chains align roughly parallel to the lamellar normals. The unusual chain folding observed for EBEE is attributed to the influence of topological constraints in the EB blocks which crystallize with the amorphous lamellar microdomains present in the heterogeneous melt phase of the block copolymers. Lamellar morphology, Chain folding, Semicrystalline block copolymer, X-ray studies of polymers.

The formation of an axially aymmetrical texture in HDPE was studied through unixial compression at room temperature. The orientation of crystallographic axes was probed at various stages of the deformation process, up to an equivalent strain of 1.86, by means of WAXS pole figures. Additionally the lamellar orientation was studied using SAXS and TEM. The results of these structural and morphological studies demonstrated that the major deformation mechanism involved in plastic deformation of the crystalline phase were (100)[001] chain slip

Diblock copolymers of norbornene and Sn[2,3-trans-bis-([tert-butylamido]methyl)norborn-5-ene]Cl 2 were prepared by ring opening metathesis polymerization using a tungstene alkylidene catalyst. TEM and SAXS data showed that these copolymers exhibited spherical, cylindrical or lamellar morphology depending on their composition and molecular weight. The phase diagram compared well with the predictions of the Helfand and Wasserman theory.

Diblock copolymers of isotactic polystyrene and 1,4 polybutadiene were successfully synthesized by two methods: a) coupling of two endfunctionalized homopolymers, and b) sequential synthesis of the two blocks. The polybutadiene blocks were prepared by anionic synthesis yielding = 90% 1,4 (cis-trans) and = 10% 1,2 addition. The preparation of the isotactic polystyrene block involved a novel anionic polymerization technique using low temperatures and the addition of BuOLi for stereospecific placement. Overall isotactic yields of 10% by weight were obtained, the remainder being unreacted monomer (50%) and atactic material (40%). The polymers were characterized by GPC, NMR and DSC to determine molecular weights, tacticity and percent crystallinity. The block-like nature of the copolymer was further analyzed through transmission electron microscopy.

The mechanics of deformation of nylon 6 is plane strain compression were elucidated by density measurements, differential scanning calorimetry, polarized light microscopy, x ray diffraction and x ray diffraction pole figures. A deconvolution procedure for separating overlapping x ray diffraction peaks and the amorphous halo was used to generate pole figures for the various alpha and gamma phase reflections exhibited by nylon 6. At compression ratios above 1.6, specimens experienced intense shear stresses at -45 deg and +45 deg with respect to the flow direction. Shear bands were formed most frequently at interspherulitic boundaries. This shearing produced a small volume fraction of gamma phase crystals in samples which originally contained only alpha crystallinity. The x ray diffraction studies showed that gamma phase crystals were oriented with their macromolecular chains along the directions of shear bands. The alpha crystals of nylon 6 underwent extensive deterioration in compression by a chain slip mechanism along the (0 0 2) planes containing hydrogen bonds. Slip also caused the rotation of fragmented lamellae that lead, at high compression ratios, to a peculiar bifurcated orientation state resembling a twinned monocrystal.

At least square peak deconvolution procedure was applied to wide angle x-ray diffraction data on uniaxially drawn nylon 6 so that pole figures could be generated from clearly separated crystallographic reflections. Beside peak total intensity pole figures a new type of pole figure, based on peak widths, was proposed and proved to be useful in elucidating the mechanisms of plastic deformation in the nylon 6 samples. In uniaxial tension alpha and gamma crystals of nylon 6 become oriented with macromolecular chains parallel to the drawing direction. In contrast to gamma crystals, alpha crystals experience a large amount of breakdown between planes containing hydrogen bonds. Macromolecules which are in the amorphous phase are mostly aligned along the drawing direction and that fraction of amorphous phase are mostly aligned along the drawing direction and that fraction of amorphous phase which is so oriented shows the best close packing.

Permeability coefficients (P) for several gases were measured in heterogeneous polystyrene/polybutadiene (PS/PB) block copolymer films before and after reaction with aqueous bromine. Films reacted to low and very high extents exhibited decreases in P and increases in selectivity compared to the starting material. At intermediate reaction extents, effective permeability coefficients in the reacted materials were higher than those in the unmodified films, resulting in membranes which exhibited both selectivity and permeability enhancement relative to the starting PS/PB system. These effects on permeability are the combined result of physical and chemical changes in the block copolymer films caused by the bromination reaction. Keywords: Block copolymers, Membranes, Bromination of polymers, Gas separations, Fluid mechanics, Polystyrene/polybutadiene, Chemical reaction, Gas permeability, Packaging materials, Modification.

Solubility and diffusion coefficients for CO2 in polystyrene polybutadiene (SB) block copolymer films were measured in a pressure decay sorption apparatus at 1 atm over a temperature range of 20 to 90 C. The morphology of the block copolymer specimens consisted of alternating S and B lamellae of approximately 100 angstrom thickness with excellent long range orientation perpendicular to the surface of the 0.02 to 0.05 cm thick films. Diffusion behavior in the copolymer was simulated using homopolybutadiene and homopolystyrene data along with a finite difference model based on the well- ordered morphology. Comparisons of model predictions with the measured values of the effective diffusion coefficient for CO2 in the copolymer revealed that the diffusion coefficient of CO2 in the polybutadiene region of the copolymer was lower than in homopolybutadiene by a factor of 1.9 at 20 C. This difference disappeared at the glass transition temperature of the polystyrene in SB. This temperature-dependent reduction of CO2 diffusion in the polybutadiene regions of the block copolymer results from restrictions on chain motions of the polybutadiene blocks arising from their connection to polystyrene blocks. (aw)

An increase of toughness by about a factor of 10 above that of polystyrene can be achieved with a 1,1% polybutadiene (MW = 2760) blend if the precipitated polybutadiene pods can be maintained at a size smaller than 0,2 μm. The origin of this effect is discussed

A theoretical model is presented for the toughening of brittle glassy polymers by the controlled solvent crazing action of precipitated low molecular weight rubber diluents existing in the form of randomly dispersed small spherical pools. The resulting expressions for the reduction of the craze flow stress with increasing volume fraction of diluent are in excellent agreement with experimental measurements

Blends of polystyrene with of spherical shell particles composed of alternating shells of PS and lightly crosslinked polybutadiene of averaze sizes of 0.32 and 2.3 μm are prepared at particle weight fractions of 0,05 and 0,15. It is found that the craze flow stress increases systematically with decreasing particle volume fraction at constant particle size and that the blends with the small particles that are less potent craze initiators have higher flow stresses than blends with large particles

Mesure de la permeabilite a 25°C dans 2 copolymeres styrenel butadiene, l'un constitue de lamelles alternees perpendiculaires a la direction de permeation l'autre de spheres de polybutadiene dans une matrice de PS, dont le comportement est lamine par le composant a basse permeabilite (PS). Presentation de modeles decrivant la permeabilite de ces sytemes

High density polyethylene (HDPE) specimens were subjected to high orientation producing deformations below the melting point using either a rolling mill or a channel-die. After appropriate annealing protocols, the crystallographic and morphological textures were examined using wide-angle x-ray diffraction pole figures, two dimensional small-angle x-ray scattering and transmission electron microscopy. Although the two deformation patterns resulted in very similar crystallographic textures, the details of the morphological arrangements of crystalline lamellae were different. Quantitative considerations of the 2-D SAXS patterns led to the conclusion that lamellae which are inclined to the macroscopic orientation direction reflect a shear process within the individual lamellae, rather than a rigid rotation inside the surrounding amorphous material. The crystalline part can deform by slip, twinning or stress- induced martensitic transformation. The goal is to simulate the texture evolution at large deformations and compare results to the experimental ones. The simulation is done by a Relaxed Hybrid model which accounts for the inextensibility of lamellae in the chain direction and by a Self-Consistent model. The amorphous behavior is included in a composite formulation of both models. Keywords: Strain rate; Plastic flow.

Channel die compression has been used successfully to orient the lamellar morphology of a polyethylene/polystyrene diblock copolymer. The lammelar orientation is retained when specimens are annealed under constraint at temperatures well above the melting point of the polyethylene crystals. Slow ccoling to room temperature then provides a means for crystallizing the polyethylene chains in the presence of a preexisting lamellar morphology. The SAXS and WAXS results completely corroborate earlier findings which showed that the polyethylene chain direction (c axis) is parallel to the lamellae (i.e. perpendicular to the lamellar normals) of the block copolymer morphology

The synthesis of amphiphilic star block copolymers by ring opening metathesis polymerization using a new cross-linking agent and appropriately functionalized norbornene-type monomers is reported

Diblock copolymers of (ethylene-co-butylene)-b-(ethylene) (EBEE) were used to evaluate scaling laws describing the molecular weight dependence of the lamellar domain spacing of semi-crystalline block copolymer systems. Small angle X-ray scattering was used to measure lamellar domain spacings for a series of EBEE samples. Experimental results were in good agreement with the predictions of the equilibrium theory of Whitmore and Noolandi.

Poly(methyl methacrylate)s (PMMA) containing both tethered and untethered polyhedral oligomeric silsesquioxanes (POSS) were examined through the use of wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and rheological characterization. The presence of tethered-POSS in entangled copolymers leads to a decrease in the plateau modulus ( ) when compared with PMMA homopolymer. Two untethered-POSS fillers, cyclohexyl-POSS and isobutyl-POSS, were blended with PMMA homopolymer. Both DSC and rheological results suggest a regime at low untethered-POSS loadings (φ ≤ 0.05) in PMMA in which much of the POSS filler resides in the matrix in a nanoscopically dispersed state. This well-dispersed POSS decreases the zero-shear-rate viscosity (η0). Above this regime, an apparent solubility limit is reached, and beyond this point additional untethered-POSS aggregates into crystallites in the PMMA matrix. These crystallites cause both the viscosity and the plateau modulus to increase in a way consist...