Crystalline stereocomplex formation of isotactic poly(methyl methacrylate) (it-PMMA) and syndiotactic poly(methyl methacrylate) (st-PMMA) induced by high-pressure CO2 at pressures in the 5−35 MPa range and at temperatures in the 30−110 °C range was demonstrated by means of differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS) investigations as a function of treatment pressure, temperature, and the it-PMMA/st-PMMA ratio. At a constant it-PMMA/st-PMMA ratio, the melting temperature of the stereocomplexes was shown to increase with increasing treatment pressure and temperature. The amount of the stereocomplex formed by high-pressure CO2 was found to be higher than that by thermal annealing in bulk. The heat of melting of the stereocomplex was the highest for the 1/2−1/1 it-PMMA/st-PMMA ratio. Compared with amorphous PMMA, the crystalline stereocomplex induced by high-pressure CO2 contributes to the superior morphology of the microcellular foams obtained. For the CO2-treated polymer, the average cell size decreases and the average cell density increases as the amount of the stereocomplex that was formed increases.

Elastomeric block copolymers are two-phase systems composed of spherical domains of a plastic component of colloidal dimensions dispersed in a matrix of rubber component. The deformation mechanism of such copolymers was investigated for A-B-type and A-B-A-type block copolymers of styrene and isoprene, as well as for mixtures of the A-B-type block copolymer with each corresponding homopolymer, by means of simultaneous measurements of the tensile stress-strain relation, small-angle light scattering, and small-angle X-ray scattering. The deformation of these materials, except for that of a mixture of the A-B-type block copolymer with homopolyisoprene, is accompanied by formation of heterogeneity in density over a considerable region which is much larger in size than the microheterogeneous structures of the materials, i.e., the domain structures formed by the microphase separation of the block segments. The elastomeric properties of the block copolymers at relatively higher elongations are associated with the formation of this localized region of lower density rather than with the uniform deformation of the rubber matrix between the hard spherical domains. On the other hand, for the exceptional specimen, the mixture of the A-B-type block copolymer with homopolyisoprene, the formation of such a localized heterogeneous region is prevented by the flow of homopolyisoprene molecules, which are not anchored to the surface of the spherical domains of polystyrene, into the region.

Polarized light scattering from several types of collagen films cast from an acid soluble collagen and solubilized collagens by proteolitic enzyme (except callagenase) and from denatured films under various conditions, was observed under H. and Vv polarization conditions. The scattering patterns from the collagen films were different from those from spherulitic films of polyalphaolefins. The patterns were analyzed in terms of a three-dimentional random assembly model of anisotropic rods resulting in the following conclusions. The polar angle of orientation of scattering elements with respect to the rod axis ranged from 50 to 70°, depending on the type of collagen film. The value of p, which is defined by (al.-a.)/(au-aJ.), changes from very positive in the air-dried state to less positive, zero, or even slightly negative in the swollen state in saline, also depending on the types of collagen film. On the other hand, the characteristic H. patterns were diminished in intensity with denaturation while the Vv patterns-as well as the wide angle X-ray diffraction patternwere not changed to the same extent. This suggests that the light scattering from denatured films arises mainly from correlation in density fluctuations rather than that of orientation of local anisotropy; that is, it is suggested that denaturation causes disintegration of the crystalline superstructure rather than of the crystallites. These crystallites are too small in their correlation distance of the orientation fluctuation to give H. scattering at such small scattering angles as several degrees only. KEY WORDS Polarized Light Scattering I Collagen Film I Denatured Film I Crystalline Texture I Anisotropic Rod I Random Assembly Model/ Calculation I Swelling I Saline I Light scattering from polymer systems in the solid state has been studied from two approaches.

Crystalline stereocomplexes of highly stereoregular isotactic poly(methyl methacrylate) (it-PMMA; mm ) 97.2%) and syndiotactic poly(methyl methacrylate) (st-PMMA; rr > 86.1%) blends formed by treatment with supercritical CO 2 at pressures from 5 to 25 MPa and at temperatures in the 30-170 °C range were investigated by means of differential scanning calorimetry (DSC) measurements as a function of treatment temperature, pressure, and it-PMMA/st-PMMA mixing ratio. The ∆H of the stereocomplex had a maximum at 33 wt % it-PMMA content, in agreement with stereocomplexes formed in some solvents and in bulk thermal annealing methods. For the case of over 50% it-PMMA content, two endothermic peaks, T m 1 and Tm 3 , were detected. Examination of the effect of heating rate from 5 to 40 °C/min on the DSC results showed that the melting temperatures, Tm 1 and Tm 3 , corresponded to the fringed micellar structure and the lamellar crystallites of the complexed sections, respectively. For 33% or less it-PMMA content, the crystalline stereocomplex formed by supercritical CO2 had only one endothermic peak that occurred over a narrow temperature range, which was comparable with that obtained by thermal annealing or solvent treatment.

tion of the equilibrium stress-optical coefficients in connection with the light-scattering results shows that the reorganized regions should exhibit a higher form anisotropy the larger the value of A/app. Such increasing form anisotropy can be either due to increasing anisometry of the regions or-at a given anisometrydue to an increasing refractive index difference with the surrounding.The reasons for the appearance of some fairly longrange anisotropic structures in the PHEMA hydrogels have previously, in the first place, been traced to the amphiphilic nature of the polymer chain, which especially in water could lead to regions of micromesomorphic order.1 234 56Inhomogeneous cross-linking may be a second contributing factor, especially if water is present during network formation.The optical behavior can be qualitatively understood Scattering from a Spherical Domain Structure 433 in terms of a somewhat organized network containing cross-links and entanglements. Any cross-link or entanglement will restrict the long-range organization.The movement of entanglements during stress relaxation will change the interchain correlations, so that a restructuring will result. At small A/app the equilibrium optical behavior will approach the Gaussian behavior because the large number of cross-links disrupts the organizing tendency of the amphiphilic system.Acknowledgments. The financial support of the Syracuse University Research Institute is gratefully acknowleged. M. I. expresses his gratitude to the Institute of Macromolecular Chemistry, Czechoslovak Academy of Sciences, for granting a leave of absence, which made his postdoctoral stay in the U. S. possible. J. Hasa, Prague, has kindly cooperated in the preparation of the samples.