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The nature of inhomogeneities in vinylpolymer gels has hardly been clarified yet. Inhomogeneities on submicron and nanometer scales in polyacrylamide gels have been investigated by using a scanning microscopic light-scattering system and applying a general formula for an ensemble-averaged correlation function. The network structure of the gels is modified by varying the preparation conditions and can be roughly divided into two types. Swelling-induced modulation of inhomogeneities depends on the type of the network structure. At low monomer concentrations in preparation, both submicron- and nanometer-scale inhomogeneities increase with swelling. At high monomer concentrations in preparation, submicron-scale inhomogeneities increase with swelling, but nanometer-scale inhomogeneities decrease anomalously. This behavior is explained by a model of inhomogeneous network structure of vinylpolymer gels, where macrogel is formed from a large number of microgel particles.

Phase separation induced by polymerization of 2-chlorostyrene (2ClS) in polystyrene (PSI/ di-n-butyl phthalate (DBP) mixtures was studied by the time-resolved light scattering (TRLS) technique and scanning electron microscopy. Measurements were performed a t a fixed composition of 2ClS:PS: DBP = 45:45:10 by weight in a temperature range from 110 to 180 "C that was above the glass transition temperature of the product. Conversion of 2C1S was estimated by gel permeation chromatography. Two distinct time regions were observed in time dependence of scattered light intensity I , and conversion of 2ClS. In the first region, Z, and conversion increased rapidly, while in the second region, conversion that had reached about 80% changed very little and the growth rate of I , became much smaller than that in the first region. The poly(2-chlorostyrene)-rich phase formed droplets, and droplets of relatively narrow distribution coexisted with much smaller droplets in an early period. Nonspherical domains were formed by coalescence of droplets. At lower temperatures, it was observed for the first time that the droplet domain structure transformed into cocontinuous domains. This morphological change occurred while the conversion changed very little. Acceleration of the phase separation rate associated with the morphological change was observed by TRLS. At higher temperatures, coalescence of droplets occurred only in a very early period, and droplets coarsened without forming cocontinuous domains in the later period. The mechanism of the polymerization-induced phase separation of this system is discussed.

The kinetics of spinodal decomposition of a binary polymer system of polystyrene/ poly ( vinylmethylether) near its critical composition has been studied by the temperature jump light scattering technique. The results indicate that the linearized theory of the Cahn-Hilliard-Cook type which includes the thermal fluctuation term can describe the polymer system very well in the early-time and shallow-quench region. The virtual structure factor Sx (q), which is a consequence of including the thermal fluctuation, has been obtained for the first time. For experiments of deeper quench, the virtual structure factor becomes small in our experimental q range, and the time dependent static structure factor, S(q,f), reduces back to the original Cahn-Hilliard type.

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