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The theoretical results availabTe for the i,nte,rpretatio~ of the dynamic scattering from polymer soJutions have been re,examined. The scattering law S~/, t) is formulated using the eigenfunction expansion method and the linear response theory. All previously known exact expressions of S(q, t) for a single unperturbed Gaussian cl~ain have been re-derived using the first method to demonstrate the interrelationships among the various approaches to calculation of S(q, t). The results are cast into new forms which, in many cases, are more convenient for both numerical and analytical discussions. The ~nfi~i~e ~hain results are obtained from the exact closed expression of S(q, t) for ring polymers as a special .case as N ~ oo. Questions like the effect of the draining parameter on the shape of S(q, t), the positive definiteness of the diffusion tensor, and the possibility of measuring the eigenvalue of the first internal mode through light scattering, have been included in the discussions. A new method has been proposed for the interpretation of the dynamic scattering experiments in terms of the initial slope, ,Q,, of In S(q, t). The quantity ~ can also be identified as the first cumulant ofS(q, t). The advantage of this method is that ~Q(q) can be calculated for all q values as a function of temperature and concentration by combining the linear response theory and the blob model of chain statistics. Consequently, one is not restricted to the asymptotic small-and intermediate-q regions in order to interpret the scattering experiments. The analytical and numerical results giving ~2(q) under various conditions have been presented. Using infinite chain results it is shown that acts as a characteristic frequency in the sense that in both the small-and intermediate-q regions, In S(q, t) can be scaled to a q-independent shape function when time is expressed as ~,t. This property facilitates the measurement of ~ from S(q, t)-data using a known shape function. The feasibility of the method has been demonstrated using light scattering data on polystyrene in toluene in the transition region between small-and intermediate q-regions.

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The dynamics of copolymer and homopolymer mixtures with an arbitrary number of components both in bulk and in solution is studied within the framework of the mean field theory, and an expression of the first cumulant of the dynamic scattering function of a labeled component is obtained in terms of the static and dynamic single-chain properties and the Flory interaction parameters. In particular, a new result is obtained to relate the mobility of the labeled chain to the mobilities of the other components, treating one of the homopolymer species as the "matrix" and using incompressibility. The case of polymers in solution is studied as a special case by treating the solvent as the matrix. The new results differ from the reported theoretical results for binary homopolymer and copolymer solutions, as well as copolymers in a homopolymer matrix. The origin of this discrepancy is explained.

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