| Abstract: | The η] of randomly branched PSty/DVB continually decreases from linear polystyrene with increasing conversion. On the other hand, the relation of the 〈S2〉 to M of both low and high conversion series is equivalent, although the actual size is smaller than that of linear polystyrene of the same M. This fact, in conjunction with the previously published reactivity ratios, allows the following interpretation of the mechanism of copolymerization: namely, that branched molecules are formed in which the center core is higher in DVB content than is the periphery. Only about 1/7 of the available DVB units act as effective tetrafunctional branch points. An analysis of GPC data correlated with light scattering and viscosity dimensions allows the g value to be determined in the lightly and highly branched fractions. The viscosity ration is related to gx, where x is 0.65 for low conversion fractions (A series) and becomes 1.41 for high conversion fractions (B series). This change in exponent is postulated to arise from an increase in branching density as conversion increases. The ratio of the hydrodynamic radius to the radius of gyration is higher for branched than for linear polymers. The theta temperature (θ) in cyclohexane for randomly branched polystyrene compared to linear polystyrene is always higher and can be as much as 2° higher. |
