CONFORMATION OF FREE LINEAR POLYMER-CHAINS IN A POLYMER NETWORK

Small angle neutron scattering has been used to measure the radius of gyration of deuterated linear polystyrene at dilute concentration cont ained in a polystyrene network with different crosslink densities. At each crosslink density, four samples with different linear chain conce ntrations (less than the overlap concentration) were made. The lower c rosslink density samples (N-c>180) remained single phase, while higher crosslink density samples showed evidence of phase separation. Zimm p lots were made for all samples which were single phase, and the second virial coefficient was obtained as a function of crosslink density. I t was found that the second virial coefficient decreased with increasi ng crosslink density. Single chain form factors were obtained by extra polating the scattering data to zero concentration of the linear chain for the single phase samples. A modified Debye equation was used to f it the zero concentration extrapolated scattering data over the entire experimental q range to obtain the radius of gyration, R-g, for the l inear chain. It was found that R-g was a function of the crosslink den sity. When the crosslink density was low (N-c > N-l), R-g did not chan ge appreciably and had a value nearly the same as in the melt. For hig her cross-link density samples (N-c < N-l), R-g was found to decrease with increasing crosslink density and the scaling relation R-g(-1) sim ilar to N-c(-1) was observed. Chain segregation was observed for the h ighest crosslink density samples. The dependence of R-g, on crosslink density can be qualitatively explained using a theory for the conforma tion of polymer chain in a random media. For the phase separated sampl es, a two correlation length theory was used to fit the scattering dat a.