FREE CHAINS TRAPPED IN A SWOLLEN GEL UNDER DIFFERENT SOLVENT CONDITIONS

Small-angle neutron scattering measurements are reported on the radius of gyration R(G) of free poly(vinyl acetate) (PVAc) chains absorbed into a PVAc network swollen in isopropyl alcohol. Measurements were made at constant concentration on the same gels both at the Theta temperature of this system, 52 degrees C, and in good solvent conditions at 70 degrees C. The neutron contrast was ensured by using fully protonated free chains and a partially deuterated network. At 52 degrees C, the radius of gyration of the trapped polymer, R(G) = 57 Angstrom, is smaller than in Theta solution (R(G) = 96 Angstrom). No measurable change was observed in the radius of gyration of the free polymer in the network between the Theta and the good solvent condition. The results can be understood in terms of recent theories describing the behavior of chains trapped in random porous media.