Although, these solvents have similar solubility parameter and molar volume, their chemical structures with
dierent functional groups must induce various donor±acceptor electron ability and charge-density arrangements.
The critical gelation concentration, C
and the gelation time in PVC/DOA solutions are smaller and shorter than
those in PVC/MOR solutions, implying that the aggregation of PVC chains in the solution with poor solvent takes
place much more easily. On the other hand, PVC/DOA gels exhibit higher gel melting and sol±gel transition
temperatures compared with those of PVC/MOR gels at a given gelation condition. The low value of the Rayleigh
ratio (R90) in PVC/MOR gel shows no signi®cant change with aging time, implying that the phase separation is
hard to proceed further. The 1H pulsed NMR measurement was used to determine the heterogeneity of the gel. The
result shows that PVC/DOA gels have a more heterogeneous network structure due to the lower degree of
molecular interaction. # 1999 Elsevier Science Ltd. All rights reserved.