Solvent effect on structural formation and molecular mobility of polyvinyl chloride gels

Abstract

In this work, the interaction between polyvinyl chloride (PVC) and organic solvents was first investigated through viscometric results and the donor-acceptor electron properties. The results clearly showed that the affinity of nitrobenzene (NrBz) to PVC is higher than that of chlorobenzene (ClBz). On the other hand, the critical gel concentrations Cgel* are 1.7 g dL-1 and 6 g dL-1, respectively, for the PVC/ClBz and PVC/NrBz solutions at 30 °C, indicating that the polymer-solvent interaction directly affects the gelation ability. Then, the structural formation and the molecular mobility of PVC gels were investigated using pulsed 1H NMR analyses. The CPMG decaying signals from pulsed NMR measurement of the PVC gels could be decomposed into three components, reflecting respectively the proton mobility in the junction zone, in the polymer-rich phase and in the solvent-rich phase of the gel network. The solutions began to appear the fraction of junction zones at PVC concentration above 1.5 g dL-1 and 6 g dL-1, respectively, in the PVC/ClBz and PVC/NrBz solutions, while the formation of the junction zones could interconnect the polymer chains into a three-dimensional network structure macro-domain. As the immobile junction zones were formed, the mobility of the PVC chains was reduced and the mobility of the solvent molecules could also be suppressed. This phenomenon typically appeared in the polymer/poor solvent (PVC/ClBz) system. Through the observation of the diffusion property of the solvent molecules, we can clearly show that the gel network in PVC/ClBz gels is denser than that of PVC/NrBz gels.