Structural expressions of long-chain esters on their plasticizing behavior in poly(vinyl chloride)

Abstract

This is the first comprehensive report on the influence of structure and molecular weight of long-chain esters on their plasticization behavior with PVC. Below a molecular weight of 550, there is a decrease in $T_g$, with molecular weight in linear, three-branched and four-branched neat esters, which is explained by the dilution effect of carbonyl groups with an increase in chain length. In the high molecular weight esters above 550, $T_g$, continuously decreases in linear esters, but in three-branched and four-branched esters it increases with the molecular weight, which is explained from the blob model. The dilution effect in the linear esters decreases the PVC-plasticizer interaction and consequently $T_g$, increases with molecular weight both in the low and the high molecular weight esters. In the three-branched and four-branched esters the dilution effect is overtaken by structural effects. The carbonyl groups are shielded and less exposed to PVC in the beginning, but as the arms grow with molecular weight, they become more flexible which facilitates their interaction with PVC. This continuously decreases the $T_g$ with molecular weight in three-branched and four-branched esters upto a molecular weight of 550, beyond which entanglement suppresses the flexibility and, as a result, $T_g$ increases with molecular weight.