Flame-retarding effects of dialkyl-p-vinylbenzyl phosphonates in copolymers with acrylonitrile

Several dialkyl‐p‐vinylbenzyl phosphonates have been synthesized and free‐radically copolymerized with acrylonitrile to give copolymers with phosphorus contents ranging from 1 to 14 wt%. The flammability and thermal degradation characteristics of these copolymers have been assayed by limiting oxygen index and thermogravimetric methods. It has been found that, despite the negative effect of the vinylbenzyl entity upon the stability of polyacrylonitrile, the incorporation of a small percentage of phosphonate has a significant effect on retarding combustion of the copolymers. The differing effects of the polymerizable function (backbone group) and the pendant phosphonate on thermal stability and flame retardance are deconvoluted by comparison of the behaviours of the acrylonitrile–dialkyl‐p‐vinylbenzyl phosphonate copolymers with the corresponding acrylonitrile–styrene copolymers. The increased flammability and reduced char formation in acrylonitrile–styrene copolymers, compared with those of polyacrylonitrile itself, are shown to recover in the presence of pendant phosphorus groups, and the particular effects of these groups are discussed. Copyright © 2005 Society of Chemical Industry