Chemical modification of polymers to improve flame retardance—I. The influence of boron-containing groups

Abstract

Samples of a linear polystyrene have been boronated, predominantly in the para-positions on the phenyl rings, by reaction first with mercuric tri-fluoroacetate and then with catechol borane, and the products then hydrolysed to give the polymeric boronic acids. Flame-retardant effects of these modifications have been assessed by measurements of limiting oxygen indices (LOI), and of weight losses and char yields on heating in air. The boron modified polymers have increased LOI values and give greater yields of char in comparison with those of the unmodified polystyrene. The surface modification of films of poly(vinyl alcohol) and of poly(ethylene-co-vinyl alcohol) with alkali metal borates has also given some encouraging results. Increases in LOI values and char yields can be optimised by adjusting the concentrations of the aqueous solutions of boric acid and sodium hydroxide used to effect the modifications.