Chemical modification of polymers to improve flame retardance .2. The influence of silicon-containing groups

Polystyrene has been silylated by a two-stage process, involving reaction with n-butyl lithium in the presence of tetramethylethylenediamine, followed by reaction with trimethylchlorosilane, dichlorodimethylsilane or trichloromethylsilane. The degree of silylation can be increased if the polystyrene is initially brominated, in the presence of thallic acetate, prior to lithiation and silylation. The surfaces of poly(vinyl alcohol) films have also been modified with a number of chlorosilanes. Flame retardant effects of these modifications have been assessed by measurements of char yields, weight losses and limiting oxygen indices. The limiting oxygen indices of the silylated polymers are all significantly higher than those of the parent polymers and small char yields are obtained on combustion of them. Silicon is shown to have a greater effect on flame retardance in the presence of halogen for each of the modified polymers. (C) 1996 Elsevier Science Limited