Modification of poly(styrene- [formula omitted]-acrylonitrile) to promote polymer blend miscibility through hydrogen-bonded (2,4-diamino-1,3,5-triazine)maleimide interactions

Abstract

The acrylonitrile units in poly(styrene- stat -acrylonitrile) (SAN) have been partially converted to the 2,4-diamino-1,3,5-triazine (DAT) moiety by the reaction with dicyandiamide in dry dimethyl sulfoxide, containing catalytic amounts of potassium hydroxide. This produced a range of terpolymers of poly(styrene- stat -acrylonitrile- stat -vinyl 2,4-diamino-1,3,5-triazine) with mol% composition in the range (54.3:43.0:2.7) to (54.3:25.0:20.7). Copolymers of methyl acrylate (MA) and maleimide (MI) were also synthesised and used to prepare blends with the modified SAN terpolymers. Here the triazine rings and the maleimide units can form complementary pairs of donor-acceptor-donor (DAD) and (ADA), triple hydrogen bonding sites. It was found that miscible, one-phase, polymer blends could be formed if the DAT content of the modified SAN terpolymers was ⩾ 10 mol% and the MI content of the (MA–MI) copolymers was > 22 mol%, or alternatively if the MI content was 9–14 mol% and the corresponding DAT content in the modified SAN was ⩾ 21 mol%. Once formed these secondary interactions were stable up to the onset of degradation of the blends and there was no evidence of a lower critical temperature for phase separation.