Efficient syntheses of the triblock copolymer styrene‐ b ‐tetrahydrofuran‐ b ‐styrene by coupling of preformed blocks

The triblock copolymer styrene‐ b ‐tetrahydrofuran‐ b ‐styrene was prepared from commercially available hydroxyl‐terminated poly(tetrahydrofuran), M n = 1,650 and mono‐hydroxyl‐terminated polystyrene, M n = 7,600. Poly(tetrahydrofuran) blocks were first chain extended by reaction by with 1.1 equivalents 4,4′‐diphenylmethane diisocyanate (MDI) and subsequently end capped with 20% excess of hydroxyl‐terminated polystyrene. Gel permeation chromatography revealed clearly the success of the end capping step to give triblock copolymer mixed with a small amount of excess polystyrene. 1 H NMR revealed a gross composition by weight of 50% styrene, 41% tetrahydrofuran, and 9% MDI. DSC revealed a 5°C elevation of the PTHF glass transition and a 15°C lowering of PS glass transition temperature as compared with those of the individual component blocks. These values along with behavior of films as a tough elastomer are consistent with triblock structure and microphase separated morphology. The polymer does not flow readily below 125°C which is well above T g of the polystyrene domains.