Synthesis and properties of multi-block thermoplastic polyurethanes constructed with polystyrene and poly(butylene adipate) sequences

A simple route is established to synthesize segmented polyurethanes constructed mainly with polystyrene and poly(butylene adipate) sequences. A long dihydroxyl terminated polystyrene (HO-PS-OH) was synthesized through the radical polymerization of styrene with 4.4′-azobis(4-cyanopentanol) as initiator. The HO-PS-OH, HO-terminated poly(butylene adipate) (HO-PBA-OH), and 4,4′-methylenediphenyl diisocyanate (MDI) were polymerized further in a one-step solution process, and a series of multi-block polystyrene-block-poly(butylene adipate) TPUs (PS–b-PBA TPUs) was prepared. Meanwhile, five two-step PS–b-PBA TPUs (ts- PS–b-PBA TPUs) were also prepared; that is, the HO-PBA-OH was first reacted with excessive MDI to obtain long OCN-terminated PBA-methylenediphenyl diurethane (PBA-MDU) prepolymers, and then it was polymerized with HO-PS-OH to form ts-PS–b-PBA TPUs. PS–b-PBA TPUs and ts-PS–b-PBA TPUs all showed two glass transition temperatures. Phase separation occurred between their hard and soft phases. Different from amorphous ts-PS–b-PBA TPUs that were constructed with long PBA-MDU soft segments (SSs) and PS-MDU hard segments (HSs), short and scattered PBA-MDU SSs and PS-MDU HSs led to crystallized PS–b-PBA TPUs that showed better mechanical property than ts-PS–b-PBA TPUs. Long amorphous PS and crystallizable PBA sequences provided the PS–b-PBA TPUs with high T g and good thermal and mechanical properties.