Synthesis and thermal properties of [n]-polyurethanes

Aliphatic [n]-polyurethanes were obtained by catalytic polycondensation of suitable α-hydroxy-ω-O-phenyl urethanes (III). 1H and 13C NMR analyses of the resulting [n]-polyurethanes (3 a–g) show a uniform microstructure consisting of urethane groups only, and with carbonate and urea groups being absent. The [n]-polyurethanes with linear alkylidene moieties (3 a–e) are highly crystalline materials, their melting points show the same odd-even effect as was observed for [n]-polyamides. The [n]-polyurethanes with branched alkylidene groups (3 f, g) show lower crystallinity (3 g) or are amorphous (3 f) materials. Upon heating, the [3]- and all the [4]-polyurethanes (3 a and 3 b, f, g) result in the corresponding cyclic urethanes by ring-closing depolymerization.