Abstract
Polyurethane elastomers were prepared from poly(oxytetramethylene)glycol (PTMG) of $M_{w}$ 1,000 as a polyol, 4,4'-diphenylmethane diisocyanate (MDI) as a diisocyanate, and N,N'-bis(6-hydroxyhexyl)-3,4,3',4-biphenyldicarboxyimide (BHHDI) as a chain extender which has a flexible spacer of 6-methylene and imide units in the chain. In this study, the polyurethane elastomers are prepared by one-step or two-step methods. In the one-step synthesis all the reactants, MDI, PTMG, BHHDI, were reacted simultaneously and in the two-step synthesis an excess of diisocyanate was first reacted with a polyol PTMG, and then with a dihydroxy compound. The effects of one- or two-step polymerization conditions on the thermal and mechanical properties were studied. The thermal and mechanical properties of polyurethane elastomers were investigated by differential scanning calorimetry, dynamic mechanical thermal analysis, tensile testing, and X-ray diffractometry. In the polyurethane elastomers obtain by one-step or two-step methods the thermal stability, tensile strength, and initial modulus increase as the hard segment content is increased, whereas elongation at break decreases with increasing hard segment content. The polyurethane elastomers prepared by an one-step method show higher crystallinity and melting temperature than the polyurethane elastomers prepared by a two-step method. This is attributed to different polymerization conditions of the polyurethanes.
