The synthesis and properties of rigid transparent polyurethane elastomers

Transparent polyurethanes have been synthesised producing flexible to rigid polymers. Thermoplastic polyurethanes as well as thermoset (crosslinked) polyurethanes have been made. The syntheses of these elastomers were all based on polycaprolactone polyols of differing molecular weight, and functionality; the thermoset polyurethanes were synthesised with triols and tetra-ols. Several diisocyanates were used, but most work concentrated on 4,4'-dicylohexylmethane diisocyanate (H12MD1 or Desmodur W); others included isophorone diisocyanate (IPDI) 1,4-cyclohexane diisocyanate (CHOI), paraphenylene diisocyanate (PPDI) and 2,2,4-(2,4,4-) and trimethyl-hexamethylene diisocyanate (TMDI). The synthesis method varied with the diisocyanate and crosslinking system used. The approach was to make a series of polyurethanes over the range flexible to rigid; this was accomplished by synthesising polymers with varying polyol molecular weights (soft segment content) and block ratios (hard segment content). Observations of physical properties gave values for modulus, ultimate tensile strength, elongation at break and hardness; some of the polyurethanes were found to have good impact and ballistic performance. Investigation of the effect of different chemical constituents on the properties was carried out by way of thermal analysis techniques such as Dynamic Mechanical Thermal Analysis (DMTA) and Differential Scanning Calorimetry (DSC). X-ray and infra-red (IR) techniques were also used to elucidate the reasons for transparency in the polymers. The long term stability of these polymers is also important and the systems used were especially chosen to maximise retention of physical properties and transparency.