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.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.