Thermoset and thermoplastic polyurethanes have been prepared
which are transparent and flexible. A synthesis technique
and reaction and curing conditions were investigated to establish
a reproducible method of obtaining these transparent urethanes:
this is based on a polycaprolactone diol/4,4 1 -methylene biscyclohexyl
diisocyanate (H12MDI) prepolymer system. Only certain
chain extenders will give transparent polyurethanes and these are
aliphatic diols, cycloaliphatic diols and triols. Their relative
reactivities with diisocyanates were studied. The way in which the various chemical constituents control
light transmission characteristics in polyurethane elastomers
has been investigated by studying the morphology using differential
scanning calorimetry (DSC), infrared spectroscopy and dynamic mechanical
thermal analysis techniques.
Physical and mechanical properties of the prepared materials
were used as the criteria of their quality and measurementswere made
of modulus, ultimate tensile strength, elongation at break, hardness,
tear strength, tension set and compression set.
The stability of these materials toward thermooxidative degradation,
UV exposure, hydrolysis and gamma radiation have been quantfied.
In Northern Australia outdoor weathering trials for retention
of transparency in these polyurethanes have been organised and these
are still progressing, but no firm conclusions can be drawn at this date
