John L. Cawse

Polymers from renewable sources: 5. myrcene-based polyols as rubber-toughening agents in glassy polyurethanes

A reactive liquid rubber based on hydroxy-functionalized polymyrcene was used to modify a highly-crosslinked, glassy polyurethane network. During the polymerization, the products formed from the reacting liquid rubber and the polyurethane matrix components become incompatible leading to precipitation of the rubber as a discrete particulate phase. Phase-separation in the resultant rubber-modified polyurethanes is essentially complete, and the materials possess improved stress-strain and impact properties relative to the unmodified network, without reduction of the glass transition temperature (155°C) of the network. Impact data have been analysed using linear elastic fracture mechanics to give GIC, the critical strain-energy release rate. On incorporating low levels of polymyrcene liquid rubber (<10% ww) in the polyurethane matrix, GIC increased and passed through a maximum value. The mechanisms of energy dissipation accounting for the toughness changes are reviewed and compared with those observed in epoxy resins modified by polybutadiene-based liquid rubbers.