Synthesis and curing of millable polyurethanes based on castor oil

This paper presents the results of studies on the synthesis and curing of millable polyurethanes based on castor oil. To facilitate the preparation of millable urethanes, the hydroxy number of castor oil was modified to about two by acetylation. It was then used with tolylene diisocyanate (NCO/OH‐ratios 1:0.9, 1:1 and 1:1.1, resp.) for polyurethane preparation. The dynamic curing of the synthesized polyurethanes was studied in a Brabender Plasticorder using various sulfur vulcanizing systems. The effect of stoichiometric ratio and choice of chain extenders on the dynamic curing behaviour was also studied. An NCO/OH ratio of 0.9 and 1,4‐butanediol (30 wt.‐%) as chain extender were found to favour the formation of a crosslinkable polyurethane. It was observed that a cure system containing sulfur, N‐cyclohexyl‐2‐benzothiazole sulfenamide and mecraptobenzothiazole was a possible choice for the preparation of a sulfur‐crosslinked polyurethane.