Situ Isocyanate and Isocyanurate Crosslinking

The reaction sequences used in this preparation followed the conventional polyurethane prepolymer sequence with the following provision that steps were made to obtain in the final PU elastomer controlled quantities of covalent-type crosslinks by leaving calculated excesses of isocyanate groups in the initially cast and cured PU. 

Two types of crosslink were considered to be formed by this method  

The conventional mixture of urethane, biuret and allophanate crosslinks formed during the final chain-extension step by means of the standard 16h at 120 C hot-air cure. 

Additional crosslinks, believed to be primarily isocyanurate in nature, formed by the combination of conditioning for 1 week at room temperature and 60% RH followed by a post-cure of 15-24 h at 130 C. 

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