Postcrosslinking of linear polyesters. I melt‐blend‐type UV‐induced crosslinking agents

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Abstract
Postcrosslinking of such linear polyesters as poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) are known to be attractive means to improve their thermal resistances without sacrificing their melt processibilities. Effective melt‐blend‐type ultraviolet‐induced crosslinking agents were investigated among allyl compounds. Such polyallyl compounds as triallyl cyanurate and triallyl isocyanurate were found to be practically promising agents from the viewpoints of crosslinkability and stability in the polyester melt. The crosslinkability of the ally compounds increased with increasing the number of the allyl groups in the molecule and electron‐withdrawing property of the neighboring group to which the allyl group was attached. The crosslinking mechanism likely includes both the polymerization of the allyl compound to form semi‐interpenetrating polymer networks in the polyester matrix and the reaction between the polyester and the allyl compound moiety. The crosslinked PET and PBT showed good mechanical properties even above the melting points of the ordinary PET and PBT.