Crosslinking agents of unsaturated polymers:: evaluation of the agent efficiency

We have performed a comparison of efficacy of several curing agents. We have synthesized curing agents with C=C-bonds of allylic, acrylic or peroxide group type, as derivatives of pyromellitic acid: diallylic ester (I), tetraallylic ester (II), di-(2-methacryloyloxy-ethyl)-pyromellitate (III), tetra-(2-methacryloyloxy-ethyl)pyromellitate (IV), ditert-butylperoxypyromellitate (V) and tetratert-butylperoxypyromellitate (VI). The possibility to use these agents for curing an unsaturated film-forming copolymer which contains polybutadiene fragments was investigated. The unsaturated curing agents (I-IV) are able to form crosslinked copolymers in the presence of peroxide initiators such as benzoyl peroxide. The gelation process orders as well as the values of the effective activation energies for all curing agents studied have been determined. In the presence of curing agents of methacrylic type (III-IV) the crosslinking proceeds more rapidly than in the presence of allylic esters. Unsaturated curing agents containing carboxylic groups (I, III) promote faster formation of three-dimensional structures than tetra- substituted derivatives of pyromellitic acid. For curing agents of the peroxide type the inverse relation is observed. The hardness of films obtained using carboxylic curing agents is higher than for noncarboxylic ones. Films obtained in the presence of unsaturated curing agents exhibit higher hardness than those obtained in the presence of peroxide agents.