The role of multifunctional acrylates in radiation grafting and curing reactions

Abstract

Multifunctional acrylates (MFAs) are used extensively in radiation rapid cure (RRC) formulations involving u.v. and EB processing to achieve fast rates of polymerization and cross-linking if required. For certain RRC applications, the ability to achieve concurrent grafting with cure can lead to improved properties of the finished product. In the current work the effect of MFAs on concurrent grafting during the curing process is evaluated from a basic study of the role of these MFAs on a typical grafting reaction initiated by u.v. or ionizing radiation. The model used for the grafting work was the copolymerization of styren to the polyolefins and cellulose. It is found that the presence of the MFA and related polyfunctional monomers (PFMs) in additive amounts in the styrene grafting solution enhances the copolymerization yield under certain radiation conditions. Synergistic effects of the MFAs and PFMs with other additives such as mineral acids, inorganic salts (e.g. lithium perchlorate) and specific organic compounds (e.g. urea) were observed in the model grafting reactions. When additives such as silanes and fluorinated alkyl esters, which are important in RRC formulations to achieve slip and flow in the cured film, are incorporated into the model grafting monomer solution, the former additive retards copolymerization whereas the latter enhances it. The inclusion of MFAs in these monomer solutions leads to large increases in graft with both silanes and fluorinated alkyl esters. The result implies that MFAs, in addition to speeding cure and cross-linking in RRC processes, may also enhance adhesion to certain substrates because of an increase in concurent grafting during cure. A mechanism for these additive effects in concurrent grafting and curing is proposed.