MECHANISM OF N-BUTYL ACRYLATE SENSITIZATION ACTION IN RADIATION VULCANIZATION OF NATURAL-RUBBER LATEX

In order to understand the role of n-butyl acrylate (nBA) in radiation vulcanization of natural rubber latex, a pulse radiolysis technique h as been used to study the mechanism and kinetics of initiation of radi ation induced polymerization of nBA in aqueous solution. The results s how that the formation kinetics of the transients produced by the reac tion of nBA with both the primary radicals i.e. . OH/H . approach the diffusion controlled limit with their respective bimolecular rate cons tant, k values being 5 x 10(9) and 2 x 10(9) dm(3) mol(-1) s(-1). Thes e transients subsequently tend to undergo dimerization with their seco nd-order decay rate parameters (2k) being in the range of 1 x 10(9) dm (3) mol(-1) s(-1). In the presence of secondary oxidizing radicals, th e formation of the radical cation transient (nBA(+)) is strongly: resi sted and has been observed only in the presence of a strongly oxidizin g secondary radical Cl-2 .(-), the bimolecular formation rate constant being 2.4 x 10(6) dm(3) mol(-1) s(-1) at pH 2. On the other hand, the radical anion transient, nBA(-.) produced in the reaction of nBA with e(aq)(-) (formation rate constant value being 6.5 x 10(9) dm(3) mol(- 1) s(-1)) decays following first-order kinetics in the presence of exc ess nBA in the solution. The high bimolecular rate constant k = 1.4 x 10(8) dm(3) mol(-1) s(-1), for the reaction indicates that the anion a lone is capable of propagating the polymerization reaction and can enh ance the vulcanization process. These results have been further confir med from the effect of electron scavengers on the radiation vulcanizat ion behavior of natural rubber latex in presence of nBA as sensitizer, wherein the electron scavengers having preferential solubility in the rubber phase exhibited a pronounced decrease in cross linking. (C) 19 98 Elsevier Science Ltd. All rights reserved.