Peroxide crosslinking of poly(n-alkyl methacrylates)

The action of dicumyl peroxide on poly(n-butyl methacrylate) and poly(n-nonyl methacrylate) produces degradation and crosslinking reactions in both polymers. Crosslinking and degradation of poly(n-alkyl methacrylates) are influenced also by the initial molecular weight of the polymer as well as by the type of alkyl group. The ratio of degradation to crosslinking p/q determined on the basis of the equation of Charlesby and Pinner, S + S^0.5 = (p/q) + (1/qP_n) is for poly(n-butyl methacrylate) of viscosity molecular weight 0.923 × 10⁶ and 2.16 × 10⁶ of 0.78 and 0.60, respectively; for poly(n-nonyl methacrylate) of weight average molecular weight 3.83 × 10⁵, p/q is 0.16. Crosslinking efficiencies (moles of crosslinks per mole of decomposed dicumyl peroxide) of the above polymers are relatively very low: 0.014, 0.005, and 0.039, respectively. The critical concentration of dicumyl peroxide necessary for the formation of gel, provided it undergoes complete decomposition, is for the above polymers 1.82, 1.65, and 0.98 wt.-%, respectively. Under the critical concentration of dicumyl peroxide the limiting viscosity number of poly(n-butyl methacrylate) increases with increasing concentration of dicumyl peroxide. An initial decrease of the value of the limiting viscosity number, which is characteristic for polymers undergoing simultaneous degradation and crosslinking, was not observed.