Chain transfer by the addition-fragmentation mechanism .6. Radical polymerization toward the synthesis of end-functional telomers, macroinitiators, and block copolymers

Acetal- or peroxyketal-terminated oligomers were prepared via a powerful process and characterized. Methanolysis of alkoxy(oxiranyl)-terminated or peralkoxy(oxiranyl)-terminated precursors were used to obtain the desired structures through an addition-substitution evolution on new chain transfer agents, 3-(cumylperoxy)-3-OY-2-phenyl-1-propene (see Chart 1) with Y = Me (CPMPP), Y = Et (CPEPP), and Y = OCMe(2)Ph (dCPPP). The free radical polymerization of methyl methacrylate (MMA), styrene (St), and methyl acrylate (MA) in the presence of such peroxyketals and precipitation of the polymer in methanol afforded directly the end-functional polymers. Chain transfer constants (C-tx) for these compounds in the monomer polymerization at 60 degrees C were determined from measurements of degrees of polymerization. C-tx values for CPMPP were determined to be 0.49, 0.92, and 1.94 in MMA, St, and MA, respectively. CPMPP behaves as an ideal transfer agent for styrene at temperatures close to 60 degrees C. The chain transfer activation energies, E(a,tr), for the reactions of PS and PMMA radicals with CPMPP were estimated to be 46.0 and 12.4 kJ . mol(-1), respectively. The thermolysis activation energies of these peroxyketals, E(a,th) = 134.7 and 127.7 kJ . mol(-1), respectively, to CPMPP and dCPPP were calculated from the Arrhenius plot of the homolytic decomposition rate constants, k(th), at various temperatures. dCPPP was used to design a monofunctional macroinitiator, a precursor of diblock copolymers.