CHAIN TRANSFER BY ADDITION-SUBSTITUTION-FRAGMENTATION MECHANISM .3. ACCESS TO LOW-MOLECULAR-WEIGHT TELECHELIC POLYMERS USING ETHYL 2-[1-(1-METHOXY-1-CYCLOHEXYLPEROXY)ETHYL]PROPENOATE

Low-molecular-weight di-end-functional (telechelic) telomers were prepared by radical addition-substitution-fragmentation transfer reactions on ethyl 2-[1-(1-methoxy-1-cyclohexylperoxy)ethyl]propenoate (EMCPEP), used as a new chain-transfer regulator in the free-radical polymerization of methyl methacrylate (MMA), styrene (St) and butyl acrylate (BA). The chain-transfer constant obtained in MMA polymerization at 60 degrees C (C-tr = 0.102) was very low compared to those obtained in St and BA polymerization in the same conditions (C-tr = 1.02 and 0.88, respectively). Such a result was attributed to the allylic steric effect of both monomer and transfer agent in the addition step of the transfer reaction. EMCPEP behaves as an ideal transfer agent for St and BA at 60 degrees C. The activation energy for the transfer reaction of EMCPEP with poly(methyl methacrylate) radicals (Ea(tr) = 31.3 kK mol(-1)) was determined from transfer constants measured in MMA polymerization performed at 50, 55, 60, 70 and 80 degrees C. The differential scanning calorimetry study of the thermal stability of peroxyketal EMCPEP gave an estimation of the rate constants and the activation energy of the thermolysis (Ea(th) = 130.3 kJ mol(-1)) at various reaction temperatures.