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

Low-molecular-weight di-end-functional (telechelic) telomers were prep ared by radical addition-substitution-fragmentation transfer reactions on ethyl -[1-(1-methoxy-1-cyclohexylperoxy)ethyl]propenoate (EMCPEP), used as a new chain-transfer regulator in the free-radical polymeriza tion of methyl methacrylate (MMA), styrene (St) and butyl acrylate (BA ). The chain-transfer constant obtained in MMA polymerization at 60 de grees C (C-tr = 0.102) was very low compared to those obtained in St a nd BA polymerization in the same conditions (C-tr = 1.02 and 0.88, res pectively). Such a result was attributed to the allylic steric effect of both monomer and transfer agent in the addition step of the transfe r reaction. EMCPEP behaves as an ideal transfer agent for St and BA at 60 degrees C. The activation energy for the transfer reaction of EMCP EP 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 scannin g calorimetry study of the thermal stability of peroxyketal EMCPEP gav e an estimation of the rate constants and the activation energy of the thermolysis (Ea(th) = 130.3 kJ mol(-1)) at various reaction temperatu res.