CHAIN TRANSFER BY AN ADDITION-SUBSTITUTION-FRAGMENTATION MECHANISM .2. PREPARATION OF ALPHA,OMEGA-DIFUNCTIONAL TELOMERS THROUGH A RADICAL TRANSFER-REACTION ON A METHACRYLIC-TYPE CYCLIC PEROXYKETAL

Ethyl 2-[1-((2-tetrahydrofuranyl)peroxy)ethyl]propenoate (ETPEP; see Chart 1) was used as a new chain transfer agent in the free radical polymerization of methyl methacrylate (MMA), styrene (St), and butyl acrylate (BA) to produce alpha,omega-difunctional telomers through a radical addition-substitution-fragmentation transfer reaction. The chain transfer constant obtained in the MMA polymerization at 60 degrees C (C-tr = 0.096) was very low compared to those obtained in styrene and butyl acrylate under the same conditions (C-tr = 0.97 and 1.02, respectively). Such a result was attributed to the bulkiness of the alpha-substituents of both monomer and transfer agent in the addition step of the transfer reaction. ETPEP behaves as an ideal transfer agent for styrene and butyl acrylate at 60 degrees C. The activation energy for the transfer reaction of ETPEP with PMMA radicals (E(a,tr)=29.9kJ.mol(-1)) was determined from transfer constants measured in MMA polymerization performed at 50, 55, 60, 70, and 80 degrees C. The thermal stability of peroxyketal ETPEP was estimated from the DSC measurements of the rate constants and from the activation energy of the thermolysis (E(a,th) = 130.1 kJ.mol(-1)) at various reaction temperatures.