Polymerization of vinyl acetate retarded by 4‐methyl‐2,6‐di‐tert‐butylphenol: Kinetic and ESR studies

Abstract

4‐Methyl‐2,6‐di‐tert‐butylphenol strongly retards the free radical polymerization of vinyl acetate initiated by azobisisobutyronitrile. The chain transfer constant, estimated from rate data, is 0.020 ± 0.004 at 35°C and does not vary significantly with temperature. Molecular weight data lead to transfer constants of 0.023, 0.020, and 0.024 at 35, 45, and 55°C, respectively. A mean kinetic isotope effect of 9.8 ± 1.0 is observed for the phenol deuterated at the OH group, showing that the main attack of poly(vinyl acetate) radicals on the phenol involves hydrogen abstraction from this group. The activation energy for hydrogen abstraction is estimated to be 7.8 kcal/mole, and the rate constant at 50°C is 160 ± 40 1./mole‐sec. The stationary concentration of 4‐methyl‐2,6‐di‐tert‐butylphenoxyl in the polymerization mixture is proportional to the phenol concentration and is independent of the initiator concentration, as shown by electron spin resonance studies. Cross termination of poly(vinyl acetate) and phenoxy radicals occurs to a greater extent than mutual termination of these radicals. The rate constant for cross termination is close to 1 × 108 1./mole‐sec at 50°C; the activation energy for cross termination is 2.9 ± 1.3 kcal/mole.

Modeling the Chain‐Length Differentiated Polymer Microstructure of α‐Olefins

“…The rate coefficients for the transfer to monomer are also derived from a combined data fit. The sources in this case are: Parnell und Russell, [17] Clarke et al, [18] Moze et al [19] and Potnis und Deshpande. [20] For intramolecular transfer there are no literature data and there are some indications that this reaction indeed is not very relevant for this monomer.…”

Effect of Phenols on the Free-Radical Photopolymerization of Vinyl Monomers in Aqueous Solution

“…Early works suggest that phenols act as retardants of methyl methacrylate, [1] styrene, [2] and vinyl acetate [3] bulk polymerizations. The high reactivity of these compounds has been attributed to the ability of the phenol group to scavenge radicals by an H-atom or electron transfer process.…”