Investigations of thermal polymerization in the stable free-radical polymerization of 2-vinylnaphthalene

The feasibility of utilizing stable free-radical polymerization (SFRP) in the synthesis of well-defined poly(2-vinylnaphthalene) homopolymers has been investigated. Efforts to control molecular weight by manipulating initiator concentration while maintaining a 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO):benzoyl peroxide (BPO) molar ratio of 1.2:1 proved unsuccessful. In addition, systematic variations of the TEMPO: BPO molar ratio did not result in narrow molecular weight distributions. In situ Fourier transform infrared spectroscopy (FTIR) indicated that the rate of monomer disappearance under SFRP and thermal conditions were identical. This observation indicated a lack of control in the presence of the stable free radical, TEMPO. The similarities in chemical structure between styrene and 2-vinylnaphthalene suggested thermally initiated polymerization occurred via the Mayo mechanism. A kinetic analysis of the thermal polymerization of styrene and 2-vinylnaphthalene suggested that the additional fused ring in 2-vinylnaphthalene increased the propensity for thermal polymerization. The observed rate constant for thermal polymerization of 2-vinylnaphthalene was determined using in situ FTIR spectroscopy and was one order of magnitude greater than styrene, assuming pseudo-first-order kinetics. Also, an Arrhenius analysis indicated that the activation energy for the thermal polymerization of 2-vinylnaphthalene was 30 kJ/mol less than styrene.