Stable Free‐Radical Polymerization of Styrene in Combination with 2‐Vinylnaphthalene Initiation

Abstract

AbstractThe elevated temperatures required for the stable free‐radical polymerization (SFRP) process lead to thermal initiation of styrene via the classic Mayo mechanism. Studies have shown the utility of styrene thermal initiation in controlled autopolymerization processes. In addition, the thermal polymerization of 2‐vinylnaphthalene (2VN), a styrenic derivative with an additional fused ring, was examined. An Arrhenius analysis of the 2VN thermal polymerization process using in‐situ FT‐IR spectroscopy demonstrated a greater propensity for 2VN thermal polymerization compared to styrene. A modified Mayo mechanism was proposed based on additional resonance stabilization in 2VN derived radicals compared to a single ring of resonance stabilization for styrene. The utility of 2VN as an initiator in the SFRP of styrene was investigated. 2VN initiation resulted in polymers that are end‐functionalized with a single 2VN unit or a polycyclic unit that results from Diels‐Alder reaction in the initiation mechanism. Variation of the styrene/2VN molar ratio in the presence of 2,2,6,6‐tetramethylpiperdinyl‐1‐oxyl enabled molecular weight control and narrow molecular weight distributions (ca. 1.1–1.2). The integrity of the polymer end groups was confirmed using 1H NMR and UV‐vis spectroscopy. In addition, the UV‐vis absorbance of the 2VN initiating unit was used for construction of a calibration curve for molecular weight prediction based on the intensity of the absorbance at 312 nm associated with 2VN initiation. The observed rate constant for the polymerization initiated with 2VN (1.73 × 10−5 s−1) was comparable to that of benzoyl peroxide (kobs = 1.99 × 10−5 s−1) initiation. SFRP of styrene thermally initiated with 2VN.imageSFRP of styrene thermally initiated with 2VN.