Electron spin resonance study of copolymerization of hexafluoroisobutylene with vinylidene fluoride

Abstract

The Copolymerization reaction of hexafluoroisobutylene (HFIB) and vinylidene fluoride (VF2) was studied using X‐band electron spin resonance (ESR) by applying a photo‐in situ method. Owing to the toxicity of HFIB monomer, the flow ESR method could not be directly applied without extensive modification. The observed ESR signal with 21‐line hyperfine structure was assigned to the copolymer radical with head‐to‐head configuration. Although the HFIB monomer radical possesses the same hyperfine pattern, the ambiguity has been removed by using CF3 as an initiator radical. Owing to the high steady‐state concentration of the observed copolymer radical with head‐to‐head configuration as well as the nature of the static photo‐in situ ESR method, we believe the actual molecular configuration for HFIB/VF2 copolymer must be head‐to‐tail. The observed hyperfine constant for AβF = 1.74 mT suggests that the geometry for HFIB/VF2 copolymer radicals with both head‐to‐head or head‐to‐tail configurations is possibly similar to that of (CF3)3C· radical. The small value for AβH indicates steric hindrance to rotation about the CαCβ bond, and this is also supported by the experimental results of nonalteration in linewidth during the temperature dependence study from −40 to about 90°C. Attempts to measure directly the monomer reactivities have been unsuccessful owing to the fact that not all the possible radicals were detected, but nevertheless the relative reactivities of VF2 and HFIB could be estimated. The relative reactivities of VF2 and HFIB monomers and the steric hindrance effect indicate that the conformation of the copolymer is head‐to‐tail; this has been further confirmed by infrared analysis.