Regulation of Photo-Induced Isomerization of C4/C5/C6 Polymers Based on an Anion-Migrated Ring-Opening Polymerization Method

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The development of nonpolar polymers with photoinduced isomerization capabilities has become a critical research direction in the field of functional polymer synthesis. This study systematically investigated the photoinduced isomerization behavior of styrene-based C4/C5/C6 polymers. Among them, the C4 polymer was synthesized by the general anionic polymerization of 2-phenyl-1,3-butadiene (2-PB), while C5/C6 polymers were prepared via an anion-migrated ring-opening polymerization (AMROP) of 1-cyclopropylvinylbenzene (CPVB)/1-cyclobutylvinylbenzene (CBVB), respectively. All three base polymers demonstrated rapid transit E -to- Z isomerization under 365 nm UV irradiation for 40 min in the presence of the photosensitizer (4,4′-dimethoxybenzophenone). Notably, the conversion efficiency showed a positive correlation with carbon backbone length (Δ Z = 29% for C4, 54% for C5, and 68% for C6 polymers), as longer carbon chains enhanced molecular flexibility through improved chain rotation. Additionally, C5 polymer derivatives containing electron-donating (methoxy) and electron-withdrawing (alkynyl) groups were synthesized to investigate substituent effects on photoinduced isomerization behavior. The electron-withdrawing group significantly suppressed E -to- Z conversion (Δ Z = 39%), while the electron-donating group exhibited minimal impact (Δ Z = 55%) compared to the parent C5 polymer. Furthermore, the effects of E/Z configurations on the thermal and fluorescence properties of the polymers were also thoroughly investigated. Remarkably, the odd–even effect in carbon atom numbers within repeating units induced diametrically opposed chain folding patterns in the corresponding polymers. Therefore, the glass transition temperature ( T g ) increased with Z -configuration content for C4 (Δ T g = +21.9 °C) and C6 (Δ T g = +8.5 °C) polymers but decreased for the C5 polymer (Δ T g = −9.0 °C). In addition, nontraditional intrinsic luminescence (NTIL) exhibited an inverse relationship with Z -configuration content, showing quantum yield reductions of 50.09% (C4 polymer), 46.18% (C5 polymer), and 24.82% (C6 polymer).