Synthesis and Stereospecific Polymerization of a Novel Bulky Styrene Derivative
journal contributionposted on 23.03.2016, 14:53 by Rong Wang, Dongtao Liu, Xiaohong Li, Jie Zhang, Dongmei Cui, Xinhua Wan
A novel vinylbiphenyl monomer, 2-methoxy-5-phenylstyrene (MOPS), was designed and efficiently synthesized to investigate the stereospecific polymerization of bulky and polar styrenic derivative. Regardless of its large side group and electron-donating o-methoxy substituent, this compound showed a high polymerizability and was readily converted to the corresponding polymers with moderate to high molecular mass through radical, anionic, and coordination polymerizations. The resultant polymers were characterized by a combination of 1H/13C NMR spectrometry, thermal analysis, and wide-angle X-ray diffraction. Radical polymerization initiated by AIBN in toluene at 60 °C produced a syndiotactic-rich (rr = 0.37) polymer as most bulky vinyl monomers, whereas anionic polymerizations induced by n-BuLi yielded only isotactic-rich polymers no matter if polar tetrahydrofuran (−78 °C, mm = 0.54) or apolar toluene (−40 °C, mm = 0.78) was employed as the solvent. The isotactic-rich microstructure obtained by anionic polymerization in polar solvent at low temperature, the condition that usually leads to syndiotactic-rich polymer, manifested the strong interactions between the o-methoxy groups of the growing chain end and the penultimate unit with the lithium counterion. Highly isotactic (mm = 0.95) and perfect syndiotactic (rr > 0.99) polymers were obtained via coordination polymerizations in toluene at ambient temperature with the β-diketiminatoyttrium precursor (I) and the heterocyclic-fused cyclopentadienylscandium complex (III) as the catalytic precursor, respectively. All the polymers were thermally stable with 5% weight loss temperatures above 360 °C. They underwent glass transitions in the temperature range of 124–140 °C depending on the tacticity, much higher than polystyrene, implying the dominant role of congestion effect of large side groups on the segment movement restriction of polymer chain. Both isotactic and syndiotactic polymers were crystalline and had melting points higher than 300 °C, although the atactic and less stereoregular polymers were amorphous. The facile synthesis in conjunction with stereostructure tailorability, high thermal stability, glass transition temperature, and melting point makes the polymer a promising candidate for not only helical functional material but also engineering plastics.