Synthesis of Highly Syndiotactic Poly(8-Vinylquinoline) via Heteroatom-Assisted Coordination Polymerization

The synthesis of novel functional polymers used for high-temperature proton exchange membranes is of fundamental interest and practical significance. But the direct synthesis is still difficult because expected materials are heteroatom-containing stereoregular polymers, and heteroatom-containing monomers usually show serious poisoning toward catalysts. In this work, we report the syndioselective polymerization of 8-vinylquinoline (8-VQ) by the combination of yttrium catalysts with alkylaluminum and [Ph3C][B(C6F5)4] via the heteroatom-assisted polymerization process. Y-4 with a pyridinyl ligated fluorenyl group shows high activity and high syndioselectivity (rr > 99%) for 8-VQ polymerization. The resultant polymers have high molecular weight (Mn 33,000–134,000 g mol–1) and high glass-transition temperature (Tg 139–147 °C), which have the application prospect of a high-temperature proton exchange membrane. The polymerization mechanistic aspect is elucidated by density functional theory calculations. We find that the σ–π coordination mode between 8-VQ and the catalytic center can weaken the difference of interaction energy between syndio- and iso-selectivity and improve the influence of steric hindrance to further promote the synthesis of highly syndiotactic P(8-VQ). We expect that our new findings could provide guidance for the synthesis of stereoregular polymers containing heteroatoms.