Simultaneously improving controls over molecular weight and stereoregularity of Poly(4-vinylpyridine) via a hydrogen bonding-facilitated controlled radical polymerization

The optimal conditions for the hydrogen bonding interaction between 4-vinylpyridine (4VP) and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) were screened via UV-vis spectroscopy. The results demonstrated that equimolar 4VP and HFIP, and temperature at 25 °C favored a better hydrogen bonding interaction. Guided by these primary results, the room-temperature Cu(0)-mediated controlled radical polymerization was selected for the controlled polymerization of 4VP in the presence of equiv. HFIP. The polymerizations produced polymers with more predictable number-average molecular weights (Mn,SEC) and narrower molecular weight distributions (Mw/Mn<1.25) in comparison with those without hydrogen bonding interaction. Moreover, the hydrogen bonding had profound impacts on the stereoregulation during polymerization, which enabled P4VP with a highly syndiotactic (60.2%) and gave rise to a higher glass transition temperature (Tg) of P4VP.