Hydroxypropyl β-Cyclodextrin Solubilizing Hydrophobic Initiator to Initiate Copper-Mediated RDRP of NIPAM in Aqueous Media

The copper mediated reversible deactivation radical polymerization (Cu⁰-RDRP) can realize the precise synthesis of vinyl polymers in aqueous media. To our best of knowledge, there are few hydrophobic initiators directly utilized to perform the aqueous Cu⁰-RDRP because the heterogeneity usually causes the polymerization to go out of control. This article first describes a very small number of hydroxylpropyl β-cyclodextrins (HP-β-CDs) enabling to solubilize a bifunctional hydrophobic initiator tetraethylene glycol bis(2-bromoisobutyrate) (T2B) into water to initiate the homogeneous Cu⁰-RDRP of N-isopropylacrylamide (NIPAM) giving rise to well-defined poly(N-isopropylacrylamide) (PNIPAM). The solubilization action is arisen from the inclusion complexation of HP-β-CDs with T2B as evidenced by 2D NOESY and 2D DOSY NMR analyses. Furthermore these entrapped HP-β-CDs show little effect on the polymerization process as they all skip off the initiator at the very beginning of the polymerization as determined by GPC and ¹H NMR measurements.