Precise Synthesis of Amphiphilic Polymeric Architectures by Grafting Poly(ethylene glycol) to End-Functionalized Block ROMP Copolymers

Abstract

Various (linear, triarms, ABA or ABCBA type) amphiphilic multiblock copolymers containing acetal-protected sugars have been prepared by the coupling of an end-functionalized ROMP copolymer with poly(ethylene glycol) (PEG). The synthesis involves three key steps: (i) termination of the block ROMP copolymer prepared by molybdenum−alkylidene initiator, [Mo(CHCMe2Ph)(N-2,6-iPr2C6H3)(OtBu)2] (1), with either TMS (SiMe3) protected 4-hydroxy- or 3,5-dihydroxybenzaldehyde; (ii) exclusive removal of the TMS protection from the terminus; and (iii) the potassium hydride mediated attachment of poly(ethylene glycol), PEG (Mn = 2200 or 4600), to the ring-opened polymers. In all cases, Mn values for resultant copolymers estimated by 1H NMR (and by GPC) were very close to those calculated based on the initial monomer/initiator loadings with low polydispersity indices (Mw/Mn = 1.05−1.20 by GPC). The preparation of a multiblock or star-shaped (triarms) amphiphilic copolymer was possible depending on which terminating agent was adopted. The cyclic acetal in the sugar-containing polymers could be hydrolyzed exclusively using a CF3CO2H/H2O mixture (9/1 v/v) affording the corresponding deprotected analogues with the Mn values calculated based on the initial molar ratios.