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(CHCMe 2 Ph)(N-2,6- i Pr 2 C 6 H 3 )(O t Bu) 2 ] ( 1 ), with either TMS (SiMe 3 ) 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 ( M n = 2200 or 4600), to the ring-opened polymers. In all cases, M n values for resultant copolymers estimated by 1 H NMR (and by GPC) were very close to those calculated based on the initial monomer/initiator loadings with low polydispersity indices ( M w / M n = 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 CF 3 CO 2 H/H 2 O mixture (9/1 v/v) affording the corresponding deprotected analogues with the M n values calculated based on the initial molar ratios.