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

摘要

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_2Ph)(N-2,6-~iPr_2C_6H_3)-(O~tBu)_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 1H 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_3CO_2H/H_2O mixture (9/1 v/v) affording the corresponding deprotected analogues with the M_n values calculated based on the initial molar ratios.