Synthesis and characterization of glycopolymer-polypeptide triblock copolymers.

Abstract

Glycopolymer-polypeptide triblock copolymers of the structure, poly(l-alanine)-b-poly(2-acryloyloxyethyl-lactoside)-b-poly(l-alanine) (AGA), have been synthesized by sequential atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP). Controlled free radical polymerization of 2-O-acryloyl-oxyethoxyl-(2,3,4,6-tetra-O-acetyl-beta-d-galactopyranosyl)-(1-4)-2,3,6-tri-O-acetyl-beta-d-glucopyranoside (AEL) by ATRP with a dibromoxylene (DBX)/CuBr/bipy complex system was used to generate a central glycopolymer block. Telechelic glycopolymers with diamino end groups were obtained by end group transformation and subsequently used as macroinitiators for ROP of l-alanine N-carboxyanhydride monomers (Ala-NCA). Gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) spectroscopy analysis demonstrated that copolymer molecular weight and composition were controlled by both the molar ratios of the Ala-NCA monomer to macroinitiator and monomer conversion and exhibited a narrow distribution (Mw/Mn = 1.06-1.26). FT-IR spectroscopy of triblock copolymers revealed that the ratio of alpha-helix/beta-sheet increased with poly(l-alanine) block length. Of note, transmission electron microscopy (TEM) demonstrated that selected amphiphilic glycopolymer-polypeptide triblock copolymers self-assemble in aqueous solution to form nearly spherical aggregates of several hundreds nanometer in diameter. Significantly, the sequential application of ATRP and ROP techniques provides an effective method for producing triblock copolymers with a central glycopolymer block and flanking polypeptide blocks of defined architecture, controlled molecular weight, and low polydispersity.