New self-assembling polyaspartamide-based brush copolymers obtained by atom transfer radical polymerization

Abstract

A simple and efficient method for the synthesis of polyaspartamide-based brush copolymers using Atom Transfer Radical Polymerization (ATRP) is here presented. The syntheses were performed by using two subsequent steps. In the first step the macroinitiator was obtained by the conjugation of a proper number of 2-bromoisobutyryl bromide (BIB) residues to the R, -poly(N-2-hydroxyethyl)-D,L-aspartamide (PHEA) side chains, obtaining the PHEA-BIB copolymer. PHEA-BIB copolymer was used as “multi-functional macroinitiator” for the polymerization via ATRP of hydrophilic methacrylic monomers, such as methacrylic acid (MA), obtaining PHEA-IB-poly(MA) copolymer, sodium methacrylate (MANa+), obtaining PHEA-IB-poly(MANa+) copolymer, or hydrophobic monomer such as butyl methacrylate (BMA), obtaining PHEA-IB-poly(BMA) copolymer. BMA was also homopolymerized subsequently MANa+ polymerization, extending the poly(MANa+) chains by poly(BMA) chains arising PHEA-IB-poly(MANa+)-block-poly(BMA) copolymer. Different solvent and temperature conditions were used in order to obtain the best ATRP conditions for each monomer in term of high polymerization efficiency in PHEA side chain. All the synthesized PHEA-based brush copolymers were widely characterized and copolymer self-assembling properties in aqueous media were evaluated by turbidimetry measurements, light scattering and SEM analyses. PHEA-IB-poly(MANa+) resulted able to form spherical microparticles at pH 2, with a diameter from 1 - 5 μm. PHEA-IB-poly(MANa+)-block-poly(BMA) copolymer formed particles at elliptic shape and an internal hollow architecture with an outer diameter of 1-4 μm. Finally, PHEA-IB-poly(BMA) copolymer resulted able to produce microfibers in aqueous medium, with an homogeneous tube shape and a thickness ranging from 3 to 5 μm.