Synthesis of thermoresponsive unimolecular polymeric micelles with a hydrophilic hyperbranched poly(glycidol) core

Abstract

This paper describes the reversible phase transition behavior of a thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) shell at the surface of a hydrophilic core. Reversible addition-fragmentation transfer (RAFT) polymerization of N-isopropylacrylamide was conducted using a hydrophilic hyperbranched poly(glycidol) (HPG)-based macroRAFT agent. At lower temperatures (o30 1C), the resultant multiarm star block copolymer (HPG-PNIPAM) exists as unimolecular micelles, with hydrophilic HPG as the core and a densely grafted PNIPAM brush as the shell. In laser light scattering (LLS) studies, the concentration used for HPG-PNIPAM is 5Â10 À6 g ml À1 , to avoid any possible aggregation between dendritic unimolecular micelles above the lower critical solution temperature (B32 1C) of PNIPAM. What we observe for the phase transition of HPG-PNIPAM involves only unimolecular process. A combination of dynamic and static LLS studies of HPG-PNIPAM in aqueous solution reveals a reversible phase transition on heating and cooling.

Living Radical Polymerization by the RAFT Process – A Third Update

“…Luo et al [625] have described the preparation of poly (NIPAm) 'stars' from a hyperbranched poly(glycidol) (HPG)-based macro-RAFT agent prepared as shown in Scheme 26.…”

Complex aggregates formed with a hyperbranched polyglycerol derivative for drug delivery

“…It has been reported that amphiphilic HPG derivatives can form unimolecular particles, which have smaller particle sizes compared with normal micelles formed by one molecule. This could be explained by their unique topologies, including their highly branched structures and spherical shapes . From dynamic light scattering results, as shown in Figure (A), we found that the size of HPG‐C18 aggregates was approximately 226.4 nm; these would be better called large aggregates rather than unimolecular particles.…”

“…In this study, a hyperbranched amphiphilic polyglycerol derivative (HPG) was synthesized and used for drug delivery. It has been reported that HPGs could form stable unimolecular micelles because of their unique topologies . HPGs also show excellent blood compatibility and have, therefore, been applied widely in biomedicine .…”

Hyperbranched aliphatic polyether polyols

“…For example, hbPG with poly(N-isopropylacrylamide) arms, that exhibits thermoresponsive properties, have been described. 176 By combination of RAFT and ATRP, the synthesis of interesting miktoarms (polystyrene and poly(tert butyl acrylate)) on a hbPG core could be realized. 177 While hbPG represents a hydrophilic core for MSPs, the utilization of hyperbranched aliphatic polyethers based on 3-alkyl-3-(hydroxymethyl)oxetanes yields hydrophobic core structures.…”