PMMA-g-OEtOx Graft Copolymers: Influence of Grafting Degree and Side Chain Length on the Conformation in Aqueous Solution.

Irina Muljajew,Ulrich S Schubert,Ivo Nischang,Christine Weber

doi:10.3390/ma11040528

Abstract

Depending on the degree of grafting (DG) and the side chain degree of polymerization (DP), graft copolymers may feature properties similar to statistical copolymers or to block copolymers. This issue is approached by studying aqueous solutions of PMMA-g-OEtOx graft copolymers comprising a hydrophobic poly(methyl methacrylate) (PMMA) backbone and hydrophilic oligo(2-ethyl-2-oxazoline) (OEtOx) side chains. The graft copolymers were synthesized via reversible addition-fragmentation chain transfer (RAFT) copolymerization of methyl methacrylate (MMA) and OEtOx-methacrylate macromonomers of varying DP. All aqueous solutions of PMMA-g-OEtOx (9% ≤ DG ≤ 34%; 5 ≤ side chain DP ≤ 24) revealed lower critical solution temperature behavior. The graft copolymer architecture significantly influenced the aggregation behavior, the conformation in aqueous solution and the coil to globule transition, as verified by means of turbidimetry, dynamic light scattering, nuclear magnetic resonance spectroscopy, and analytical ultracentrifugation. The aggregation behavior of graft copolymers with a side chain DP of 5 was significantly affected by small variations of the DG, occasionally forming mesoglobules above the cloud point temperature (Tcp), which was around human body temperature. On the other hand, PMMA-g-OEtOx with elongated side chains assembled into well-defined structures below the Tcp (apparent aggregation number (Nagg = 10)) that were able to solubilize Disperse Orange 3. The thermoresponsive behavior of aqueous solutions thus resembled that of micelles comprising a poly(2-ethyl-2-oxazoline) (PEtOx) shell (Tcp > 60 °C).

Highlights

Poly(2-oxazoline)s (POx) can be obtained via a living cationic ring-opening polymerization (CROP)
The aggregation behavior of graft copolymers with a side chain degree of polymerization (DP) of 5 was significantly affected by small variations of the degree of grafting (DG), occasionally forming mesoglobules above the cloud point temperature (Tcp ), which was around human body temperature
A series of PMMA-g-OEtOx graft copolymers containing a hydrophobic poly(methyl methacrylate) (PMMA) backbone and hydrophilic oligo(2-ethyl-2-oxazoline) (OEtOx) side chains were synthesized via reversible addition-fragmentation chain transfer (RAFT) copolymerization of MMA and OEtOx-methacrylate macromonomers of varying DPs

Summary

Introduction

Poly(2-oxazoline)s (POx) can be obtained via a living cationic ring-opening polymerization (CROP). The hydrophilic poly(2-methyl-2-oxazoline) (PMeOx) and poly(2-ethyl-2oxazoline) (PEtOx) have recently experienced increasing interest due to their favorable properties for biomedical applications [1]. Similar to poly(ethylene glycol) (PEG), these POx are non-toxic, protein repellent, and exhibit a so-called “stealth effect” in vivo as they are barely recognized by the immune system [2]. This results in elongated blood circulation times and makes them appealing as building blocks for various drug delivery systems. Micellar carriers based on block copolymers have been intensively investigated [3].

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Conclusion