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

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).

Reincarnation of the Analytical Ultracentrifuge: Emerging Opportunities for Nanomedicine

“…For example, Muljajew et al have studied the aggregation of graft copolymers comprising a hydrophobic poly(methyl methacrylate) (PMMA) backbone and hydrophilic oligo(2ethyl-2-oxazoline) (OEtOx) side chains (PMMA-g-OEtOx). 57 These copolymer systems enabled formation of micelle structures, which could carry small guest molecules. The authors studied the molar mass of unimeric species, i.e., the polymers in a good solvent for the polymer, and that of micelle structures in water including determination of the partial specific volume, υ. Conclusively, and by making use of intrinsic estimates of s, i.e., [s] (eq 4) and the modified Svedberg equation (right-hand side of eq S5), they found that, depending on the initial polymer composition, the degree of aggregation of polymers could be designed to result in numbers of aggregation up to roughly ten in an aqueous solution.…”

“…For example, Muljajew et al have studied the aggregation of graft copolymers comprising a hydrophobic poly­(methyl methacrylate) (PMMA) backbone and hydrophilic oligo­(2-ethyl-2-oxazoline) (OEtOx) side chains (PMMA- g -OEtOx) . These copolymer systems enabled formation of micelle structures, which could carry small guest molecules.…”

Oxazoline-methacrylate graft-copolymers with upper critical solution temperature behaviour in Yubase oil

“…[50][51][52][53] More complex architectures have also been studied in order to enhance the properties of the final material and have a better control over the temperature range of the phase transition. 19,23,34,54,55 However, despite the large amount of work on 2-oxazoline polymers showing an LCST behaviour, only a limited number of poly(2-alkyl-2-oxazoline)s is reported to show a upper critical solution temperature (UCST) phase transition, which only occurs in alcohol/water mixtures. 52,[56][57][58] In this study, linear homo and copolymers of 2-stearyl-2oxazoline (SteOx) and 2-ethyl-2-oxazoline (EtOx) are synthesized via living CROP resulting in well-defined copolymers with varying oil solubility behaviour.…”

Synthesis of Poly(ester-graft-methyl methacrylate) on a Macroinitiator with Lateral Sulfonyl Chloride Groups by Atom Transfer Radical Polymerization

“…It should be noted that a significant difference in the nature of the backbone and carbochain side chains determines the amphiphilicity of hybrid brushes owing to the selectivity of components with respect to solvents of different nature. This structural feature is responsible for the segregation of fragments of the graft copolymer in solution and the formation of supramolecular structures which cannot be obtained for polymers with a different architecture [7][8][9][10]. In addition, such brushes are characterized by a significantly rarer grafting of side chains compared to carbonchain molecular brushes, which allows a much more pronounced conformational freedom of both the main and side chains.…”