P(LMA-co-tBMA-co-MAA) Copolymers Bearing Amphiphilic and Polyelectrolyte Characteristics: Synthetic Aspects and Properties in Aqueous Solutions

Abstract

In this study, we explore the design of novel random poly(lauryl methacrylate-co-tert-butyl methacrylate-co-methacrylic acid), P(LMA-co-tBMA-co-MAA) copolymers via the RAFT copolymerization of LMA and tBMA followed by the selective hydrolysis of tBMA segments. For the molecular characterization of the novel copolymer, a series of physicochemical techniques were implemented, including size exclusion chromatography (SEC), proton nuclear magnetic resonance (¹H-NMR) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Our experimental results confirmed the successful synthesis of the targeted copolymers. The compositions were in accordance with the targeted differing fraction of hydrophobic tBMA/LMA elements, and hydrolysis resulted in at least 64% conversion to hydrophilic MAA units. The copolymers, bearing both an amphiphilic character and polyelectrolyte properties while being composed of randomly distributed monomeric segments of biocompatible materials, were subsequently investigated in terms of their self-assembly behavior in aqueous solutions. Dynamic light scattering and fluorescence spectroscopy experiments demonstrated the formation of self-assembled nanoaggregates (average hydrodynamic radii, R_h < 100 nm) that formed spontaneously, having low critical aggregation concentration (CAC) values (below 3.5 × 10^-6 g/mL), and highlighted the feasibility of using these copolymer systems as nanocarriers for biomedical applications.

Keywords: RAFT; amphiphilic random copolymers; hydrolysis; nanoaggregates; pH responsive; polyelectrolytes; post-polymerization modification; self-assembly.

Scheme 1

Synthesis route for P(LMA-co-tBMA-co-MAA) copolymers.

Figure 1

SEC traces of synthesized precursor copolymers.

Figure 2

¹H NMR spectra of PC1 and PC2 in CDCl₃ (letters label different types of protons based on their chemical shift while solvent protons are denoted with an asterisk).

Figure 3

¹H NMR spectra of C1 and C2 in THF-d8 (letters label different type of protons based on their chemical shift while solvent protons are denoted with an asterisk).

Figure 4

FTIR spectra of solid (a) copolymer 1 and (b) copolymer 2 before and after hydrolysis.

Figure 5

CAC determination in aqueous solution at pH = 7 for (a) C1 and (b) C2 copolymers.

Figure 6

R_h distribution curves of (a) C1 and (b) C2 copolymers in aqueous solutions of varying pH, obtained from CONTIN analysis.

Figure 7

R_h distribution curves of (a) C1 and (b) C2 copolymers from repetitive measurements of pH 7 aqueous solutions, obtained from CONTIN analysis.