Interactions and Dynamics in Aqueous Solutions of pH-Responsive Polymers: A Combined Fluorescence and Dielectric Relaxation Study

Dynamical signature of the onset of sol-gel phase transition in aqueous solutions of hydrophobically modified poly(acrylic acid)-based copolymers

Sol-gel transition-driven relaxation dynamics of aqueous solutions of rationally designed polyacrylic acid (PAA)-based copolymers with hydrophobic modifications were explored by employing time-resolved fluorescence and MHz-GHz dielectric relaxation (DR) measurements. This sol-gel transition driven dynamics was monitored over an incubation period of 30 days, as these systems were found to undergo gelation after a few weeks. The designed PAA-based homo (P0), hydrophobically modified (∼4%) copolymers (P4, P6), and their coumarin 343 (C343) attached analogous copolymers (P4', P6') were synthesized by reversible addition-fragmentation chain transfer polymerization and characterized by 1H NMR spectroscopy and size exclusion chromatography (SEC). Dynamic light scattering experiments of aqueous copolymer solutions showed a gradual increment of hydrodynamic diameter (Dh) up to ∼4000 nm, and the onset of sol-gel transition was estimated by locating the intersection of two distinct slopes produced by the plots of average Dh as a function of incubation time. The sol-gel transition for these copolymer solutions (aqueous) was clearly demonstrated by the progressive slowing down of DR times and the rotational fluorescence anisotropy times tracked over the entire incubation period. Interestingly, the onset time for the sol-gel transition was found to be insensitive to the chemical binding of the fluorescent probe to these polymers. A comparison between the steady state UV-VIS absorption and fluorescence spectral characteristics of aqueous solutions of these copolymers with chemically bound and externally added C343 suggested that the sol-gel transition involved polymer aggregation. This study may be useful for designing supramolecular polymer gels for biomedical applications.

Methyl Methacrylate-Based Copolymers: Recent Developments in the Areas of Transparent and Stretchable Active Matrices

The recent advancements of poly(methyl methacrylate) (PMMA) as a transparent flexible polymer material have been utilized in numerous areas of engineering and materials science. PMMA-based copolymers demonstrate outstanding mechanical and optical properties owing to high transparency, lightweight nature, high impact resistance, and stress relaxation across glass transition temperature. These copolymers have unique characteristics of retaining optical and microstructural integrities during successive bending or elongations which make them an attractive choice for materials of stretchable electronics. In particular, there has been an escalated rise in the use of methyl methacrylate (MMA)-based transparent and stretchable copolymer films during the recent decades. Therefore, we have highlighted these recent developments into a comprehensive review in order to aid the future progress in these diverse fields. Herein, we have highlighted the scope of MMA as an important building block for the synthesis of highly transparent and flexible materials. The synthetic pathways of these copolymer materials and the resulting mechanical properties have been discussed. Moreover, the immense scope of these copolymer films has been highlighted by virtue of their applications in various industries.