Living spontaneous gradient copolymers of acrylic acid and styrene: one-pot synthesis of pH-responsive amphiphiles

Abstract

RAFT polymerization was used to prepare copolymers of acrylic acid (AA) and styrene (STY) with mole fractions of STY (F STY ) ranging from 0.1 to 0.3 and targeted degrees of polymerization between 50 and 150. The high reactivity of AA-terminal radicals towards STY in this system (r AA ¼ 0.082) resulted in the spontaneous formation of composition gradients, resulting in polymers with block-like structures comprising a STY-rich segment, a relatively short transitional segment, and a segment of AA homopolymer. Atomic force microscopy analysis of thin films of the copolymer revealed phase separated structures which developed after exposure to water. Dynamic light scattering measurements showed pH-responsive amphiphilicity that resulted in dissolved polymer at neutral and basic pH and self-assembly in weakly acidic solutions.

High‐Throughput Method for RAFT Kinetic Investigations and Estimation of Reactivity Ratios in Copolymerization Systems

“…The integrated copolymerization equation was fitted to conversion, monomer fraction and copolymer composition data, assuming non‐negligible errors in all variables. As noted before,1, 21 this method is computationally inefficient but simple to implement in the conventional Microsoft Excel 2003 software 1. The instantaneous copolymer composition at various conversions was determined from the individual monomer to polymer conversions estimated by 1 H‐NMR, which, in general, showed that MA was consumed much more rapidly than VAc.…”

“…Detailed and consistent kinetic investigations of controlled radical polymerizations can be a time‐consuming and demanding task when carried out using traditional experimental techniques 1–3. This is mainly due to the fact that radical polymerizations can be very susceptible towards oxygen traces present in the reaction mixtures 4, 5.…”

“…Thus, in order to have reliable kinetic information about a particular (controlled) radical polymerization reaction, it is mandatory to utilize an appropriate and reproducible degassing method to thoroughly eliminate oxygen from the system. In this regard, one of the preferred methods to properly degas polymerization reaction mixtures is freeze‐evacuate‐thaw repeated cycles (3 at least) in flame‐sealed glass ampoules using high‐vacuum techniques, which can be time‐consuming and limits investigations to a few samples a day 1–3. Recently, an automated parallel freeze‐evacuate‐thaw degassing method for a commercially available parallel synthesizer has been reported by our group 6.…”

“…The utilized experimental technique allowed reliable and comprehensive kinetic data ( i.e. , evolution in time of the conversion of the monomers, and molar mass and dispersity of the formed polymers) to be collected in a short period of time; this kinetic information was used to estimate the reactivity ratios of the co‐monomer system using a computer program1 based on the visualization of the sum of residual space method developed by van Herk and co‐workers 21. The obtained reactivity ratios of the system are in good agreement with literature values 22.…”

Controlled radical copolymerization of styrene with acrylic acid and tert-butyl acrylate under conditions of reversible addition-fragmentation chain transfer: Control of the chain microstructure

“…use of the literature data on copolymerization in bulk (r styrene = 0.21 and r AA = 0.08) [16] and in DMF (r styrene = 1.03 and r AA = 0.4) [17] as well as the relative activities of the monomers calculated from the exper imental data obtained in this study via the KelenTüdös method for the copolymerization of styrene and AA in bulk in the presence of BB (r styrene = 0.31 and r AA = 0.05). The copolymer prepared via copolymer ization in bulk is more enriched with AA units than the copolymer prepared in DMF.…”