RAFT Emulsion Polymerization: MacroRAFT Agent Self-Assembly Investigated Using a Solvachromatic Dye

Abstract

Polymerization-induced self-assembly (PISA) and amphiphilic-macroRAFT-mediated emulsion polymerization are commonly used approaches for synthesis of well-defined polymers and sophisticated particle morphologies. One aspect of these systems that remains relatively unexplored is the conformational state of macroRAFT agents in aqueous solution. To redress this deficiency, we have used fluorescence spectrometry experiments to conduct detailed investigations of the coil conformation across a wide range of pH values for a series of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) macroRAFT agents with different Z-groups (-S-(CH 2 ) 2 -COOH, -S-(CH 2 ) 3 -CH 3 , and -S-(CH 2 ) 11 -CH 3 ), as well as amphiphilic macroRAFT agents (PMAA-b-poly(methyl methacrylate)-(PMMA) and PAA-b-polystyrene(PS)). The critical aggregate concentrations (CAC) or critical micelle concentrations (CMC) for all systems ranged from 7.48 × 10 −7 to 2.57 × 10 −3 mol L −1 . Overall, an extensive library of CAC/CMC values has been compiled for PAA-and PMAAbased macroRAFT agents at different pH conditions, providing important information related to the mechanistic understanding and optimization of macroRAFT-assisted emulsion polymerization.

Polymerization-induced self-assembly via RAFT in emulsion: effect of Z-group on the nucleation step

“…Our group conducted further fluorescence studies to confirm if this change in conformation also applies to PMAA-based macroRAFT with other Z-groups. 30 Interestingly, hyper-coiled PMAA chains were observed under acidic conditions regardless of Z-group hydrophobicity for the Z-groups investigated (-S-(CH2)11-CH3, -S-(CH2)3-CH3, -S-(CH2)3-COOH). Furthermore, DLS measurements indicated the formation of small aggregates comprising a few chains rather than single chain conformation.…”

“…How does this minor change in RAFT agent structure so dramatically influence the polymerization? Before discussing the polymerization mechanism, it is important to address the conformation of PMAA 25,30 in aqueous solution, and how this can affect the PISA process. Chaduc et al 25 conducted fluorescence studies of short chain PMAA macroRAFT (< 5000 g mol -1 with Z-group S-(CH2)2-CH3) at different pH.…”

“…The RAFT agents (Scheme 1) 4-((((2-carboxyethyl)thio)carbonothioyl)thio)-4-cyanopentanoic acid (RAFT1, >95%), 4-cyano-4-((dodecylsulfanylthiocarbonyl)sulfanyl)pentanoic acid (RAFT3, >97%) and 2-(((dodecylthio)carbonothioyl)thio)propanoic acid (RAFT5, >97%) were all purchased from Boron Molecular and used as received. The RAFT agents 4-cyano-4thiothiobutylsulfanylpentanoic acid (RAFT2) 30 and 2-(((butylthio)carbonothioyl)thio)-2methylpropanoic acid 31 were synthesized according to reported protocols. 30,31 The initiators potassium persulfate (KPS, Sigma-Aldrich) and 4,4'-azobis(4-cyanopentanoic acid) (ACPA, Wako) were used as received.…”

“…The RAFT agents 4-cyano-4thiothiobutylsulfanylpentanoic acid (RAFT2) 30 and 2-(((butylthio)carbonothioyl)thio)-2methylpropanoic acid 31 were synthesized according to reported protocols. 30,31 The initiators potassium persulfate (KPS, Sigma-Aldrich) and 4,4'-azobis(4-cyanopentanoic acid) (ACPA, Wako) were used as received. Methacrylic acid (MAA, Sigma-Aldrich) and acrylic acid (AA, Sigma-Aldrich) were used with no further purification.…”

“…Seven different PAA-and PMAA-based macroRAFTs were synthesized via RAFT polymerization using RAFT agents containing Zgroups of different hydrophilicity. Previously, in a very recent paper, we investigated 30 the aqueous phase conformation of these PMAA-and PAA-based macroRAFTs. These hydrophilic macroRAFTs were subsequently employed in aqueous PISA of styrene.…”