PEGMAs with short and long side chains: what is the effect in the formation of stars and brushes by RAFT polymerization?

Reversible addition fragmentation chain transfer (RAFT) polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMAn, where n is the PEG side chain length) for the formation of star-like molecules and bottlebrushes was systematically studied using ethanol as solvent at 70 & DEG;C. The effect of PEG units in the side chain on the kinetics of the (macro)monomers 2-ethoxy ethyl methacrylate (EEMA1), PEGMA9, and PEGMA23 was investigated in the presence of 4-cyano-4-(dodecylsulfanylthiocarbonyl) pentanoic acid (CDP) as RAFT agent and 4,4 & PRIME;-azobis(4-cyanopentanoic acid) (ACPA) as initiator. Two periods could be distinguished in the kinetics: (i) the initialization stage related to the pre-equilibrium and competition between the propagation and the first addition of monomer to primary radicals, and (ii) a main equilibrium process; both were quantified via the apparent rate constants kapp1 and kapp2, respectively. While EEMA1 and PEGMA9 RAFT polymerization presented an initiator concentration-dependent acceleration in the first stage, PEGMA23 exhibited inhibition, with practically no polymerization, when the CDP amount was decreased. A retardation effect was observed during the main stage, which decreased at longer PEG side chains of the (macro)monomer. Finally, 1,4-dioxane was used as a solvent for PEGMA23 polymerization and the resulting data were compared with those for the kinetics using ethanol; the former presented not only a strong acceleration in the first stage of the polymerization, reaching 60% conversion at a short time, attributed to the enhanced solubility of PEGMA23, but also stronger discrepancies for RAFT polymerization from experimental and theoretical data. PEGMA RAFT polymerization presents diverse kinetic characteristics, such as initiation rate (acceleration or inhibition), retardation effect, and dispersity, according to the length of the PEG side chain.