Tunable pH- and Temperature-Sensitive Copolymer Libraries by Reversible Addition−Fragmentation Chain Transfer Copolymerizations of Methacrylates

Reversible addn.-fragmentation chain transfer (RAFT) polymns. were performed on a Chemspeed Accelerator SLT100 automated synthesizer to polymerize N,N-(dimethylamino)ethyl methacrylate (DMAEMA) and poly(ethylene glycol) Me ether methacrylate (PEGMA) at 70 DegC. Azobis(isobutyronitrile) (AIBN) was used as source of radicals and 2-cyano-2-Bu dithiobenzoate (CBDB) as RAFT agent. A complete screening in compn. of P(DMAEMA-stat-PEGMA) copolymers was elaborated from 0% of PEGMA to 100% of PEGMA. All polydispersity indexes of the obtained copolymers are comprised between 1.11 and 1.30. The reactivity ratios were detd. by the extended Kelen-Tuedoes method (rDMAEMA = 0.93 and rPEGMA = 0.66). The behavior of the pH- and temp.-sensitive copolymers was studied in aq. soln. by measuring the lower crit. soln. temp. (LCST) by UV/vis spectroscopy. The measurements were performed at three different pH values (4, 7, and 10). At pH 7 and pH 10 the LCST is increasing linearly with the wt. % PEGMA in the copolymer feed. On the contrary, at pH 4, the hydrophilicity of the P(DMAEMA-stat-PEGMA) copolymers is too high due to the protonation of the DMAEMA units. Thus, no LCST was detected for most of them. By varying the pH and the compn. of the P(DMAEMA-stat-PEGMA) copolymers, the LCST can be easily tuned between 34.7 and 82.0 DegC.