Temperature and pH-responsive triblock copolymers: synthesis and solution properties

Triblock copolymers based on poly(oligo(ethylene glycol) methyl ether) methacrylate (POEGMA), a thermoresponsive polymer, and poly(4-vinyl pyridine) (P4VP), a pH-responsive polymer, or poly(dimethylaminoethyl methacrylate) (PDMAEMA), a thermo- and pH-responsive polymer were synthesized using the addition-fragmentation reversible chain transfer polymerization (RAFT). POEGMA with a similar degree of polymerization (DP) but with OEG side chain with different DP were synthesized using S,S-Bis(?,?' dimethyl-?''acetic acid) (CMP) as a symmetric bifunctional chain transfer agent (CTA), and used as macro-CTA for copolymerization with 4VP or DMAEMA. The copolymers self-assemble in aqueous solutions, forming structures that can be affected by the preparation method, concentration, pH, and temperature. The preparation method had a more pronounced effect on the self-assembled structures of the POEGMA-b-P4VP-b-POEGMA copolymer with a longer P4VP block. Spherical particles were observed at pH > pKa of P4VP, while interconnected micelles were observed at pH 3 and T > Tcp (critical temperature) of POEGMA, due to the P4VP-bridging between the POEGMA block in adjacent cores. The critical micellar concentration at pH 3 and T > Tcp was 0.022 mg mL-1. The self-assembly resulted in structures capable of encapsulating Nile red at pH ? 7. Furthermore, the coordination of P4VP blocks with Cu2+ resulted in a nanogel responsive to temperature and pH. The copolymerization of POEGMA with DMAEMA was more effective to produce copolymers with a wider composition range than that observed for the POEGMA-b-P4VP-b-POEGMA series, due to the similar stability between the radicals from the CTA and the monomers. Both POEGMA and PDMAEMA blocks are hydrophilic depending on temperature and pH. Cryo-EM images showed that the POEGxMAy-b-PDMAEMAz-b-POEGxMAy copolymers self-assemble as spherical and elongated micelles depending on their concentration and temperature. The phase behavior was investigated by 1H NMR spectroscopy at pH 9 and different temperatures. At pH 9, the PDMAEMA blocks are deprotonated and the increase in temperature resulted in a dehydration of both PDMAEMA and POEG5MA blocks and the formation of aggregates. At low concentrations (0.125 mg mL-1), these aggregates remained stable over the entire temperature range. However, at high concentrations (5 mg mL-1) precipitation occurred above 70 °C. The increase in the molar mass of the PDMAEMA block caused a decrease in the hydrodynamic radius (RH) of aggregates at pH 7 and 9, at 25 °C. This effect was gradually attenuated by the increase in the OEG side chain and, therefore, increased hydrophilicity, which increased the Tcp of the copolymers. Reichardt dye incorporation showed that POEGMA-b-PDMAEMA-b-POEGMA copolymers can incorporate hydrophobic molecules and that increasing the temperature of the solutions does not change the microenvironment in which the dye was incorporated (AU)