Thermosensitive ABC triblock copolymers with different block lengths and block orders were prepared by reversible addition− fragmentation chain transfer (RAFT) polymerization. Using a nonionic macro-RAFT agent containing poly(ethylene oxide) (PEO, average degree of polymerization 17), either N-acryloylglycinamide (NAGA) or N-isopropylacrylamide (NIPAM) was first polymerized to diblock copolymers. The diblock copolymers exhibited typical thermoresponsive character of PNAGA and PNIPAM in aqueous solutions. Chain extension of the diblock copolymers was then made to prepare PEO-b-PNAGA-b-PNIPAM and PEO-b-PNIPAM-b-PNAGA triblock copolymers. Investigations of the polymer solutions showed that the triblock copolymers exhibited both UCST and LCST type transitions. The phase transitions induced the formation of polymer aggregates below UCST and above LCST, and the aggregate structures were inverted upon heating and cooling. The order of the polymer blocks with respect to PEO as well as the block sizes contributed to the thermal response.
A prospective technology for reversible enzyme complexation accompanied with its inactivation and protection followed by reactivation after a fast thermocontrolled release has been demonstrated. A thermoresponsive polymer with upper critical solution temperature, poly(N-acryloyl glycinamide) (PNAGA), which is soluble in water at elevated temperatures but phase separates at low temperatures, has been shown to bind lysozyme, chosen as a model enzyme, at a low temperature (10 °C and lower) but not at room temperature (around 25 °C). The cooling of the mixture of PNAGA and lysozyme solutions from room temperature resulted in the capturing of the protein and the formation of stable complexes; heating it back up was accompanied by dissolving the complexes and the release of the bound lysozyme. Captured by the polymer, lysozyme was inactive, but a temperature-mediated release from the complexes was accompanied by its reactivation. Complexation also partially protected lysozyme from proteolytic degradation by proteinase K, which is useful for biotechnological applications. The obtained results are relevant for important medicinal tasks associated with drug delivery such as the delivery and controlled release of enzyme-based drugs.
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