Abstract
We compared the influence of the polymerization mechanism onto the physical characteristics of thermoresponsive hydrogels. The Poly(N-isopropylacrylamide) (PNIPAAm) hydrogels were successfully synthesized using reversible addition-fragmentation chain-transfer (RAFT) and free radical polymerization (FRP). The gels were prepared while using different crosslinker feed and monomer concentration. The swelling, dye release, and hydrolytic stability of the gels were investigated in water, or in representative komostrope and chaotrope salt solutions at room temperature and at 37 °C. It was found that the swelling ratio (SR) of the RAFT gels was significantly higher than that of the FRP gels; however, an increased crosslinking density resulted in a decrease of the SR of the RAFT gels as compared to the corresponding gels that are made by FRP, which indicates the limitation of the cross-linking efficiency that is attained in RAFT polymerization. Additionally, an increased monomer concentration decreased the SR of the RAFT gels, whereas a similar SR was observed for the FRP gels. However, the SR of both RAFT and FRP gels in NaSCN and Na2SO4 solutions were similar. Finally, the rate of dye release was significantly slower from the RAFT gels than the FRP gels and the hydrolytic stability of the RAFT gels was lower than that of FRP gels in water, but maintained similar stability in Na2SO4 and NaSCN solutions.
Highlights
IntroductionThe most widely used reversible-deactivation polymerizations (RDRPs) include nitroxide-mediated polymerization (NMP) [4,5,6], atom transfer radial polymerization (ATRP) [7,8,9,10,11,12,13], and reversible addition-fragmentation chain transfer (RAFT) polymerization [14,15,16,17,18]
The PNIPAAm gels were successfully prepared with different amounts of crosslinker and monomer concentration while using reversible addition-fragmentation chain transfer (RAFT) polymerization and free radical polymerization (FRP)
The swelling profile of the RAFT and FRP made gels was markedly different, which indicated the influence of the polymerization mechanism on the hydrogels macroscopic properties
Summary
The most widely used reversible-deactivation polymerizations (RDRPs) include nitroxide-mediated polymerization (NMP) [4,5,6], atom transfer radial polymerization (ATRP) [7,8,9,10,11,12,13], and reversible addition-fragmentation chain transfer (RAFT) polymerization [14,15,16,17,18] These methods allow for unprecedented control on the molecular structure of the final polymer and confer synthetic fidelity and reproducibility that was inaccessible with traditional polymerization methods (i.e., free radical polymerization, FRP). RAFT produced gels with narrow polymer mesh distributions with very good control on the polymerization kinetics
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