Thermosensitive Triterpenoid‐Appended Polymers with Broad Temperature Tunability Regulated by Host–Guest Chemistry

Abstract

Thermoresponsive water-soluble polymers are of great importance since they typically show a lower critical solution temperature (LCST) in aqueous media. In this research, the LCST change in broad temperature ranges of copolymers composed of natural glycyrrhetinic acid (GA)-based methacrylate and N,N'-dimethylacrylamides (DMAs) was investigated as a function of the concentration and the content of GA pendants. By complexation of GA pendants with β-cyclodextrin (β-CD), a side-chain polypseudorotaxane was obtained, which exhibited a significant increase in the LCST of copolymers. Moreover, the precisely reversible control of the LCST behavior was realized through adding a competing guest molecule, sodium 1-admantylcarboxylate. This work illustrates a simple and effective approach to endow water-soluble polymers with broad temperature tunability and helps us further understand the effect of a biocompatible host-guest complementary β-CD/GA pair on the thermoresponsive process.

Tunable UCST thermoresponsive copolymers based on natural glycyrrhetinic acid

“…4B, a tiny increase of concentration ratio from 0 to 0.03 would result in a decrease of 5 o C in UCST. This was totally different from the behavior of LCST polymers in the presence of β-CD as reported in our previous work, where an increase of [β-CD]/[GA] ratio from 0 to 5 only resulted in an increase of 13 o C for the cloud point [21]. As γ-CD had a stronger binding ability with GA and a better hydrophilicity compared with β-CD, it was more effective in regulating the USCT behavior of P(AAm-co-GAA-3%).…”

“…These characteristics can be used to make low molecular weight gels [16,17], supramolecular chiral structures [18], and functional polymers [19,20]. In our previous works, GA has been incorporated into LCST-based polymers, "necklace"-like polypseudorotaxanes, and selfhealable hydrogels [21][22][23]. In this work, we proposed to take advantage of the hydrophobic backbone of GA to construct new biocompatible HB-UCST polymers.…”

Biobased thermosensitive polyrotaxanes constructed by polymerization of cyclodextrin-triterpenoid inclusion complexes

“…19 More importantly, it can form a stable host-guest complex with CD. 20,21 Using these GA-CD host-guest pairs, self-healable supramolecular hydrogels have been successfully prepared in our previous works. 22 Obviously, GA would be an ideal guest molecule in the construction of biocompatible CD-based PRs.…”

Tough Polymeric Hydrogels Formed by Natural Glycyrrhetinic Acid-Tailored Host–Guest Macro-Cross-Linking toward Biocompatible Materials

“…Upon addition of PCD, signals for methyl protons (positions 23−29) appeared because of the complexation of GA with PCD (Figure 2B, bottom). 19,20,25 comparison with that of PCD (Figure 2A). According to Formula S1 in the Supporting Information, the molar ratio between β-CD and GADA was calculated to be 2:1.…”

“…No signal of methyl groups on GA moiety was observable in 1 H NMR spectrum of GADA in D2O (Figure 2B, up), which indicated the formation of aggregates due to the hydrophobic nature of GA. Upon addition of PCD signals for methyl protons (positions 23-29) appeared on account of the complexation of GA with PCD (Figure 2B, bottom) [19,20,25] . It was consistent with the SEC results, where a larger molecular weight (Mn) 9400 Da of HGMC was detected in comparison with that of PCD (Figure 2A).…”