Effect of Hydrophobic Interactions on Lower Critical Solution Temperature for Poly(N-isopropylacrylamide-co-dopamine Methacrylamide) Copolymers

Abstract

For the preparation of thermoresponsive copolymers, for e.g., tissue engineering scaffolds or drug carriers, a precise control of the synthesis parameters to set the lower critical solution temperature (LCST) is required. However, the correlations between molecular parameters and LCST are partially unknown and, furthermore, LCST is defined as an exact temperature, which oversimplifies the real situation. Here, random N-isopropylacrylamide (NIPAM)/dopamine methacrylamide (DMA) copolymers were prepared under a systematical variation of molecular weight and comonomer amount and their LCST in water studied by calorimetry, turbidimetry, and rheology. Structural information was deduced from observed transitions clarifying the contributions of molecular weight, comonomer content, end-group effect or polymerization degree on LCST, which were then statistically modeled. This proved that the LCST can be predicted through molecular structure and conditions of the solutions. While the hydrophobic DMA lowers the LCST especially the onset, polymerization degree has an important but smaller influence over all the whole LCST range.

Functional Polymer Solutions and Gels—Physics and Novel Applications

“…Polymer solutions with catechol functionalities were shown to significantly influence thermoresponsive behavior as well as the end groups, which could be modeled statistically, demonstrating the combined effects of the end groups derived from the rather hydrophobic RAFT agents and catechol groups [7], which has led to further elucidation as well as confirmed previous observations on the properties of thermoresponsive polymers containing catechol moieties [8,9]. This work also extends on previous reports on PNIPAM-based polymer with other structures [10][11][12].…”

“…Interestingly, the results show that it is possible to have a decoupling of gelation and turbidity, which is counterintuitive and expands upon earlier knowledge on the physicochemical behavior of PNIPAM in ionic liquids [2]. These results show the relevance of ionic liquids for the solubilization of polymers, which has revolutionized the unwrapping of tightly packed crystalline cellulose [3][4][5][6].Polymer solutions with catechol functionalities were shown to significantly influence thermoresponsive behavior as well as the end groups, which could be modeled statistically, demonstrating the combined effects of the end groups derived from the rather hydrophobic RAFT agents and catechol groups [7], which has led to further elucidation as well as confirmed previous observations on the properties of thermoresponsive polymers containing catechol moieties [8,9]. This work also extends on previous reports on PNIPAM-based polymer with other structures [10][11][12].…”

Surrounding Interactions on Phase Transition Temperature Promoted by Organometallic Complexes in Functionalized Poly(N‐isopropylacrylamide‐co‐dopamine methacrylamide) Copolymers

“…Of note, the samples without titanocene, C4, C7, and C14, only show a slight pinkish hue, which is the onset of catechol tanning, which means that the oxidation level is very low, based on previous experience. [ 32,37–40 ]…”

Temperature and Redox‐Responsive Hydrogels Based on Nitroxide Radicals and Oligoethyleneglycol Methacrylate

“…However, the value of the cloud‐point could be influenced by neighboring hydrophilic/hydrophobic groups. [ 11,14 ] Generally, hydrophobic groups lower the cloud‐point while hydrophilic groups shift the cloud‐point toward higher temperature. [ 15 ] In Figure 3, one can observe that, whatever the value of X TEMPO + , the swelling factors values are slightly decreasing as temperature increases and dramatically drop down between 70 and 80 °C.…”

“…Moreover, since the redox process utilized in this contribution results in the transformation of TEMPO, which essentially behave as an hydrophobic unit, into oxidized TEMPO (TEMPO + ) which is hydrophilic, an interplay between the redox and temperature behaviors is expected because the cloud point of polymers is known to be influenced by either the presence of neighboring hydrophobic or hydrophilic units. [ 11 ]…”