Tertiary-Amine-Containing Thermo- and pH-Sensitive Hydrophilic ABA Triblock Copolymers: Effect of Different Tertiary Amines on Thermally Induced Sol–Gel Transitions

Abstract

This Article reports on the synthesis of a series of well-defined, tertiary-amine-containing ABA triblock copolymers, composed of a poly(ethylene oxide) (PEO) central block and thermo- and pH-sensitive outer blocks, and the study of the effect of different tertiary amines on thermally induced sol-gel transition temperatures (T(sol-gel)) of their 10 wt % aqueous solutions. The doubly responsive ABA triblock copolymers were prepared from a difunctional PEO macroinitiator by atom transfer radical polymerization of methoxydi(ethylene glycol) methacrylate and ethoxydi(ethylene glycol) methacrylate at a feed molar ratio of 30:70 with ∼5 mol % of either N,N-diethylaminoethyl methacrylate (DEAEMA), N,N-diisopropylaminoethyl methacrylate, or N,N-di(n-butyl)aminoethyl methacrylate. The chain lengths of thermosensitive outer blocks and the molar contents of tertiary amines were very similar for all copolymers. Using rheological measurements, we determined the pH dependences of T(sol-gel) of 10 wt % aqueous solutions of these copolymers in a phosphate buffer. The T(sol-gel) versus pH curves of all polymers exhibited a sigmoidal shape. The T(sol-gel) increased with decreasing pH; the changes were small on both high and low pH sides. At a specific pH, the T(sol-gel) decreased with increasing the hydrophobicity of the tertiary amine, and upon decreasing pH the onset pH value for the T(sol-gel) to begin to increase noticeably was lower for the more hydrophobic tertiary amine-containing copolymer. In addition, we studied the effect of different tertiary amines on the release behavior of FITC-dextran from 10 wt % micellar gels in an acidic medium at 37 and 27 °C. The release profiles for three studied hydrogels at 37 °C were essentially the same, suggesting that the release was dominated by the diffusion of FITC-dextran. At 27 °C, the release was significantly faster for the DEAEMA-containing copolymer, indicating that both diffusion and gel dissolution contributed to the release at this temperature.

Polyvinyl Alcohol‐Based Thermogel with Tunable Gelation and Self‐Healing Property

“…Indeed, the T sol–gel decreases with the increase in pH, from 35 °C at pH = 13 to 70 °C at pH = 9.5 (10 mg mL −1 PVA‐DEEDA‐Borax, Figure b; Figure S7, Supporting Information), showing a sharpness of around 10 °C per pH unit. This value is higher than previously reported . Note that the pK a of PVA‐DEEDA‐Borax solution is about 9.2 based on titration.…”

“…By contrast, for the PVA‐DEEDA‐Borax solution of pH 12.6, a sigmoidal reduction in the mobility of C H 3 terminals can be observed. This can be rationalized by considering that the tertiary amine becomes less charged at a higher pH, and thus osmotic pressure becomes lower in the formed hydrogel, facilitating the dehydration process. As the pH decreases to 9.7, a considerable fraction of amine groups based on PVA‐DEEDA‐Borax have been protonated because the pK a of PVA‐DEEDA‐Borax is 9.2.…”

Gelation characteristics, physico-mechanical properties and degradation kinetics of micellar hydrogels

“…A-B-A triblock copolymers are known to form stimuli-responsive micellar gels in aqueous solution [35,36]. Typically in micelle forming A-B-A copolymers, one of the “A” or “B” blocks is hydrophilic and the other block is hydrophobic or becomes hydrophobic in response to an external stimulus like temperature, pH, ionic strength or enzyme concentration [32,37–39]. When the “A” block is permanently hydrophilic, A-B-A copolymers form star-like micelles at low concentrations [36].…”

Temperature and pH responsive hydrogels based on polyethylene glycol analogues and poly(methacrylic acid) via click chemistry

“…Pan et al reported the preparation of the temperature and pH responsive network grafted PDMAEMA‐ g ‐PNIPAM hydrogel based on PNIPAM having two azide groups at one chain end [PNIPAM‐(N 3 ) 2 ] and alkyne‐pending P(DMAEMA‐ co ‐ProA) via click chemistry . (3) Temperature and pH responsive hydrogels were fabricated through self‐assembling of a macromolecular chain that incorporates distinct temperature and pH sensitive building blocks . For example, Schmalz et al prepared the temperature and pH sensitive terpolymer poly(2‐vinylpyridine)‐ b ‐poly(ethylene oxide)‐ b ‐poly(glycidyl methyl ether‐ co ‐ethyl glycidyl ether), and the multisensitive terpolymer underwent a sol‐to‐gel phase transition with changing temperature and pH .…”