Abstract
AbstractThermoresponsive polymers are frequently involved in the development of materials for various applications. Here, polymers containing poly(2‐ benzhydryl‐2‐oxazine) (pBhOzi) repeating units are described for the first time. The homopolymer pBhOzi and an ABA type amphiphile comprising two flanking hydrophilic A blocks of poly(2‐methyl‐2‐oxazoline) (pMeOx) and the hydrophobic aromatic pBhOzi central B block (pMeOx‐b‐pBhOzi‐b‐pMeOx) are synthesized and the latter is shown to exhibit inverse thermogelling properties at concentrations of 20 wt.% in water. This behavior stands in contrast to a homologue ABA amphiphile consisting of a central poly(2‐benzhydryl‐2‐oxazoline) block (pMeOx‐b‐pBhOx‐b‐pMeOx). No inverse thermogelling is observed with this polymer even at 25 wt.%. For 25 wt.% pMeOx‐b‐pBhOzi‐b‐pMeOx, a surprisingly high storage modulus of ≈22 kPa and high values for the yield and flow points of 480 Pa and 1.3 kPa are obtained. Exceeding the yield point, pronounced shear thinning is observed. Interestingly, only little difference between self‐assemblies of pMeOx‐b‐pBhOzi‐b‐pMeOx and pMeOx‐b‐pBhOx‐b‐pMeOx is observed by dynamic light scattering while transmission electron microscopy images suggest that the micelles of pMeOx‐b‐pBhOzi‐b‐pMeOx interact through their hydrophilic coronas, which is probably decisive for the gel formation. Overall, this study introduces new building blocks for poly(2‐oxazoline) and poly(2‐oxazine)‐based self‐assemblies, but additional studies will be needed to unravel the exact mechanism.
Highlights
Materials chemistry and design can be used to develop smart materials that react to external stimuli and adapt or change their properties
All substances used for polymerization, methyl trifluoromethylsulfonate (MeOTf) and MeOx were refluxed over CaH2 for several hours and distilled prior to use
The synthesis of the monomers was carried out according to a well-known route established by Witte and Seeliger.[45]
Summary
Materials chemistry and design can be used to develop smart materials that react to external stimuli and adapt or change their properties. Many new materials and polymers have been developed that respond to various stimuli.[1,2,3] A controlled chemical reaction,[4] modification of polymer properties by changing the temperature,[5] the pH,[6] the absorption of electromagnetic radiation[7] or the action of mechanical,[8] magnetic,[9] or electrical forces[10] have been described in the literature. Thermoresponsive polymers change their properties by changing temperature beyond critical transition temperature. In addition to biomedicine,[11] these properties are used in separation science,[12] water purification,[13] and optical devices.[14] The thermoresponsive transitions arise from various changes in polymer–polymer and polymer–solvent interactions at different temperatures. A lower critical solution temperature (LCST) system is characterized by a miscible
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