When a Small Amount of Comonomer Is Enough: Tailoring the Critical Solution Temperature of LCST-Type Thermoresponsive Random Copolymers by PEG Methyl Ether Methacrylate with 1100 g/mol Molecular Weight.

Tuning the critical solution temperature (CST) of thermoresponsive polymers is essential to exploit their immense potential in various applications. In the present study, the effect of PEG-methyl ether methacrylate with a higher molecular weight of 1100 g/mol (mPEGMA) as a comonomer was investigated for its suitability for the CST adjustment of LCST-type polymers. Accordingly, a library of mPEGMA-based copolymers was established with varying compositions () using four main comonomers, namely di(ethylene glycol) ethyl ether acrylate, -isopropyl acrylamide and methacrylamide, and mPEGMA, with different CST values (cloud points, , and clearing points, , by turbidimetry). It was found that less than 20 mol% of the mPEGMA in the copolymers is practically sufficient for tuning the CST in the entire measurable temperature range, i.e., up to 100 °C, regardless of the CST of the homopolymer of the main comonomer (CST). Moreover, a predictive asymptotic model was developed based on the measured CST values, which strikingly revealed that the CSTs of mPEGMA-containing copolymers depend only on the two main parameters of these copolymers, and the CST of the homopolymer of the main comonomer (CST), that is, . The revealed two-parameter relationship defines a surface in 3D plotting, and it is applicable to determine the CST of copolymers in advance for a given composition or to define the suitable composition for a required CST value. These unprecedented results on the dependence of CSTs on two major well-defined parameters enable to design a variety of novel macromolecular structures with tailored thermoresponsive properties.