When a Small Amount of Comonomer Is Enough: Tailoring the Critical Solution Temperature of LCST-Type Thermoresponsive...

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 (mPEGMA₁₁₀₀) as a comonomer was investigated for its suitability for the CST adjustment of LCST-type polymers. Accordingly, a library of mPEGMA₁₁₀₀-based copolymers was established with varying compositions (X_mPEGMA1100) using four main comonomers, namely di(ethylene glycol) ethyl ether acrylate, N-isopropyl acrylamide and methacrylamide, and mPEGMA₃₀₀, with different CST values (cloud points, T, and clearing points, T, by turbidimetry). It was found that less than 20 mol% of the mPEGMA₁₁₀₀ 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 (CST₀). Moreover, a predictive asymptotic model was developed based on the measured CST values, which strikingly revealed that the CSTs of mPEGMA₁₁₀₀-containing copolymers depend only on the two main parameters of these copolymers, X_mPEGMA1100 and the CST of the homopolymer of the main comonomer (CST₀), that is, CST = f(CST. 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.