Lower Critical Solution Temperature in Poly(N-Isopropylacrylamide): Comparison of Detection Methods and Molar Mass Distribution Influence

Poly(N-Isopropylacrylamide) has a broad potential range of biomedical applications owing to its lower critical solution temperature (LCST). This work tries to elucidate the real influence of several parameters on LCST by comparing homopolymers prepared by free radical polymerization and reversible addition-fragmentation chain transfer (RAFT) polymerization using conventional calorimetry, turbidimetry, and rheology as well as how three different methods can be used to detect the LCST. These methods are compared to gain a deeper understanding of the underlying processes and how they are related to molar mass and synthesis methods. The diverse interactions associated with the LCST transitions are more sensitive depending on the ratio defined between polymerization degrees and end-group effects. Thus, the selection of a high sensitive method for LCST detection depends on the molecular features defined from the homopolymer. In addition, this work shows also the importance of the RAFT agent selected for the synthesis, which can modify substantially the LCST in comparison with other methods reported where the use of chemicals, complex processes, and costs considerably increase.