Thermoresponsive ureido-derivatized polymers: the effect of quaternization on UCST properties
A series of thermoresponsive ureido-derivatized polymers were synthesized via atom transfer radical polymerization (ATRP) and a post-modification process. All of the polymers were designed to exhibit an upper critical solution temperature (UCST) in aqueous solution, which was mainly dependent on (i) the presence of ureido moieties, (ii) the chain length of the side groups, and (iii) the degree of quaternization (DQ) on a triazole ring. Side group modification of PHEMA was carried out by DCC coupling with 4-pentynoic acid to prepare PHEMA-alkyne (PHA). 2-Azidoethylurea and 3-azidopropylurea were combined with the PHA backbone via click reaction, resulting in triazole-ring containing ureido-derivatized polymers. Quaternization reactions with methyl iodide were conducted on the triazole ring of each polymer to further control the UCSTs. Results showed that the UCST could be precisely tuned by the level of DQ.