Novel pH-Sensitive Hydrogels of Segmented Poly(amine ureas) Having a Repetitive Array of Polar and Apolar Units in the Main Chain

Abstract

The pH-responsive swelling/deswelling of novel segmented poly(amine ureas) (SPAU) with a repetitive array of polar (N,N'-diethylethylenediamine) and apolar (diethylenephenylene) units in the main chain was examined as a function of ionic strength and temperature. An end-isocyanated polyamine was prepared by the 2:1 addition reaction of 4,4'-methylenediphenyldiisocyanate (MDI) to telechelic polyamine having secondary amino groups at both ends. The isocyanated polyamine was extended by the reaction with equimolar ethylenediamine to form a segmented poly(amine urea) (SPAU). The SPAU exhibited reproducible swelling/deswelling in response to pH changes. A discontinuous 270-fold change in the swelling degree was observed at a critical pH, indicating a phase transition. The shift of ethylenediamine units to the trans conformation on double protonation may play a role in the swelling transition through a stiffening of the polymer strands. The hysteresis observed in the swelling/deswelling cycle in water at 30 o C disappeared upon addition of 0.05 M NaCl or upon lowering of the temperature to 4 o C. The regulation of solute transport across the SPAU matrix responding to a change in external pH was demonstrated using vitamin B 12 as a model solute, suggesting the formation of a barrier layer at the surface of the film that stopped solute diffusion at high pH. SPAUs can be cast on substrates of any shape, providing mechanically strong pH-responsive surface coatings