Syntheses and characterization of physically crosslinked hydrogels from dithiocarbamate-derived polyurethane macroiniferter

Abstract

A dithiocarbamate (DC)-based polyurethane macroiniferter (PUMI) was synthesized and used to prepare physically crosslinked polyurethane-block-poly (acrylamide) (PU-b-PAAm) and polyurethane-block-poly(vinyl pyrrolidone) (PU-b-PVP) hydrogels. The success of the reactions has been confirmed by FTIR, 1H-NMR, and 13C-NMR Spectroscopy analyses. The number average molecular weight of the block copolymers increased linearly with conversion and copolymerization time and thus followed a "living" radical mechanism. The water transport behavior of these polyurethane-based hydrogels such as water uptake rate, equilibrium water content (EWC), transport number (n), characteristic diffusion rate constant (K), diffusion coefficient (D), and pH effect on EWC has been investigated. The results revealed that PU-b-PAAm hydrogels followed Fickian diffusion suggesting diffusion controlled swelling kinetics, whereas the PU-b-PVP hydrogels followed non-Fickian diffusion indicating that both diffusion and structural relaxation controlled the water transport. The PU-b-PAAm hydrogels showed higher swelling at both low and high pH than at a neutral pH. This is attributed to protonation of the tertiary amines of N,N-diethyl-N,N′-bis8(2-hydroxyethyl) thiuram disulfide (DHTD) at low pII and base hydrolysis of amide segments at high pH. In the thermogravimetric analysis; PUMI, PU-b-PVP and PU-b-PAAm have degraded in three distinct stages related to CS2 evolution, hard segment degradation, and soft segment degradation. © 2008 Wiley Periodicals, Inc.