Variable architecture polymeric materials that can respond with a change in conformation to relevant stimuli action, such as temperature, pH, ionic strength, biological molecules are of considerable interest for a wide range of applications because of their sensitivities to the modification in environmental conditions. Variable architecture polymeric materials, have been as developed covering interpolymeric complexes, graft copolymers and hydrogels constituted from natural and synthetic polymers which offer unique properties such as, responsiveness to temperature and/or pH, biodegradability, specificity, and biocompatibility.

By combining a temperature-sensitive polymer/monomer usually N-isopropylacrylamide with one pH-sensitive in different architectures, dual/multiple-responsive materials can be obtain. The poly(N-isopropyl acryl amide) (PNIPAM) or hydroxypropyl cellulose (HPC) as thermoresponsive component were used.

Graft copolymers, interpolymeric complexes and blends of PNIPAM with carboxymethylcellulose (CMC) exhibit “thermothickening”. Enzymatic degradation is influenced by molecular interactions in the studied system.

Interpolymeric complexes of PNIPAM with a dicarboxylic copolymer as maleic acid-alt-vinylacetate have a compact structure similar with those of PNIPAM with hydroxypropylcellulose, their stability depends on chemical nature and environmental conditions (pH, temperature). Graft copolymers of PNIPAM with dicarboxylic copolymer as maleic acid-alt-vinyl acetate also exhibit a very strong “thermothickening” effect.

The interpolymeric complexes and hydrogels of PNIPAM with alginate or chitosan behave as “smart” dual-responsive materials with transition temperature/pH values close to the physiological ones. 

This new class of interpolymeric complexes, graft copolymers and hydrogels can sense environmental changes in the physiological range and has found usefulness in drug delivery .  Kinetics of the loading and release of some drugs has been evaluated.

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