MECHANICAL-PROPERTIES OF COPOLY(N-HYDROXYETHYL L-GLUTAMINE-CO-N-HYDROXYPENTYL L-GLUTAMINE) HYDROGELS

Random copolymers, poly(N-hydroxyethyl L-glutamine-co-N-hydroxypentyl L-glutamine) (PHPeEG) as well as the corresponding homopolymers, poly(N-hydroxyethyl L-glutamine) (PHEG) and poly(N-hydroxypentyl L-glutamine) (PHPeG), were prepared by aminolysis with a mixture of 2-amino-1-ethanol (EA) and 5-amino-1-pentanol (PeA) in the presence of crosslinking agent, octamethylenediamine (OMDA), on membranes of poly(gamma-benzyl L-glutamate). The properties of the resultant membranes, such as the degree of swelling Q(w), conformational properties and mechanical properties were studied in the pseudo-extracellular fluid (PECF). Q(w) and helix content are dependent on the composition of the random copolymers. The mechanical strength of PHEG hydrogel was improved largely by introducing HPeG residues, while low Young's modulus, high swelling and low helix content were found to remain unchanged. The transition from the elastomer-type mechanical behavior to the skin-type mechanical behavior was observed at 82-90% of helix content and 110-160% of Q(w) for the copolymers from tensile tests. The difference in mechanical behavior was investigated in detail by creep, stress relaxation and hysteresis experiments.