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Two polyamines with different conformational properties, poly(α-l-lysine) and polyallylamine, were chemically cross-linked to evaluate the effects of polypeptide secondary structures on gel properties. Both cationic gels are highly swollen at low pH and shrink as it increases primarily due to the reduction in of the concentration of associated counterions in the gel as its ionization decreases. Network shear moduli were determined under uniaxial compression. For the polyallylamine gels, the shear modulus (G) scales as φ2 0.31, where φ2 denotes the polymer volume fraction, over the entire pH range. This result is in favorable agreement with the G ∼ φ2 1/3 relationship predicted for networks of flexible chains. Poly(α-l-lysine) gels swollen below pH 11.0 obey the same scaling behavior. At higher pH levels, however, organized secondary structures are believed to develop, and the composition dependence of the modulus at high pH becomes consistent with the scaling relationship predicted for rigid-rod chain networks connected by flexible junctions (G ∼ φ2 3/2). Further evidence of the existence of more organized microstructures in the poly(α-l-lysine) gels at high pH is provided from complementary thermoelasticity and morphological analyses.

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