Structure‐Property Relationships for Model Heterocyclic Polymer Networks: Effect of Network Density

Abstract

Chain motion dynamics around and through the glass transition region of a series of heterocyclic polymer networks (HPN) were characterized by dynamic mechanical spectroscopy and differential scanning calorimetry. The effective network densities of those HPN prepared by simultaneous trimerization of a bifunctional (1,6‐hexamethylene diisocyanate, HDI) and a monofunctional (hexyl isocyanate, HI) monomers were systematically varied by changing the HDI/HI ratio in the reaction mixture, whereas their overall chemical structure remained essentially unchanged. The increasing difference between the experimental and theoretical values of the mean molar masses of chain strands between network junctions, the lower the HDI/HI ratio, was assumed to be the result of deviations from the exact chemical stoichiometry due to subsidiary reactions between isocyanate groups of the same monomer. The increase of the effective network density was accompanied by narrowing of the glass transition interval and by its systematic shi...