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Gel point conversions and equilibrium tensile moduli of polyester-based polyurethane networks were determined for different dilutions during network formation. Also, the limiting dilution beyond which the network was not formed at full conversion of functional groups was determined. It ranged between 92 and 94% of diluent. The scaling dependences against the reference states – the ring-free case and the limiting dilution case – showed that the excluded volume effects were operative and structural changes associated with cyclization affected the rates of both the intramolecular and the intermolecular reactions.

A model describing swelling changes of covalently crosslinked gels caused by unfolding of crosslinks of folded chains built-in in the gel matrix was proposed. By unfolding, a new interacting surface is exposed which may differ from the interacting sites of the gel polymer. Non-ionic as well as ionic interactions are considered. A certain force generated by the swelling pressure acts on the ends of the folded crosslinks and unfolding starts when this force exceeds a certain limiting value. The continuation or arrest of unfolding depends on whether the exposure of the new interacting surface decreases or increases this force. The unfolding process is considered to be irreversible but possible reversibility can be considered. This model relates to biohybrid gels in which the folded domain of the crosslink is composed of elements of the muscle protein titin. The model is based on the statistical-mechanical theory of swelling of crosslinked polymers. A change in external variables such as temperature or degree of ionization can cause an abrupt change in volume of the swollen gel (transition) within a certain range of parameters characterizing the gel and polymer-solvent interactions.

During formation of films from solutions of reactive polymers, crosslinking and solvent evaporation occur simultaneously but with different rates. If the film adheres to the substrate, the formed network shrinks only in the direction normal to the film surface and lateral strains develop. It was demonstrated theoretically that the lateral strain reduces the activity of the solvent in the film and thus lowers the evaporation rate.