  By phantom chain simulations, it has been recently discovered that the
fracture characteristics of star polymer networks with different node
functionality and conversion ratios can be described by the cycle rank of the
networks [Masubuchi et al., Macromolecules, doi: 10.1021/acs.macromol.3c01291].
However, due to the employed simplifications and idealizations of the examined
model networks, the results cannot be cast into realistic systems
straightforwardly. For instance, the equimolar reaction was assumed in a
limited volume for the binary mixture of star prepolymers. For this issue, the
present study investigated the effects of stoichiometry by phantom chain
simulations. Examined polymer networks were created from binary mixtures of
star prepolymers with various mixing ratios by the end-linking reaction via
Brownian dynamics simulations. The networks were stretched with energy
minimization until the break. From the mechanical response, strain and stress
at break and work for fracture were obtained. These fracture characteristics
slightly decrease with increasing the contrast of volume fractions of the
binary prepolymer blends when the node functionality is small and the
conversion ratio is large. For the other cases, the stoichiometry does not
impact the fracture behavior. The number ratio of broken bonds and the cycle
rank exhibit similar stoichiometry dependence. Consequently, stoichiometry of
prepolymer blends does not disturb the previously reported relationships
between the fracture characteristics and the cycle rank.
