  Elastomers are used in a wide range of applications because of their large
strain to failure, low density, and tailorable stiffness and toughness. The
mechanical behavior of elastomers derives mainly from the entropic elasticity
of the underlying network of polymer chains. Elastomers under large deformation
experience bonds breaking within the polymer network. This breaking of chains
damages the network, can lead to material failure, and can be utilized as an
energy dissipation mechanism. In the case of reversible bonds, broken chains
may reform and heal the damage in the network. If the reversible bonds are
dynamic, chains constantly break and reform and create a transient network. A
fundamental constitutive theory is developed to model the mechanics of these
polymer networks. A statistical mechanical derivation is conducted to yield a
framework that takes in an arbitrary single-chain model (a Hamiltonian) and
outputs: the single-chain mechanical response, the breaking and reforming
kinetics, the equilibrium distribution of chains in the network, and the
partial differential equations governing the deformation-coupled network
evolution. This statistical mechanical framework is then brought into the
continuum scale by using macroscopic thermodynamic constitutive theory to
obtain a constitutive relation for the Cauchy stress. The
potential-supplemented freely jointed chain ($u$FJC) model is introduced, and a
parametric study of its mechanical response and breaking kinetics is provided.
This single-chain model is then implemented within the constitutive framework,
which we specialize and apply in two exemplary cases: the mechanical response
and irreversible breakdown of a multinetwork elastomer, and the mechanical
response of a dual crosslink gel. After providing a parametric study of the
general constitutive model, we apply it to a hydrogel with reversible
metal-coordination crosslinks.
