 If we assume that the initial configuration of a chain can be described by a random walk, then the initial chain length is
If we assume that one end of the chain is at the origin, then the probability that a block of size formula_74 around the origin will contain the other end of the chain, formula_75, assuming a Gaussian probability density function, is
The configurational entropy of a single chain from Boltzmann statistical mechanics is
where formula_78 is a constant.The total entropy in a network of formula_2 chains is therefore
where an affine deformation has been assumed.Therefore the strain energy of the deformed network is
where formula_4 is the temperature.