Thermodynamic Considerations for Copolymer Solutions

In the case of copolymer solutions, the melting temperature also depends on interactions between the different monomeric imits and the solvent. Considering the case in which the crystalline phase is pure (i.e., only monomeric units of a single type crystallize and no solvent is present in the lattice), the decrease in the melting temperature can be derived in a similar manner as for the homopolymer solution case using the Flory-Huggins theory with an appropriate modification [15]. To take into accoimt the interactions between both comonomers and solvent, the net interaction parameter for binary copolymers should be calculated as follows  

If the steric structures of both comonomer imits in random copolymers are similar, the melting temperature depression equation will be the same as Eq. 1, with the interaction parameter calculated with Eq. 4. For a given copolymer, the crystallizabilities of copolymer chains in dilute solution strongly depend on the chain composition. From thermodynanuc considerations, this can be explained from the fact that changes in copolymer composition alter the value of the interaction parameter de ed by Eq. 4. For copolymers with two chemically similar comonomers, xia will be very dose to xiB, ind Xab will approach zero, hi this system, one can simply use Eq. 1 with Xl = XiA Xib- 

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