Theory of crystallizable block copolymer blends

An equilibrium theory of blends is presented, which incorporates diblock pure copolymers in which one of the copolymer blocks is crystallizable and the other is amorphous. The material is assumed to order in a lamellar structure of alternating semicrystalline and amorphous layers with the chemical bonds which connect the copolymer blocks lying in the interfacial regions between the layers. The amorphous blocks are modelled as flexible chains, each with one end (the joint) anchored in an interface. Their contribution to the free energy is calculated via the self-consistent solution of the modified diffusion equations. The crystalline regions are modelled as folded chains, also with one end in an interfacial region (bonded to the corresponding end of an amorphous block). The calculated amorphous block free energies can be expressed as a single universal function depending on the total degree of polymerization of the amorphous block, its stretching, and a parameter proportional to the thickness of the interface. An analytical form has been fitted to this function, which can be used for any amorphous block, and combined with a model of the crystallizable block to obtain an analytic expression for the lamellar thickness. As an example, the theory is applied specifically to PEO-block--PS copolymers. 19 ref.--AA