| Abstract: | An equilibrium theory is proposed for crystallization of (A, B) binary copolymers whose comonomeric unit sequences are statistically described by conditional pair probabilities PAA, PAB, PBA, and PBB. These are linked to the product of the reactivity ratios by r = rArB = (PAAPBB)/(PABPBA). Three cases are considered here, (i) B units are rejected from the crystals, (ii) cocrystallization of A and B comonomeric units is possible in the full range of compositions within a single crystal structure (copolymer isomorphism), (iii) cocrystallization takes place either in a poly(A)-type or in a poly(B)-type structure, depending on composition (copolymer isodimorphism). For case (i) crystallization the theory demonstrates, according to expectation, that alternating copolymers (r = 0) produce the largest melting point depression, whereas in case (ii) they give rise to the smallest composition difference between the crystals and the liquid. The theory developed here further illustrates that for binary copolymers which are isodimorphic (case iii), a phase diagram is obtained similar to that for a classical binary system of small molecules. |
