Crystallization Of Random Copolymers Research Articles

Polymorph selection during crystallization of random copolymers

Many polymers show polymorphous behavior that they can crystallize into different crystalline modifications under different circumstances. For a particular polymer material, in most of the cases, one of the several possible modifications is generally preferentially developed. Therefore, selective control of the specific polymorphous modification thus properties in polymeric materials is highly desired. This article discusses underlying mechanism of polymorph selection during crystallization of random copolymers. Following a general discussion of theoretical considerations, we present case studies of butene-1/ethylene and propylene/ethylene random copolymers. Our results indicate that polymorph selection during crystallization of random copolymers is primarily controlled by the nucleation process. Nucleation of different polymorphs can be easily tuned via creating differently structured melt.

Crystal and Pseudo-Crystal Phases in Main Chain Mesogenic Homo- and Copolymers with Flexible Spacers

Abstract Some packing principles of polymers containing rigid and flexible segments are presented, as revealed by X-ray diffraction of crystal phases. Two types of conformationally disordered crystal states are recognized: (a) with "layered" disorder (quasi-2-dimensional) and (b) with “occluded” disorder (3-dimensional). In both cases the flexible spacer is non-crystalline, which is ascribed to the mismatch in cross-sectional areas of the spacer and the mesogen. The relative ease of crystallization of random copolymers containing spacers of varying length is attributed to their miscibility in the disordered layers.

Copolyester studies. II. Melting and crystallization behavior of tetramethylene terephthalate–tetramethylene sebacate copolymers

The melting and crystallization behavior of poly(tetramethylene terephthalate) and its copolymers with tetramethylene sebacate (≯ 20 mol %) has been studied using differential scanning calorimetry (DSC). The effect of the sebacate concentration on equilibrium melting temperature and crystallization behavior is discussed in terms of the theory of equilibrium crystallization of random copolymers. The multiple-melting behavior of these systems is described and interpreted in terms of the theory of equilibrium melting of chain-folded crystals, together with molecular fractionation during crystallization and melting and recrystallization during the DSC scan.

Problems and theories of polymer crystallization

AbstractThis paper discusses four general problem areas and their associated theories: the relationship between crystal growth and nucleation; the concentration dependence of crystal growth rates; the crystallization of random copolymers, and the annealing (thickening) behavior of polymer crystals.

Thermodynamics and Crystallization of Random Copolymers

Thermodynamics and Crystallization of Random Copolymers

Crystallization of Random Copolymers.

A theory of crystallization is formulated for random copolymers which crystallize with the non-crystallizable co-units incorporated into the crystalline lattice as defects. The appropriate melting point equation and other associated thermodynamic properties are derived for this model as a function of crystal thickness and comonomer concentration. The formation of lamellar type morphology is assumed to be a kinetically determined phenomena and nucleation theory is utilized accordingly. The isothermal lamella thickness is predicted to increase in a definitive manner as the noncrystallizable comonomer concentration X increases, while the associated isothermal growth rate is predicted to decrease. The variation of lamella thickness with X when the copolymer is quenched or cooled at a uniform rate is also qualitatively predicted. Under these conditions lamella thickness decreases with increasing X, which is in accord with previous experimental observations on random copolymers of tetrafluoroethylene and hexafluoropropylene as well as other random copolymers. Theory also suggests how the surface free energy parameters σ e and σ can be determined from isothermal crystallization experiments for a series of random copolymers of varying composition.