Crystallization of random copolymers

Abstract

A theory of crystallization is formulated for random copolymers which crystallize with the noncrystallizable 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 lam ellar type morphology is assumed to be a kinetically determined phenomena and nucleation theory is utilized accordingly. The isothermal lamella thickne ss 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 de creases 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 fre e energy parameters (T e and (T can be d~termin ed from isothermal crystallization experiments for a series of random copolymers of varying composition.

Crystallization kinetics of poly(L-lactide-co-meso-lactide)

“…Parameter value (estimated standard error) A = 68.0 (7.3) B = 84.5 (wt %)-I (37) C = 76900 (18800) UY/R = 675 K (64) y = 267 K (22) Kg = 535000 K2 (54000) Figure 5 shows predicted versus measured rate constants for the samples in this study. The agreement over a wide range of rates is satisfactory and this model can be used to predict crystallization rates for a range of optical composition, talc levels, and temperatures.…”

Properties of potentially biodegradable copolyesters of (succinic acid-1,4-butanediol)/(dimethyl terephthalate-1,4-butanediol)

“…The ®rst, proposed by Flory, 6 assumes that the comonomeric units B are not included in crystallites but remain in the amorphous phase. According to the second model, developed by Eby,7,8 there is full compatibility between the monomers of both types, ie comonomer B together with A build up the crystalline lattice. Wegner 9 compared the two models and concluded that they merely represent two extreme cases.…”

The influence of chain defects on the crystallisation behaviour of isotactic polypropylene

“…We saw from growth rate measurements that the regio-defects have a more pronounced influence on the crystallization rate as compared to the stereo-defects. In order to obtain a better understanding of the influence of the amount and different types of defects on the growth rate we analysed our data with a theory originally developed by Lauritzen and Hoffman (LH-theory) [41,42], and later modified by Sanchez and Eby [22,23]. Although the LH-theory served as the basis for the derivation the theory, the final result will be independent of the exact molecular mechanisms (and thus the molecular background for the theory) involved for the particular case studied.…”

“…A discussion about the origin of the growth rate difference between the !-and "-phase as function of defect fraction is provided. Results obtained from the crystallization experiments are analyzed with the theory of Sanchez and Eby [22,23].…”