Chlorinated Polyethylene. III. Relationships of Microstructure and Thermal Properties

Abstract

ABSTRACT:The thermal properties (viz., second-order transitions, melting points, dynamic and isothermal heat behaviour) of chlorinated polyethylene (CPE) samples are studied here. Thermomechanical analysis (TMA), differential thermal analysis (DTA), and thermogravimetric analysis (TGA) results are listed together to correlate the thermal properties and the microstructure of CPE samples, of various chlorine contents by weight, produced from thermal chlorinated or photochlorinated linear and branched polyethylene samples. The dehydrochlorination rate of a CPE sample is shown to be strongly dependent on its microtacticity up to a 56-61-% chlorine content by weight value· Beyond this 56-61-%Cb interval the microtacticity influence is screened by the steric hindrance introduced by the err (-CHz-C!:!Cl-CCb-or -CHCl-C!:!Cl-CCb-), an -CHCl-C!:!Cl-CHCl-or -CHz-C!:!Cl-CHCl-), and [3n (-CHCl-C!:!z-CCb-) structures. At the saturation level (73-% Clz), the higher a CPE ratio, nb CHCllnb CHz, is, the lower is its maximum dehydrochlorination rate. When its ratio, nb 2 CHCllnb CHz, is less than 4, a saturated (73%) CPE sample has a unique global dehydrochlorination activation energy (Ea); when this ratio stands between 4 and 6, there are two global dehydrochlorination E.. The structures which could be regarded as responsible for these different global Ea and the second-order transitions are specified.KEY WORDS Chlorinated Polyethylene I Thermomechanical Analysis I Differential Thermal Analysis I Thermogravimetric Analysis I Second-Order Transitions I Maximum Dehydrochlorination Rate I Very few studies have been published about the thermal properties of CPE. The first one, made by Oswald and Kubu 1 dealt with glass-transition temperatures (Tg)· Era and Lindberg 2 showed the effect of heat treatment on crystallinity. Abu I sa 3 studied the dechlorination mechanism and the effect of added antimony oxide on the rate of dehydrochlorination. Saglio, et at., 4 studied the degradation of saturated (73 %) CPE and showed that fibers of saturated CPE can be used as a carbon fiber precursor.relate their microstructure and thermal properties in this paper.In carbon backbone high polymers secondary transitions can be detected besides the main second-order transition, i.e., the glass-transition temperature (T g), and the main first-order transition, i.e. the solid-liquid-transition or the melting temperature. They are:(1) The secondary second-order transitions occuring, generally, at temperatures less than Tg. They are related to the motion of short segments of the polymer's backbone (viz., branchings, substituants, "crankshaft" or "kink" mechanisms11'12) related to motions in the amorphous or crystalline phase.The CPE samples used for the above studies were, generally, commercial ones supplied without the specific conditions of their preparation which are required 5 to correlate microstructure and properties. In addition, their microstructural characterizations have been made only with infrared analysis, which is not sufficient.Since we have...

Chlorinated Polyethylene. I. Infrared Study

“…A comparative differential thermal analysis of the films and the powder of the CPE samples 8 showed that the structure of the chlorinated products is not affected by these various treatments. The spectra of the films are solventband-free.…”

Chlorinated Polyethylene. II. Mechanisms of Chlorination

“…!Cl-CH2) triads would appear on the NMR spectra from the beginning of the reaction and not from the 20-25-% chlorine-content interval (Figures 2 and 3). In addition, the thermal CPE samples with chlorine-content value up to 33% still have melting points, 11 which indicates the presence of unchlorinated polyethylene sequences of relatively important lengths. If the chlorineradicals gave -CHCl-units instead of CC1 2 units, there would be 1 -CHCl-unit for 5 -CH2-units in the chain of a 33-% thermal CPE sample; such a product would not keep crystallinity and melting points could not be detected.…”