Structure effects and related polymer properties in polybutadiene. I. Preparation and characterization

Abstract

SynopsisStereoregular polybutadienes, of both high trans and high cis contents, were isomerized to provide polymers of varying &-trans content. These isomeriates were used to study structural effects on physical properties. The isomerizations were carried out under photosensitized conditions in benzene solution at 25'C. The reaction was controlled to deliver polymers over the range &95% trans content. This range was selected to provide crystalline and semicrystalline polymers whose structures could be examined in terms of sequencing or blocking by established x-ray techniques. Isomer contents were measured accurately by infrared traces. Isomerizations reached an equilibrium of 77% trans regardless of whether the reaction started with high trans or high cis polybutadienes. Intrinsic viscosity was found to increase regularly with trans content in conformity with the larger size of the trans unit. 'lap/c versus c relations were observed to give a complicated form and this subject was deferred for further study. Crystallinity decreased regularly with reduced trans content m the equilibrium of 77% trans was approached. Continued isomerization a t the point of equilibrium produced a completely amorphous polymer. The melting temperatures of the crystalline polymers were studied in detail by x-ray camera and counting techniques.One form was stable up to 60°C. and invariant with cis-trans content in the range 80-95% trans. Below 80% trans the melting point of this form decreased with further reduction in trans content. The melting temperature of the other crystal form was dependent on trans content and decremed with decreased trans content until it coincided with the melting temperature of the other form. The distributions of trans and cis units and sequences of them were calculated through construction of matrices of transition probabilities. Copolymer theory was invoked to calculate pseudo reactivity ratios for the trans and cis forms. The melting temperatures of the two crystals were found to follow the predicted curves for random copolymers, although not simultaneously. This behavior is discussed. The crystallinity of the isomerizates of high trans content was found to be similar to block copolymers in spite of the fact that the method of their preparation would require that they be characterized as random. The importance of a crystal transition in this case is stressed along with the general effects due to the amount and type of the noncrystallisable unit.These polymers exhibited two crystal forms.

Morphological Consequences of Catalytic Hydrogenation of Polymers in the Bulk

“…Two endotherms, one at 42 0 C and one at 68 0 C, are present in the DSC plot for unreacted 1,4-PB, consistent with previous studies [9,10]. Upon deuteration, a substantial new endotherm appears due to the hydrogenated polybutadiene product which is similar to LDPE [ii].…”

Rheological Behavior of Unvulcanized Rubber

“…This increases the crystallization temperature T m . An experimental study showing the validity of the foregoing equation for high-trans-1,4 polybutadienes has been carried out by Mandelkern et al [171] and by Berger and Buckley [23], and similar effects have been described in eis-1,4-polybutadienes [19,210]. A more striking and important aspect is the increased rate of crystallization caused by strains or-probably better-stresses.…”

Quantitative description of the metathesis polymerization/depolymerization equilibrium in the 1,4-polybutadiene system, 2. Unusual behaviour at lower temperature

“…10). This behaviour is well known from the literature and can be explained through a phase transfer concerning the first peak and the melting of the material detected in the second peak 4) . The quantity of heat for both processes is the sum that is gained for the system by the crystallization of the polymer.…”