X‐ray studies of low‐temperature polybutadiene and butadiene‐styrene copolymers

Abstract

The fine structures of emulsion polybutadiene prepared at temperatures ranging from 55°C. to −20°C. and of various butadiene‐styrene copolymers prepared at −20°C. have been studied by x‐ray methods. The ability of emulsion‐polymerized butadiene to crystallize was found to depend to a large extent on the temperature of polymerization. Butadiene polymerized at 30°C. and above showed no evidences of crystallization when cooled unstretched to −70°C. as observed by x‐ray diffraction methods; however, butadiene polymerized at 20°C. and below showed crystallization effects when cooled unstretched to −70°C. These crystallization effects became more pronounced for samples polymerized at lower temperatures. Layer‐line diffraction patterns of butadiene polymerized at 30°C. and below were obtained by stretching the polymer at about 0°C. From these patterns the geometrical repeat distance along the polymer chains was found to be 5.1 ± 0.1 Å. This corresponds to a fully extended butadiene unit in the trans configuration. An anomaly was observed in the diffraction patterns of crystallizable polybutadiene stretched at 0°C. Some of the layer‐line spots varied in position with per cent elongation of the sample. This suggests that the molecules in crystallites of the polymer are inclined to the stretch axis at low elongations and that they become more nearly parallel to the stretch axis at higher elongations. A small addition of styrene as comonomer at −20°C. polymerization temperature did not prevent crystallization and preferred orientation effects in the polymer, since these effects could still be found in a 90/10 charge copolymer. Larger amounts of styrene did prevent crystallinity and preferred orientation as shown by the amorphous nature of an 80/20 charge copolymer. The ability of a compounded vulcanizate of a given polymer to crystallize is less than that of the purified polymer under the same conditions. This may be due to the combined effects of milling, vulcanization, and the presence of carbon black particles in the polymer. A description of the apparatus and techniques used for cooling and stretching these polymers is given.

Evaluation of Diene-Type Elastomers for Oil and Solvent Resistance and Low Temperature Flexibility

“…An index of zero represents the best processability and a value of 20 the poorest (10). polybutadiene as the polymerization temperature was lowered is consistent with the tendency for this type of polymer to crystallize under stress (4) as the polymerization temperature is lowered.…”

Infrared Studies of 1,2- and trans 1,4-Structure of Polybutadiene and Butadiene--Styrene Copolymers Polymerized at Various Temperatures

“…This result has been demonstrated by the previously mentioned X-ray results. 5 Effect of Combined Styrene.-Figure 4 also shows that the per cent. 1,2-addition in butadiene 71-styrene 29 copolymers decreases as the temperature of polymerization is lowered.…”

“…Preparations of 2-vinylbenzimidazole by other methods invariably led to polymers of this substance indicating its great readiness to polymerize. A group of substituted 2-ethylbenzimidazoles (5)…”

Effects of Polymerization Temperature on Structure

“…The major portion of the polymer is undoubtedly crystalline and most of the double bonds are therefore in the trans configuration. According to Beu et al (4) purified polymers contain 14% vinyl side groups resulting from 1,2 addition which are presumably distributed at random along the chain. These groups are probably not included in the crystalline regions, for they would prevent periodicity in the structure.…”