Applications of Infra-Red Methods in the Structural Examination of Synthetic Rubber

Abstract

The physical properties of a synthetic polymer are associated with variations in molecular structure which are dependent on the conditions of the polymerizing reaction and the monomers used. In some cases, structural differences of significance for physical properties cannot be detected by infra-red methods because the relative number of chemical linkages affected is too small. An important structural detail which can be followed by infra-red analysis is the relative amount of 1,2 and 1,4 polymerization occurring in polymerization reactions of butadiene. Absorption curves are reproduced to show the wide range in the relative amounts of these two structures. A description is given of an attempt to obtain a quantitative measure of this ratio by means of a calibration curve derived from known mixtures of pure octene 1 and octene 2. For polyisoprene, variations in the proportions of 1,4 and 1,2 or 3,4 structure also occur depending upon the type of polymerization. Comparison with Hevea rubber and Balata fails to disclose definite evidence of trans-isomerism in synthetic polyisoprene. Structural differences due to oxidation of polymers may be readily apparent in infra-red spectra, hydroxyl and carbonyl groups being especially prominent. The effectiveness of anti-oxidant in preventing structural changes caused by oxidation is shown in a series of absorption curves for samples of GR-S with and without anti-oxidant. When the samples were heat-treated in air, pronounced structural changes occurred for the sample without anti-oxidant, but no perceptible changes were evident for the sample with anti-oxidant. On the other hand, the anti-oxidant used (phenyl-β-naphthylamine) was ineffective for stabilizing the structure toward ultraviolet light.

Oxidation of GR-S and Other Elastomers

“…In marked contrast, however, the butadiene polymers exhibited a definite tendency to undergo further polymerization or cross linking. Synthetic emulsion polymers are known to differ from natural rubber in structural features (9,14,25). Since the net effect of oxidation on natural and emulsion isoprene polymers was chain scission, whereas cross linking predominated with butadiene polymers, variations in polymer structure do not seem to explain the difference observed in the aging of GR-S and natural rubber.…”

“…Application of the hydroperoxide theory of oxidation to syn- thetic elastomers is complicated by the fact that polymerization of dienes usually occurs by both 1,2 and 1,4 addition to the conjugate system. In the case of isoprene 3,4 addition also occurs (9). There is evidence that the C-H bond energy decreases in the order primary > secondary > tertiary.…”

Analysis of Natural and Synthetic Rubber by Infrared Spectroscopy

“…Analysis of Standard Natural-GR-S Blends Natural GR-S Blend F-620 (100% GR-S) 1 (90% GR-S) (10% natural) 2 (80% GR-S) (20% natural) 3 (70% GR-S) (30% natural) i (60% GR-S) (40% natural) o (50% GR-S) (50% natural) 6 (40% GR-S) (60% natural) 7/ (30% GR-S) (70% natural) Experimental Results.…”

Butadiene Polymers and Polyisoprene - Prepared By Alfin and Emulsion Processes

“…Unstretched A considerable increase in the absorption intensity of the 880 cm.-1 band is shown in the Alfin isoprene polymer as compared to the emulsion polymer. Because this band is thought to arise from structures of the type R,R2C=CH2, it is believed that an appreciable amount of 3,4-addition is included in the structure (6). This seems to be consistent with the increased tendency of the Alfin butadiene polymers and copolymers to polymerize by 1,2-addition.…”