Determination of Polymer Composition of Rubber Vulcanizates

Abstract

Abstract Various methods exist for the quantitative determination of the polymer composition in vulcanized stocks. These methods consist of dissolving the vulcanizates in boiling o-dichlorobenzene, removal of the carbon black by filtration, and then infrared determination of the polymer. Pyrolysis of the stock followed by infrared analysis of the products has also been used. This technique had the disadvantages of requiring an analysis of products other than the original polymer or polymers. The infrared calibration based on polymers would no longer be valid. There may also be some uncertainty about changes in the relationship between the original microstructure and the pyrolysis products. Other infrared studies have been made but no quantitative measurements were reported. Recently an NMR method was published for vulcanizate analysis. The method consisted of dissolving the vulcanizate in hexachlorobutadiene, recording the NMR spectrum of the solution, and determining the total amount of butadiene, styrene, and natural rubber from the spectrum. Good results were obtained on a variety of vulcanizates. The one disadvantage of the method was that only a limited amount of microstructure data could be obtained. This was due to the lack of resolution of the 60-megacycle NMR. We have now developed a technique which allows enough of the rubber to dissolve in carbon disulfide for infrared analysis. This solution is free of carbon black. Infrared analysis provides microstructure data on the butadiene and/or isoprene portions as well as the total styrene content.