Synthesis and evaluation of poly(isoprene-co-acrylonitrile) as synthetic rubber with enhanced oil resistance

Increasing demand for durable rubber and rapid advancement in the automotive sector has made oil-resistant rubber an increasingly important material. Among them, nitrile rubber (NBR) is the most iconic due to its extraordinary oil resistance contributed by the polar nitrile pendant groups. Synthesis of NBR, however, is highly hazardous due to the explosive nature of the gaseous monomer butadiene. In this work, poly(isoprene-co-acrylonitrile) (NIR) was synthesized using free radical emulsion polymerization, with liquid monomer isoprene as the diene in the rubber formulation. The spectroscopic analysis confirmed the formation of NIR and indicated that the polymerized isoprene in the rubber is predominantly of 1,4-microstructure. A series of rubbers with different contents of acrylonitrile were produced and the mechanical, thermal, as well as oil resistant property of the resultant rubber films were evaluated. Vulcanized NIR films displayed glass transition temperatures from –9.4 to 20.2 °C, suggesting that the polymers are rubbery at ambient and higher temperatures. The NIR rubber films exhibited excellent oil resistance with less than 2% swelling in mineral oil, good thermal stability with onset degradation temperature in the range of 361.3 to 369.9 °C, and adequate mechanical strength from 1.61 to 8.23 MPa. The synthesized NIR rubber has the potential to serve as an alternative to NBR which had been traditionally used for oil resistance applications.