Temperature rising elution fractionation and fraction characterization of Trans-1, 4-poly(isoprene-co-butadiene)

In order to analyze the chain structure and sequence distribution of trans-1,4-poly(isoprene-co-butadiene) copolymers (TBIR) with different butadiene content, a preparative-temperature rising elution fractionation (P-TREF) technique was used to fractionate the TBIR into 10 to 12 fractions based on the elution temperature ranged from -40 degrees C to 70 degrees C. NMR, DSC and GPC were used to characterize the microstructure, butadiene incorporation, [BI], [II] and [BB] dyad sequence concentration, melting point, molecular weight and molecular weight distribution of the fractions. Two or multi-model GPC curves are observed for the lower temperature elution fractions and the molecular weight of the fractions shows an increased tendency with an increase in the elution temperature. The fractions obtained at -40 degrees C elution temperature are copolymers with short trans-1, 4-polyisoprene (TPI) blocks, high butadiene incorporation and lower melting temperature. The fractions obtained at 50 degrees C elution temperature are copolymers containing medium-length TPI blocks and short trans-1, 4-butadiene (TPB) blocks. The fractions obtained at the other elution temperatures are mainly copolymers with medium-length TPI blocks. The chain structure models of the TBIR fractions are proposed and possible formation mechanism is discussed.