Isothermal crystallization fractionation and fraction characterization of trans-1,4-poly(isoprene-co-butadiene)

Publication date: 27 January 2017
Source:Polymer, Volume 109
Author(s): Qingtao Niu, Chen Zou, Xiangyu Liu, Riguo Wang, Aihua He
Polymer chain structural factors, like chain microstructure, comonomer content in copolymer, dyad sequence distribution, molecular weight (MW) and molecular weight distribution (MWD), etc. have a great influence on the properties and applications of polymer materials. In this paper, chain structural factors and thermal behaviors of novel trans-1,4-poly (isoprene-co-butadiene) copolymers (TBIR-15, TBIR-20, TBIR-40) with various comonomer contents synthesized by TiCl4/MgCl2-Al (i-Bu)3 catalyst system were studied by ¹³C-NMR, GPC, DSC and WAXD. Eight fractions for each TBIR sample were obtained through isothermal crystallization fractionation of TBIR in dilute solution. It is proved that all fractions in the TBIR samples were high trans-1,4-configuration copolymers (>89 mol%). The TBIR copolymers were mainly composed by G fractions (44∼76 wt%), which cannot be crystallized from the dilute solutions at −20 °C. The G fractions of the TBIR-15 and TBIR-20 were multi-block copolymers composed by short trans-1,4-polyisoprene (TPI) blocks with the number-average sequence length of isoprene units (nIp)∼6. The G fraction of TBIR-40 was random copolymer with the melting temperature (Tm) as low as −3.4 °C and the crystallinity (Xc) as low as 4.4%. Fractions D and E in TBIR-15 and TBIR-20 were multi-block copolymers with long TPI blocks (nIp = 6∼24) and the above two fractions show decreased Tm (29∼38 °C) from imperfect TPI crystals. A special fraction A in TBIR-40 was random copolymer containing a few TPI and trans-1,4-polybutadiene (TPB) blocks, and both TPI and TPB blocks had the ability to crystallize. The Mw for each fraction was in the range of 2–6 × 10⁵ and Mw/Mn was in the range of 2–6. Based on the analysis, the possible chain sequence distribution model for each fraction was proposed. It was expected that this research would provide a further understanding about the TBIR copolymer chain structures and inspire the copolymer synthesis with ideal structure and composition as high performance rubber material.

Graphical abstract

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