Polymer chain structural factors, like chain microstructure, comonomer content in copolymer, dyad sequence distribution, molecular weight (M-w) 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 TiCI4/MgC12-Al (i-Bu)(3) catalyst system were studied by C-13-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 similar to 76 wt%), which cannot be crystallized from the dilute solutions at -20 degrees 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)similar to 6. The G fraction of TBIR-40 was random copolymer with the melting temperature (Tm) as low as -3.4 degrees 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 (n(IP) = 6 similar to 24) and the above two fractions show decreased Tm (29 similar to 38 degrees 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 x 10(5) and M-W/M-n 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. (C) 2016 Elsevier Ltd. All rights reserved.