Cobalt dichloride complexes (Co1–Co9) carrying a novel type of hemilabile donor PN3 (L1–L3) or XPN3 (L4–L6, X = O; L7–L9, X = S) are reported as precursors for controlled polymerization of isoprene. The nature of the hemilabile donor (P, O and S) determines the coordination chemistry of the complexes. X-ray analysis reveals that the P-ligated complex Co3 has two nuclear centres, with one being bis-chelated by L3 and the other with four chlorides. The complex Co4 is formed through N,N,O(P) tridentate coordination, and the S donor for complex Co7, however, lies out of the coordination sphere. Activated by AlEt2Cl, all complexes are highly active with nearly full monomer conversion within 2 h and have a controlled cis-1,4 selectivity at 77.5–99.0% for isoprene polymerization. The P-ligated complexes (Co1–Co3) have higher cis-1,4 selectivities up to 99.0%, albeit a typical molecular weight controlled characteristic is not found. The generated polymers for Co4–Co9 all exhibit well-controlled molecular weights up to 29.1 × 104 and narrow molecular weight distributions (PDI < 1.25). The kinetic studies reveal that the catalyst systems follow a typical living mechanism. Correlating the hemilabile donor with the catalytic performances shows that the presence of the PO (Co4–Co6) or PS (Co7–Co9) moiety in the auxiliary ligand is essential for the living nature; by trapping the Al species, the moiety –HN–PX (X = O, S) makes propagating chain transfer to Al impossible, which was responsible for irreversible reaction in most dienes polymerization. The possible reversible coordination of the allylic end of the propagating chain to Al is proposed for the dual cis-1,4 and 3,4 selectivities for Co4–Co9. This study represents the first example of cobalt catalyzed molecular weight and microstructure controlled polymerization of isoprene ever known.

Three pyridinyl based compounds, diphenylpyridin-2-yl phosphate (DPPyP), phenyldipyridin-2-yl phosphate (PDPyP), and tripyridin-2-yl phosphate (TPyP), were designed, synthesized, and applied in an iron catalyst as donors for 1,2-stereopolymerization of 1,3-butadiene in hexane. In combination with AliBu3, the DPPyP assisted iron catalyst is capable of 1,2-syndiotactic polymerization (1,2-selectivity, syndiotacticity) of 1,3-butadiene with high activity reaching 258 480 kg(polymer)/mol(Fe)·h at a butadiene/Fe feeding ratio of 8000 at 50 °C. The 1,2-regioselectivity, activity, and the morphology of resultant polymers can be controlled by the donor structures. The thermal stability of the catalysts were significant because a remarkably enhanced activity was observed while the high 1,2-stereoselectivity was unaltered in the range 50–80 °C. This work enabled us to have access to a highly active, 1,2-syndiotactic and thermally robust catalyst with ease of catalyst preparation, which could match the availability in industrial application for 1,2-syndiotactic polybutadiene.

•The catalyst has high 1,2-syndiotactic selectivity in 1,3-butadiene polymerization.•The catalyst shows remarkable thermal stability in the range of 50–100 °C.•The catalyst has potential application in industry production of 1,2-polybutadiene.A novel class of organic phosphates were synthesized and applied in iron catalyst as additive for 1,2-syndiotactic polymerization of 1,3-butadiene in combination with aluminum alkyls (Ali−Bu3 or AlEt3) in hexane at industrial favorable 50–100 °C. Remarkable enhanced polymer productivity (up to 486 kg (polymer)/mol(Fe) h) and excellent 1,2-syndiotactic regularity have been achieved at 50–100 °C in all examing cases. All the polymers obtained under various polymerization conditions possess prevailingly 1,2 inserted homo-sequences up to 94.7% 1,2-selectivity in syndiotactic arrangements (up to 94.4%, denoted by rrrr) with melting point ranging from 170 to 182 °C. The current in-situ generated catalyst systems feature high productivity, selectivity, robustness (e.g. high thermal stability, good tolerance to poisons and environmentally friendly hexane as solution polymerization medium) and single-site behaviour. These all extend the practical usefulness of these versatile phosphates assisted catalyst, and they are promising candidates to act as ancillary additive for industrial applicable 1,2-syndiotactic polymerization of 1,3-butadiene.

•The novel PN3 and the CoCl2PN3 are synthesized and characterized.•The CoCl2PN3 is half-oxidized to CoCl2OPN3 in presence of H2O2.•X-ray finds CoCl2PN3 and CoCl2OPN3 are co-crystallized in one unit.•The complexes are active in cis-1,4 selective butadiene polymerization.Incomplete oxidation of (N-di-tert-butylphosphino)-6-(2-methyl-2′H-benzoimidazole)-2-aminepyridine dichlorocobalt (PN3CoCl2) in DMF results in a unique co-crystal I formed with three parts including DMF, unit A and unit B complex with Co1 and Co2, respectively (PN3 ligand in unit A: (N-di-tert-butylphosphino)-6-(2′-methyl-2′H-benzoimidazole)-2-aminepyridine, and OPN3 ligand in unit B: (N-di-tert-butylphosphinoxide)-6-(2′-methyl-2′H-benzoimidazole)-2-aminepyridine), with 1:1:1 molar ratio. Co1 and Co2 complexes both display a five-coordinated distorted-square-pyramidal geometry around the metal center. The Co1 center is coordinated with PN3 ligand via two N atoms from pyridine, benzoimidazole moiety as well as one P atom, and the Co2 center is coordinated with the oxidized ligand OPN3 via two N atoms from pyridine, benzoimidazole moiety as well as one O atom from DMF molecule, while the oxidized phosphine moiety (OP) being excluded from the coordination sphere. Activated with AlEt2Cl, the co-crystallized complexes I are able to actively convert butadiene to polybutadiene, affording cis-1,4 polybutadiene with cis-1,4 unit up to 95.5–97.8% and number average molecular weight of cal. 105 g/mol. The high cis-1,4 selectivity and monomodal GPC curve of resultant polymer imply that the identical active species generated from two distinctive cobalt centers.Mixed-ligands ligated cobalt complexes were prepared. The complexes are high active in butadiene polymerization. The obtained polymer has cis-1,4 unit up to 95.5–97.8%.

•Ethylene-co-aryl ether polymers have been successfully synthesized via ADMET.•Crystalline polymers exhibit a sequence of melting/crystallization phenomenon.•Reducing the density of aryl ether units could alter the crystallization behavior.•Incorporation of aryl ether units has improved the thermal stability of polymers.A new family of polyolefins containing various aryl ether units have been designed and synthesized, and their thermal properties were studied. We prepared six acyclic diene monomers di(undec-10-enyloxy)aryl ether by a two-step approach and the corresponding homopolymers and copolymers with 1,9-decadiene by ADMET. Subsequent hydrogenation gave the corresponding ethylene-co-aryl ether polymers. The structures of these polymers were confirmed by 1H NMR, 13C NMR and FT-IR. Additionally, crystallization behaviors and thermal properties were investigated by differential scanning calorimetry (DSC), X-ray diffraction and thermal gravimetric analysis (TGA). The results show that incorporation of these aryl ether units has improved the thermal stability of polymers. And these polymers show a tendency of semicrystallinity to amorphous state with the insertion of more rigid phenyl rings in functional sites of polymers' main chain. Interestingly, DSC analysis reveals that a sequence of melting/crystallization phenomenon occurs in the crystalline saturated homopolymers.

•New Cr(III) complexes bearing bis(imino)pyridyl are synthesized and well characterized.•The complexes show good trans-1,4 selectivity with acceptable activity in butadiene polymerization.•The ortho-positioned substitute of ligand exerts significant effects on the selectivity and activity.•Conjugated diene mechanism study infer high trans-1,4 selectivity is ascribed to trans-η2 coordination of butadiene to metal center.Tridentate chromium complexes (Cr1–Cr7) incorporated with symmetrical pincer ligand bis(arylimino)pyridine and bis(pyrzaolyl)pyridine have been synthesized and characterized by elemental analyis, FT-IR as well as ESI-MS. X-ray diffraction reveals solids-state structures of Cr2, Cr4 and Cr6 all adopt pseudo-octahedral coordination environment with respect to metal center. All complexes have been tested in stereoregulated polymerization of butadiene under various polymerization conditions. The trans-1,4 and cis-1,4 enchainment of resultant polymer are found to be dependent on the structure of ligand and amount of activator used. Under the optimized condition, free ortho-substitutes Cr catalysts Cr1, Cr3, Cr4 and Cr6 are capable of initiating high trans-1,4 selectivity (trans-1,4: 89.2%–92.0%) with good polymer yields (71.5%–78.0%), while counterparts with ortho-positioned alkyl groups Cr2, Cr5 and Cr7 display mixed selectivities with moderate polymer yields. The sterical effect of ligand and amount of MMAO on the catalytic performance, in particular, the stereoselectivity and polymer yield, has been also elucidated by conjugated diene polymerization mechanism.New CrCl3 complexes ligated with structural modified 2,6-bis[1-(phenylimino)ethyl]pyridine and 2,6-bis(pyrazol)pyridine have been prepared, well characterized and examined in butadiene polymerization. Complexes bearing non-substituent at ortho-positions displayed high activity (99%) and mainly trans-1,4 selectivity (92.0%).