Dirong Gong

Regio- and stereo-selective polymerization of 1,3-butadiene catalyzed by phosphorus–nitrogen PN3-pincer cobalt(II) complexes

A new family of cobalt complexes (CoCl2-H, CoCl2-Me, CoCl2-iPr, CoBr2-H, CoBr2-Me, CoBr2-iPr, CoI2-H, CoI2-Me, and CoI2-iPr) supported by a PN3 ligand (6-(N,N-di-t-butylphosphino)-2-pyrazol-yl-aminopyridine) have been prepared and fully characterized by FT-IR, elemental analysis, and X-ray analysis. The X-ray analysis reveals a trigonal bipyramidal conformation in the solid state for all representative complexes, CoCl2-H, CoBr2-H, CoBr2-iPr and CoI2-Me. The cobalt center is chelated by the PN3 ligand through the pyridinyl nitrogen, the pyrazol nitrogen and the phosphorus donor, with a long Co-P bond distance indicating a labile character. On activation with AlEt2Cl, Al2Et3Cl3, MAO, [Ph3C]+[B(C6F5)4]-/AliBu3 or AliBu3, cis-1,4 selective butadiene polymerization was achieved with up to 98.6% selectivity. The polymerization results show that the cis-1,4 selectivity is influenced by the steric hindrance, increasing with the bulkiness of the substituent groups (CoX2-iPr > CoX2-Me > CoX2-H) at the 3,5-positions of the pyrazole moiety, together with a slight decrease in activity. The activity changes in the order CoCl2L ≈ CoBr2L > CoI2L (for the same ligand L) when MAO is used as the activator, while the high level of cis-1,4 selectivity is maintained. It is possible to switch the selectivity from cis-1,4 to syndiotactic-1,2 by adding PPh3.

Controlled polymerization of isoprene promoted by a type of hemilabile XPN3 (X = O, S) ligand supported cobalt(II) complexes: the role of a hemilabile donor on the level of control

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.

Polymerization of Isoprene Promoted by Aminophosphine(ory)-Fused Bipyridine Cobalt Complexes: Precise Control of Molecular Weight and cis-1,4-alt-3,4 Sequence

Ligands N-(dialkyl or arylphosphino)-(2,2-bipyridin)-6-amine (L1, aryl = Ph; L2, alkyl = tBu; L3, alkyl = adamantyl (Ad)) as well as the corresponding oxidized N-(2,2-bipyridin-6-yl)- P, P-dialkyl or aryl phosphinic amide (L4, aryl = Ph; L5, alkyl = tBu; L6, alkyl = Ad) congeners were designed and coordinated to cobalt dichloride. The structures of formed complexes were characterized by IR and elemental analyses, as well as characterizations of the X-ray diffractions for complexes Co4 and Co6, which revealed the cobalt center is expectedly pentacoordinated in a distorted trigonal bipyramidal configuration with a prolonged Co-O(═P) bond . In combination with MMAO, complex Co2 was highly active in cis-1,4- alt-3,4 enchained polymerization. The hemilabile nature of O═P is possible for the alternating η4- cis-1,4 and η2-3,4 coordination, and insertion at the metal-carbon bond ensued. In combination with AlEt2Cl, each of complexes Co4, Co5, and Co6 was capable of converting isoprene to polyisoprene in a control mode with observed polymerization rate constants ( kobs = 0.1531 L mol-1 min-1 (Co4), 0.1382 L mol-1 min-1 (Co5), and 0.0902 L mol-1 min-1 (Co6)). The activation energy of the polymerization by Co4 falls in the range of 27-31 kJ/mol by determining kobs values at 0, 30, and 50 °C. The 13C NMR analyses of the obtained polyisoprene revealed that complexes Co4, Co5, and Co6 have a cis-1,4 selectivity of 86.6-93.4% with a 3,4 selectivity of 6.6-13.4%. This catalyst system can also be applied to block copolymerization of isoprene and myrcene in a living cis-1,4 fashion; therefore, a new biosourced monomer-based elastomer has been achieved.

Zwitterion-functionalized polymer microspheres as a sorbent for solid phase extraction of trace levels of V(V), Cr(III), As(III), Sn(IV), Sb(III) and Hg(II) prior to their determination by ICP-MS

AbstractThis paper describes the preparation of zwitterion-functionalized polymer microspheres (ZPMs) and their application to simultaneous enrichment of V(V), Cr(III), As(III), Sn(IV), Sb(III) and Hg(II) from environmental water samples. The ZPMs were prepared by emulsion copolymerization of ethyl methacrylate, 2-diethylaminoethyl methacrylate and triethylene glycol dimethyl acrylate followed by modification with 1,3-propanesultone. The components were analyzed by elemental analyses as well as Fourier transform infrared spectroscopy, and the structures were characterized by scanning electron microscopy and transmission electron microscopy. The ZPMs were packed into a mini-column for on-line solid-phase extraction (SPE) of the above metal ions. Following extraction with 40xa0mM NH4NO3 and 0.5xa0M HNO3 solution, the ions were quantified by ICP-MS. Under the optimized conditions, the enrichment factors (from a 40 mL sample) are up to 60 for the ions V(V), As(III), Sb(III) and Hg(II), and 55 for Cr(III) and Sn(IV). The detection limits are 1.2, 3.4, 1.0, 3.7, 2.1 and 1.6xa0ngxa0L−1 for V(V), Cr(III), As(III), Sn(IV), Sb(III) and Hg(II), respectively, and the relative standard deviations (RSDs) are below 5.2%. The feasibility and accuracy of the method were validated by successfully analyzing six certified reference materials as well as lake, well and river waters.n Graphical abstractZwitterion-functionalized polymer microspheres (ZPMs) were prepared and packed into a mini-column for on-line solid-phase extraction (SPE) via pump 1. Then V(V), Cr(III), As(III), Sn(IV), Sb(III) and Hg(II) ions in environmental waters were eluted and submittedxa0to ICP-MS via pump 2.

Polyethylene-block-hyperbranched polyglycerol diblock copolymers: synthesis, thermal property and compatibilization

AbstractThe linear-b-hyperbranched copolymers (LHBCs) consisting of linear polyethylene (PE) block and hyperbranched polyglycerol (hbPG) segment were synthesized with a sequential method starting with V(III)-catalyzed coordination polymerization and followed by ring-opening multibranching polymerization (ROMBP). The hydroxyl groups in hbPG block are further modified to benzoyl groups to improve the solubility. Ultimately, the structures and thermal properties of LHBCs were clearly characterized by 1H/13C NMR, GPC, TGA and DSC. The SEM images show that the LHBCs are effective compatibilizers in LLDPE/PCL blends. This paper represents the first case of generation of LHBCs combining hbPG with nonpolar and crystalline polyethylene block instead of polar and/or noncrystalline linear blocks. As a result, the crystallinity of linear polyethylene can be combined with low viscosity and a large number of terminal functional groups of hbPG.n Graphical abstractThe polyethylene-b-hyperbranched polyglycerol copolymersxa0(PE-b-hbPG) were synthesized and characterized. The thermal and crystallization property of polyethylene can be combined with low viscosity and a large number of terminals of hbPG block. The SEM images showed that the compatibilization was determined by the hydrogen bonds between hbPG and PCL matrix, which was obviously different from the traditional compatibilizers.