A novel supported salenCrIIICl catalyst for alternating copolymerization of cyclohexene oxide with carbon dioxide

Polyaniline supported Salen complex as highly active and recyclable catalysts for copolymerization of CO2 and epoxides

Air-stable di-nuclear yttrium complexes as versatile catalysts for lactide polymerization and copolymerization of epoxides with carbon dioxide or phthalic anhydride

The alternating copolymerization of carbon dioxide (CO2) and cyclohexene oxide (CHO) with an aluminum Schiff base complex in conjunction with an appropriate additive as a novel initiator is demonstrated. A typical example is the copolymerization of CO2 and CHO with the (Salophen)AlMe (1a)–tetraethylammonium acetate (Et4NOAc) system. When a mixture of the 1a–Et4NOAc system and CHO was pressurized by CO2 (50 atm) at 80 °C in CH2Cl2, the copolymerization of CO2 and CHO took place smoothly and produced a high polymer yield in 24 h. From the IR and NMR spectra, the product was characterized to be a copolymer of CO2 and CHO with an almost perfect alternating structure. The matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis indicated that an unfavorable reaction between Et4NOAc and CH2Cl2 and a possible chain‐transfer reaction with concomitant water occurred, and this resulted in the bimodal distribution of the obtained copolymer. With carefully predried reagents and apparatus, the alternating copolymerization in toluene gave a copolymer with a unimodal and narrower molecular weight distribution. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4172–4186, 2005

Introduction LLDPE is the common name for copolymers of ethylene with α-olefin comonomer. The comonomers most frequently used commercially are butene, hexene, and octene. Commercial grade LLDPE resins with 4-methyl-1-pentene (4-MP-1) as comonomer is also available. LLDPE prepared by the conventional Ziegler-Natta (Z-N) catalyst system always exhibit high heterogeneity in the intermolecular distribution of comonomer units along the polymer chains. The branches are preferentially located in the lower molecular weight chains; thus the bulk of LLDPE behaves as if it were a blend of high molecular weight, linear molecules and low molecular weight, branched molecules. LLDPE differs from LDPE principally through a lack of long-chain branching (LCB) and a narrower molecular weight distribution (MWD). New types of LLDPEs based on the metallocene catalyst technology have been introduced recently in the market place. Such LLDPEs are characterized by narrower molecular weight and homogeneous short-chain branching distribution. Some of the metallocene catalyst-based octene-1 LLDPE copolymers made by the Dow Chemical Company are known to have LCB. For the properties of metallocene LLDPE see the entry Polyethylene, metallocene linear low density, in this handbook. LLDPE is commercially available in wide variety of melt indexes (MI) and density ranges. The properties of LLDPE are functions of molecular weight (MW), MWD, density, type, and amount of comonomer. The comonomers are also referred to as short-chain branches (SCB). Consequently, physical and mechanical properties also vary accordingly. Mechanical properties such as tensile, tear, and impact are strongly dependent on the chemical nature of the comonomer type. Therefore, it is difficult to list all properties separately. The values of the properties shown in the following table are given in ranges because of their dependence on molecular structure and type of comonomer and are intended to represent the best published examples of the most commonly used commercial grades of LLDPE resins. The physical properties of extruded materials may vary substantially from those of the compression molded materials. For illustration purposes, a few of the physical properties that depend on the chemical nature of the comonomer are presented in Tables 3, 6, 7, and 8.

Liquid fuel synthesis via CO2 hydrogenation by coupling homogeneous and heterogeneous catalysis

peer reviewed

Sulfonated polyisobutylene (PIB) telechelic ionomers with narrow molecular weight distribution (MWD) have been recently developed, providing additional control over the structure and properties of these novel polymers. A small angle X-ray scattering (SAXS) peak often associated with the aggregation of the ionic species in the bulk, and a secondary peak, were recently observed in the narrow MWD sulfonated PIB telechelics for the first time. SAXS evidence, given earlier as part I of this two-part series, suggests that compression-molded sulfonated PIB telechelic ionomers with a narrow MWD (M¯w/M¯n ≈ 1.15) may have a local secondary structure of ionic lamellae or cylinders, and no such structure is found in similar broad MWD (M¯w/M¯n ≈ 1.8) telechelics. It is shown that narrowing the MWD, which acts to promote locally continuous structure in the tri-arms, alters the character of the network, in that the modulus of the tri-arm telechelic systems increases and the elongation at break is lowered by narrowing the MWD or decreasing the M¯n. The tri-arms of the highest M¯n (49.5 kg/mol) exhibit strain hardening and the lowest modulus, highest-breaking stress, and highest elongation at break in the ionomers studied. The presence of local ionic structure is also indicated by stress relaxation experiments in which the long-term or near-equilibrium stress is seen to decrease when the MWD is broadened or M¯n increases. It is believed that the difunctional materials do not form extensive ionic networks at all, but principally chain-extend, as has also been found before. It is observed that the properties of a solution “blend” of narrow MWD ionomers that has the same counterion, M¯n, and polydispersity as a broad MWD system exhibits lower elongation to break, lower breaking stress, and modulus of narrow MWD systems relative to the broader MWD material. Dynamic mechanical data indicate that narrowing the MWD or decreasing M¯n increases the flow transition temperature and rubbery plateau modulus. The “blend” exhibits dynamic mechanical properties between the narrow and broad, having a higher flow transition temperature than the broad MWD, but lower than the narrow MWD, and a rubbery plateau modulus between the other two. © 1997 John Wiley & Sons, Inc.

Hydroxyl functional star oligomers prepared by ring-opening polycondensation have a narrow molecular weight and composition distribution. Such oligomers give a solids/viscosity advantage over linear structures at the same molecular weight and can be used in low VOC two component polyurethane coatings. The solids/viscosity advantage is a combination of the highly branched structure and the narrow molecular weight distribution. Acrylic polyols formulated at the same molecular weight/polarity/average functionality and hydroxyl value give poorer drying properties. This difference can be explained by the fact that the free radical polymerisation technique leads to polymer compositions having a broad molecular weight and functionality distribution and high fractions of polymer with a low functionality. The potlife of acrylic polyols based formulations is adversely affected by the higher fractions of high molecular weight material and with a high average functionality. In low VOC polyurethane formulations star oligomers need to be formulated within a narrow range of compositions (TG, polarity), functionality and molecular weight to get an optimum balance of drying properties and potlife.

Two series of hydrophobe-modified, ethoxylated urethane (HEUR) polymers were synthesized. The first series was prepared by the step-growth (S-G) polymerization of poly(oxyethylene) (POE) of Mn = 6000, with a slight excess of different aliphatic diisocyanates in a 4.2 to 3.2 mole ratio to produce a S-G polymer with Mn of ∼20 000. The terminal isocyanate groups were reacted with alkylamines of different hydrocarbon chain lengths. The second series was produced by reacting POE of Mn = 20 000 with a large excess of the diisocyanate to produce POE with terminal isocyanate functionality, followed by reaction with alkylamines. The molecular weight distribution of the second series was narrow compared to the first series, prepared by S-G polymerization. The hydrocarbon chain length of the alkylamine, the coupling diisocyanate, and the molecular weight distributions were systematically varied by the proper choice of synthetic conditions. The changes in structures were correlated with the rheological behavior of aqueous HEUR solutions. Their aqueous solution behaviors also were evaluated in the presence of anionic and nonionic surfactants. HEUR thickeners prepared with bis(4-isocyanatocyclohexyl)methane (H12MDI) were more effective in building viscosity than HEURs prepared from hexamethylene diisocyanate (HDI). In general, HEURs, with a narrow molecular weight distribution, gave higher aqueous solution viscosities than their corresponding broad molecular weight distribution counterparts at equal concentrations. Approximately twice the concentration of the broad molecular weight distribution HEUR with terminal C12H25−H12MDI hydrophobes was required to achieve comparable viscosity with the narrow molecular weight distribution HEUR. Despite the differences in concentration, the storage and loss moduli responses were similar. Solutions with small terminal alkyl groups were predominantly viscous in their viscoelastic response. The size of the “effective” terminal alkyl groups dominated aqueous solution rheological responses of both narrow and broad molecular weight distribution HEURs.

Chlorides of group 4 metals containing the bis(imino)phenoxide ligand scaffold were synthesized from a direct reaction between the respective ligand and metal chlorides MCl 4 (M=Ti, Zr and Hf). These complexes were thoroughly characterized using various spectroscopic methods and single crystal X‐ray diffraction studies. They are potent catalysts for the polymerization of rac ‐lactide ( rac ‐LA), L ‐lactide ( L– LA), ϵ ‐caprolactone ( ϵ ‐CL), epoxides such as, rac ‐cyclohexene oxide ( rac ‐CHO), rac ‐propylene oxide ( rac ‐PO), rac ‐styrene oxide ( rac ‐SO) and ethylene, resulting in polymers with high number average molecular weights ( M n ) and narrow molecular weight distributions (MWDs). The kinetic and mechanistic studies associated with the polymerization of lactide, ϵ ‐CL and CHO has been investigated in details.

The factors that determine the Wurtz‐type reductive coupling of dichloroorganosilanes by alkali metals are reviewed. A strong recommendation is advanced for carrying out all such polysilane syntheses in tetrahydrofuran at ambient temperature, conditions under which the reaction gives far higher yields and generally much narrower product molecular weight distributions. The higher yields are attributed to the ability of the solvent to sequester the sodium ion and thereby stabilize the anionic chain carriers. The bimodal molecular weight distributions of the product polymers, which are ubiquitous when such reactions are carried out in high‐boiling‐point aromatic solvents under reflux, as is common practice, are attributed to it being a defect‐diffusion‐controlled polymerization at the alkali metal surface. The narrower molecular weight distributions that result from syntheses in tetrahydrofuran are attributed to the suppression of defect diffusion rates at lower temperatures. Copyright © 2005 Society of Chemical Industry

Polypyrrole(PPy) supported Cr(III)(salen)Cl catalyst was prepared for alternating copolymerization of cyclohexene oxide and carbon dioxide. The supported catalyst and the copolymerization products were characterized by FTIR, XRD, XPS, ICP-MS, SEM, TEM, NMR, gel permeation chromatography, thermogravimetric analysis and differential scanning calorimetry. After the study, we concluded that the homogeneous Cr(III)(salen)Cl is successfully supported on the PPy, and its catalytic performance is much better than the homogeneous one. Moreover, the copolymerization product catalyzed by PPy-Cr(III)(salen)Cl exhibits higher molecular weight, narrower molecular weight distribution, superior thermal stability and selectivity.

Copolymerization of a series of cyclic acid anhydrides with several epoxides using (salen)CrCl/onium salt catalysts has afforded polyesters with high molecular weights and narrow molecular weight distributions. The (salen)CrCl catalyst in the presence of the onium salts with formula PPNX (X = Cl–, N3–) for the copolymerization of the anhydrides, maleic (MA), succinic (SA), phthalic (PA), cyclohexene (CHE), and cyclohexane (CHA) with the epoxides, cyclohexene oxide (CHO), propylene oxide (PO), and styrene oxide (SO) resulted in completely alternating enchainment of monomers to provide pure polyesters. Temperature dependent studies of the ring-opening copolymerization of phthalic anhydride and cyclohexene oxide monomers in toluene solution have yielded activation parameters of ΔH‡ = 67.5 kJ mol–1 and ΔS‡ = −95.3 J mol–1, where the rate limiting step was ring-opening of the epoxide by the enchained anhydride. For the cyclic acid anhydride (CHA), the relative order of reactivity with epoxides decreased PO > CHO ≥ SO, and for the epoxide (CHO) the relative rate of copolymerization was CHA > PA > CHE. The (salen)CrCl/PPNN3 catalyst system was also shown to effectively terpolymerize CHO/phthalic anhydride/CO2 to afford diblock copolymers, thereby producing in a one pot synthesis poly(ester-co-carbonate). Tg values of the synthesized polyesters displayed a temperature range over 130 °C, from +95 °C to −39 °C.

Study on the preparation and performance comparison of side-chain hydroxyl-terminated polybutadiene derivatives with narrowly molecular weight distribution used for polyurethane

The first synthesis of well-defined narrow molecular weight (MW) distribution macrocyclic poly(2-vinylnaphthalene) (P2VN) containing a single 1,4-benzylidene or 9,10-anthracenylidene unit is reported. The synthesis involves the potassium naphthalide (K-Naph) or potassium 1,1,4,4,7,7,10,10-octamethyl-1,2,3,4,7,8,9,10-octahydronaphthacene (K-OMOHN) initiated polymerization of 2-vinylnaphthalene (2VN) in THF at -78 °C, followed by end-to-end coupling of the resulting P2VN dianions under high dilution conditions (10 -6 -10 -4 M). Narrow MW distribution (1.11-1.26) P2VN macrocycles with MW's between 740 and 13 200 have hydrodynamic volumes that are between 5% and 29% smaller than those of the matching linear chains. The glass transition temperatures of macrocyclic P2VN do not deviate from the limiting value (151 °C) ofthe high MW P2VN, decreasing only below a DP n of about 20. Compared to the linear analogues, macrocyclic P2VN shows higher nonoxidative thermal decomposition stability.