Synthesis and ethylene trimerisation capability of new chromium(II) and chromium(III) heteroscorpionate complexes.

Reaction of (Me(2)pz)(2)CHSiMe(2)N(H)R (R = (i)Pr or Ph) or (Me(2)pz)(2)CHSiMe(2)NMe(2) with CrCl(3)(THF)(3) or CrCl(2)(THF)(2) gave Cr{(Me(2)pz)(2)CHSiMe(2)NR(1)R(2)}Cl(3) (R(1) = H, R(2) = (i)Pr (10) or Ph (11); R(1) = R(2) = Me (15)) or Cr{(Me(2)pz)(2)CHSiMe(2)NR(1)R(2)}Cl(2)(THF) (R(1) = H, R(2) = (i)Pr (12) or Ph (13); R(1) = R(2) = Me (16)), respectively. Compounds 10 and 11 were crystallographically characterized and the magnetic behaviour of all the new compounds was evaluated using SQUID magnetometry. Reaction of CrCl(3)(THF)(3) with Li{C(Me(2)pz)(3)}(THF) gave the zwitterionic complex Cr{C(Me(2)pz)(3)}Cl(2)(THF) (17) containing an apical carbanion. Reaction of the analogous phenol-based ligand (Me(2)pz)(2)CHArOH (ArO = 2-O-3,5-C(6)H(2)(t)Bu(2)) with CrCl(3)(THF)(3) gave Cr{(Me(2)pz)(2)CHArOH}Cl(3) (19) whereas the corresponding reaction with CrCl(2)(THF)(2) unexpectedly gave the Cr(III) phenolate derivative Cr{(Me(2)pz)(2)CHArO}Cl(2)(THF) (20) which could also be prepared from CrCl(3)(THF)(3) and the sodiated ligand [Na{(Me(2)pz)(2)CHArO}(THF)](2). Reaction of the corresponding ether (Me(2)pz)(2)CHArOMe with CrCl(3)(THF)(3) or CrCl(2)(THF)(2) gave Cr{(Me(2)pz)(2)CHArOMe}Cl(3) (23) and Cr{(Me(2)pz)(2)CHArOMe}Cl(2)(THF) (24), respectively. The catalytic performance in ethylene oligomerisation/polymerisation of all of the new Cr(II) and Cr(III) complexes was evaluated. Most of the complexes showed high activity, but produced a Schultz-Flory distribution of alpha-olefins. Compound 23 had an exceptionally low alpha-value of 0.37 and showed a preference for 1-hexene and 1-octene formation. While replacing a secondary amine (10-13) for a tertiary amine (15-16) resulted in loss of catalytic activity, replacing a phenol (19) for an anisole (23) group afforded a more selective and more active catalyst. Changing from MAO to DIBAL-O as cocatalyst induced a switch in selectivity to ethylene polymerisation.

Dicationic and zwitterionic catalysts for the amine-initiated, immortal ring-opening polymerisation of rac-lactide: facile synthesis of amine-terminated, highly heterotactic PLA.

Dicationic, zwitterionic and "conventional" yttrium compounds act as catalysts for the primary or secondary amine-initiated immortal ROP of rac-lactide; amine-terminated, highly heterotactic poly(rac-lactides) with narrow polydispersities and well-controlled molecular weights are prepared in this manner.

Incorporation of isosorbide into poly(butylene terephthalate) via solid-state polymerization.

The biomass-based monomer isosorbide was incorporated into poly(butylene terephthalate) (PBT) by solid-state polymerization (SSP) using the macrodiol monomer BTITB-(OH) 2, which consists of isosorbide (I), terephthalic acid (T), and 1,4-butandiol (B) residues. This macromonomer can be synthesized by a simple one-pot, two-step reaction. Polymers with number-average molecular weights up to 100,000 g x mol (-1) were readily synthesized from various ratios of PBT/BTITB-(OH) 2. Their molecular weights, thermal properties, and colors were compared with corresponding copolyesters that were obtained by melt polycondensation. We found that T m, T c, and especially T g were superior for materials that were obtained by SSP. This is ascribed to differences in the microstructures of both types of copolyesters; the SSP products exhibit a more blocky structure than do the more random melt-polymerized counterparts. The SSP method resulted in much higher molecular weights and much less colored polymers, and it seems to be the preferred route for incorporating biobased monomers that exhibit limited thermal stability into engineering plastics.

Zwitterionic bis(phenolate)amine lanthanide complexes for the ring-opening polymerisation of cyclic esters.

The reaction of Sm{N(SiMe3)2}3 with the bis(phenol)amines H2O2N(R) (H2O2N(R) = RCH2CH2N(2-HO-3,5-C6H2(t)Bu2)2; R = OMe, NMe2 or Me) gave exclusively zwitterions Sm(O2N(R))(HO2N(R)). For R = OMe or NMe2 these were efficient catalysts for the ring-opening polymerisation of epsilon-caprolactone and D,L-lactide with a tendency to form cyclic esters; in contrast, no polymerisation was observed for R = Me.

Enhancing the functionality of biobased polyester coating resins through modification with citric acid.

Citric acid (CA) was evaluated as a functionality-enhancing monomer in biobased polyesters suitable for coating applications. Model reactions of CA with several primary and secondary alcohols and diols, including the 1,4:3,6-dianhydrohexitols, revealed that titanium(IV) n-butoxide catalyzed esterification reactions involving these compounds proceed at relatively low temperatures, often via anhydride intermediates. Interestingly, the facile anhydride formation from CA at temperatures around CA's melting temperature ( T m = 153 degrees C) proved to be crucial in modifying sterically hindered secondary hydroxyl end groups. OH-functional polyesters were reacted with CA in the melt between 150 and 165 degrees C, yielding slightly branched carboxylic acid functional materials with strongly enhanced functionality. The acid/epoxy curing reaction of the acid-functional polymers was simulated with a monofunctional glycidyl ether. Finally, the CA-modified polyesters were applied as coatings, using conventional cross-linking agents. The formulations showed rapid curing, resulting in chemically and mechanically stable coatings. These results demonstrate that citric acid can be applied in a new way, making use of its anhydride formation to functionalize OH-functional polyesters, which is an important new step toward fully biobased coating systems.

Polyamide synthesis from 6-aminocapronitrile, part 1: N-alkyl amide formation by amine amidation of a hydrolyzed nitrile.

The synthesis of N-hexylpentanamide from a stoichiometric amount of pentanenitrile and hexylamine has been studied as a model reaction for the synthesis of nylon-6 from 6-aminocapronitrile. The reaction was carried out under mild hydrothermal conditions and in the presence of a homogeneous ruthenium catalyst. For the mild hydrothermal conditions the presence of hexylamine distinctively increases the nitrile hydrolysis compared to the nitrile hydrolysis in the absence of hexylamine. Amine-catalyzed nitrile hydrolysis mainly produces the N-substituted amide. A clear product development is observed, consisting of first the terminal amide formation and second the accumulation of N-hexylpentanamide. With a maximum conversion of only 80 % after 18 h, the nitrile hydrolysis rate at 230 degrees C is still much too low for nylon-6 synthesis. Ruthenium dihydride phosphine was therefore used as a homogeneous catalyst, which significantly increases the nitrile hydrolysis rate. At a temperature of 140 degrees C and with only 0.5 mol % [RuH(2)(PPh(3))(4)] a 60 % nitrile conversion is already reached within 2 h. Initially the terminal amide is the sole product, which is gradually converted into N-hexylpentanamide. The reaction has a high initial rate, however, for higher conversions a strong decrease in hydrolysis rate is observed. This is ascribed to product inhibition, which results from the equilibrium nature of the reaction.

Polyamide synthesis from 6-aminocapronitrile, part 2: heterogeneously catalyzed nitrile hydrolysis with consecutive amine amidation.

To test the potential of heterogeneous catalysts for the nylon-6 synthesis from 6-aminocapronitrile, a number of zeolites, aluminum silicate, and metal oxides were tested as catalysts for the model reaction of pentanenitrile with water and hexylamine to N-hexylpentanamide. All zeolitic and aluminum silicate systems showed an insufficient performance, while the metal oxides (TiO(2), ZrO(2), Nb(2)O(5)) showed very promising results. The kinetic behavior of the metal oxides was further investigated. First the nitrile was catalytically hydrolyzed to the terminal amide and subsequently the amidation of the hexylamine occurred. To polymerize 6-aminocapronitrile into nylon-6, more than 99 % nitrile conversion was required to obtain a high-molecular-weight polymer. Pentanenitrile conversions larger than 99 % can be obtained within six hours, at 230 degrees C, by using ZrO(2) as the catalyst. A kinetic study (by using IR spectroscopy) on the behavior of the metal oxides demonstrated that the adsorbed nitrile was catalytically hydrolyzed at the surface, but remained tightly bound to the surface. Zirconia-catalyzed polymerizations of 6-amino-capronitrile demonstrated that high-molecular-weight nylon-6 is feasible by using this route.

Co- and terpolyesters based on isosorbide and succinic acid for coating applications: synthesis and characterization.

Co- and terpolyesters based on succinic acid and isosorbide in combination with other renewable monomers such as 2,3-butanediol, 1,3-propanediol, and citric acid were synthesized and characterized. Linear polyesters were obtained via melt polycondensation of nonactivated dicarboxylic acids with OH functional monomers. Polymer end functionality (i.e., hydroxyl or carboxylic acid) was controlled by adjusting the monomer stoichiometry. The glass transition temperatures of the resulting polyesters could be effectively adjusted by varying the polymer composition and molar mass. By adding polyfunctional monomers such as trimethylolpropane or citric acid, polyesters with enhanced functionality were obtained. These biobased polyesters displayed functionalities and Tg values in the appropriate range for (powder) coating applications. The polyesters were cross-linked using conventional curing agents. Coatings from branched polyesters--hydroxyl as well as acid functional--showed significantly improved mechanical and chemical resistance compared to those formulated from linear polymers. These renewable polyesters proved to be suitable materials for coating applications with respect to solvent resistance, impact resistance, and hardness.

Topology characterization by MALDI-ToF-MS of enzymatically synthesized poly(lactide-co-glycolide).

Lipase catalyzed copolymerization of the monomers lactide and glycolide by Pseudomonas cepacia employing a molar ratio of 80L/20G has been studied. The copolymers were characterized by MALDI-ToF-MS, DSC, SEC and NMR. MALDI-ToF-MS has successfully been used not only to determine end groups and chemical composition but even the microstructure of the copolymers. We demonstrated that for this lipase catalyzed copolymerization, the main product of the reaction at 100 degrees C was linear homopolymer of lactide while at 130 degrees C the main product was cyclic random copolymer.

Role of the metal oxidation state in the SNS-Cr catalyst for ethylene trimerization: isolation of di- and trivalent cationic intermediates.

The reaction of the highly selective [CySCH2CH2N(H)CH2CH2SCy]CrCl3 catalyst precursor with alkyl aluminum activators was examined with the aim of isolating reactive intermediates. Reaction with Me3Al afforded a cationic trivalent chromium alkyl species {[CySCH2CH2N(H)CH2CH2SCy]CrMe(mu-Cl)}2{(AlMe3)2(m-Cl}2.(C7H8)2 (1a). Although it was not possible to obtain crystalline samples of sufficient quality from the reaction with MAO (the most preferred activator), the near-to-identical EPR spectra indicated a very close structural similarity with 1a. Ethylene oligomerization tests clearly revealed that 1 and other cationic trivalent dimeric complexes {[CySCH2CH2N(H)CH2CH2SCy] CrCl(mu-Cl)}2{AlCl4}2.(C7H8)1.5 (2), monomeric [(CySCH2CH2N(H)CH2CH2SCy)CrCl2 (THF)][AlCl4] (3), and {[CySCH2CH2N(H)CH2CH2SCy]Cr(eta2-AlCl4)}{Al2Cl7} (4) adducts display the same catalyst selectivity as the [CySCH2CH2N(H)CH2CH2SCy]CrCl3 complex and, therefore, are probably all precursors to the same catalytically active species. 2, 3, and 4 were obtained upon treatment of [CySCH2CH2N(H)CH2CH2SCy] CrCl3 with different stoichiometric ratios of AlCl3.. When i-BAO activator was used, reduction of the metal center occurred readily, affording {([CySCH2CH2N(H)CH2CH2S Cy]Cr)(mu-Cl)]2}{(i-Bu)2AlCl2}2 (5). 5 is also a selective catalyst, thus indicating that trivalent species are most probably precursors to a divalent catalytically active complex. Reaction of CrCl2(THF)2 with the ligand afforded the labile divalent adduct [CySCH2CH2N(H)CH2CH2SCy]CrCl2(THF) (6), also catalytically active and selective. Instead, deprotonation of the ligand with n-BuLi followed by reaction with CrCl2(THF)2 gave the dinuclear complex [(mu-CySCH2CH2NCH2CH2SCy)CrCl]2 (7), which did not produce oligomers.