End-functional styrene-maleic anhydride copolymers via catalytic chain transfer polymerization

Styrene-maleic anhydride copolymers have been successfully synthesized using catalytic chain transfer polymerization employing the low spin [bis(difluoroboryl)dimethylglyoximato]cobalt(II) (COBF) complex. By partially replacing styrene with α-methylstyr

Preparation of Well-Compatibilized PP/PC Blends and Foams Thereof

The performance of polypropylene-poly(ethylene brassylate) block and graft copolymers and a polypropylene-polycaprolactone graft copolymer as compatibilizers for polypropylene-rich polypropylene/bisphenol A polycarbonate (PP/PC, 80/20 wt/wt) blends was elucidated. The copolymers were synthesized either by metal-catalyzed ring-opening polymerization or transesterification of a presynthesized polyester, initiated by hydroxyl-functionalized PPs, which themselves were obtained by catalytic routes or reactive extrusion, respectively. Spectroscopic fingerprints of the copolymers from liquid-state nuclear magnetic resonance (NMR) in combination with scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic mechanical thermal analysis (DMTA), and rheology analyses of the blends indicated that the compatibilizers spontaneously organize at the interface of the two immiscible polymers leading to the formation of uniform, stable, nanophase morphologies. The effect of the compatibilizers on the performance of the PP/PC blends was evaluated, and well-compatibilized PP/PC blends showed improved melt strength and strain hardening when compared to pure PP. This was verified by the successful foam extrusion using isobutane as a blowing agent of well-compatibilized PP/PC blends to low-density PP-based foams, for which normally long-chain branched PP is required

Ancillary ligand effects in organoyttrium chemistry

Although the development of organometallic chemistry and homogeneous catalysiss tarted seperately in the early fifties, these fields of research have become tirmly intertwined during the last decade. This stems lrom the fact that transition metalc arbon and hydrido bonds play a key role in many C-X (X = C, H, hetero atom) transformation. Zie: summary/samenvatting

Ethylene Oligomerization Promoted by a Silylated-SNS Chromium System

The ethylene trimerization SNS ligand has been modified by replacing the methylene carbons flanking the nitrogen atom with dimethyl silyl groups. Three ligands, CySCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SCy (a), (t-Bu)SCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2S(t-Bu) (b), and PhSCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SPh (c), have been prepared. Ligand a in either protonated or deprotonated forms was reacted with CrCl3(THF)(3) to afford the corresponding monomeric [CySCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SCy]CrCl3 (1a) or dimeric {[CySCH2Si(CH3)(2)NSi(CH3)(2)CH2SCy] CrCl(mu-Cl)}(2) (2a). One-pot reaction of a in the presence of Et2AlCl with either Cr(III) or Cr(II) chlorides afforded in either case the divalent {[CySCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SCy]Cr{(mu-Cl)Al(CH2CH3)(2)Cl)(2) (3a). To deprotonate the N-H function of the Si-SNS ligand, n-BuLi was used for the purpose of preparing the divalent chromium analogue. The reaction afforded in the case of both a and b the two nearly isostructural divalent complexes {[CySCH2Si(CH3)(2)NSi(CH3)(2)CH2SCy]Cr(mu-Cl)}(2) (4a) and {[(t-Bu)SCH2Si(CH3)(2)NSi(CH3)(2)CH2S(t-Bu)]Cr(mu-Cl)}(2) (4b) in crystalline form. To further clarify the interaction of 4 with aluminate species, we have carried out in situ complexation in the presence of either AlCl3 or AlMe3 and using divalent instead of trivalent chromium salts. In the cases of ligands a and c and AlCl3, two isostructural complexes, {[CySCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SCy]Cr{(mu-Cl)AlCl3}(2) (5a) and {[PhSCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SPh]C{(mu-Cl)AlCl3}(2) (5c), have been obtained. The reaction with AlMe3 afforded {[CySCH2Si(CH3)(2)N(Al(CH3)(2)(mu-Cl)Si(CH3)(2)CH2SCy] Cr{(mu-Cl)Al(CH3)(3)} (6a). Its structure was informative, showing a possible catalyst deactivation pathway. To better evaluate the role of the N-H function, we have also methylated ligand a at the N atom. The complexation to chromium was successful only in the presence of Me2AlCl and if a divalent chromium precursor was used. The reaction afforded the catalytically inactive divalent {[CySCH2Si(CH3)(2)N(CH3)Si(CH3)(2)CH2SCy]Cr(mu-Cl)}(2){(Al(CH3)(2)Cl)(2))(mu-Cl)}(2) (7d). Most of these species showed good catalytic activity upon activation but produced only statistical distributions of oligomers

Ethylene Oligomerization Promoted by a Silylated-SNS Chromium System

The ethylene trimerization SNS ligand has been modified by replacing the methylene carbons flanking the nitrogen atom with dimethyl silyl groups. Three ligands, CySCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SCy (a), (t-Bu)SCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2S(t-Bu) (b), and PhSCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SPh (c), have been prepared. Ligand a in either protonated or deprotonated forms was reacted with CrCl3(THF)(3) to afford the corresponding monomeric [CySCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SCy]CrCl3 (1a) or dimeric {[CySCH2Si(CH3)(2)NSi(CH3)(2)CH2SCy] CrCl(mu-Cl)}(2) (2a). One-pot reaction of a in the presence of Et2AlCl with either Cr(III) or Cr(II) chlorides afforded in either case the divalent {[CySCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SCy]Cr{(mu-Cl)Al(CH2CH3)(2)Cl)(2) (3a). To deprotonate the N-H function of the Si-SNS ligand, n-BuLi was used for the purpose of preparing the divalent chromium analogue. The reaction afforded in the case of both a and b the two nearly isostructural divalent complexes {[CySCH2Si(CH3)(2)NSi(CH3)(2)CH2SCy]Cr(mu-Cl)}(2) (4a) and {[(t-Bu)SCH2Si(CH3)(2)NSi(CH3)(2)CH2S(t-Bu)]Cr(mu-Cl)}(2) (4b) in crystalline form. To further clarify the interaction of 4 with aluminate species, we have carried out in situ complexation in the presence of either AlCl3 or AlMe3 and using divalent instead of trivalent chromium salts. In the cases of ligands a and c and AlCl3, two isostructural complexes, {[CySCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SCy]Cr{(mu-Cl)AlCl3}(2) (5a) and {[PhSCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SPh]C{(mu-Cl)AlCl3}(2) (5c), have been obtained. The reaction with AlMe3 afforded {[CySCH2Si(CH3)(2)N(Al(CH3)(2)(mu-Cl)Si(CH3)(2)CH2SCy] Cr{(mu-Cl)Al(CH3)(3)} (6a). Its structure was informative, showing a possible catalyst deactivation pathway. To better evaluate the role of the N-H function, we have also methylated ligand a at the N atom. The complexation to chromium was successful only in the presence of Me2AlCl and if a divalent chromium precursor was used. The reaction afforded the catalytically inactive divalent {[CySCH2Si(CH3)(2)N(CH3)Si(CH3)(2)CH2SCy]Cr(mu-Cl)}(2){(Al(CH3)(2)Cl)(2))(mu-Cl)}(2) (7d). Most of these species showed good catalytic activity upon activation but produced only statistical distributions of oligomers

Mono(pentamethylcyclopentadienyl)yttrium Compounds Stabilized by N,N´-Bis(Trimethylsilyl)benzamidinate Ligands

Reaction of YCl3·3.5THF with Cp*K followed by [PhC(NSiMe3)2]Li·OEt2 in THF gives the surprisingly stable yttrium cyclopentadienyl-benzamidinate chloride {Cp*[PhC(NSiMe3)2]Y(μ-Cl)}2 (1). Thermally induced redistribution of the various ligands leading to disproportionation of the molecule was not observed. The dimer does not split easily, e.g., it does not react with THF to give Cp*[PhC(NSiMe3)2]YCl·THF. Attempts to produce monomeric derivatives of 1 by substitution of the chloride by alkoxy, amide, or alkyl substituents using salt metathesis methodology were not successful. Reaction of 1 with 2 equiv of MeLi in the presence of TMEDA (TMEDA = N,N,N´,N´-tetramethylethylenediamine) afforded the structurally characterized Cp*[PhC(NSiMe3)2]Y(μ-Me)2Li·TMEDA (2). Compound 2 is a useful precursor for other yttrium pentamethylcyclopentadienyl-benzamidinate derivatives by controlled protolysis: with HC≡CCMe3 or HOAr it yields Cp*[PhC(NSiMe3)2]Y(μ-C≡CCMe3)Li·TMEDA (3) and Cp*[PhC(NSiMe3)2]YOAr (4), respectively.