Gerrit A. Luinstra

Poly(Propylene Carbonate), Old Copolymers of Propylene Oxide and Carbon Dioxide with New Interests: Catalysis and Material Properties

Current research efforts in the field of poly(propylene carbonate) prepared from carbon dioxide and propylene oxide are reviewed. Interest in the polymer has been revived in light of the current discussion on sustainability and biodegradability. The progress in understanding and increasing the activity of heterogeneous zinc catalysts is steadily increasing, but without a quantum leap. The microstructure, the properties of the melt, and the solid material are given. The material property profile can be expanded through the synthesis of terpolymers based on propylene oxide, carbon dioxide and other epoxides, lactones or anhydrides etc. with the same catalyst; or the preparation of poly(propylene carbonate) blends with biodegradable or biocompatible components like calcium carbonate, wood flour, fibers, or other biodegradable polymers.

CH activation by aqueous platinum complexes: A mechanistic study

Abstract Detailed mechanistic studies are reported on the oxidation of alkanes by aqueous [PtCl 6 ] 2− /[PtCl 4 ] 2− to alcohols plus alkyl chlorides, via proposed (alkyl)Pt II and (alkyl)Pt IV intermediates. Reactions of [PtCl 4 ] 2− with RI (R = CH 3 , CH 2 CH 2 OH) in water yield [PtCl 5 R] 2− , which were isolated as their NMe 4 salts. Kinetic rate laws of their decomposition in aqueous chloride solution to ROH and RCl support S N 2 displacement by Cl − or H 2 O as the mechanism of the last step. erythro- and threo -[PtCl 5 (CHDCHDOH)] 2− are obtained by oxidation of [PtCl 3 ( trans - and cis -CHDCHD)] − respectively, and react with Cl − with inversion of stereochemistry at carbon, consistent with the S N 2 mechanism. [PtCl 5 (CH 2 CH 2 OH)] 2− is also obtained by oxidation of Zeises salt with [PtCl 6 ] 2− . Kinetics indicate that attack of water on coordinated ethylene to give a β-hydroxyethyl group precedes oxidation of Pt II to Pt IV , rather than the reverse order, and that this reaction is a model for the oxidation of (alkyl)Pt II to (alkyl)Pt IV during alkane functionalization. 195 Pt isotopic labeling demonstrates that the oxidation is not accompanied by transfer of the β-hydroxyethyl group from one Pt center to another.

Material Properties of Poly(Propylene Carbonates)

Abstract The material properties of poly(propylene carbonate) (PPC) are discussed with respect to thermal features, viscoelastic and mechanical properties, processability, characteristics in solution, biodegradability, and biocompatibility. Thermal decomposition proceeds in two steps: (1) backbiting at temperatures as low as 150°C in the presence of catalyst residues, giving cyclic propylene carbonate; and (2) chain scission at temperatures over 200°C with possible involvement of initial hydrolysis. PPC shows one thermal transition at a glass temperature of around 40°C. PPC is a pseudoplastic material, and a master curve constructed for frequency-dependent viscosity shows no real plateau for material of number-average molecular weight (Mn) < 50 kDa. At temperatures in the range of the glass transition, the apparent activation energy for flow changes rapidly from 500 kJ/mol to about 40 kJ/mol. The viscosity of PPC has an activation energy in the range of 5–25 kJ/mol (Mn < 50 kDa). The modulus of elasticity (around 800 MPa) and yield strength (10–20 MPa) are reminiscent of low-density polyethylene. PPC has a large elongation at break, and may be useful for the preparation of composites and blends. Biodegradation of PPC is dominated by hydrolysis, which can be accelerated by Lewis acid catalyst residues. Biocompatibility is excellent in the sense that it does not induce an inflammatory reaction in tissue.

Effects of phosphine substituents on CO and norbornene insertion rates into (P,N)–Pd–alkyl and –acyl bonds

Abstract The synthesis is described of (P,N)–PdMe(X) (P,N=R 2 P- o -C 6 H 4 CH 2 NMe 2 ( L1 ), Me 2 N- o -C 6 H 4 CH 2 –PR 2 ( L2 ), 1-(dimethylamino)-8-(R 2 phosphino)naphthalene ( L3 ) with R 2 =Ph 2 ( a ), Cy 2 ( b ), Me,Ph ( c , for L1 only); X=Cl, OTf) and cationic (P,N)–PdMe(L) + (L, MeCN, CO; anion, − B[3,5-Ph–(CF 3 ) 2 ] 4 ). The complexes react with CO to give (P,N)–Pd{C(O)Me}(X/L + ) derivatives. Carbonylation is faster in complexes with the more basic phosphines of type 1 , but slower in ligand type 2 and 3 . Norbornene inserts slowly into the (P,N)–Pd–acetyl bond of the cationic borate complexes with L1 – 3 , and for L2 with X=Cl, OTf. Cationic palladium complexes with phenyl substituted phosphine ligands are more reactive toward CO/norbornene mixtures than those with cyclohexyl and complexes of L2 and L1 react faster than that of L3 . The observed reactivity is described in terms of differences in CO insertion rates and a rate determining isomerization or trapping by norbornene of the intermediates, trans -P (P,N)–Pd{C(O)Me} + complexes.

Lead dichloride: a mild reagent for the oxidation of tervalent titanium compounds (η2-C5Me5)2TiR to monochloride derivatives (η5-C5Me5)2TiR(Cl)

Lead dichloride reacts smoothly and stoichiometrically with (η5-C5Me5)2TiR (R = Cl, alkoxide, alkyl, hydride, etc.) complexes to form diamagnetic (η5-C5Me5)2TiR(Cl) derivatives and elemental lead.

Synthesis and reactivity of titanocene and zirconocene triflates

Abstract The synthesis of triflate derivatives of titanocene and zirconocene from the corresponding dimethyl complexes and triflic acid (HOTf) is described. Comproportionation of Cp2M(OTf)2 with Cp2MX2 gives Cp2M(OTf)X (MTi, X  Cl, F, Me; M  Zr, X  Cl, Me, BH4). Cp2TiMe(OTf) reacts with ROH (R  Me3Si or Me2tBuSi) to give Cp2TiOR(OTf). Cp2TiMe(OTf) and Cp2TiOSiMe3(OTf) react with H2O to give the oxo-bridged dimer (Cp2TiOTf)2(μ-O). The triflate in Cp2TiX(OTf) (X  Cl, F, Me, OSiMe3) is substituted by −OSiMe3 to give compounds Cp2TiX(OSiMe3). Cp2Ti(OMe)OR (R = Me, SiMe3) could not be obtained.

Post-polymerization modification of reactive polymers derived from vinylcyclopropane: 1. synthesis and thermo-responsive behaviour

A new reactive vinylcyclopropane monomer, 1-cyano-1-pentafluorophenoxycarbonyl-2-vinylcyclopropane, has been synthesized and polymerized. The obtained polymer contained exclusively the pent-3-enyl repeating unit in the polymer backbone. Taking advantage of activated ester chemistries, post-polymerization modifications with different aliphatic amines have been conducted. All prepared polymers exhibited an upper critical solution temperature (UCST) in ethanol and ethanol–water. It was found that the UCST was directly related to the amide moiety of the polymer. An increased solubility of the polymer in ethanol with the increase of the volume of the aliphatic amide moiety was observed. The reverse effect was found when adding water to the ethanolic solution of the polymer.

Post-polymerization modification of reactive polymers derived from vinylcyclopropane: a poly(vinylcyclopropane) derivative with physical gelation and UCST behaviour in ethanol–water mixtures

In this paper we describe a new polymer that combines an upper critical solution temperature (UCST) and reversible physical gelation in ethanol–water mixtures. The polymer, namely poly(1-cyano-N-propylcarboxyamidovinylcyclopropane) (poly(CNPCAVCP)), was synthesized by post-polymerization modification of poly(1-cyano-1-pentafluorophenoxycarbonyl-2-vinylcyclopropane) (poly(CPFPCVCP)) with n-propylamine. The stimuli responsiveness of the polymer was investigated in ethanol and ethanol–water mixtures by varying the water concentration in the mixture. It was found that, depending on the water concentration, the mixture features an upper critical solution temperature (UCST), physical gelation or both. In addition, it was observed that the hysteresis between the heating and the cooling phase was very large (about 45 °C).

Structure-property relationships of carboxymethyl hydroxypropyl guar gum in water and a hyperentanglement parameter.

The viscoelastic properties of carboxymethyl hydroxypropyl guar gum (CMHPG) in aqueous solution were determined as function of concentration and of molecular weight, using SEC/MALLS/dRI and viscometry. The chain is more rigid as in native guar as was deduced from the molecular parameter in dilute solution. Superstructures are formed in moderately concentrated solutions as is shown from the comparison of steady state shear and small amplitude oscillatory shear (SAOS) experiments. The shear rate dependent viscosity of CMHPG can satisfactorily be described by the Carreau-Yasuda model with the rheological parameters (η0, λ0, n, b) obtained from the evaluation of viscosity data. A quantitative hyperentanglement parameter is introduced to account for the differences in responses in shear and SAOS experiments.

Synthesis and thermolysis of Cp∗(C5Me4CH2) TiR complexes

Abstract Substitution of the chloride in Cp ∗ FvTiCl with MR (Fv  C 5 Me 4 CH 2 ; R  Me, CH 2 SiMe 3 , CH 2 CMe 3 , CH  CH 2 , M  Li; R  CH 2 Ph, M  K; R  C 3 H 5 , M  MgCl; R  Ph, M  Na · NaCl) gives Cp ∗ FvTiR. NMR spectroscopic evidence points towards a series of structurally related compounds with a bent-sandwich geometry. The substituent R is positioned in the wedge, midway below the exocyclic methylene group and a neighbouring methyl group of the fulvene. Thermolysis of Cp ∗ FvTiR gives, dependent on the substituent R, reduction to Cp ∗ FvTi (R  CH 2 Ph) or the double ring metallated Cp ∗ [C 5 Me 3 (CH 2 ) 2 ]Ti (R  CH 2 XMe 3 , X  C, Si) or Cp ∗ FvTiCH=CHMe (R = η 3 -C 3 H 5 ).