Emulsion Copolymerization of alpha-Olefins with Carbon Monoxide Using Water-Soluble Palladium(II) Complexes

Abstract

The objective of this thesis was the development of stable dispersions for aqueous polyketone latices on the basis of the copolymers propene/undecenoic acid/CO, butene/undecenoic acid/CO, and propene/butene/undecenoic acid/CO. Therefore, attention has been focused on the design of new water-soluble palladium(II) catalysts for the production of stable polymer latices with (i) high solids contents, (ii) high molecular weights, (iii) particle sizes in the range between 50 and 500 nm, and (iv) glass transition temperatures with values below room temperature. In the first chapter of this thesis the synthesis and characterization of novel diphosphine ligands and their palladium(II) complexes is described. The diphosphines R2P(CH2)3PR2 [R = (CH2)nP(O)(OEt)2, n = 2-6, 8; (CH2)nOH, n = 6; (CH2)nNH2, n = 3] were obtained by heating P(OEt)3 with 1,3-dibromopropane according to a Michaelis-Arbuzov reaction, followed by reduction of the resulting diphosphate with LiAlH4 in diethyl ether to give H2P(CH2)3PH2. An excess of the corresponding olefin CH2=CH.(CH2)n.X (X = OH, n = 4; P(O)(OEt)2, n = 0-4, 6; NH2, n = 1) was photochemically hydrophosphinated with the diprimary phosphine H2P(CH2)3PH2 over night. This convenient synthesis is nearly quantitative and simplifies the purification of the products. Purification is achieved by removing excess alkene under reduced pressure. The alkenyl phosphonates CH2=CH.(CH2)n.P(O)(OEt)2 were obtained either from commercial suppliers (n = 0, 1) or prepared by literature methods (n = 2.4, 6). All diphosphines resulted as colorless, air-sensitive, and oily products. They are soluble in water and chlorinated hydrocarbons like dichloromethane and chloroform. Upon reaction of palladium(II) acetate with these hydroxyalkyl, phosphonate and aminophosphine ligands in a 1 : 1 mixture of dichloromethane and acetonitrile at room temperature the corresponding diacetatodiphosphinepalladium(II) complexes (R2P(CH2)3PR2)Pd(OAc)2 [R = (CH2)nP(O)(OEt)2, n = 2-6, 8; (CH2)nOH, n = 6; (CH2)nNH2, n = 3 ] could be isolated. They are soluble in water, alcohols, and in organic solvents of medium polarity and offer an easy way to generate catalytically active precursor species in one step by addition of excess Brønsted acid to a solution in water. The structure of the complex (R2P(CH2)3PR2)Pd(OAc)2 [R = (CH2)6OH] additionally was investigated by an X-ray structural analysis. All diphosphine ligands and their palladium(II) complexes were characterized by means of MS, IR, and NMR spectroscopy. The 31P{1H}-NMR spectra of the phosphonate ligand R2P(CH2)3PR2 [R = (CH2)2P(O)(OEt)2] and its palladium(II) complex (R2P(CH2)3PR2)Pd(OAc)2 [R = (CH2)2P(O)(OEt)2] display two signals in a 2 : 1 ratio, assigned to the phosphonate and phosphine substituents. A marked shift and significant change of the multiplicity in the 31P{1H}-NMR spectra for the phosphine group in this ligand from a triplet (δ = -22) to a multiplet at δ = 22 upon reaction of palladium(II) acetate with R2P(CH2)3PR2 [R = (CH2)2P(O)(OEt)2] have been observed. The second part of this thesis is devoted to the catalytic activity of these palladium(II) complexes for the copolymerization of α-olefins with carbon monoxide. Indeed the diacetatodiphosphinepalldium(II) complexes (R2P(CH2)3PR2)Pd(OAc)2 proved to be highly active catalysts for the co- and terpolymerization of several α-olefins with carbon monoxide in the presence of excess HBF4. Latices of aliphatic polyketones (propene/undecenoic acid/CO, butene/undecenoic acid/CO, and propene/butene/undecenoic acid/CO copolymers) prepared by a transition metal catalyzed polymerization are described for the first time. These aqueous polyketone latices exhibit high solids contents of up to 23% and high molecular weights of up to 6.3.104 g mol-1 at narrow polydispersities (Mw/Mn . 2). Also they are produced at rates similar to the commercially process performed in methanol. Stable dispersions are obtained by the introduction of undecenoic acid as a third or fourth comonomer and no phase separation, or the formation of a coagulum within ten weeks were observed. In these latices, hydrophilic carboxylic acid moieties covalently bound to the particle surface contribute to stabilization. In addition, for practical applications it is desirable to find routes to set the Tg values significantly below room temperature. The introduction of 5.10% (wt/wt) of undecenoic acid to the olefin during the polymerization process indeed resulted in markedly decreased Tg values from room temperature to .2°C. With glass transitions being below room temperature, α-olefin/CO copolymers are well suited for the formation of films. In contrast to elastic materials obtained with (dppp)Pd, complexes (R2P(CH2)3PR2)Pd(OAc)2 produce non-elastic thermoplastics. The α-olefin/CO copolymer latices exhibit particle sizes between 60 and 224 nm, which are in the desirable range for latex applications. The co- and terpolymerization of hydrophobic monomers in the emulsion polymerization in the presence of methyl-β-cyclodextrin (W7 M 1.8) as a phase transfer agent enables the production of higher solids contents of the polyketones and a higher productivity of the catalysts. Water-insoluble molecules become water-soluble by treatment with aqueous solutions of cyclodextrins. The 13C{1H}-NMR spectra (in CDCl3) of the propene/CO, butene/CO, and propene/butene/CO copolymers, respectively, show only a single peak for the carbonyl group and this gives an indication that perfectly head-to-tail regioregular polyketones have been formed. Complexes (R2P(CH2)3PR2)Pd(OAc)2 [R = (CH2)nP(O)(OEt)2; n = 6, 3] are highly active catalysts in the copolymerization of butene/undecenoic acid/CO, propene/butene/undecenoic acid/CO, and propene/undecenoic acid/CO, respectively, with productivities of up to 1.0.104 (mol(substr) mol(Pd).1). Generally the molecular weight of α-olefin/CO copolymers increase significantly as the chain length of the monomers decreases. Depending on the chain-length of the phosphorus attached substituents in the palladium catalysts (R2P(CH2)3PR2)Pd(OAc)2, four variables for the propene/CO, butene/CO, and propene/butene/CO copolymers can be controlled: (i) the regioregularity, (ii) the molecular weight, (iii) the glass transition temperature, and the melting point (Tg and Tm). This indicates clearly that the steric properties of the catalyst control the molecular weights and the microstructure (e.g. the regioregularity) of the copolymers. The conformational flexibility of the four P-bonded hydroxyalkyl, phosphonate, or amine substituents combined with their steric demand and amphiphilic character generate a kind of hydrophobic catalytic pocket in the environment of the metal center in which aliphatic substrate molecules and the growing polymer chain nicely fit.

Die Zielsetzung dieser Arbeit war die Entwicklung stabiler Dispersionen für wäßrige Polyketon-Latices auf der Basis von Copolymeren aus Propen/Undecensäure/CO, Buten/Undecensäure/CO und Propen/Buten/Undecensäure/CO. Deshalb wurde die Aufmerksamkeit auf das Design der neuen wasserlöslichen Palladium(II)-Katalysatoren gerichtet, um stabile Polymer Latices mit (i) hohem Feststoffgehalt, (ii) hohen Molekulargewichten, (iii) Teilchengrößen im Bereich zwischen 50 und 500 nm und (iv) Glasübergangstemperaturen mit Werten unterhalb der Raumtemperatur zu erhalten. Drei Arten von Palladiumkomplexen mit Hydroxyalkyl-, Phosphonat- und Aminsubstituenten, an die Phosphordonoren angebunden wurden, wurden in der Emulsionskopolymerisation von Propen/CO, von Buten/CO und von Propen/Buten/CO eingesetzt. Abhängig von der Kettenlänge der am Phosphor angebrachten Substituenten der Katalysatoren, wurden vier Variablen für die Propen/CO, Buten/CO und Propen/Buten/CO Copolymere überprüft: (i) die Regioregularität; (ii) das Molekulargewicht (iii) die Glasübergangstemperatur und (iv) der Schmelzpunkt (Tg und Tm). Beständige Dispersionen werden durch Zugabe von Undecensäure als drittes oder viertes Monomeres in die Propen/CO, in Buten/CO und in Propen/Buten/CO Copolymere erreicht. Es wurde innerhalb von 10 Wochen keine Phasentrennung oder Bildung von Koagulaten beobachtet. In diesen Latices tragen die hydrophilen Carboxylsäure Anteile, die kovalent an die Partikeloberfläche gebunden sind, zur Stabilisierung bei. Mit Phasentransfer-Reagenzien, z.B. Methyl-b-Cyclodextrin (W7 M 1,8), konnten bei der Co- und Terpolymerisation von hydrophoben Monomeren in der Emulsionspolymerisation bessere Resultate erzielt werden. Ein höherer Feststoffgehalt der Polyketone und eine höhere Produktivität der Katalysatoren wurden beobachtet.