Catalyst for epoxide polymerization

Hexacyanometalate Salt Complexes as Catalysts for Epoxide Polymerizations... 

Reasoning from the success of Price (16) and others with zinc compounds as catalysts for epoxide polymerizations, the zinc hexacyano-... 

Although significant advances in stereoselective epoxide polymerization have been achieved over the last half-century, few known catalysts are capable of excellent levels of stereocontrol. Historically, most catalysts for epoxide polymerization have been of the heterogeneous variety and have exhibited poor selectivity. It is our opinion that the most fertile area for future catalyst exploration involves homogeneous, discrete catalysts that are capable of involving multiple metal centers in the polymerization mechanism. If the spatial environment of the active catalyst is precisely controlled, new generations of stereoselective epoxide polymerization catalysts will become available. Our current research focuses on the search for such catalysts. 

In conclusion, i lle It Is evident that much has been learned about reactions producing polyethers and important factors which affect them, there remain Intriguing unanswered questions. While there has been much speculation, it Is not clear that we know in any detail the structural features of stereoselective and stereoelective coordination catalysts for epoxide polymerization. 

Diehlorotriphenylantimony has been suggested as a flame retardant (177,178) and as a catalyst for the polymerization of ethylene carbonate (179). Dihromotriphenylantimony has been used as a catalyst for the reaction between carbon dioxide and epoxides to form cycHc carbonates (180) and for the oxidation of a-keto alcohols to diketones (181). 

Zinc compounds have recently been used as pre-catalysts for the polymerization of lactides and the co-polymerization of epoxides and carbon dioxide (see Sections 2.06.8-2.06.12). The active catalysts in these reactions are not organozinc compounds, but their protonolyzed products. A few well-defined organozinc compounds, however, have been used as co-catalysts and chain-transfer reagents in the transition metal-catalyzed polymerization of olefins. 

Interest in organozinc cations increased substantially when they were shown to be excellent catalysts for the polymerization of esters and epoxides. 

Soluble polymer-bound catalysts for epoxidation reactions have also been explored, with a complete study into the nature of the polymeric backbone performed by Janda [70]. Chiral (salen)-Mn complexes were appended to MeO-PEG, NCPS, Jan-daJeF and Merrifield resin via a glutarate spacer. It was found that for the Jacobsen epoxidation of ds-/ -mefhylstyrene, the enantioselectivities for each polymer-supported catalyst were comparable (86-90%) to commercially available Jacobsen catalyst (88%). Both soluble polymer-supported catalysts could be used twice before a decline in yield and enantioselectivity was observed. However, neither soluble polymer support proved as suitable as the insoluble JandaJel-supported (salen)-Mn complex for the epoxidation because residual impurities during precipitation and leaching of Mn from the complex, resulted in lowered yields. 

Since group 4 derived species are of particular interest as catalysts for olefin polymerization and epoxidation reactions, the thermal stability of surface metal-alkyl species, as weU as their reactivity towards water, alcohols and water, deserve some attention. On the other hand, mono(siloxy) metaUiydrocarbyl species can be converted into bis- or tris(siloxy)metal hydrides by reaction with hydrogen [16, 41, 46-48]. Such species are less susceptible to leaching and can be used as pre-catalysts for the hydrogenolysis of C-C bonds, alkane metathesis and, eventually, for epoxidation and other reactions. 

In the following sections, we describe the recent development of catalyst systems for epoxide polymerization, focusing on homopolymerization, (alternating) co-polymerization with CO or GO2 reported from 1993 to 2004. Although aluminum and zinc are not classified as transition metals, polymerization catalyst systems using those metals will be discussed since they greatly contribute to the field of epoxide polymerization. 

Ishimori,M., Nakasugi,0., Takeda,N, Tsuruta,T. Studies on organometallic compounds as polymerization catalysts. II. Diethylzinc/water system for epoxide polymerization. Makromol. Chem 115,103 (1968). 

Many different photoinitiators based on onium -type compounds with anions of low nucleophilicity also have been described in the literature as effective catalysts for the polymerization of epoxides Thus, diaryliodonium salts diaryliodosyl salts triarylsulfonium salts and related compoundstri-phenylsulfoxonium saltsdialkylphenacylsulfonium salts and dialkyl-4-hydroxyphenylsulfonium salts seem to be most suitable as photoinitiators for epoxy curing. Some of the principles of the reaction mechanism involving these initiators are discussed in detail in the following Sections. Various other onium photoinitiators such as diarylchloronium and diarylbromonium salts , thiopyrylium salts 3), triarylselenonium salts and onium salts of group Va elements >... 

Anionic polymerization of epoxides can be induced by Lewis bases (usually tertiary amines) or by metal hydroxides. The amine-type catalysts are by far the most Important type of catalyst for epoxide homopolymerization. The initiation of the polymerization of epoxides has been proposed by Narracott (15) and Newey (16) to result from the attack by the tertiary amine on the epoxide (Reaction 35), with the resulting alkoxlde amine being the propagating species (Reaction 36). 

The research focus of the Coates Group is the development of new catalysts for the synthesis of macromolecules as well as small molecules. Professor Coates research concentrates on developing new methods for reacting commodity feedstocks in unprecedented ways. His current research centers on the development of homogeneous catalysts for olefin polymerization, heterocyde carbonylation, epoxide homo- and copolymerization, and utilization of carbon dioxide in polymer synthesis. 

NFPA Health 3, Flammability 4, Reactivity 3 Uses Catalyst for Ziegler-Natta polymerization of olefins and dienes catalyst for epoxidation in organic synthesis synthesis of cyclopropanes and ketocarbenes in preservation of archival papers reactant in prod, of transition metal catalysts Manuf./Distrib. ABCR http //www.abcr.de, Acros Org. http //www.acros.be, Akzo Nobel http //www.akzonobel.com, Aldrich http //www.sigma-aldrich.com, FIuka http //www.sigma-aldrich. com Difenacoum CAS 56073-07-5... 

A new class of catalysts for the polymerization of 1,2-expox-ides was discovered in our laboratories and subsequently patented (l) in 1969. These catalysts consist of complexes containing hexacyanometalate salts. The composition of a typical catalyst can be represented as Zng [Co(CSr)g ]g 2.h(CH30CHaCI 0CH3)0.85ZnCl8 These complexes are unique as polymerization catalysts for 1,2-epoxides in two respects. First, they are not especially sensitive to the atmosphere and will retain their activity when stored at room temperature in a conventionally capped vial. 

The polymerization o oxetanes with cationic catalysts has been studied by many investigators. (1.H2) RoseC. ), in particular, first reported the homopolymerization of the parent compound, tri-methylene oxide (TMO), with a Lewis acid catalyst, boron trifluoride. The use of coordination catalysts to polymerize oxetanes has been reported in the patent literature by Vandenberg.W In this work, Vandenberg polymerized oxetanes with the aluminum trialkyl -water-acetylacetone coordination catalyst (referred to as chelate catalyst) that he discovered for epoxide polymerization . This paper describes the homo- and co-polymerization of TMO with these coordination catalysts. Specific TMO copolymers, particularly with unsaturated epoxides such as allyl glycidyl ether (AGE), are shown to provide the basis for a new family o polyether elastomers. These new elastomers are compared with the related propylene oxide-allyl glycidyl ether (PO-AGE) copolymer elastomers. The historical development and general characteristics of polyether elastomers and, in particular, the propylene oxide elastomers, are reviewed below. 

The first coordination epoxide polymerization catalytic system was reported by Pmitt and Baggett in 1955. It was based on iron tricbloride. Since that time, metal-based catalysts bave been widely exploited for epoxide polymerization. Tbe most studied systems are those based on zinc or aluminum derivatives. A first group consists of diethylzinc or trialkylaluminum associated to a cocatalyst, wbicb is generally water or an organic compound (alcohol, amine, and other compoimds) that reacts with the alkyl metal to form in situ new metal derivatives as the true catalytic system exploited (see Table 6). For a detailed review on the coordination polymerization of epoxides, see Kman. ... 

This means that the process is kinetically controlled and the growing centers are not blocked by the formation of partially crystalline polymer. A very important finding is that the effective activation energy is 7-8 kcal mol", which is much lower than the typical values 18-20 kcal mol" for epoxide polymerization processes. The low activation energy is apparently the main factor responsible for the efficiency of the Ca amide-modified catalysts. 

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