Oxirane polymerization catalyst

Five-coordinate aluminum alkyls are useful as oxirane-polymerization catalysts. Controlled polymerization of lactones102 and lactides103 has been achieved with Schiff base aluminum alkyl complexes. Ketiminate-based five-coordinate aluminum alkyl (OCMeCHCMeNAr)AlEt2 were found to be active catalyst for the ring-opening polymerization of -caprolactone.88 Salen aluminum alkyls have also been found to be active catalysts for the preparation of ethylene carbonate from sc C02 and ethylene oxide.1 4 Their catalytic activity is markedly enhanced in the presence of a Lewis base or a quaternary salt. 

Many group 13 compounds have been prepared with porphyrins. The majority of these compounds were created to serve as models for the active sites of enzymes, such as cytochrome c oxidase. Additionally, the gallium compounds are more robust than their iron counterparts. To a much lesser extent the Por-AlX compounds are used as oxirane polymerization catalysts [8]. 

In the three-membered heterocycles, the oxiranes, polymerization has been induced with basic catalysts. Usually, these polymerizations are slow, and the polymers formed are of relatively low molecular weight. Certain, specially prepared carbonates and amides of calcium constitute a limited exception to this generalization, as they allow the formation of a solid polymer from ethylene oxide. 

Tsuruta, T. Molecular level approach to the origin of the steric control in organozinc catalyst for oxirane polymerization. Makromol. Chem., Macromol. Symp. 1986,6, 23-31. 

The main representatives of multinuclear catalysts for oxirane polymerization are Al and Zn compounds, which are characterized by moderate nucleophilicity and relatively high Lewis acidity. The appropriate Lewis acidity of the metal and the appropriate nucleophilicity of the metal substituent in these catalysts make monomer coordination preferable to the... 

The oxirane ring-opening reaction requires the presence of a basic catalyst. An acidic catalyst also works, but the polymerization of the oxirane limits its usehilness. In the case of 2-mercaptoethanol (eq. 8), the product has been found to be autocatalytic, ie, the product is a catalyst for the reaction. 

Besides direct hydrolysis, heterometaHic oxoalkoxides may be produced by ester elimination from a mixture of a metal alkoxide and the acetate of another metal. In addition to their use in the preparation of ceramic materials, bimetallic oxoalkoxides having the general formula (RO) MOM OM(OR) where M is Ti or Al, is a bivalent metal (such as Mn, Co, Ni, and Zn), is 3 or 4, and R is Pr or Bu, are being evaluated as catalysts for polymerization of heterocychc monomers, such as lactones, oxiranes, and epoxides. An excellent review of metal oxoalkoxides has been pubUshed (571). 

The living polymerization of lactones, oxiranes, and thiiranes became also possible by improved preparation of the Al—Zn oxyalkoxides. These catalysts were first studied by Tsuruta 6) and by Vanderberg 7), and later by Teyssie 8 b). 

Lipase-catalyzed synthesis of polyesters from cyclic anhydrides and oxi-ranes was reported. The polymerization took place by PPL catalyst and the molecular weight reached 1 x 10" under the selected reaction conditions. During the polymerizahon, the enzymatically formed acid group from the anhydride may open the oxirane ring to give a glycol, which is then reacted with the anhydride or acid by lipase catalysis, yielding the polyesters. 

Organotin compounds with the general formulae RSnX3, R2SnX2, R3SnX and RSnOOH (R = alkyl or aryl and X = Cl, Br or J) are efficient catalysts for the polymerization of oxiranes 73). 

Equation 1 expresses a state of equilibrium between an alcohol A. on a molecule whose degree of polymerization is j, the catalyst C and the alkoxide anion A.C. In Relation 2 this activated intermediate reacts with monomeric anhydride A, forming an acid adduct A.AC, which dissociates, forming an unassociable carboxylic acid A.A. Reactions 3-5 depict the union of a carboxylic intermediate with a monomeric epoxide E, or with pendant oxiranes on macromole- ... 

Polymerization of oxiranes with succinic anhydride proceeded in the presence of PPL at 60 °C or 80 °C [63]. The ring-opening of the oxirane might proceed by a carboxylic acid catalyst, which is formed by the reaction of succinic anhydride with serine residue of the lipase catalyst. 

Martin E, Dubois P, Jerome R (2003) Preparation of supported yttrium alkoxides as catalysts for the polymerization of lactones and oxirane. J Polym Sci A Polym Chem 41 569-578... 

Early-on it was discovered that these Salen compounds, and the related six-coordinate cations [6], were useful as catalysts for the polymerization of oxiranes. These applications were anticipated in the efforts of Spassky [7] and in the substantial work of Inoue [8]. Subsequently, applications of these compounds in organic synthesis have been developed [9]. Additional applications include their use in catalytic lactide polymerization [10], lactone oligomerization [11], the phospho-aldol reaction [12], and as an initiator in methyl methacrylate polymerization [13]. 

The relative rates of oxirane ethanolysis with acid and basic catalysts are summarized in Table 9. It can be seen that the relative reactivity of the monomer in cationic polymerization is controlled by the basicity of the cyclic ether. 

Most polymerizations of cyclic monomers are ionic processes. Coordination catalysts are effective only for some heterocycles (oxirane and its derivatives, lactones). Ziegler-Natta catalysts can only be used for cycloalkene polymerization by metathesis heterocycles act as a catalytic poison. Smooth radical polymerization of hydrocarbon monomers with ring strain is unsuccessful [304], The deep-rooted faith that ring strain represents a major contribution to the driving force in ring opening (polymerization) has to be revised [305, 306]. 

The following mechanism of polymerization was proposed platinum catalyst is reduced by Si-H compound to platinum colloid, which activates another molecule of Si-H compound and facilitates a nucleophilic attack of oxygen atom in the monomer on silicon atom (e.g., for substituted oxirane) ... 

As discussed already for cationic polymerization of oxiranes, cycliza-tion can be eliminated if polymerization is performed under the conditions at which the activated monomer mechanism operates. This approach was used for cationic polymerization of e-caprolactone and other higher lactones [191]. Thus, in the polymerization of e-caprolactone in the presence of ethylene glycol (EG) and (C2Hs)30 +, PF6- catalyst, linear increase of molecular weight with conversion was observed up to M 3000 and polymers with DP = [M]o/[EG]0 and relatively narrow molecular weight distribution (MJM 1.3) were obtained. No cyclic oligomers were detected in reaction products. Similar results were obtained for polymerization of 5-valerolactone and j8-butyrolactone. Kinetic studies of the AM polymerization of lactones have been reported [192]. 

Cationic polymerization is induced by Lewis acid catalysts. This type is mainly used in connection with higher cyclic ethers, since oxiranes produce only low-molecular-weight polymers. The propagation step is illustrated in Eq. 398. 

There are various procedures for the preparation of polyethers. These procedures typically start with oxirane or oxirane derivatives (e.g. propylene oxide, etc.). Base catalyzed anionic polymerization, acid initiation, or complex coordination catalysis can be used for the reaction [1-3], Not only oxiranes can generate polyethers. Diols also can be used for polyether synthesis. Other source compounds include tetrahydrofuran, which can be polymerized to a polyether using fluorosulfonic acid (HSO3F) as a catalyst, oxetane (trimethylene oxide) or oxetane derivatives, which can be polymerized to generate polyethers with practical applications such as poly[bis(chloromethyl)oxetane], etc. 

It is widely recognized that Et Zn-H O system is one of the most active catalysts for the stereospecific polymerization of oxiranes. A variety of chemical species are formed in the following way rapid formation of ethylzinc hydroxide, its aggregation, and elimination of ethane to form zinc oxide structure. The maximum catalyst activity was achieved when the mole ratio of zinc to water was one to one, where the predominant formation of a species, Et(ZnO) H, (III), was observed. If we use less amount of water, another species, Et(ZnO) ZnEt, (IV), was also produced concurrently. Contrary to the anionic nature of the former species (III), the latter species (IV) exhibited a cationic nature. For instance, more than 957o of ring cleavage of methyloxirane takes place at O-CH bond with species (III), while the cleavage at 0-CH bond also takes place concurrently with species (IV). 

When racemic methyloxirane is polymerized with zinc dimethoxide, D-and L-monomers are separately incorporated into growing chains to form an isotactic polymer consisting of poly(D-methyl-oxirane) and poly(L-methyloxirane). This stereoselective polymerization can be satisfactorily explained in terms of the enantio-morphic catalyst sites model (1 ). The d -sites accept D-methyl-oxirane in preference to the L-monomer, resulting in the formation of -DDDD- isotactic sequences. The same situation is valid for the l -catalyst sites. 

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