Propylene oxide anionic polymerization

Propylene oxide and other epoxides polymerize by ring opening to form polyether stmctures. Either the methine, CH—O, or the methylene, CH2—O, bonds ate broken in this reaction. If the epoxide is unsymmetrical (as is PO) then three regioisomers are possible head-to-tad (H—T), head-to-head (H—H), and tad-to-tad (T—T) dyads, ie, two monomer units shown as a sequence. The anionic and... 

Fig. 2. Reaction scheme for the anionic polymerization of propylene oxide.

Polymerization to Polyether Polyols. The addition polymerization of propylene oxide to form polyether polyols is very important commercially. Polyols are made by addition of epoxides to initiators, ie, compounds that contain an active hydrogen, such as alcohols or amines. The polymerization occurs with either anionic (base) or cationic (acidic) catalysis. The base catalysis is preferred commercially (25,27). 

Anionic polymerization of alkylene sulfides was extensively studied by Sigwalt and collaborators. In contrast to propylene oxide, anionic polymerization of pro-... 

The range of monomers that can be incorporated into block copolymers by the living anionic route includes not only the carbon-carbon double-bond monomers susceptible to anionic polymerization but also certain cyclic monomers, such as ethylene oxide, propylene sulfide, lactams, lactones, and cyclic siloxanes (Chap. 7). Thus one can synthesize block copolymers involving each of the two types of monomers. Some of these combinations require an appropriate adjustment of the propagating center prior to the addition of the cyclic monomer. For example, carbanions from monomers such as styrene or methyl methacrylate are not sufficiently nucleophilic to polymerize lactones. The block copolymer with a lactone can be synthesized if one adds a small amount of ethylene oxide to the living polystyryl system to convert propagating centers to alkoxide ions prior to adding the lactone monomer. 

The anionic polymerization of epoxides such as ethylene and propylene oxides can be initiated by metal hydroxides, alkoxides, oxides, and amides as well as metal alkyls and aryls, including radical-anion species such as sodium naphthalene [Boileau, 1989 Dreyfuss and Drefyfuss, 1976 Inoue and Aida, 1984 Ishii and Sakai, 1969]. Thus the polymerization of ethylene oxide by M+A involves initiation... 

Excluding polymerizations with anionic coordination initiators, the polymer molecular weights are low for anionic polymerizations of propylene oxide (<6000) [Clinton and Matlock, 1986 Boileau, 1989 Gagnon, 1986 Ishii and Sakai, 1969 Sepulchre et al., 1979]. Polymerization is severely limited by chain transfer to monomer. This involves proton abstraction from the methyl group attached to the epoxide ring followed by rapid ring cleavage to form the allyl alkoxide anion VII, which isomerizes partially to the enolate anion VIII. Species VII and VIII reinitiate polymerization of propylene oxide as evidenced... 

Anionic polymerization of propylene oxide is usually limited to producing a relatively low-molecular-weight polymer. Discuss the reasons for this occurrence. 

Polyethers are prepared by the ring opening polymerization of three, four, five, seven, and higher member cyclic ethers. Polyalkylene oxides from ethylene or propylene oxide and from epichlorohydrin are the most common commercial materials. They seem to be the most reactive alkylene oxides and can be polymerized by cationic, anionic, and coordinated nucleophilic mechanisms. For example, ethylene oxide is polymerized by an alkaline catalyst to generate a living polymer in Figure 1.1. Upon addition of a second alkylene oxide monomer, it is possible to produce a block copolymer (Fig. 1.2). 

Monomers devoid of polar groups generally undergo anionic polymerization in a predictable manner. With polar monomers sometimes side reactions occur during the process transfer reactions in the case of acrylonitrile, or propylene oxide, and even more so with alkylacrylates deactivations (or "killing") reactions in the case of halogen substituted styrene or dienes. 

These ligands form extremely stable cation inclusion complexes, called cryptates, In which the cation Is completely surrounded by the ligand and hidden Inside the molecular cavity, and this leads to a considerable Increase of the interionic distance In the ion pairs. It has been shown that such ligands have a marked activating effect on anionic polymerizations (4,5,6). Moreover, the aggregates are destroyed and simple kinetic results have been obtained In the case of propylene sulfide (7,8,9). ethylene oxide (9,10,11) and cycloelloxanes (12) polymerizations. Though the... 

In conclusion, it has been shown that use of cryptates for the anionic polymerization of heterocyclic monomers leatis to a tremendous increase of the rates of polymerization. There are two main causes to the higher reaction rates observed with cryptates. The first one is a suppression of the association between ion pairs in the non polar media, and the second one is the possibility of ion pairs dissociation into free ions in ethereal solvents like THP or THF. By this way, it has been possible to make detailed studies of the propagation reaction for propylene sulfide, ethylene oxide, and cycloslloxanes. 

Synthetic methods have limited the preparation of saturated perfluoropolyethers. The most successful perfluoropolyether synthetic chemistry has been DuPont s anionic polymerization of perfluoroepoxides, particularly hexafluoro-propylene oxide and tetrafluoroethylene oxide (39). Their synthetic procedure is a three-step scheme for saturated perfluoropolyether production involving oxidation of perfluoroolefins to perfluoroepoxides, anionic polymerization to acyl fluoride terminated perfluoropolyethers, and conversion of acyl fluoride end groups to unreactive end groups by decarboxylation reactions or chaincoupling photolytic decarboxylate reactions. 

Initiators -for acrylamide [ACRYLAMIDE POLYMERS] (Vol 1) -anionic initiators [INITIATORS - ANIONIC INITIATORS] (Voll4) -cationic initiators [INITIATORS - CATIONIC INITIATORS] (Vol 14) -in emulsion polymerization [LATEX TECHNOLOGY] (Vol 15) -for fluorocarbon elastomers [ELASTOMERS, SYNTHETIC - FLUOROCARBON ELASTOMERS] (Vol 8) -Free-radical initiators [INITIATORS - FREE-RADICAL INITIATORS] (Voll4) -organohthium compounds as [LITHIUM AND LITHIUM COMPOUNDS] (Vol 15) -peroxides as [PEROXIDES AND PEROXIDE COMPOUNDS - INORGANIC PEROXIDES] (Vol 18) -for propylene oxide [PROPYLENE OXIDE] (Vol 20) -for PUR polyols [POLYETHERS - PROPYLENE OXIDE POLYMERS] (Vol 19) -of suspension polymerization [ACRYLIC ESTER POLYMERS - SURVEY] (Vol 1)... 

The ring-opening polymerization of cyclic monomers can be performed by ionic chain polymerization, as is the case of epoxy monomers. Anionic polymerization of ethylene oxide propylene oxide, and caprolactone can be initiated by alkoxides ... 

Graft copolymer, polyclhylene-gra/f-poly(propylcnc oxide) (PE-g-PPG), has been synthesized by ring opening anionic polymerization of propylene oxide with a phosphazene catalyst and hydroxylated polyethylene (Mn = 12400, [OH] = 5 units/chain). Polymerization of propylene oxide was carried out in tetraline at 120 °C for 20 hours. The 13C NMR analysis of PE-g-PPG suggested that all the hydroxyl groups were consumed for propylene oxide polymerization (Fig. 6). 

Other important examples of ring-opening polymerizations are the synthesis of polyethylene oxide and the block copolymer of ethylene oxide and propylene oxide. Polyethylene oxide, also known as polyethylene glycol (PEG), is commonly produced by anionic polymerization and has a low molecular weight of less than 20,000. 

In the polyurethane industry, the polymeric glycols are prepared by anionic polymerization of epoxides such as ethylene oxide and propylene oxide. Poly(tetra-methylene glycol), which was prepared by polymerization of tetrahydrofuran, was subjected to chain extension by reaction with diisocyanate (polyurethane formation) and with dimethyl terephthalate (polyester by alcoholysis). 

Hence, in conclusion, studies on the oxidation of PC solutions clearly differentiate between LiC104 solutions and other salt solutions. It is clear that C104 oxidation occurs in parallel to solvent oxidation, and the latter is accelerated by anion oxidation. Obvious products obtained from PC oxidation are C02 and polymeric species, probably derivatives of poly(propylene oxide). In the case of BF4 or PF6 salts, the oxidation products also include fluorinated derivatives of... 

Polyether polyols are prepared by the anionic polymerization of alkylene oxides, such as propylene oxide and/or ethylene oxide, in the presence of an initiator and a catalyst, as shown in the following equation ... 

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. 

Poly(propylene oxide) is typically obtained by base catalyzed anionic polymerization of propylene oxide [12]. Both stereospecific and atactic forms are known. The polymer is used as a soft polyether unit in polyurethane elastomers and foams in polymer electrolytes as surfactants (lubricants, dispersants, antistatic agents, foam control agents) in printing inks, as solubilizers in hydraulic fluids, coolant compositions in various medical applications (protective bandages, drug delivery systems, organ preservation, dental compositions), etc. 

Side Reactions in the Anionic Polymerization of Propylene Oxide... 

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