Ethers, polymeric

Lithium hexafluoroarsenate is thermally stable [54, 55] but shows environmental risks due to possible degradation products [56-58], even though it is itself not very toxic. Its LD 50 value is similar to that of lithium perchlorate [55]. Just like lithium hexafluorophosphate, it can initiate the polymerization of cyclic ethers. Polymerization may be inhibited by tertiary amines [59], or 2-methylfuran [60], yielding highly stable electrolytes. 

A special case of the internal stabilization of a cationic chain end is the intramolecular solvation of the cationic centre. This can proceed with the assistance of suitable substituents at the polymeric backbone which possess donor ability (for instance methoxy groups 109)). This stabilization can lead to an increase in molecular weight and to a decrease in non-uniformity of the products. The two effects named above were obtained during the transition from vinyl ethers U0) to the cis-l,2-dimethoxy ethylene (DME)1U). An intramolecular stabilization is discussed for the case of vinyl ether polymerization by assuming a six-membered cyclic oxonium ion 2) as well as for the case of cationic polymerization of oxygen heterocycles112). Contrary to normal vinyl ethers, DME can form 5- and 7-membe red cyclic intermediates beside 6-membered ringsIl2). 

The second part of the theory, which is a logical consequence of the first, is that monomers that have more than one basic site, e.g., an aromatic ring or an oxygen atom, can form more than one type of complex with the carbenium ion this idea was first proposed by Plesch (1990) in the context of chemically initiated polymerizations. It helps to explain why aryl alkenes and alkyl vinyl ethers polymerize more slowly than isobutene and cyclopentadiene. The reason is that all the complexes formed by the alkyl alkenes are propagators, whereas for the aryl alkenes and vinyl ethers only a fraction of the population of complexes can propagate. 

Kinetic Data. Let us now consider the kinetics of a reversible cyclic ether polymerization. For such a polymerization in... 

Kinetic Analysis of Cyclic Ether Polymerization by Fourier Transform NMR ... 

Cationic photoinitiators are used in coatings, printing inks, adhesives, sealants, and photoresist applications. Most of the applications involve vinyl ether polymerizations or ringopening polymerizations of epoxy monomers (Sec. 7-2b). 

Transfer and termination occur by the modes described previously for cyclic ether polymerizations. Chain transfer to polymer (both inter- and intramolecular) is facilitated in cyclic acetal polymerizations compared to cyclic ethers because acetal oxygens in the polymer chain are more basic than the corresponding ether oxygens [Penczek and Kubisa, 1989a,b]. Working at high monomer concentrations, especially bulk polymerizations, is used to depress cyclic oligomer formation. 

The initiator used is important for copolymerizations between monomers containing different polymerizing functional groups. Basic differences in the propagating centers (oxonium ion, amide anion, carbocation, etc.) for different types of monomer preclude some copolymerizations. Even when two different monomer types undergo polymerization with similar propagating centers, there may not be complete compatibility in the two crossover reactions. For example, oxonium ions initiate cyclic amine polymerization, but ammonium ions do not initiate cyclic ether polymerization [Kubisa, 1996]. 

Tetrahydrofuran, a five-member cyclic ether, polymerizes cationically to yield an elastomeric polymer [28]. Oxepane, a seven-member analog, polymerizes to a crystalline polymer. 

Fig. 9. Kinetic curves of phenylglycidyl ether polymerization in chlorobenzene solution under the action of dimethylbenzylamine and in the presence of isopropyl alcohol at 343 K 14). 1 E0 = A3 0 = 1.75 mol r, 2H0 = 0. The introduction of fresh monomer is shown by an arrow...

The structure of the epoxy polymers formed in the curing process has been thoroughly investigated using phenylglycidyl ether polymerization as an example. 

Fig. 10. Kinetic curves of phenylglycidyl ether polymerization (7.0 mol I-1) under the action of dimethylbenzylamine (0.25 mol 1 ) in the presence of isopropyl alcohol (0.25 mol I"1) and in the accumulation of hydroxyl and vinyl groups in the system at 353 K 149 1501...

Fig. 11. Kinetic curve of phem Iglycidyl ether polymerization in solution of chlorobenzene at 343 K (1) (E0 = Ho = 1.75 mol I-1, A30 = 0.25 moll 1) and the change of the relative rate (2) and conductivity (3) of the system during the process 4I. The symbols are the same as in Fig. 9...

Fig. 12. Kinetic curve of phenylglycidyl ether polymerization (see Fig. 10) according to eq. (35) 141...

Fig. 14. Kinetic curves of phenylglycidyl ether polymerization (6.67 mol I-1) under the action of dimethylamine (0.66 moll-1) at 343 K. 1 Pure (chromatography grade) undried phenylglycidyl ether, 2 dried with calcium hydride and dosed in dry argon, 3 precision drying and purification of the reagents in the reaction vessels, reagent dosed in vacuo 1+91...

In the past few years the use of aluminum alkyls as catalysts for cyclic ether polymerizations has received much attention. Two different mechanisms have been proposed to explain the catalytic activity of the aluminum alkyl catalysts. Saegusa, Imai, and Furukawa (75) suggest that a cationic mechanism is produced. They feel it is not related to the coordinate anionic mechanism presumed to take place with related catalyst systems used for aldehydes and epoxides. They propose that the Lewis acid first reacts with adventitious water to form a Bronsted acid. ... 

Enantiomer selection is also found in vinyl ether polymerization [226,227], The polymerization of cis- and trans- 1-methylpropyl propenyl ethers using (-)-menthoxyaluminum dichloride [227] and the copolymerization of rac- 1-methylpropyl vinyl ether with optically active monomers [226] are enantiomer selective. 

Miscible with water, alcohol, and ether. Polymerizes.1... 

The copolymerization of trioxane with cyclic ethers or formals is accomplished with cationic initiators such as boron trifluoride dibutyl etherate. Polymerization by ring opening of the six-membered ring to form high molecular weight polymer does not commence immediately upon mixing monomer and initiator. Usually, an induction period is observed during which an equilibrium concentration of formaldehyde is produced. 

Recently Vandenberg (189) published additional information on vinyl ether polymerizations with Ziegler type catalysts. Details of the catalyst preparations, polymerization conditions and polymer characterization were presented together with an excellent discussion of mechanism. 

Table 5. Comparison of Different Catalysts for Vinyl lsobutyl Ether Polymerization...

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