Oxepane polymerization

How do the rates of oxepane polymerization compare to those of oxetane and tetrahydrofuran What affects these rates ... 

T. K. Wu The largest ring used so far was oxepane, but we are planning to go in the other direction, using four membered rings. However, in this case complications arise because the strained oxetane ring does not undergo equilibrium polymerization. 

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

Polymerization is frequently observed as a side reaction in acid-catalyzed reactions, and under appropriate conditions many oxetanes can be quantitatively transformed into high molecular weight linear polyethers with useful properties. Polymerization is very general for oxetanes and is closely related to Lewis acid-catalyzed polymerization of oxiranes, THF and oxepane, but oxetanes generally polymerize much more rapidly than THF and oxepane and at a rate similar to oxiranes (72MI51300). 

The polymerization kinetics of alkali salts of living vinyl polymers In ethereal solvents, such as tetrahydrofuran CD, tetrahydropyran (2), dlmethoxyethane Q), oxepane (4) and dloxane... 

The A-B di-block copolymer of -CL and oxepan-2,7-dione has been synthesized using aluminum isopropoxide as initiator [114] (Scheme 16). In order to prepare the ABA tri-block copolymer, a difunctional initiator [Et2AlO(CH2)4OAlEt2] was used to polymerize B followed by the addition of monomer A. However, the rate of polymerization was lower than in the Al(0 Pr)3-initiated system. Increasing the temperature to 70 °C increased the rate but a broadening of MWD was observed due to intramolecular back-biting reactions and intermolecular transesterification reactions. The addition of 1 equiv. of pyridine with respect to Al increased the polymerization rate and reduced the MWD from 1.95 to 1.25 [95]. 

Cyclic ethers of various ring size polymerize by cationic mechanism, including oxiranes (3-membered), oxetanes (4-membered), oxolanes (5-membered), oxepanes (7-membered), and larger rings. Six-membered cyclic ethers do not polymerize because of the thermodynamic restrictions. Oxiranes may be also polymerized by anionic mechanism, whereas for other groups the cationic polymerization is the only mechanism of polymerization. 

NMR studies of the polymerization of THF, oxepane, 3,3-dimethylthietane, 2-methoxy-2-oxo-l,3,2-dioxaphosphorinane and 2-methyl-2-oxazoline revealed that the structures of the growing qj ies are the corresponding onium ions these structures are given in Table 7 (earlier, the first reaction products, formed upon initiation, were observed in the polymerization of THF ). 

The polymerization of oxepane has provided very simflar results , Goethals has observed that in the polymerization of 3,3-dimethylthietane k, is also larger in CH2CI2 than in C6HsN02 >. 

More recently, the application of H-NMR confirmed that in the polymerization of oxepane the transfer to pobmiei (reaction (81)) has no kinetic importance ). There is, however, no evidence that in the polymerization of other cydic ethers, particularly more strained ones like oxe-tane and 3,3-dimethyloxetane, a portion of tertiary oxonium ions is not in the form of the dormant , non-reactive spedes. A few papers have reported the formation of larger rings, apparently by unimolecular back-biting, which may reduce the concentration of active spedes and eventually give wrong values of kp , if the method used for the determination of [P ] does not discriminate between two kinds of oxonium ions given in Eq. (81). 

Fig. 14. The propagation step in the polymerization of styrene (counter-ion, sodium). Variation of fegpp mole" sec" ) with inverse square root of concentration of active centres. Solvents ( ) tetrahydrofuran 25°C [16] (O) tetrahydropyran 30°C [106] (A) oxepane 30°C [105] ( ) dioxane 25°C [104].

Fig. 17. Variation of ion-pair propagation coefficients, fep, with temperature in styrene polymerization (counter-ion, sodium). Solvents ( ) oxepane [105] ( ) tetrahydropyran [116] (o) tetrahydrofuran [111] ( ) tetrahydrofuran [110] ( ) dimethoxyethane [112] ( ) dimethoxyethane [110]. More data are now available over a wider range of experimental conditions, see ref. 233.

Kinetic parameters for ring-opening polymerization of oxepane" [118]... 

More recent results indicate that in the polymerization of the 7-membered cyclic ether oxepane (Ox), both intra- and intermolecular ionizations have to be... 

Processes that do not terminate were described for the polymerization of five- and seven-membered cyclic ethers THF (4, 91) and oxepane (93). Under proper working conditions both cyclic acetals, namely 1,3-dioxolane and 1,3-dioxepane (94. 95). as well as bicyclic acetals or 1,6-anhydro-l,3,4-tri-0-benzyl-a-D-glucopyranose (96) can polymerize under living conditions. 

Various other 1,6-anhydro sugars have been polymerized to relatively high-mole-cular-weight polysaccharides. All of them contain fused 1,3-dioxolane (0,1,0,5,6), oxane (tetrahydropyran (0,1,2,3,4,5) and oxepane (0,1,2,3,4,5,6) rings and differ only by the configuration on carbons 2,3 and 4 ... 

---