Trioxepane, polymer

The next structural study of polydioxolans of DP ranging from 7 to 70 by Plesch and Westermann [6] confirmed the regular structure of the polymer. It was also shown that when a polydioxolan was formed and then depolymerised in solution by perchloric acid, the only product was monomer. This is apparently in conflict with the findings of Miki, Higashimura, and Okamura [7] who reported that a reaction mixture, in which dioxolan had been polymerised for 3 hours at 35 °C by BF3-Et20, contained 1,3,5-trioxepan, 1,4-dioxane, trioxane, and other compounds. Most probably the difference is at least partly due to the long reaction time and the use of boronfluoride, which is well known to produce more side-reactions than protonic acids. 

Fig. 9. Kinetic curves of the reagents conversion in liquid-phase cationic copolymerization of formaldehyde with 1,3-dioxolane. 1) 1,3 dioxolane consumption 2) 1,3,5-trioxepane yield 3) yield of ethylene oxide units in copolymer 4) yield of soluble polymer...

An interesting system related to those discussed previously was investigated by Schulz et al.200, namely a cationic polymerization of trioxepane. This monomer may be treated as a cyclic co-polymer of ethylene oxide (E) and two molecules of formaldehyde (M)... 

Its cationic polymerization yields a living polymer terminated by -0=CH2 group, whereas the energetically improbable -OCH2CH2+ group is never formed. Electrophilic attack of the -0=CH2 on oxygens of trioxepane yields two kinds of terminal sequences, either... 

Since the two modes of addition are equally probable, the resulting polymer has a random structure with hetero-diads such as MEMEMM and EMMMEM as well as homodiads, viz. EMMEMM and MEMMEM. Its degradation may yield other monomers than trioxepane. The latter results from the reactions... 

Schulz studies of cationic trioxepane polymerization demonstrated that the system rapidly approaches a state in which the living polymers cease to grow while the concentrations of the three monomers, trioxepane, dioxolane, and formaldehyde approach some stationary values as illustrated by Fig. 12. 

The following treatment accounts for the behavior of this system204 Its final state is not that of equilibrium but rather of a stationary state. We could visualize a genuine equilibrium between each monomer and its living, perfectly uniform, high-molecular weight polymer. For example, the concentration of trioxepane in equilibrium with its living, uniform homo-polymer, i.e. 

The variations are due to polymeriza-D = EM jjon 0j trioxepane and the degradation F M of the resulting polymers into dioxolane and formaldehyde. Note the simultaneous approach to the final stationary state of the system... 

Note that the pseudo-equilibrium concentrations of the monomers depend on the composition of the polymer and therefore on the composition and concentration of the initial feed. For example, let us consider polymerization initiated in a solution of trioxepane having initial concentration Q. The stoichiometric balance requires... 

The detailed treatment of trioxepane polymerization serves to illustrate the complexities that could be encountered in living polymer systems and to outline the approaches helpful in unraveling the resulting problems. 

But as we found, in the gas chromatogramm of the reaction mixture, dioxolane too is formed during polymerization (see Fig.3). This fact explains the NMR-spectroscopic statement, that the polymer does not have the same composition as the monomer, but contains an excess of M-units. The concentration of dioxolane also reaches a final value, which increases with rising polymerization temperature (see Table 2). But this means, that the composition of polymer depends on temperature and approaches the theoretical value only at low polymerization temperature. The described results show, that in the polymerization of trioxepane... 

Figure 2. C-NMR spectrum of a polymer of trioxepane (CDCU 25, 2 MHz). (1) MEMEM (2) MMMEM (3) EMMEM (4) MMMMM (5) EMMMM (6) EMMME (7) MMEMM (8) kMEME, EMEMM.

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