Equilibria in living Poly-Trioxepane System

In conclusion, a conversion of a cyclic monomer into a living linear polymer is thermodynamically allowed, provided that the reaction reduces the free energy of the system. However, the ultimate state of equilibrium corresponds to a mixture of cyclic oligomers and living linear polymers in appropriate proportion. 

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 

The first sequence is briefly denoted as -MEMM+ second, as -MMEM+. Both are approximately equally probable because the statistical factor of 2 due to the presence of two identical oxygens (1 and 5) is balanced by the factor of 2 arising from the availability of two equivalent modes of opening acetal bonds following the attack on oxygen 3. 

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 

---