Synthesis and degradation of polymers containing polyacetal segments

Polymerizations which have relatively low polymerization enthalpy are characterized by a correspondingly low ceiling temperature. The ceiling temperature (Tc ) is the temperature at which the rate of polymerization is equal to the rate of depolymerization. Since the former is proportional to the monomer concentration whereas the latter is not, the ceiling temperature is monomer-concentrationdependent. Inversely, an equilibrium monomer concentration, M e , at different temperatures can be calculated from the thermodynamic parameters. The mathematical expression for M e is For cyclic monomers, the enthalpy of polymerization is determined by the ring-strain of the cycles. Therefore, a number of polymerizations of low strain cyclic monomers are characterized by low Tc s or high M e s. The corresponding pure polymers are thermodynamically unstable and tend to depolymerize until the M e , corresponding to the temperature used, is reached. This depolymerization, however, will occur only if the active species necessary for the establishment of the equilibrium are introduced in the polymer. This means that the polymer can be used in normal atmospheric conditions and may even show a relatively high thermal stability as long as the active species remain absent