Polymerization of BCMO in the Solid-State

BCMO can be polymerized in the solid state under the influence of ionizing radiation 23 25 . This is a handy method of preparing polymer directly from monomer, in the absence of solvent and initiators. Polymerizations proceed to limited conversions (maximum 15-20% was observed at temperatures just below the melting point Tm = 18.5 °C). The rate increases with increasing temperatures (up to the melting point), irradiation time, dose rate and the size of the monomer crystals. Molecular weights are relatively high, fn] = 0.5 dl/g (in cyclohexanone at 40 °C). 

It is generally accepted that the solid state polymerization of BCMO initiated with y-radiation proceeds by a cationic mechanism. Typical radical inhibitors affect neither the rate nor the final yield of polyBCMO. On the basis of the dependence of the polymer yield on the size of monomer crystals and the observed high degree of orientation in the polymers, it was originally suggested that the structure of the monomer crystal lattice directly imposes order and orientation upon the polymer 35 . 

Wegner, however, established that radiation-induced solid-state polymerization of BCMO leads to a polymer morphology, which is incompatible with the so-called topochemical polymerization, i.e., a process in which monomer molecules are transformed into polymer without destruction of the crystal lattice 36). Electron microscopy, X-ray analysis and electron diffraction studies, have shown that polymerization starts at the edges and imperfections of the monomer crystals and that amorphous polymer is formed initially. Further transition from the amorphous state leads to the thermodynamically unstable monoclinic p-form. Density measurements indicate that the polymer is only 45-50% crystalline. The density of the amorphous poly-BCMO is 1.368 g/cm3 the density calculated for the crystalline polymer from crystallographic data of the p-form is 1.456 g/cm3. The density of the product of the radiation-induced solid-state polymerization is 1.41 g/cm3 36). 

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Polymerization of BCMO in the solid state can also be induced by radiation 23 25) this subject is discussed separately. 

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