Tacticity of Polypropylene Oxide

Uryu and Alyiiruk [113] have shown that PPO can be fractionally crystallised from dilute isooctane solutions, into fractions differing in stereoregularity. They also present some experimental data on the C-NMR spectra of these fractions. 

Fractionation was achieved by crystallisation from 2 litres of isooctane solution (1 g/1) at 27 °C by lowering the temperatnre incrementally to 0 °C. At each precipitation step the temperature of the system, Tp, was kept constant for 48 hours prior to isolation of the precipitated polymer. The supernatant was filtered through a glass-wool pad. 

DSC data T bulk melting temperature measured by DSC Reproduced with permission from N. Uryu and K. Alyiiruk, Journal of Polymer  

During the filtration precautions were taken to keep the temperature at Tp. K polymers are insoluble in isooctane, D polymers are soluble in isooctane. 

The precipitate was collected and dissolved in benzene and filtered. Prior to freeze drying (except for a small portion of the solution, which was reserved for C-NMR characterisation), antioxidant was added. Although each fraction should be defined by a temperature range, lying between the initial temperature of the solution T and Tp since the upper limit T, of each fraction coincides with the crystallisation temperature Tp of the preceeding fraction, only Tp values are given in Table 8.6 which shows typical results obtained in a fractionation of PPO. 

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