| Abstract: | The preparation, fractionation and characterisation of synthetic cyclic polysiloxanes (R(CH3)SiO)x are reviewed. Particular emphasis is given to the cyclic poly(dimethylsiloxanes) (PDMS) (R is CH3) cyclic poly(phenylmethylsiloxanes)(PPMS) (R is C6H5) and cyclic poly(vinylmethylsiloxanes) (PVMS) (R is CH2=CH). The application of high performance liquid chromatography (HPLC) and analytical and preparative gel permeation chromatography (GPC) to the preparation and characterisation of cyclic polysiloxanes is discussed. The methods include preparation of sharp fractions of relatively high molar mass cyclic polymers (with heterogeneity indices typically ca. 1.05) and comparison of the GPC and retention volumes of cyclics with the corresponding linear polymers. Investigations of the cyclic polymers prepared have been made using a number of experimental methods and techniques. These include dilute solution viscometry and low angle neutron scattering. Comparisons are drawn between cyclic PDMS and other cyclic polysiloxanes and also between cyclic polysiloxanes and the corresponding commercially-important linear polymers. |
