SYNTHESIS AND CHARACTERIZATION OF NARROW MOLECULAR-WEIGHT DISTRIBUTION POLYSTYRENE POLY(DIMETHYLSILOXANE) MACROCYCLIC BLOCK-COPOLYMERS AND THEIR ISOBARIC PRECURSORS

The first synthesis of a well-defined and monodisperse macrocyclic polystyrene (PS)-poly-(dimethylsiloxane) (PDMS) block copolymer is reported. The two-ended linear PDMS-b-PS-b-PDMS precursor is prepared through initiation of styrene by lithium naphthalenide in THF at -78-degrees-C, followed by addition of hexamethylcyclotrisiloxane (D3) to the LiPSLi. The cyclization is carried out by reaction with dichlorodimethylsilane at high dilution. For higher MW linear precursors, side reactions were observed but could be prevented by capping the highly reactive LiPSLi with 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane (EDS) followed by addition of D3. The macrocyclic PS-PEDS-PDMS-PEDS tetrablock copolymer is synthesized in a similar manner. Both macrocyclic block copolymers and their linear precursors are characterized by SEC and NMR. In addition to smaller (17-31%) hydrodynamic volumes observed by SEC, distinct differences between a macrocyclic and its linear block copolymer are shown by proton, C-13, and Si-29 NMR.