Self-assembly of organometallic block copolymers: The role of crystallinity of the core-forming polyferrocene block in the micellar morphologies formed by poly(ferrocenylsilane-b-dimethylsiloxane) in n-alkane solvents

The organometallic-inorganic diblock copolymer poly(ferrocenyldimethylsilan e-b-dimethylsiloxane) (PFDMS-b-PDMS) with a 1:6 block ratio unexpectedly fo rms:long rodlike micelles rather than spherical structures in a variety of PDMS-selective n-alkane solvents when the solutions are prepared:at. or nea r ambient; temperature. The cylindrical structures represent the thermodyna mically preferred morphology and consist of an iron-rich PFDMS core and a c orona of PDMS. The length of the micelles can be varied from 70 nm to 10 mu m by altering the method of sample preparation. In addition; the dimensions of the micellar core can be controlled through variations in the length of the PFDMS block,which is achieved by altering the molecular weight of the diblock copolymer while maintaining a constant block ratio. In contrast, wh en micelles are formed above the T-m of PFDMS (ca. 120-145 degreesC), spher ical aggregates are formed, which suggests that crystallization of the core polymer is the driving force for the formation; of wormlike micelles below T-m,. Furthermore, the analogues with amorphous polyferrocene blocks, poly (ferrocenylmethylphenylsilane-b-dimethylsiloxane) (PFMPS-b-PDMS) and poly(f errocenylmethylethylsilane-b-dimethylsiloxane) (PFMES-b-PDMS), form spheric al micelles in hexane at room temperature. This lends further support to th e proposition that the crystalline nature of the PFDMS block plays a pivota l role in the unexpected formation of cylindrical micelles. To provide an a pplication of this concept, an analogous PFDMS block copolymer With polyiso prene, PI-b-PFDMS, was prepared and, as predicted, was found to form cylind rical micelles in hexane.