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(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFDMS-b-PDMS) with a 1:6 block ratio unexpectedly forms:long rodlike micelles rather than spherical structures in a variety of PDMS-selective n-alkane solvents when the solutions are prepared:at. or near ambient; temperature. The cylindrical structures represent the thermodynamically preferred morphology and consist of an iron-rich PFDMS core and a corona of PDMS. The length of the micelles can be varied from 70 nm to 10 mum 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, when micelles are formed above the T-m of PFDMS (ca. 120-145 degreesC), spherical 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(ferrocenylmethylethylsilane-b-dimethylsiloxane) (PFMES-b-PDMS), form spherical micelles in hexane at room temperature. This lends further support to the proposition that the crystalline nature of the PFDMS block plays a pivotal role in the unexpected formation of cylindrical micelles. To provide an application of this concept, an analogous PFDMS block copolymer With polyisoprene, PI-b-PFDMS, was prepared and, as predicted, was found to form cylindrical micelles in hexane.