Supramolecular organometallic polymer chemistry: Multiple marphologies andsuperstructures from the solution self-assembly of polyferrocene-block-polysiloxane-block-polyferrocene triblock copolymers

The solution self-assemblv of an organometallic-inorganic triblock copolyme r, poly(ferrocenyldimethylsilane)-block-poly(dimethylsiloxane)-block-poly(f errocenyldimethylsilane) (PFDMS-b-PDMS-b-PFDMS. 3b: block ratio 1:13:1: M-n = 2.88 x 10(4) gmol(-1), polydispersity (PDL) = 1.43 (gel permeation chrom atography. GPC)) was studied in n-hexane, a PDMS block selective solvent. T ransmission electron microscopy (TEM). atomic force microscopy (AFM). and T EM with negative staining analysis of these micellar solutions after solven t evaporation revealed the presence of multiple micellar morphologies inclu ding spheres, cylinders, and novel newer-like supramolecular aggregates. TE M analysis of samples fractionated by ultracentrifugation and preparative s ize-exclusion chromatography suggest that the formation of multiple morphol ogies is a consequence of compositional variations. When micellar solutions were prepared at 50 degreesC (above the glass transition of the PFDMS core -forming block) flower-like micellar aggregates similar to those present in micellar solutions prepared at room temperature also formed. However. afte r solvent evaporation, TEM analysis of micellar solutions prepared in decan e at about 150 degreesC, above the melt temperature of the PFDMS core (ca. 120-145 degreesC), revealed the presence of spherical micelles (when decane solutions at 150 degreesC were rapidly cooled to room temperature) and rod -like cylindrical micelles (when decane solutions at 150 degreesC were slow ly cooled to room temperature). In contrast, poly(ferrocenylmethylethylsila ne)block-poly(dimethylsiloxane)-block-poly(ferrocenylmethylethylsilane) (PF MES-b-PDMS-b-PFMES, 4, block ratio 1:16:1; M-n = 2.90 x 10(4) g mol(-1), PD I = 1.42 (GPC)) and poly(ferrocenylmethylphenylsilane)-block-poly(dimethyls iloxane)-block-poly(ferrocenylmethylphenylsilane) (PFMPS-b-PDMS-b-PFMPS, 5: block ratio 1:15:1, M-n = 3.00 x 10(4) g mol(-1), PDI = 1.38 (GPC)), which possess completely amorphous organometallic core-forming blocks, formed on ly spherical micelles in hexane at room temperature. These observations ind icate that crystallinity of the insoluble polyferrocenylsilane block is a c ritical factor in the formation of the nonspherical micelle morphologies.