Synthesis and solution self-assembly of coil-crystalline-coil polyferrocenylphosphine-b-polyferrocenylsilane-b-polysiloxane triblock copolymers

A series of well-defined coil-crystalline-coil PFP-b-PFS-b-PDMS triblock copolymers (PFP = poly(ferrocenylphenylphosphine), PIPS = poly(ferrocenyldimethylsilane), and PDMS = poly(dimethylsiloxane)) of narrow polydispersity (PDI 1.04-1.06) with short PFP blocks of variable length and PFS: PDMS ratios of ca. 1:5-1:12 were prepared by sequential anionic ring-opening polymerization of the [1]phosphaferrocenophane fcPPh (fc = Fe(eta-C5H4)(2)), the [1]silaferrocenophane fcSiMe(2), and the cyclic siloxane [Me2SiO](3). Hexane is a selective solvent for PDMS in these ABC triblock copolymers. In the case of the very short PFP blocks (DP less than or equal to 6), self-assembly afforded cylindrical micelles with an organometallic core and a PDMS corona. For the sample with the longest PFP block (DP = 11), we found spherical micelles. These results are consistent with increased disruption of the crystallization of the PFS block as the PFP block is increased in length, favoring formation of spherical rather than low curvature cylindrical structures. Results of wide-angle X-ray diffraction measurements support this conclusion.