Poly(ferrocenylmethylsilane): An Unsymmetrically Substituted, Atactic, but Semicrystalline Polymetallocene

Polyferrocenylsilanes (PFSs) [Fe­(μ-C₅H₄)₂SiRR′]_<i>n</i> are generally atactic and amorphous when unsymmetrically substituted at silicon (R ≠ R′) but are often able to crystallize if the substitution is symmetrical (R = R′). In this paper we report detailed studies of the ring-opening polymerization (ROP) of [1]­methylsilaferrocenophane Fe­(μ-C₅H₄)₂SiMeH (<b>1</b>) by thermal, anionic and photolytic methods to yield an unsymmetrically substituted yet crystallizable poly­(ferrocenylmethylsilane) (<b>PFMS</b>) (R = Me, R′ = H) with Me and H substituents at silicon (designated <b>PFMS</b>_<b>T</b>, <b>PFMS</b>_<b>A</b>, and <b>PFMS</b>_<b>P</b>, respectively). The structures of the resulting polymers were shown to possess significant differences as revealed by MALDI–TOF mass spectroscopy experiments. For example, <b>PFMS</b>_<b>A</b> prepared using <i>n</i>-BuLi as an initiator was shown to contain cyclic contaminants whose formation indicated the existence of backbiting reactions during polymer chain growth. On the other hand, photolytic ROP of <b>1</b> using Na­[C₅H₅] as an initiator led only to the formation of linear material but was not a living process due to side reactions between the initiator (and presumably the propagating polymeric anions) and the Si–H groups in the monomer <b>1</b>. Transition metal-catalyzed ROP of <b>1</b> was also explored and, in contrast, was found to afford a hyperbranched and amorphous low molar mass polyferrocenylsilane (<b>4</b>), presumably also as a result of side reactions involving the Si–H groups in the monomer. High resolution ¹H and ¹³C NMR spectroscopic studies revealed that <b>PFMS</b>_<b>T</b>, <b>PFMS</b>_<b>A</b>, and <b>PFMS</b>_<b>P</b> were all atactic, irrespective of the polymerization route utilized. The crystallization of the samples was investigated by wide-angle X-ray scattering (WAXS), which showed a reflection corresponding to a <i>d</i>-spacing of 6.32 Å, by differential scanning calorimetry (DSC), which revealed melting endotherms in the range 106–139 °C, and by polarizing optical microscopy (POM)

Branched Cylindrical Micelles via Crystallization-Driven Self-Assembly

We report the preparation of branched micelles by the growth of thinner-core cylindrical micelles at the termini of the thicker-core cylindrical micelle seeds through crystallization-driven self-assembly of polyferrocenylsilane block copolymers. The branched micelles possessed structures with monodisperse middle segments and, in most cases, two branches at the seed terminus. After cross-linking of the coronas, the branched micelles become resistant to dissolution in good solvents for both blocks and can be manipulated as colloidally stable nanomaterials

Branched Micelles by Living Crystallization-Driven Block Copolymer Self-Assembly under Kinetic Control

We have found that the width and shape (from rectangular to elliptical, to almost circular in cross-section) of the crystalline core of fiberlike micelles of polyferrocenyldimethylsilane (PFDMS) diblock copolymers can be varied by altering the degree of polymerization of PFDMS, and also the chemistry of the complementary corona-forming block. This enabled detailed studies of living crystallization-driven self-assembly (CDSA) processes that involved the addition of unimers with a short, crystallizable core-forming PFDMS block to a seed solution of short micelles with a large diameter crystalline core, derived from block copolymers with a longer PFDMS block. The morphology of resultant micelles was found to be highly dependent on the polarity of the solvent and temperature. For example, linear micelles were formed in less polar solvents (which are moderately poor solvents for PFDMS) and/or at higher temperatures. In contrast, the formation of branched structures could be “switched on” when the opposite conditions were used. Thus, the use of more polar solvents (which are very poor solvents for PFDMS) and ambient or subambient temperatures allowed the formation of branched micelles and block comicelles with variable and spatially distinct corona chemistries, including amphiphilic nanostructures. Rapid crystallization of added unimers at the seed micelle termini under nonequilibrium self-assembly conditions appears to facilitate the formation of the branched micellar structures as a kinetically trapped morphology. This is evidenced by the transformation of the branched micelles into linear micelles on heating at elevated temperatures

Branched Micelles by Living Crystallization-Driven Block Copolymer Self-Assembly under Kinetic Control

We have found that the width and shape (from rectangular to elliptical, to almost circular in cross-section) of the crystalline core of fiberlike micelles of polyferrocenyldimethylsilane (PFDMS) diblock copolymers can be varied by altering the degree of polymerization of PFDMS, and also the chemistry of the complementary corona-forming block. This enabled detailed studies of living crystallization-driven self-assembly (CDSA) processes that involved the addition of unimers with a short, crystallizable core-forming PFDMS block to a seed solution of short micelles with a large diameter crystalline core, derived from block copolymers with a longer PFDMS block. The morphology of resultant micelles was found to be highly dependent on the polarity of the solvent and temperature. For example, linear micelles were formed in less polar solvents (which are moderately poor solvents for PFDMS) and/or at higher temperatures. In contrast, the formation of branched structures could be “switched on” when the opposite conditions were used. Thus, the use of more polar solvents (which are very poor solvents for PFDMS) and ambient or subambient temperatures allowed the formation of branched micelles and block comicelles with variable and spatially distinct corona chemistries, including amphiphilic nanostructures. Rapid crystallization of added unimers at the seed micelle termini under nonequilibrium self-assembly conditions appears to facilitate the formation of the branched micellar structures as a kinetically trapped morphology. This is evidenced by the transformation of the branched micelles into linear micelles on heating at elevated temperatures