The first tricoordinate fluorosilylenoid, (t-Bu2MeSi)2SiFLi.3THF (1), was synthesized, and its X-ray molecular structure was determined. 1 was synthesized in 40% yield by a bromine-lithium exchange reaction in THF of the corresponding fluorobromosilane with t-Bu2MeSiLi. 1 is best described as an R2SiF- anion attracted to a (Li.3THF)+ cation with a small contribution of resonance structure that consists of a silylene fragment and FLi.3THF. 1 reacts as a nucleophile with MeCl, PhH2SiCl, H2O, and MeOH, as an electrophile with MeLi, and as a silylene with Li (or t-BuLi) and Na, yielding alpha-lithium and alpha-sodium silyl radicals, respectively. Either photolysis or thermolysis of 1 yields the corresponding disilene R2Si=SiR2 (R = t-Bu2MeSi), probably via dimerization of R2Si:.

We describe the synthesis and characterization of a family of diblock copolymers with 5 units of a dihexyloxy-phenylenevinylene block (OHPV) connected to a series of poly(ethylene glycol) (PEG) chains of different average lengths (12, 45 and 115 PEG units: OHPV5-b-PEG12, OHPV5-b-PEG45, OHPV5-b-PEG115). All three polymers underwent self-assembly in ethanol, a good solvent for the PEG units, but poor for the OHPV segment. The nature of the structures formed depends sensitively on the length of the PEG block. OHPV5-b-PEG115 formed long fiber-like micelles of uniform width, whereas OHPV5-b-PEG45 formed fragile broad ribbons. We also obtained thin ribbons with OHPV5-b-PEG12 but they tend to fold and twist upon themselves. The structures obtained were characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM), as well as by wide-angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC). In addition, their photophysical properties were examined by UV-vis, steady state fluorescence and fluorescence decay measurements. The results of these experiments indicate that the OHPV groups pack differently in the fiber-like micelles of OHPV5-b-PEG115 than in the lamellar structures formed by OHPV5-b-PEG45.

The emergence of one-dimensional (1D) micelles obtained from the crystallization driven self-assembly (CDSA) in solution of crystalline-coil block copolymers has opened the door to the fabrication of a variety of sophisticated structures. While the development of these fascinating nanomaterials is blossoming, there is very little fundamental work dedicated to understanding the morphological evolution of these 1D micelles in solution. Here, using a combination of transmission electron microscopy, electron tomography, and static and dynamic light scattering, we studied the effect of annealing on a colloidal suspension of 1D micelle fragments formed by the self-assembly of a crystalline-coil poly(ferrocenyldimethylsilane)-block-poly(isoprene) (PFS-b-PI) block copolymer in decane, a solvent selective for PI. We are particularly interested in studying the evolution of the rectangular cross-section of the crystalline core of these micelle fragments. By electron tomography, we observed that the shorter dimension of the cross-section became even thinner upon annealing at elevated temperatures, while the longer dimension increased. In parallel, we observed an increase in packing density of the crystalline block as the fragments were annealed at temperatures above 60 °C. From these results, we concluded that annealing the micelle fragments induces a thinning of the crystalline core coupled with a lateral growth.

Multistep crystallization-driven self-assembly has great potential to enable the construction of sophisticated hybrid mesostructures. During the assembly procedure, each step modifies the properties of the overall structure. Here, we demonstrate the flexibility and efficiency of this approach by preparing polymer-carbon nanotube (CNT) hybrid mesostructures. We started by growing polyferrocenyldimethylsilane (PFS) homopolymer crystals onto multiwalled CNTs. This first step facilitated the redispersion of the coated CNTs in both polar (2-propanol) and nonpolar (decane) solvents. In the second step of hybrid construction, a unimer solution of a PFS block copolymer was added into the PFS-CNT solution. The PFS coating on the CNT initiated the growth of elongated micelles, resulting in structures that resembled hairy caterpillars. PFS-b-P2VP (P2VP = poly-2-vinylpyridine) micelles were grown from the surface of PFS-CNT hybrids in 2-propanol, and PFS-b-PI (PI = polyisoprene) micelles were grown from these hybrids in decane. These micelles, by transmission electron microscopy were seen to have an unusual wavy kinked structure, very different from the uniform smooth structures normally formed by both block copolymers. For hybrids with PFS-b-PI micelles, cross-linking of the micelle coronas locked the whole structure in place and allowed us to use the partial oxidation of PFS components to grow metal nanoparticles in the core of these micelles. We finally investigated the influence of the corona-forming block used to grow the micelles on the wettability of films made from these mesostructures. Films formed with CNT hybrids grafted with PFS-b-PI micelles were superhydrophobic (contact angle, 152°). In contrast, the surface of the films was much more hydrophilic (contact angle, 54°) when they were prepared from CNT hybrids grafted with PFS-b-P2VP micelles.

No abstract