Stimulus-responsive self-assembly: reversible, redox-controlled micellization of polyferrocenylsilane diblock copolymers

In depth studies of the use of electron transfer reactions as a means to control the self-assembly of diblock copolymers with an electroactive metalloblock are reported. Specifically, the redox-triggered self-assembly of a series of polystyrene-block-polyferrocenylsilane (PS-b-PFS) diblock copolymers in dichloromethane solution is described. In the case of the amorphous polystyrene(n)-b-poly(ferrocenylphenylmethylsilane)(m) diblock copolymers (PS(n)-b-PFMPS(m): n = 548, m = 73; n = 71, m = 165; where n and m are the number-averaged degrees of polymerization), spherical micelles with an oxidized PFS core and a PS corona were formed upon oxidation of more than 50% of the ferrocenyl units by [N(C(6)H(4)Br-4)(3)][SbX(6)] (X = Cl, F). Analogous block copolymers containing a poly(ferrocenylethylmethylsilane) (PFEMS) metalloblock, which has a lower glass transition temperature, behaved similarly. However, in contrast, on replacement of the amorphous metallopolymer blocks by semicrystalline poly(ferrocenyldimethylsilane) (PFDMS) segments, a change in the observed morphology was detected with the formation of ribbon-like micelles upon oxidation of PS(535)-b-PFDMS(103) above the same threshold value. Again the coronas consisted of fully solvated PS and the core consisted of partially to fully oxidized PFS associated with the counteranions. When oxidation was performed with [N(C(6)H(4)Br-4)(3)][SbF(6)], reduction of the cores of the spherical or ribbon-like micelles with [Co(η-C(5)Me(5))(2)] enabled full recovery of the neutral chains and no significant chain scission was detected.     

Optical properties of anatase and rutile titanium dioxide: Ab initio calculations for pure and anion-doped material

The optical properties of rutile and anatase titanium dioxide (TiO₂) are calculated from the imaginary part of the dielectric function using pseudopotential density functional method within its generalized gradient approximation (GGA) and a scissors approximation. The fundamental absorption edges calculated for the unit cell of both rutile and anatase are consistent with experimentally reported results of single crystal rutile and anatase TiO₂ and with previous theoretical calculations. A significant optical anisotropy is observed in the anatase structure which holds promise for investigating the band gap modification with better visible-light response and provides a reliable foundation for addressing the effect of impurities on the fundamental absorption edge/band gap of anatase TiO₂. Further calculations on the electronic structure and the optical properties of C-, N-, and S-doped anatase TiO₂ are performed. The results are analyzed and discussed in terms of optical anisotropy and scissors approximations.     

ChemInform Abstract: (Cu2S2)(Sr3Se2O5) — A Layered,Direct Band Gap,p‐Type Transparent Conducting Oxychalcogenide: A Theoretical Analysis.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Tailored polymers by free radical processes

This paper describes a versatile and effective method for the control of free radical polymerization and its use in the preparation of narrow polydispersity polymers of various architectures. Living character is conferred to conventional free radical polymerization by the addition of a thiocarbonylthio compound of general structure S=C(Z)SR, for example, S=C(Ph)SC(CH₃)₂Ph. The mechanism involves Reversible Addition-Fragmentation chain Transfer and, for convenience of referral, we have designated it the RAFT polymerization. The process is compatible with a very wide range of monomers including functional monomers such as acrylic acid, hydroxyethyl methacrylate, and dimethylaminoethyl methacrylate. Examples of narrow polydispersity (≤1.2) homopolymers, copolymers, gradient copolymers, end-functional polymers, star polymers, A-B diblock and A-B-A triblock copolymers are presented.