Liquid Crystalline Ordering in the Self-Assembled Monolayers of Tethered Rodlike Polymers

We show that tethering rodlike polymers onto solid surfaces by their chain ends with a moderate grafting density can lead to highly oriented anisotropic self-assembled monolayers (SAM) with thickness identical to the diameter of single chain through liquid crystalline ordering. The polymers employed for this study were di- or triblock copolymers composed of poly(n-hexylisocyanate)(PHIC), a rodlike polymer, and poly(2-vinylpyridine)(P2VP), a surface-reactive coil. The block copolymers formed SAM of PHICs tethered to the surface through adsorption of P2VP onto mica. Planar nematic ordering occurred to the PHIC chains when the monolayer was exposed to the vapor of selective solvents. Anisotropic SAMs with long-range order were obtained by exposing the monolayer to THF vapor, which was accounted for by reorganization of PHIC chains with change of anchoring points through partial sorption/desorption of P2VP segments by THF vapor

Formation of Intermicellar-Chained and Cylindrical Micellar Networks From an Amphiphilic Rod−Coil Block Copolymer: Poly(<i>n</i>-hexyl isocyanate)-<i>block</i>-poly(2-vinylpyridine)

Morphologies of the poly(n-hexyl isocyanate)-block-poly(2-vinylpyridine) (PHIC-b-P2VP, fP2VP = 0.3) amphiphilic rod−coil block copolymer were studied in rod-selective chloroform (CHCl3), both-block-soluble tetrahydrofuran (THF), and CHCl3/THF mixed solvent systems. Spherical, solid micelles with a P2VP core and PHIC shell were formed in CHCl3, whereas a microphase-separated liquid crystalline morphology was prominent in the presence of THF. In the CHCl3/THF mixed solvent system, a unique long-range intermicellar-chained network (v/v = 7/3) and a more evolved cylindrical micellar network (v/v = 3/7) were remarkably formed, respectively. PHIC-b-P2VP network nanostructures were used as a template for the in situ synthesis of Au nanoparticles (8 nm) selectively within the functional P2VP core domains

Self-Organization of an Amphiphilic Rod−Coil−Rod Block Copolymer into Liquid Crystalline, Substrate-Supported Monolayers and Bilayers

We report that the amphiphilic rod−coil−rod triblock copolymer with a coil attractive to the substrate surface self-organize into liquid crystalline monolayers or bilayers of a few nanometers thickness on the substrate surface. The copolymer investigated is a triblock copolymer, poly(n-hexyl isocyanate-b-2-vinylpyridine-b-n-hexyl isocyanate) (PHIC-b-P2VP-b-PHIC). Key processes of self-organization in the thin films, such as adsorption, desorption, diffusion, nematic and smectic ordering, and microphase separation, are tuned by exposing dip- or immersion-coated nanoscale films to the vapor of solvents which are rod (PHIC)-selective, coil (P2VP)-selective, or good to both blocks. Reorganization of the rod−coils in the nanofilms yielded various morphologies in the monolayer or bilayer, including unique long-range-ordered, smectic-on-nematic biphasic sheets. The results offer understanding on the complex morphological evolution in amphiphilic rod−coil block copolymers on the substrate surface

Model Branched Polymers: Synthesis and Characterization of Asymmetric H-Shaped Polybutadienes

A new type of model branched polymer, asymmetric H-shaped polybutadienes, consisting of central crossbars having various combinations of short and long arms attached to the ends of the crossbars, was synthesized using living anionic polymerization and chlorosilane linking chemistry. The linking agent 4-(dichloromethylsilyl)­diphenylethylene provides selective reactivity to attach short or long arms on one side or both sides as desired. The samples were characterized thoroughly by size exclusion chromatography with light scattering detection (SEC-LS) and found to exhibit controlled molecular weights, as well as narrow polydispersity indices (PDIs of 1.01–1.06). Temperature gradient interaction chromatography, a method with far superior resolution as compared to SEC, also shows that these materials are well-defined, with minimal and identifiable impurities

Surface-Grafted Rodlike Polymers: Adaptive Self-Assembled Monolayers and Rapid Photo-Patterning of Surfaces

We present a new concept of functionalizing solid surfaces using polymeric self-assembled monolayers (PSAM) that are obtained by grafting onto solid surfaces an asymmetric block copolymer composed of a long rodlike block and a short surface-reactive block. Poly(n-hexylisocyanate)-b-poly[3-(trimethoxysilyl)propyl methacrylate] (PHIC-b-PTMSM) is synthesized via a living anionic polymerization and an atom transfer radical polymerization. The new rod–coil block copolymer forms a polymeric self-assembled monolayer (PSAM) through covalent bonding of the sticky PTMSM block and planar adsorption of PHIC rodlike chains onto the substrate surface. The uniform PSAM with a thickness identical to the diameter of the rodlike chain is produced by the immersion coating method in a range of immersion solution concentrations and coating times. The PSAMs present unique properties thanks to the freedom of rotation of the end-grafted rodlike chains. The PSAMs exhibit nematic liquid crystalline ordering when the monolayer is fluidized by solvent vapor. A mixed SAM with a nanodot pattern is obtained by introducing a second coating agent of octadecyltrimethoxysilanes (ODTMS) onto the PSAM-coated substrate. The PSAM is micropatternable using photochemical cleavage of the anchoring blocks by brief exposure to UV. Use of the PSAMs as an additional dielectric layer in P3HT-based field effect transistors (FETs) is also demonstrated

Unprecedented Control over Polymerization of <i>n</i>-Hexyl Isocyanate using an Anionic Initiator Having Synchronized Function of Chain-End Protection

The living anionic polymerization of isocyanates carried out using conventional initiators is associated with side reactions due to rapid initiation rates as well as back-biting by the growing chain, resulting in a lack of control on the molecular weight (MW) and molecular weight distribution (MWD) of the polymers. Successful control over the reaction was possible by using additives that could prevent back-biting. We find an initiator in sodium benzanilide (Na−BA), which has a slow initiation rate combined with additive function, so that use of an external additive is eliminated. The initiator has resulted in polymers with high yields and an unprecedented control over the MW and MWD. It is possible to introduce a number of functionalities at the termini of the polymer by using Na−BA derivatives as well as suitable terminating agents, leading to macromonomer, reactive and chiral polymers, and chiral macromonomer in ∼100% yields. In the process, the finding has expanded the scope of polyisocyanates in diverse applications