Rod-rod Block Copolymers Research Articles

Poly(arylenevinylene)s through Ring-Opening Metathesis Polymerization of an Unsymmetrical Donor-Acceptor Cyclophane.

Reported are well-defined donor-acceptor alternating copolymers prepared using ring-opening metathesis polymerization (ROMP). Unsymmetrical cyclophanedienes comprising electron-donating (4-methoxy-1-(2-ethylhexyl)oxy)benzene (MEH) and electron-accepting benzothiadiazole (BT) rings were synthesized from the corresponding [3.3]dithiaparacyclophanes. ROMP of the strained unsymmetrical and "electronically-ambiguous" cyclophanedienes proceeded in a controlled manner in the presence of either Hoveyda-Grubbs II or Grubbs II initiator in wake of both steric and electronic encumbrance. The resulting polymers, comprising alternating BT and MEH-PPV units, are achieved in molecular weights exceeding 20k with Đ values ranging from 1.1-1.4. The living nature of the polymerization is verified through the formation of rod-coil and rod-rod block copolymers. Our strategy to develop previously unrealized polymers from functional building blocks featuring a locked-in D-A unit is significant in a field striving to achieve well-defined and sequence-specific materials.

Exploiting Host-Guest Interactions for the Synthesis of a Rod-Rod Block Copolymer with Crystalline and Liquid-Crystalline Blocks.

By making use of the host-guest interactions between the host molecule tris-o-phenylenedioxycyclotriphosphazene (TPP) and the rod-coil block copolymer (BCP) poly(ethylene oxide)-block-poly(octyl 4'-octyloxy-2-vinylbiphenyl-4-carboxylate) (PEO-b-PVBP), the supramolecular rod-rod block copolymer P(EO@TPP)-b-PVBP was constructed. It consists of a crystalline segment P(EO@TPP) with a hexagonal crystalline structure and a columnar nematic liquid-crystalline segment (PVBP). As the PVBP segments arrange themselves as columnar nematic phases, the crystalline structure of the inclusion complex P(EO@TPP), which has a smaller diameter, is destroyed. The self-assembled nanostructure is thus clearly affected by the interplay between the two blocks. On the basis of wide- and small-angle X-ray scattering analysis, we conclude that the supramolecular rod-rod BCP can self-assemble into a cylinder-in-cylinder double hexagonal structure.

Synthesis and self-assembly of a triarm star-shaped rod-rod block copolymer

We designed and synthesized a triarm star-shaped rod-rod block copolymer (BCP), (poly{2,5-bis[(4-methoxyphenyl)-oxycarbonyl]styrene}-block-poly(γ-benzyl-l-glutamate))3, (PMPCS-b-PBLG)3. The triarm core with three PMPCS-N3 segments was prepared by copper-mediated atom transfer radical polymerization of 2,5-bis[(4-methoxyphenyl)-oxycarbonyl]styrene initiated by a trifunctional initiator and a subsequent azide reaction. And the PBLG block with alkyne functionality was synthesized through ring-opening polymerization of γ-benzyl-l-glutamate N-carboxyanhydride initiated by propargylamine. Finally, Huisgen’s 1,3-dipolar cycloaddition was employed to combine the triarm (PMPCS-N3)3 and PBLG segments. The chemical structure of the BCP was confirmed by 1H-NMR spectroscopy, Fourier-transform infrared spectroscopy, and gel permeation chromatographic analysis. Results from differential scanning calorimetry, polarized light microscopy, one-dimensional and two-dimensional wide-angle X-ray diffraction, and transmission electron microscopy techniques demonstrate that the triarm star-shaped rod-rod BCP self-assembles into a hexagon-in-lamella morphology, with the PMPCS block in the columnar nematic phase and the PBLG block in the hexagonal columnar arrangement packed in bilayers due to the rigid nature of the two blocks and the covalent connections in the star-shaped BCP.

Nanocrystal Self-Assembly with Rod-Rod Block Copolymers

Two distinct morphologies of hexylselenophene-hexylthiophene rod-rod block copolymer films can be prepared depending on the molecular weight of the sample (see picture: left M(n) =12.9, right M(n) =3.9 kg mol(-1)). These polymers can be used to organize spherical CdSe nanocrystals (yellow) into either dispersed or aligned hierarchical structures. Scale bars: 200 nm.

Self-assembly of rod-rod conjugated block copolymer

All-conjugated block copolymers of the rod-rod type has been developed into a new kind of conjugated polymer materials in recent years, and came into the focus of interest because of their unique and attractive combination of electronic activity and controllable nanostructure formation. Based on their rigid-rod structure, rod-rod block copolymers show a preferred tendency to self-assemble into low-curvature vesicular or lamellar nanostructures. In this article the self-assembly properties of rod-rod conjugated block copolymer material was reviewed, including the self-assembly in solution and the solid state, and the relationship between morphologies of the conjugated block copolymer thin films and properties.

Detergent-Aided Polymersome Preparation

Until now, most preparative methods used to form polymeric vesicles involve either organic cosolvents or sonication. In this communication, we demonstrate for the first time a detergent-aided method to produce polymersomes. Peptidic polymersomes were formed from the rod-rod block copolymer PBLG(36)-E, where PBLG is hydrophobic poly(gamma-benzyl l-glutamate) and E is a hydrophilic designed peptide. The block copolymer was first solubilized by detergent micelles in aqueous buffer, after which the concentration of detergent was reduced by dilution, transforming the particle morphology in solution from mixed micelles to polymersomes. The polymersome formation was monitored with dynamic light scattering and confirmed with transmission electron microscopy. Polymersomes with average diameters of approximately 300 nm were obtained as well as discs with average diameters of approximately 100 nm. This detergent-based method can be used to create polymersomes with a range of properties, as verified by its application to another biocompatible block copolymer, the flexible polybutadiene(46)-b-poly(ethylene glycol)(30). The technique will be particularly useful when delicate biomacromolecules such as (membrane) proteins, peptides, or nucleic acids are to be encapsulated in the polymersomes because the detergents used are compatible with these compounds, and the possible denaturing effect of sonication or organic solvents on the biological activity of the molecule of interest is avoided.

All‐Conjugated, Rod‐Rod Block Copolymers‐Generation and Self‐Assembly Properties

Based on their rigid-rod structure all-conjugated, rod-rod block copolymers show a preferred tendency to self-assemble into low-curvature vesicular or lamellar nanostructures independent from their specific chemical structure and composition. This unique and attractive behaviour is clearly illustrated in a few examples of such all-conjugated block copolymers. The resulting nanostructured heteromaterials may find applications in electronic devices or artificial membranes.