Anthraquinodimethane-Based Molecular Switches Tethered by Four-Arm Star-like Polymers.

Molecular switches that reversibly change their structures and physical properties are important for applications such as sensing and information processing at molecular scales. In order to avoid the intermolecular aggregation that is often detrimental to the stimuli-responses of molecular switches, previous studies of molecular switches have been often conducted in dilute solutions which are difficult for applications in solid-state devices. Here we report molecular design and synthesis that integrates anthraquinodimethane as molecular switching units into polymers with amenable processibility in solid states. Optical and electron spin resonance characterizations indicate that the four-arm polymers of poly(ϵ-caprolactone) or poly(D,L-lactide) tethered from anthraquinodimethane slow down the dynamics of the conformational switching between the folded and the twisted conformations, enhance the photoluminescence in solid states and impart materials with a small energy gap from singlet ground state to thermally accessible triplet state.

Lewis Pair-Mediated Surface-Initiated Polymerization.

We present the first example of surface-initiated polymerization mediated by Lewis pairs for the synthesis of polymer brushes on planar substrates. The method enables the rapid grafting polymerization from the self-assembled monolayer or surface-attached macroinitiators, furnishing linear polymer brushes and bottle-brush brushes. Both homopolyester and block copolyester brushes can be synthesized via this versatile approach. This work not only opens up new opportunities for the application of Lewis pair-mediated polymerization but also enriches the surface-initiated polymerization on different surfaces.

Controlled Growth of Metal-Organic Frameworks on Polymer Brushes.

Polymer brushes are for the first time used to induce the synthesis of metal-organic frameworks (MOFs). The semi-fixed polymer chains provide a confined environment, which allows a mild growth of MOFs in between polymer chains to give surface-attached spherical MOF nanoparticles, in contrast to the larger MOF cubes/plates formed simultaneously in solution. Polymer brushes bearing carboxylate acid functionalities are indispensable for the formation of surface bound MOFs, while no MOF nanoparticles are observed on neutral polymer brushes. Characterization of the resultant MOF/polymer brushes hybrid film indicates the formation of crystalline MOF structure. The dimension of surface-attached MOFs can be fine-tuned from 20 nm to 1.4 µm simply by varying the structural parameter of polymer brushes and the nucleation duration. The method is not only applicable to the synthesis of MOF-5 and MIL-125, but shows great potential for the preparation of other surface-attached MOFs.

Indocyanine green-functionalized bottle brushes of poly(2-oxazoline) on cellulose nanocrystals for photothermal cancer therapy.

Deriving from the most abundant and renewable material, cellulose nanocrystals (CNCs) have drawn increasing attention in nanomedicine as well as other biomedical fields due to their excellent physicochemical properties and unique rod-like geometry. In this work, we report an efficient procedure to create biocompatible poly(2-oxazoline)s with a defined bottle brush architecture on CNCs through UV-induced photopolymerization and subsequent living cationic ring-opening polymerization. Characterization of the poly(2-oxazoline) modified CNCs indicates an improved thermal stability with the crystalline structure as well as the rod-like contour intact. The side chain terminal piperidinium of the bottle brush was utilized to immobilize indocyanine green (ICG) via electrostatic interactions. The resulting nanorods exhibit low toxicity in the dark and an efficient photothermal therapeutic effect against HeLa cells under 808 nm near infrared laser irradiation after being internalized by cancer cells. Moreover, bottle brushes on CNCs with amphiphilic poly(2-n-propyl-2-oxazoline) side chains show a higher efficiency in stabilizing ICG in comparison to those with hydrophilic poly(2-methyl-2-oxazoline) side chains, thus a higher photostability and a greater therapeutic effect were revealed for amphiphilic polymer modified CNCs. This work indicates that poly(2-oxazoline) functionalized CNCs represent a novel and promising platform for the design of other CNC-based drug delivery systems.

Polymer brushes on planar TiO2 substrates.

A facile and universal method is presented for the preparation of polymer brushes on amorphous TiO2 film. Homogeneous and stable poly(methyl methacrylate), polystyrene, poly(4-vinylpyridine), and poly(N-vinyl imidazole) (PNVI) brushes up to 550 nm are directly created onto TiO2 via UV-induced photopolymerization of corresponding monomers. Kinetic studies reveal a linear increase in thickness with the polymerization time. Characterization of the resulting polymer brushes by FTIR spectroscopy, X-ray photoelectron spectroscopy, contact angle, and atomic force microscopy (AFM) indicates an efficient UV-grafting reaction. Finally, we have demonstrated the possibility in converting the PNVI brushes to poly(vinyl imidazolium bromide), i.e., poly(ionic liquid) brushes by polymer-analogous reactions.