Jing M. Ren

Synthesis of novel cylindrical bottlebrush polypseudorotaxane via inclusion complexation of high density poly(ε-caprolactone) bottlebrush polymer and α-cyclodextrins

Poly(e-caprolactone) (PCL) macromonomers (MMs) with norbornenyl end groups were synthesized viaring-opening polymerization (ROP) of e-caprolactone using stannous 2-ethylhexanoate (Sn(Oct)2) as catalyst. Then ring-opening metathesis polymerization (ROMP) of these MMs was carried out using the highly active, fast-initiating ruthenium olefin metathesis catalyst (H2IMes)(pyr)2(Cl)2RuCHPh to form high molecular weight (Mn = 420–1346 kDa) and high density PCL bottlebrush polymers. The inclusion complexation of the prepared PCL bottlebrush polymers and α-cyclodextrins (α-CDs) afforded the novel bottlebrush polypseudorotaxanes with a length of 350 ± 50 nm and a width of 50 ± 10 nm. The formation of bottlebrush polypseudorotaxane was confirmed by nuclear magnetic resonance (NMR) spectroscopic analysis, X-ray diffractogram analysis and dynamic light scattering (DLS) measurements. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that the bottlebrush polypseudorotaxane displays higher thermal stability and weaker melting and crystallization behavior in comparison to its PCL bottlebrush precursor. Transmission electron microscopy (TEM) revealed that the resultant bottlebrush polypseudorotaxanes possess a unique elongated cylindrical morphology.

A Versatile and Scalable Strategy to Discrete Oligomers.

A versatile strategy is reported for the multigram synthesis of discrete oligomers from commercially available monomer families, e.g., acrylates, styrenics, and siloxanes. Central to this strategy is the identification of reproducible procedures for the separation of oligomer mixtures using automated flash chromatography systems with the effectiveness of this approach demonstrated through the multigram preparation of discrete oligomer libraries (Đ = 1.0). Synthetic availability, coupled with accurate structural control, allows these functional building blocks to be harnessed for both fundamental studies as well as targeted technological applications.

A novel solid state photocatalyst for living radical polymerization under UV irradiation

This study presents the development of a novel solid state photocatalyst for the photoinduced controlled radical polymerization of methacrylates under mild UV irradiation (λmax ≈ 365 nm) in the absence of conventional photoinitiators, metal-catalysts or dye sensitizers. The photocatalyst design was based on our previous finding that organic amines can act in a synergistic photochemical reaction with thiocarbonylthio compounds to afford well controlled polymethacrylates under UV irradiation. Therefore, in the current contribution an amine-rich polymer was covalently grafted onto a solid substrate, thus creating a heterogeneous catalyst that would allow for facile removal, recovery and recyclability when employed for such photopolymerization reactions. Importantly, the polymethacrylates synthesized using the solid state photocatalyst (ssPC) show similarly excellent chemical and structural integrity as those catalysed by free amines. Moreover, the ssPC could be readily recovered and re-used, with multiple cycles of polymerization showing minimal effect on the integrity of the catalyst. Finally, the ssPC was employed in various photo-“click” reactions, permitting high yielding conjugations under photochemical control.

Photocontrolled Cargo Release from Dual Cross-Linked Polymer Particles.

Burst release of a payload from polymeric particles upon photoirradiation was engineered by altering the cross-linking density. This was achieved via a dual cross-linking concept whereby noncovalent cross-linking was provided by cyclodextrin host-guest interactions, and irreversible covalent cross-linking was mediated by continuous assembly of polymers (CAP). The dual cross-linked particles (DCPs) were efficiently infiltrated (∼80-93%) by the biomacromolecule dextran (molecular weight up to 500 kDa) to provide high loadings (70-75%). Upon short exposure (5 s) to UV light, the noncovalent cross-links were disrupted resulting in increased permeability and burst release of the cargo (50 mol % within 1 s) as visualized by time-lapse fluorescence microscopy. As sunlight contains UV light at low intensities, the particles can potentially be incorporated into systems used in agriculture, environmental control, and food packaging, whereby sunlight could control the release of nutrients and antimicrobial agents.

Azobenzene-Functionalised Core Cross-Linked Star Polymers and their Host–Guest Interactions

Water-soluble poly(2-hydroxyethyl acrylate) (PHEA)-based core cross-linked star polymers were efficiently synthesised with high macroinitiator-to-star-conversion (>95 %) in a one-pot system via single electron transfer-living radical polymerisation. The star polymers display excellent water solubility and the pendant hydroxyl groups provide a platform for facile post-functionalisation with various molecules. In demonstrating this, a photo-isomerisable molecule, 4-(phenylazo)benzoic acid was conjugated onto the preformed stars through partial esterification of the available hydroxyl groups (5–20 %). The azobenzene functionalised stars were subsequently employed to form reversible inclusion complexes with α-cyclodextrin.

Fabrication of ultra-thin polyrotaxane-based films via solid-state continuous assembly of polymers

Surface-confined ultra-thin polyrotaxane (PRX)-based films with tunable composition, surface topology and swelling characteristics were prepared by solid-state continuous assembly of polymers (ssCAP). The PRX-based films supported cell attachment, and their degradation in biological media could be tuned. This study provides a versatile nano-coating technology with potential applications in biomedicine, including tissue engineering and medical devices.

A Versatile and Efficient Strategy to Discrete Conjugated Oligomers

An efficient and scalable strategy to prepare libraries of discrete conjugated oligomers (Đ = 1.0) using the combination of controlled polymerization and automated flash chromatography is reported. From this two-step process, a series of discrete conjugated materials from dimers to tetradecamers could be isolated in high yield with excellent structural control. Facile and scalable access to monodisperse libraries of different conjugated oligomers opens pathways to designer mixtures with precise composition and monomer sequence, allowing exquisite control over their physical, optical, and electronic properties.

Control of Amphiphile Self-Assembly via Bioinspired Metal Ion Coordination

Inspired by marine siderophores that exhibit a morphological shift upon metal coordination, hybrid peptide-polymer conjugates that assemble into different morphologies based on the nature of the metal ion coordination have been designed. Coupling of a peptide chelator, hexahistidine, with hydrophobic oligostyrene allows a modular strategy to be established for the efficient synthesis and purification of these tunable amphiphiles (oSt(His)6). Remarkably, in the presence of different divalent transition metal ions (Mn, Co, Ni, Cu, Zn, and Cd) a variety of morphologies were observed. Zinc(II), cobalt(II), and copper(II) led to aggregated micelles. Nickel(II) and cadmium(II) produced micelles, and multilamellar vesicles were obtained in the presence of manganese(II). This work highlights the significant potential for transition metal ion coordination as a tool for directing the assembly of synthetic nanomaterials.

Controlled Formation and Binding Selectivity of Discrete Oligo(methyl methacrylate) Stereocomplexes

The triple-helix stereocomplex of poly(methyl methacrylate) (PMMA) is a unique example of a multistranded synthetic helix that has significant utility and promise in materials science and nanotechnology. To gain a fundamental understanding of the underlying assembly process, discrete stereoregular oligomer libraries were prepared by combining stereospecific polymerization techniques with automated flash chromatography purification. Stereocomplex assembly of these discrete building blocks enabled the identification of (1) the minimum degree of polymerization required for the stereocomplex formation and (2) the dependence of the helix crystallization mode on the length of assembling precursors. More significantly, our experiments resolved binding selectivity between helical strands with similar molecular weights. This presents new opportunities for the development of next-generation polymeric materials based on a triple-helix motif.