Rueben Pfukwa

Templated hierarchical self-assembly of poly(p-aryltriazole) foldamers

A biomimetic approach has been used for the templated self-assembly of a helical poly(para-aryltriazole) foldamer. The solvophobic folding process yields helices that further self-assemble into long nanotubes (see picture; scale bar: 100 nm). Constructs of controlled length and chirality can be generated by applying a poly(γ-benzyl-l-glutamate) scaffold at the appropriate assembly conditions, mimicking tobacco mosaic virus self-assembly.

Improved control through a semi-batch process in RAFT-mediated polymerization utilizing relatively poor leaving groups

The negative effect that a RAFT agent with a poor leaving group has on the evolution of molecular dispersity in a RAFT-mediated polymerization was shown to be mitigated by performing the polymerization in semi-batch mode. The result is attributed to an increase in the probability of transfer between the propagating radical and the leaving group during the polymerization. Also for RAFT-mediated polymerizations that use RAFT agents with efficient leaving groups, the evolution of molecular dispersity during a semi-batch polymerization improves compared to that for an analogous batch-mode reaction.

Synthesis, Characterization, and Evaluation of Cytotoxicity of Poly(3-methylene-2-pyrrolidone).

The homo- and copolymerization of 3-methylene-2-pyrrolidone (3M2P) is introduced. 3M2P is readily polymerized via conventional free radical polymerization, and two reversible deactivation radical polymerization methods including reversible addition-fragmentation (chain) transfer and single-electron-transfer living radical polymerization. Poly(3M2P) has a high thermal stability and a very high glass transition temperature. Poly(3M2P) does not dissolve in most common organic solvents, but it has a high aqueous solubility. Cytotoxicity tests reveal that it is nontoxic to cells, even up to concentrations of 1 mg/mL. This adds poly(3M2P) to the family of water-soluble and biocompatible pyrrolidone-based vinyl polymers.

Synthesis of α,ω-heterotelechelic PVP for bioconjugation, via a one-pot orthogonal end-group modification procedure

A simple one pot orthogonal procedure for synthesizing α-aldehyde, ω-thiol heterotelechelic poly(N-vinylpyrrolidone) (PVP) is introduced. Firstly we designed a xanthate chain transfer agent with an acetal protected aldehyde functionality in the leaving group, then we synthesized α-acetal ω-xanthate end-functional PVP, via a RAFT-mediated polymerization. The end-groups were modified via a facile, modular protocol, by first aminolysing the ω-xanthate end-groups to form thiols, using an excess of a primary amine, and subsequently acidifying the reaction medium to simultaneously convert excess primary amine to its (non-interfering) quaternary ammonium salt form, as well as effect the acid-catalysed deprotection of the acetal into an aldehyde functionality, to access the α-aldehyde, ω-thiol-PVP. Finally, we demonstrated the utility of these end-groups by performing conjugations with model small molecules. This study establishes a facile procedure for accessing different and bio-relevant end-functional groups with a biocompatible vinyl polymer, suitable for making drug delivery vehicles.

Smart block copolymers of PVP and an alkylated PVP derivative: synthesis, characterization, thermoresponsive behaviour and self-assembly

Stimuli responsive block copolymers of biocompatible poly(3-ethyl-N-vinylpyrrolidone) and poly(N-vinylpyrrolidone), i.e. EPVP–PVP, were readily synthesized via RAFT-mediated polymerization. The thermoresponsive behaviour and temperature induced self-assembly, in aqueous solutions, was studied using various spectroscopic and microscopy techniques. We obtained different morphologies, i.e. spherical and cylindrical micelles, and vesicles, via temperature induced self-assembly, of aqueous solutions of a single diblock copolymer by simply adjusting the solution concentration. This study establishes the biocompatible EPVP/PVP combination as a versatile stimuli responsive block copolymer system suitable for applications in drug delivery.