Richard Bradley Whitfield

Last Name

Whitfield

First Name

Richard Bradley

ORCID

0000-0003-4787-2060

Organisational unit

09644 - Anastasaki, Athina / Anastasaki, Athina

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Publications 1 - 10 of 45

Efficient Binding, Protection, and Self-Release of dsRNA in Soil by Linear and Star Cationic Polymers
Whitfield, Richard Bradley; Anastasaki, Athina; Truong, Nghia P.; et al. (2018)
ACS Macro Letters
Sequence-controlled Polymers via Controlled Radical Polymerization
Whitfield, Richard Bradley; Truong, Nghia P.; Anastasaki, Athina (2019)
Chimia
Chemical recycling of bromine-terminated polymers synthesized by ATRP
Mountaki, Styliani; Whitfield, Richard Bradley; Parkatzidis, Kostas; et al. (2024)
RSC Applied Polymers
Chemical recycling of polymers is one of the biggest challenges in materials science. Recently, remarkable achievements have been made by utilizing polymers prepared by controlled radical polymerization to trigger low-temperature depolymerization. However, in the case of atom transfer radical polymerization (ATRP), depolymerization has nearly exclusively focused on chlorine-terminated polymers, even though the overwhelming majority of polymeric materials synthesized with this method possess a bromine end-group. Herein, we report an efficient depolymerization strategy for bromine-terminated polymethacrylates which employs an inexpensive and environmentally friendly iron catalyst (FeBr2/L). The effect of various solvents and the concentration of metal salt and ligand on the depolymerization are judiciously explored and optimized, allowing for a depolymerization efficiency of up to 86% to be achieved in just 3 minutes. Notably, the versatility of this depolymerization is exemplified by its compatibility with chlorinated and non-chlorinated solvents, and both Fe(II) and Fe(III) salts. This work significantly expands the scope of ATRP materials compatible with depolymerization and creates many future opportunities in applications where the depolymerization of bromine-terminated polymers is desired.
Thermal Solution Depolymerization of RAFT Telechelic Polymers
De Alwis Watuthanthrige, Nethmi; Whitfield, Richard Bradley; Harrisson, Simon; et al. (2024)
ACS Macro Letters
Thermal solution depolymerization is a promising low-temperature chemical recycling strategy enabling high monomer recovery from polymers made by controlled radical polymerization. However, current methodologies predominantly focus on the depolymerization of monofunctional polymers, limiting the material scope and depolymerization pathways. Herein, we report the depolymerization of telechelic polymers synthesized by RAFT polymerization. Notably, we observed a significant decrease in the molecular weight (M-n) of the polymers during monomer recovery, which contrasts the minimal M-n shift observed during the depolymerization of monofunctional polymers. Introducing Z groups at the center or both ends of the polymer resulted in distinct kinetic profiles, indicating partial depolymerization of the bifunctional polymers, as supported by mathematical modeling. Remarkably, telechelic polymers featuring R-terminal groups showed up to 68% improvement in overall depolymerization conversion compared to their monofunctional analogues, highlighting the potential of these materials in chemical recycling and the circular economy.
Protein-polymer bioconjugates via a versatile oxygen tolerant photoinduced controlled radical polymerization approach
Theodorou, Alexis; Liarou, Evelina; Haddleton, David M.; et al. (2020)
Nature Communications
The immense application potential of amphiphilic protein-polymer conjugates remains largely unexplored, as established “grafting from” synthetic protocols involve time-consuming, harsh and disruptive deoxygenation methods, while “grafting to” approaches result in low yields. Here we report an oxygen tolerant, photoinduced CRP approach which readily affords quantitative yields of protein-polymer conjugates within 2 h, avoiding damage to the secondary structure of the protein and providing easily accessible means to produce biomacromolecular assemblies. Importantly, our methodology is compatible with multiple proteins (e.g. BSA, HSA, GOx, beta-galactosidase) and monomer classes including acrylates, methacrylates, styrenics and acrylamides. The polymerizations are conveniently conducted in plastic syringes and in the absence of any additives or external deoxygenation procedures using low-organic content media and ppm levels of copper. The robustness of the protocol is further exemplified by its implementation under UV, blue light or even sunlight irradiation as well as in buffer, nanopure, tap or even sea water.
Understanding dispersity control in photo-atom transfer radical polymerization: Effect of degree of polymerization and kinetic evaluation
Rolland, Manon; Lohmann, Victoria; Whitfield, Richard Bradley; et al. (2021)
Journal of Polymer Science
In photo-atom transfer radical polymerization (ATRP), dispersity can be efficiently controlled by varying the deactivator concentration. In this work, we provide mechanistic insight into dispersity-controlled photo-ATRP by conducting detailed kinetics under a range of conditions. For the lower dispersity polymers, a conventional first-order kinetic profile was observed accompanied by a linear evolution of number average molecular weight (Mn) with conversion while the reactions reached moderate to high conversions (between 66% and 93%). Whereas, when polymers of high dispersity were targeted, the Mn remained relatively constant throughout the polymerization and the reactions ceased at less than 50% of conversion. In particular, for Ð = 1.84, a significant deviation between theoretical and experimental molecular weights was evident. This deviation was unambiguously attributed to slow initiation as indicated by 1H NMR, where significant percentages of unreacted initiator were observed. Importantly, the addition of ligand at the polymerization plateau re-initiated the polymerization and led to the complete consumption of the unreacted initiator, thus enabling the synthesis of one-pot diblock copolymers. We subsequently evaluated the effect of the degree of polymerization (DP) on the obtained dispersity when a constant catalyst ratio was maintained. Based on the interpolation of those experiments results, we could predict experimental conditions for any desirable DPs and dispersities.
Network Polymer Properties Engineered Through Polymer Backbone Dispersity and Structure
Raji, Ibrahim O.; Dodo, Obed J.; Saha, Nirob K.; et al. (2024)
Angewandte Chemie. International Edition
Dispersity (& ETH; or Mw/Mn) is an important parameter in material design and as such can significantly impact the properties of polymers. Here, polymer networks with independent control over the molecular weight and dispersity of the linear chains that form the material are developed. Using a RAFT polymerization approach, a library of polymers with dispersity ranging from 1.2-1.9 for backbone chain-length (DP) 100, and 1.4-3.1 for backbone chain-length 200 were developed and transformed to networks through post-polymerization crosslinking to form disulfide linkers. The tensile, swelling, and adhesive properties were explored, finding that both at DP 100 and DP 200 the swelling ratio, tensile strength, and extensibility were superior at intermediate dispersity (1.3-1.5 for DP 100 and 1.6-2.1 for DP 200) compared to materials with either substantially higher or lower dispersity. Furthermore, adhesive properties for materials with chains of intermediate dispersity at DP 200 revealed enhanced performance compared to the very low or high dispersity chains.
Low ppm CuBr-Triggered Atom Transfer Radical Polymerization under Mild Conditions
Whitfield, Richard Bradley; Parkatzidis, Kostas; Bradford, Kate G.E.; et al. (2021)
Macromolecules
Conventional atom transfer radical polymerization, also referred to as traditional or normal ATRP, typically operates in the presence of large amounts of a CuBr activator and at relatively high temperatures (>60 °C). In this work, we report that ppm concentrations of CuBr are capable of triggering an efficient ATRP reaction at ambient temperature. In the presence of an excess ligand and the absence of any external CuBr2 deactivator, narrow molecular weight distributions can be achieved, even at quantitative monomer conversions (Z as low as 1.05 at >99% conversion). High end-group fidelity was demonstrated by matrix-assisted laser desorption/ionization time of flight mass spectrometry and further exemplified by in situ chain extensions upon sequential monomer addition, furnishing well-defined diblock copolymers with equally low dispersities. Although dimethylsulfoxide was found to be the most efficient solvent, methanol, trifluoroethanol, N,N-dimethylformamide, and acetonitrile could also be employed, showing good control over the polymerization, albeit exhibiting slower polymerization rates. Detailed UV-vis measurements in a range of solvents in conjunction with polymerization experiments starting with CuBr2/Me6TREN show reduction of CuBr2 under the conditions employed, suggesting a hybrid mechanism of ARGET and conventional ATRP.
Controlling polymer dispersity using switchable RAFT agents: Unravelling the effect of the organic content and degree of polymerization
Antonopoulou, Maria-Nefeli; Whitfield, Richard Bradley; Truong Phuoc, Nghia; et al. (2022)
European Polymer Journal
Dispersity can significantly affect material properties and related applications and as such is a significant parameter to control in polymer design. Switchable RAFT agents were recently utilized as an efficient tool to tailor polymer dispersity. In this work, we investigate the effect of the organic solvent and targeted degree of polymerization (DP) in attaining dispersity-controlled homopolymers and block copolymers. By varying the addition of acid in pure aqueous media we found that a dispersity range between 1.16 and 1.58 could be obtained while the gradual incorporation of the organic content led to broader dispersity ranges. Pleasingly, when the polymerizations were performed in aqueous media, dispersity could be efficiently controlled regardless of the targeted degree of polymerization (from DP 50 to DP 800). Instead, in mixtures containing [DMF]:[H2O] = 4:1, dispersity could be successfully tailored only up to DP = 200 while for higher targeted DPs, a reduction in the final dispersity was not feasible. To expand the scope of our system, we subsequently exploited alternative organic solvents including DMAc, dioxane, DMSO, and ACN. While DMAc showed a side reaction attributed to the high amounts of acid employed, the other solvents successfully resulted in an efficient control over dispersity with ACN requiring the lowest amount of acid to achieve the lowest dispersity value (i.e. 2 equivalents of acid yielded D ~ 1.19). Notably, the highest D polymers synthesized in the various solvents displayed very high end group fidelity as characterized by mass-spectrometry and in-situ chain extensions. After establishing optimal reaction conditions, we also synthesized a range of exemplary diblock and triblock copolymers (with alternating low and high D) demonstrating excellent dispersity control upon subsequent block additions.
Controlling primary chain dispersity in network polymers: elucidating the effect of dispersity on degradation†
Shimizu, Takanori; Whitfield, Richard Bradley; Jones, Glen R.; et al. (2023)
Chemical Science
Although dispersity has been demonstrated to be instrumental in determining many polymer properties, current synthetic strategies predominantly focus on tailoring the dispersity of linear polymers. In contrast, controlling the primary chain dispersity in network polymers is much more challenging, in part due to the complex nature of the reactions, which has limited the exploration of properties and applications. Here, a one-step method to prepare networks with precisely tuned primary chain dispersity is presented. By using an acid-switchable chain transfer agent and a degradable crosslinker in PET-RAFT polymerization, the in situ crosslinking of the propagating polymer chains was achieved in a quantitative manner. The incorporation of a degradable crosslinker, not only enables the accurate quantification of the various primary chain dispersities, post-synthesis, but also allows the investigation and comparison of their respective degradation profiles. Notably, the highest dispersity networks resulted in a 40% increase in degradation time when compared to their lower dispersity analogues, demonstrating that primary chain dispersity has a substantial impact on the network degradation rate. Our experimental findings were further supported by simulations, which emphasized the importance of higher molecular weight polymer chains, found within the high dispersity materials, in extending the lifetime of the network. This methodology presents a new and promising avenue to precisely tune primary chain dispersity within networks and demonstrates that polymer dispersity is an important parameter to consider when designing degradable materials.

Publications 1 - 10 of 45

Richard Bradley Whitfield

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