Protocol for Automated Kinetic Investigation/Optimization of the RAFT Polymerization of Various Monomers

Streamlining the Generation of Advanced Polymer Materials Through the Marriage of Automation and Multiblock Copolymer Synthesis in Emulsion

Synthetic polymers are of paramount importance in modern life - an incredibly wide range of polymeric materials possessing an impressive variety of properties have been developed to date. The recent emergence of artificial intelligence and automation presents a great opportunity to significantly speed up discovery and development of the next generation of advanced polymeric materials. We have focused on the high-throughput automated synthesis of multiblock copolymers that comprise three or more distinct polymer segments of different monomer composition bonded in linear sequence. The present work has exploited automation to prepare high molar mass multiblock copolymers (typically>100,000 g mol-1) using reversible addition-fragmentation chain transfer (RAFT) polymerization in aqueous emulsion. A variety of original multiblock copolymers have been synthesised via a Chemspeed robot, exemplified by a multiblock copolymer comprising thirteen constituent blocks. Moreover, libraries of copolymers of randomized monomer compositions (acrylates, acrylamides, methacrylates, and styrenes), block orders, and block lengths were also generated, thereby demonstrating the robustness of our synthetic approach. One multiblock copolymer contained all four monomer families listed in the pool, which is unprecedented in the literature. The present work demonstrates that automation has the power to render complex and laborious syntheses of such unprecedented materials not just possible, but facile and straightforward, thus representing the way forward to the next generation of complex macromolecular architectures.

High-Throughput and Combinatorial Approaches for the Development of Multifunctional Polymers

High-throughput (HT) development of new multifunctional polymers is accomplished by the combination of different HT tools established in polymer sciences in the last decade. Important advances are robotic/HT synthesis of polymer libraries, the HT characterization of polymers, and the application of spatially resolved polymer library formats, explicitly microarray and gradient libraries. HT polymer synthesis enables the generation of material libraries with combinatorial design motifs. Polymer composition, molecular weight, macromolecular architecture, etc. may be varied in a systematic, fine-graded manner to obtain libraries with high chemical diversity and sufficient compositional resolution as model systems for the screening of these materials for the functions aimed. HT characterization allows a fast assessment of complementary properties, which are employed to decipher quantitative structure-properties relationships. Moreover, these methods facilitate the HT determination of important surface parameters by spatially resolved characterization methods, including time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy. Here current methods for the high-throughput robotic synthesis of multifunctional polymers as well as their characterization are presented and advantages as well as present limitations are discussed.

High-Throughput Routes to Biomaterials Discovery

Many existing clinical treatments are limited in their ability to completely restore decreased or lost tissue and organ function, an unenviable situation only further exacerbated by a globally aging population. As a result, the demand for new medical interventions has increased substantially over the past 20 years, with the burgeoning fields of gene therapy, tissue engineering, and regenerative medicine showing promise to offer solutions for full repair or replacement of damaged or aging tissues. Success in these fields, however, inherently relies on biomaterials that are engendered with the ability to provide the necessary biological cues mimicking native extracellular matrixes that support cell fate. Accelerating the development of such "directive" biomaterials requires a shift in current design practices toward those that enable rapid synthesis and characterization of polymeric materials and the coupling of these processes with techniques that enable similarly rapid quantification and optimization of the interactions between these new material systems and target cells and tissues. This manuscript reviews recent advances in combinatorial and high-throughput (HT) technologies applied to polymeric biomaterial synthesis, fabrication, and chemical, physical, and biological screening with targeted end-point applications in the fields of gene therapy, tissue engineering, and regenerative medicine. Limitations of, and future opportunities for, the further application of these research tools and methodologies are also discussed.

Automation of Controlled/Living Radical Polymerization

Controlled/living radical polymerization (CLRP) techniques are widely utilized to synthesize advanced and controlled synthetic polymers for chemical and biological applications. While automation has long stood as a high-throughput (HTP) research tool to increase productivity as well as synthetic/analytical reliability and precision, oxygen intolerance of CLRP has limited the widespread adoption of these systems. Recently, however, oxygen-tolerant CLRP techniques, such as oxygen-tolerant photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT), enzyme degassing of RAFT (Enz-RAFT), and atom-transfer radical polymerization (ATRP), have emerged. Herein, the use of a Hamilton MLSTARlet liquid handling robot for automating CLRP reactions is demonstrated. Synthesis processes are developed using Python and used to automate reagent handling, dispensing sequences, and synthesis steps required to create homopolymers, random heteropolymers, and block copolymers in 96-well plates, as well as postpolymerization modifications. Using this approach, the synergy between highly customizable liquid handling robotics and oxygen-tolerant CLRP to automate advanced polymer synthesis for HTP and combinatorial polymer research is demonstrated.

Semiautomated Parallel RAFT Copolymerization of Isoprene with Glycidyl Methacrylate

Copolymerization of isoprene (IP) with glycidyl methacrylate (GMA) was performed under RAFT (reversible addition-fragmentation chain-transfer) polymerization conditions in a platform for high-output experimentation. Covering the range between 1 and 0.2 molar fraction of IP in the feed, four sets of reactions were carried out at 10, 15, 20, and 30 h at 115 °C. The kinetic data obtained were used to estimate the reactivity ratios using a nonlinear least-squares approach (NLLS). Reactivity ratios r_GMA = 0.61 and r_IP = 0.74 indicate that both monomers tend to crosspropagate in agreement with known literature values. Concerning the RAFT study, relatively good control and livingness of the copolymerization was observed except for the experiment in which IP represents 20 mol % in the feed. ¹H NMR characterization confirmed the presence of both monomers in the final copolymer, particularly the presence of the epoxy ring of GMA which is susceptible to post polymerization reactions. Finally, preliminary results on the hydrogenation of various polymers are discussed.

Enzyme Degassing for Oxygen-Sensitive Reactions in Open Vessels of an Automated Parallel Synthesizer: RAFT Polymerizations

An enzyme degassing method for oxygen-intolerant polymerizations was implemented in a commercially available automated parallel synthesizer and tested for reversible addition-fragmentation chain transfer (RAFT) polymerizations performed in open vessels. For this purpose, a recently reported methodology that employs the enzyme glucose oxidase (GOx) to deplete oxygen in reaction media was utilized. The effectiveness of this approach to perform unattended parallel polymerization reactions in open vessels was demonstrated by comparing experimental results to those obtained under similar experimental conditions but utilizing the common degassing method of sparging N₂ to remove oxygen. The proposed experimental technique displayed good precision in performing RAFT polymerizations and good control of the obtained polymers and could be easily adapted to other systems where the removal of oxygen is mandatory. This alternative high-throughput/high-output method may have the potential to increase productivity in research projects where oxygen-intolerant reactions are involved.

Optimization of the high-throughput synthesis of multiblock copolymer nanoparticles in aqueous media via polymerization-induced self-assembly

High-throughput synthesis of multiblock copolymer nanoparticles via PISA.

Polymer-protein conjugation via a ‘grafting to’ approach – a comparative study of the performance of protein-reactive RAFT chain transfer agents

The performances of various protein-reactive RAFT CTAs to afford polymer-protein conjugation via a grafting-to approach were compared.

Thermoresponsive polymer coated gold nanoparticles: from MADIX/RAFT copolymerization of N-vinylpyrrolidone and N-vinylcaprolactam to salt and temperature induced nanoparticle aggregation

In the present contribution, we report the synthesis of thermoresponsive homo and statistical copolymers of N-vinylcaprolactam and N-vinylpyrrolidone and the corresponding responsive gold nanoparticles.

Cu(0)-mediated polymerization of hydrophobic acrylates using high-throughput experimentation

In this paper the optimization of the Cu(0)-mediated polymerization of n-butyl acrylate and 2-methoxyethyl acrylate is reported using an automated parallel synthesizer.

Automated parallel freeze-evacuate-thaw degassing method for oxygen-sensitive reactions: RAFT polymerization

An automated and parallel freeze-evacuate-thaw degassing method in a commercially available synthesizer is disclosed and tested for its applicability to reversible addition-fragmentation chain transfer (RAFT) polymerization. The effectiveness of this method to eliminate oxygen in polymerization reactions is demonstrated by directly comparing it against experiments performed using conventional laboratory techniques. Apart from the demonstrated accuracy, the proposed method has also shown significant precision when performing RAFT polymerizations. The reported experimental technique can be easily adapted to other chemical systems where the removal of oxygen is mandatory. This new high-throughput method has the potential to significantly increase the productivity and/or research outcomes in laboratories where oxygen-sensitive reactions are carried out.

Living Radical Polymerization by the RAFT Process - A Second Update

This paper provides a second update to the review of reversible deactivation radical polymerization achieved with thiocarbonylthio compounds (ZC(=S)SR) by a mechanism of reversible addition–fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379–410). The first update was published in November 2006 (Aust. J. Chem. 2006, 59, 669–692). This review cites over 500 papers that appeared during the period mid-2006 to mid-2009 covering various aspects of RAFT polymerization ranging from reagent synthesis and properties, kinetics and mechanism of polymerization, novel polymer syntheses and a diverse range of applications. Significant developments have occurred, particularly in the areas of novel RAFT agents, techniques for end-group removal and transformation, the production of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.