High Throughput Multidimensional Kinetic Screening in Continuous Flow Reactors

An automated high throughput multidimensional reaction screening platform based on an inline Fourier-transform infrared spectroscopy is presented. By combining flow chemistry, machine automation and inline analysis, the platform is able to screen reactions in multidimensions (residence time, monomer concentration, degree of polymerization, reaction temperature and monomer conversion) rapidly and efficiently way. Kinetic data libraries associated with high data precision (absolute error <4 %), high reproducibility and high data density are built with ease from the platform. To test the method, we screened the reversible addition-fragmentation chain transfer polymerization of methyl acrylate in unmatched detail, and the ring opening metathesis polymerization of methyl-5-norbornene-2-carboxylate. The method we introduce is a key step in providing "big data" for data driven research in the future, and already at present allows for precise prediction of reaction outcomes within the high-dimensional chemical parameter space that is screened.

Multiblock copolymer synthesis via RAFT emulsion polymerization

A multiblock copolymer is a polymer of a specific structure that consists of multiple covalently linked segments, each comprising a different monomer type. The control of the monomer sequence has often been described as the "holy grail" of synthetic polymer chemistry, with the ultimate goal being synthetic access to polymers of a "perfect" structure, where each monomeric building block is placed at a desired position along the polymer chain. Given that polymer properties are intimately linked to the microstructure and monomer distribution along the constituent chains, it goes without saying that there exist seemingly endless opportunities in terms of fine-tuning the properties of such materials by careful consideration of the length of each block, the number and order of blocks, and the inclusion of monomers with specific functional groups. The area of multiblock copolymer synthesis remains relatively unexplored, in particular with regard to structure-property relationships, and there are currently significant opportunities for the design and synthesis of advanced materials. The present review focuses on the synthesis of multiblock copolymers via reversible addition-fragmentation chain transfer (RAFT) polymerization implemented as aqueous emulsion polymerization. RAFT emulsion polymerization offers intriguing opportunities not only for the advanced synthesis of multiblock copolymers, but also provides access to polymeric nanoparticles of specific morphologies. Precise multiblock copolymer synthesis coupled with self-assembly offers material morphology control on length scales ranging from a few nanometers to a micrometer. It is imperative that polymer chemists interact with physicists and material scientists to maximize the impact of these materials of the future.

Reverse Sequence Polymerization‐Induced Self‐Assembly in Aqueous Media

We report a new aqueous polymerization‐induced self‐assembly (PISA) formulation that enables the hydrophobic block to be prepared first when targeting diblock copolymer nano‐objects. This counter‐intuitive reverse sequence approach uses an ionic reversible addition–fragmentation chain transfer (RAFT) agent for the RAFT aqueous dispersion polymerization of 2‐hydroxypropyl methacrylate (HPMA) to produce charge‐stabilized latex particles. Chain extension using a water‐soluble methacrylic, acrylic or acrylamide comonomer then produces sterically stabilized diblock copolymer nanoparticles in an aqueous one‐pot formulation. In each case, the monomer diffuses into the PHPMA particles, which act as the locus for the polymerization. A remarkable change in morphology occurs as the ≈600 nm latex is converted into much smaller sterically stabilized diblock copolymer nanoparticles, which exhibit thermoresponsive behavior. Such reverse sequence PISA formulations enable the efficient synthesis of new functional diblock copolymer nanoparticles.

EFFECT OF EMULSION SBR PREPARED BY ASYMMETRIC REVERSIBLE ADDITION-FRAGMENTATION TRANSFER AGENT ON PROPERTIES OF SILICA-FILLED COMPOUNDS

The development of ultra-high-performance tires that satisfy fuel efficiency, traction, handling performance, and abrasion resistance has gained significant importance in the tire industry. Solution SBR has been used as a raw material, owing to its useful characteristics (e.g., narrow dispersity controllable microstructure and chain-end functionalization). In a recent improvement, emulsion SBR (ESBR), a high-molecular-weight compound with narrow dispersity, has been reported for application in the tire tread compounds. In particular, S,S-dibenzyl trithiocarbonate (DBTC) reversible addition-fragmentation transfer (RAFT) ESBR has exhibited excellent abrasion resistance and fuel efficiency in unfilled and carbon black–filled vulcanizates. However, owing to the symmetrical structure of DBTC RAFT ESBR, the polymer chain was shortened by the reaction of a silane coupling agent with trithiocarbonate, leading to poor abrasion resistance and fuel efficiency in the case of silica-filled vulcanizates. In this study, benzyl (4-methoxyphenyl) trithiocarbonate (BMPTC), an asymmetric RAFT agent that promotes unilateral polymer growth, was synthesized and used in the polymerization of BMPTC RAFT ESBR. Chain cleavage was not observed. Upon application to silica-filled vulcanizates, BMPTC RAFT ESBR exhibited improved abrasion resistance (by 9%), improved fuel efficiency (by 20%), and improved wet traction performance (by 10%) compared with the DBTC RAFT ESBR.

Synthesis of ABA triblock copolymer nanoparticles by polymerization induced self-assembly and their application as an efficient emulsifier

ABA triblock copolymer nanoparticles of PHPMA-b-PS-b-PHPMA were synthesized by PISA and demonstrated to be an efficient emulsifier.

Initiation of RAFT Polymerization: Electrochemically Initiated RAFT Polymerization in Emulsion (Emulsion eRAFT), and Direct PhotoRAFT Polymerization of Liquid Crystalline Monomers

We report on two important advances in radical polymerization with reversible addition–fragmentation chain transfer (RAFT polymerization). (1) Electrochemically initiated emulsion RAFT (eRAFT) polymerization provides rapid polymerization of styrene at ambient temperature. The electrolytes and mediators required for eRAFT are located in the aqueous continuous phase separate from the low-molar-mass-dispersity macroRAFT agent mediator and product in the dispersed phase. Use of a poly(N,N-dimethylacrylamide)-block-poly(butyl acrylate) amphiphilic macroRAFT agent composition means that no added surfactant is required for colloidal stability. (2) Direct photoinitiated (visible light) RAFT polymerization provides an effective route to high-purity, low-molar-mass-dispersity, side chain liquid-crystalline polymers (specifically, poly(4-biphenyl acrylate)) at high monomer conversion. Photoinitiation gives a product free from low-molar-mass initiator-derived by-products and with minimal termination. The process is compared with thermal dialkyldiazene initiation in various solvents. Numerical simulation was found to be an important tool in discriminating between the processes and in selecting optimal polymerization conditions.

Effect of Reversible Addition-Fragmentation Transfer Emulsion Styrene Butadiene Rubber (RAFT ESBR) on the Properties of Carbon Black-Filled Compounds

Tread is an important component that directly affects the performance of passenger car radial (PCR) tires. Styrene-butadiene rubber (SBR) is mainly used for tire tread and it includes solution styrene-butadiene rubber (SSBR) and emulsion styrene-butadiene rubber (ESBR). Although SSBR is mainly used, the manufacturing process for SSBR is more challenging than ESBR, which is environmentally friendly, but has the disadvantage of a broad molecular weight distribution. To overcome this, a reversible addition-fragmentation radical transfer (RAFT) polymerization technique is used in ESBR polymerization. An environmentally friendly RAFT ESBR with a narrow dispersity can be polymerized. Here, carbon black-filled compounds were manufactured while using RAFT ESBR, and their properties were compared to ESBR. The analysis showed a low crosslink density of RAFT ESBR, due to the high polysulfide crosslink structure. We manufactured a carbon black-filled compound with the same crosslink density and structure as the ESBR carbon black-filled compound, and the effect of the dispersity of the base polymer was investigated. RAFT ESBR showed 9% better abrasion resistance and 29% better fuel efficiency than ESBR, according to the analysis of the data. The narrow dispersity can reduce energy loss and positively influence the abrasion resistance and fuel efficiency.