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Recent developments in polymerization reactions utilizing thiocarbonylthio compounds have highlighted the surprising versatility of these unique molecules. The increasing popularity of reversible addition–fragmentation chain transfer (RAFT) radical polymerization as a means of producing well‐defined, ‘controlled’ synthetic polymers is largely due to its simplicity of implementation and the availability of a wide range of compatible reagents. However, novel modes of thiocarbonylthio activation can expand the technique beyond the traditional system (i.e., employing a free radical initiator) pushing the applicability and use of thiocarbonylthio compounds even further than previously assumed. The primary advances seen in recent years are a revival in the direct photoactivation of thiocarbonylthio compounds, their activation via photoredox catalysis, and their use in cationic polymerizations. These synthetic approaches and their implications for the synthesis of controlled polymers represent a significant advance in polymer science, with potentially unforeseen benefits and possibilities for further developments still ahead. This Research News aims to highlight key works in this area while also clarifying the differences and similarities of each system.

Sequence control in chain-growth polymerization is still one of the most challenging topics in synthetic polymer chemistry in contrast to natural macromolecules with completely sequence-regulated structures like proteins and DNA. Here, we report the quantitative and highly selective 1:2 sequence-regulated radical copolymerization of naturally occurring (+)-d-limonene (L) and a maleimide (M) in fluoroalcohol giving chiral copolymers with high glass transition temperatures (220-250 degrees C) originating from the specific rigid cyclic structures of the monomers. Furthermore, the combination with a reversible addition-fragmentation chain transfer (RAFT) agent (C-S) via the controlled/living radical polymerization resulted in end-to-end sequence-regulated copolymers [C-(M-M-L)(n)-M-S] with both highly sequenced chain ends and main-chain repeating units as well as controlled molecular weights.

A metal-free, cationic, reversible addition-fragmentation chain-transfer (RAFT) polymerization was proposed and realized. A series of thiocarbonylthio compounds were used in the presence of a small amount of triflic acid for isobutyl vinyl ether to give polymers with controlled molecular weight of up to 1×10(5) and narrow molecular-weight distributions (Mw /Mn <1.1). This "living" or controlled cationic polymerization is applicable to various electron-rich monomers including vinyl ethers, p-methoxystyrene, and even p-hydroxystyrene that possesses an unprotected phenol group. A transformation from cationic to radical RAFT polymerization enables the synthesis of block copolymers between cationically and radically polymerizable monomers, such as vinyl ether and vinyl acetate or methyl acrylate.

Block copolymer lithography holds promise as a next-generation technique to achieve the sub-20 nm feature sizes demanded by semiconductor roadmaps. While molecular weight and block immiscibility have traditionally been used to control feature size, this study demonstrates that macromolecular architecture is also a powerful tool for tuning domain spacing. To demonstrate this concept, a new synthetic strategy for cyclic block polymers based on highly efficient "click" coupling of difunctional linear chains is developed, and the thin film self-assembly of cyclic polystyrene-block-polyethylene oxide (cPS-b-PEO) is compared with the corresponding linear analogues. The reduced hydrodynamic radii of the cyclic systems result in ~30% decrease in domain spacing over the corresponding linear polymers.

Proteins and nucleic acids are sequence-regulated macromolecules with various properties originating from their perfectly sequenced primary structures. However, the sequence regulation of synthetic polymers, particularly vinyl polymers, has not been achieved and is one of the ultimate goals in polymer chemistry. In this study, we report a strategy to obtain sequenceregulated vinyl copolymers consisting of styrene, acrylate and vinyl chloride units using metalcatalysed step-growth radical polyaddition of designed monomers prepared from common vinyl monomer building blocks. Unprecedented ABCC-sequence-regulated copolymers with perfect vinyl chloride -styrene -acrylate -acrylate sequences were obtained by copper-catalysed step-growth radical polymerization of designed monomers possessing unconjugated C = C and reactive C -Cl bonds. This strategy may open a new route in the study of sequence-regulated synthetic polymers.

The simultaneous control of the tacticity and molecular weight of poly(N-vinylpyrrolidone) during radical polymerization is reported for the first time. For molecular weight control, xanthates of (O-ethylxanthylmethyl)benzene and [1-(O-ethylxanthyl)ethyl]benzene were used as RAFT/MADIX chain transfer agents (CTAs) for the radical polymerization of N-vinylpyrrolidone (NVP). Both led to a controlled/living radical polymerization, and the latter showed higher chain transfer ability under the optimal conditions; the molecular weight distribution was 1.36 when the molecular weight was up to 26 700. The polymerization was studied between 20 and 120 °C and at various concentrations of CTA. All the polymerizations showed an induction period and rate retardation dependent on both the concentration of CTA and temperature. For tacticity control, the polymerization was carried out in fluoroalcohols via a conventional radical process without CTAs to give syndiotactic polymers. The polymer tacticity was dependent on the amount of the fluoroalcohol, and a more acidic and bulkier fluoroalcohol led to a higher syndiotacticity. Especially with (CF3)3COH, the r dyad increased to 62.6% from 53.5% for the atactic poly(NVP) obtained in the usual solvents. The 1H NMR analysis of the mixture of NVP and the fluoroalcohols indicated that a 1:1 hydrogen-bonding complex was formed, suggesting that the complex was responsible for the tacticity control of the polymer. When the CTA was used in the fluoroalcohols, the living and syndiospecific polymerization proceeded to enable the simultaneous control of the molecular weight and the tacticity.

Natural biopolymers, such as DNA and proteins, have uniform microstructures with defined molecular weight, precise monomer sequence, and stereoregularity along the polymer main chain that affords them unique biological functions. To reproduce such structurally perfect polymers and understand the mechanism of specific functions through chemical approaches, researchers have proposed using synthetic polymers as an alternative due to their broad chemical diversity and relatively simple manipulation. Herein, we report a new methodology to prepare sequence-controlled and stereospecific oligomers using alternating radical chain growth and sequential photoinduced RAFT single unit monomer insertion (photo-RAFT SUMI). Two families of cyclic monomers, the indenes and the N-substituted maleimides, can be alternatively inserted into RAFT agents, one unit at a time, allowing the monomer sequence to be controlled through sequential and alternating monomer addition. Importantly, the stereochemistry of cyclic monomer insertion into the RAFT agents is found to be trans-selective along the main chains due to steric hindrance from the repeating monomer units. All investigated cyclic monomers provide such trans-selectivity, but analogous acyclic monomers give a mixed cis- and trans-insertion.