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1. Versatile synthesis of siloxane‐based graft copolymers with tunable grafting density

   https://doi.org/10.1002/pol.20230615  

   D'Ambra, Colton A. ; Czuczola, Michael ; Getty, Patrick T. ; Murphy, Elizabeth A. ; Abdilla, Allison ; Biswas, Souvagya ; Mecca, Jodi M. ; Bekemeier, Thomas D. ; Swier, Steven ; Hawker, Craig J. ; et al ( October 2023 , Journal of Polymer Science)

   A versatile synthetic platform is reported that affords high molecular weight graft copolymers containing polydimethylsiloxane (PDMS) backbones and vinyl‐based polymer side chains with excellent control over molecular weight and grafting density. The synthetic approach leverages thiol‐ene click chemistry to attach an atom‐transfer radical polymerization (ATRP) initiator to a variety of commercially available poly(dimethylsiloxane‐co‐methylvinylsiloxane) backbones (PDMS‐co‐PVMS), followed by controlled radical polymerization with a wide scope of vinyl monomers. Selective degradation of the siloxane backbone with tetrabutylammonium fluoride confirmed the controlled nature of side‐chain growth via ATRP, yielding targeted side‐chain lengths for copolymers containing up to 50% grafting density and overall molecular weights in excess of 1 MDa. In addition, by using a mixture of thiols, grafting density and functionality can be further controlled by tuning initiator loading along the backbone. For example, solid‐state fluorescence of the graft copolymers was achieved by incorporating a thiol‐containing fluorophore along the siloxane backbone during the thiol‐ene click reaction. This simple synthetic platform provides facile control over the properties of a wide variety of grafted copolymers containing flexible PDMS backbones and vinyl polymer side chains.

    

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2. Employing Heterocyclic Hypervalent Iodine Compounds with ICl Bonds as Initiators and Chain Transfer Agents in the Synthesis of Branched Polymers

   https://doi.org/10.1002/macp.201800471  

   Cao, Yakun ; Kumar, Rajesh ; Tsarevsky, Nicolay V. ( January 2019 , Macromolecular Chemistry and Physics)

   Heterocyclic hypervalent (HV) iodine(III) compounds with ICl bonds and various substituents at the N atom are synthesized and found to be very efficient chain transfer agents in the polymerization of styrene with transfer coefficients exceeding that of CCl₄by 2–3 orders of magnitude, depending on the structure. The chain transfer rate coefficients are also determined. Due to the presence of thermally labile HV bonds, the compounds degrade homolytically upon heating and can initiate radical polymerization. For instance, 1‐chloro‐2‐hexyl‐1,2‐benziodazol‐3(2H)‐one, is used in the polymerization of styrene, which yields low molecular weight polymers with alkyl chloride groups at the α‐ (initiation) and the ω‐chain ends (transfer). Chain‐end functionalization reactions with azide and chain extension under low‐catalyst‐concentration atom transfer radical polymerization (ATRP) conditions of the prepared telechelic polymers are carried out. The same initiator/chain transfer agent is successfully employed in the synthesis of highly branched polymers with multiple alkyl chloride‐type chain ends when added to mixtures of styrene and 1,4‐divinylbenzene containing 10–80 mol% of the divinyl crosslinker, or even pure crosslinker. In all cases, soluble hyperbranched polymers are obtained up to moderate monomer conversions. The effects of crosslinker and HV iodine(III) compound concentrations on the polymerization outcome are studied systematically.

    

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3. Electrochemically mediated atom transfer radical polymerization with dithiocarbamates as alkyl pseudohalides

   https://doi.org/10.1002/pola.29197  

   Wang, Yi ; Fantin, Marco ; Matyjaszewski, Krzysztof ( September 2018 , Journal of Polymer Science Part A: Polymer Chemistry)

   Electrochemically mediated atom transfer radical polymerizations (ATRPs) provide well‐defined polymers with designed dispersity as well as under external temporal and spatial control. In this study, 1‐cyano‐1‐methylethyl diethyldithiocarbamate, typically used as chain‐transfer agent (CTA) in reversible addition–fragmentation chain transfer (RAFT) polymerization, was electrochemically activated by the ATRP catalyst Cu^I/2,2′‐bipyridine (bpy) to control the polymerization of methyl methacrylate. Mechanistic study showed that this polymerization was mainly controlled by the ATRP equilibrium. The effect of applied potential, catalyst counterion, catalyst concentration, and targeted degree of polymerization were investigated. The chain‐end functionality was preserved as demonstrated by chain extension of poly(methyl methacrylate) withn‐butyl methacrylate and styrene. This electrochemical ATRP procedure confirms that RAFT CTAs can be activated by an electrochemical stimulus. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.2019,57, 376–381

    

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4. Fully oxygen-tolerant atom transfer radical polymerization triggered by sodium pyruvate

   https://doi.org/10.1039/d0sc03179h  

   Szczepaniak, Grzegorz ; Łagodzińska, Matylda ; Dadashi-Silab, Sajjad ; Gorczyński, Adam ; Matyjaszewski, Krzysztof ( August 2020 , Chemical Science)

   null (Ed.)

   ATRP (atom transfer radical polymerization) is one of the most robust reversible deactivation radical polymerization (RDRP) systems. However, the limited oxygen tolerance of conventional ATRP impedes its practical use in an ambient atmosphere. In this work, we developed a fully oxygen-tolerant PICAR (photoinduced initiators for continuous activator regeneration) ATRP process occurring in both water and organic solvents in an open reaction vessel. Continuous regeneration of the oxidized form of the copper catalyst with sodium pyruvate through UV excitation allowed the chemical removal of oxygen from the reaction mixture while maintaining a well-controlled polymerization of N -isopropylacrylamide (NIPAM) or methyl acrylate (MA) monomers. The polymerizations of NIPAM were conducted with 250 ppm (with respect to the monomer) or lower concentrations of CuBr 2 and a tris[2-(dimethylamino)ethyl]amine ligand. The polymers were synthesized to nearly quantitative monomer conversions (>99%), high molecular weights ( M n > 270 000), and low dispersities (1.16 < Đ < 1.44) in less than 30 min under biologically relevant conditions. The reported method provided a well-controlled ATRP ( Đ = 1.16) of MA in dimethyl sulfoxide despite oxygen diffusion from the atmosphere into the reaction system. 

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5. Internal plasticization of poly(vinyl chloride) by grafting acrylate copolymers via copper‐mediated atom transfer radical polymerization

   https://doi.org/10.1002/app.50747  

   Li, Longbo ; Schneider, Yanika ; Hoeglund, Adrienne B. ; Braslau, Rebecca ( March 2021 , Journal of Applied Polymer Science)

   Internal plasticization of poly(vinyl chloride) (PVC) was achieved in one‐step using copper‐mediated atom transfer radical polymerization to graft different ratios of randomn‐butyl acrylate and 2–2‐(2‐ethoxyethoxy)ethyl acrylate copolymers from defect sites on the PVC chain. Five graft polymers were made with different ratios of poly(butyl acrylate) (PBA) and poly(2–2‐(2‐ethoxyethoxy)ethyl acrylate) (P2EEA); the glass transition temperatures (T_g) of functionalized PVC polymers range from − 25 to − 50°C. SingleT_gvalues were observed for all polymers, indicating good compatibility between PVC and grafted chains, with no evidence of microphase separation. Plasticization efficiency is higher for polyether P2EEA moieties compared with PBA components. The resultant PVC graft copolymers are thermally more stable compared to unmodified PVC. Increasing the reaction scale from 2 to 14 g produces consistent and reproducible results, suggesting this method could be applicable on an industrial scale.

    

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