Reflection on the Matyjaszewski Lab Webinar Series and the Rise of Webinars in Polymer Chemistry

Webinar series are helping our community of polymer scientists to stay engaged and connected, despite the cancellation of in-person meetings and the periodic closure of laboratories to contain the spread of the coronavirus pandemic. The sustainable and inclusive character of these virtual events make them valuable learning and networking opportunities. As organizers of the Matyjaszewski Lab Webinar Series, we share herein our experience, highlighting the benefits of virtual meetings and providing a short guide for webinar organizers. Researchers, particularly young scientists, are encouraged to organize such virtual events to broaden their skills and strengthen their professional network

Photoinduced atom transfer radical polymerization in ab initio emulsion

Atom transfer radical polymerization (ATRP) performed in ab initio emulsion provides access to well-defined polymers in a low-cost, eco-friendly environment. Herein, photoinduced ab initio emulsion ATRP of various (meth)acrylate monomers is reported. The polymerization rate increased with the solubility of the monomer in water. Well-controlled (co)polymerizations were achieved under violet light and low catalyst loading, even in an open-to-air system through enzymatic degassing

Mesoporous graphitic carbon nitride as a heterogeneous catalyst for photoinduced copper(I)-catalyzed azide-alkyne cycloaddition

A new protocol has been developed for the photoinduced CuAAC click reaction using heterogeneous mesoporous graphitic carbon nitride as the photocatalyst.</p

Depolymerization of P(PDMS11MA) Bottlebrushes via Atom Transfer Radical Polymerization with Activator Regeneration

Depolymerization of vinyl polymers into monomers is energy-intensive due to the high thermal and chemical stability of the backbone. Depolymerizations of methacrylic polymers are typically conducted above the ceiling temperature and thermal degradation temperature to degrade polymers by bond scission. This work investigates the catalyzed depolymerization of a Cl-capped poly(poly(dimethylsiloxane) methacrylate) (P(PDMS11MA-Cl)) polymer mediated by an atom transfer radical polymerization catalyst: copper(II) chloride/tris(2-pyridylmethyl)amine (CuCl2/TPMA) at 170 °C. The depolymerization yield, rate, and selectivity were improved by increasing the ratio of [TPMA]/[CuCl2]. Electron transfer from the ligand contributed to the Cu(I) activator (re)generation at high temperature (T> 130 °C), as proven by ultraviolet-visible spectroscopy. The bottlebrush could be partially depolymerized and repolymerized over a few cycles

Red-Light-Induced, Copper-Catalyzed Atom Transfer Radical Polymerization

Despite advances in photochemical atom transfer radical polymerization (photoATRP), these systems often rely on the use of UV light for the activation/generation of the copper-based catalytic species. To circumvent the problems associated with the UV light, we developed a dual photoredox catalytic system to mediate photoinduced ATRP under red-light irradiation. The catalytic system is comprised of a Cu catalyst to control the polymerization via ATRP equilibrium and a photocatalyst, such as zinc(II) tetraphenylporphine or zinc(II) phthalocyanine, to generate the activator CuIspecies under red-light irradiation. In addition, this system showed oxygen tolerance due to the consumption of oxygen in the photoredox reactions, yielding well-controlled polymerizations without the need for deoxygenation processes

Surface-Initiated Photoinduced ATRP: Mechanism, Oxygen Tolerance, and Temporal Control during the Synthesis of Polymer Brushes

Surface-initiated, photoinduced atom transfer radical polymerization (SI-photoATRP) enables the controlled and rapid synthesis of compositionally diverse polymer brushes over large areas by employing very small reaction volumes under ambient conditions and without the need for prior deoxygenation of monomer mixtures. The concentration of copper species and the type and content of amine-based ligands determine the mechanism of SI-photoATRP, regulate the kinetics of polymer-brush growth, and govern the tolerance of this polymer-grafting method toward oxygen. Despite mechanistic analogies with the corresponding solution processes, the intrinsic, highly confined nature of SI-photoATRP leads to significant differences from polymerizations within homogeneous systems. This is especially important to attain controlled/living polymerization and temporal control over polymer-brush growth by using UV light as a trigger

Assemblies of Polyacrylonitrile-Derived Photoactive Polymers as Blue and Green Light Photo-Cocatalysts for Cu-Catalyzed ATRP in Water and Organic Solvents

Photoluminescent nanosized quasi-spherical polymeric assemblies prepared by the hydrothermal reaction of polyacrylonitrile (PAN), ht-PLPPAN, were demonstrated to have the ability to photo-induce atom transfer radical polymerization (ATRP) catalyzed by low, parts per million concentrations of CuII complex with tris(2-pyridylmethyl)amine (TPMA). Such photo induced ATRP reactions of acrylate and methacrylate monomers were performed in water or organic solvents, using ht-PLPPAN as the photo-cocatalyst under blue or green light irradiation. Mechanistic studies indicate that ht-PLPPAN helps to sustain the polymerization by facilitating the activation of alkyl bromide species by two modes: 1) green or blue light-driven photoreduction of the CuII catalyst to the activating CuI form, and 2) direct activation of dormant alkyl bromide species which occurs only under blue light. The photoreduction of the CuII complex by ht-PLPPAN was confirmed by linear sweep voltammetry performed under illumination. Analysis of the polymerization kinetics in aqueous media indicated even though CuI complexes comprised only 1–1.4% of all Cu species at equilibrium, they exhibited high activation rate constant and activated the alkyl bromide initiators five to six orders of magnitude faster than ht-PLPPAN

Effect of Added Salt on Disordered Poly(ethylene oxide)-Block-Poly(methyl methacrylate) Copolymer Electrolytes

We studied the effect of salt addition on a diblock copolymer system with a negative Flory-Huggins interaction parameter, χ, indicative of attractive interactions between the two blocks. The system studied is poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-PMMA) with added lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. We studied two asymmetric block copolymers, PEO-PMMA(10-33) and PEO-PMMA(10-64), where the numbers refer to the molar masses of the blocks in kg mol-1. The small-angle X-ray scattering (SAXS) profiles for PEO-PMMA(10-33) were featureless at all salt concentrations. In contrast, PEO-PMMA(10-64) exhibited SAXS peaks when the salt concentration was between 0.22 ≤ m (mol Li/kg polymer) ≤ 0.44. The appearance of SAXS peaks only in PEO-PMMA(10-64) is consistent with the predictions of ionic self-consistent field theory developed by de la Cruz and co-workers, which predicts that in systems with negative χ, ordered phases are only found when the volume fraction of the ionic block is about 10%

Conjugated Cross-linked Phenothiazines as Green or Red Light Heterogeneous Photocatalysts for Copper-Catalyzed Atom Transfer Radical Polymerization

Using the power of light to drive controlled radical polymerizations has provided significant advances in synthesis of well-defined polymers. Photoinduced atom transfer radical polymerization (ATRP) systems often employ UV light to regenerate copper activator species to mediate the polymerization. Taking full advantage of long-wavelength visible light for ATRP would require developing appropriate photocatalytic systems that engage in photoinduced electron transfer processes with the ATRP components to generate activating species. Herein, we developed conjugated microporous polymers (CMP) as heterogeneous photocatalysts to exploit the power of visible light in promoting copper-catalyzed ATRP. The photocatalyst was designed by cross-linking phenothiazine (PTZ) as a photoactive core in the presence of dimethoxybenzene as a cross-linker via the Friedel-Crafts reaction. The resulting PTZ-CMP network showed photoactivity in the visible region due to the extended conjugation throughout the network because of the aromatic groups connecting the PTZ units. Therefore, photoinduced copper-catalyzed ATRP was performed with CMPs that regenerated activator species under green or red light irradiation to start the ATRP process. This resulted in efficient polymerization of acrylate and methacrylate monomers with high conversion and well-controlled molecular weight. The heterogeneous nature of the photocatalyst enabled easy separation and efficient reusability in subsequent polymerizations