¹H NMR Study of Hydrogen Abstraction in Model Compound Mimics of Polymers

Abstract

Small molecules representing common synthetic polymers were subjected to photochemically induced hydrogen abstraction by benzophenone. Reactions were monitored using 1 H NMR to query the factors that influence preferential abstraction of protons in unique chemical environments. Differences in bond dissociation energies do not fully explain the observed hydrogen abstraction preferences. To that end, we identify contributions to abstraction from prereactive complexation, radical stability, steric effects and charge transfer effects. Using representative small molecule model compounds in lieu of polymeric materials is a novel approach to understanding photochemical reaction in polymers; however, it cannot probe the contributions of macromolecular effects-e.g. polymer rigidity or side chain and backbone mobility-to preferential hydrogen abstraction.

Ultra-High Molecular Weight Alpha-Amino Poly(Methyl Methacrylate) with HighTgthrough Emulsion Polymerization by Using Transition Metal Cation-Tertiary Amine Pairs as a Mono-Centered Initiator

“…Furthermore, Fe II species could form highly active oxidative complexes with O 2 or H 2 O 2 in a form of Fe III OOH, Fe IV = O etc., which steadily oxidize unactivated aliphatic C–H moieties of PMMA chains, including in‐chain –CH 2 –, alpha –CH 3 and –OCH 3 groups, to C radicals via an ET–PT, HAT or proton‐coupled electron transfer (PCET) mechanism . Poly( n ‐butyl acrylate) (P n BA) has been reported to be a multi‐functional macro‐sensitizer (proton donor via ET–PT or hydrogen‐atom donor via HAT) in UV‐induced benzophenone‐initiated radical coupling, leading to branched or crosslinked P n BA . PMMA in‐chain macro‐radicals initiate polymerization of MMA in monomer‐swollen polymer particles, leading to slightly long‐chain branched PMMA with a higher MW.…”

Multifunctional and spatially controlled bioconjugation to melt coextruded nanofibers

“…25,26 The pendant functional group attached to the benzophenone is then available for secondary modification. The photochemical scheme was chosen for its simplicity and ability to spatially pattern molecules onto the fiber surface.…”

“…The fiber modification scheme utilizes photochemistry in which a benzophenone derivative is irradiated with ultraviolet light and undergoes a radical insertion into the PCL backbone. 25,26 The pendant functional group attached to the benzophenone is then available for secondary modification. The photochemical scheme was chosen for its simplicity and ability to spatially pattern molecules onto the fiber surface.…”

A Mechanically Robust, Stiff, and Tough Hyperbranched Supramolecular Polymer Hydrogel

“…In the general mechanism of Type II photoinitiated SCVP, the Type II photoinitiator such as benzophenone (BP) and camphorquinone(CQ) are activated by light to abstract hydrogen from hydrogen donating sites of the inimers (i.e., 2‐hydroxyethyl methacrylate and 2‐(dimethylamino)ethyl methacrylate to form initiating/branching radical species). The hydrogen donating sites can be primary amides, amines, alcohols, and ethers …”