Control of molecular weight by living radical polymerization with a nitroxyl radical

Living Radical Polymerization by Biradical Compounds of Tetramethylpiperidine-1-oxyl

“…12 Although TEMPO has no ability to initiate radical polymerization of styrene, TEMPO serves as a conter radical for the autopolymerization to give a polymer with narrow polydispersity. In order to avoid dimerization of the polymers, the polymerization was carried out without BPO at 125 • C (Scheme 3).…”

“…We have already found in the TEMPO-mediated polymerization, that all the polymer chains obtained have TEMPO moiety at the chain end. 12 The absolute molecular weights of the oligomers were estimated based on intensity of the aromatic protons of styrene units and the TEMPO derivatives. The molecular weights were summarized in Table II.…”

“…It is expected that the formation of the initiator radicals was induced by the TEMPO compounds, based on our previous study. 12 The study demonstrated that concentration of the growing chain end was identical to the initial concentration of TEMPO and that all the polymer chains had TEMPO moiety at the chain end. It can be regarded that the TEMPO compounds are a kind of thermal-latent initiators when it is taken into account that the formation of initiator radicals were thermally induced by TEMPO having no ability to initiate the polymerization.…”

“…This is based on the fact that concentration of a growing polymer chain end is determined by the initial concentration of TEMPO. 12 For the preparation of symmetric block copolymers by radical polymerization, difunctional compounds of TEMPO can be substituted for initiators giving both propagating chain ends. In the polymerization using biradical compounds of TEMPO, monomers are inserted between the growing carbon radical and TEMPO, so that the following monomers form the middle segments in symmetric diblock copolymers (Scheme 1).…”

Challenges for Natural Monomers and Polymers: Novel Design Strategies and Engineering to Develop Advanced Polymers

“…New techniques for polymerization and novel methods of characterization and analytical tools have been developed to meet the challenge to make polymers with absolutely uniform length with control on polymer stereochemistry and co-polymers with precisely determined sequences and to provide control of both topology and molecular geometry. Novel anionic and cationic polymerizations [54], ring-opening polymerization [55,56], atom-transfer polymerization (ATRP) (see Scheme 1) [57], reversible addition-fragmentation chain-transfer (RAFT) polymerization [58], nitroxyl-radical-mediated polymerization [59,60], 'click' chemistry [61], etc., could be used to make predictable polymer backbone structures. The introduction of novel polymer topologies made from bio-polymers and synthetic polymers, the potential of macromolecules to form supramolecular assemblies with unique properties, the use of supercritical fluids, high-pressure or catalytic processes with specially designed carriers, etc., have contributed immensely for the bio-inspired synthesis of novel synthetic bio-polymers of sophisticated properties [62,63] Polymers with uniform structures are characterized by a narrow molecular weight distribution (MWD).…”