Synthesis of block and star copolymers by photoinduced radical coupling process

Abstract

The general design for the synthesis of AB diblock, and A2B and AB2 star copolymers based on the statistical coupling of poly(styrene) (PSt) and poly (methyl methacrylate) (PMMA) macromolecules containing photoreactive benzophenone is presented. For this purpose, mono‐ and bifunctional initiators for Atom Transfer Radical Polymerization (ATRP) bearing benzophenone group were synthesized and characterized. End‐ and mid‐chain benzophenone functional PSt and PMMA with low molecular weights were obtained by ATRP using these initiators in the presence of CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) catalytic complex. Poly(styrene‐block‐methyl methacrylate) (PSt‐b‐PMMA) copolymers were prepared by photolysis of the solutions containing end functional PSt and PMMA in THF at λ = 350 nm for 60 min in the presence of a hydrogen donor such as N‐methyldiethanolamine (NMDEA). The proposed mechanism assumes hydrogen abstraction of photoexcited benzophenone moiety by NMDEA. Ketyl radicals resulting from abstraction reaction undergo radical‐radical coupling to form benzpinacol structure at the core. Formation of A2B and AB2 type star copolymers upon irradiation of solutions containing appropriate combinations of end‐ and mid‐chain functional polymers was also demonstrated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2938–2947, 2009

Hydrophilicity Tunable Hyperbranched Polymers by Visible Light Induced Self‐Condensing Vinyl Polymerization

“…Photoinduced approaches, commonly utilized for various polymerizations, possess several advantages consisting of low temperature conditions, requirement of little energy and minimized side reaction . Based on mentioned advantages, such light‐triggered systems have successfully been employed for the preparation of different macromolecular architectures such as block, graft copolymers, hydrogels, cryogels, and nanocomposites …”

Synthesis of H-shaped complex macromolecular structures by combination of atom transfer radical polymerization, photoinduced radical coupling, ring-opening polymerization, and iniferter processes

“…However, photoinduced processes, such as radical‐radical coupling reactions, have the advantage of being applicable at low temperatures and possibility of producing reactive sites at definite positions. Recently, we have introduced a photochemical strategy for the synthesis of block and star copolymers by radical‐radical coupling reactions . Benzophenone end‐ and mid‐chain functionalized polymers were photocoupled in solution to form block and star copolymers.…”

Synthesis of main chain polymeric benzophenone photoinitiator via thiol‐ene click chemistry and Its use in free radical polymerization

“…In our previous studies, to overcome some of the problems, we successfully synthesized novel side chain thioxanthone and benzophenone containing polystyrene based polymeric photoinitiators and they were used as polymeric photoinitiators in free radical polymerization 5, 6, 10, 14–16…”

“…Over the last decade, efficient and versatile cross reactions such as radical coupling reactions,14, 17, 18 click chemistry,5, 16, 19–32 diels alder reactions,5, 33, 34 thio‐bromo click reaction,35–37 etc., have been used to obtain functional polymers in quantitative yield. Cu (I) catalyzed 1,3‐Huisgen dipolar cycloaddition is the most widely used reaction to synthesize telechelic polymers,26, 27 functional dendrimers,23, 38, 39 hyperbranched polymers,40 biopolymers,41 polymeric photoinitiators5, 16 and so on.…”