Fluorescent Labelling of RAFT-Generated Poly(N-Isopropylacrylamide) Via a Facile Maleimide-Thiol Coupling Reaction


We report a facile labeling technique in which the telechelic thiocarbonylthio functionality of well-defined poly-(N-isopropylacrylamide) (PNIPAM) prepared by room temperature RAFT polymerization is first converted to the thiol and subsequently reacted with a maleimido-functional fluorescent dye, N-(1-pyrene)maleimide (PM). Nearly monodisperse PNIPAM (Mn = 39 500 g/mol, Mw/Mn = 1.07) was synthesized using a trithiocarbonate-based CTA, 2-dodecylsulfanylthiocarbonylsulfanyl-2-methyl propionic acid (DMP), and a conventional azo-initiator, namely, 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70), as the primary source of radicals. The key to successful conjugation of PM to PNIPAM is the implementation of a two-step reduction process involving (1) the cleavage of the trithiocarbonate with a strong reducing agent, in this case, NaBH4, to form a mixture of polymeric thiols and disulfides and (2) the conjugation of PM to the pure polymeric thiol in the presence of tris(2-carboxyethyl)phosphine·HCI (TCEP). We show that TCEP efficiently eliminates the formation of polymeric disulfides and thus allows for the desired addition of the free polymeric thiol across the maleimide double bond. This concept is demonstrated using SEC-MALLS and UV-vis spectroscopy measurements.


Materials Science and Engineering

Keywords and Phrases

Chemical bonds; Free radicals; Initiators (chemical); Mixtures; Organic compounds; Polymerization; Reduction; Synthesis (chemical); Ultraviolet spectroscopy, Poly N-isopropylacrylamide; Polymeric disulfide; Polymeric thiol; Propionic acid; Thiol, Acrylics, 2,2' azobis(2,4 dimethylvaleronitrile); maleimide derivative; poly(n isopropylacrylamide); thiol derivative; tris(2 carboxyethyl)phosphine; acrylamide derivative; biopolymer; dyes, reagents, indicators, markers and buffers; fluorescent dye; n isopropylacrylamide; N-isopropylacrylamide; pyrene derivative; thiol derivative, addition reaction; article; chemical bond; conjugation; controlled study; cross coupling reaction; dispersion; fragmentation reaction; polymerization; priority journal; reduction; room temperature; ultraviolet spectroscopy; chemistry; synthesis, Acrylamides; Biopolymers; Fluorescent Dyes; Indicators and Reagents; Maleimides; Pyrenes; Sulfhydryl Compounds

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Article - Journal

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© 2006 American Chemical Society (ACS), All rights reserved.

Publication Date

01 May 2006

PubMed ID