Article pubs.acs.org/Macromolecules
Improved Mechanistic Insights into Radical Sulfinyl Precursor MDMO-PPV Synthesis by Combining Microflow Technology and Computer Simulations Neomy Zaquen,† Paul H. M. Van Steenberge,‡ Dagmar R. D’hooge,*,‡,§ Marie-Francoise Reyniers,‡ Guy B. Marin,‡ Joke Vandenbergh,† Laurence Lutsen,∥ Dirk J. M. Vanderzande,†,∥ and Thomas Junkers*,†,∥ †
Polymer Reaction Design Group (PRD), Institute for Materials Research (IMO-IMOMEC), Hasselt University, Agoralaan Building D, B-3590 Diepenbeek, Belgium ‡ Laboratory for Chemical Technology (LCT), Ghent University, Technologiepark 914, B-9052 Gent, Belgium § Department of Textiles, Ghent University, Technologiepark 907, B-9052 Gent Belgium ∥ IMEC associated laboratory IMOMEC, Wetenschapspark 1, B-3590 Diepenbeek, Belgium S Supporting Information *
ABSTRACT: A kinetic model using Predici is developed and applied to obtain an improved mechanistic understanding of the radical sulfinyl precursor polymerization route for poly(2methoxy-5-(3′-7′-dimethyloctyloxy-4-((octylsulfinyl)methyl))1,4-phenylenevinylene) (MDMO-PPV) synthesis. In this route, the premonomer1-(chloromethyl)-5-((3,7-dimethyloctyl)oxy)-2-methoxy-4-((octylsulfinyl)methyl) benzene (MDMO)is subjected to a base-induced elimination reaction using NatBuO as base and s-BuOH as solvent. Microreactors are used to ensure rapid mixing of reaction components and sharp quenching at precisely determined time points. Systematic kinetic data that follows the very fast precursor polymerizations with reaction time have in this way become available for the first time. Via the applied kinetic model, the presence of a chain transfer reaction is unambiguously confirmed and kinetic rate coefficients have been deduced, which fall within the typical expectations of radical chain reactions. Two models were further compared, one including chain reinitiation (noninhibition model) and one excluding reinitiation (inhibition model) of the by chain transfer-generated radical species. Investigation of trend lines suggest a preference of the reinitiation model, thereby implying that MDMO-PPV synthesis follows mostly a conventional free radical polymerization mechanism that only differs with respect to its initiation mode and the biradical nature of the propagation step.
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excellent fluorescent properties and low charge carrier mobility of PPVs make them ideal candidates to replace existing bioimaging agents such as organic fluorescent markers. Many synthesis routes were to date developed for PPVs, from which the so-called indirect or “precursor” routes are the most widely used and best known and studied pathways toward soluble and processable high molecular weight polymer materials (Scheme 1).12−18 Among the different precursor routes,19−24 the sulfinyl25 route, studied in the present work, is the most versatile route to obtain conjugated PPVs via a distinct two-step mechanism. The general polymerization mechanism proceeds via a self-initiating p-quinodimethane moiety, which is formed upon the 1,6-base-induced elimination
INTRODUCTION In recent years, significant advances toward the synthesis and characterization of conjugated polymers were made. Considerable interest in these materials stems from their excellent optoelectronic characteristics and their use in device fabrication in flexible electronic applications such as organic light emitting diodes,1−3 field effect transistors,4 and organic photovoltaic devices.5 Since the discovery of the excellent luminescence by Burroughes and co-workers,6 poly(p-phenylenevinylene)s (PPV)s and its derivatives are one of the most studied conjugated polymers.5−8 Although high reproducibility with respect to synthesis and optical properties is displayed, PPVs have been successively replaced by other polymers in photovoltaic applications, due to their comparatively low power conversion efficiencies.9−11 More recent developments opened a variety of additional application pathways for PPVs in the area of biosensors and biomedical research. Also, the © XXXX American Chemical Society
Received: August 26, 2015 Revised: October 21, 2015
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DOI: 10.1021/acs.macromol.5b01884 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules Scheme 1. General Scheme for the Synthesis of PPVs via a Radical or Anionic Pathway Using “Precursor” Routes
Retrieval of accurate data during PPV synthesis is however difficult due to the high reaction rate and the inherent selfinitiation that occurs even at low reaction temperatures (
