Abstract
A systematic investigation into the chain transfer polymerization of the so-called radical precursor polymerization of poly(p-phenylene vinylene) (PPV) materials is presented. Polymerizations are characterized by systematic variation of chain transfer agent (CTA) concentration and reaction temperature. For the chain transfer constant, a negative activation energy of −12.8 kJ·mol−1 was deduced. Good control over molecular weight is achieved for both the sulfinyl and the dithiocarbamate route (DTC). PPVs with molecular weights ranging from thousands to ten thousands g·mol−1 were obtained. To allow for a meaningful analysis of the CTA influence, Mark–Houwink–Kuhn–Sakurada (MHKS) parameters were determined for conjugated MDMO-PPV ([2-methoxy-5-(3',7'-dimethyloctyloxy)]-1,4-phenylenevinylene) to α = 0.809 and k = 0.00002 mL·g−1. Further, high-endgroup fidelity of the CBr4-derived PPVs was proven via chain extension experiments. MDMO-PPV-Br was successfully used as macroinitiator in atom transfer radical polymerization (ATRP) with acrylates and styrene. A more polar PPV counterpart was chain extended by an acrylate in single-electron transfer living radical polymerization (SET-LRP). In a last step, copper-catalyzed azide alkyne cycloaddition (CuAAC) was used to synthesize block copolymer structures. Direct azidation followed by macromolecular conjugation showed only partial success, while the successive chain extension via ATRP followed by CuAAC afforded triblock copolymers of the poly(p-phenylene vinylene)-block-poly(tert-butyl acrylate)-block-poly(ethylene glycol) (PPV-b-PtBuA-b-PEG).
Highlights
Poly(p-phenylene vinylene)s (PPV)s are an important class of semiconducting polymer materials that display excellent optical and electrical properties and are one of the most studied conjugated polymers to date [1,2,3,4]
A good correlation between the molecular weight of conjugated MDMO-PPV—synthesized via the sulfinyl route—and the transfer agent concentration is reported in a previous study [39], resulting in polymers with molecular weights ranging from a Mn of 12,000 to 25,000 g·mol−1 with a dispersity (Ð) of ~2.0
The concept of controlling the precursor polymerization of PPV via the use of a CBr4 chain transfer agent has been studied in detail
Summary
Poly(p-phenylene vinylene)s (PPV)s are an important class of semiconducting polymer materials that display excellent optical and electrical properties and are one of the most studied conjugated polymers to date [1,2,3,4]. Other well-suited materials have made their way into the field of such electronic devices, PPVs are still interesting because of their high synthetic reliability and simple scale up possibilities [7], resulting in the potential high industrial relevance of these polymers [8,9]. Their outstanding fluorescence properties leave room for use in biomedical applications such as biosensors and fluorescent markers. Significant research has been performed towards the synthesis of PPVs, resulting in the indirect or so-called “precursor” route as the most established and reliable synthetic pathway [10,11,12,13,14,15,16,17,18,19,20,21]
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