Downloaded from orbit.dtu.dk on: Oct 09, 2021 Synthetic Strategies for High Dielectric Constant Silicone Elastomers Madsen, Frederikke Bahrt Publication date: 2014 Document Version Publisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Madsen, F. B. (2014). Synthetic Strategies for High Dielectric Constant Silicone Elastomers. Technical University of Denmark, Department of Chemical and Biochemical Engineering. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Synthetic Strategies for High Dielectric Constant Silicone Elastomers Frederikke Bahrt Madsen Ph.D. Thesis August 2014 Frederikke BahrtFrederikke Madsen Synthetic Strategies for High Dielectric Constant Silicone Elastomers Frederikke Bahrt Madsen Ph.D. Thesis August 2014 1 Copyright©: Frederikke Bahrt Madsen August 2014 Address: The Danish Polymer Centre Department of Chemical and Biochemical Engineering Technical University of Denmark Building 227 DK-2800 Kgs. Lyngby Denmark Phone: +45 4525 6801 Web: www.dpc.kt.dtu.dk Print: J&R Frydenberg A/S København Decenber 2014 ISBN: 978-87-93054-56-1 2 Preface The work presented herein is the result of my PhD study carried out at the Danish Polymer Centre (DPC), Department of Chemical and Biochemical Engineering, Technical University of Denmark, DTU. The project was carried out as a part of the research project DEAP, a joint project with DTU, Aalborg University, AAU, University of Southern Denmark, SDU, Danfoss Polypower A/S, Bang & Olufsen A/S, ESS Technology A/S and Wavestar A/S. The project is funded by InnovationsFond- en. All the work was carried out between August 15th, 2011 and August 14th, 2014. First of all, thanks should be directed to my main supervisor Anne Ladegaard Skov for offering me this opportunity and for her continuous and excellent guidance and support during the project work. I have really appreciated your friendly approach towards me and through the different chal- lenges that have occurred during the project. I would also like to thank you for the many amazing and fun experiences at conferences around the world. I also owe many thanks to my two co-supervisors; Anders Egede Daugaard for his invaluable ide- as and advice on synthesis and characterisation related issues and Søren Hvilsted for great ad- vice and knowledge during the project, especially on how to present research results. Special thanks are directed to my colleagues at DPC for creating a wonderful working environ- ment and for many fun gatherings and occasions, Irakli Javakhishvili for guidance during experi- mental work and helpful and interesting discussions, Liyun Yu for exceptionally competent help with film preparation and testing, Kim Chi Szabo for help with TGA, DSC and the many other la- boratory issues. Finally I thank my family and friends for your encouragement and interest during these years. Kgs. Lyngby, August 2014 Frederikke Bahrt Madsen 3 4 Til Anders 5 Abstract Dielectric electroactive polymers (DEAPs) are a new and promising transducer technology and are often referred to as ‘artificial muscles’, due to their ability to undergo large deformations when stimulated by electric fields. DEAPs consist of a soft and thin elastomeric film (an elastomer) sandwiched between compliant electrodes and have many interesting properties such as a simple working principle, large achievable strains, high-energy densities and the fact that they are light weight and low in cost. Some issues, however, limit the current commercial viability of the tech- nology, as high driving voltages (several kV’s), for instance, are necessary to activate the materi- al. Driving voltage can be lowered by increasing the energy density of the DEAP elastomer film, achieved by creating elastomers with high dielectric constants, which is a material’s ability to store electrical energy. Two synthetic strategies were developed in this Ph.D. thesis, in order to create silicone elasto- mers with high dielectric constants and thereby higher energy densities. The work focused on maintaining important properties such as dielectric loss, electrical breakdown strength and elastic modulus. The methodology therefore involved chemically grafting high dielectric constant chemi- cal groups onto the elastomer network, as this would potentially provide a stable elastomer sys- tem upon continued activation of the material. The first synthetic strategy involved the synthesis of a new type of cross-linker for silicone poly- mer networks. The silicone compatible cross-linker allowed for copper-catalysed azide-alkyne cy- cloadditions (CuAAC) and thereby the attachment of functional groups to the network cross- linking point. The functional groups were very well-distributed in the silicone elastomer matrix, and various functional groups provided a number of elastomers with diverse properties. High dielectric constant molecules, such as the dipolar 4-nitrobenzene and nitroazobenzene, resulted in elasto- mers with an approximately 20% increase in dielectric constant at low concentrations of dipolar species (~0.5 wt%). The second synthetic strategy was to create elastomers with high concentra- tions of functional groups and thereby even higher dielectric constants through the synthesis of novel copolymers. Two different routes were followed to accomplish this aim. One route involved the synthesis of a so-called ‘chain extender’ that allowed for chemical modifications such as Cu- AAC. This route was promising for one-pot elastomer preparation and as a high dielectric con- stant additive to commercial silicone systems. The second approach used the borane-catalysed Piers-Rubinsztajn reaction to form spatially well-distributed copolymers where functional groups could be attached along the polymer backbone. The functional copolymers contained vinyl or allyl end groups that allowed for elastomer synthesis. The dielectric properties of the formed elasto- mers were found to increase significantly and an optimum concentration of functional groups was identified. At a concentration of 5.6 wt% of a nitrobenzene functional group the dielectric permittiv- ity increased 70% while at this loading important properties such as electrical breakdown strength, elastic modulus and dielectric loss were not significantly compromised. The developed synthetic strategies facilitate new ways of functionalising elastomers in general and dielectric elastomers in particular. 6 Resumé Dielektriske elektroaktive polymerer (DEAP) er en ny lovende transducerteknologi, der ofte bliver refereret til som ’kunstige muskler’ pga. deres evne til at udvise store deformationer, når en elek- trisk spænding sættes til materialet. En DEAP består sædvanligvis af en tynd elastisk polymerfilm (en elastomer), der er anbragt mellem to ultratynde og fleksible elektroder. DEAP har mange inte- ressante egenskaber såsom et simplet funktionsprincip, store opnåelige udvidelser, høj energi- tæthed, lav vægt og lave fremstillingsomkostninger. Teknologien har dog enkelte nuværende pro- blemer, der begrænser den kommercielle bæredygtighed, da f.eks. meget store spændinger (kilo- volt) er nødvendige for at aktivere DEAP’en. Aktiveringsspændingen kan sænkes ved at fremstille elastomermaterialer med højere dielektriske konstanter, dvs. bedre evne til at lagre elektrisk energi. I denne ph.d.-afhandling blev to forskellige syntesestrategier til at lave silikoneelastomerer med høje dielektriske konstanter, og dermed højere energitæthed, udviklet. Udviklingsarbejdet fokuse- rede samtidig på at bibeholde vigtige materialeegenskaber såsom det dielektriske tab, den elek- triske sammenbrudstyrke og elasticitetsmodulet. Fremgangsmåden var derfor at koble molekyler med høje dielektriske konstanter kemisk på elastomernetværker, da dette potentielt vil give et stabilt elastomersystem ved langvarig brug af DEAP’en. Den første syntesestrategi var baseret på udviklingen af en ny type tværbinder til silikoneelasto- merer. Denne tværbinder muliggjorde kobber-katalyseret azid-alkyn cycloaddition (CuAAC) og dermed fastgørelse af funktionelle grupper i elastomerens tværbindingspunkt. De påsatte funktio- nelle grupper viste sig at være godt fordelt i elastomermatricen, og forskellige funktionelle grupper gav elastomerer med varierende egenskaber. Molekyler med høje dielektriske konstanter såsom 4-nitrobenzen og nitroazobenzen gav elastomerer med 20% forhøjet dielektrisk konstant ved lave koncentrationer af de dipolære molekyler (~0,5 vægtpct). Den anden syntesestrategi blev udviklet for at lave elastomerer med endnu højere indhold af funktionelle grupper og dermed endnu højere dielektriske konstanter. Dette blev realiseret ved at syntetisere nye copolymerer via to forskellige synteseveje. Den første syntesevej var baseret på syntesen af en såkaldt kædeforlænger, der muliggjorde kemiske modifikationer såsom CuAAC. Denne syntesevej