Simple Synthesis of End Functionalized Regioregular Poly (3-Hexyl thiophene) by Catalytic-Initiated Kumada Catalyst Transfer Polymerization Koomkoom Khawas, 1 Soumili Daripa, 2 Pallavi Kumari, 1 Manas K. Bera, 3 Sudip Malik, 3 Biplab K. Kuila 2 1 Department of Chemistry, Central University of Jharkhand, Brambe, Ranchi 835205, Jharkhand, India 2 Department of Chemistry, Institute of Science, Banaras Hindu University, Varanasi 221005, Uttar Pradesh, India 3 School of Applied and Interdisciplinary Sciences, Indian Association for the Cultivation of Science, 2A&2B Raja S. C. Mullick Road, Kolkata 700032, West Bengal, India Correspondence to: B. K. Kuila (E-mail: bkkuila.chem@bhu.ac.in) Received 2 January 2019; accepted 17 February 2019; published online 15 March 2019 DOI: 10.1002/pola.29349 KEYWORDS: conjugated polymer; poly(3-hexyl thiophene); Kumada catalyst transfer polymerization (KCTP); end-functionalized polymer INTRODUCTION π-conjugated polymers have attained signifi- cant research attention within the burgeoning field of organic electronic and optoelectronic research. 1–5 Among these poly- mers, poly(3-hexyl-thiophene) (P3HT) remains frontrunner in the research of conjugated polymers and work horse for organic electronic devices, such as photovoltaics, organic field- effect transistors, and so on. 6,7 With the rapid development of nanotechnology and block copolymer science, there is a tre- mendous demand of simple and novel strategies for the prepa- ration of P3HTs with well-defined end functional groups as they can be used for the synthesis of more complex polymer structures of P3HT like star polymers, polymer brushes, block copolymers (BCP), polymer nanohybrids, and so on. 8–19 The synthesis of P3HT-based BCP or their complex architectures is sometimes necessary in order to manipulate the P3HT chains arrangement, assembly, or orientation in nanoscale level in thin-film devices to obtain better device performance. 8,20–22 Generally, three different synthetic strategies are adopted for the synthesis of end-functionalized P3HT: (a) Grignard metath- esis (GRIM) for in situ modification of reactive P3HT end groups, (b) postpolymerization modification of the terminal aromatic moiety or functional group relying on the conversion of aryl bromides or other groups installed using GRIM to achieve the desired functionality, and (c) use of Ni-based cata- lytic initiators in combination with Kumada catalyst-transfer polymerization (KCTP). End functionalization via GRIM involves in situ quenching of living end of the resulting polymer by KCTP with different types of Grignard reagents including allyl, vinyl, aryl, alkyl, and so forth. 23,24 In this case, the degree of end-functionalization is determined solely by the nature of the Grignard reagent where allyl, ethynyl, and vinyl groups produce monofunctional polymers, while other Grignard reagents result primarily in bis-end-functionalized poly- mers. 8 The extent of end functionality is solely dependent on poly- merization mechanism and reactivity of the Grignard reagents used for end functionalization. Any undesired chain termination during polymerization results in P3HT without end functionality. In post- functionalized approach, synthesized P3HT having mainly bromo or hydrogen group at one or both chain ends was further converted into suitable functional group by appropriate single or a multiple chemical transformations. 12,25–31 Although the postpolymerization strategy is versatile, the multistep nature and need for specific cou- pling reagents are the limitation of this method and should be fac- tored into any design scheme. 8 In the third and most elegant approach, Ni-based functional initiators equipped with functional moiety are utilized for the synthesis of P3HT with well-defined end-functional groups. 32–35 Successful synthesis of different end functional P3HTs with (protected) alcohol, ethynyl, carboxylic acid, amine, or phosphonate groups proves the versatility of this approach. 36–38 Recently, the concept of Ni-based external initiators was introduced and has been successfully employed for the prepa- ration of P3HTs with different end groups, hybrid materials using a variety of inorganic nanoparticles, and complex polymeric architec- tures including brushes and BCPs. 13,17,39 In spite of great success, there are still very limited number of approaches for the synthesis of Ni initiator and their further use for successful synthesis of well-defined end-terminated regioregular poly(3-hexyl thiophene) Additional supporting information may be found in the online version of this article. © 2019 Wiley Periodicals, Inc. JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2019, 57, 945–951 945 JOURNAL OF POLYMER SCIENCE WWW.POLYMERCHEMISTRY.ORG RAPID COMMUNICATION