Star-like polymer click-functionalized with small capping molecules: an initial investigation into properties and improving solubility in liquid crystals† James Iocozzia, a Hui Xu, b Xinchang Pang, a Haiping Xia, b Timothy Bunning, c Timothy White * c and Zhiqun Lin * a A novel class of polymer, star-like poly(tert-butyl acrylate) (PtBA) capped with 4-isocyano-4 0 -(prop-2-yn-1- yloxy)biphenyl (CNBP), with a well-defined size was synthesized via atom transfer radical polymerization (ATRP) and click reaction (i.e., azide–alkyne cyclization). The star-like architecture was composed of 21 separate arms connected to a high-functionality b-cyclodextrin (b-CD) core. The inner star-like PtBA blocks were hydrolyzed into poly(acrylic acid) (PAA), yielding star-like CNBP-capped PAA (i.e., star-like PAA-CNBP). The starlike polymers were characterized by gel permeation chromatography (GPC) and dynamic light scattering (DLS) to confirm narrow size distribution, as well as being examined by proton nuclear magnetic resonance ( 1 H-NMR), Fourier transform infrared spectroscopy (FTIR), Raman, and atomic force microscopy (AFM) to verify successful attachment of the click-functionalized capping agent (i.e., CNBP) with structural similarity to low molar mass liquid crystal, 4-cyano-4 0 -pentylbiphenyl (5CB). Structure and phase behavior were evaluated by AFM and optical imaging. Star-like PAA-CNBP was found to possess improved solubility in a liquid crystal host and interesting surface structures. Introduction Thermotropic liquid crystals (LCs) are a well-known class of matter that forms in certain molecular systems between that of a pure liquid and a pure solid. 1,2 LCs are prevalent in many technologies and nature. 3,4 The anisotropy of LC systems, and non-uniform property variations are what make them attractive active media as they selectively respond to myriad perturba- tions, including deformation, radiation and magnetization. 5 Investigations into the properties of pure or mixed liquid crys- talline phases is an ongoing area of research, however the use of LCs as a host species for other chemically-modied active species, such as polymers and nanoparticles, is an emerging area which takes advantage of the unique properties of LCs with the desire to incorporate additional functionality through doping. By far the most common class of material investigated for doping into LCs has been nanoparticles (NPs) of one form or another. 6–13 NPs have been of particular interest because the physics and properties of materials on this scale generally differ from their bulk, macroscopic counterparts. 14,15 Parameters such as size, size distribution, and spatial arrangement greatly affect how NPs respond due to properties such as local surface plas- mon resonance (LSPR), 9 quantum connement, 16 and energy level mixing. 17–19 Research into nanoparticle-liquid crystal composites (NP-LCs) promises a wide spectrum of applications, including advanced display technology, 3,4,20 photonics, 5,21,22 optics, 3,5,17,23 sensors and metamaterials. 3,17 Furthermore, the assembly (self or directed) of NPs has proven to be successful by many other techniques spanning a broad range of disciplines. 24 One specic area of investigation is the use of LCs as a means of assembling dopant species into various arrange- ments. 7,8,11,25 The idea being that dopants would align within the LC matrix and have an order to their assembly imposed by the LC host. Unfortunately, the realization of this technique has not been easy. A few active research areas on NPs include gold NPs and quantum dots (QDs) variously passivated with alkylthiolate, alkylthiol, or (S)-naproxen ligand species. 7,8,12,13,16,26,27 There are myriad techniques for making NPs (particularly Au, 2,28 Ag, 1 and metal oxides 29 ) variably capped with many species in large yield. 8,13 However, some techniques yield NPs with non-uniform size and shapes, while the others cannot afford the synthesis of NPs with tunable size (i.e., limited applicability/variability). 8,30 a School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA. E-mail: zhiqun.lin@mse.gatech.edu; Fax: +1-404-385-3734; Tel: +1- 404-385-4404 b State Key Laboratory of Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 36105, China c Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright Patterson Air Force Base, OH, 45433, USA. E-mail: timothy.white.24@us.af.mil † Electronic supplementary information (ESI) available. See DOI: 10.1039/c4ra09597a Cite this: RSC Adv. , 2014, 4, 50212 Received 1st September 2014 Accepted 30th September 2014 DOI: 10.1039/c4ra09597a www.rsc.org/advances 50212 | RSC Adv. , 2014, 4, 50212–50219 This journal is © The Royal Society of Chemistry 2014 RSC Advances PAPER Published on 30 September 2014. Downloaded by Georgia Institute of Technology on 15/10/2014 20:12:54. View Article Online View Journal | View Issue