Suppression of Melt-Induced Dewetting in Cyclic Poly(ε- caprolactone) Thin Films Giovanni M. Kelly, † Farihah M. Haque, ‡ Scott M. Grayson, ‡ and Julie N. L. Albert* ,† † Department of Chemical and Biomolecular Engineering and ‡ Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States * S Supporting Information ■ INTRODUCTION In the past decade, the pace of research studying cyclic and other nonlinear polymer architectures has increased dramati- cally due to the development of novel synthetic routes to control polymer architecture, size, dispersity, and composition while also maintaining the high purity necessary for phenomenological study. Specifically, advances in conjugation reactions have led to the use of the copper(I)-catalyzed azide- alkyne cycloaddition (CuAAC) “click” reactions to efficiently synthesize cyclic homopolymers, 1 cyclic block copolymers, 2 star polymers, 3 and multicyclic topologies. 4 It has been known for some time that very small amounts of linear impurities (0.1%) can significantly alter some cyclic polymer properties, 5 making their study challenging and some previously reported results difficult to reproduce. Because of the quantitative and highly efficient nature of the CuAAC coupling chemistry, the presence of linear impurities can be nearly eliminated. 6 These advances have allowed researchers to begin to better understand the fundamental differences between the linear and cyclic topology. Progress in the synthesis of cyclic polymers has taken place alongside significantly increased interest in studying polymers confined to thin and ultrathin films, which are relevant to applications in photolithography 7,8 and nanoscale mem- branes. 9-13 However, thin film confinement often produces dramatic and sometimes deleterious effects on physical properties, such as the depression or elevation of thermal transitions. 14-20 Additionally, poor substrate adhesion can lead to film dewetting. 21-35 By contrast, several groups have shown that the cyclic architecture exhibits unique and useful phenomena, such as a decrease in domain size in cyclic block copolymer thin films, 8,36 and a lack of T g depression in cyclic polystyrene thin films. 37 In this Note, we describe our observation that low molecular weight cyclic poly(ε-caprolac- tone) (PCL) resists thin film dewetting in the melt state better than its linear analogue, regardless of linear PCL end-group chemistry. As research focuses more closely on polymers confined to thin and ultrathin films, the suppression of dewetting will become necessary as an unstable, discontinuous layer is impractical for most applications. Our results show that the cyclic topology may offer a practical solution to the problem of film dewetting. ■ EXPERIMENTAL SECTION Nomenclature. The following nomenclature will be used throughout: l-PCL 6k and c-PCL 6k designate the linear and cyclic poly(ε-caprolactone), respectively (see Figure 1). Unless otherwise noted, l-PCL 6k refers to α-propagyl-ω-hydroxy-poly(ε-caprolactone). The subscript “6k” indicates the molecular weight (M n = 6 kDa). Synthetic and Analytical Methods. In order to synthesize l- PCL 6k , distilled ε-caprolactone (εCL) was polymerized in the presence of propargyl alcohol to install the necessary alkyne moiety. The terminating hydroxy group allowed for end-group functionalization with an azide-containing carboxylic acid using ethyl(dimethyl- aminopropyl) carbodiimide (EDC)-based ester coupling chemistry. With the synthesized α-propargyl-ω-azide-polymer, the final CuAAC “click” cyclization coupling was performed to generate the desired c- PCL 6k (see Scheme 1). Gel permeation chromatography (GPC) was used to quantify relative molecular weights (M n and M w ) and dispersity (Đ). GPC also Received: October 13, 2017 Revised: November 26, 2017 Figure 1. Structures of l-PCL 6k and c-PCL 6k . The numbers (1) and (3) correspond to the synthetic identification of these polymers in the “Synthetic Protocols” section of the Supporting Information. Scheme 1. Synthesis of Cyclic PCL Note Cite This: Macromolecules XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acs.macromol.7b02200 Macromolecules XXXX, XXX, XXX-XXX