Influence of Topology on the Gelation Behavior of Coordination Polymers Prepared via ROMP of Macrocyclic Olefins Simone Albano, 1 Alessio Fantozzi, 1 Jos e Augusto Berrocal, 2 Stefano Di Stefano 1 1 Dipartimento di Chimica, Universit a degli Studi di Roma “La Sapienza” and Istituto CNR di Metodologie Chimiche (IMC-CNR), Sezione Meccanismi di Reazione, Piazzale Aldo Moro 5, Roma, 00185, Italy 2 Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands Correspondence to: S. Di Stefano (Email: stefano.distefano@uniroma1.it) Received 3 November 2016; accepted 2 December 2016; published online 00 Month 2017 DOI: 10.1002/pola.28488 ABSTRACT: This work reports on the consequences of concatena- tion of two twin macrocycles on the gelation behavior of coordina- tion polymers obtained via ring-opening metathesis polymerization (ROMP) initiated by 2 nd generation Grubbs’ catalyst. The influence of concatenation is evaluated by comparison with the behavior of a non-interlocked model complex under the same reaction condi- tions. The suitability of the choice of the non-interlocked model complex is discussed in terms of molecular structure and effective molarity (EM). It is found that concatenation has a primary role in the gelation process, resulting in lower critical gelation concentra- tions for the endotopic, interlocked complex compared with the exotopic, non-interlocked one. V C 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 00, 000–000 KEYWORDS: catenanes; coordination polymer gels; Jacobson- Stockmayer theory; mechanical bond; ring-opening metathesis polymerization INTRODUCTION There is a growing interest toward polymers based on mechanically interlocked bonds, 1 such as polyrotax- anes 2 and polycatenanes. 3 These polymeric materials (are expected to) present a large variety of mechanical, dynamic, rheological, and thermal properties different from those relat- ed to conventional polymers based on classical covalent bonds only. In the case of catenane-based polymers, many strategies have been adopted to achieve polycatenanes of varying struc- tural types but the preparation of catenane-only structures, solely formed from catenane subunits, still remains an open challenge. 4 We recently found 5 that a polymeric material mainly consisting of interlocked cyclic molecules can be easily obtained by ring-opening metathesis polymerization (ROMP) of 30 mM catenate 1 6 in the presence of 3 mol % 2 nd genera- tion Grubbs’ catalyst G2 in CH 2 Cl 2 at 30 8C (chemical struc- tures in Fig. 1). After 30 min a dark red gel is formed which assumes the shape of the reactor where the reaction is car- ried out. For instance, when carried out in a spinning NMR tube, the reaction affords a rod-like material which is easy to deform, being mechanically stable and flexible in the wet state. Upon releasing the mechanical stress, the original shape is spontaneously restored in a spring-like fashion. In stark contrast, the dry material showed antithetical mechanical properties such as rigidity and brittleness. At this point we became interested in investigating the influ- ence of the mechanical interlocking between the two macro- cycles of catenate 1 on the gelation process. Our purpose was to study what happens when the analogous complex 2, consisting of two non-interlocked macrocycles very similar to those of 1, is subjected to ROMP in the presence of cata- lyst G2 under the same experimental conditions. EXPERIMENTAL Instruments, General Methods, and Materials NMR spectra were recorded with 300 MHz spectrometer at room temperature unless otherwise stated and were internal- ly referenced to the residual proton solvent signal. Mass spec- tra were recorded with an ESI-TOF mass spectrometer. UV-vis spectra were recorded with a double-ray spectrophotometer using a standard quartz cell (path length: 1 cm) at room temperature. All reagents and solvents were purchased at the highest com- mercial quality and were used without further purification unless otherwise stated. The glassware was either flame- or ovendried. 2,9-Dimethyl-4,7-dihydroxy-1,10-phenanthroline 3 was prepared according to a literature procedure 7 starting from o-phenylenediamine, Meldrum’s acid and trimethyl orthoacetate Additional Supporting Information may be found in the online version of this article. V C 2017 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2017, 00, 000–000 1 JOURNAL OF POLYMER SCIENCE WWW.POLYMERCHEMISTRY.ORG ARTICLE