Citation: Waleed, H.Q.; Pecsmány, D.; Csécsi, M.; Farkas, L.; Viskolcz, B.; Fejes, Z.; Fiser, B. Experimental and Theoretical Study of Cyclic Amine Catalysed Urethane Formation. Polymers 2022, 14, 2859. https:// doi.org/10.3390/polym14142859 Academic Editor: Shaojun Chen Received: 17 May 2022 Accepted: 11 July 2022 Published: 13 July 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). polymers Article Experimental and Theoretical Study of Cyclic Amine Catalysed Urethane Formation Hadeer Q. Waleed 1,2 ,Dániel Pecsmány 1,2 , Marcell Csécsi 1 ,László Farkas 3 ,Béla Viskolcz 1 , Zsolt Fejes 1, * and Béla Fiser 1,2,4, * 1 Institute of Chemistry, University of Miskolc, 3515 Miskolc-Egyetemváros, Hungary; kemhader@uni-miskolc.hu (H.Q.W.); pecsmany.daniel@gmail.com (D.P.); csecsi.marcell2@gmail.com (M.C.); kemviskolcz@uni-miskolc.hu (B.V.) 2 Higher Education and Industrial Cooperation Centre, University of Miskolc, 3515 Miskolc-Egyetemváros, Hungary 3 Wanhua-BorsodChem Zrt, Bolyai tér q. 1, 3700 Kazincbarcika, Hungary; laszlo.farkas@borsodchem.eu 4 Ferenc Rákóczi II Transcarpathian Hungarian College of Higher Education, 90200 Beregszász, Ukraine * Correspondence: kemfejes@uni-miskolc.hu (Z.F.); kemfiser@uni-miskolc.hu (B.F.) Abstract: The alcoholysis of phenyl isocyanate (PhNCO) using stoichiometric butan-1-ol (BuOH) in acetonitrile in the presence of different cyclic amine catalysts was examined using a combined kinetic and mechanistic approach. The molecular mechanism of urethane formation without and in the presence of cyclic amine catalysts was studied using the G3MP2BHandHLYP composite method in combination with the SMD implicit solvent model. It was found that the energetics of the model reaction significantly decreased in the presence of catalysts. The computed and measured thermodynamic properties were in good agreement with each other. The results prove that amine catalysts are important in urethane synthesis. Based on the previous and current results, the design of new catalysts will be possible in the near future. Keywords: amine catalysts; kinetics; catalyst free; composite method; ab initio 1. Introduction Polyurethanes (PUs) represent an important class of polymers that have found widespread use in many products in our daily life. PU is a macromolecular polymer including several urethane linkages that are formed by the reaction between -NCO groups (isocyanate) and -OH groups (polyol). Isocyanates and polyols are responsible for the different properties of PU products such as flexibility and hardness. Due to the fact of their excellent properties, such as high-temperature resistance, good flexibility, and excellent mechanical properties, the application range of PU is becoming wider and wider including adhesives, coatings, and rubbers [1–4]. It has been one of the most important automotive seating materials since 1960. Nowadays, seating foams are usually produced in a cold cure process, which generally requires that the polyol components be premixed with the crucial additives of the foam (i.e., catalysts, surfactants, blowing agent, crosslinker, fillers, and pigments). During manufacturing, the premix should be mixed with the isocyanate component in the calculated ratio and dosed into the preheated mould (~50–60 ◦ C) [5,6]. Synthesizing PU from isocyanates and alcohol under industrial conditions requires a com- bination of catalysts which will expedite the chemical reactions [7,8]. All in all, catalysts can be considered as one of the most important components of the reaction system besides the starting materials [9]. The resulting foam quality is strongly dependent on the two primary catalytic reactions of polyurethane foaming. The first is the gelling reaction, where the chains are growing, and the second is the foaming reaction, where CO 2 is inflating the material, which leads to the cellular structure of the foam. These reactions must be balanced for the proper quality of the final product and depends on the used catalysts [10]. Tertiary- amine-containing structures are usually used as catalysts in polyurethane reactions [11]. Polymers 2022, 14, 2859. https://doi.org/10.3390/polym14142859 https://www.mdpi.com/journal/polymers