## 1 Introduction
The furan ring is one of the most important dienes used in DA reactions due to its exceptional dienic character, which makes it specifically suitable in terms of kinetics and yields [17]. On top of that, furan compounds are often obtained from renewable sources. Furthermore, maleimides are commonly used as dienophilic counterparts because of their highly reactive nature due to electron-withdrawing substituents adjacent to the double bond [17]. The coupling (DA) and decoupling (rDA) temperatures for the furan-maleimide pair (-50 \({}^{\circ}\)C and 150 \({}^{\circ}\)C, respectively) make this couple very suited for this application. Finally, the Diels-Alder reaction can be performed without a solvent and does not need a third chemical such as a catalyst to function [18; 19; 20]. If this mechanism would be used as a cross-linking system in thermoset polymers it would greatly increase the mobility of the chains at higher temperatures. (i.e., above the rDA temperature). When the rDA temperature is below the degradation temperature of the material or in general, the temperature at which side reactions occur, the polymeric system is regarded as fully thermoreversible. An important element in the concept of thermoreversible cross-linking is that often not all the cross-links have to be broken for the system to be recyclable, as long as the extent of bond breakage results in a flowable polymer melt [19]. Thermoreversible systems employing Diels-Alder cross-linking chemistry give rise not only to improved processability and recyclability but also to very specific and novel, unique applications such as self-healing/remedable polymers [6; 14; 20; 21; 22; 23; 24; 25], shape-memory materials [7; 26], probe-based lithographic and data-storage applications [27], removable foams for electronic encapsulation [28], thermally reversible gels [29; 30], polymeric encapsulants [22], and thermally removable adhesives [31]. In this work, the preparation and characterization of a (partially) bio-based thermoreversible polyester resin is discussed. One of the main building blocks of this polyester is diphenolic acid, which can be derived from the bio-based building block levulinic acid [32]. Diphenolic acid is an acid-functionalized structural analog of bisphenol A (BPA), which is widely used for commercial polycarbonate, epoxy, and polyester resins [33; 34]. The acid functionality of diphenolic acid is further functionalized with a furan group, introducing a Diels-Alder capable moiety. Finally, a polyester base polymer is obtained via interfacial polycondensation of the furan-modified diphenolic acid and terephthalacyl chloride, using phenol as a chain stopper (PE-fur, Figure 1). The addition of a chain stopper should lower the average chain length of the polymer obtained, which in turn should reduce the glass transition temperature (T\({}_{\text{g}}\)) of the material. This reduction is needed because it has been demonstrated that the T\({}_{\text{g}}\) of PE-fur (without a chain stopper) is too high for processing (e.g., the required processing temperature in order to assure proper polymer flow is too close to the degradation temperature) [35]. Phenol is of particular interest since it conserves aromaticity, readily takes part in the condensation synthesis and shares a structural similarity with diphenolic acid. Furthermore, it can be obtained from bio-based sources [36; 37].