Structural analysis of biodegradable low-molecular mass copolyesters based on glycolic acid, adipic acid and 1,4 butanediol and correlation with their hydrolytic degradation Spyridon Soulis a, * , Despina Triantou a , Steffen Weidner b , Jana Falkenhagen b , Johannis Simitzis a a National Technical University of Athens, School of Chemical Engineering, Department III “Materials Science and Engineering”, Laboratory Unit “Composite and Advanced Materials”, 9 Heroon Polytechniou str., Zografou Campus, 157 73 Athens, Greece b BAM, Federal Institute for Materials Research and Testing,1.3, Structure Analysis, Richard-Willstaetter-Strasse 11,12489 Berlin, Germany article info Article history: Received 15 June 2012 Received in revised form 16 August 2012 Accepted 2 September 2012 Available online 7 September 2012 Keywords: Biodegradable Biopolymers Hydrolytic degradation Ft-IR Matrix-assisted laser desorption/ionization- time-of-flight-mass spectrometry (MALDI- TOF MS) abstract Copolyesters of glycolic acid combined with adipic acid and 1,4 butanediol were synthesized, their in vitro hydrolytic degradation was studied and correlated with their structure. The hydrolytic degra- dation of the copolyesters was directly related with the degree of crystallinity and the diameter of the crystallites. It was found that glycolate units disturb the ordering of the butylene adipate units, which results in a decrease of the crystallinity. By comparing the hydrolysis parameters of synthesized copo- lyesters with those of similar aliphatic copolyesters a hydrolysis mechanism was proposed. According to this mechanism, the degradation takes place not only by the loss of end units, but also through the removal of larger segments. MALDI-TOF MS data showed that the possibility of a copolyester macro- molecule forming cyclic structures correlates with the arrangement of ester groups in the macromole- cules and the structure of the linear segments. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Aliphatic polyesters made from bifunctional acids (e.g. adipic acid) [1,2] and diols are expected to belong to the most economi- cally competitive biodegradable polymers, because they can be degraded and digested completely by microorganisms [1]. In literature, there are reports on the crystal structure and the hydrolytic degradation of poly(ethylene adipate) [2,3] and poly(- butylene adipate) [4], as well as on the degradation of poly(- propylene adipate) [5]. Moreover, the crystal structure, melting behavior and enzymatic degradation of poly(ethylene succinate), poly(butylene succinate) and poly(propylene succinate) have also been studied [6,7]. However, it should be noticed that in the majority of the reports the hydrolytic degradation is studied using enzymatic (i.e. catalytic) hydrolysis. Arguably, in vivo degradation and/or enzymatic hydrolysis of polyesters are very complex phenomena. Thus, it would have been very helpful if the effect of specific parameters could be disentangled. However, high- molecular mass polyesters used as commercial products, practi- cally cannot be hydrolyzed by deionized water. Generally, aliphatic polyesters are inherently degradable, a property which makes them highly interesting for agricultural geomembranes, and applications, where the effects on the envi- ronment are of importance, e.g. in packaging. Apart from these, they are also of great interest in drug delivery matrices, and in biomedical applications, where temporary aid is needed, typically for sutures and bone pins [8]. Water access to the ester bond is governed by hydrophobicity of the structural units, the molecular mass of the polyester, its glass transition temperature, the crystal- linity of the material, as well as the dimensions of the bulk sample [1,9e15]. Because water rapidly plasticizes these polymers, degra- dation proceeds through the entire mass simultaneously, often ultimately leading to mechanical distortion, cracking, pitting and fissure of the material in uncontrolled ways [9]. There have been a number of reports that provide strong indications that the degradation kinetics cannot only be described by random chain scission, but that the end groups may play an important role in this process [3,12e15]. To control the degradation behavior of the copolyesters, it is necessary to gain detailed knowledge of the structure of the * Corresponding author. E-mail addresses: sksoulis@central.ntua.gr, sksoulis@gmail.com (S. Soulis). Contents lists available at SciVerse ScienceDirect Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab 0141-3910/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.polymdegradstab.2012.09.002 Polymer Degradation and Stability 97 (2012) 2091e2103