Bio-based poly(ethylene terephthalate) copolyesters made from cyclic monomers derived from tartaric acid Cristina Japu, Antxon Martínez de Ilarduya, Abdelilah Alla, Sebastián Muñoz-Guerra * Departament d’Enginyeria Química, Universitat Politècnica de Catalunya, ETSEIB, Diagonal 647, 08028 Barcelona, Spain article info Article history: Received 11 December 2013 Received in revised form 6 March 2014 Accepted 10 March 2014 Available online 24 March 2014 Keywords: Bio-based polyester Bio-based poly(ethylene-terephthalate) Tartaric acid derived polyesters abstract Two cyclic acetal compounds, 2,3-O-methylene L-threitol and dimethyl 2,3-O-methylene L-threarate, both coming from naturally-occurring tartaric acid, were used as comonomers to replace ethylene glycol and dimethyl terephthalate respectively, in the preparation of PET-based copolyesters by poly- condensation in the melt. Synthesis results, structure and thermal properties of the two afforded copolyester series were evaluated and compared regarding composition and type of comonomer used in each case. All the copolyesters had a random microstructure and molecular weights in the 25,000 e35,000 g$mol 1 range. Their thermal properties varied logically with composition along each series but they significantly changed according to which acetal comonomer was used. PET copolyesters made from acetalized L-threitol displayed thermal stability and T g comparable to PET, whereas these two properties were depressed in the copolyesters containing threarate units. Both types of copolyesters were able to crystallize for contents in tartaric acid derived units up to around 30% by adopting the crystal structure of PET. Crystallization rates and melting temperatures decreased with copolymerization in the two series but this effect was more noticeable in copolyesters made from threitol. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The interest in carbohydrate derivatives as monomers for polycondensation to bio-based polymers has grown greatly in these last years [1]. Carbohydrates are very well positioned feed- stock because they are yearly renewable and easily available, they occur in a wide variety of structures, and are fully biodegradable. Carbohydrates are however multifunctional compounds that need certain chemical protection in order to avoid branching or cross- linking reactions. Although some linear polymers have been syn- thesized using carbohydrate-based monomers bearing more than two reactive functions [2,3], most of the synthesis reported to date have been carried out with derivatives in which the secondary hydroxyl groups were protected by either etherification or esteri- fication [4,5]. Protection of alditols and aldaric acids by internal cyclization is a very convenient method when stiffness of the resulting polymer is a priority. Internally anhydridized alditols (iso- hexides) [6] as well as diacetalized alditols and aldaric acids are bicyclic compounds that have been extensively explored as suitable monomers for replacing alkanediols and dicarboxylic acids in both aliphatic and aromatic polyesters [7]. The resulting polymers have a bio-based grade depending on composition, and they are distinguished by displaying high T g , good thermal sta- bility and satisfactory mechanical behavior [8]. The outstanding capacity of these bicyclic monomers to enhance T g is manifested not only on flexible aliphatic polyester but also on the highly rigid poly(ethylene terephthalate) (PET) and poly(butylene tere- phthalate) (PBT) aromatic polyesters. Moreover some suscepti- bility to biodegradation is displayed by all these copolyesters according to their content in carbohydrate units and their configuration [8c]. Although monocyclic monomers are also rigid, they are expected to be less effective in providing chain stiffness due to their less bulkiness, a difference that will become more apparent when they are used to replace the terephthalate units in aromatic polyesters. An exceptional situation is however observed for 2,5-furandicarboxylic acid (FDCA), which is a monocyclic structure but of aromatic nature. In fact this com- pound is able to replace terephthalic acid in PET and PBT without significant alteration of T g [9,10]. This paper describes the synthesis, chemical characterization and thermal properties of bio-based PET copolyesters containing * Corresponding author. E-mail address: sebastian.munoz@upc.edu (S. Muñoz-Guerra). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer http://dx.doi.org/10.1016/j.polymer.2014.03.018 0032-3861/Ó 2014 Elsevier Ltd. All rights reserved. Polymer 55 (2014) 2294e2304