Thermogravimetric investigation of two classes of block copolymers based on poly(lactic-glycolic acid) and poly(e-caprolactone) or poly(ethylene glycol) Salvatore D’Antone a , Fabio Bignotti b , Luciana Sartore b , Alberto D’Amore b , Gloria Spagnoli b , Maurizio Penco b, * a DipartimentodiChimicaeChimicaIndustriale,viaRisorgimento35,56100Pisa,Italy b DipartimentodiChimicaeFisicaperl’IngegneriaeperiMateriali-Unita ` INFM,Universita `diBrescia,viaValotti9,25133Brescia,Italy Received 12 March 2001; received in revised form 24 April 2001; accepted 29 April 2001 Abstract The thermogravimetric analysis (TGA) of two classes of multi-block copolymers based on poly(d,l-lactic-glycolic acid) (PLGA) and diol-terminated poly(e-caprolactone) (PCDT) or poly(ethylene glycol) (PEG) segments is reported. These materials, having the structure of poly(ester-carbonate)s, were synthesized by a chain extension reaction. The influence of the length of PCDT or PEG segments and of the molar ratio of d,l-lactic acid (LA) and glycolic acid (GA) residues on thermal stability in air and nitrogen atmosphere has been investigated. For comparison purposes the degradation behaviour of starting oligomers was also studied. TGA under nitrogen shows two degradation processes that can be ascribed to the PLGA and PCDT or PEG segments, respectively. In addition, the thermal stability increases with the LA content in the PLGA blocks. In the tests run under air two degradation steps have also been observed, though the former occurs in general at higher temperatures. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Poly(lactic-glycolic acid); PLGA; Diol-terminated poly(e-caprolactone); Poly(ethylene glycol); Block copolymers; Bioerodible polymers; Thermal properties; Thermal degradation; Thermogravimetric analysis 1. Introduction Poly(lactic-glycolic acid) (PLGA) is a well known family of bioerodible polymers used in the biomedical field as surgical materials, bone repair or drug delivery systems [1–7] and scaffolds for tissue regeneration [8– 11]. In view of such applications, moulding procedures involving thermal treatments such as melt encapsulation [12],extrusion[8]andthermalsterilisation[13]havebeen developed, which can induce degradation with decrease of molecular weight [14] and loss of volatile products, depending on the processing temperature [15,16]. Therefore, the calorimetric properties and thermal sta- bility of PLGA are of great interest from the technolo- gical point of view. The aim of the present work was to investigate by thermogravimetric analysis (TGA) the susceptibility to thermal degradation of two classes of multi-block copolymers containing PLGA and diol-terminated poly(E-caprolactone) (PCDT) or poly(ethylene glycol) (PEG) segments with the aim of relating the molecular structure with their thermodegradative behaviour. To that purpose, the thermal susceptibility of starting oli- gomers was also studied. The copolymers investigated have a poly(ester-carbonate) structure (see Scheme 1) and were synthesised by a chain extension reaction where oligomeric PLGA is reacted with either PCDT or PEG bearing chloroformate end-groups. It is worth noting that this process, whose synthetic pathway was reported in previous papers [17–19], allows the pre- paration of bioerodible materials with a wide range of properties by a proper selection of the PLGA composi- tion and of the type (PCDT or PEG) and length of the segments. 0141-3910/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0141-3910(01)00110-0 Polymer Degradation and Stability 74 (2001) 119–124 www.elsevier.com/locate/polydegstab * Corresponding author. Fax +39-(0)30-3715788. E-mailaddress: penco@ing.unibs.it (M. Penco).