631 Research Article Received: 4 June 2014 Revised: 30 July 2014 Accepted article published: 19 August 2014 Published online in Wiley Online Library: 1 September 2014 (wileyonlinelibrary.com) DOI 10.1002/pi.4799 Towards a better control of the radical functionalization of poly(lactic acid) Ilaria Domenichelli, a,b Serena Coiai, a Francesca Cicogna, a Calogero Pinzino a and Elisa Passaglia a* Abstract The radical functionalization of poly(lactic acid) (PLA) with maleic anhydride (MA) was thoroughly investigated using dif- ferent chemical approaches with the purpose of controlling both the grafting degree and the structure/architecture of the final products. First, a new methodology was developed able to provide clear evidence of the grafting and to identify the structure of the inserted groups. The method consists in the derivatization reaction of the grafted succinic anhydride with a fluorescent derivative (1-naphthylmethylamine), which allows the functionalization to be assessed qualitatively and quantitatively and therefore improves understanding of the radical functionalization mechanism. Then, in order to control the incidence of secondary reactions, which affect the radical process in the presence of MA, new chemicals were inves- tigated as functionalizing agents or as functionalizing co-agents together with MA. Butyl 3-(2-furyl)propenoate was used as a functional molecule capable of stabilizing the macroradical intermediate and then controlling the  -scission reaction. 4-Benzoyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl was tested as a radical mediator capable of modulating the insertion of MA through a simple reversible coupling reaction. The results obtained by both approaches suggest the possibility of stabilizing the PLA macroradical intermediates and accordingly keeping the radical process under control. © 2014 Society of Chemical Industry Supporting information may be found in the online version of this article. Keywords: PLA; radical functionalization; post-derivatization reaction; co-agent; radical stability INTRODUCTION Poly(lactic acid) (PLA) is a particularly attractive synthetic aliphatic polyester owing to its unique advantages to conjugate the typical properties of thermoplastic resins (i.e. processability and recy- clability) with the characteristics of bio-plastics, such as being produced from renewable resources, being biodegradable and being compostable. The recent literature reports several papers dealing with the use of PLA as a bio-based and biodegradable compatibilizer (or compatibilizer polymer precursor) in blends and composites, 1 – 5 especially with agricultural residues. 6 – 8 For such purposes, PLA is generally modified with functional or reac- tive groups able to improve the interfacial adhesion between the components and thus to promote thermal and mechanical properties suitable for the final applications. Among the grafting techniques, the post-polymerization free-radical functionalization process, generally performed in the melt by using extruders or melt mixers, is considered as one of the most practical, cost effective and also green approach, since it is a solvent-free method, and it can be applied for large-scale production. However, even if this method has been successfully applied for the modification of polyolefins, 9 – 12 radical functional- ization with peroxide and functionalizing unsaturated monomers such as maleic anhydride (MA) is a complex process that depends on the polymer nature and on the feed ratio between the reagents. Moreover, many concurrent side reactions can limit the grafting and change the polymer structure. Despite these drawbacks, this kind of approach has also been applied to PLA. In the literature, data concerning the occurrence of grafting, the content of grafted groups and the structure of the polymer after processing are reported for MA and acrylic derivatives. 13 – 20 The grafting of these moieties was achieved by using a peroxide or a UV activator 19 for macroradical genera- tion. However, only in a few cases a mechanism of reaction is discussed. 17 The main results show that the number of grafted groups is low compared with the values obtained for polyolefins and this is probably because of a lower number of available graft- ing sites, due to the structure and specific reactivity of tertiary car- bon atoms in the PLA backbone towards the peroxide radicals. In addition, treating PLA in the melt with a peroxide, side reactions such as branching and crosslinking are predominant, 21,22 while an opposite tendency is observed on adding MA. In this last case a reduction of the polymer molecular weight has been evidenced, which has been connected with the  -scission reaction of poly- mer chains. 15,17 Moreover, while in the case of polyolefins the side reactions can be partially avoided by tuning and optimizing the ∗ Correspondence to: Elisa Passaglia, Istituto di Chimica dei Composti Organo Metallici (ICCOM), Consiglio Nazionale delle Ricerche, UOS Pisa, Via G. Moruzzi 1, 56124 Pisa, Italy. E-mail: passaglia@pi.iccom.cnr.it a Istituto di Chimica dei Composti Organo Metallici (ICCOM), Consiglio Nazionale delle Ricerche, UOS Pisa, Via G. Moruzzi 1, 56124 Pisa, Italy b Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy Polym Int 2015; 64: 631–640 www.soci.org © 2014 Society of Chemical Industry