Thermal degradation and theoretical interpretation of vibrational spectra of poly (b,L-malic acid) Deepika Chaturvedi a , Soni Mishra a , Poonam Tandon a, * , José A. Portilla-Arias b , Sebastián Muñoz-Guerra b a Department of Physics, University of Lucknow, Lucknow-226 007, India b Departament d’Enginyeria Química, Universitat Politècnica de Catalunya, ETSEIB, Diagonal 647, 08028 Barcelona, Spain article info Article history: Received 30 December 2010 Received in revised form 26 April 2011 Accepted 7 May 2011 Available online 23 May 2011 Keywords: Poly(b,L-malic acid) Dispersion curves TGA/DTA/FT-IR spectroscopy abstract Poly (b,L-malic acid) (PMLA) was obtained by Physarum polycephalum. The FT-IR and FT-Raman spectra were recorded experimentally and used for normal mode analysis using Wilson GF matrix method and phonon dispersion of PMLA. The non redundant set of internal coordinate are simplified. Urey-Bradley force field approximation was employed in normal mode analysis and to calculate the potential energy distribution (PED) of each fundamental vibration. Apart from detailed assignment, various characteristic features of dispersion curve have also been explained, arising due to internal symmetry in energy momentum space. Predictive values of the intramolecular contribution to the heat capacity of this polymer calculated by the density of states, are also been reported. The thermal degradation of PMLA was investigated in nitrogen atmosphere by thermogravimetric analysis in combination with DTA and FT-IR. The spectra of gases found in the thermal degradation of PMLA are very much similar to the spectra of gases released during decomposition of fumaric acid. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The poly (b,L-malic acid) (PMLA) [eCH(COOH)eCH 2 eCOOe] n is highly water-soluble, perfectly biodegradable and biocompatible [1]. The properties of PMLA [Fig. 1a and b] can be changed to diversify its applications (the chemical modification of the pendent carboxylic groups). The methylation of pendent carboxyl groups allowed formulation of stable, water insoluble nanoparticles that could be loaded with proteins or drugs for delivery applications [2,3]. The most advanced application reported for PMLA is the development of “Polycefin”, a nanoconjugate prototype vehicle for the cellular delivery of antisense oligonucleotides or other drugs, and simultaneously several antibodies, which can bind specifically to cell surface antigens during drug delivery [4]. Both a- and b-structures, either racemic or optically pure, may be obtained by chemical methods whereas microorganisms exclusively generate PMLA of extremely high optical purity. The FT-IR, Raman spectra and inelastic neutron scattering from the polymeric systems are very complex and cannot be unraveled without full knowledge of the dispersion curves. Vibrational spectroscopy is an important tool for probing chemical, conforma- tional and morphological structure of polymers beside this, it provide information about dynamical behavior of polymers. Recently the vibrational spectra of polymers have been interpreted using normal coordinate analysis and quantum chemical method [5e8]. We have obtained PMLA of microbial origin. In continuation of our earlier works on biodegradable and other polymers [9e14] in the present communication we report FT-IR, FT-Raman spectra, normal modes and their dispersion in the PMLA. Optimized structure of PMLA was obtained with Goussian03. The Urey-Bradley force field approximation was employed in normal mode analysis to calculate the potential energy distribution (PED) of each funda- mental vibration. The non redundant set of internal coordinate are simplified. The heat capacity via density-of-states is also evaluated. The thermal degradation process of PMLA is discussed in nitrogen environment. The combination of thermogravimetric analysis (TGA) with differential thermal analysis (DTA) and FT-IR spectros- copy is a powerful technique for the study of polymer decompo- sition [15e19]. In principle, a sample is heated beyond the decomposition temperature and the weight loss of the polymer is recorded while the gaseous decomposition products are measured by gas-phase FT-IR spectroscopy. Simultaneously, a DTA curve is recorded, which provides qualitative information about trans- formations of the analyzed sample. * Corresponding author. Tel.: þ91 522 2782653; fax: þ91 522 2740840. E-mail addresses: poonam_tandon@yahoo.co.uk, poonam_tandon@hotmail.com (P. Tandon). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2011.05.011 Polymer 52 (2011) 3118e3126