A study of vibrational dynamics of poly (α-N-butyl-β-L-aspartate) (PANBLA)
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Date
2009
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Publishing House of Lviv Polytechnic National University
Abstract
Poly(α-N-butyl-β-L-aspartate) (PANBLA) is nylon-3 derivative in which an alcoxycarbonyl group has been stereoregularly attached to b-carbon of the repeating unit. Like poly(a-isobutyl-b-L-aspartate) (PAIBLA) exists in two helical forms, namely hexagonal form (13/4 helix) and tetragonal form (4/1 helix), were characterized by Xray diffraction. The hexagonal form appears to be poorly crystalline and it could not be obtained well oriented. On the other hand tetragonal form turns to be highly crystalline. Both molecular mechanics calculations and the linked-atom least square (LALS) methodology using X-ray diffraction data have revealed that an antiparallel packing of 13/4 helices with a right handed (2R) scheme of hydrogen bonds is most favourable for hexagonal form of PANBLA. Regarding tetragonal form the above
techniques favour a parallel arrangement of 4/1 helices according to right handed 4R model. IR dichroism studies also support the above results. Although the vibrational dynamics of both forms of PAIBLA has been studied, no such study has been performed for PANBLA. In the present communication the vibrational dynamics of PANBLA in tetragonal form (4/1 helix) has been studied through the dispersion of normal modes. The effect of side chain nature on the dynamical behaviour has also been analyzed. Apart from detailed assignments of modes, various characteristic features of dispersion curves have been explained as arising due to internal symmetry in energy momentum space. Finally, the density of states has been used to calculate heat capacity of this polymer. Вивчено полі(α-N-бутил-β-L-аспарта) (PANBLA), який є похідною Найлону-3, і в якому алкоксикарбонільна група стереорегулярно приєднана до β-вуглецю у ланці що повторюється. Аналогічно полі(α-N-бутил-β-L-аспарта) (PANBLA), досліджуваний полімер який існує в двох спіральних формах, а саме в гексагональній (13/4 спіралі) і тетрагональній (4/1 спіралі) був охарактеризований рентген-дифракцією. В роботі приведені результати досліджень динаміки коливань PANBLA в тетрагональній формі (4/1 спіралі) за допомогою дисперсії власних коливань. Крім детального опису власних коливань, пояснено характеристичні особливості дисперсійних кривих завдяки інтервальній симетрії в енергії імпульсного простору. Густину стану використовували для розрахунку теплоємності полімеру.
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Keywords
poly(α-N-butyl-β-L-aspartate), density of states, phonon dispersion, heat capacity, полі(α-N-бутил-β-L-аспарта), густина стану, дисперсія футонів, теплоємність
Citation
A study of vibrational dynamics of poly (α-N-butyl-β-L-aspartate) (PANBLA) / Singh Mahendra, Kumar Anuj, Kumar Naresh, Tandon Poonam, Dayal Gupta Vishwambhar // Chemistry & Chemical Technology. – 2009. – Volume 3, number 1. – P. 7–18. – Bibliography: 22 titles.