Chinese Journal of Magnetic Resonance

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13C HIGH-RESOLUTION SPECTRUM OF POLY(N-ISOPROPYLACRYLAMIDE) AS ASSIGNED WITH THE AID OF GAUSSIAN98 QUANTUM CHEMICAL CALCULATION

LIU Song-bai1, CHEN Qun1*, YANG Guang1, YAN Xiao-hu2   

  1. 1.Analytical Center and Key Laboratory of Educational Ministry for Optics and Magnetic Resonance, East China Normal University, Shanghai 200062; 2.Department of Chemistry, Nanjing University, Nanjing 210093
  • Received:2001-02-16 Published:2001-06-05 Online:2001-06-05
  • About author:*Corresponding author
  • Supported by:
    教育部全国高校百名优秀青年教师教学与科研奖励基金及上海市优秀学科带头人计划资助项目

Abstract:

The quantitative 13C high resolution NMR spectrum of poly(N-isopropylacrylamide) (PNIPAAM) was assigned with the aid of Gaussian98 calculation. Two methods, γ-gauche effect and ab initio calculation, have been applied to calculate the 13C NMR chemical shifts of stereosequences of PNIPAAM. The parameters for γ-gaucheeffect were developed from the ab initio calculations of diads. The basis set used was 6-31G*, and the method was GIAO-CHF. For ab initio calculation, all geometries were optimized via AM1 method and the 13C NMR chemical shifts were calculated via GIAO-CHF method with STO-3G basis set. Stereosequences to triad level were considered for the methine carbon of main chain, while for the methylene and methyl carbons, stereosequences to tetrad and pentad level were considered respectively. It was found that the ab initio calculation can well reproduce the obse
rved 13C NMR spectrum, while the γ-gauche effect method failed to give satisfactory result. Thus, based on the result of ab initio calculation, the signals of m
ethine carbons, methylene carbon and methyl carbon were assigned and the tacticity of PNIPAAM was turn out to be random. As a result, the ab initio calculation was proved to be an effective method to investigate the tacticities of macromolecules.

Key words: Poly(N-isopropylacrylamide), Tacticity, Modeling NMR Chemical Shifts

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