A Density Functional Theory Study on the Ring-Opening Polymerization of d-Lactide Catalyzed by a Bifunctional-Thiourea Catalyst

Rong-Xiu Zhu; Ruo-Xi Wang; Dong-Ju Zhang; Cheng-Bu Liu

doi:10.1071/CH08118

RESEARCH ARTICLE

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A Density Functional Theory Study on the Ring-Opening Polymerization of d-Lactide Catalyzed by a Bifunctional-Thiourea Catalyst

Rong-Xiu Zhu ^A , Ruo-Xi Wang ^A ^B , Dong-Ju Zhang ^A ^C and Cheng-Bu Liu ^A

+ Author Affiliations

- Author Affiliations

^A Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, Institute of Theoretical Chemistry of Shandong University, Jinan 250100, China.

^B Criminal Technological Department, Shandong Police College, Jinan 250014, China.

^C Corresponding author. Email: zhangdj@sdu.edu.cn

Australian Journal of Chemistry 62(2) 157-164 https://doi.org/10.1071/CH08118
Submitted: 21 March 2008 Accepted: 28 September 2008 Published: 19 February 2009

Abstract

The thiourea-catalyzed methanolysis of d-lactide, a model system for the initiation and propagation of the organocatalyzed ring-opening polymerization (ROP) of lactide, has been studied by performing density functional theory calculations. Both the catalyzed and uncatalyzed reactions are explored along two possible pathways: one involves the stepwise addition–elimination pathway and the other is related to the concerted pathway. It is found that the reaction without the presence of the catalyst is difficult because the barrier involved is as high as 176 kJ mol^–1. With the aid of a thiourea catalyst, the barrier is reduced to 88 kJ mol^–1 with a preference for the stepwise addition–elimination mechanism over the concerted one. The role of the catalyst has been rationalized by analyzing the frontier molecular orbital interactions between the catalyst and substrates and by performing natural population analysis. Finally, another mechanism involving acyl transfer is discussed for the thiourea-catalyzed ROP.

Acknowledgements

The work described in the present paper is supported by the National Natural Science Foundations of China (grants no. 20773078, 20873076, 20873075, and 20633060) and the National Basic Research Program of China (973 Program) (grant no. 2007CB936602).

References

A Density Functional Theory Study on the Ring-Opening Polymerization of d-Lactide Catalyzed by a Bifunctional-Thiourea Catalyst

Abstract

Acknowledgements

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