Acceleration of the Polymerization of Rodlike Molecules by Flow

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• 作者：Ameya Agge ; Sumeet Jain ; and D. V. Khakhar
• 刊名：Journal of the American Chemical Society
• 出版年：2000
• 出版时间：November 8, 2000
• 年：2000
• 卷：122
• 期：44
• 页码：10910 - 10913
• 全文大小：40K
• 年卷期：v.122,no.44(November 8, 2000)
• ISSN：1520-5126

文摘

Polymerization of rigid rodlike molecules with reactive end groups (e.g., poly(p-phenyleneterephthalamide)) requires near parallel orientation of the molecules. The reaction becomes diffusion-limitedas the rotational diffusivity of the reacting molecules decreases to low values in the later stages of the reaction,and this ultimately limits the molecular weight of the polymers formed. Here a theoretical study of the step-growth reaction between rodlike molecules in a solution under extensional flow is carried out. A model for theprocess is developed using the Smoluchowski approach which yields the effective reaction rate constant forthe process in terms of the system parameters. The rate of reaction increases with extensional rate because offlow-induced orientation of molecules, and for sufficiently high extensional rates, the rate constant becomeshigher than the intrinsic value. This is an instance where flow has a catalyst-like effect on the reaction. Theresults indicate that flow can be a useful tool for accelerating reactions and thus improving yield and selectivityfor orientation-dependent reactions between large anisotropic molecules.