Research Of Anionic Polymerization Of Acrylonitrile In Lewis Base/Electron-Deficient Alkyne System

Polyacrylonitrile (PAN) is a polymer material of wide application, which can be applied in PAN fiber, modified PAN fiber, precurcor of acrylonitrile-based carbon-fiber and PAN based porous materials. The process of polymerization includes radical polymerization, anionic polymerization, controlled radical polymerization and coordination polymerizaton. With bimolecular termination in radical polymerization, it is hard to control the molecular weight and distribution; as the strong extraction of electrons caused by nitrile group, anionic polymerization of acrylonitrile has lots of side reactions and can not achieve high molecular weight and living polymerization characeristics.Through the necleophilicc attack of Lewis Base onto electron-deficient alkyne and the intramolecular proton transfer reaction, a zwitterion system is formed. In this paper, we use this zwiterion system as the anionic initiator to polymerize acrylonitrile. The process of reaction has an obvious characteristic of living polymerization, and the convertion-time plots and the molecular weight-convertion plots are well linear correlated. In the temperature range of 20-40℃the reaction can process smoothly with proper rate, and the convertion can reach above 70% after 5 hours polymerization. With GPC test the molecular weight of products can reach 5×104 at most, with distribution ranged from 1.52 to 4.20.With large amount of chain transfer reactions, the PAN synthesized in this system is branched. The degree of branch structure is related to the ion-pair, which is the substituent group connected to N atom in alkyne, and the steric effect of the Lewis Base. The branch structure can be restrained by controlling the chain transfer reaction. Therefore, it can be concluded as a special living polymerization system with characteristics of slow initiation, much transferition without termination.