Effect of tacticity on the cyclization of polyacrylonitrile copolymers.

This work investigated polyacrylonitrile copolymers synthesized using methyl acrylate (MA) and dimethyl itaconate (DMI) as second monomers by bulk polymerization in the presence of magnesium chloride as a reagent to control the tacticity of polyacrylonitrile copolymers. The copolymers synthesized by solution polymerization were used as a control group to study the tacticity effect. The C-NMR results confirm that the isotacticity by bulk polymerization is increased approximately double for either P(AN- co-MA) or P(AN- co-DMI). The X-ray diffraction (XRD) and the isothermal DSC results show that the P(AN- co-MA) produced by bulk process, as compared to that by solution polymerization, has higher domain size ( L ) and crystallinity (CI); moreover, its cyclization period is decreased significantly. It indicates that the increase of isotacticity for P(AN- co-MA) makes the crystalline domain larger and the cyclization takes place more easily. However, such positive correlations do not hold good for the P(AN- co-DMI) system. It is due to the high steric-hindrance effect for the DMI monomer, which has long reactive branches on both sides of the vinyl DMI monomer, complicating the mechanisms of crystallization and cyclization and resulting in diminishing the contribution of high isotacticity to lower the barrier of cyclization reaction. [ABSTRACT FROM AUTHOR]