Synthesis of syndiotacticity-rich high polymerization degree PVA polymers with VAc and VPa, fabrication of PVA fibers with superior mechanical properties by wet spinning

PVA fibers with high strength and high modulus are very attractive in many potential applications. However, there is a difficulty when enhancing the strength and modulus of PVA fibers. To overcome this difficulty, here we report a method to enhance the strength and modulus of PVA fibers by synthesis of high polymerization degree (DP) and high syndiotacticity diad content (S-diad) PVA polymers with vinyl acetate (VAc)/ vinyl propionate (VPa) as monomers via non-emulsifier emulsion polymerization. The synthesized PVA polymers with different mass ratio of VAc/VPa were characterized by fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (1H-NMR) and gel permeation chromatography (GPC), it demonstrated that the ratio of VPa monomer has a significant effect on the DP and S-diad of PVA polymers. In addition, a series of PVA fibers have been fabricated using the synthesized polymers by wet spinning method, and the mechanical and thermal properties of PVA fibers have been investigated by tensile tester, differential scanning calorimeter (DSC), thermogravimetric analyzer (TGA), X-ray diffractometer (XRD) and field emission scanning electron microscope (FE-SEM), and it found that there is a substantial increase in strength and modulus of PVA fibers with the increase of DP and S-diad of PVA polymer. However, too high DP and S-diad of PVA polymers had an opposite effect on the spinning fluid, spinnability and properties of PVA fibers.