Perfluoro-2,2-dimethyl-1,3-dioxole-tetrafluoroethylene(PDD-TFE)copolymers are high-performance fluoropolymers,and studies on mean molecular weight(MW),molecular weight distribution(MWD)and rheological properties of PDD-TFE copolymers are helpful for their processing and application.Because of difficulty in measuring MW and MWD of PDD-TFE copolymers using methods based on copolymer solutions.An improved method to measure the MW and MWD of PDD-TFE copolymers by dynamic rheological and viscoelastic methods was developed.The relationship between the zero-shear viscosity and MW was established based on Fox equation and structural and property parameters of copolymers.The zero-shear viscosity was obtained by fitting the complex viscosity-frequency relationship through Carreau-Yasuda equation.Based on the experimental measurements of the storage modulus-frequency relationships of PDD-TFE copolymers,the MW and MWD of PDD-TFE copolymers were obtained by a dynamic viscoelastic method.Effects of MW and MWD of PDD-TFE copolymers on melt rheological properties at 220℃ were further studied.The results show that the"shear thinning"behavior is more obvious as MWD becomes wider,and the non-Newton character becomes stronger when MW increases.
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