全氟-2,2-二甲基-1,3-二氧环戊烯-四氟乙烯共聚物平均分子量、分子量分布和流变特性

Mean molecular weight,molecular weight distribution and rheological properties of perfluoro-2,2-dimethyl-1,3-dioxole-tetrafluoroethylene copolymers

全氟-2,2-二甲基-1,3-二氧环戊烯-四氟乙烯(PDD-TFE)共聚物是高性能含氟聚合物,开展PDD-TFE共聚物平均分子量(MW)、分子量分布(MWD)和流变特性研究对拓展其加工应用有重要意义。鉴于溶液法测定PDD-TFE共聚物MW及MWD存在难度,建立了由动态流变法和动态黏弹法获得PDD-TFE共聚物MW及MWD的改进方法。根据Fox方程、共聚物结构和性能参数得到了PDD-TFE共聚物的零切黏度与MW之间的关系;通过Carreau-Yasuda方程拟合PDD-TFE共聚物的复数黏度与频率之间的关系,得到了零切黏度。在实验测定PDD-TFE共聚物的储能模量与频率关系基础上,应用动态黏弹法得到其MW及MWD,并进一步研究了220℃时PDD-TFE共聚物的MW及MWD对共聚物熔体流变特性的影响,发现共聚物的MWD越宽,共聚物熔体的“剪切变稀”行为越明显;随着共聚物MW增大,共聚物熔体的非牛顿性越强。

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.