Free volume characteristics of 2, 2‐bistrifluoromethyl‐4, 5‐difluoro‐1, 3‐dioxole‐co‐tetrafluoroethylene copolymers: Effect of composition and molecular weight. Issue 9 (4th March 2021)

• Record Type: Journal Article
• Authors: Yu, Dayang; Mao, Guoliang; Cai, Huaixun; Wang, Shuhua; Liu, Jiandang; Pan, Pengju; Bao, Yongzhong
• Is Part Of: Journal of polymer science. Volume 59:Issue 9(2021)
• Page Start: 754
• Page End: 763
• Publication Date: 2021-03-04
• Subjects: 2, 2‐bistrifluoromethyl‐4, 5‐difluoro‐1, 3‐dioxole -- composition -- copolymer -- free volume -- molecular dynamics simulation -- positron annihilation lifetime -- tetrafluoroethylene; Polymers -- Periodicals; Polymerization -- Periodicals; Polymerization; Polymers; Periodicals; 547.7
• DOI: 10.1002/pol.20200834
• Languages: English
• ISSNs: 2642-4150

Abstract

Abstract: 2, 2‐bistrifluoromethyl‐4, 5‐difluoro‐1, 3‐dioxole‐ co ‐tetrafluoroethylene (PDD‐TFE) copolymer is a good candidate to prepare gas separation membranes with excellent permeability due to its free volume characteristics. However, the influence of PDD‐TFE copolymer structure on its free volume characteristics is less studied. In this paper, PDD‐TFE copolymers with different compositions and molecular weights were synthesized, and their free volume characteristics were analyzed by positron annihilation lifetime spectroscopy and a molecular dynamics simulation. It indicated that the molar fraction of PDD in copolymers had a significant effect on free volume characteristics, while the molecular weight of copolymers exerted a slight influence on free volume when the molecular weight exceeded a critical region (intrinsic viscosity [ η ] > 68 ml g −1 ). PDD‐TFE copolymers with greater PDD molar fractions (i.e., 72% and 84%) showed bimodal distributions in positron lifetime and free volume size distributions, while PDD‐TFE copolymers with lower PDD molar fractions (i.e., 27% and 35%) exhibited a single peak. The long‐lifetime parameter τ 3 was assigned to micro‐cavities formed by [‐(TFE) y ‐PDD‐] segments and τ 4 was attributed to micro‐cavities formed by [‐(PDD) x ‐TFE‐] segments. The cis and trans transitions of PDD led to a local multilayer spiral structure with a 2.6–4.3 Å layer spacing, which would also increase the free volume of copolymers. Abstract :