Preparation And Properties Of Thermal Rearrangement Polymer Membranes Based On Cardo Structure

Polyimides（PI）have been used as gas separation membrane materials due to their good comprehensive properties.However,it’s low gas permeability could not meet industrial needs.Thermal rearrangement（TR）polymers transformed from o-hydroxyl-containing polyimides have both high gas permeability and selectivity,which have become a new generation of gas separation membrane materials.Therefore,we introduced the fluorenyl Cardo structure into the hydroxyl-containing polyimide precursors to prepare TR polymers by thermal treatment,and the structures and properties of TR polymers were further adjusted by copolymerization.This article mainly includes the following four parts:（1）9,9’-bis[4-（4-amino-3-hydroxyphenoxy）phenyl]fluorene（BAHPPF）was synthesized and polymerized with 4,4’-（hexafluoroisopropylidene）diphthalic anhydride（6FDA）,1,2,3,4-cyclobutane tetracarboxylic dianhydride（CBDA）,pyromellitic dianhydride（PMDA）,3,3’,4,4’-biphenyl tetracarboxylic dianhydride（BPDA）,3,3’,4,4’-benzophenone tetracarboxylic dianhydride（BTDA）and3,3’,4,4’-diphenyl ether tetracarboxylic dianhydride（ODPA）,respectively.A series of hydroxyl-containing poly（ether-imide）s（HPEIs）were prepared by thermal imidization,and the corresponding thermal rearrangement membranes（PEBOs）were obtained by further thermal treatment.The data of gas permeabilities showed that with the thermal treatment temperature increasing,the gas permeabilities of the TR polymer membranes gradually increased.Among them,PEBO-6FDA exhibited excellent gas permeabilities,the permeabilities of H₂,CO₂,O₂ and N₂ reached 272.34,245.04,60.73 and 10.58 barrer,respectively,and the selectivity of O₂/N₂ was close to the 2008 Robeson limit.（2）The diamine monomer 9,9’-bis（3-amino-4-hydroxyphenyl）fluorene（BAHPF）was synthesized,and a series of thermal rearrangement copolymer membranes（TRCPs）were prepared by copolymerization of BAHPF with BAHPPF and 6FDA.It was found that with the increase of heat treatment temperature,the mechanical properties of the TR membrane materials decreased rapidly,but the tensile strength of TRCP-4:6 still retained 21.2 MPa.Moreover,H₂,CO₂,O₂,N₂ and CH₄ permeabilities of TRCP-4:6 were 244.4,269.0,46.8,5.20,and 4.60 barrer respectively,coupled with CO₂/CH₄selectivity of 58.48 and O₂/N₂ of 9.00,exceeding the 2008 Robeson upper limit.（3）The cross-linked rearrangement polymer membranes（TR-PBOs）were prepared by copolymerization of BAHPPF,3,5-diaminobenzoic acid（DABA）and6FDA.With the increase of DABA content,the proportion of the rigid biphenyl structure produced by cross-linking was increased,so the thermal performance and gas permeabilities of the TR-PBO membranes were improved obviously.In these crosslinked rearrangement membranes,the H₂,CO₂,O₂,N₂ and CH₄ permeabilities of TR-PBO-7:3 reached 320.9,369.7,54.3,15.0 and 11.0 barrer respectively,and the selectivity of CO₂/CH₄ was close to the 2008 Robeson limit.（4）3,3’-Diaminophenolphthalein（DAPP）was synthesized and copolymerized with BAHPPF and 6FDA to prepare cross-linked rearrangement polymer membranes（TR-PBOIs）.With the thermal treatment temperature increasing,the mechanical properties of the TR membranes declined rapidly,but the tensile strength of TR-PBOI-6:4 still maintianed 15.6 MPa.When the content of DAPP was increased,the thermal properties and gas permeabilities of the TR-PBOI membranes were improved.Among these membranes,the separation performance of TR-PBOI-6:4 for O₂/N₂ was close to the 2015 upper limit,and the selectivity of CO₂/CH₄ was close to the 2008 Robeson upper limit.