Thermal Cross Linking of Novel Azide Modified Polymers of Intrinsic Microporosity-Effect of Distribution and the Gas Separation Performance.

Silvio Neumann,Gisela Bengtson,Volkan Filiz,David Meis

doi:10.3390/polym11081241

Abstract

The synthesis of polymers of intrinsic microporosity (PIM) modified with azide groups, the cross linkage by nitrene reaction and their performance as gas separation membranes are reported. The azide modification of the spirobisindane units in the polymer backbone was done by post functionalization of methylated spirobisindane containing polymers. These polymers differ in distribution and concentration of the azide group containing spirobisindane units by applying perfectly alternating and randomly distributed copolymers along the polymer chains. To investigate the influence of concentration of the azide groups, additionally the homopolymer of methylated spirobisindane was synthesized and subjected to identical treatments and characterizations as both copolymers. Cross linkage by nitrene reaction was examined by different temperature treatments at 150, 200, 250 and 300 °C. Characterization of the new polymers was performed by NMR, SEC and FT-IR. Furthermore, the crosslinking process was investigated by means of solid state NMR, TGA-FTIR, DSC and isoconversional kinetic analysis performed with TGA. Gas permeability of CO2, N2, CH4, H2 and O2 was determined by time lag experiments and ideal selectivities for several gas pairs were calculated. The two azide groups per repeating unit degrade during thermal treatments by release of nitrogen and form mechanically stable PIM networks, leading to an increase in gas permeability while selectivity remained nearly constant. Measured diffusivity and solubility coefficients revealed differences in the formation of free volume elements depending on distribution and concentration of the azide groups. Aging studies over about five months were performed and physical aging rates (βP) were evaluated with regard to the concentration and distribution of curable azide functionalities. Subsequently, the enhanced sieving effect during aging resulted in membrane materials that surpassed the Robeson upper bound in selected gas pairs.

Highlights

Microporous materials have been of great interest for many applications in fields such as clean energy, catalysis and storage media due to their extraordinarily high porosity and surface area.Following the recent definition from the International Union of Pure and Applied Chemistry (IUPAC), microporous materials involve extremely small pores with average sizes of less than 2 nm [1]
Azide modified polymers of intrinsic microporosity with different distribution of functionalities and different degrees of modification were successfully synthesized by post modification of methylated
The substitution of bromine with azide in an SN 2 mechanism was performed quantitatively and the structures were verified by 1 H, 13 C-NMR as well as heteronuclear single quantum correlation (HSQC), Size exclusion chromatography (SEC) and FTIR (ATR) measurements

Summary

Introduction

Microporous materials have been of great interest for many applications in fields such as clean energy, catalysis and storage media due to their extraordinarily high porosity and surface area.Following the recent definition from the International Union of Pure and Applied Chemistry (IUPAC), microporous materials involve extremely small pores with average sizes of less than 2 nm [1]. Microporous materials have been of great interest for many applications in fields such as clean energy, catalysis and storage media due to their extraordinarily high porosity and surface area. The easy processability of microporous polymers has demonstrated a great advantage with respect to the scale-up for commercial applications [2,3,4]. Over the last 40 years, substantial studies on polymeric membrane materials have been executed with the goal to improve their gas separation performance. In this context, gas separation performance is described by gas permeability and selectivity. Gas separation performance is described by gas permeability and selectivity Both permeability and selectivity, have been improved compared to first

Methods

Results

Conclusion