Development of Highly Permeable and Selective Membranes using PEG/PPG, Pebax and PIM-based Polymers for CO2 Separation = PEG/PPG, Pebax 및 PIM 기반 폴리머를 사용한 CO2 분리를 위한 고투과성 및 선택성 멤브레인 개발

다국어 초록 (Multilingual Abstract)

In recent years, demand for efficient, environmentally sustainable gas separation technologies has increased significantly due to a sharp rise in atmospheric levels of carbon dioxide (CO2), a major greenhouse gas, primarily from the combustion of fossil fuels in industrial processes, power generation, and other human activities. This escalating concentration of CO2 gas in the atmosphere has led to several adverse environmental consequences, the most critical of which is global warming. Consequently, developing effective CO2 separation and sequestration technologies has gained considerable attention due to their low energy requirements, ease of use, scalability, and operational simplicity. The prime objective of this thesis is the development and characterization of advanced polymer membranes for the efficient separation of CO2 from gas mixtures.
This research encompasses four main categories of membrane systems: (i) rubbery crosslinked synthetic membranes, (ii) rubbery crosslinked mixed matrix membranes (MMMs), (iii) MMMs fabricated from commercially available rubbery polymers, and (iv) glassy crosslinked synthetic membranes. The development of these advanced polymer membranes is expected to play a significant role in the efficient separation of CO2 from other gases, as well as in addressing global warming and purifying natural gas. This dissertation contains five chapters, the contents of which have been summarized as follows:
Chapter 1 presents an overview of the importance of CO2 separation and discusses a range of technologies developed and used for this purpose. It also emphasizes the significance of membrane-based technologies for gas separation and outlines their advantages over other separation techniques. To provide a comprehensive understanding of membrane-based separation technology, this chapter discusses the underlying theory, mechanisms of gas transport across the membrane, fundamental parameters, and key factors influencing the gas separation performance of polymer membrane–based processes. This chapter concludes by presenting approaches for fabricating novel polymer membrane materials to achieve efficient CO2 separation.
Chapter 2 describes the development of a series of crosslinked rubbery polymer membranes [PEG/PPG-2CZPImide (x:y)] based on poly(ethylene glycol)-block-poly(propylene glycol) (PEG/PPG)- and 5,6-di(9H-carbazol-9-yl)isoindoline-1,3-dione (2CZPImide), prepared via ring-opening metathesis polymerization (ROMP) by varying the molar ratio of the norbornene-functionalized PEG/PPG oligomer (NB-PEG/PPG-NB) and 2-(bicyclo[2.2.1]hept-5-en-2-ylmethyl)-5,6-di(9H-carbazol-9-yl)isoindoline-1,3-dione (2CZPImide-NB) in the reaction feed from 10:1 to 6:1. The comonomer 2CZPImide-NB is a monofunctional monomer for ROMP reaction. Hence, ROMP copolymerization of dinorbornene-functionalized NB-PEG/PPG-NB with this monomer (NB-2CzPimide) forms voids in the crosslinked polymer matrix due to the absence of regular PEG/PPG polymer chain segments within the crosslinked network. This phenomenon effectively widens the d-spacing between the PEG/PPG segments and enhances gas diffusivity across the membranes (Figure A1) The synthesized crosslinked PEG/PPG-2CZPImide (x:y) membranes displayed excellent thermal stability with good CO2 separation performance having CO2 permeabilities ranging from 311.1 to 418.1 Barrer and CO2/N2 and CO2/CH4 selectivities of 39.4–52.0 and 13.4–16.0, respectively. Moreover, the crosslinked membrane PEG/PPG-2CZPImide (6:1), displayed good plasticization resistance up to 10 atm.

Figure A1. Schematic illustration of the crosslinked PEG/PPG-2CZPImide (x:y) membrane, showing its enhanced CO2 transport behavior compared with the pristine crosslinked PEG/PPG membrane.

Chapter 3 presents the development of a series of c-4CzTPN porous carbon–doped CO2-philic poly(ethylene glycol)/poly(propylene glycol) (PEG/PPG)–based crosslinked rubbery polymer membranes via in situ ROMP polymerization, aimed at enhancing CO2 transport without significantly compromising the CO2/N2 and CO2/CH4 selectivities (Figure A2). The porous carbon c-4CzTPN was derived from the carbonization of poly[2,3,5,6-tetra(carbazol-9-yl)terephthalonitrile] (p-4CzTPN). By combining the porous c-4CzTPN with the high CO2/light gas selectivity of the crosslinked PEG/PPG polymer matrix, the resulting mixed matrix membrane (MMM), PEG/PPG-c-4CzTPN-x, obtained via the incorporation of c-4CzTPN into the crosslinked PEG/PPG matrix (using in situ ROMP polymerization), exhibited high CO2 permeability along with moderate CO2/N2 and CO2/CH4 selectivities. The incorporation of c-4CzTPN filler into the crosslinked PEG/PPG network enhanced the gas diffusivity and facilitated CO2 transport across the PEG/PPG polymer matrix. Moreover, the high CO2/light gas selectivity of crosslinked PEG/PPG matrix ensured minimal reduction in CO2/N2 and CO2/CH4 selectivities. Hence, the membranes exhibited high CO2 permeabilities and good CO2/N2 and CO2/CH4 selectivities. In particular, the PEG/PPG-c-4CzTPN-0.25 and PEG/PPG-c-4CzTPN-0.5 membranes surpassed Robeson’s 2008 upper bound for CO2/N2 separation (Figure A2). The crosslinked PEG/PPG- structure of the polymer matrix provided excellent anti-aging and anti-plasticization properties.

Figure A2. Conceptual schematic of the PEG/PPG-c-4CzTPN-x membranes, illustrating their structural features and the resulting CO₂/N₂ and CO₂/CH₄ separation behavior.
Chapter 4 describes the fabrication of Pebax-based MMMs using sterically bulky 4,5-bis(9H-carbazol-9-yl)phthalic acid (2CzPA) as a filler, aimed at enhancing CO2 transport and thermomechanical properties. The sterically bulky 2CzPA acid was synthesized as an intermediate in the preparation of the final 2CzPImide monomer described in Chapter 1. Adding the sterically bulky 2CzPA filler to the Pebax matrix served dual functions: first, strong hydrogen-bonding interactions between the -COOH groups of 2CzPA and the -NH groups of the imide functionalities in the PA segments of Pebax enhanced the interfacial compatibility of the filler and the polymer matrix (Figure A3). Second, the 1,2-disubstituted carbazole moieties in 2CzPA induced steric hindrance that perturbed the regular chain packing of the polyethyleneoxide (PEO) segments (Figure A3). Both these factors promoted CO2 diffusion and solubility in the Pebax membrane, enhancing CO2 transport across the MMMs compared to a neat Pebax membrane. Moreover, the filler–polymer interaction also enhanced the thermomechanical properties compared to the neat Pebax. The optimal CO2 transport and mechanical properties were obtained at 1 wt% filler loading with a CO2 permeability of 227.51 Barrer, a Young’s modulus of 137.7 MPa, and elongation at break of 652%.


Figure A3. Conceptual schematic of the Pebax/2CzPA-x mixed-matrix membranes (MMMs), illustrating the interaction between 2CzPA and the Pebax matrix.
Chapter 5 explores the synthesis, characterization, and gas separation performance of biphenyl-crosslinked PIM–polyimide membranes. The ultimate aim was to develop spirobisindane-based, crosslinked glassy polymer membranes that combine high CO2 permeability with enhanced resistance to aging and plasticization. The crosslinked membranes were obtained via controlled heat treatment of spirobisindane-based PIM–polyimide polymer membranes. These spirobisindane-based PIM–polyimide polymer membranes incorporate thermally labile lactone functionalities within the phenolphthalein unit with sterically hindered spirobisindane and durene diamine (DDA) moieties within the polymer chain segments. Heating pristine polymers at 400 °C generated free radicals via thermal decomposition of the thermally labile lactone moieties in phenolphthalein. Subsequent coupling of free radicals in an inert atmosphere led to biphenyl crosslinking between polymer chain segments (Figure A4). These phenomena generated additional free volume within the polymer matrix, which in turn enhanced gas diffusivities and permeabilities. Moreover, the biphenyl-crosslinked structure formed between adjacent polymer chain segments conferred high thermal stability to the crosslinked polymer membranes, along with excellent anti-plasticization and anti-aging properties. (Figure A4).

Figure A4. Conceptual schematic of the phenolphthalein-based thermally crosslinked PIM-polyimide x-PIM(mP-nD) membrane, illustrating its structure along with the anti-aging and anti-plasticization characteristics.

국문 초록 (Abstract)

지난 수백년간 산업 공정, 발전, 그리고 기타 인간 활동에서의 화석연료 연소로 인해 주요 온실가스인 이산화탄소(CO₂)의 대기 중 농도가 급격히 증가하고 있다. 이러한 CO₂ 농도 증가는 다양한 환경 문제를 야기하며, 그 중에서도 지구 온난화는 가장 심각한 문제로 대두되고 있다. 이에 따라 낮은 에너지 소모, 공정의 단순성, 우수한 확장성, 그리고 운전의 용이성을 장점으로 갖는 CO₂ 분리 및 저장 기술에 대한 관심이 크게 증가하고 있다.
본 학위논문에서는 가스 혼합물로부터 CO₂를 효율적으로 분리할 수 있는 고성능 고분자 막을 개발하고, 그 분리 성능 및 물리·화학적 특성을 체계적으로 분석하였다.
이를 위해 본 연구에서는 네 가지 주요 막 시스템을 다루었다. 즉, (i) 고무상 가교 합성막, (ii) 고무상 가교 혼합매질막(mixed-matrix membranes, MMMs), (iii) 상업적으로 이용 가능한 고무상 고분자를 기반으로 한 혼합매질막, 그리고 (iv) 유리상 가교 합성막이다. 이러한 고성능 고분자 막의 개발은 CO₂를 다른 가스로부터 효율적으로 분리하는 데 기여할 뿐만 아니라, 지구 온난화 문제 해결과 천연가스 정제 공정 등 다양한 응용 분야에서도 중요한 역할을 할 것으로 기대된다.
본 학위논문은 총 5개의 장으로 구성되어 있으며, 각 장의 주요 내용은 다음과 같다.
제1장에서는 CO₂ 분리의 중요성을 개괄하고, 이를 위해 개발·활용되고 있는 다양한 분리 기술을 소개한다. 또한 가스 분리 분야에서 막 기반 기술의 중요성을 강조하고, 다른 분리 공정과 비교한 막 공정의 장점을 설명한다. 막 기반 분리 기술에 대한 포괄적인 이해를 제공하기 위해, 본 장에서는 막을 통한 가스 수송 메커니즘과 기본 이론, 핵심 물성 인자, 그리고 고분자 막 공정의 분리 성능에 영향을 미치는 주요 요인들을 논의한다. 마지막으로, 효율적인 CO₂ 분리를 달성하기 위한 고성능 고분자 막 소재의 설계 및 제조 전략을 제시하였다.
제2장에서는 PEG/PPG와 5,6-di(9H-carbazol-9-yl)isoindoline-1,3-dione를 기반으로 한 가교 고무상 고분자 막 [PEG/PPG-2CZPImide (x:y)]의 합성 및 CO2 분리 특성을 다룬다. 해당 막은 norbornene 기능화 PEG/PPG 올리고머와 2CZPImide-NB를 개환 메타세시스 중합(ROMP)으로 합성하였으며, 반응물 몰비를 10:1–6:1 범위에서 조절하였다. 이때 기능성 모노머로 작용하는 2CZPImide-NB의 도입은 가교 고분자 네트워크 내 공극 형성을 유도하여 PEG/PPG 세그먼트 간 간격을 증가시키고, 이에 따라 가스 확산도가 향상되었다. 합성된 가교막은 우수한 열적 안정성과 함께 CO₂ 투과도 311.1–418.1 Barrer, CO₂/N₂ 선택도 39.4–52.0, CO₂/CH₄ 선택도 13.4–16.0의 뛰어난 분리 성능을 나타냈으며, 특히 PEG/PPG-2CZPImide (6:1) 막은 10 atm까지 우수한 가소화 저항성을 보였다.

그림 A1. 가교된 PEG/PPG-2CZPImide (x:y) 막의 개략도.
제3장에서는 CO₂/N₂ 및 CO₂/CH₄ 선택도의 저하를 최소화하면서 CO₂ 수송 특성을 향상시키기 위해, in situ ROMP 중합을 통해 다공성 탄소 c-4CzTPN이 도핑된 CO₂ 친화성 PEG/PPG 기반 가교 고무상 혼합매트릭스막(PEG/PPG-c-4CzTPN-x)을 개발하였다. 탄화된 poly[2,3,5,6-tetra(carbazol-9-yl)terephthalonitrile]로부터 제조된 c-4CzTPN을 가교 PEG/PPG 매트릭스에 도입함으로써 가스 확산도와 CO₂ 수송이 효과적으로 향상되었으며, 동시에 PEG/PPG 매트릭스의 높은 선택도로 인해 CO₂/N₂ 및 CO₂/CH₄ 선택도 감소는 최소화되었다. 그 결과, 해당 막들은 높은 CO₂ 투과도와 우수한 CO₂/N₂ 및 CO₂/CH₄ 선택도를 동시에 나타냈으며, 특히 PEG/PPG-c-4CzTPN-0.25 및 -0.5 막은 CO₂/N₂ 분리에 대해 Robeson 2008 상한선을 초과하는 성능을 보였다. 또한 가교 PEG/PPG 구조는 우수한 노화 방지 및 가소화 저항 특성을 제공하였다.

그림 A2. PEG/PPG-c-4CzTPN-x 막의 개념도.
제4장에서는 CO₂ 수송 특성과 열·기계적 물성 향상을 위해 입체적으로 부피가 큰 4,5-bis(9H-carbazol-9-yl)phthalic acid(2CzPA)를 충전제로 도입한 Pebax 기반 혼합매트릭스막을 개발하였다. 2CzPA의 –COOH 작용기와 Pebax의 PA 세그먼트 간 강한 수소 결합은 계면 적합성을 향상시켰으며, 동시에 입체적 장애 효과로 PEO 세그먼트의 규칙적인 사슬 패킹을 교란하여 CO₂의 확산 및 용해도를 증가시켰다. 그 결과, 해당 혼합매트릭스막은 순수 Pebax 대비 향상된 CO₂ 수송 성능과 함께 우수한 열·기계적 물성을 나타냈으며, 최적의 성능은 충전제 1 wt%에서 CO₂ 투과도 227.51 Barrer, 영률 137.7 MPa, 파단 신율 652%로 달성되었다
.
그림 A3. Pebax/2CzPA-x 혼합매트릭스막(MMMs)의 개념도.
제5장에서는 비페닐 가교된 스피로비스인단 기반 PIM–폴리이미드 막의 합성, 구조적 특성 및 가스 분리 성능을 고찰한다. 본 연구에서는 제어된 열처리를 통해 스피로비스인단 기반 PIM–폴리이미드 막 내 페놀프탈레인 단위의 열적으로 불안정한 락톤 기능기를 분해하여 자유 라디칼을 생성하고, 이들의 결합을 통해 인접한 고분자 사슬 간 비페닐 가교 구조를 형성하였다. 이러한 가교 과정은 고분자 매트릭스 내 자유 부피를 증가시켜 가스 확산도와 CO₂ 투과도를 향상시키는 동시에, 비페닐 가교 구조를 통해 우수한 열적 안정성, 가소화 저항성 및 노화 방지 특성을 부여하였다.


그림 A4. 페놀프탈레인 기반 열 가교된 PIM–폴리이미드 x-PIM(mP-nD) 막의 개념도.

다국어 초록 (Multilingual Abstract)

In recent years, demand for efficient, environmentally sustainable gas separation technologies has increased significantly due to a sharp rise in atmospheric levels of carbon dioxide (CO2), a major greenhouse gas, primarily from the combustion of fossil fuels in industrial processes, power generation, and other human activities. This escalating concentration of CO2 gas in the atmosphere has led to several adverse environmental consequences, the most critical of which is global warming. Consequently, developing effective CO2 separation and sequestration technologies has gained considerable attention due to their low energy requirements, ease of use, scalability, and operational simplicity. The prime objective of this thesis is the development and characterization of advanced polymer membranes for the efficient separation of CO2 from gas mixtures.
This research encompasses four main categories of membrane systems: (i) rubbery crosslinked synthetic membranes, (ii) rubbery crosslinked mixed matrix membranes (MMMs), (iii) MMMs fabricated from commercially available rubbery polymers, and (iv) glassy crosslinked synthetic membranes. The development of these advanced polymer membranes is expected to play a significant role in the efficient separation of CO2 from other gases, as well as in addressing global warming and purifying natural gas. This dissertation contains five chapters, the contents of which have been summarized as follows:
Chapter 1 presents an overview of the importance of CO2 separation and discusses a range of technologies developed and used for this purpose. It also emphasizes the significance of membrane-based technologies for gas separation and outlines their advantages over other separation techniques. To provide a comprehensive understanding of membrane-based separation technology, this chapter discusses the underlying theory, mechanisms of gas transport across the membrane, fundamental parameters, and key factors influencing the gas separation performance of polymer membrane–based processes. This chapter concludes by presenting approaches for fabricating novel polymer membrane materials to achieve efficient CO2 separation.
Chapter 2 describes the development of a series of crosslinked rubbery polymer membranes [PEG/PPG-2CZPImide (x:y)] based on poly(ethylene glycol)-block-poly(propylene glycol) (PEG/PPG)- and 5,6-di(9H-carbazol-9-yl)isoindoline-1,3-dione (2CZPImide), prepared via ring-opening metathesis polymerization (ROMP) by varying the molar ratio of the norbornene-functionalized PEG/PPG oligomer (NB-PEG/PPG-NB) and 2-(bicyclo[2.2.1]hept-5-en-2-ylmethyl)-5,6-di(9H-carbazol-9-yl)isoindoline-1,3-dione (2CZPImide-NB) in the reaction feed from 10:1 to 6:1. The comonomer 2CZPImide-NB is a monofunctional monomer for ROMP reaction. Hence, ROMP copolymerization of dinorbornene-functionalized NB-PEG/PPG-NB with this monomer (NB-2CzPimide) forms voids in the crosslinked polymer matrix due to the absence of regular PEG/PPG polymer chain segments within the crosslinked network. This phenomenon effectively widens the d-spacing between the PEG/PPG segments and enhances gas diffusivity across the membranes (Figure A1) The synthesized crosslinked PEG/PPG-2CZPImide (x:y) membranes displayed excellent thermal stability with good CO2 separation performance having CO2 permeabilities ranging from 311.1 to 418.1 Barrer and CO2/N2 and CO2/CH4 selectivities of 39.4–52.0 and 13.4–16.0, respectively. Moreover, the crosslinked membrane PEG/PPG-2CZPImide (6:1), displayed good plasticization resistance up to 10 atm.

Figure A1. Schematic illustration of the crosslinked PEG/PPG-2CZPImide (x:y) membrane, showing its enhanced CO2 transport behavior compared with the pristine crosslinked PEG/PPG membrane.

Chapter 3 presents the development of a series of c-4CzTPN porous carbon–doped CO2-philic poly(ethylene glycol)/poly(propylene glycol) (PEG/PPG)–based crosslinked rubbery polymer membranes via in situ ROMP polymerization, aimed at enhancing CO2 transport without significantly compromising the CO2/N2 and CO2/CH4 selectivities (Figure A2). The porous carbon c-4CzTPN was derived from the carbonization of poly[2,3,5,6-tetra(carbazol-9-yl)terephthalonitrile] (p-4CzTPN). By combining the porous c-4CzTPN with the high CO2/light gas selectivity of the crosslinked PEG/PPG polymer matrix, the resulting mixed matrix membrane (MMM), PEG/PPG-c-4CzTPN-x, obtained via the incorporation of c-4CzTPN into the crosslinked PEG/PPG matrix (using in situ ROMP polymerization), exhibited high CO2 permeability along with moderate CO2/N2 and CO2/CH4 selectivities. The incorporation of c-4CzTPN filler into the crosslinked PEG/PPG network enhanced the gas diffusivity and facilitated CO2 transport across the PEG/PPG polymer matrix. Moreover, the high CO2/light gas selectivity of crosslinked PEG/PPG matrix ensured minimal reduction in CO2/N2 and CO2/CH4 selectivities. Hence, the membranes exhibited high CO2 permeabilities and good CO2/N2 and CO2/CH4 selectivities. In particular, the PEG/PPG-c-4CzTPN-0.25 and PEG/PPG-c-4CzTPN-0.5 membranes surpassed Robeson’s 2008 upper bound for CO2/N2 separation (Figure A2). The crosslinked PEG/PPG- structure of the polymer matrix provided excellent anti-aging and anti-plasticization properties.

Figure A2. Conceptual schematic of the PEG/PPG-c-4CzTPN-x membranes, illustrating their structural features and the resulting CO₂/N₂ and CO₂/CH₄ separation behavior.
Chapter 4 describes the fabrication of Pebax-based MMMs using sterically bulky 4,5-bis(9H-carbazol-9-yl)phthalic acid (2CzPA) as a filler, aimed at enhancing CO2 transport and thermomechanical properties. The sterically bulky 2CzPA acid was synthesized as an intermediate in the preparation of the final 2CzPImide monomer described in Chapter 1. Adding the sterically bulky 2CzPA filler to the Pebax matrix served dual functions: first, strong hydrogen-bonding interactions between the -COOH groups of 2CzPA and the -NH groups of the imide functionalities in the PA segments of Pebax enhanced the interfacial compatibility of the filler and the polymer matrix (Figure A3). Second, the 1,2-disubstituted carbazole moieties in 2CzPA induced steric hindrance that perturbed the regular chain packing of the polyethyleneoxide (PEO) segments (Figure A3). Both these factors promoted CO2 diffusion and solubility in the Pebax membrane, enhancing CO2 transport across the MMMs compared to a neat Pebax membrane. Moreover, the filler–polymer interaction also enhanced the thermomechanical properties compared to the neat Pebax. The optimal CO2 transport and mechanical properties were obtained at 1 wt% filler loading with a CO2 permeability of 227.51 Barrer, a Young’s modulus of 137.7 MPa, and elongation at break of 652%.


Figure A3. Conceptual schematic of the Pebax/2CzPA-x mixed-matrix membranes (MMMs), illustrating the interaction between 2CzPA and the Pebax matrix.
Chapter 5 explores the synthesis, characterization, and gas separation performance of biphenyl-crosslinked PIM–polyimide membranes. The ultimate aim was to develop spirobisindane-based, crosslinked glassy polymer membranes that combine high CO2 permeability with enhanced resistance to aging and plasticization. The crosslinked membranes were obtained via controlled heat treatment of spirobisindane-based PIM–polyimide polymer membranes. These spirobisindane-based PIM–polyimide polymer membranes incorporate thermally labile lactone functionalities within the phenolphthalein unit with sterically hindered spirobisindane and durene diamine (DDA) moieties within the polymer chain segments. Heating pristine polymers at 400 °C generated free radicals via thermal decomposition of the thermally labile lactone moieties in phenolphthalein. Subsequent coupling of free radicals in an inert atmosphere led to biphenyl crosslinking between polymer chain segments (Figure A4). These phenomena generated additional free volume within the polymer matrix, which in turn enhanced gas diffusivities and permeabilities. Moreover, the biphenyl-crosslinked structure formed between adjacent polymer chain segments conferred high thermal stability to the crosslinked polymer membranes, along with excellent anti-plasticization and anti-aging properties. (Figure A4).

Figure A4. Conceptual schematic of the phenolphthalein-based thermally crosslinked PIM-polyimide x-PIM(mP-nD) membrane, illustrating its structure along with the anti-aging and anti-plasticization characteristics.

목차 (Table of Contents)

• CONTENTS
• Abstract I
• Acknowledgements VII
• Contents X
• List of Schemes XIV
• List of Tables XV
• List of Figures XVI
• Abbreviations IX
• Chapter 1: Insight into Carbon Dioxide (CO2) Separation and the Role of Membrane Technology 1
• 1.1 Importance of CO2 Separation 1
• 1.2 CO2 Separation Process 5
• 1.2.1 Pre-combustion process 5
• 1.2.2 Post-combustion capture 6
• 1.2.3 Oxy-fuel combustion 6
• 1.2.4 Chemical looping combustion (CLC) 7
• 1.3 Membrane-Based Separation of CO2 7
• 1.3.1 Technology related to membrane-based separation 7
• 1.3.2 Stages of membrane technology development 8
• 1.4 Theories on Membrane-Based Gas Separation 10
• 1.4.1 Hagen–Poiseuille flow 11
• 1.4.2 Knudsen diffusion 12
• 1.4.3 Molecular sieving 13
• 1.4.4 Capillary condensation 14
• 1.4.5 Surface diffusion 14
• 1.4.6 Solution–diffusion 15
• 1.4.7 Facilitated transport 16
• 1.5 Parameters Related to Gas Separation Processes 16
• 1.5.1 Permeability and permeance 17
• 1.5.2 Selectivity 18
• 1.5.3 Diffusion 19
• 1.5.4 Solubility 19
• 1.5.5 Free volume and fractional free volume 20
• 1.6 Henry’s Law and Dual-Mode Absorption 23
• 1.7 Factors Affecting Gas Transport 25
• 1.7.1 Diffusant size and shape 25
• 1.7.2 Condensability of the penetrant 27
• 1.7.3 Pressure 27
• 1.7.4 Operating temperature 27
• 1.7.5 Polarity 28
• 1.7.6 Free volume and packing density chain mobility of polymers 30
• 1.7.8 Crystallinity 30
• 1.7.9 Crosslinking 31
• 1.7.10 Thermal processing history 31
• 1.7.11 Molecular weight 32
• 1.8 Other Important Phenomena 33
• 1.8.1 Plasticization 33
• 1.8.2 Aging 34
• 1.8.3 Robeson upper bound 35
• 1.8.4 Diffusivity coefficient and time-lag during diffusion 36
• 1.9 Membrane Fabrication 40
• 1.10 Membrane Classification and Membrane Material Types 41
• 1.10.1 Inorganic membranes 42
• 1.10.2 Organic polymer membranes 42
• 1.10.3 Hybrid or mixed-matrix membranes (MMMs) 44
• 1.11 Instrumental 46
• 1.11.1 Characterization and measurement 46
• 1.11.2 Gas permeation measurement 48
• 1.12 Key challenges and emerging strategies for enhancing polymer membrane-based CO2 separation performance 51
• 1.12.1 Aim of the present study 59
• 1.13 References 60
• Chapter 2: Enhancing CO2 transport across the PEG/PPG based crosslinked rubbery polymer membranes with a sterically bulky
• carbazole-based ROMP comonomer 88
• 2.1 Introduction 88
• 2.2 Results and discussion 91
• 2.2.1 Synthesis and characterization of PEG/PPG-2CZPImide (x:y) crosslinked Copolymer membranes 1 91
• 2.2.2 Thermal properties of the crosslinked PEG/PPG-2CZPImide (x:y) 1 membranes 104
• 2.2.3 Morphological analysis by XRD and SEM 109
• 2.2.4 Gas separation performance of the Cross-linked copolymer membranes 113
• 2.2.5 Permeability vs selectivity 118
• 2.2.6 Anti-aging and anti-plasticization performance 120
• 2.3 Conclusion 122
• 2.4 Experimental 124
• 2.4.1 Materials 124
• 2.4.2 Synthesis of Norbornene-functionalized Precursor monomer and oligomer 124
• 2.4.2.1 Synthesis of 4,5-Di(9H-carbazol-9-yl)phthalonitrile 2CzPN a 124
• 2.4.2.2 Synthesis of 4,5-Bis(9H-carbazol-9- yl)phthalic Acid (2CzPA) b 125
• 2.4.2.3 Synthesis of 2-(bicyclo[2.2.1]hept-5-en-2-ylmethyl)-5,6-di(9H-carbazol-9-yl) isoindoline-1,3-dione (2CzPImide-NB)3 126
• 2.4.2.4 Norbornene-functionalized PEG/PPG oligomer 2 127
• 2.4.2.5 Synthesis of in situ crosslinked copolymer membrane, PEG/PPG:2CZPImide (x:y) 1 128
• 2.5 References 129
• Chapter 3: c-4CzTPN porous carbon-doped crosslinked rubbery PEG/PPG membranes synthesized via ROMP for enhanced CO2 separation 137
• 3.1 Introduction 137
• 3.2 Results and discussion 140
• 3.2.1. Synthesis of crosslinked PEG/PPG-c-4CzTPN-x (x = 0.25/0.5 /1.0) membranes 140
• 3.2.2 Characterization of PEG/PPG-c-4CzTPN-x (x = 0.25/0.5/1.0) membranes 148
• 3.2.3 Thermal properties of PEG/PPG-c-4CzTPN-x (x = 0.25/0.5 /1.0) membranes 149
• 3.2.4 Morphological properties of PEG/PPG-c-4CzTPN-x (x = 0.25/0.5 /1.0) membranes 151
• 3.2.5 Gas separation performance of crosslinked copolymer membranes 153
• 3.2.6 Permeability versus selectivity, anti-plasticizatin and anti-aging properties 159
• 3.3 Conclusion 162
• 3.4 Experimental 163
• 3.4.1 Materials 163
• 3.4.2 Synthesis of NB-PEG/PPG-NB monomer 164
• 3.4.3 Synthesis of 2,3,5,6-tetra(carbazol-9-yl)terephthalonitrile (4CzTPN) 164
• 3.4.4 Synthesis of poly[2,3,5,6-tetra(carbazol-9-yl)terephthalonitri le] (p-4CzTPN) 165
• 3.4.5 Synthesis of porous carbonaceous material (c-4CzTPN) 166
• 3.4.6 Synthesis of PEG/PPG-c-4CzTPN-x crosslinked membranes 1 166
• 3.5 References 167
• Chapter 4: Enhancing CO2 transport across Pebax-based mixed-matrix membranes using a sterically bulky aromatic diacid 174
• 4.1 Introduction 174
• 4.2 Results and discussion 178
• 4.2.1 Synthesis and characterization of 4,5-bis(9H-carbazol-9-yl)phthalic acid (2CzPA) 178
• 4.2.2 Preparation and characterization of Pebax/2CzPA-x MMMs 183
• 4.2.3 Thermal properties of Pebax/2CzPA-x MMMs 186
• 4.2.4 Morphological analysis 188
• 4.2.5 Mechanical properties of Pebax and Pebax/2CzPA MMMs 195
• 4.2.6 Gas separation performances 197
• 4.2.7 Polymer-filler compatibility and its effect on selectivity 200
• 4.2.8 Permeability versus selectivity 202
• 4.2.9 Effects of temperature, pressure and long-term stability 203
• 4.3 Conclusion 209
• 4.4 Experimental 210
• 4.4.1 Chemicals and materials 210
• 4.4.2 Synthesis of 4,5-di(9H-carbazol-9-yl)phthalonitrile (2CzPN) 210
• 4.4.3 Synthesis of 4,5-Bis(9H-carbazol-9- yl)phthalic Acid (2CzPA) 211
• 4.4.4 Membrane preparation 212
• 4.5 References 213
• Chapter 5: Plasticization- and Aging-Resistant Phenolphthalein-Based Thermally Crosslinked PIM-Polyimide Membranes for Efficient CO2 Separation 218
• 5.1 Introduction 218
• 5.2 Results and Discussion 222
• 5.2.1 Synthesis and characterization of phenolphthalein-based PIM-polyimides, PIM(mP-nD) 222
• 5.2.2 Synthesis and characterization of phenolphthalein-based crosslinked PIM-polyimides, X-PIM(mP-nD) 234
• 5.2.3 Gas separation performance 242
• 5.2.4 Anti-plasticization and anti-aging properties 253
• 5.3 Conclusion 257
• 5.4 Experimental 258
• 5.4.1 Materials 258
• 5.4.2 Synthesis and characterization of spirobisindane-based dianhydride (DAn) monomer 4.3 258
• 5.4.2.1 Preparation of bisphthalonitrile 5.1 258
• 5.4.2.2 Preparation of tetracarboxylic acid (TCA) monomer 5.2 259
• 5.4.2.3 Preparation of spirobisindane dianhydride monomer (DAn) 5.3 260
• 5.4.2.4 Synthesis of 3,3′-bis[4-(4-nitrophenoxy)phenyl] phthalide (BNPPP) 5.4 260
• 5.4.2.5 Synthesis of 3,3′-bis[4-(4-aminophenoxy)phenyl] phthalide (BAPPP) 5.5 261
• 5.4.3 Synthesis of phenolphthalein-based PIM-copolyimides, PIM(mP-nD), 1a–1d 262
• 5.4.3.1 Synthesis of PIM(25P-75D), 1a 262
• 5.4.3.2 Synthesis of PIM(50P-50D), 1b 263
• 5.4.3.3 Synthesis of PIM(75P-25D), 1c 263
• 5.4.3.4 Synthesis of PIM(100P-0D), 1d 264
• 5.4.4 Polymer membrane preparation 264
• 5.4.5 Preparation of phenolphthalein-based crosslinked PIM-copolyimides, X-PIM(mP-nD), 2a–2d 265
• 5.5 References 266
• Scheme 2.1 Schematic representation preparation of crosslinked PEG/PPG-2CZPImide (x:y) 1 membranes, with varying monomer ratios (x:y = 10:1, 8:1, 6:1), where x and y indicated the molar amounts of NB-PEG/PPG/NB and NB-2CzPImide, respectively 92
• Scheme 2.2 Synthetic route for NB-PEG/PPF-NB 93
• Scheme 2.3 Synthesis of NB-2CZPImide 94
• Scheme 3.1 Synthesis of crosslinked PEG/PPG-c-4CzTPN-x 1 MMMs 140
• Scheme 5.1 Synthesis of phenolphthalein-based thermally crosslinked PIM-polyimides, X-PIM(mP-nD) 222
• Scheme 5.2 Synthesis of spirobisindane dianhydride (DAn) monomer 223
• Scheme 5.3 Synthesis of 3,3′-bis[4-(4-aminophenoxy)phenyl]phthalide (BAPPP) from phenolphthalein 224
• Table 1.1 Physical properties of gases 13
• Table 1.2 Examples of rubbery and glassy polymers commonly used in gas separation 45
• Table 2.1 Physical and thermal properties of membranes 105
• Table 2.2 SEM EDS Elemental analysis results for the crosslinked PEG/PPG-2CZPImide membranes 112
• Table 2.3 Gas permeability (P) and selectivity (α) of PEG/PPG-2CZPImide crosslinked membranes at 1 atm and 30 ℃ 114
• Table 2.4 Gas diffusivity and solubility coefficients, and diffusivity and solubility selectivities of the crosslinked membranes 114
• Table 2.5 Pure gas (CO2 and N2) permeability and CO2/N2 selectivity data for the PEG/PPG-2CZPImide (6:1) membrane during the stability test (up to 20 days) at 1 atm and 30 ℃ 122
• Table 3.1 BET parameters of p-4CzTPN and c-4CzTPN 146
• Table 3.2 Physical and thermal properties of PEG/PPG-c-4CzTPN-x membranes 148
• Table 3.3 Gas permeabilitiesa and selectivities of the membranes measured at 1 atm and 30 °C 155
• Table 3.4 Gas diffusivity coefficientsa and solubility coefficientsb at 1 atm and 30 °C 155
• Table 3.5 Gas permeabilitiesa and selectivities of the PEG/PPG-c-4CzTPN-0.25 and PEG/PPG-p-4CzTPN-0.25 membranes measured at 1 atm and 30 °C 158
• Table 3.6 Gas diffusivity coefficientsa and solubility coefficientsb of the PEG/PPG-c-4CzTPN-0.25 and PEG/PPG-p-4CzTPN-0.25 membranes measured at 1 atm and 30 °C 158
• Table 3.7 Pressure-dependent CO2 and N2 gas permeabilities and corresponding CO2/N2 selectivities of PEG/PPG-c-4CzTPN-0.5 at 30 ℃ 161
• Table 3.8 CO2 and N2 permeabilities and corresponding CO2/N2 selectivity for PEG/PPG-c-4CzTPN-0.5 during the stability test (up to 236 days) at 1 atm and 30 ℃ 162
• Table 4.1 The chemicals required for the synthesis of 2CzPA from its starting material is listed below with their prices (as on 11th August, 2025) 182
• Table 4.2 A comparison of cost for 10 g of commercially available fillers with the production cost for 10 g of 2CzPA filler (as on 11th August, 2025) 183
• Table 4.3 Physical properties of the Pebax/2CzPA-x membranes 190
• Table 4.4 Calculation of size of the crystallites from WAXD 192
• Table 4.5 Mechanical properties of neat Pebax and Pebax/2CzPA-x 196
• Table 4.6 Gas permeabilitiesa and selectivities of the membranes, measured at 2 atm and 30 °C 198
• Table 4.7 Gas diffusivity coefficientsa and solubility coefficientsb at 2 atm and 30 °C 198
• Table 4.8 Comparison of pure and mixed-gas separation performances of Pebax/2CzPA-1.0 membrane 201
• Table 4.9 CO2, CH4, and N2 permeabilities and CO2/N2 and CO2/CH4 selectivities of Pebax/2CzPA-1.0 at various temperatures and a feed pressure of 2 atm 205
• Table 4.10 Pure gas permeability of CO2, N2, and CH4 at different temperatures, and activation energies for permeation of CO2, N2, and CH4 gases in Pebax/2CzPA-1.0 membrane at 2 atm 206
• Table 5.1 IR stretching frequencies with corresponding modes of vibration observed in BNPPP, BAPPP, bisphthalonitrile, TCM and DAn 225
• Table 5.2 1H NMR peaks of the BAPPP (in DMSO-d6) and DAn (in CDCl3) monomers 226
• Table 5.3 1H NMR peak assignment for PIM(mP-nD) polymers (analyzed in CDCl3) 231
• Table 5.4 Physical properties of the PIM(mP-nD) membranes 232
• Table 5.5 Solubility of the synthesized PIM(mP-nD) and X-PIM(mP-nD) polymers in different organic solvents 234
• Table 5.6 XPS analysis of PIM(50P-50D) and X-PIM(50P-50D) 238
• Table 5.7 Calculation of d-spacing from WAXD spectra of PIM(mP-nD) and X-PIM(mP-nD) polymers 240
• Table 5.8 Gas permeabilities and selectivities of the membranes at 2 atm and 30 °C 245
• Table 5.9 Gas diffusivity coefficientsa and solubility coefficientsb at 2 atm and 30 °C 245
• Table 5.10 Pure and mixed gas separation performance of X-PIM(25P-75D) 250
• Table 5.11 CO2/N2 mixed-gas separation performance at different pressures 251
• Table 5.12 CO2 permeability of the PIM(25P-75D) and X-PIM(25P-75D) membranes as a function of the upstream gas pressure 255
• Table 5.13 Pure gas (CO2 and N2) permeability and CO2/N2 selectivity data for X-PIM(25P-75D) during the aging test at 2 atm and 30 °C 256
• Figure 1.1 Mechanism of solar heat radiation trapping by atmospheric greenhouse gases 2
• Figure 1.2 (a) CCS process [34], (b) Potential pathway of CCS and/or CCU 4
• Figure 1.3 Technologies developed for CO2 separation 8
• Figure 1.4 Breakthroughs in the use of membrane technologies for gas separation 10
• Figure 1.5 Schematic illustration of seven distinct mechanisms for gas separation across membranes 11
• Figure 1.6 Schematic representation of gas transportation across a dense polymeric membrane 15
• Figure 1.7 Schematic representation of permeation of a gas across a membrane with thickness, l; transmembrane pressure difference, p; and gas concentration, c 17
• Figure 1.8 Representation of the excess free volume 21
• Figure 1.9 Schematic representation of sorption isotherms for (a) Henry’s law, b) Florry–Huggins law, and c) dual-mode sorption 23
• Figure 1.10 Intrinsic diffusion coefficient as a function of reciprocal absolute temperature. o methyl acetate; ● ethyl acetate; ⊙ n-propyl acetate; ⨂ n-butyl acetate 26
• Figure 1.11 The effect of acrylonitrile content on gas solubility in poly(butadiene-co-acrylonitrile) at 25°C 29
• Figure 1.12 Plasticization in polymers 34
• Figure 1.13 Robeson upper bound plots for CO2/N2 and CO2/CH4 obtained from the separation performance data of a wide range of gas pairs 36
• Figure 1.14 Membrane type based on several parameters 41
• Figure 2.1 A comparison of 1H NMR spectra of (a) 2CZPN, (b) 2CZPA and (c) 2CZPAnhydride 96
• Figure 2.2 A comparison of FTIR spectra of 2CZPN, 2CZPA, 2CZPAnhydride, and NB-2CZPImide 97
• Figure 2.3 1H NMR spectrum of (a) 5-Norbornene-2-methyl amine and (b) NB-2CZPImide 98
• Figure 2.4 Comparision of 1H NMR spectra of NB(a), NH2-PEG/PPG-NH2 (b) and NB-PEG/PPG-NB 99
• Figure 2.5 FTIR spectra of NB, NH2-PEG/PPG-NH-2 and NB-PEG/PPG-NB monomers 100
• Figure 2.6 Photographic images of PEG/PPG-2CzPImide (x:y) membranes 1 [x:y= 10:1/ 8:1/6:1] 101
• Figure 2.7 A comparison of the FTIR spectra of synthesized monomers and fabricated crosslinked polymers representing in two different ranges of (a) 400 cm-1 - 4000 cm-1 and (b) 400 cm-1 -1600 cm-1 103
• Figure 2.8 Thermal analysis of the crosslinked PEG/PPG-2CZPImide (x:y) membranes; (a) TGA-DTG curves and (b) DSC curves for the crosslinked PEG/PPG-2CZPImide (x:y) membranes 107
• Figure 2.9 Wide-angle X-ray diffraction (WAXD) patterns for the synthesized membranes 110
• Figure 2.10 Cross sectional SEM images for the membranes (a) PEG/PPG-2CZPImide (10:1) (b) PEG/PPG-2CZPImide (8:1) and (c) PEG/PPG-2CZPImide (6:1) 111
• Figure 2.11 Cross-sectional morphology of PEG/PPPG-2CzPImide (x;y) crosslinked membranes analyzed by SEM: (a1, a2, a3)- secondary electron images, (b1, b2, b3,)- EDS mapping (layered) images with atomic distribution, (c1, c2, c3)-carbon elemental maps, (d1, d2, d3)- nitrogen elemental maps and (e1, e2, e3)- oxygen elemental maps. The subscripts 1, 2 and 3 are for PEG/PPG-2CZPImide (10:1), PEG/PPG-2CZPImide (8:1) and PEG/PPG-2CZPImide (6:1) respectively 112
• Figure 2.12 (a) Measured gas permeabilities and selectivities of the crosslinked PEG/PPG-2CZPImide (x:y) 1 membranes, with varying NB-2CZPImide loading, (b) Corresponding diffusivity and diffusivity selectivity trends of the crosslinked PEG/PPG-2CZPImide (x:y) 1 membranes with varying loading of NB-2CZPImide 115
• Figure 2.13 Robeson upper bound plots illustrating the performance of PEG/PPG-2CZPImide (x:y) 1 membranes with data adopted from the published reports 119
• Figure 2.14 (a) CO2 and N2 permeability with CO2/N2 selectivity of the PEG/PPG-2CZPImide (6:1) membrane as a (a) function of time and (b) as a function of applied external pressure 121
• Figure 3.1 Synthesis of (a) 4CzTPN and (b) p-4CzTPN, and (c) preparation of porous c-4CzTPN particles from p-4CzTPN 141
• Figure 3.2 (a) ATR-FTIR and (b) 1H NMR spectra of the 4CzTPN precursor 143
• Figure 3.3 ATR-FTIR spectra of 4CzTPN, p-4CzTPN, and c-4CzTPN 144
• Figure 3.4 SEM images of (a) p-4CzTPN and (b) c-4CzTPN 145
• Figure 3.5 Porous nature of p-4CzTPN and c-4CzTPN. (a) N2 adsorption-desorption isotherm, (b) pore diameters of p-4CzTPN and c-4CzTPN analyzed by BJH method 145
• Figure 3.6 Images of the crosslinked membranes of NB-PEG/PPG-NB and the porous c-4CzTPN material obtained via ROMP 147
• Figure 3.7 (a) FTIR spectra of NB-PEG/PPG-NB, c-4CzTPN, and PEG/PPG-c-4CzTPN-x (x = 0.25, 0.5, 1.0) crosslinked membranes, the red dashed line shows >C=O stretching modes in NB-PEG/PPG-NB. The orange and blue dashed lines represent cis-1,2-disubstituted C–H bending vibrations in NB moiety. The black dashed lines indicate cis-1,2-disubstituted C=C bending vibrations of the NB group. (b) TGA–DTG thermograms of PEG/PPG-c-4CzTPN-x (x = 0.25/0.5/1.0) membranes and (c) DSC curves of PEG/PPG-c-4CzTPN-x (x = 0.25/0.5/1.0) membranes 150
• Figure 3.8 WAXD of PEG/PPG-c-4CzTPN-x (x = 0.25/0.5/1.0) membranes 152
• Figure 3.9 (a1–a3) Surface and (b1–b3) cross-sectional SEM images of PEG/PPG-c-4CzTPN-x membranes: (a1, b1) PEG/PPG-c-4CzTPN-0.25, (a2, b2) PEG/PPG-c-4CzTPN-0.5, and (a3, b3) PEG/PPG-c-4CzTPN-1.0 153
• Figure 3.10 Gas separation performances: (a) CO2 permeability versus CO2/N2 and CO2/CH4 selectivity, (b) diffusivity, and (c) solubility of PEG/PPG-c-4CzTPN-x (x = 0.25/0.5/1.0) membranes examined by pure gas permeation analysis 154
• Figure 3.11 Robeson upper bound plots for PEG/PPG-c-4CzTPN-x (x = 0.25, 0.5, 1.0) crosslinked MMMs- (a) CO2/N2 upper bound plots, (b) CO2/CH4 upper bound plots. Reference data from previous studies are included for comparison [19, 24, 50-58]. Variation of CO2 and N2 gas permeabilities and corresponding CO2/N2 selectivities of the neat PEG/PPG-c-4CzTPN-0.5 membrane as a function of (c) the feed gas pressure and (b) time 161
• Figure 4.1 Schematic representation of the fabrication of Pebax/2CzPA-x MMMs 177
• Figure 4.2 Schematic representations of the synthesis of (a) 2CzPA filler and (b) Pebax/2CzPA-x MMMs 179
• Figure 4.3 Characterization of 2CzPA filler: (a) 1H NMR spectrum, (b) ATR-FTIR spectrum, (c) XRD pattern, and (d) SEM image 184
• Figure 4.4 Photographs of neat Pebax and Pebax/2CzPA-based membranes 184
• Figure 4.5 FTIR spectra of Pebax and Pebax-2CzPA-x membranes; (a) from 400–4000 cm−1; enlarged view in the wavenumber ranges from (b) 3050–3550 and (c) 1500–1800 cm−1 185
• Figure 4.6 Water contact angle for (a) Pebax (neat), (b) Pebax/2CzPA-0.5, (c) Pebax/2CzPA-1.0, and (d) Pebax/2CzPA-2.0 186
• Figure 4.7 (a) TGA-DTG curves of Pebax/2CzPA-x membranes compared with Pebax (neat); (b) an enlarged view of the TGA-DTG curves between 325 and 460 °C; and DSC plots for Pebax (neat) and Pebax/2CzPA-x membranes from (c) −60 to 50 °C and (d) −75 to 240 °C 187
• Figure 4.8 WAXD spectra of Pebax and Pebax/2CzPA-x membranes for 2θ ranges of (a) 5°–60° and (b) 14°–30° 191
• Figure 4.9 FE-SEM surface images of (a1, a2) neat Pebax, (b1, b2) Pebax/2CzPA-0.5, (c1, c2) Pebax/2CzPA-1.0, and (d1, d2) Pebax/2CzPA-2.0 membranes at different magnifications 193
• Figure 4.10 Cross-sectional FE-SEM images of (a) neat Pebax, (b) Pebax/2CzPA-0.5, (c) Pebax/2CzPA-1.0, and (d) Pebax/2CzPA-2.0 membranes 194
• Figure 4.11 Stress–strain curves of neat Pebax and Pebax/2CzPA-x MMMs 195
• Figure 4.12 Gas separation performance of neat Pebax and Pebax/2CzPA-x MMMs: (a) CO2 permeability versus CO2/N2 selectivity, (b) diffusivity, and (c) solubility 197
• Figure 4.13 Robeson upper bound plots for Pebax/2CzPA-x (x = 0.5, 1.0, and 2.0) MMMs: (a) CO2/N2 and (b) CO2/CH4 selectivities. Reference data from previously reported Pebax-based MMMs are included for comparison 203
• Figure 4.14 (a) Variation of CO2, CH4, and N2 gas permeabilities and selectivities of Pebax/2CzPA-1.0 membrane with temperature; (b) Arrhenius plot for CO2, CH4, and N2 gas permeabilities 205
• Figure 4.15 Pressure-dependent CO2 and N2 gas permeabilities and corresponding CO2/N2 selectivities of neat Pebax and Pebax/2CzPA-1.0 membranes 207
• Figure 4.16 Long-term stability test for Pebax/2CzPA-1.0 membrane up to 100 days 209
• Figure 5.1 Thermal decomposition and subsequent crosslinking in PIM(mP-nD) polymers 221
• Figure 5.2 ATR-FTIR spectra of (a) phenolphthalein, BAPPP and BNPPP (b) Bisphthalonitrile, tetracarboxylic acid (TCA), and spirobisindane dianhydride (DAn) monomers 225
• Figure 5.3 1H NMR spectra of the (a) DAn and (b) BAPPP monomers 227
• Figure 5.4 FTIR spectra of synthesized phenolphthalein-based PIM polymers. The yellow, blue, and green shaded areas indicate asymmetric and symmetric C=O vibrations, C=O stretching, and C-N-C stretching in the imide groups, respectively 228
• Figure 5.5 1H NMR spectra of (a) PIM(25P-75D) and (b) PIM(50P-50D) 229
• Figure 5.6 1H NMR spectra of (a) PIM(75P-25D) and (b) PIM(100P-0D) 230
• Figure 5.7 The GPC chromatograms of the (a) PIM(100P-0D), (b) PIM(75P-25D), (c) PIM(50P-50D) and (d) PIM(25P-75D) 233
• Figure 5.8 Photographs of (a) PIM(mP-nD) copolyimide membranes and (b) X-PIM(mP-nD) thermally treated membranes 235
• Figure 5.9 Thermograms of (a) pristine PIM(mP-nD) copolymers and (b) thermally treated X-PIM(mP-nD) membranes after heating at 400 °C 236
• Figure 5.10 XPS spectra of PIM(50P-50D) and X-PIM(50P-50D): (a) C1s spectrum of PIM(50P-50D), (b) C1s spectrum of X-PIM(50P-50D), (c) O1s spectrum of PIM(50P-50D), and (d) O1s spectrum of X-PIM(50P-50D) 237
• Figure 5.11 WAXD patterns of (a) PIM(mP-nD) copolymer and (b) thermally treated crosslinked X-PIM(mP-nD) membranes 239
• Figure 5.12 Comparison of (a, c) permeability and selectivity, and (b, d) diffusivity and selectivity of various gases across the (a, b) non-crosslinked and (c, d) thermally crosslinked copolymer membranes. The permeability, diffusivity, and selectivity increases of the non-crosslinked membranes were calculated based on the initial permeability of the membrane with no durene content, PIM(100P-0D). The performance of the crosslinked membranes was evaluated relative to that of their corresponding non-crosslinked versions 246
• Figure 5.13 (a) Normalized permeability versus normalized perm-selectivity and (b) normalized diffusivity versus normalized diffusivity selectivity curves for PIM(mP-nD) and X-PIM(mP-nD) membranes. The letters A, B, C, D, E, F, G, and H on the horizontal axes represent PIM(100P-0D), PIM(75P-25D), PIM(50P-50D), PIM(25P-75D), X-PIM(100P-0D), X-PIM(75P-25D), X-PIM(50P-50D), and X-PIM(25P-75D), respectively. The normalization was performed with respect to the PIM(100P-0D) membrane 247
• Figure 5.14 CO2 adsorption isotherms at 273.15 K for PIM(100P-0D) and X-PIM(100P-0D) 248
• Figure 5.15 Permeability–selectivity relationship of the PIM(mP-nD) 2 and X-PIM(mP-nD) 1 membranes with regard to the (a) CO2/N2 and (b) CO2/CH4 separation performances. The reference data were taken from the literature 253
• Figure 5.16 Pressure dependence of the CO2 separation performance of the PIM(25P-75D) and X-PIM(25P-75D) polymer membranes at 30 °C 254
• Figure 5.17 CO2 and N2 permeabilities and CO2/N2 selectivity of X-PIM(25P-75D) as a function of time 256