This study details the enhancement of CO2 selectivity in ring opening metathesis polymerization (ROMP) polymers that contain nitrile moieties and micro-pore generating ladder side chains. A material, CN-ROMP homopolymer, with nitriles in the ladder side chains was originally targeted and synthesized, however its low molecular weight and backbone rigidity precluded film formation. As a result, an alternative method was pursued wherein copolymers were synthesized using norbornene (N) and nitrile norbornene (NN). Herein, we report an investigation of the structure–property relationships of backbone functionalization and grafting density on the CO2 transport properties in these ROMP polymers. Nitrile-containing copolymers showed an increase in CO2/CH4 sorption selectivity and a concomitant increase in CO2/CH4 permselectivity when compared to the unfunctionalized (nitrile free) analogs. The stability in CO2 rich environments is enhanced as grafting density of the rigid, pore-generating side chains increases and an apparent tunability of CO2 plasticization pressure was observed as a function of norbornene content. Lower loadings of norbornene resulted in higher plasticization pressure points. Gas permeability in the ROMP copolymers was found to correlate most strongly with the concentration of ladder macromonomers in the polymer chain.
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Polymers with Side Chain Porosity for Ultrapermeable and Plasticization Resistant Materials for Gas Separations
Polymer membranes with ultrahigh CO2permeabilities and high selectivities are needed to address some of the critical separation challenges related to energy and the environment, especially in natural gas purification and postcombustion carbon capture. However, very few solution‐processable, linear polymers are known today that access these types of characteristics, and all of the known structures achieve their separation performance through the design of rigid backbone chemistries that concomitantly increase chain stiffness and interchain spacing, thereby resulting in ultramicroporosity in solid‐state chain‐entangled films. Herein, the separation performance of a porous polymer obtained via ring‐opening metathesis polymerization is reported, which possesses a flexible backbone with rigid, fluorinated side chains. This polymer exhibits ultrahigh CO2permeability (>21 000 Barrer) and exceptional plasticization resistance (CO2plasticization pressure > 51 bar). Compared to traditional polymers of intrinsic microporosity, the rate of physical aging is slower, especially for gases with small effective diameters (i.e., He, H2, and O2). This structural design strategy, coupled with studies on fluorination, demonstrates a generalizable approach to create new polymers with flexible backbones and pore‐forming side chains that have unexplored promise for small‐molecule separations.
more » « less- Award ID(s):
- 1410718
- PAR ID:
- 10461469
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 31
- Issue:
- 21
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Donor–acceptor (D–A) type semiconducting polymers have shown great potential for the application of deformable and stretchable electronics in recent decades. However, due to their heterogeneous structure with rigid backbones and long solubilizing side chains, the fundamental understanding of their molecular picture upon mechanical deformation still lacks investigation. Here, the molecular orientation of diketopyrrolopyrrole (DPP)‐based D–A polymer thin films is probed under tensile deformation via both experimental measurements and molecular modeling. The detailed morphological analysis demonstrates highly aligned polymer crystallites upon deformation, while the degree of backbone alignment is limited within the crystalline domain. Besides, the aromatic ring on polymer backbones rotates parallel to the strain direction despite the relatively low overall chain anisotropy. The effect of side‐chain length on the DPP chain alignment is observed to be less noticeable. These observations are distinct from traditional linear‐chain semicrystalline polymers like polyethylene due to distinct characteristics of backbone/side‐chain combination and the crystallographic characteristics in DPP polymers. Furthermore, a stable and isotropic charge carrier mobility is obtained from fabricated organic field‐effect transistors. This study deconvolutes the alignment of different components within the thin‐film microstructure and highlights that crystallite rotation and chain slippage are the primary deformation mechanisms for semiconducting polymers.
