Molecular Mobility and Gas Transport Properties of Mixed Matrix Membranes Based on PIM‑1 and a Phosphinine Containing Covalent Organic Framework

Polymers with intrinsic microporosity (PIMs) are gaining attention as gas separation membranes. Nevertheless, they face limitations due to their pronounced physical aging. In this study, a covalent organic framework containing λ5-phosphinine moieties, CPSF-EtO, was incorporated as a nanofiller (concentration range 0–10 wt %) into a PIM-1 matrix forming dense films with a thickness of ca. 100 μm. The aim of the investigation was to investigate possible enhancements of gas transport properties and mitigating effects on physical aging. The incorporation of the nanofiller occurred on an nanoaggregate level with domains up to 100 nm, as observed by T-SEM and confirmed by X-ray scattering. Moreover, the X-ray data show that the structure of the microporous network of the PIM-1 matrix is changed by the nanofiller. As molecular mobility is fundamental for gas transport as well as for physical aging, the study includes dielectric investigations of pure PIM-1 and PIM-1/CPSF-EtO mixed matrix membranes to establish a correlation between the molecular mobility and the gas transport properties. Using the time-lag method, the gas permeability and the permselectivity were determined for N2, O2, CH4, and CO2 for samples with variation in filler content. A significant increase in the permeability of CH4 and CO2 (50% increase compared to pure PIM-1) was observed for a concentration of 5 wt % of the nanofiller. Furthermore, the most pronounced change in the permselectivity was found for the gas pair CO2/N2 at a filler concentration of 7 wt %

First Clear-Cut Experimental Evidence of a Glass Transition in a Polymer with Intrinsic Microporosity: PIM‑1

Polymers with intrinsic microporosity (PIMs) represent a novel, innovative class of materials with great potential in various applications from high-performance gas-separation membranes to electronic devices. Here, for the first time, for PIM-1, as the archetypal PIM, fast scanning calorimetry provides definitive evidence of a glass transition (<i>T</i>_g = 715 K, heating rate 3 × 10⁴ K/s) by decoupling the time scales responsible for glass transition and decomposition. Because the rigid molecular structure of PIM-1 prevents any conformational changes, small-scale bend and flex fluctuations must be considered the origin of its glass transition. This result has strong implications for the fundamental understanding of the glass transition and for the physical aging of PIMs and other complex polymers, both topical problems of materials science

First Clear-Cut Experimental Evidence of a Glass Transition in a Polymer with Intrinsic Microporosity: PIM‑1

Polymers with intrinsic microporosity (PIMs) represent a novel, innovative class of materials with great potential in various applications from high-performance gas-separation membranes to electronic devices. Here, for the first time, for PIM-1, as the archetypal PIM, fast scanning calorimetry provides definitive evidence of a glass transition (<i>T</i>_g = 715 K, heating rate 3 × 10⁴ K/s) by decoupling the time scales responsible for glass transition and decomposition. Because the rigid molecular structure of PIM-1 prevents any conformational changes, small-scale bend and flex fluctuations must be considered the origin of its glass transition. This result has strong implications for the fundamental understanding of the glass transition and for the physical aging of PIMs and other complex polymers, both topical problems of materials science

Synthesis and Characterization of Poly(vinylphosphonic acid-<i>co</i>-acrylic acid) Copolymers for Application in Bone Tissue Scaffolds

Poly­(vinylphosphonic acid-<i>co</i>-acrylic acid) (PVPA-<i>co</i>-AA) has recently been identified as a possible candidate for use in bone tissue engineering. It is hypothesized that the strong binding of PVPA-<i>co</i>-AA to calcium in natural bone inhibits osteoclast activity. The free radical polymerization of acrylic acid (AA) with vinylphosphonic acid (VPA) has been investigated with varying experimental conditions. A range of copolymers were successfully produced and their compositions were determined quantitatively using ³¹P NMR spectroscopy. Monomer conversions were calculated using ¹H NMR spectroscopy and a general decrease was found with increasing VPA content. Titration studies demonstrated an increase in the degree of dissociation as a function of VPA in the copolymer. However, a VPA content <i>ca</i>. 30 mol % was found to be the optimum for calcium chelation, suggesting that this composition is the most promising for biomaterials applications. Assessment of cell metabolic activity showed that PVPA-<i>co</i>-AA has no detrimental effect on cells, regardless of copolymer composition