Oxygen Permselectivity Research Articles

Synthesis and Direct Observation of Molecules of 2D Polymers: With High Molecular Weights, Large Areas, Small Micropores, Solubility, Membrane Forming Ability, and High Oxygen Permselectivity.

If ideal 2D polymer (2DP) macromolecules with small pores that are similar in size to gas molecules, large areas, small thickness, and excellent membrane-forming ability are synthesized, ultimate gas separation membranes would be obtained. However, as far it is known, such ideal well-characterized 2DP macromolecules are not isolated. In this study, an ideal 2DP macromolecule is synthesized by using the successive three reactions (Glaser coupling, SCAT reaction, and the introduction of octyl groups), in which the conjugated framework structure is maintained, from a fully conjugated 1D polymer. Because this exfoliated 2DP is soluble, the macromolecular structure can be fully characterized by 1H-NMR, GPC, SEM, AFM, and its dense membrane with no defects can be fabricated by the solvent cast method. This soluble 2DP macromolecule has very small micropores (6.0Å) inside the macromolecule, a large area (30×68nm by SEM and AFM), high molecular weight (Mn=2.80×105 by GPC), and a small thickness (4.4Å by AFM). This membrane shows the highest oxygen permselectivity exceeding Robeson's upper line because of the high molecular sieving effect of the controlled small micropores.

Synthesis of a Two-dimensional Multi-functional Macromonomer and Oxygen Permselectivity of Its Supramolecular and Covalent Polymer Membranes

Abstract Although polymers having small micropores are promising for good gas permselective membranes, such polymers tend to have no membrane-forming ability. In this study, a polymer including micropores was synthesized from two-dimensional fully-conjugated macromonomer (2DM) with multi-acetylene and hydroxyl groups. In spite of the low molecular weight, its solvent-cast membrane (supra-poly(2DM)) showed good oxygen permselectivity. In addition, soluble high molecular weight network poly(2DM) membrane obtained from supra-poly(2DM) membrane showed higher oxygen permselectivity due to the increased number of micropores.

Oxygen Permeability of Fully Conjugated Polymers Consisting of (Di)ethynylene and Phenylene Groups Synthesized by Glaser or Sonogashira Coupling Polycondensation

Fully conjugated polymers are candidates as rigid polymers for good oxygen permselective membrane materials. In this study, we synthesized a series of such polymers with a rigid backbone consisting of (di)ethynylene and phenylene groups and alkyl side groups by Glaser or Sonogashira coupling polycondensation. Some of these polymers gave self-supporting membranes and their oxygen permselectivities were influenced by the alkyl groups. Oxygen permselectivities of polymers containing diynes in the main chain were determined for the first time.

Preparation and oxygen permeability of pure supramolecular polymer membranes synthesized from poly (substituted phenylacetylene)

We previously reported a new preparation method for supramolecular polymers having self-membrane forming ability from poly (substituted phenylacetylene)s using highly selective photocyclic aromatization (the SCAT reaction). However, since mechanical strengths of their membranes were not enough for oxygen permeation process, we could not estimate their oxygen permselectivities. In this study, we successfully obtained oxygen permselectivities from the experimental data for their pure supramolecular polymer membranes prepared on porous supports. This is the first example of gas permeability data for pure supramolecular polymer membranes. Surprisingly, the oxygen permselectivities were higher than those for their corresponding conventional polymer membranes. It may be because the supramolecular polymer membranes had denser and less defected structures than their corresponding conventional polymer membranes. It was thought that the supramolecularly-bonded main chains in these pure supramolecular polymers worked like the covalently-bonded main chains in the conventional polymers in the permeation.

Synthesis and oxygen permselectivity of multi-stranded graft copolymers

New types of multi-stranded graft copolymers ( AGS s) were synthesized by selective three-step polymerization of monomer M having three deferent polymerizable groups. First, a rigid cis -cisoidal helical polyphenylacetylene ( A ) with bromo substituents at the pendants was synthesized by addition polymerization of the triple bond in M with a rhodium catalyst, and then graft copolymers ( AG s) with polyphenyleneethynylene grafts having many hydroxy groups were synthesized by Sonogashira-coupling polycondensation in the presence of the rigid polyphenylacetylenes. Finally, multistrands were synthesized in the grafts by etherification of the hydroxyl groups with dibromomethane or dibromoethane. The degree of polymerization of the grafts (q) and the second strands (r) were determined by 1 H NMR and IR, respectively. The q and r could be controlled. Oxygen permeabilities for all the polymers ( A , AG s, and AGS s) were able to be measured. AGS s showed the best performance among the three. This may be because micropores and ultramicropores formed in the AGS s played a very important role in enhancing both permeability and permselectivity. ・ •A novel monomer bearing three different polymerizable groups was synthesized. • Graft copolymers were synthesized by addition and condensation polymerization of the monomer. • Novel multi-stranded graft copolymers were synthesized from these graft copolymers. • The degree of polymerization of the grafts and the second strands were controlled. • Oxygen permeation may be improved by ultramicropores and micropores formed in these polymers.

Macromolecular Design for Oxygen/Nitrogen Permselective Membranes-Top-Performing Polymers in 2020.

Oxygen/nitrogen permselective membranes play particularly important roles in fundamental scientific studies and in a number of applications in industrial chemistry, but have not yet fulfilled their full potential. Organic polymers are the main materials used for such membranes because of the possibility of using sophisticated techniques of precise molecular design and their ready processability for making thin and large self-supporting membranes. However, since the difference in the properties of oxygen and nitrogen gas molecules is quite small, for example, their kinetic diameters are 3.46 Å and 3.64 Å, respectively, the architectures of the membrane macromolecules should be designed precisely. It has been reported often that oxygen permeability (PO2) and oxygen permselectivity (α = PO2/PN2) have trade-off relationships for symmetric membranes made from pure polymers. Some empirical upper bound lines have been reported in (ln α − ln PO2) plots since Robeson reported an upper bound line in 1991 for the first time. The main purpose of this review is to discuss suitable macromolecular structures that produce excellent oxygen/nitrogen permselective membranes. For this purpose, we first searched extensively and intensively for papers which had reported α and PO2 values through symmetric dense membranes from pure polymers. Then, we examined the chemical structures of the polymers showing the top performances in (ln α − ln PO2) plots, using their aged performances. Furthermore, we also explored progress in the molecular design in this field by comparing the best polymers reported by 2013 and those subsequently found up to now (2020) because of the rapid outstanding growth in this period. Finally, we discussed how to improve α and PO2 simultaneously on the basis of reported results using not only symmetric membranes of pure organic polymers but also composite asymmetric membranes containing various additives.

Improvement of oxygen permselectivity of a rigid helical polyphenylacetylene: Effect of flexible groups, degree of polymerization, composites, thickness, orientation, and network formation

In order to improve oxygen permselectivity of a rigid helical poly(alkenylphenylacetylene) membrane having a columnar liquid crystalline structure, several chemical and membrane structures including the degree of polymerization and the orientation of the macromolecules were modified and controlled. Introduction of longer alkenyl or flexible siloxane groups significantly enhanced oxygen permeability (PO2) and by reducing the degree of polymerization and the thickness of the membranes, or by the formation of network structures oxygen permselectivity (α = PO2/PN2) was effectively enhanced. The membranes from polymers with very small degree of polymerization and perpendicular orientation had extremely high α. In spite of the membranes from the polymers having the identical chemical structure, their performances could be optimized by controlling several membrane structures.

Synthesis of Cis-Cisoid or Cis-Transoid Poly(Phenyl-Acetylene)s Having One or Two Carbamate Groups as Oxygen Permeation Membrane Materials.

Three new phenylacetylene monomers having one or two carbamate groups were synthesized and polymerized by using (Rh(norbornadiene)Cl)2 as an initiator. The resulting polymers had very high average molecular weights (Mw) of 1.4–4.8 × 106, with different solubility and membrane-forming abilities. The polymer having two carbamate groups and no hydroxy groups in the monomer unit showed the best solubility and membrane-forming ability among the three polymers. In addition, the oxygen permeability coefficient of the membrane was more than 135 times higher than that of a polymer having no carbamate groups and two hydroxy groups in the monomer unit with maintaining similar oxygen permselectivity. A better performance in membrane-forming ability and oxygen permeability may be caused by a more extended and flexible cis-transoid conformation and lower polarity. On the other hand, the other two new polymers having one carbamate group and two hydroxy groups in the monomer unit showed lower performances in membrane-forming abilities and oxygen permeabilities. It may be caused by a very tight cis-cisoid conformation, which was maintained by intramolecular hydrogen bonds.

Synthesis and Permselectivity of a Soluble Two-Dimensional Macromolecular Sheet by Solid–Solid Interfacial Polycondensation Followed by Chemical Exfoliation

Two-dimensional (2D) network polymers with nano-sized pores are generally insoluble, and therefore, it is difficult to determine their molecular structures and to fabricate their membranes. Soluble 2D network polymer membranes with angstrom-sized pores and thicknesses have not been reported. Herein, novel soluble 2D macromolecular sheets with angstrom-sized pores (24.6 Å) and thickness (3.4 Å) are synthesized by solid–solid interface polycondensation in laminated membranes of two cis–cisoid poly(imino-containing phenylacetylene)s followed by highly selective photocyclic aromatization (SCAT). First, a two-layered laminated polymer membrane that is self-supporting is prepared, and solid–solid interfacial polycondensation is performed. The insoluble three-dimensional (3D) network polymer layer formed is isolated by removing the soluble unreacted polymer layers. Finally, a SCAT reaction is carried out by irradiation of visible light on the insoluble 3D membrane to produce a soluble 2D macromolecular sheet. The precise 2D molecular structure can be displayed, such as the degree of polymerization, thickness, fraction of rings (pores), and pore size, estimated by GPC, AFM, 1H-NMR, IR, and XRD, because the macromolecule is soluble. Composite membranes containing the 2D macromolecular sheet show good oxygen permselectivity exceeding the Robeson upper line, possibly because the angstrom-sized pores and thicknesses produce high oxygen permselectivity without suppressing the permeability.

New Synthetic Methods of Novel Nanoporous Polycondensates and Excellent Oxygen Permselectivity of Their Composite Membranes.

Two kinds of novel nanoporous polycondensates (sc(Rf)) have been synthesized by two new preparation methods consisting of polycondensation and highly selective photocyclicaromataization of 1/3 helical cis-cis polyphenylacetylenes with polymerizable groups. By the original methods, new well-defined sheet polymers having nanopores or nanospaces have been synthesized for the first time. Their composite membranes, containing small amounts (1.0 wt%) of sc(Rf), had ultrahigh oxygen permeability (Po2 > 1000 barrer), and their plots were beyond the Robeson’s upper bound line in the graph of oxygen permselectivity (α = Po2/PN2) versus Po2. Both α and Po2 values were enhanced by adding only small amounts (1.0 wt%) of sc(Rf). One of the sc(Rf)s synthesized on the base membrane surface showed the best performance, i.e., Po2 = 5300 barrer and α = 2.5. The membrane surface was effectively covered by sc(Rf), judging from the contact angle values. It is thought that nanopores and nanospaces created in and between sc(Rf) molecules played an important role for the enhancement of both α and Po2/PN2.

Ultrahigh oxygen permeability of chemically-modified membranes of novel (co)polyacetylenes having a photodegradative backbone and crosslinkable side chains

Four new partly modified membranes of novel (co)polyacetylenes having a photodegradative backbone and crosslinkable side chains showed excellent performances as oxygen permselective membranes, that is, ultrahigh oxygen permeability (PO2) with relatively high oxygen permselectivity (α = PO2/PN2). In α vs. PO2 plots, two of them showed a performance close to Robeson's upper bound 2008 and the other two exceeded Robeson's upper bound 1991. The combination of the rigid main chain of the (co)polymers, the regular structure of the supramolecular polymer, and the flexible crosslinking structure may have produced these excellent performances.

Subnanoporous Highly Oxygen Permselective Membranes from Poly(conjugated hyperbranched macromonomer)s Synthesized by One-Pot Simultaneous Two-Mode Homopolymerization of 1,3-Bis(silyl)phenylacetylene Using a Single Rh Catalytic System: Control of Their Structures and Permselectivities

Novel well-defined complex polymers, polymers of acetylene-type macromonomers having silylene–vinylene–phenylene–ethynylene hyperbranches, investigated as a new class of subnanoporous oxygen permselective membrane materials, were synthesized very easily by one-pot simultaneous two-mode homopolymerization of a single monomer with a single catalyst. For this “simultaneous polymerization” we synthesized AB2-type monomers (1,3-bis(dimethylsilyl)phenylacetylenes) containing one terminal triple bond and two Si–H groups. The resulting poly(hyperbranched macromonomer)s had high molecular weights, low densities, high solubility, and good self-membrane forming ability. They had higher oxygen permselectivities (α = PO2/PN2) than any other reported polymers having similar oxygen permeabilities (PO2). These excellent polymer membranes could be obtained only by the simultaneous polymerization. In the one-pot simultaneous polymerization, the two different modes of polymerizations, i.e., addition polymerization of the tr...

Oxygen permselectivities through supramolecular polymer membranes prepared by highly selective photocyclic aromatization of poly(substituted acetylene)

In order to estimate oxygen permselectivities through a supramolecular polymer membrane for the first time, we prepared three kinds of composite membranes consisting of a supramolecular polymer membrane and a conventional organic polymer membrane. Supramolecular polymer membranes were prepared by using highly selective photocyclic aromatization of poly(substituted acetylene)s. It was found that the supramolecular polymer membrane had oxygen permselectivity (α = PO2/PN2) around three in spite of its low molecular weight.

Oxygen Permselectivities of Novel Multi-bridged Copolymers Synthesized by Imine Metathesis between N-Imines and C-Imines in the Pendant Groups of Two Poly(substituted acetylene)s

New types of multi-bridged copolymers were designed and examined as oxygen permselective membrane materials. The multi-bridged copolymers were synthesized by imine metathesis reactions between N-imine (synthetic equivalent of amine)-containing poly(substituted acetylene)s and C-imine (synthetic equivalent of aldehyde)-containing poly(substituted acetylene)s in the membrane state. The resulting copolymers maintained good self-membrane forming ability. The introduction of multibridge structures enhanced both oxygen permselectivities and oxygen permeabilities simultaneously.

Synthesis and oxygen permselectivity of copoly(substituted acetylene)s with bulky fused polycyclic aliphatic groups

Abstract We synthesized six phenylacetylenes (RCOPAs, RSOPAs, and RSPAs) having a bulky fused polycyclic aliphatic group, which is adamantyl(Ad), pinanyl(Pi), or cholesteryl(Ch) via oxycarbonyl (CO) or oxydimethylsilyl(SO), and the other two phenylacetylenes having less or non-bulky substituents, i.e., menthyloxycarbonylphenylacetylene (MtCOPA) or ethoxydimethylsilylphenylacetylene (EtSOPA) (Et = Ethyl). The new monomers were polymerized and copolymerized with p-trimethylsilylphenylacetylene (SPA) by using catalyst [Rh(nbd)Cl]2 (nbd = 2,5-norbornadiene) in trimethylamine to give soluble high molecular-weight polymers in relatively good yields. The resulting copolymers were fabricated to self-supporting membranes which had enough strength for separation membranes by solution casting method. As a result, we can discuss the relationship between bulky chemical structures and permeation behavior systematically for the first time. Oxygen permselectivities (PO2/PN2) of copolyRSOPAs having the bulky fused polycyclic aliphatic groups such as Ad and Pi were higher than those of copolyEtSOPAs. PO2/PN2 values of copolyRCOPAs were higher than those of polyRSOPAs when they had the same content of the identical bulky groups. The rigid spacer was effective for enhancing PO2/PN2. Among copolyRCOPAs with bulky fused polycyclic aliphatic groups, the copolymers with spherical substituents such as Pi and Ad groups showed higher PO2/PN2 values than those with a planer substituent i.e., Ch groups. PO2 values of copolyRSOPAs and copolyRCOPAs were 130–220 and 50–90 barrer, respectively. The flexible silyloxy spacers in RSOPAs were effective in enhancing their PO2 values.

High Oxygen Permselectivity through a Membrane from Novel Soluble Imido-bridged Ladder Polysiloxane

A novel soluble well-defined ladder polysiloxane bridged by imido linkages having a high molecular weight was successfully synthesized via the corresponding supramolecular intermediate and was fabr...

Synthesis of a Fluorine-Containing Cis-Cisoidal One-Handed Helical Polyphenylacetylene and Application of Highly Selective Photocyclic Aromatization Product on Oxygen Permselective Membrane.

A novel phenylacetylene monomer having a perfluorinated alkyl group (M-F) was synthesized and polymerized in a chiral catalytic system to yield a one-handed helical polymer. The ability and efficiency of the chiral induction of the fluorine-containing monomer in the helix-sense-selective polymerization (HSSP) was much higher than those of a monomer having the corresponding alkyl group (M-H) we reported before. The resulting polymer showed cis-cisoidal one-handed helical conformation, and was suitable for highly selective photocyclic aromatization (SCAT) to give a 2D surface modifier (). Oxygen permselectivity through a base polymer membrane was highly enhanced from 1.83 to 2.36 by adding a small amount (1-5 wt%) of the 2D surface modifier . The improvement was thought to be caused by improvement of solution selectivity on the membrane surface which the 2D surface modifier effectively covered.

Synthesis and oxygen permeation of novel polymers of phenylacetylenes having two hydroxyl groups via different lengths of spacers

Three novel phenylacetylenes having two hydroxyl groups via different kinds of spacers between the two hydroxyl groups and benzyl group were synthesized and polymerized. Two of the resulting polymers having oxyalkylene spacers between the hydroxyl group and benzyl group had good membrane forming ability, relatively high oxygen permselectivity and high oxygen permeability. By introducing the oxyalkylene spacers, the membrane forming abilities and oxygen permselectivity were enhanced. Oxygen permselectivity (PO2/PN2=2.67) of the polymer membrane having the longest spacers was higher than that (2.19) of polymer without any spacers. It may be because the columnar content and then defects decreased when the cis-cisoid conformation was changed to cis-transoid conformation. In addition, by decreasing the columnar content of the membrane from the polymer without any spacers, which could be controlled by conditions in membrane preparation, the membrane forming ability and oxygen permselectivity were effectively enhanced (from 2.19 to 2.61) without any drop of oxygen permeability.

Facile synthesis of five 2D surface modifiers by highly selective photocyclic aromatization and efficient enhancement of oxygen permselectivities of three polymer membranes by surface modification using a small amount of the 2D surface modifiers

A facile synthesis of novel five 2D (planar) surface modifiers having a triphenylbenzene derivatives as a 2D structure has been achieved by the highly selective photocyclic aromatization reaction. Efficient enhancement of oxygen permselectivities through the three polymer membranes has been achieved by adding a small amount (<5.0 wt%) of the 2D surface modifiers. Among the five 2D surface modifiers, a modifier compound having oligoethylene oxide groups showed the best performance for the enhancement. These improvements were thought to be caused mainly by improvement of the solution selectivity on the membrane surface where the 2D surface modifiers were accumulated. In some of the surface-modified blend membranes, their plots in the PO2-α graph were over or close to the upper boundary line by Robeson in 1991. Since all the membranes containing the 2D surface modifiers showed better permselectivities than the corresponding substrate membranes, it is very promising for the future.

Facile Synthesis of an Amphiphilic 1,3,5-Trisubstituted Benzene as a Novel Surface Modifier by Selective Photocyclic Aromatization and Efficient Improvement of Oxygen Permselectivity by the Addition of the Surface Modifier

Abstract An amphiphilic 1,3,5-trisubstituted benzene as a new 2D surface modifier (T-EO) which has six hydroxy groups and three oligoethylene groups was successfully and easily synthesized by selective photocyclic aromatization in high conversion and selectivity for the first time. We prepared four kinds of blend membranes based on PVA or poly(trimethylsilylphenylacetylene) (poly(SPA)) containing the new amphiphilic cyclic trimer (T-EO) or the corresponding polymer (P-EO), that is, T-EO/PVA, P-EO/PVA, and T-EO/poly(SPA) membranes prepared by conventional solvent casting method (Method I) and T-EO/poly(SPA) membranes prepared by a new solvent casting method (Method II). T-EO/PVA membranes by Method I and T-EO/poly(SPA) membranes by Method II showed better performance in oxygen permeation than P-EO/PVA membranes by Method I and T-EO/poly(SPA) membranes by Method I, respectively. A PVA-based membrane containing 1.0 wt % T-EO showed the best performance, that is, the α became twice that of the original PVA membrane without any decrease in PO2. The ideal improvement may be caused by effective surface modification by T-EO.