Polyimides with low coefficient of thermal expansion derived from diamines containing benzimidazole and amide: Synthesis,properties, and the N-substitution effect

Three novel diamines, incorporating benzimidazole and amide moieties, namely 4-amino-N-(5-amino-benzimidazol-2-yl)-benzamide (6a), 4-amino-N-(5-amino-1- methyl-benzimidazol-2-yl)-benzamide (6b), and 4-amino-N-(5-amino-1-phenyl -benzimidazol-2-yl)-benzamide (6c), were designed and synthesized. A series of poly(benzimidazole-amide-imide) (PBIAI) films were prepared from the resulting diamines and 4,4-biphthalic dianhydride (BPDA). These flexible polyimides (PIs) showed high glass transition temperatures (T_g = 353–379°C), low coefficients of thermal expansion (CTE = 3.7–12.3 ppm K⁻¹) and good mechanical properties (σ = 152–207 MPa and E = 4.5–7.7 GPa), promising candidates for applications in flexible-display substrates. Furthermore, the data guided a feasible method to enhance T_g and reduce CTE by introducing benzimidazole and amide units into PI main chains, and the effect of different N-substituents on performance was revealed.     

Synthesis,properties, and molecular simulations of high-barrier polyimide containing carbazole moiety and amide group in the main chain

An intrinsic high-barrier polyimide (2,7-CPAPPI) containing rigid planar carbazole moiety and amide group in main chain was prepared. The 2,7-CPAPPI shows very attractive barrier performances, possessing water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) low to 0.04 g m⁻² day⁻¹ and 0.11 cm³ m⁻² day⁻¹, respectively. Meanwhile, 2,7-CPAPPI also displays exceptional thermal stability with a glass transition temperature (T_g) of 552°C and coefficient of thermal expansion (CTE) of 15.48 ppm/K. The barrier performances of 2,7-CPAPPI are compared with those of a structural analog (2,7-CPPI, containing only carbazole moiety in the main chain) and a typical polyimide (Kapton). The structure–barrier performances relationship was investigated by molecular simulations, wide angle X-ray diffraction (WAXD), and positron annihilation lifetime spectroscopy (PALS). The results show that 2,7-CPAPPI has more number of intermolecular hydrogen bonds among the three PIs, which leads to close chain packing and thereby high crystallinity, low free volume, and poor chains mobility. That is, the high crystallinity and low free volume of 2,7-CPAPPI decrease the diffusion and solubility of gases. Meanwhile, the poor chains mobility further reduces the gases diffusion. The decreased diffusion and solubility of gases consequently promote the improvement of barrier properties for 2,7-CPAPPI.     

Effect of nanoscale confinement on the glass transition temperature of free-standing polymer films: Novel,self-referencing fluorescence method

The effect of nanoscale confinement on the glass transition temperature, T_g, of freely standing polystyrene (PS) films was determined using the temperature dependence of a fluorescence intensity ratio associated with pyrene dye labeled to the polymer. The ratio of the intensity of the third fluorescence peak to that of the first fluorescence peak in 1-pyrenylmethyl methacrylate-labeled PS (MApyrene-labeled PS) decreased with decreasing temperature, and the intersection of the linear temperature dependences in the rubbery and glassy states yielded the measurement of T_g. The sensitivity of this method to T_g was also shown in bulk, supported PS and poly(isobutyl methacrylate) films. With free-standing PS films, a strong effect of confinement on T_g was evident at thicknesses less than 80–90 nm. For MApyrene-labeled PS with M_n = 701 kg mol⁻¹, a 41-nm-thick film exhibited a 47 K reduction in T_g relative to bulk PS. A strong molecular weight dependence of the T_g-confinement effect was also observed, with a 65-nm-thick free-standing film exhibiting a reduction in T_g relative to bulk PS of 19 K with M_n = 701 kg mol⁻¹ and 31 K with M_n = 1460 kg mol⁻¹. The data are in reasonable agreement with results of Forrest, Dalnoki-Veress, and Dutcher who performed the seminal studies on T_g-confinement effects in free-standing PS films. The utility of self-referencing fluorescence for novel studies of confinement effects in free-standing films is discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2754–2764, 2008     

Conformational Dependence of Triplet Energies in Rotationally Hindered N- and S-Heterocyclic Dimers: New Design and Measurement Rules for High Triplet Energy OLED Host Materials

A series of four heterocyclic dimers has been synthesized, with twisted geometries imposed across the central linking bond by ortho-alkoxy chains. These include two isomeric bicarbazoles, a bis(dibenzothiophene-S,S-dioxide) and a bis(thioxanthene-S,S-dioxide). Spectroscopic and electrochemical methods, supported by density functional theory, have given detailed insights into how para- vs. meta- vs. broken conjugation, and electron-rich vs. electron-poor heterocycles impact the HOMO–LUMO gap and singlet and triplet energies. Crucially for applications as OLED hosts, the triplet energy (E_T) of these molecules was found to vary significantly between dilute polymer films and neat films, related to conformational demands of the molecules in the solid state. One of the bicarbazole species shows a variation in E_T of 0.24 eV in the different media—sufficiently large to “make-or-break” an OLED device—with similar discrepancies found between neat films and frozen solution measurements of other previously reported OLED hosts. From consolidated optical and optoelectronic investigations of different host/dopant combinations, we identify that only the lower E_T values measured in neat films give a reliable indicator of host/guest compatibility. This work also provides new molecular design rules for obtaining very high E_T materials and controlling their HOMO and LUMO energies.     

Polymer thin film properties as a function of temperature and pressure

We report on evanescent wave optical measurements of the glass transition temperature, T_g, of spin-cast PMMA films as a function of film thickness and molecular weight. It was found that for films of high molecular weight PMMA (M_n > 100,000 g mol⁻¹) a strong T_g depression occurs for films that are thinner than 100 nm in case they are deposited on hydrophobic substrates. This strong T_g depression of up to 25°C decreases if similarly thick films of PMMA of low molecular weights are investigated and vanishes completely for PMMA with M_n < 12,000 g mol⁻¹. For films made of these materials T_g is found to be identical to that of the bulk even for films as thin as 5 nm. The results might be interpreted in terms of free volume considerations. To check this assumption we also designed and built a pressure cell that can be used together with the evanscent wave optical techniques for similar measurement, but with the additional option to do the measurements at different pressures up to ca. 100 MPa to further vary the free volume of these polymer films in constrained geometry. Some first results obtained with this setup are also described.     

How does the type of counterion influence the polymerization rate and thermal properties of tailored choline-based linear- and star-shaped poly(ionic liquid)s PILs?

The synthesis of tailored [2-(methacryloyloxy)ethyl]-trimethylammonium chloride (ChMA/Cl⁻) and bis(trifluoromethanesulfonate) imide (ChMA/NTf₂⁻)-based ionic homopolymers by sustainable activators generated by electron transfer atom transfer radical polymerization (ATRP) method has been demonstrated. Linear and four-arm star-shaped macromolecules were obtained with the use of two synthetic strategies: (a) direct polymerization of ionic monomers with counterions differing in hydrophilicity (prepolymerization) and (2) modification by ion exchange from Cl⁻ to NTf₂⁻ (postpolymerization) using both classical ATRP initiator and pentaerythritol-based initiator. The effect of counterions on the polymerization kinetics and the physicochemical and thermodynamical properties of resulted poly(ionic liquid)s (PILs) has been investigated. Results showed that polymerizations of ChMA/NTf₂⁻ proceeded with higher rate in comparison to ChMA/Cl⁻ one independently on the predetermined topologies (linear and four-arm star-shaped). From thermodynamical point of view, the glass transition temperature T_g increased with molecular weight M_n for linear- and star-shaped PILs for both types of counterion. In addition, star-shaped polymers of comparable M_n to linear ones were characterized by slightly higher T_g values. The resulting polyelectrolytes, after modification via exchange of Cl⁻ anions to NTf₂⁻ ones were characterized by much higher T_g in comparison to those produced by direct polymerization of ionic monomer, indicating the crucial role of postpolymerization modification on thermodynamical properties of PILs. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2681–2691     

Thickness dependence of structural relaxation in spin‐cast polynorbornene films with high glass transition temperatures (>613 K)

The isothermal structural relaxation (densification) of a family of glassy polynorbornene films with high glass transition temperatures (T_g > 613 K) is assessed via spectroscopic ellipsometry. Three polymers were examined: poly(butylnorbornene) (BuNB), poly(hydroxyhexafluoroisopropyl norbornene) (HFANB), and their random copolymer, BuNB‐r‐HFANB. The effective aging rate, β(T), of thick (∼1.2 μm) spun cast films of BuNB‐r‐HFANB is approximately 10⁻³ over a wide temperature window (0.49 < T/T_g < 0.68). At higher temperatures, these polymers undergo reactions that more dramatically decrease the film thickness, which prohibits erasing the process history by annealing above T_g. The aging rate for thick BuNB‐r‐HFANB films is independent of the casting solvent, which infers that rapid aging is not associated with residual solvent. β (at 373 K) decreases for films thinner than ∼500 nm. However, the isothermal structural relaxation of thin films of BuNB‐r‐HFANB exhibits nonmonotonic temporal evolution in thickness for films thinner than 115 nm film. The thickness after 18 h of aging at 373 K can be greater than the initial thickness. The rapid aging of these polynorbornene films is attributed to the unusual rapid local dynamics of this class of polymers and demonstrates the potential for unexpected structural relaxations in membranes and thin films of high‐T_g polymers that could impact their performance. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 53–61     

Highly refractive polymer resin derived from sulfur‐containing aromatic acrylate

New sulfur‐containing polymers with high‐refractive indices and low birefringences have been developed as UV‐curable high‐refractive polymer resins. The polymers derived from 2,7‐bis[(2‐acryloylethyl)sulfanyl]thianthrene (2,7‐BAST) and 4,4′‐bis[(acryloyloxyethylthio)diphenylsulfide (4,4′‐BADS) were prepared by photopolymerization under UV irradiation. Transparent UV‐cured films were obtained in both cases. Both polymers showed good thermal stability, such as a 5% weight‐loss temperature at 355 °C under nitrogen and glass transition temperatures (T_g) in the range of 94–143 °C. They also showed high‐refractive indices of 1.6531 and 1.6645 at 632.8 nm and low birefringences of 0.0039 and 0.0069 in addition to high transparency in the visible region. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2604–2609, 2010     

Synthesis of novel phosphinic acid-containing polymers

Three arylene difluoride monomers containing phosphine oxide ( 1 ), phosphinic acid ( 2 ), or phosphinate ester ( 3 ) groups were prepared and polymerized with bisphenol A to give novel poly-(arylene ether)s ( 4 , 5 , and 6 ). The polymers obtained had moderate molecular weights (η_inh: 0.14–0.30 dL g⁻¹ in N-methylpyrrolidinone) and glass-transition temperatures (T_g: 102–200 °C), depending on the phosphine group in the main chain. Using bis(4-fluorophenyl)sulfone as a comonomer improved the polymerization to give copolymers with higher solution viscosities. The stoichiometric investigation revealed that 7 mol % excess of fluoride monomer gave the highest molecular weight copolymer 8 with η_inh of 0.78 dL g⁻¹, which had a T_g of 176 °C, a T of 432 °C, and formed a hard film by casting from solution. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1854–1859, 2001     

Copoly(arylene ether nitrile) and copoly(arylene ether sulfone) ionomers with pendant sulfobenzoyl groups for proton conducting fuel cell membranes

Three series of fully aromatic ionomers with naphthalene moieties and pendant sulfobenzoyl side chains were prepared via K₂CO₃ mediated nucleophilic aromatic substitution reactions. The first series consisted of poly(arylene ether)s prepared by polycondensations of 2,6‐difluoro‐2′‐sulfobenzophenone (DFSBP) and 2,6‐dihydroxynaphthalene or 2,7‐dihydroxynaphthalene (2,7‐DHN). In the second series, copoly(arylene ether nitrile)s with different ion‐exchange capacities (IECs) were prepared by polycondensations of DFSBP, 2,6‐difluorobenzonitrile (DFBN), and 2,7‐DHN. In the third series, bis(4‐fluorophenyl)sulfone was used instead of DFBN to prepare copoly(arylene ether sulfone)s. Thus, all the ionomers had sulfonic acid units placed in stable positions close to the electron withdrawing ketone link of the side chains. Mechanically strong proton‐exchange membranes with IECs between 1.1 and 2.3 meq g⁻¹ were cast from dimethylsulfoxide solutions. High thermal stability was indicted by high degradation temperatures between 266 and 287 °C (1 °C min⁻¹ under air) and high glass transition temperatures between 245 and 306 °C, depending on the IEC. The copolymer membranes reached proton conductivities of 0.3 S cm⁻¹ under fully humidified conditions. At IECs above ∼1.6 meq g⁻¹, the copolymer membranes reached higher proton conductivities than Nafion^® in the range between −20 and 120 °C. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

柔性OLED用高耐热聚酰亚胺薄膜的制备与性能

聚酰亚胺(PI)薄膜作为柔性有机发光显示(OLED)基板材料应用时, 需要满足玻璃化转变温度(T_g)大于450 ℃和热膨胀系数(CTE)在0~5×10^-6 K^-1之间. 为了提高PI薄膜的热性能, 本文合成了2,7-占吨酮二胺 (2,7-DAX), 并将其与均苯四甲酸二酐(PMDA)和2-(4-氨基苯基)-5-氨基苯并噁唑(BOA)共聚制备了一系列新型PI薄膜. 研究了PI薄膜的聚集态结构、 耐热性能、 尺寸稳定性和力学性能. 结果表明, 占吨酮结构和苯并噁唑结构提高了PI分子链的刚性与线性, 使分子链在平面内紧密堆积与取向, 制备的PI薄膜综合性能优异, 玻璃化转变温度高于408 ℃, CTE在-5.0×10^-6~8.1×10^-6 K^-1之间, 拉伸强度大于140 MPa, 拉伸模量大于4.2 GPa, 断裂伸长率为7.1%~20%, 5%热失重分解温度(T_5%)在601~624 ℃之间. 其中, PI-50和PI-60薄膜具有超高玻璃化转变温度和超低热膨胀系数, T_g高于450 ℃, CTE分别为2.1×10^-6 K^-1和1.6×10^-6 K^-1. 制备的系列PI薄膜作为柔性OLED基板材料有潜在应用前景.     

Synthesis and properties of poly(ether imide)s derived from 2,7-bis(3,4-dicarboxyphenoxy)naphthalene dianhydride and various aromatic diamines

A naphthalene unit-containing bis(ether anhydride), 2,7-bis(3,4-dicarboxyphenoxy)naphthalene dianhydride, was prepared in three steps starting from the nucleophilic nitrodisplacement reaction of 2,7-dihydroxynaphthalene and 4-nitrophthalonitrile in N,N-dimethylformamide (DMF) solution in the presence of potassium carbonate followed by alkaline hydrolysis of the intermediate bis(ether dinitrile) and subsequent dehydration of the resulting bis(ether diacid). High-molar-mass aromatic poly(ether imide)s were synthesized using a conventional two-stage polymerization process from the bis(ether anhydride) and ten aromatic diamines. The intermediate poly(ether amic acid)s had inherent viscosities of 0.95–2.67 dL/g. The films of poly(ether imide)s derived from two rigid diamines, that is, p-phenylenediamine and benzidine, crystallized and embrittled during the thermal imidization process. The other poly(ether imide)s belonged to amorphous materials and could be fabricated into transparent, flexible, and tough films. These poly(ether imide) films had yield strengths of 91–115 MPa, tensile strengths of 89–136 MPa, elongation to break of 11–45%, and initial moduli of 1.7–2.2 GPa. The T_gs of poly(ether imide)s were recorded in the range of 222–256°C depending on the nature of the diamine moiety. All polymers were thermally stable up to 500°C, with 10% weight loss being recorded above 540°C in air and nitrogen atmospheres. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2281–2287, 1997     

Chlorophyll-Based Organic Heterojunction on Ti3C2Tx MXene Nanosheets for Efficient Hydrogen Production

The Z-scheme process is a photoinduced electron-transfer pathway in natural oxygenic photosynthesis involving electron transport from photosystem II (PSII) to photosystem I (PSI). Inspired by the interesting Z-scheme process, herein a photocatalytic hydrogen evolution reaction (HER) employing chlorophyll (Chl) derivatives, Chl-1 and Chl-2, on the surface of Ti₃C₂T_x MXene with two-dimensional accordion-like morphology, forming Chl-1@Chl-2@Ti₃C₂T_x composite, is demonstrated. Due to the frontier molecular orbital energy alignments of Chl-1 and Chl-2, sublayer Chl-1 is a simulation of PSI, whereas upper layer Chl-2 is equivalent to PSII, and the resultant electron transport can take place from Chl-2 to Chl-1. Under the illumination of visible light (>420 nm), the HER performance of Chl-1@Chl-2@Ti₃C₂T_x photocatalyst was found to be as high as 143 μmol h⁻¹ g_cat⁻¹, which was substantially higher than that of photocatalysts of either Chl-1@Ti₃C₂T_x (20 μmol h⁻¹ g⁻¹) or Chl-2@Ti₃C₂T_x (15 μmol h⁻¹ g⁻¹).     

Electrochromic material containing unsymmetrical substituted N,N,N′,N′‐tetraaryl‐1,4‐phenylenediamine: Synthesis and their optical,electrochemical, and electrochromic properties

A novel dibromo compound containing unsymmetrical substituted bi‐triarylamine was synthesized. A conjugated polymer was prepared via the Suzuki coupling from the newly prepared dibromo compound and 9,9‐dioctylfluorene‐2,7‐bis(trimethyleneboronate). The glass transition temperature (T_g) of the conjugated polymer was 140 °C, 10% weight‐loss temperatures (T_d10) in nitrogen was 458 °C, and char yield at 800 °C in nitrogen higher than 64%. Cyclic voltammogram of the polymer film cast onto an indium‐tin oxide (ITO)‐coated glass substrate exhibited two reversible oxidation redox couples at 0.70 and 1.10 V versus Ag/Ag⁺ in acetonitrile solution. The polymer films revealed excellent stability of electrochromic characteristics, with a color change from yellow green of the neutral form to the dark green and blue of oxidized forms at applied potentials ranging from 0 to 1.3 V. The color switching time and bleaching time were 4.25 and 7.22 s for 860 nm and 5.51 s and 6.48 s for 560 nm. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1469–1476, 2010     

Poly(ester imide)s possessing low coefficients of thermal expansion (CTE) and low water absorption (III). Use of bis(4-aminophenyl)terephthalate and effect of substituents

A variety of poly(ester imide)s (PEsIs) were prepared using bis(4-aminophenyl)terephthalate (BPTP) and substituted BPTP (BPTP series) for applications to novel base film materials in flexible printed circuit boards (FPC). BPTP series were all highly reactive with various tetracarboxylic dianhydrides and led to considerably high molecular weights of PEsI precursors. The thermally imidized BPTP-based PEsI films achieved lower extents of water absorption (W_A) than the corresponding 4-aminophenyl-4′-aminobenzoate (APAB)-based PEsI systems while keeping other target properties, in particular, the linear coefficient of thermal expansion (CTE) much lower than that of copper foil as a conductive layer in FPC. The lower W_A is attributed to the decreased imide contents in the structure by using BPTP. The considerably low CTE can be explained in terms of intimate stacking between the p-aromatic ester fragments with an extended conformation. The BPTP-based PEsI system also exhibited a considerably low dissipation factor (tan δ = 1.91 × 10⁻³) at a high-frequency electric field of 18.3 GHz, comparable to a liquid-crystalline polyester. An effect of substituents on the film properties was also investigated in this work. Incorporation of methyl substituents on BPTP was very effective for property improvement, whereas methoxy substituents on BPTP, as well as methyl substituents onto hydroquinone bis(trimellitate anhydride) (TAHQ), showed a trend to significantly increase the CTE. Copolymerization with an adequate amount of a typically flexible monomer, 4,4′-oxydianiline (4,4′-ODA), allowed the CTE matching with copper foil and the film toughness improvement at the same time. The PEsI copolymer prepared from TAHQ (10 mmol) with methyl-substituted BPTP (7 mmol) and 4,4′-ODA (3 mmol) achieved excellent combined properties, namely, a very high T_g at 410 °C, a slightly lower CTE (10.0 ppm/K) than that of copper foil, suppressed water absorption (0.35%), an extremely low linear coefficient of humidity expansion (CHE = 3.4 ppm/RH%), and good film toughness (the elongation at break, ε_b = 50.7%). Thus, BPTP- and methyl-substituted BPTP-based PEsI systems can be promising candidates as a next generation of FPC base film materials.     

Heat-resistant polyimides with low CTE and water absorption through hydrogen bonding interactions

A novel diamine, 1H,1′H-(2,2′-bibenzimidazole)-5,5′-diamine (DPABZ), containing bisbenzimidazole unit was successfully synthesized, and used to prepare a series of copolyimides BPDA:(ODAm/DPABZn) by polycondensation with 4,4-diaminodiphenyl ether (ODA) and 4,4-biphthalic anhydride (BPDA). For comparison, a series of copolyimides BPDA:(ODAm/PABZn) based on another benzimidazole diamine 5-amino-2-(4-aminobenzene)-benzimidazole (PABZ) was also prepared. As a result, with the increase of PABZ or DPABZ content, the heat resistance (T_g and T_d) and mechanical properties (σ and E) of the resulting polyimide (PI) films increased, while the coefficient of thermal expansion (CTE) decreased. Overall, the DPABZ-based PIs showed higher T_g values and much lower CTE values than PABZ. As the content of PABZ increased, the water absorption of PABZ-based PIs increased obviously, but no significant change in DPABZ-based PIs. The intramolecular hydrogen bonding in DPABZ-based PIs caused by the diamine DPABZ was believed to be the reason for the aforementioned differences. The BPDA: DPABZ film with low-water adsorption of 2.1%, high-T_g value of 436°C and low-CTE value of 5.4 ppm/°C could be a promising new generation of flexible display substrates.     

Study of carbonaceous clusters in irradiated polycarbonate with UV–vis spectroscopy

The formation of carbonaceous clusters in ion‐irradiated polymer films was investigated extensively. Information about these clusters may be obtained with ultraviolet–visible (UV–vis) spectroscopy. The optical band gap (E_g), calculated from the absorption edge of the UV spectra of these polymers, can be correlated to the number of carbon atoms (N) in a cluster with the modified Tauc equation. The structure of the cluster is also related to E_g; for example, a six‐membered‐benzene‐ring‐type structure has an E_g of ≈5.3 eV, whereas a buckminsterfullerene‐type structure has an E_g of ≈4.9 eV. These clusters are responsible for the electrical conductivity in these films. In this work, polycarbonate films (20 μm thick) were irradiated with 45‐MeV Li ions at fluences of 1 × 10¹² to 1 × 10¹³ cm⁻² and were characterized with UV–vis spectroscopy and impedance measurements. The E_g values, calculated from the absorption edge in the 280–315‐nm region with the Tauc relation, varied from 4.39 to 4.35 eV for the pristine and various irradiated samples, respectively. The cluster size showed a range of 60–62 carbon atoms per cluster. The sheet conductivity (σ_dc) and loss (tan δ) values of 10⁻¹⁶ Ω⁻¹cm⁻¹ and 10⁻³ for the pristine sample changed to 10⁻¹⁵ Ω⁻¹cm⁻¹ and 10⁻², respectively, for the irradiated samples. This increase in the values of σ_dc and tan δ may be correlated to the increase in the size of the carbonaceous clusters. This study provides insight into the mechanism of electrical conductivity in irradiated polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1589–1594, 2000     

Oxyalkylene polymers with alkylsulfonylmethyl side chains: Gas barrier properties

Gas barrier properties of alkylsulfonylmethyl-substituted poly(oxyalkylene)s are discussed. Oxygen permeability coefficients of three methylsulfonylmethyl-substituted poly(oxyalkylene)s, poly[oxy(methylsulfonylmethyl)ethylene] (MSE), poly[oxy(methylsulfonylmethyl)ethylene-co-oxyethylene] (MSEE), and poly[oxy-2,2-bis (methylsulfonylmethyl)trimethylene oxide] (MST) were measured. MSEE, which has the most flexible backbone of the three polymers, had an oxygen permeability coefficient at 30°C of 0.0036 × 10⁻¹³ cm³(STP)·cm/cm²·s·Pa higher than that of MSE, 0.0014 × 10⁻¹³ cm³(STP)·cm/cm²·s·Pa, because the former polymer's T_g was near room temperature. MST with two polar groups per repeat unit and the highest T_g showed the highest oxygen permeability, 0.013 × 10⁻¹³ cm³(STP) · cm/cm²·s·Pa, among the three polymers, probably because steric hindrance between the side chains made the chain packing inefficient. As the side chain length of poly[oxy(alkylsulfonylmethyl)ethylene] increased, T_g and density decreased and the oxygen permeability coefficients increased. The oxygen permeability coefficient of MSE at high humidity (84% relative humidity) was seven times higher than when it was dry because absorbed water lowered its T_g. At 100% relative humidity MSE equilibrated to a T_g of 15°C after 2 weeks. A 50/50 blend of MSE/MST had oxygen barrier properties better than the individual polymers (O₂ permeability coefficient is 0.0007 × 10⁻¹³ cm³(STP)·cm/cm² ·s·Pa), lower than most commercial high barrier polymers. At 100% relative humidity, it equilibrated to a T_g of 42°C, well above room temperature. These are polymer systems with high gas barrier properties under both dry and wet conditions. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 75–83, 1998     

Synthesis of cyclic polysulfides: Controlled ring‐expansion polymerization of cyclic tetrathioester with thiirane

We synthesized cyclic tetrathioesters containing thioester moieties at the o‐position (o‐CTE) and m‐position (m‐CTE) of an aromatic skeleton. The reaction of phenoxy propylenesulfide (PPS) with o‐CTE and m‐CTE was examined using tetrabutylammonium chloride as a catalyst in 1‐methyl‐2‐pyrrolidinone, yielding the corresponding cyclic polysulfides poly[o‐CTE(PPS)_n] with M_n's = 37,000–54,000 at 34–61% yields and poly[m‐CTE(PPS)_n] with M_n's = 46,600–107,200 at 63–>99% yields. Although the molecular weights of poly[o‐CTE(PPS)_n] could not be controlled, those of poly[m‐CTE(PPS)_n] could be controlled by the feed ratios of PPS and reaction temperature. Furthermore, the glass transition temperature (T_g) and thermal decomposition temperature (T_dⁱ) of poly[m‐CTE(PPS)_n] increased with decreasing molecular weights. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 857–866     

Organic Polymer Dots Photocatalyze CO2 Reduction in Aqueous Solution

Developing low-cost and efficient photocatalysts to convert CO₂ into valuable fuels is desirable to realize a carbon-neutral society. In this work, we report that polymer dots (Pdots) of poly[(9,9′-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-thiadiazole)] (PFBT), without adding any extra co-catalyst, can photocatalyze reduction of CO₂ into CO in aqueous solution, rendering a CO production rate of 57 μmol g⁻¹ h⁻¹ with a detectable selectivity of up to 100 %. After 5 cycles of CO₂ re-purging experiments, no distinct decline in CO amount and reaction rate was observed, indicating the promising photocatalytic stability of PFBT Pdots in the photocatalytic CO₂ reduction reaction. A mechanistic study reveals that photoexcited PFBT Pdots are reduced by sacrificial donor first, then the reduced PFBT Pdots can bind CO₂ and reduce it into CO via their intrinsic active sites. This work highlights the application of organic Pdots for CO₂ reduction in aqueous solution, which therefore provides a strategy to develop highly efficient and environmentally friendly nanoparticulate photocatalysts for CO₂ reduction.