Preparation of a bipolar membrane by photografting polymerization

A single-sheet bipolar membrane was synthesized via photografting polymerization of an acrylic acid cation exchange layer onto the surface of a commercial homogeneous anion exchange membrane with benzophenone (BP) as the main initiator, diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide (TPO) and 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173) as coinitiators and divinylbenzene (DVB) or neopentylene glycol diacrylate (NPGDA) as crosslinking agent. It was found that when benzophenone was used as single initiator and the crosslink agent is absent, the grafting degree (D _g) increases with the prolongation of irradiation time. The grafting degree reaches a maximum at 60 seconds reaction time when the crosslinking agent is added, and the grafting degree is higher when using NPGDA instead of DVB as crosslinking agent. The grafting degree increases as the composite initiator system is used. When polymerization was initiated by BP and TPO, and the dosage of NPGDA was 2.5% mol concentration of monomer, the grafting degree reaches 30.1%. __________ Translated from Journal of Beijing Technology and Business University, 2007, 25(1): 15–18 [译自: 北京工商大学学报]     

Studies on photocrosslinking and flame‐retardant properties of chalcone‐based polyacrylamides

A photocrosslinkable polycyclic chalcone‐based acrylamide has been synthesized by Claisen–Schmidt condensation reaction and then polymerized via free radical polymerization technique using azobisisobutyronitrile (AIBN) as an initiator. The resulting polymers have been characterized by FT‐IR, ¹H‐NMR and ¹³C‐NMR analytic techniques. The molecular weights of the polymers were determined by gel permeation chromatography. The thermal properties of synthesized polymers were characterized by TGA analysis, and the obtained results show good thermal and thermo‐oxidative stability which is required for a negative photo resist. The high flame‐retardant properties are calculated from limiting oxygen index (LOI) values and are found to be 36.9 and 32.0 for naphthyl and anthryl chalcone‐based polymers, respectively. The experimentally determined LOI values of polymers (PMNPA and PAPA) are 34.3 and 30.2, respectively, and the values are closer to theoretically found LOI values. However, the cone calorimetry of flame‐retardant PMNPA only showed a slight decrease in peak of heat release rate (PHRR) and total heat release (THR) compared to PAPA but the ignition time (TTI) of PMNPA is slightly higher than PAPA. The photocrosslinking properties of the polymers were investigated by UV spectroscopy technique and were found that with the increase in number of aromatic rings, the rate of crosslinking decreases. Thus polyacrylamides are useful in photolithography technology as well as flame‐retardant property in electrical appliances. Copyright © 2015 John Wiley & Sons, Ltd.     

Dynamic behavior of water in hydro-swollen crosslinked polymer gel as studied by PGSE 1H NMR and pulse 1H NMR

¹H NMR measurements on spin-lattice relaxation time (T₁) and spin-spin relaxation time (T₂) were carried out on hydro-swollen crosslinked poly(methacrylic acid) (PMAA) gel to elucidate molecular motion of water molecules contained in the gel as a function of the degree of crosslinking. From these experimental results, it was found that ¹H T₁ and T₂ decrease with an increase of the degree of crosslinking. This shows that molecular motion of water molecules is strongly restrained owing to crosslinking. Further, pulsed-field-gradient spin-echo ¹H NMR measurements were carried out to determine the self-diffusion coefficient of water molecules (D_H2O contained in the PMAA gel at 300 K as a function of the degree of crosslinking. From these experimental results, it was found that the D_H2O value decreases with an increase of the degree of crosslinking. This shows that translational molecular motion of water molecules is restrained by crosslinking.     

Synthesis and characterization of 3-aryl-2-(polystyryl)cyclopropenones via cyclopropenium ion substitution on polystyrene

Electrophilic substitution of cyclopropenium ions on aromatic polymers offers a unique opportunity to introduce polar functionality in a controlled manner to conventional, nonpolar polymers. Phenylcyclopropenone substituted polystyrene with predictable chemical composition and narrow molecular weight distribution were prepared. Size exclusion chromatography (SEC) analysis demonstrated the absence of branching or crosslinking in these functionalized polystyrenes during electrophilic substitution of the parent homopolymer. ¹³C-NMR confirmed that the degree of phenylcyclopropenone substitution was both highly efficient and predictable over a broad compositional range. The glass transition temperature (T_g) of the polymers was found to vary linearly with mole % phenylcyclopropenone substitution of the polystyrene. Thermal gravimetric analysis (TGA) indicated that thermal decarbonylation of the appended cyclopropenones occurred at approximately 180°C. Weight loss vs. temperature profiles correlated reasonably well with levels of substitution based on ¹³C-NMR analysis, confirming that decarbonylation of the calculated cyclopropenone substituents was the predominant thermal decomposition pathway. © 1995 John Wiley & Sons, Inc.     

Thermal properties of wholly aromatic polyamides

Various wholly aromatic polyamides based on m-and p-phenylene diamines and isophthaloyl and terephthaloyl chloride have been synthesized and their thermal properties and oxygen index values have been studied. The effect of different substituents on the aromatic ring of the diamine have been explored by comparing their differential thermal analysis (DTA) and thermogravimetric analysis (TGA) behavior, their relative char yields at 700°C, and their oxygen indices. The ? Cl, ? NO₂, and ? OH substituted polyamides have been found to produce the highest char yields. The high char yields are probably associated with crosslinking occurring at high temperatures. Attempts at correlating char yield with oxygen index indicated enhancement for the chlorosubstituted aramids.     

Polymerization of vinyl chloride at reduced monomer accessibility. II. Polymerization at subsaturation pressure with emulsion PVC as seed

Vinyl chloride was polymerized at 59–92% of saturation pressure in a water-suspended system at 45–65°C with an emulsion poly(vinyl chloride) (PVC) latex as a seed. A water-soluble initiator was used in various concentrations. The monomer was continuously charged as vapor from a storage vessel kept at lower temperature. Characterization included determination of molecular-weight distribution and degree of long-chain branching by gel permeation chromatography (GPC) and viscometry, thermal dehydrochlorination, and microscopy. The polymerization rate decreases with decreasing pressure but is reasonable even at the lowest pressure. The molecular weight decreases with decreasing pressure and increasing initiator concentration and also with increasing polymerization temperature, if the initiator concentrations are chosen to give a constant initiator radical concentration. The degree of long-chain branching increases with increasing initiator concentration and decreasing monomer pressure but is unaffected by the polymerization temperature, if the initiator radical concentration is kept constant. The thermal stability decreases with decreasing M _n, while the degree of long-chain branching has only a minor influence. The most important factor in the system influencing the molecular parameter is the monomer accessibility.     

Reactive Polymers and Oligomers from Cyclic Ethers and Cyclic Sulfides

(2-Bromoethyl)oxirane is converted in 39% yield to poly-[(2-bromoethyl)oxirane] of inherent viscosity 1.99 dL/g. The AlEt₃/H₂O/AcAc system is a very effective initiator for the polymerization of (2-bromoethyl)oxirane. Poly[(2-bromoethyl)-oxirane] is a white elastomer, soluble in CHCl₃ and insoluble in CH₃OH. Polyether-urethane hydrogels are prepared by the room temperature crosslinking of poly[(3-hydroxypropyl)oxirane] with aliphatic or aromatic diisocyanates. These networks absorb 100–200% of their weights in water, and can be prepared in transparent form with potential application as biomaterials or contact lenses.     

Redox initiator systems for emulsion polymerization of acrylates

The performance of different redox initiator couples to initiate the emulsion polymerization of butyl acrylate at low temperature (40–50 °C) was investigated in both batch and seeded semibatch polymerizations. Polymerizations were carried out mimicking industrial conditions, that is, technical grade monomer and no N₂ purging was used during the polymerizations. The redox systems used contained as oxidants persulfates or hydroperoxides and as reducing agents ascorbic acid, formaldehyde sulfoxilate (SFS), tetramethyl ethylene diamine (TMEDA), Bruggolit 6 and 7 (FF6 and FF7), and sodium metabisulfites. Batch experiments showed that for systems using persulfates, the ammonium persulfate (APS)/TMEDA system provided the lower induction period and higher conversion, whereas for the systems with hydroperoxide oxidants, tert‐butyl hydroperoxide (TBHP)/FF7, TBHP/SFS, and H₂O₂/FF7 were the best alternatives. When these selected systems were used in seeded semibatch experiments of BA with allyl methacrylate, it was found that to obtain similar kinetics and microstructure (gel content and crosslinking density) than in case of using a thermal initiator at 80 °C, the polymerization could be run at 40 °C if the reactor was purged with N₂. Alternatively, in absence of N₂ polymerization, temperature should be increased to 50 °C and initiator concentration increased. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2917–2927, 2009     

Photovoltaic properties of the polymer solar cells comprising crosslinked maleimide polymers and fullerene‐derivative PCBM

A series of crosslinkable maleimide conjugated polymers with different vinyl group contents as side‐chain crosslinking sites have been synthesized by the Suzuki coupling reaction. Polymer solar cells (PSCs) were fabricated based on an interpenetrating network of the crosslinkable maleimide polymers as the electron donor, and a fullerene derivative, (6,6)‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM), as the electron acceptor. The crosslinkable maleimide polymers underwent crosslinking reaction at the side‐chain vinyl groups upon the thermal treatment with or without the addition of initiator, azobisisobutyronitrile (AIBN). Better photovoltaic (PV) performances were obtained for the PSCs based on the polymer crosslinking without using initiator, whereas poorer PV performances were observed for the PSCs based on the polymer crosslinking with the AIBN initiator. In addition, higher operational stability was observed for the crosslinked polymer based solar cell as compared to the solar cell based on the un‐crosslinked polymer. The photo‐physical and PV properties of the cross‐linked maleimide polymers/PCBM based PSCs are discussed in detail as the morphology and crosslinking density of the polymers are taken into account. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermodynamics of adsorption of aromatic compounds from non-aqueous solutions by MIL-53(Al) metal-organic framework

The thermodynamics of adsorption of mono-, di-, and tricyclic aromatic compounds by MIL-53(Al) metal-organic framework from their solutions in MeCN, MeOH and n-C₆H₁₄–PrⁱOH was studied for the first time. It was found that the adsorption of the test substances from solutions in MeCN and MeOH is characterized by positive values of enthalpy and entropy changes, and the adsorption from n-C₆H₁₄–PrⁱOH medium is characterized by negative enthalpy and entropy changes. Upon adsorption by MIL-53(Al) framework from polar media, aromatic compounds were proposed to transfer from the liquid phase with a higher degree of association into the solvent medium with a lower degree of association, molecules of which are disordered due to the strong interaction with the hydrophobic walls of the framework pores. It was concluded that the driving force of adsorption by MIL-53(Al) from MeCN and MeOH is increase in entropy of the system, while the factor of adsorption from n-C₆H₁₄–PrⁱOH medium is decrease in enthalpy of the adsorption system. The compensation effect in liquid-phase adsorption of aromatic compounds by MIL-53(Al) framework was discovered. The effect of the liquid phase nature on selectivity of adsorption from solutions onto investigated metal-organic framework was demonstrated.     

Chain transfer to solvent in BN 2-vinylnaphthalene radical polymerization

The synthesis of vinyl alcohol copolymers is limited due to the poor radical reactivity of vinyl acetate (VAc), the traditional precursor to polyvinyl alcohol (PVA). Main group monomers such as BN 2-vinylnaphthalene (BN2VN) have attracted attention as alternatives to VAc to form side chain hydroxyls via oxidation, but outstanding questions of molecular weight control remain. Herein we report systematic investigation of solvent, temperature, and initiator concentration as factors influencing BN2VN degree of polymerization. We find increased chain transfer to toluene, hypothesized to arise from differences in radical stabilization and reactivity by aromatic and BN aromatic rings. As a result of these combined efforts, high molecular weight (M_w ~ 10⁵ g mol⁻¹) BN2VN homopolymers and BN2VN-styrene copolymers were obtained.     

Kinetic studies on the imine base/isocyanate‐induced radical polymerization of vinyl monomers

Specific imine bases (IB) in conjunction with various isocyanates (IC) mediate the radical polymerization of radically polymerizable monomers such as methyl methacrylate (MMA). Advantageously, the 2‐(methylmercapto)‐2‐thiazoline MMT/IC combination as initiator works even at room temperature for polymerization of MMA. The coefficients a, b, and c of the basic rate law of monomer consumption d[M]/dt = k_p·[IC]^a·[IB]^b·[M]^c were determined. The order a has been determined to 0.5 showing the root law of radical polymerization with respect to the IC component as initiator. Moreover, b and c amount 1. The initiator combination MMT/ IC was applied to determine the influence of the molecular structure of the IC on the rate of monomer conversion. For aromatic isocyantes, the gross rate constant of monomer consumption correlates with the Hammet constant of aromatic substituents. The activation energies of the gross polymerization rate constant of several initiator mixtures were determined whereby the value of E_A,Br was found to be between typical values of radical polymerization initiated by photochemical reactions (～20 kJ/mol) and commonly used thermal decomposing initiators (～80 kJ/mol). Presumptions on the initiating and terminating step of the IB/IC mediated polymerization were done by means of electrospray ionization mass spectrometry, NMR spectroscopy, and the elemental composition of the head and end group of the resulting polymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Recent Development of Hypercrosslinked Microporous Organic Polymers

Hypercrosslinked polymers (HCPs) are currently receiving great interest due to their easy preparation, high chemical and thermal stability, and low cost. Combined with the lightweight properties and high surface areas HCPs can be considered as promising materials for gas storage and separation, catalysis, and heavy metal ions removal in wastewater treatment. This Feature Article summarizes strategies for the preparation of HCPs, comprising the post‐crosslinking of “Davankov‐type” resins, direct polycondensation of aromatic chloromethyl (or hydroxymethyl) monomers, and knitting aromatic compound polymers (KAPs). The HCPs applications, such as H₂ storage, CO₂ capture, and heterogeneous catalysis, are also discussed throughout in the article. Finally, the outlook of this research area is given.     

Kinetics and molecular orbital calculations of desulfonation of strong acid cation-exchange resin

This paper deals with the desulfonation properties of some strong acid cation-exchange resins. The sulfate concentration in solution is continuously increased when a strong acid cation-exchange resin is mixed with water. The leaching of sulfate results from the desulfonation of the fixed group, and the amount of leached sulfate depends on the counter ion charge, the crosslinking degree and the exchanger matrix. The effects of the counter ion charge on the desulfonation rate suggested that the counter ion induces the nucleophilic attack of a water molecule on the sulfo group. This interpretation was supported by semiempirical molecular orbital calculations for the C₆H₅SO₃⁻M^m+ (M^m+ = Na⁺, Mg²⁺ and Al³⁺) systems, and the transition state of the Na⁺ system was successfully predicted by DFT calculations. The crosslinking degree influenced the desulfonation rate, which can be related to the decreasing hydration number of each counter ion in the resin phase with the increasing crosslinking degree. Furthermore, different exchanger matrices produced the differences in the rates, which may be derived from the electron-density donation from the exchanger matrix to the sulfo group. The desulfonation is governed by the electron-density of the sulfur atom and the water activity in the solid phase.     

Chain transfer in anionic polymerization. Determination of chain-transfer constants by using carbon-14-labeled chain transfer agents

A method is described in which ¹⁴C-labeled chain-transfer agents are employed to measure chain-transfer constants in anionic polymerization as low as 10^?6. Each chain-transfer step incorporates one molecule of the chain-transfer agent into the polymer so that measurement of the activity and conversion allows evaluation of the chain-transfer constant. This method is independent of the initiator concentration and efficiency, making the technique especially useful when problems with the initiator are encountered. The experimental procedure is described in detail for the case of chain transfer to toluene in the n-butyllithium-initiated polymerization of styrene, where C_RH was found to be 5 × 10^?6. A mathematical treatment is given showing the relationship between the degree of polymerization (DP _n) and chain transfer.     

Permanganate-Pyruvic Acid Initiated Polymerization of Methacrylamide

A combined system of potassium permanganate and pyruvic acid was found to initiate radical polymerization of vinyl monomers, especially acrylamides. From kinetic investigations of the polymerization of methacrylamide, it was found that this initiator induced a radical polymerization which proceeded with an overall activation energy of 15.7 kcal/mol. The rate is given by

R_p=K[methacrylamide] ¹ [pyruvic acid]° [KMnO₄]¹ in aqueous and water-DMF mediums. In the presence of DMF the initial rate was found to decrease but the kinetic equation remained the same. The investigations were done at 35 ± 0.2°C in nitrogen.

Besides the clinical importance of pyruvic acid found in blood, urine, muscles, etc., it is a good initiator in conjunction with KMnO₄ for vinyl polymerization. It is therefore interesting to study the polymerization of methacrylamide using the KMnO₄-pyruvic acid redox couple in aqueous systems in order to find whether this system follows the same kinetic features of vinyl polymerization by a radical mechanism.     

Grafting of glycidyl methacrylate onto polypropylene using supercritical carbon dioxide

Free-radical grafting of glycidyl methacrylate (GMA) onto polypropylene (PP) films has been studied using supercritical carbon dioxide (SC-CO₂) as a solvent and a swelling agent. As the reaction temperature was below the melting point, PP was modified in the solid phase. The PP film was first soaked with the monomer GMA and benzoyl peroxide (BPO) as an initiator using SC-CO₂ at different experimental conditions of pressure, temperature, and thermal treatment time. After releasing CO₂, film GMA molecules were grafted onto PP in different times. Using this method, the degree of grafting and the morphology could be controlled through the combination of pressure, temperature, and soaking time. FTIR spectra confirmed that GMA had been grafted onto PP and that polypropylene-graft-glycidyl methacrylate (PP-g-GMA) presented a high surface reactivity for conductive polyaniline anchoring. DSC measurements and TG analyses showed that the thermal profiles of the graft copolymer and virgin PP are quite similar and that the graft PP does not exhibit changes in terms of thermal degradation profile and melting temperature, respectively. X-ray data showed that a high degree of grafting leads to a lower degree of crystallinity of polypropylene.     

Polymerization initiated by ylide: Polymerization of ethyl methacrylate with the use of 4-picolinium p-chloro phenacylide as initiator

The ylide 4-picolinium, p-chloro phenacylide-initiated thermal polymerization of ethyl methacrylate (EMA) was studied. 4-Picolinium p-chloro phenacylide induces the thermal polymerization of ethyl methacrylate at 65°C. The rate of polymerization (R_p) rose as the initiator concentration increased from 2 × 10^?3 to 4 × 10^?3 M and the initiating exponent was computed as 1.9. The R_p decreased as the concentration of ylide increased from 6 × 10^?2 to 1M. The greater initiator concentration also affected the molecular weight inversely. The polymerization was carried out at different temperatures and the overall activation energy was computed as 4.08 Kcal/mol. Polymerization was inhibited in the presence of hydroquinone as a radical scavenger. Kinetic studies and other data show that the overall polymerization takes place in a radical mechanism. The various kinetic parameters, such as the rate and average degree of polymerization, molecular weight, and energy of activation of the present system, were evaluated.     

Solution and thermal properties of poly(1,3-dioxocane)

Poly( 1,3-dioxocane) was synthesized by cationic ring-opening polymerization with triphenyl-methane hexafluoroantimoniate as the initiator and was studied with regard to its solubility, unperturbed chain dimensions, and thermal transitions. The intrinsic viscosity and Flory-Huggins interaction parameter were used to determine the solubility parameter, δ_p = 9.6 cal^1/2cm^?3/2, a value that agrees with that calculated empirically. Fractions were obtained from the solvent/non-solvent system benzene/methanol at 25°C. The number-average molecular weight M_n and intrinsic viscosity [η] were measured in toluene at 25°C. The relation [η] = 1.45₉. 10^?4 M_n^0.79 was found. A value of 5.3 was obtained for the characteristic ratio 〈r²〉₀/nl². Results are correlated with the main thermal transitions of this polyformal.     

Chemical and thermal stability of N‐heterocyclic ionic liquids in catalytic C–H activation reactions

¹H‐NMR spectrum analyses are applied to study the chemical and thermal stability of selected N‐heterocyclic ionic liquids within the reaction system that can highly efficiently activate a C–H bond of methane and convert it into the C–O bond in methanol. Our results indicate that under such reaction conditions involving using a powerful Pt‐based catalyst and strong acidic solvent, the aromatic ring of an imidazolium cation becomes unstable generating an ammonium ion (NH₄⁺). Our results also suggest that the instability of the imidazolium ring is more chemically (participation in reactions) than thermally based. Modifications of the aromatic ring structure such as pyrazolium and triazolium cations can increase the chemical/thermal stability of ionic liquids under these reaction conditions. Copyright © 2014 John Wiley & Sons, Ltd.