Sorption of benzene by poly(ethylene oxide)

The activity of benzene in poly(ethylene oxide), PEO, has been determined over the concentration range 0.3 to ～35 wt% benzene using the piezoelectric sorption method. The temperature range was 64° to 97°C and the molecular weights of polymer samples were 1.0 × 10⁵, 6.0 × 10⁵, and 5.0 × 10₆ g/g mol. The Flory-Huggins interaction parameters, χ, determined in this work agree within experimental error with χ values determined by gas chromatography and by vapour pressure measurement. The values of χ extrapolated to zero solvent concentration, χ^∞, have a minimum and negative value in the vicinity of 85°C for the sample of molecular weight 1.0 × 10⁵, 84°C for the sample of molecular weight 6.0 × 10⁵, and 77°C for the sample of molecular weight 5.0 × 10⁶. In the vicinity of 65°C, χ^∞ is negative for each molecular weight of polymer and increases to positive values with an increase in temperature. For all samples studied, the χ^∞ parameters reach constant values (0.22 to 0.30) at temperatures higher than 90°C.     

Grafting of styrene onto poly(butyl acrylate) in emulsion

The effect of time, temperature, the concentration of initiator and emulsifier, and the ratio of starting polymer to monomer on the degree of conversion (MC) of styrene and the grafting efficiency (GE) of polystyrene has been investigated. The reaction was initiated with potassium persulphate. It has been found that the degree of conversion of styrene and the grafting efficiency change in opposite directions when plotted as functions of the reaction parameters studied. The graft copolymerization is assisted by short reaction times and weight ratios of poly(butyl acrylate) to styrene greater than unity. The results obtained suggest that higher grafting efficiencies are obtained when the concentration of emulsifier is below its c.m.c. (critical micellar concentration) value. When using two different anionic emulsifiers it has been observed that the effect of initiator concentration on the degree of conversion of styrene and the grafting efficiency is complicated. Both the quantities studied (MC and GE) exhibit extrema in the range of initiator concentration studied (3.7?33.3 × 10^?5 mol dm^?3 of H₂O). No meaningful effect of temperature in the range 60°–90°C or that of dodecyl mercaptan (molecular weight regulator) used in an amount 0–0.4% in relation to poly(butyl acrylate) and styrene has been observed on the MC and GE values.     

Unperturbed dimension of poly(4-acetoxystyrene) measured in good and theta solvents

In order to obtain the additional data concerning the unperturbed dimension of poly-4-substituted styrene, light scattering measurements are performed on the twenty-two fractions with molecular weight of (0.91–352)·10⁴ of poly(4-acetoxystyrene) in dioxan at 25°C, from which the molecular weight obtained was found easily to be evaluated with the gel permeation chromatography using THF. Phase separation experiments for this polymer indicate that the theta state is attained in isopropyl acetate at 19.7°C and butyl acetate at 26.8°C. By making viscosity measurements at that state, the value of K_Θ is directly evaluated as 5.4·10^?4 dl g^?1. The limiting viscosity number is also obtained in good solvents, THF and dioxan, at 25°C and constants of the Mark-Houwink-Sakurada equation in each solvent are determined. Further, approximately the same K_Θ as above is obtained from these data with the Stockmayer-Fixman plot. The calculated value of steric factor, 2.37, on this polymer may be plausible, compared with those of polyvinylaromatic derivatives.     

GPC observations of branching effects in anionic polymerization of methyl methacrylate: A preliminary study

The anionic polymerization of methyl methacrylate was performed in tetrahydrofuran (THF) at ?78°C, using sec‐butyllithium/1,1‐diphenylethylene (DPE) as the initiation system. The effects of polymerization time and initiator concentration on the branching reaction were studied. High vacuum was used to prevent contamination during the polymerization. Gel permeation chromatography (GPC) was used to characterize the branching effect qualitatively. Experimental results indicated that the monomer conversion reached more than 98% in a polymerization time of 10 min. The branching reaction occurred after high monomer conversion, resulting in a tail of high molecular weight in the GPC trace. This branching effect, observed by GPC, increased with polymerization time. Rapid termination was thus probably required immediately after all of the monomer was consumed in the preparation of a well‐defined PMMA without a high‐molecular‐weight tail in this diphenylbutylllithium/THF/?78°C system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Devulcanization of nitrile butadiene rubber in nitrobenzene

Sulfur‐crosslinked nitrile butadiene rubber (s‐NBR) was found to be devulcanized when it was heated with nitrobenzene at 200°C for 3 h. The tetrahydrofuran (THF)‐soluble fraction from s‐NBR heated with nitrobenzene was purified by reprecipitation with THF/n‐hexane, chloroform/n‐hexane, and THF/n‐hexane systems and was then characterized by means of Fourier transform infrared (FTIR) spectroscopy, ¹H‐NMR, gel permeation chromatography, dynamic thermogravimetry/differential thermal analysis (DTA), and differential scanning calorimetry (DSC). FTIR and ¹H‐NMR results revealed that the THF‐soluble fraction contained aromatic rings derived from nitrobenzene. Furthermore, the molecular weight of the THF‐soluble fraction was much lower than that of the parent noncrosslinked poly(acrylonitrile‐co‐butadiene). Although the weight loss of THF‐soluble fraction began at a lower temperature than that of the nonheated original nitrile butadiene rubber, the residual weight at 700°C tended to be higher for the former. This tendency became more marked with increasing time of heat treatment with nitrobenzene. The DSC‐determined glass‐transition temperature of the THF‐soluble fraction was higher than that of the original s‐NBR. To elucidate the devulcanization mechanism, we investigated two types of model reactions; one was the reaction of diphenyl disulfide with nitrobenzene, and the other was the reaction of polybutadiene with nitrobenzene. The former reaction, carried out at 250°C in diphenyl ether, yielded diphenyl sulfide with a loss of diphenyl disulfide and nitrobenzene. The use of a higher molar ratio of nitrobenzene to diphenyl disulfide resulted in a depression of diphenyl sulfide formation. The reaction of p‐chloronitrobenzene with diphenyl disulfide also gave diphenyl sulfide. The reaction of polybutadiene with nitrobenzene at 200°C resulted in the backbone scission of the polymer. The THF‐soluble solid product of the latter model reaction was found by FTIR and ¹H‐NMR to contain aromatic rings derived from nitrobenzene. The devulcanization mechanism is discussed on the basis of a comparison of the results of the model reactions with those of the s‐NBR devulcanization. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3342–3353, 2004     

Effects of chain ends and molecular weight on specific volumes of anionic polystyrene melts

Specific volumes of anionic polystyrenes prepared by butyl lithium initiation have been measured at temperatures between 110° and 237°C. Molecular weights of the fractions studied ranged from 2500 to 700 000. Plots of isothermal specific volume against reciprocal molecular weight (M^?1) are fitted by two straight lines intersecting at a molecular weight near 10 000. This parallels the behaviour of thermally initiated polystyrene fractions, which have different end-groups. Volumes attributable to end-groups are greater for the anionic polymers. The specific volume-molecular weight-temperature relations in the M ≤ 10 000 region are explained quite well by the equation of Francois and coworkers, in terms of end-group volumes and a uniform volume contribution from internal repeating units. Restraints on the motion of the butyl end-groups in these polymers by the attached polystyrene chain appear to be temperature dependent in terms of this model. Specific volumes of polymers with M ≥ 10 000 are affected by chain ends and by variation of the volumes of non-end repeating units with molecular weight. The present results parallel those which have been reported for partial specific volumes of polystyrenes in dilute solution and suggest that the same factors operate in both cases.     

Crystallization of polyformals: 2. Influence of molecular weight and temperature on the morphology and growth rate in poly(1,3-dioxolane)

The morphology and growth rates of crystallized molecular weight fractions of poly(1,3-dioxolane) covering the range M_n = 8 800 to 120 000 have been studied by polarized light microscopy. Two different supermolecular structures, dependent on molecular weight and crystallization temperature have been found. Spherulites are formed after rapid crystallization and a more disordered morphology is formed at the lowest undercoolings but there is a temperature region where both forms are observed. The disordered form appears first and a consecutive spherulitic growth takes place. The crystallization kinetics were analysed over the temperature range 10°C to 36°C. At crystallization temperatures lower than 15°–18°C, the growth rate is linear and only spherulites are found. In the temperature range from 18°C to 36°C a well defined break is observed in the growth rate but the spherulitic growth rate is always higher than that of the irregular form. The growth rate temperature coefficient was studied and the usual plots are not linear in the whole range of crystallization temperatures. For the high crystallization temperature region, the slope is about twice as great as the low crystallization temperature slope. This is the region where regular spherulites are formed. The comparison between dilatometric and growth rate data has shown that the overall rate and growth rate temperature coefficients are the same.     

Synthesis and characterization of novel poly(arylene ether)s based on 9,10‐bis‐(4‐fluoro‐3‐trifluoromethylphenyl) anthracene and 2,7‐bis‐(4‐fluoro‐3‐trifluoromethylphenyl) fluorene

Two new bisfluoro monomers 9,10‐bis‐(4‐fluoro‐3‐trifluoromethylphenyl) anthracene and 2,7‐bis‐(4‐fluoro‐3‐trifluoromethylphenyl) fluorene have been synthesized by the cross‐coupling reaction of 2‐fluoro‐3‐trifluoromethyl phenyl boronic acid with 9,10‐dibromo anthracene and 2,7‐dibromo fluorine, respectively. These two bisfluoro compounds were used to prepare several poly(arylene ether)s by aromatic nucleophilic displacement of fluorine with various bisphenols; such as bisphenol‐A, bisphenol‐6F, bishydroxy biphenyl, and 9,9‐bis‐(4‐hydroxyphenyl)‐fluorene. The products obtained by displacement of the fluorine atoms exhibits weight‐average molar masses up to 1.5 ×10⁵ g mol^?1 and number average molecular weight up to 6.8 × 10⁴ g mol^?1 in GPC. These poly(arylene ether)s show very high thermal stability even up to 490°C for 5% weight loss occurring at this temperature in TGA in synthetic air and showed glass transition temperature observed up to 310°C. All the polymers are soluble in a wide range of organic solvents, e.g., CHCl₃, THF, NMP, and DMF. Films cast from DMF solution are brittle in nature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Chain reaction mechanism of cellulose pyrolysis

Chatterjee and Conrad¹ studied the kinetics of pyrolysis of cotton cellulose in the temperature range 270–310°C and proposed a chain reaction mechanism. Lipska and Parker⁸ studied the pyrolysis of the α-cellulose in the temperature range 250–300°C and interpreted the kinetic data differently. Both articles were published almost simultaneously. In this paper Lipska and Parker's complete data have been again analyzed and reinterpreted in light of the chain reaction mechanism. The energies of activation for initiation and propagation steps of the cellulose decomposition reaction are discussed.     

Effects of culture temperature on the production of bioactive polysaccharides by Agaricus blazei in batch cultures

Effects of culture temperature ranging from 20 to 34 °C on cell growth, polysaccharide biosynthesis and the bioactivity of polysaccharides of Agaricus blazei were evaluated via eight batch cultures in steps of 2 °C in a stirred tank bioreactor. Results indicated that the optimal temperature for the biomass was 28 °C with a cell yield of 780 mg g^?1, while that for polysaccharide formation was 30 °C with a product yield of 230 mg g^?1. Both the β‐glucan content and average molecular weight of the polysaccharides from different temperature‐controlled cultures were closely correlated with their tumour necrosis factor‐α (TNF‐α) release capability on macrophage cells. The polysaccharides from the low temperature range (20–24 °C) not only had higher relative content of β‐glucan and average molecular weight but also exhibited higher bioactivity compared with those from the high temperature range (30–34 °C). The optimal temperature for the production of bioactive polysaccharides of A. blazei was 24 °C, at which their relatively high molecular weight, β‐glucan content and TNF‐α release capability on macrophage cells were 1650 kDa, 188 mg g^?1 and 1560 pg per 5 × 10⁴ cells respectively. Copyright © 2007 Society of Chemical Industry     

Determination of the molecular weight and hydrodynamic dimensions of micelles formed from a block copolymer

An investigation has been made of micelle formation by a polystyrene-polyisoprene two-block copolymer in n-decane. For the sample studied the number-average molecular weights of the polystyrene block and overall copolymer chain were 13 000 and 51 000 respectively. Light-scattering studies in n-decane were made within the temperature range 25–65°C. Conventional light scattering was used to obtain weight-average molecular weights; at 25°C, M_w of the micelles was 1·73±0·14×10⁶. Translational diffusion coefficients were determined from Rayleigh linewidth measurements; the micelles were found to have a hydrodynamic radius of 19·6nm at 25°C. Intrinsic viscosities were determined for the copolymer in n-decane and methyl cyclohexane within the temperature range ?20° to 75°C. Finally, data obtained earlier in an electron microscopy study of freezeetched specimens were compared with the results obtained in the present study.     

Synthesis of poly(ether amide)s from p‐xylylene glycol and bis(ether nitrile)s

BACKGROUND: Poly(ether amide)s have been well studied in terms of improving the physical and thermal properties of aromatic polyamides. Poly(ether amide)s of high enough molecular weight to be useful for industrial purposes are generally difficult to prepare. The objective of this project was to introduce a simple and commercially feasible process to prepare poly(ether amide)s by a polymerization reaction at relatively low temperature. RESULTS: A series of poly(ether amide)s were prepared by direct polyamidation of p‐xylylene glycol with bis(ether nitrile)s via the Ritter reaction using concentrated H₂SO₄ in acetic acid. The synthesized poly(ether amide)s showed good solubility in polar aprotic solvents. The resultant poly(ether amide)s had inherent viscosities in the range 0.36–1.03 dL g^?1. The glass transition temperatures of the poly(ether amide)s were determined using differential scanning calorimetry to be in the range 190–258 °C. Thermogravimetric analysis data for these polymers indicated the 10% weight loss temperatures to be in the range 290–390 °C in nitrogen atmosphere. CONCLUSION: The Ritter reaction was applied for the synthesis of a variety of poly(ether amide)s with moderate to high molecular weights. This procedure provides a simple polymerization process for the convenient preparation of poly(ether amide)s in high yield at room temperature. Copyright © 2009 Society of Chemical Industry     

Properties of syndiotacticity-rich poly(vinyl alcohol) thin film in water. IV. Elastic behavior of untreated thin film by repeated elongation and contraction in water

The activation energy ΔE_a for diffusion of water molecules into untreated thin film of poly(vinyl alcohol) (PVA_VTFA) derived from vinyl trifluoroacetate was estimated as 30.3 kcal/mol from the temperature dependence of the initiation time of swelling. The degree of equilibrium swelling increases with the increase in temperature in the range of 10–70°C, passing through the constant range between 30 and 50°C. Under the forced, repeated elongation and contraction for swollen PVA_VTFA thin film in water, the perfect elastic behavior is kept up to higher elongation with the increase in temperature and especially up to about three times equilibrium swelling length at 70°C. Young's modulus of swollen PVA_VTFA thin film in water was 6.47 × 10⁶ to 1.60 × 10⁶ dyn/cm² at 25–70°C. The molecular weight between junctions M_c increased with the increase in temperature; M_c was nearly equal to about one-sixth of the molecular weight of raw polymer M at 25°C and about one-third of M at 70°C. The interaction parameter between PVA_VTFA and water X₁, was 0.493–0.497 at 25–70°C.     

Light scattering properties of acacia catechuic acid. Effects of urea and temperature

Association of acacia catechuic acid (ACA) molecules was established in ethanol–water medium². This association was further tested in pure aqueous medium as well as by using urea in increasing amounts in aqueous solutions. The 5M urea depressed the molecular weight to 2.82 × 10⁶, as against 5.04 × 10⁶ in aqueous solution of NaCl or KCl. This reduction has been explained as due either to rupture of the molecule itself or dissociation of molecules which normally remain associated in water. The diminution of root-mean-square end-to-end distance in urea from 323 mμ in water³ to 290 mμ has also been attributed to the disaggregation of the associated molecules. To test this point further, the effect of increasing the temperature was next studied. The molecular weight was observed to be lower at higher temperature (actual value at 47°C was nearly half the original value at 28°C). This considerable reduction positively points to a dissociation of the molecule which was first suspected in our study with urea. The root-mean-square end-to-end distance also diminished to a certain extent, but not so much as the molecular weight. This has been explained as due to the stretching of the molecule when the solvent behaves as a better solvent at higher temperature.     

Ultra-high strength polyethylene filaments by solution spinning/drawing. 3. Influence of drawing temperature

The influence of the temperature on the drawing behaviour of gel-fibres, which were obtained by spinning of a 2% w/w solution of high molecular weight polyethylene (M_w = 1.1 × 10⁶) in decalin, was studied in the range from 70 to 143°C. It was found that the drawing temperature, like the presence of solvent in the gel-fibres, affected the maximum attainable draw ratio, but did not influence the effectiveness of the hot drawing below the melting point of the polymer.     

Poly(ethyl-n-butylsilylene): Structural,thermal, and flow properties of a liquid crystalline polysilane

Poly(ethyl-n-butylsilylene) (PEBS) was synthesized by sodium coupling of ethyl-n-butyldichorosilane and separated into fractions with differing molecular weights,M _w=1.4×10⁶ and 2.0×10⁴. Both fractions were studied by differential scanning calorimetry and by X-ray diffraction, UV spectroscopy, polarizing optical microscopy, and capillary rheometry, all as a function of temperature. Both samples adopt a hexagonal columnar liquid crystalline structure at room temperature and below. They undergo a weak endothermic transition at ?20°C and a first-order phase transition to a nematic liquid crystalline form at 90°C for the low and 170°C for the highM _w fraction. Melting to an isotropic liquid takes place at 106°C for the low and 185°C for the highM _w polymer. Both samples undergo two successive thermochromic transitions in the UV, one near the first-order exothermic transition and one near the ?20°C transition; the reasons underlying these thermochromic transitions are discussed. Flow properties of PEBS were investigated as a function of molecular weight.     

Effect of electron donors on 1,3‐butadiene polymerization by a Ziegler–Natta catalyst based on neodymium

High‐cis polybutadiene produced by catalyst systems based on a rare earth is an elastomer used to produce green tires. This type of tire presents lower rolling resistance, which allows higher fuel economy, and thus fewer chemical compounds are discharged into the atmosphere. In this work, the influence of electron donors [tetrahydrofuran (THF) and tetramethylethylenediamine (TMEDA)] present in the polymerization solvent on the microstructure and molecular weight characteristics of the polybutadiene produced by neodymium catalysts was studied. The catalyst synthesis was carried out in glass bottles for 1 h at a temperature between 5 and 10°C. The catalyst components were diisobutylaluminum hydride, neodymium versatate, and tert‐butyl chloride. The polymerization reaction was carried out for 2 h. The reaction temperature was kept at 70± 3°C. The addition of TMEDA or THF above a determined concentration reduced the catalytic activity, molecular weight, and concentration of cis‐1,4 units (<96%), whereas the polydispersity increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2539–2543, 2005     

Condensation polymerization of pyrogallol and benzaldehyde

Novolac-type polycondensation of benzaldehyde (B) and pyrogallol (P) has been carried out at 60°C, 75°C and 90°C and at B/P mole ratios of 1.5 and 3.0 using phosphoric acid as catalyst. The reaction follows a 2nd order rate law. By using GC consumption data of benzaldehyde and pyrogallol, kinetic parameters such as the overall rate constants, activation energies (E_a) and logA values are investigated. The activation energies for 1.5 and 3.0 B/P mole ratios are found as 62.3 kJ mol^?1 and 56.4 kJ mol^?1, respectively. The molecular weights of the resins determined by measuring intrinsic viscosities (25°C, THF) are in the range of 0.03 to 0.07 dL g^?1 at various temperatures and B/P mole ratios.     

Studies on the Synthesis and the Reaction Mechanism of Epoxy-Terminated Polystyrene Oligomer

The living poly(styryl)lithium was prepared by anionic polymerization with the protection of argon under normal pressure, where styrene, cyclohexane, THF and n-butyllithium were used as monomer, solvent, polar reagent and initiator, respectively. Epoxy-terminated polystyrene oligomers with narrow molecular weight distribution were synthesized by the copolymerization of the end groups of poly(styryl)lithium with glycidyl methacrylate (GMA) at a moderate temperature. The oligomers were characterized using GPC, FT-IR, ¹H-NMR, ¹³C-NMR and Hydrochloric acid-Dioxane Argentimetric method. The effects of GMA dosage, copolymerization duration and temperature on the content of epoxy end group were also studied. The results indicated that the double bond of GMA could polymerize with poly(styryl) carbanion and the content of epoxy end group could be adjusted. It was found that the optimal conditions for the copolymerization were reaction temperature at 10 °C and 2 h for copolymerization duration.     

Synthesis and characterization of polyimides from 4,4′-(3-(<Emphasis Type="Italic">tert</Emphasis>-butyl)-4-aminophenoxy)diphenyl ether

A novel diamine 4,4′-(3-(tert-butyl)-4-aminophenoxy)diphenyl ether (4) was synthesized from 2-tert-butylaniline and 4,4′-oxydiphenol through iodination, acetyl protection, coupling reaction and deacetylation protection. Then some polyimides (PIs) were obtained by one-pot polycondensation of diamne 4 with several commercial aromatic dianhydrides respectively. They all exhibit enhanced solubility in organic solvents (such as NMP, DMF, THF and CHCl₃ etc.) at room temperature. Their number-average molecular weights are in the range of (2.1–3.7)?×?10⁴ g/mol with PDI from 2.25 to 2.74 by GPC. They can form transparent, tough and flexible films by solution-casting. The light transparency of them is higher than 90% in the visible light range from 400 nm to 760 nm and the cut-off wavelengths of UV–vis absorption are below 370 nm. They also display the outstanding thermal stability with the 5% weight loss temperature from 525 °C to 529 °C in nitrogen atmosphere. The glass transition temperatures (T _g s) are higher than 264 °C by DSC. XRD results demonstrate that these PIs are amorphous polymers with the lower water absorption (<0.66%). In summary, the incorporation of tert-butyl groups and multiple phenoxy units into the rigid PI backbones can endow them excellent solubility and transparency with relatively high T _g s.