Radiolyse des hydrocarbures. 21e communication. Mécanismes radicalaires et non-radicalaires dans les n-alcanes en phase liquide

Contributions of radical and non-radical processes have been determined in the formation of radiolysis products of n-heptane, n-octane, n-nonane and n-decane in a large range of temperature. Calculations are based on the combination and the dismutation of radicals, both reactions having nearly the same importance. Hydrogen abstraction reactions become important above – 25°. Intermediate molecular weight products and dimers are formed by statistical combination of the various radicals resulting from C? C and C? H scission. At low temperature, low molecular weight products are formed by both radical and non-radical processes, the second one being more important (3/4 for alcanes and 2/3 for olefins). The yield of radicals increases with the chain length of the irradiated n-alkane and amounts to 4.5 for n-heptane and 6.8 for n-decane at – 25°. This increase is due only to radicals from C? H scission, while the yield of radicals from C? C scission remains constant. Scission of CH₂? CH₂ bonds is favored for bonds inside the molecule, but this affect diminishes with chain length and CH₂? CH₂ rupture is equally probable at all positions for n-alcanes heavier than decane. Methyl C? H scission is 2.7 times less probable than methylene C? H scission. The radiolysis of mixtures of protonated and deuterated n-alcanes is shown to be able to give information concerning basic processes in radiation chemistry.     

Molecular weight characterization of soluble high performance polyimides. 1. Polymer-solvent-stationary phase interactions in size exclusion chromatography

Soluble, fully cyclized m-amino phenyl acetylene terminated polyimides based on several anhydride/diamine monomers were prepared in N-methylpyrrolidine (NMP) and cyclized by solution imidization to controlled molecular weight. The polyimides and a polyamic acid precursor were successfully analyzed by size exclusion chromatography (SEC) utilizing online parallel coupled refractive index and differential viscometer detectors. The calculated M _nvalues were varied from 3,000 to 20,000 daltons. N-methylpyrrolidone (NMP), tetrahydrofuran (THF), and chloroform served as mobile phases for the cross-linked polystyrene gel packings. Normal retention behavior of the polyimides was observed in chloroform, THF, and NMP containing LiBr, or in NMP stirred over P₂O₅ before use. Values of Mark-Houwink-Sakurada exponents for narrow distribution linear polystyrene indicate that pure NMP and NMP with 0.06 M LiBr are good solvents for polystyrene standards at 60°C. In contrast, SEC behavior of polyimides in pure NMP leads to splitting of the peaks with the major portion observed to pass through the columns at the exclusion limit. In contrast to strong polymeric chain expansion of the polyamic acid in dilute solution, presumably due to a polyelectrolyte effect, no increase of intrinsic viscosity of polyimide samples in pure NMP was observed. This exclusion effect of polyimides analyzed in NMP is discussed in terms of possible ion-exclusion from pores of the stationary phase. Differences in polystyrene calibration in NMP with or without additives and the temperature dependence of calibration curves in these mobile phases is discussed as well. ©1995 John Wiley & Sons, Inc.     

Preparation of phosphorus-containing polymers—XXIII: Phenoxaphosphine-containing polyimides

New phenoxaphosphine-containing polyimides were synthesized from 10-phenylphenoxaphosphine-2,3,7,8-tetracarboxylic dianhydride 10-oxide (IV) and diamines via polyamic acids in two steps. (IV) was prepared by dehydration of 10-phenylphenoxaphosphine-2,3,7,8-tetracarboxylic acid 10-oxide (III) derived from 2,3,7,8-tetramethyl-10-phenylphenoxaphosphine (I) or 2,3,7,8-tetramethyl-10-phenylphenoxaphosphine 10-oxide (II) by pyridine-permanganate oxidation. (I) was synthesized from bis(3,4-dimethylphenyl)ether and phenylphosphonous dichloride by the Friedel-Crafts reaction. The resulting polyimides had reduced viscosities of 0.13–0.84 di/g in cone H₂SO₄ at 30°. They were also soluble in dichloroacetic acid and some of them dissolved in DMA, DMSO. DMF and chloroform. Aromatic phenoxaphosphine-containing polyimides exhibited excellent thermal properties and hardly degraded below about 500°; the aliphatic polyimides decomposed at around 500. The aromatic polyimides had thermal stability similar or superior to aromatic polypyromellitimides and better heat resistance than linear open-chain phosphorus-containing polyimides. These polyimides showed retardance to inflammation.     

Synthesis and Properties of Polyamides and Polyimides Derived From Diamines Having 2-Phenyl-4,5-Oxazolediyl Units and Polyamide/Montmorillonite Composite

Aromatic polyamides were synthesized from 4,5-bis(4-aminophenyl)-2-phenyloxazole (APO) or 4,5-bis[4(4-aminophenoxy)phenyl]-2-phenyloxazole (APPO) containing 2-phenyl-4,5-oxazolediyl units with several aromatic carboxylic dichlorides by a low-temperature solution polycondensation method. The polyamides were obtained quantitatively, and their inherent viscosities ranged from 0.48 to 1.25 dL g^?1. The glass transition temperatures (T _gs) were displayed between 234 to 311°C, and the residual weight at 600°C (Res.wt₆₀₀) exceeded 52% in nitrogen atmosphere. The polyamides showed good solubility in several aprotic polar solvents, such as N,N-dimethylacetoamide (DMAc), N-methyl-2-pyrrolidone (NMP), and dimethyl sulfoxide (DMSO). Aromatic polyimides were derived from APO or APPO with aromatic carboxylic dianhydrides through polyamic acids. The inherent viscosities of the polyamic acids, which were 0.53 to 1.02 dL g^?1, T _gs of the polyimides were observed between 259 to 361°C and their Res.wts₆₀₀ were above 70%. The polyamides and polyimides were amorphous and afforded thin, flexible and tough films. We also prepared a nanocomposite of the polyamide derived from APPO with organophilic montmorillonite clay.     

Synthesis and characterization of polyimides based on novel tricyclo[6,2,2,02,7] dianhydride

3-Phenyl-tricyclo [6,2,2,0^2,7]dodeca-2,11-ene-5,6,9,10-tetracarboxylic dianhydride was prepared from 1,1-diphenyl ethylene and maleic anhydride in 1 : 2 mole ratio by [4 + 2]π Diels-Alder cycloaddition. The structure of the dianhydride was determined by mass spectroscopy, IR, ¹H-NMR, elemental analyses, and single crystal x-ray diffraction. The monomer was condensed with several diamines in N-methyl pyrrolidone or m-cresol. The polyamic acids and the polyimides synthesized had inherent viscosities in the range of 0.19–0.31 and 0.17–0.25 dL/g, respectively, measured in N-methyl pyrrolidone at 30°C. Both the polyamic acids and the polyimides were found to be soluble in m-cresol, N-methyl pyrrolidone, dimethylacetamide, dimethyl formamide, and dimethyl sulfoxide. The polymides showed a low degree of crystallinity from wide angle x-ray diffraction. Thermal analysis of these polyimides revealed that their glass transition temperatures (T_g) were in the 215–237°C range and they decomposed in two stages. The first-stage decomposition temperatures were almost the same in O₂ or N₂ atmospheres, but the polymers showed a better thermal stability in O₂ rather than in N₂ in the second stage. The mechanism of thermal degradation is discussed.     

Radiation Degradation of Poly(olefin Sulfone)s: A Volatile Product Study

The predominant degradation reaction in the γ-irradiation of nine poly(olefin sulfone)s was found to be C-S bond scission with elimination of SO₂ and olefin. The extent of depolymerization, measured by the yields of the two comonomers, increased over five irradiation temperatures from 0 to 150° C and could be correlated with the ceiling temperature. Thus G (total volatile products) increased from 10 to 10,000 over this temperature range. Minor radiolysis products included the alkanes corresponding to (1) loss of the side chain group and (2) scavenging of the side chain radical by monomer olefin. There was a deficiency of olefin relative to SO₂, except at high temperatures, and isomerization of the product olefin in some cases. These observations are attributed to reactions of radiation-induced polymeric cations.     

Heat-resistant polymers containing bipyridyl units. III. Polyimides having o-, m-, or p-phenylenedioxy linkage

New series of diamines having pyridine rings and o-, m-, or p-phenylenedioxy linkages were prepared by condensation of chloronitropyridine with isomeric dihydroxybenzenes followed by chemical reduction. The polymerization of the diamines with benzo-phenonetetracarboxylic acid dianhydride gave polyamic acids with the inherent viscosities in the range 0.21 to 1.30 dl/g. The conversion of these polyamic acids to polyimides was carried out thermally and the resulting polyimides exhibited very good solubility in organic solvents.     

Preparation and properties of polyamides and polyimides derived from 1,3-diaminoadamantane

1,3-Diaminoadamantane (I) was used as a monomer with various aromatic dicarboxylic acyl chlorides and dianhydrides to synthesize polyamides and polyimides, respectively. Polyamides having inherent viscosities of 0.10–0.27 dL/g were prepared by low-temperature solution polycondensation. The polyamides were soluble in a variety of solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), pyridine, dioxane, and nitrobenzene. These polyamides had glass transition temperatures in the 179–187°C range and 5% weight loss temperatures occurred at up to 354°C. Polyimides based on diamine I and various aromatic dianhydrides were synthesized by the two-stage procedure that included ring-opening to form polyamic acids, followed by thermal conversion to polyimides. The polyamic acids had inherent viscosities of 0.14–0.38 dL/g. The glass transition temperature of these polyimides were in the 245–303°C range and showed almost no weight loss up to 350°C under air and nitrogen atmosphere. © 1996 John Wiley & Sons, Inc.     

Liquid crystalline comb-like polyimides with biphenyl-based side groups

We have synthesized series of comb-like polyimides with mesogenic units in their side groups. Such comb-like polyimides were obtained by polycondensation of aromatic diamines bearing biphenyl-based mesogenic moieties with bicyclo[2,2,2]oct-7-ene 2,3,5,6-tetracarboxylic dianhydride (BCDA). The different diamines, with two lengths of spacer (with 6 and 11 methylene groups), were synthesized in three steps using as mesogenic groups: biphenyl, 4-cyanobiphenyl and 4-(2-methyl-1-butoxy)biphenyl. The synthesis of the polyimides was performed in two steps: polycondensation of a dianhydride with a diamine in N-methyl-2-pyrrolidone at room temperature giving the corresponding polyamic acid, followed by thermal cyclization into the corresponding polyimide. The comb-like polyimides were studied by X-ray diffraction between room temperature and 250°C. Two types of smectic structure were established: SmA₁ for the long spacer and SmC₁ for the short spacer.     

Preparation and properties of new photosensitive polyimides from bis(4-aminophenyl)tetramethyldisilane and various aromatic tetracarboxylic dianhydrides

New photosensitive polymides containing photosensitive disilane unit were synthesised from 1,2-bis(4-aminophenyl)tetramethyldisilane and various aromatic tetracarboxylic dianhydrides by the usual two-step procedure that includes ring-opening polyaddition to yield the precursor polyamic acids, followed by cyclodehydration giving the respective polyimides. The polymaic acids had inherent viscosities between 0.63 and 0.85 dL/g depending on the tetracarboxylic dianhydride used. Excepting the polyimide obtained from pyromellitic dianhydride, all other polyimides were soluble in N-methyl-2-pyrrolidone, m-cresol, and pyridine. While the polyimide containing diphenyl sulfone unit was amorphous, the other polyimides were semi-crystalline polymers based on their x-ray diffractograms. The polyimides had glass transition temperatures between 235 and 304°C. They were thermally stable up to 380°C in both air and nitrogen atmospheres. All the polyamic acids showed a drastic decrease in the inherent viscosity upon UV light irradiation, implying the inherent photosensitivity of the polymers containing the disilane moiety.     

Radiation effects on silicon-containing polyacetylenes

Si-containing mono- and disubstituted polyacetylenes(? [CMe?C(SiMe₃)] _n? , ? [CH?H(n? C₅H₁₁)SiMe₃]_n? , etc.) underwent degradation in air; many of them exhibited relatively high yields of main-chain scission (G_s > 1). The G_s values for the polymers having a long n-alkyl group were usually large (ca. 2). In contrast, no polymer degradation occurred in vacuum, indicating that oxygen is necessary for the radiolysis. The polymers irradiated in air contained C?O and Si? O groups, and dissolved in polar solvents, which are nonsolvents of the starting polymers. From the radiation sensitivity and thermal degradability of these polymers, it is concluded that disubstituted polymers with high Si contents (? [CMe?C(SiMe₃)]_n? , ? [CMe?C(SiMe₂CH₂SiMe₃)]_n? , etc.) are not only radiation-sensitive but also thermally stable.     

Polyimide solution properties

Solution characterization measurements indicate that cylization of the polyamic acid from 2,4-diaminoisopropylbenzene and pyromellitic dianhydride (PMDA) to the polyimide can be effected with small change in number-average degree of polymerization. An increase in weight-average molecular weight on conversion to polyimide is attributed to branching side reactions. Inherent viscosities of polyimides from 4,4′-diaminodiphenyl ether and PMDA decreased slowly with time in concentrated (97%) sulfuric acid, probably as a result of hydrolytic cleavage. The zero-time viscosity intercepts were related to both the precursor and the estimated polyimide molecular weight. The latter gave η_inh (c = 0.5% solids) = 2.76 × 10^?3M?^0.53_w for 60,000 < M_w < 300,000. The exponent is near the lower limit of 0.5 found in theta solvents. The characteristic ratio of the root-mean-square end-to-end distance of a chain to the square root of its molecular weight is 1.1 Å and the steric factor is 1.1; these results suggest that the unperturbed polyimide chain is almost as extended as an equivalent freely rotating chain, a general feature of long-bonded polymers with p-phenylene rings in the chain backbone.     

Sorption of carbon dioxide in fluorinated poyimides

Sorption isotherms of CO₂ for ten fluorinated polyimides measured at 35°C and up to about 25 atm are analyzed according to the dual-mode sorption model. Sorption properties for these polyimides are compared with those for other glassy Polymers including unfluorinated polyimides. The glassy polymers with higher glass transition temperatures T_g tend to show greater CO₂ sorption. Introduction of a ? C (CF₃)₂? linkage into the repeat unit of the main chain increases the sorption by 20–80%. For glassy polymers, including the fluorinated and unfluorinated polyimides, the Langmuir affinity constant b and Henry's law solubility constant k_D are correlated with the content of functional (carbonyl or sulfonyl) groups [FG], and composite parameter reflecting the magnitude of both [FG] and free-space fraction V_F, respectively, with some exceptions. The Langmuir capacity constant C′_H is correlated with T_g, but there are two correlation lines; one for unfluorinated polyimides and a different one for other glassy polymers including fluorinated polyimides. The slope of the former group is smaller probably because of smaller differences in thermal probably because of smaller differences in thermal expansion coefficients in rubbery and glassy states. Most fluorinated polyimides show greater solubility of CO₂ than unfluorinated polyimides and other glassy polymers, because of their larger C′_H and k_D. © 1993 John Wiley & Sons, Inc.     

Polyimides having pendant hydroxy and acetoxy groups. II. Polyimides derived from bisaminoalcohols

Polyamic acids were prepared from bisaminoalcohols and pyromellitic dianhydride. They were converted to polyimides having pendant hydroxy groups by heating them in toluene or xylene (η_inh = 0.22–0.34 dl/g). Treatment of these polyamic acids with a mixture of pyridine and acetic anhydride gave polyimides having pendant acetoxy groups (η_inh = 0.22–1.04 dl/g). These acetoxypolyimides were converted to hydroxypolyimides (η_inh = 0.20–0.81 dl/g) by an ester-exchange reaction. Furthermore, the hydroxypolyimides were easily acetylated to give acetoxypolyimides.     

Main chain scission reaction of poly(methyl methacrylate) caused by two-photon ionization of dopant

The main chain scission reaction of poly(methyl methacrylate) (PMMA) doped with N,N,N,′,N′-tetramethyl-p-phenylenediamine (TMPD) was examined by ESR spectroscopy and GPC measurement, and the scission mechanism was analyzed. The two-photon ionization of TMPD with excimer laser excitation at 77 K produced an ester radical anion of PMMA (PMMA·m?), which becomes the main chain tertiary radical ? CH₂? C˙(CH₃)? CH₂? after the detachment of the ester side group by annealing of the sample at room temperature. The main chain scission radical ˙C(CH₃)(COOCH₃)? (PMMA˙) which was produced by the β-scission from? CH₂? ˙C(CH₃)? CH₂? showed the 13-line ESR spectrum instead of the ordinary 9-line, due to the fast quenching of the sample to 77 K. The change of the molecular weight distribution was measured by GPC after several irradiation-and-annealing operations. The simulation of the GPC curve confirmed that the scission re-action occurs at random in the PMMA chain in the solid and the main chain scission yield from the ester radical anion, [PMMA˙]/[PMMA·m?], is 0.30. © 1995 John Wiley & Sons, Inc.     

Copolymer of trifluoroethylmethacrylate–N-p-methoxyphenyl citraconimide as high TgE-beam resist

Copolymers of 2,2,2-trifluoroethyl methacrylate (TFEMA) and N-p-methoxyphenyl citraconimide (MCM) have been synthesized. The T_g varies with composition reaching 150°C with 34% MCM. The copolymer has good radiation sensitivity according to both G values for chain scission and E-beam measurements. Though they have lower contrast than PMMA, they have much higher resistance to plasma etching. The resistance increases markedly with MCM content to values comparable to that for polyimides. Therefore, TFEMA–MCM copolymers of high MCM content can be useful as high temperature plasma etchable positive E-beam resists.     

Conductometric Determination of Sulfur Dioxide in Wine Using a Multipumping System Coupled to a Gas-Diffusion cell

A conductometric system with a multipumping module and a gas-diffusion cell has been developed to determine free and total sulfur dioxide (SO₂) in wine. The developed method has two protocols to determine both types of SO₂ using the same system. For free SO₂, sulfite is converted to H₂SO₄ by acidification and diffusion with H₂O₂ in an acceptor channel. The sample was previously hydrolyzed by mixing the sample with NaOH and heated at 70?°C prior making the determination of total SO₂ in order to break the bonds of the combined SO₂. Free and total SO₂ were determined in the ranges of 2.5–25.4 and 10.2–76.2?mg L^?1 with a sample throughput of 13 and 12?h^?1, respectively. The calibration curves of free and total SO₂ were in the range of ΔG (mS cm^?1)?=?(–1.0242?±?0.2871)?+?(0.6613?±?0.0201) [SO₂, mg L^?1], r² of 0.997 and ΔG (mS cm^?1)?=?(–0.5850?±?0.1678)?+?(0.1236?±?0.0033) [SO₂, mg L^?1], r² of 0.997. The proposed automated method is simple and easy to apply for the determination of SO₂ in wine using simple reagents.     

Free radical copolymerization of sulfur dioxide with 1-alkynes

Free radical copolymerization of SO₂ with 1-alkynes (AY) was studied by evaluation of the copolymerization rate under controlled conditions of copolymerization temperature and monomer concentration product ([AY][SO₂]). The poly(alkyne sulfone)s always contained equimolar units of SO₂ and alkyne, regardless of the copolymerization conditions. Using 1-hexyne (HY) and 1-octyne (OY) as comonomers of SO₂, the values of ceiling temperature (T_c) were determined: when [HY][SO₂] = [OY][SO₂] = 0.25 mol²/L², the values of T_c were 90.5 and 84.5°C, respectively. T_c increases with increasing monomer concentration product. The activation energies for propagation (E_p) and depropagation (E_d) of the SO₂-alkynes copolymerization system were investigated, using the SO₂? OY copolymerization system, and estimated to be 12.2 and 26.7 kcal/mol, respectively. The value of E_d is high compared with that of the copolymerization of SO₂ and 1-butene (20.3 kcal/mol), demonstrating that the free radical endings (～ OY? SO₂ and ～ SO₂? OY) are difficult to depropagate, compared with those formed from the copolymerizaton of SO₂ and 1-butene. ΔS and ΔH_p, calculated from experiments, were found to be ?37.7 cal/mol K and ?14.3 kcal/mol, respectively     

Gas permeability and permselectivity of polyimides with large aromatic rings

Polyimides with large aromatic rings were prepared from 3,6-diaminocarbazole (CDA), N-ethyl-3,6-diaminocarbazole (ECDA), 2,7-diaminofluorene (DAF), 2,7-diaminofluorenon (DAFO), and dimethyl-3,7-diaminodibenzothiophene-5,5-dioxide (DDBT) with 2-bis(2,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). Their physical properties, including gas permeability and permselectivity, were investigated in comparison with those of the related polyimides from 1,3-phenylenediamine (mPD). Glass transition temperatures of the polyimides with large aromatic rings were much higher than those of the mPD-based polyimides as a result of increased rigidity of the former polymer chains. With changing diamine from mPD to the large aromatic diamines, charge transfer (CT) interaction between the moieties of acid anhydride and diamine seems to be enhanced, judging from the red shift of absorption edge of the polyimide films and the red shift of CT excitation band of the 6FDA-based polyimides in solution. Fraction of free space (V_F) was a little smaller for the polyimides with large aromatic rings except DDBT than for the mPD-based polyimides, probably because of enhancement in polymer chain-chain interactions as a result of the increased CT interaction. The DDBT-based polyimides had large V_F than the mPD-based polyimides because of the nonplanar structure of neighboring dibenzothiophene-5,5-dioxide and imide rings. For the 6FDA-based polyimides, permeability coefficients to H₂, O₂, N₂, CO₂, and CH₄ were in the order, DAFO < mPD ～ DAF < CDA < ECDA < DDBT. As for the membrane performance for H₂/CH₄, CO₂/CH₄, and O₂/N₂ systems, it is significant to change diamine from mPD to DDBT or CDA, but not to DAF or DAFO. The DDBT-based polyimides were excellent for H₂/CH₄ and CO₂/CH₄ separations. © 1995 John Wiley & Sons, Inc.     

Effect of curing accelerators on thermal imidization of polyamic acids at low temperature

The effect of new additives on the thermal conversion of a range of polyamic acids to polyimides at temperatures lower than 100°C was investigated using infrared spectroscopy. Additives such as m-hydroxybenzoic acid, p-hydroxyphenylacetic acid, and p-hydroxybenzenesulfonic acid were found to be highly effective as curing catalysts or accelerators. The degree of imidization of polyamic acids in the presence of additives increased with an increase in the reaction temperature, and complete imidization was achieved at 140–200°C. The reaction was characterized by a rapid rate that slowed with time. © 1996 John Wiley & Sons, Inc.