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1.
A kinetic study was carried out on the acetalization reaction of 1,3-butanediol, as a model compound for poly(vinyl alcohol) (PVA), in water, under acidic conditions. Since these equilibrium constants of ketalization reaction of 1,3-butanediol and ethylene glycol are so small, the kinetic parameters were estimated from the hydrolysis reactions of the corresponding ketals. It was made clear that these reactions proceed in the reversible bimolecular reaction, and the heat of reaction and activation energy are nearly equal to that of PVA. The rate constants of hydrolysis reaction (k′s) of model compounds were calculated on the basis of value of acetone ketal, Hammett-Taft's equation log k′s/k′so – 0.54(n – 6) = ρ*σ* was established, and the value of ρ* was obtained (3.60), which coincided with the value of PVA. Therefore, it was made clear that the hydrolysis reactions of acetals and ketals are electrophilic reaction (SE II reaction) and the step of rate determination is the formation of hemiacetal and hemiketal. The rate constants of hydrolysis reaction of 1,3-butanediol acetals and ketals were approximately 10–20 larger, and those of ethylene glycol were approximetly 50–80 larger except for ketals, and those of ethanol were roughly 2000–10,000 larger compared with that of high-molecular weight compound (PVA). It can be well explained that these differences in the rate constant depend on their entropy and the mobility of molecules. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1719–1931, 1997  相似文献   

2.
Poly(vinyl chloride) pendant with polysulfide (PS–PVC) having various degrees of substitution, various S substituents, and various numbers of atoms in the sulfur chain has been synthesized by the reaction of poly(vinyl chloride) with a thiol, sulfur, and triethylamine in dimethylformamide at 30°C for 0.4–5 hr. The photocrosslinking reaction has been investigated under ultraviolet irradiation at 250–450 mμ. The photocrosslinking reaction of PS–PVC is influenced by the degree of substitution, the nature of the S substituent, and the number of atoms in the sulfur chain. The degree of photocrosslinking r increased in the order, n-C4H9? < n-C8H17? < C6H5CH2? < i-C3H7? < t-C4H9? . On the photocrosslinking of PS–PVC having two different S substituents, r increases in the similar order for aliphatic substituents and in the order NO2C6H4? < ClC6H4? < C6H5CH2? < CH3C6H4? < t-C4H9C6H4? < C6H5? for the aromatic substituents. Further, r increases markedly with the increase of sulfur chain number for all PS–PVC. The chemical structure of the crosslinks and the crosslinking mechanism are discussed on the basis of the results.  相似文献   

3.
The kinetics of thermal decomposition of solid In(S2CNR2)3 complexes, (R=CH3, C2H5, n-C3H7,i-C3H7, n-C4H9 and i-C4H9), has been studied using isothermal and non-isothermal thermogravimetry. Superimposed TG/DTG/DSC curves show that thermal decomposition reactions occur in the liquid phase, except for the In(S2CNMe2)3 and In(S2CNPri 2)3 compounds. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

4.
The polymerization of diisobutylvinyloxyaluminum, CH2?CHOAl(i-Bu)2, and diethylvinyloxyaluminum, CH2?CHOAlEt2, did not take place in the presence of typical radical or cationic initiators. The polymerization was realized at 60°C by the addition of tetrahydrofuran (THF) or tetrahydropyran, no conventional initiator being required. Diethyl ether, glyme, and dioxane were not effective on the polymerization. At Dry Ice–acetone temperature, polymerization did not take place, even in the presence of tetrahydrofuran, but did take place in the presence of both THF and SnCl4. The role of cyclic ethers in the polymerization was studied. Polymers were converted into poly(vinyl alcohol) (PVA) by solvolysis. All the resulting PVA was syndiotactic; particularly polymers obtained at ?78°C showed syndiotactivity of 89%, which is the highest value ever reported.  相似文献   

5.
A composite film consisting of poly(o-phenylenediamine) (PoPD) and poly(vinyl alcohol) (PVA) has been prepared, and the effect of the protonation level of PoPD on the response of the composite to humidity been investigated by ac impedance measurements. The electrochemical system of the PoPD/PVA composite in a humid atmosphere is represented by an electrochemical equivalent circuit containing film (Rfilm, Cfilm), Warburg (W) and interfacial (Rct, Cdl) impedance. Rfilm was increased with decreasing protonation level of the PoPD in relative humidity regions higher than 40%, but it was almost independent of the protonation level in humidity regions lower than this percentage.  相似文献   

6.
The total Mulliken charges on the carbon atoms of the vinyl group, populations of S-trans-(N1)conformers, and internal rotation energies were calculated ab initio (HF/6-31G**, MP2/6-31G**, and MP2/6-31G**//AM1) for a series of 2R-5-vinyltetrazoles (R = CH3, C2H5, i-C3H7, t-C4H9, C6H5). The calculation results were compared to the available experimental data.  相似文献   

7.
Abstract

The first examples of compounds R1R2GeSe2C6H4R3 (R1,R2=CH3 C2H5, C3H2, n-C4H9, i-C5H11, Ph, p-CH3Ph. R3=H, CH3, OCH3) were easily obtained (40–80% yield) from electrophilic cleavage of diselenophenylene zirconocenes by dialkyl or diaryl dichlorogermanes. The synthesis of a spirodi-selenagermole was achieved in the same way using germanium tetrachloride. Analytical data, 1H and 77Se NMR. mass spectra are perfectly consistent with the expected structures.  相似文献   

8.
The 13C n.m.r. spectra of forty alkoxysilanes of the general type XnSi(OR)4–n (X = CH3, C6H5, H; R = CH3, C2H5, n-C3H7, i-C3H7, n-C4H9, i-C4H9, s-C4H9, n-C5H11, CH(CH3)(C6H5), C6H5) have been recorded and assigned. The chemical shifts of the α-carbon resonances of the alkoxy groups are shown to depend on both the nature of the alkoxy group and the number and type of substituents on the silicon. Regression analyses of the data give empirical substituent chemical shift (SCS) parameters for the silyl substituents. The β-carbon resonances are shown to be dependent on the presence of the silyl group, but not the specific silyl substituents.  相似文献   

9.
Permeation of eight gases (He, Ne, Ar, Kr, O2, N2, CO2, and CH4) in three isomeric poly(vinyl methylbenzoates) was measured by the time-lag method, and the effects of the shape of side groups on gas transport in the polymers were investigated. The p-methylphenyl side group of poly(vinyl p-methylbenzoate), which increases both interchain and intrachain distances, caused an increase in gas diffusivity. The diffusivity and density data were consistent with free volume theory. Two other isomeric polymers, poly(vinyl o-methylbenzoate) and poly(vinyl m-methylbenzoate), had lower gas diffusivities than poly(vinyl p-methylbenzoate) and poly(vinyl benzoate). The o-methyl and m-methyl groups on the phenyl ring were found to hinder gas diffusion, i.e., decrease the free volume. In contrast, the solubility of the gases in all these polymers was similar because of their similar chemical structures. The effects of hydroxyl groups also were investigated by the use of poly(vinyl m-methylbenzoate) containing a small number of vinyl alcohol units. The decrease in gas diffusivity was attributed to the decrease of free volume due to hydrogen bonding, but the change of gas solubility was still negligible.  相似文献   

10.
A convenient procedure to prepare photosensitive poly(vinyl alcohol) by acetalization with 1-methyl-4-(p-formylstyryl)pyridinium methosulfate in heterogeneous condition is described. The reaction of fully saponified poly(vinyl alcohol) was carried out in suspension in acidic aqueous solution, while partially saponified poly(vinyl alcohol) was acetalized in acidic aqueous organic solvent. The photosensitive poly(vinyl alcohol) thus prepared was purified by filtration and successive washing out with methanol. The effect of the preparative condition on the electronic absorption spectra of the styrylpyridinium group attached to poly(vinyl alcohol) is discussed.  相似文献   

11.
Telechelic ( 8 ) and end-functionalized four-arm star polymers ( 9 ) were synthesized through the coupling reactions of end-functionalized living poly(isobutyl vinyl ether) ( 5; DP n ~ 10) with the bi-and tetrafunctional silyl enol ethers, H4-nC? [CH2OC6H4C(OSiMe3) = CH2]n ( 3: n = 2; 4: n = 4). The precursor polymers 5 were prepared by living cationic polymerization with functionalized initiators, CH3CH(Cl)OCH2CH2X(6), in conjunction with zinc chloride in methylene chloride at ?15°C. The initiators 6 were obtained by the addition of hydrogen chloride gas to vinyl ethers bearing pendant functional groups X , including acetoxy [? OC(O)CH3], styryl (? OCH2C6H4-p-CH = CH2), and methacryloyl [? OC(O)C(CH3) = CH2]. The coupling reactions with 3 and 4 in methylene chloride at ?15°C for 24 h afforded the end-functionalized multiarmed polymers ( 8 and 9 ) in high yield (>91%), where those with styryl or methacryloyl groups are new multifunctional macromonomers. © 1994 John Wiley & Sons, Inc.  相似文献   

12.
Abstract

Durch selektive Grignardierungsreaktionen werden Verbindungen des Typs R(i-C3H7)PBr erhalten und in R(i-C3H7)P(S)Br überführt. Die chemische Verschiebung δ p in RR'P(S)Br (R,R' = CH3, C2H5, i-C3H7, t-C4H9) wächst linear mit der Zahl der ß-ständigen Methylgruppen in R und R'. AB3C3X-Spektren der i-C3H7P-Struktur-elemente werden berechnet.

Selective Grignard-type reactions lead to R(i-C3H7)PBr which are converted to R(i-C3H7)P(S)Br. Chemical shift values δ p in RR'P(S)Br (R,R' = CH3, C2H5, i-C3H7, t-C4H9) increase linearly with the number of ß-methyl groups in R and R'. AB3C3X-spectra are calculated for i-C3H7P-moieties.  相似文献   

13.
Tris-chloromethyl-phosphine oxide, (ClCH2)3 P?O(I), is obtained by chlorination of (HOCH2)3P?O with PCl5 or (C6H5)3PCl2, and also by oxidation of (CICH2)3P?O and (ClCh2)2(CH3)P?O. High yields of tris-(dialkyloxyphosphonly-methyl)-phosphine oxides, [RO2(O)PCH2]2P?O (II) (R?CH3, C2H5, iso-C3H7, n-C4H9, 2- ethyl-hexyl), tris (alkyloxyphosphinyl-methyl)-phosphine oxides, [R2(O)PCH2]3P?O(R = C6H5, CH3) are obtained by heating tris-chloromethyl-phosphine oxides, [(RO) (R′) (O)PCH2]3P?O (R = C4H9, R′? C6H5) and tris-(oxophosphoranyl-phosphine oxides with phosphites, phosphonites and phosphinites, respectively, at 170–180°C for several hours. Compounds II possess an extraordinarily high absorption capacity. Thus a warm. 2% solution of II (R = C2H5) in benzene solidifies completely on cooling so that no benzene can be poured off. Tris-dihydroxyphosphonyl-methyl)-phosphine oxide, [(HO)2(O)PCH2]3P?O, obtained by hydrolysis of II (R ? C2H5) with refluxing conc. HCl or by thermal decomposition of II (R ? iso-C3H7) at 190°, titrates in aqueous solution as a hexabasic acid with breaks at pH = 4,4 (three equivalents) and pH = 10,7 (three equivalents). It forms crystalline salts with amines, alkali and alkaline earth metals, and is an excellent chelating agent. The 1H- and 31?P-NMR. spectra of all the compounds prepared are discussed.  相似文献   

14.
The behaviour under electron impact (70 eV) which includes some rearrangement processes of some tetraorganodiphosphanedisulfides R2P(S)-P(S)R2 (R ? CH3, C2H5, n-C3H7, n-C4H9, C3H5, C6H5) and CH3RP(S)–P(S)CH3R (R ? C2H5, n-C3H7, n-C4H9, C6H5, C6H5, C6H5,CH2) is reported and discussed. Fragmentation patterns which are consistent with direct analysis of daughter ions and defocusing metastable spectra are given. The atomic composition of many of the fragment ions was determined by precise mass measurements. In contrast to compounds R3P(S) loss of sulphur is not a common process here. The first step in the fragmentation of these compounds is cleavage of one P–C bond and loss of a substituent R?. The second step is elimination of RPS leading to [R2PS]+ from which the base peaks in nearly all the spectra arise. The phenyl substituted compounds give spectra with very abundant [(C6H5)3P]+. and [(C6H5)2CH3P]+. ions respectively, resulting from [M]+. by migration of C6H5. Rearrangement of [M]+. to a 4-membered P-S ring system prior to fragmentation is suggested.  相似文献   

15.
The spontaneous polymer formed from 3-hydroxyoxetane (HO), as first reported by Wojtowicz and Polak, is linear, low molecular weight, water-soluble, atactic, poly(3-hydroxyoxetane) (PHO) of high crystallinity with ? OCH2CH(OH)CH2OH end units. The highly crystalline nature of this atactic polymer may be related to the crystalline nature of atactic poly(vinyl alcohol) since PHO can be considered a copolymer of vinyl alcohol and formaldehyde. Spontaneous PHO apparently is formed in a cationic polymerization by the carboxylic acids produced by the air oxidation of HO on standing at room temperature for several months. The polymerization can be duplicated by the addition of 2% hydroxyacetic acid to HO. The rate of this unusual cationic polymerization increases greatly with acid strength, e.g., trifluoromethanesulfonic acid reacts explosively with pure HO. A mechanism is proposed for this cationic polymerization. High molecular weight, water-soluble, linear atactic, and highly crystalline PHO (mp = 155°C) was made by polymerizing the trimethylsilyl ether of HO with the i-Bu3Al–0.7 H2O cationic catalyst followed by hydrolysis. Two 1H-NMR methods for measuring the tacticity of PHO were developed based on finding two different types of methylene units at 400 MHz with the methine protons decoupled. Also, an 1H-NMR method was developed for measuring branching in HO polymers. High molecular weight, linear PHO with enhanced isotacticity (80%) has been obtained in low yield as a water-insoluble fraction with Tm = 223°C. The low molecular weight PHO prepared previously by the base-catalyzed, rearrangement polymerization of glycidol is highly branched.  相似文献   

16.
Divinyl esters of dibasic acids, CH2?CHOCO(CH2)n?2COOCH?CH2, n = 2–10, were synthesized and polymerized with a radical initiator, and the structure of poly(vinyl alcohol)(PVA) derived from the polymers were studied. The cyclopolymerizability of these monomers was nearly equal to or less than that of divinyl carbonate which was previously reported, and the extent of cyclization was 15–65%. All the monomers yielded gelled polymers. The monomers which are to yield even-membered rings tend to cyclopolymerize more easily than those of odd-membered rings. PVA derived from these polymers showed a similar structure with respect to 1,2-glycol content and stereoregularity to that from poly(vinyl acetate).  相似文献   

17.
Five-membered cyclic esters of phosphoric acid of the general formula: ? CH2CH(R)OP(O)-(OR′)O? polymerize readily to solid, soluble polymers of high molecular weight without any rearrangement known for various tri- and pentavalent organophosphorus monomers. 1H-, 13C-, and 31P-NMR spectra of polymers confirmed their linear structure: where R is H, with R′ = CH3, C2H5, n-C3H7, i-C3H7; n-C4H9, CCl3CH2, or C6H5, or R is CH2Cl and R′ is C2H5. The use of n-C4H9Li, (C5H5)2Mg, or (i-C4H9)3Al as initiators leads to polymers with M n = 104–105.  相似文献   

18.
The dilute-solution behavior of poly(vinyl alcohol) (PVAVTFA), derived from vinyl trifluoroacetate, in water-dimethylsulfoxide (DMSO) mixtures was investigated. With solvent mixtures ranging from 10 to 20 vol % DMSO, the relation between the reduced viscosity ηsp/C and the polymer concentration C was linear for polymer concentrations above 0.2 g/dL, whereas in solutions in mixed solvents of other compositions the dependence was linear for polymer concentrations above 0.1 g/dL. The relation between the intrinsic viscosity [η] obtained for aqueous solutions of PVAVTFA and the molecular weight M estimated from viscosity measurements in solutions of poly(vinyl acetate) (PVAVTFA), obtained by acetylation of PVAVTFA, was given by [η] = 7.34 × 10?4 M0.63. The value of [η] was greatest for the solvent mixture with 10 vol % DMSO and smallest for about 50 vol % DMSO, and Huggins constants k were smallest and greatest for these two cases, respectively. The turbidity of the solutions of low-molecular-weight PVAVTFA, was higher than that of high-molecular-weight PVAVTFA up to 30 vol % DMSO, and the reverse relation held for 40-70 vol % DMSO.  相似文献   

19.
η2-Acyl and σ-Alkyl(carbonyl) Coordination in Molybdenum and Tungsten Complexes: Synthesis and Studies of the Isomerization Equilibria and Kinetics The anionic molybdenum and tungsten complexes [LRM(CO)3]? (LR? = [(C5H5)Co{P(O)R2}3]?, R = OCH3, OC2H5, O-i-C3H7; M = Mo, W) have been alkylated with the iodides R′ I, R′ = CH3, C2H5, i-C3H7, and CH2C6H5. The reactivity pattern of the alkylation is in accord with a SN2 mechanism. Depending on M, R′, reaction temperature, and time the η-alkyl (carbonyl) compounds [LRM(CO)3R′] and/or the isomeric η2-acyl compounds [LRM(CO)22-COR′)] can be obtained. 8 new σ-alkyl(carbonyl) compounds and 15 new η2-acyl compounds have been isolated and characterized. The 1H NMR and the IR spectra give conclusive evidence that the σ-alkyl(carbonyl) compounds [LRM(CO)3R′] are formed as the primary products of the alkylation and that they isomerize partly or completely to give the η2-acyl compounds [LRM(CO)22-COR′)]. The position of the equilibrium σ-alkyl(carbonyl)/η2-acyl is controlled by the steric demands of the groups R′ and the ligands LR?. The molybdenum compounds isomerize much more readily than the tungsten compounds. The rate constants of the isomerization processes [LRMo(CO)3CH3] → [LRMo(CO)22-COCH3)], R = OCH3, OC2H5, and O-i-C3H7, measured at 305 K in acetone-d6, are 6–8 x 10?3 s?1.  相似文献   

20.
Preparation of poly(phosphonoacetals) (PPA) by transacetalation of poly(vinyl alcohol) with diethyl-phosphonoacetal is described. PPA with a degree of substitution of 60% is an alcoholsoluble polymer with a glass transition temperature (Tg) of 67°C. High resolution 1H and 13C NMR spectra reveal the presence of hemiacetals alongside the six-membered acetal ring with an approximate ratio of 2:8 of these substituents. A possible correlation between the microtacticity of the parent PVA and the structure of PPA is indicated; the syndiotactic and isotactic sequences on the parent polymer controls the relationship between the two pendant groups.  相似文献   

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