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1.
James C. W. Chien Phillipe Bres 《Journal of polymer science. Part A, Polymer chemistry》1986,24(8):1967-1988
The effect of external Lewis base (Be) on the polymerization of ethylene by the MgCl2/ethyl benzoate/p-cresol/AlEt3/TiCl4 catalyst was studied by activation with AlEt3 alone without the use of methyl-p-toluate. The initially formed active site concentration, [Ti], is about doubled in the absence of Be; at 50°C about 93% of the total titanium became catalytic. The same increment of [Ti] was observed without Be. The rate constants of propagation are not appreciably affected by Be; the values are the same at 50° with and without Be. At other temperatures the kp values are somewhat smaller without Be. One major effect was the very large k values for chain transfer with aluminum alkyls in the absence of Be as compared to those with Be. This can be attributed to the greater monomeric AlEt3 concentration in the former, but in much smaller amounts in the presence of Be due to complexation. The rate constants of chain transfer with hydrogen are not much affected by Be. However, the termination rate constants are generally much smaller when Lewis base is not present. 相似文献
2.
James C. W. Chien Phillipe L. Bres 《Journal of polymer science. Part A, Polymer chemistry》1986,24(10):2483-2505
Polymerizations of ethylene by the MgCl2/ethylbenzoate/p-cresol/AlEt3 TiCl4-AlEt3/methyl-p-toluate (CW-catalyst) have been studied. The initially formed active site concentration, [Ti] has a maximum value of 50% of total titanium at 50°C and lower values at other temperatures. The Ti decays rapidly to Ti sites with conc. ca. 10 mol %/mol Ti. The rate constants for four chain transfer processes have been obtained at 50°C: for transfer with AlEt3, k = 2.1 × 10?4 s?1 and k = 4.8 × 10?4 s?1; for transfer with monomer, k = 3.6 × 10?3 (M s)?1 and K = 8.3 × 10?3 (M s)?1; for β-hydride transfer, k = 7.2 × 10?4 s?1 and k = 4.9 × 10?4 s?1; and transfer with hydrogen, k = 4.0 × 10?3 torr1/2 s? and k = 5.1 × 10?3 torr1/2 s?1. The rate constants for the termination assisted by hydrogen is k = 1.7 (M1/2 torr1/2 S)?1. If monomer is assisting termination as was observed for propylene polymerization, then k = 7.8 (M3/2 s)?1. Values of all the rate constants can be higher or lower at other temperatures. Detailed comparisons were made with the results of propylene polymerizations. There are more than four times as many Ti active sites for ethylene polymerization than there are for stereospecific polymerization of propylene; the difference is more than a factor of two for the Ti sites. Certain rate constants are nearly the same for both monomers while others are markedly different. Some of the differences can be explained by stereoelectronic effects. 相似文献
3.
4.
Pierre Lebreton Bernard Boutevin 《Journal of polymer science. Part A, Polymer chemistry》2000,38(10):1834-1843
Acrylamide was polymerized in acetonitrile at 82 °C with a perfluorinated azo‐derivative initiator. The polymerization proceeded heterogeneously. Varying amounts of initiator and monomer were used. The activation energy was deduced from three experiments carried out at 59, 71, and 82 °C. The following kinetic law, deviating a great deal from the classical law, was obtained: R ∼ [I2][M](0.05% < [I2]o/[M]o < 1.00%) and R ∼ [I2][M](1% < [I2]o/[M]o < 7%). These results can be interpreted in light of the contribution of primary radical termination and the emergence of occlusion. The development of a new kinetic relationship allowed us to confirm the existence of both of these termination reactions. The calculation of the kprt /ki · kp ratio was also achieved. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1834–1843, 2000 相似文献
5.
Tokio Hagiwara Takamasa Shimizu Tomonori Uda Hiroshi Hamana Tadashi Narita 《Journal of polymer science. Part A, Polymer chemistry》1990,28(1):185-192
The kinetic feature of the anionic polymerization of N-PMI was investigated in THF. The polymerization system initiated with lithium tert-butoxide was revealed to be so-called “slow-initiation” system. The rate constant of the initiation reaction, ki, was obtained to be 4.2 × 10?3 (L mol?1 s?1) at ?72°C. The apparent rate constants of the propagation reaction, k, at ?72°C were individually obtained from each slope of the first-order plots in the later stages of the polymerizations for four different initiator concentrations. Each k is fairly close to that of initiation rate around 10?3. The propagation reaction was concluded to be dominated by ion-pair mechanism from the analysis of the kinetic data and the results of the addition effects of crown ether and common salt. 相似文献
6.
Takashi Nozaki James C. W. Chien 《Journal of polymer science. Part A, Polymer chemistry》1991,29(12):1807-1817
Solvay type S –VCl3 catalyst has 7% of catalytically active vanadium sites ([C*]) with kp (rate constant of propagation) = 31 (M s)?1 for ethylene polymerization. Addition of a comonomer, propylene of 4-methylpentene-1 (4-MP) significantly raised the ethylene polymerization activity. S –VCI3 catalyst has very small amounts of catalytically active vanadium for propylene polymerizations: [C] = 0.19% with kp,i = 857 (M s)?1 and [C] = 0.45% with kp,a = 23 (M s)?1 for isospecific and nonspecific sites, respectively. Addition of a conomer, ethylene or 4-MP. lowered the propylene polymerization activity. S –VCI3 is more easily reduced to the divalent ion by AIR3 than S –TiCl3. Methyl-p-toluate moderates the reducting power of AIR3; it increase the productivity and stereoselectivity of the S –YiCl3 catalyst, VCI3 supported on MgCl2 (CW–V catalyst) has enhanced rate constant of propylene polymerization but has the opposite effects on the S –TiCl3 Catalyst. VCI3 supported on MgCl2 (CW–V catalyst) has enhances rate constant of propylene polymerization but only a minute fraction of the supported vanadiums are catalytically active: [C] = 0.019% and kp,i = 1580 (Ms)?1, [C] = 0.057% and kp,i = 58 (M s)?1. This is compared with far greater number of catalytically active titanium sites in the TiCl3 supported on MgCl2 catalyst: [C] = 6% and kp,i = 200 (M s)?1, [C] = 6% and kp,a = 16(M s)?1. Therefore, both the S –VCI3 and CW–V catalysts are highly stereoselective but low in efficiency with respect to the utilization of the vanadium ion in the catalysis. 相似文献
7.
James C. W. Chien Zdenek Salajka 《Journal of polymer science. Part A, Polymer chemistry》1991,29(9):1253-1263
Syndiospecific polymerization of styrene was catalyzed by monocyclopentadienyltributoxy titanium/methylaluminoxane [CpTi (OBu)3/MAO]. The atactic and syndiotactic polystyrenes were separated by extracting the former with refluxing 2-butanone. The activity and syndiospecificity of the catalyst were affected by changes in catalyst concentration and composition, polymerization temperature, and monomer concentration. Extremely high activity of 5 × 107 g PS (mol Ti mol S h)?1 with 99% yield of the syndiotactic product were achieved. The concentration of active species, [C*], has been determined by radiolabeling. The amount of the syndiospecific and nonspecific catalytic species, [C] and [C] respectively, correspond to 79 and 13% of the CpTi(OBu)3. The rate constants of propagation for C and C at 45°C are 10.8 and 2.0 (M s)?1, respectively, the corresponding rate constants for chain transfer to MAO are 6.2 × 10?4 and 4.3 × 10?4s?1. There was no deactivation of the catalytic species during a batch polymerization. The rate constant of chain transfer with monomer is 6.7 × 10?2 (M s)?1; the spontaneous β-hydride transfer rate constant is 4.7 × 10?2 s?1. The polymerization activity and stereospecificity of the catalyst are highest at 45°C, both decreasing with either higher or lower temperature. The stereoregular polymer have broad MW distributions, M?w/M?n = 2.8–5.7, and up to three crystalline modifications. The Tm of the s-PS polymerized at 0–90°C decreased from 261.8 to 241°C indicating thermally activated monomer insertion errors. The styrene polymerization behaviors were essentially insensitive to the dielectric constant of the medium. 相似文献
8.
Katherine B. Aubrecht Karen Chang Marc A. Hillmyer William B. Tolman 《Journal of polymer science. Part A, Polymer chemistry》2001,39(2):284-293
In quest of new, single‐site catalysts for cyclic ester polymerizations, a series of mononuclear yttrium(III) complexes of N,N′‐bis(trimethylsilyl)benzamidinate ([LTMS]−) and hindered N,N′‐bis‐(2,6‐dialkylaryl)toluamidinates ([LEt]−, aryl = Et2C6H3, and [LiPr]−, aryl = iPr2C6H3) were synthesized and characterized by X‐ray diffraction: LY(μ‐Cl)2Li(TMEDA) ( 1 ), LY(OC6H2tBu2Me) ( 2 ), LY(OC6H3Me2)2Li(THF)4 ( 3 ), LY(μ‐OtBu)2Li(THF) ( 4 ), LiPrY[N(SiMe2H)2]2(THF) ( 5 ), LY(THF)(Cl)(μ‐Cl)Li(THF)3 ( 6 ), and LY[N(SiMe2H)2] ( 7 ). Coordination numbers ranging from five to seven were observed, and they appeared to be controlled by the steric bulk of the supporting amidinate and alkoxide, phenoxide, or amide coligands. Complexes 2 – 5 and 7 are active catalysts for the polymerization of D,L ‐lactide (e.g., with 2 and added benzyl alcohol, 1000 equiv of D,L ‐lactide were polymerized at room temperature in less than 1 h, with polydispersities less than 1.5). The neutral complexes 2 , 5 , and 7 were more effective than the anionic complexes 3 and 4 . In addition, the presence of the more hindered amidinate ligands [LEt]− and [LiPr]− on yttrium‐amides slowed the polymerizations ( 7 < 5 < Y[N(SiMe2H)2]3). © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 284–293, 2001 相似文献
9.
James C. W. Chien Tsunle Ang 《Journal of polymer science. Part A, Polymer chemistry》1987,25(3):919-934
Decene-l was polymerized with the MgCl2/ethylebenzoate/p-cresol/AIEt3/TiCl4-AlEt3/methyl-p-toluate catalyst at 50° using an A/T ratio of 167 and a range of monomer concentration. The concentration of the two kinds of active sites are [Ti] = 12% and [Ti] = 4% of the total titanium. The rate constants of propagation are 24 M?1 s?1. Chain transfers to AIEt3, monomer, and by β-hydride elimination have rate constant values of 1.7 × 10?3 M?1 s?1, 1.34 × 10?2 M?1 s?1, and 1.7 × 10?2 s?1, respectively. Poly(decene-l) have relatively narrow MW which are unchanged during the course of a polymerization. Therefore, the active site concentrations in the CW catalyst for propylene and decene polymerization are identical and their rate constant values agree within a factor of 2. However, the rate of decene polymerization depends on fractional order of monomer concentration and decreases with the increase of activator concentration. Furthermore, the formation of metal polymer bonds has a rate independent of these concentrations. These kinetic behaviors are a manifestation of absorption processes of these species which are not seen in propylene polymerizations. 相似文献
10.
Gorkem Yilmaz Selim Beyazit Yusuf Yagci 《Journal of polymer science. Part A, Polymer chemistry》2011,49(7):1591-1596
The free radical promoted cationic polymerization cyclohexene oxide (CHO), was achieved by visible light irradiation (λinc = 430–490 nm) of methylene chloride solutions containing thioxanthone‐fluorene carboxylic acid (TX‐FLCOOH) or thioxanthone‐carbazole (TX‐C) and cationic salts, such as diphenyliodonium hexafluorophosphate (Ph2I+PF) or silver hexafluorophosphate (Ag+PF) in the presence of hydrogen donors. A feasible initiation mechanism involves the photogeneration of ketyl radicals by hydrogen abstraction in the first step. Subsequent oxidation of ketyl radicals by the oxidizing salts yields Bronsted acids capable of initiating the polymerization of CHO. In agreement with the proposed mechanism, the polymerization was completely inhibited by 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy and di‐2,6‐di‐tert‐butylpyridine as radical and acid scavengers, respectively. Additionally polymerization efficiency was directly related to the reduction potential of the cationic salts, that is, Ag+PF (E = +0.8 V) was found to be more efficient than Ph2I+PF (E = ?0.2 V). In addition to CHO, vinyl monomers such as isobutyl vinyl ether and N‐vinyl carbazole, and a bisepoxide such as 3,4‐epoxycyclohexyl‐3′,4′‐epoxycyclohexene carboxylate, were polymerized in the presence of TX‐FLCOOH or TX‐C and iodonium salt with high efficiency. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
11.
Pierre Sigwalt Michel Moreau 《Journal of polymer science. Part A, Polymer chemistry》2010,48(12):2666-2680
In carbocationic polymerization and copolymerization, a recent publication concluded that the substituent effect on carbocation reactivity is much larger than its effect on monomer reactivity, and this by a factor 106 in the case of the rate constant k12capp for p‐methylstyrene addition (monomer M2) on, respectively, poly(p‐methoxystyrene)± or poly(p‐methylstyrene)± (M). This conclusion is disputed, as well as the assumption that the rate constants of capping (k12capp) obtained in deactivation reactions of poly(p‐methoxystyrene)± are identical with cross propagation rate constants in copolymerization (k12copol). It is shown that the large calculated k12capp are based on propagation constant values for p‐methylstyrene (k ≈ 109) obtained by the diffusion‐clock method. They are 104 times smaller as found for all styrenes, that is, between 104 and 105 when they are based on the ionic species concentrations. In such a case, the available data are still in agreement with an approximate compensation between the reactivities of a monomer and of the corresponding carbocation. It is also shown that copolymerization data for styrenes are not compatible with k values near to diffusion control, and that variations of log k12capp and log k12copol with the nucleophilicity parameter N of the monomers indicate a much lower selectivity of the monomers in the case of copolymerization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2666–2680, 2010 相似文献
12.
James C. W. Chien Tsunle Ang 《Journal of polymer science. Part A, Polymer chemistry》1986,24(9):2217-2230
Decene-1 was polymerized with the CW catalyst and fractionated by precipitation technique. Light-scattering and viscometric measurements on these fractions established the relationship [η] = 5.19 × 10?3 M . The unperturbed mean square end-to-end distance is (〈R〉/M)1/2 = (6.17 ± 0.34) × 10?9. Light-scattering data is consistent with a relatively stiff molecule with length of L = 1.75 × 10?5 cm for poly(decene-1) with MW = 397,000. Its mean square radius of gyration 〈R〉 is 2.79 × 10?11 cm.2 The ratio of L2/〈R〉 = 11 is close to the theoretical ratio of 12 for this kind of macromolecule. 相似文献
13.
Yohann Guillaneuf Jean‐Philippe Lamps Jean‐Marie Catala Didier Gigmes Eric Drockenmuller 《Journal of polymer science. Part A, Polymer chemistry》2012,50(18):3750-3757
A new dialkylated α‐hydrogenated linear nitroxide and the corresponding 1‐phenylethyl alkoxyamine were synthesized in two and three steps, respectively. The alkoxyamine was involved in the polymerization of styrene at 60 °C, and the in situ concentration of nitroxide was monitored by electron spin resonance spectroscopy. The enhanced characteristics of these new alkylated alkoxyamine and nitroxide (k = 1.5 × 10?4 s?1 and k = 5.7 × 104 L mol?1 s?1) yielded a monomer consumption one order of magnitude higher than styrene thermal polymerization. This resulted in well‐defined polystyrenes up to 70,000 g mol?1 and the observation of a control occurring through the establishment of the radical persistent effect, that is, ln([M]0/[M]) = t2/3. Experimentally determined kinetic constants were involved in PREDICI modelings to investigate the influence of temperature and initial alkoxyamine concentration on the kinetics as well as on the livingness and the controlled character of the polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
14.
Koji Ishizu Masataka Nunomura Takashi Fukutomi 《Journal of polymer science. Part A, Polymer chemistry》1987,25(4):1163-1175
Soluble microgels with several pendant vinyl groups were synthesised by radical copolymerization of methyl methacrylate (MMA) with p-divinyl benzene (p-DVB). The competitive reactions of intermolecular and intramolecular crosslinkings of these microgels were carried out at 40°C in the presence of 1-buten-3-ol as a degradative chain transfer agent. The rate constant of intermolecular crosslinking (k) was estimated by GPC (gel permeation chromatography) analysis on the polymer produced from intermolecular propagation between bimolecules. The k depended strongly on the internal structure of microgels. Network formation was discussd inclusive of informations for the rate constant of intramolecular crosslinking (k). 相似文献
15.
Bin Luan Bao‐Qing Zhang Cai‐Yuan Pan 《Journal of polymer science. Part A, Polymer chemistry》2006,44(1):549-560
A well‐defined branched copolymer with PLLA‐b‐PS2 branches was prepared by combination of reversible addition‐fragmentation transfer (RAFT) polymerization, ring‐opening polymerization (ROP), and atom transfer radical polymerization (ATRP). The RAFT copolymerization of methyl acrylate (MA) and hydroxyethyl acrylate (HEA) yielded poly(MA‐co‐HEA), which was used as macro initiator in the successive ROP polymerization of LLA. After divergent reaction of poly(MA‐co‐HEA)‐g‐PLLAOH with divergent agent, the macro initiator, poly(MA‐co‐HEA)‐g‐PLLABr2 was formed in high conversion. The following ATRP of styrene (St) produced the target polymer, poly(MA‐co‐HEA)‐g‐(PLLA‐b‐PS2). The structures, molecular weight, and molecular weight distribution of the intermediates and the target polymers obtained from every step were confirmed by their 1H NMR and GPC measurements. DSC results show one T = 3 °C for the poly(MA‐co‐HEA), T = ?5 °C, T= 122 °C, and T = 157 °C for the branched copolymers (poly(MA‐co‐HEA)‐g‐PLLA), and T = 51 °C, T = 116 °C, and T = 162 °C for poly(MA‐co‐HEA)‐g‐(PLLA‐b‐PS2). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 549–560, 2006 相似文献
16.
Li‐Ming Huang Guo Cheng Huang Ten‐Chin Wen 《Journal of polymer science. Part A, Polymer chemistry》2006,44(22):6624-6632
Poly(2,5‐dimethoxyaniline) (PDMA)–Ag composites were successfully obtained through the oxidative polymerization of 2,5‐dimethoxyaniline in poly(styrene sulfonic acid) with CH3SO3Ag and AgNO3 as oxidants. In situ ultraviolet–visible spectroscopy results showed that the growth rate of PDMA was strongly affected by CH3SO and NO. The coupling reaction of PDMA and NO was proposed to explain the lower growth rate of PDMA with AgNO3 as the oxidant in comparison with CH3SO3Ag. X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to validate the proposed coupling reaction through the monitoring of the side products and oxidized state of PDMA. The results showed that there were more side products and lower oxidized states for the composite structure in the presence of NO than in the presence of CH3SO, and this agreed with the proposal. Transmission electron microscopy showed that the Ag nanoparticles had almost the same size, regardless of the anions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6624–6632, 2006 相似文献
17.
Mohammed Hmamouchi Robert E. Prud'homme 《Journal of polymer science. Part A, Polymer chemistry》1988,26(6):1593-1607
R(+) and S(?) enantiomers of α-methyl β-propiolactone (MPL) have been synthesized from the corresponding α-methyl β-hydroxymethylpropionates and racemic MPL from methyl methacrylate. The optical purity and absolute configuration of these lactones were determined using 1H-NMR spectroscopy after complexation with a chiral compound: 2,2,2-trifluoro-1-(9-anthryl)-ethanol. Optical purities of 100% were obtained for both the S(?) ([α0] = ?10.4°, c = 1.3 g/dL in CHCl3) and the R(+) ([α0] = +10.5°, c = 1.0 g/dL in CHCl3) enantiomers. The corresponding racemic and optically active polylactones [poly(MPL)] were prepared by anionic polymerization, in bulk and in solution, as well as poly(MPL)s of intermediate optical purities. The polymers thus obtained are optically active ([α0] = 16.2° in CHCl3 for the optically pure polymer, S configuration) and exhibit significant differences. For example, the racemic poly(MPL) is soluble in several organic solvents such as tetrahydrofuran, benzene, CCl4, CH2Cl2, hexafluoroisopropanol, and CHCl3, whereas the optically active poly(MPL)s are soluble in CHCl3 and hexafluoroisopropanol only. Moreover, racemic poly(MPL) is amorphous whereas optically active poly(MPL)s are semicrystalline for optical purities larger than 51%. Melting temperatures and enthalpies of fusion of the semicrystalline polylactones vary with optical purity whereas glass transition temperatures remain invariant for all polymers, at about ?28°C. The poly(MPL) of highest optical purity exhibits a melting temperature of 95°C and an enthalpy of fusion of 61 J/g. 相似文献
18.
Norio Tsubokawa Yu Jian Yasuo Sone 《Journal of polymer science. Part A, Polymer chemistry》1988,26(10):2715-2724
The cationic ring-opening polymerization of oxepane was found to be initiated by carbon black having acylium perchlorate (CO+CIO) groups, which were introduced by the reaction of acyl chloride groups with silver perchlorate. It was confirmed that polyoxepane, i.e., poly(oxyhexamethylene), was propagated from CO+CIO groups on carbon black and effectively grafted on the surface. The rate of the polymerization and the percentage of grafting of poly(oxyhexamethylene) remarkably increased by the addition of epichlorohydrin (ECH) as a promoter: the percentage of grafting in the presence of ECH increased to about 100% with an increase in conversion. Furthermore, CO+CIO groups on carbon black have an ability to initiate the cationic ring-opening copolymerization of oxepane with ECH to give poly(oxepane-co-ECH) with various composition. The ring-opening copolymerization of oxepane with phthalic anhydride was also initiated by CO+CIO groups to give polyether ester, i.e., poly(hexamethylene phthalate) containing poly(oxyhexamethylene) sequence. In the copolymerization, polyether or polyether ester was effectively grafted from carbon black based on the propagation of these polymers from CO+CIO groups. 相似文献
19.
M. Fernndez‐García M. Fernndez‐Sanz E. L. Madruga 《Journal of polymer science. Part A, Polymer chemistry》2004,42(1):130-136
The free‐radical copolymerization of styrene and butyl acrylate has been carried out in benzene at 50 °C. The lumped k p/k parameter (where k p and k t are the average copolymerization propagation and termination rate constants, respectively) has been determined. Applying the implicit penultimate unit model for the overall copolymerization propagation rate coefficient and the terminal unit effect for the overall copolymerization termination rate coefficient and using the homopolymerization kinetic coefficients, we have found good qualitative agreement between the experimental and theoretical k p/k values. The variation of the copolymerization rate in solution with respect to the values previously found in bulk has been ascribed to a chain length effect on the copolymerization termination rate coefficient. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 130–136, 2004 相似文献
20.
Se Geun Lee Jae Pil Kim Ick Chan Kwon Ki Hong Park Seok Kyun Noh Sung Soo Han Won Seok Lyoo 《Journal of polymer science. Part A, Polymer chemistry》2006,44(11):3567-3576
Poly(vinyl alcohol) (PVA)/poly(vinyl acetate) (PVAc) microspheres with a skin/core structure were prepared through the heterogeneous surface saponification of PVAc microspheres suspension‐polymerized. The PVA skin formed through the heterogeneous saponification was hydrogel swellable in water. In addition, to obtain monodisperse PVA/PVAc microspheres having various skin/core ratios and morphologies, the ion‐specificities to the heterogeneous saponification were investigated using SO, Cl?, NO, Br?, and I? for anions and Li+, Na+, and K+ for cations, respectively. The ions were not specific significantly to the rate of the heterogeneous saponification, while were related to the degree of saponification (DS). DSs had different values between by weight loss (DSw) and by proton nuclear magnetic resonance spectroscopy (DSNMR) measurements. The order of DSws was SO < Cl? < NO < Br? < I? for anions and K+ < Na+ < Li+ for cations, and that of DSNMRs, I? < Br? < NO < Cl? < SO for anions and Li+ < Na+ < K+ for cations. The differences in values between DSws and DSNMRs were caused by the dissolution of PVA skin and were significantly decreased for SO. The peaks at melting temperature of PVA were sharp and their areas were large for ions deswelling PVA skins. 相似文献