摘要:

AbstractWe measured the15N‐,1H‐, and13C‐NMR chemical shifts for a series of aromatic diamines and aromatic tetracarboxylic dianhydrides dissolved in DMSO‐d6, and discuss the relationships between these chemical shifts and the rate constants of acylation (k) as well as such electronic‐property‐related parameters such as ionization potential (IP), electronic affinity (EA), and the energy ε of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The15N chemical shifts of the amino group of diamines (δN) depend monotonically on the logarithm ofk(logk) and on IP. We inferred the reactivities of diamines whose acylation rates have not been measured from their δN, and we propose an arrangement of diamines in the order of their reactivity. The1H chemical shift of amino hydrogens (δH) and the13C chemical shift of carbons bonded to nitrogen (δC) are roughly proportional to δN, but these shifts are not as closely correlated with logkand IP. Although the13C chemical shifts of the carbonyl carbon of dianhydrides (δC,) varies much less than the δCand δNof diamines, δC, can be an index of acylation reactivity for dianhydrides because it is closely correlated with εLUMO. These facts indicate that the chemical shifts of diamines and dianhydrides are displaced according to their electron‐donor and electron‐acceptor properties, and that these chemical shifts can be used as indices of the electronic properties of monomers. Changes in reactivity caused by the introduction of trifluoromethyl groups into diamines and dianhydrides are inferred from the displacements of δNand δ

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301101

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractAcid‐catalyzed hydolysis of bis(ethyl acetoacetato) zirconium dialkoxide in methanol or THF was investigated. The hydrolysis of the chelates in the molar ratios of H2O/ chelate = 1.0–2.0 and HCl/chelate = 0.1–0.2 provided concentrated solutions (ca. 83 wt %) of polyzirconoxanes (PZO) which showed excellent spinnability and stability to self‐condensation. Continuous gel fibers were prepared by dry spinning the solutions. Polyzirconoxanes were isolated as powders when the concentrated solution was precipitated with hexane. Silylation allowed the investigation of the structure of PZO. It was confirmed to be the polymers of a low degree of polymerization with the ligand and hydroxy group as pendants. © 1992 John Wiley&S

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301102

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractAllyl cellulose was synthesized by reacting cellulose with allyl bromide in homogeneous LiCl/DMAc solution containing NaOH powder. The degree of substitution (DS) per anhydroglucose (AHG) unit was determined by titrating the allyl cellulose with bromine in chloroform solution, and an allyl DS of 2.80 was found. Glycidyl cellulose was then prepared by reacting this allyl cellulose with peracetic acid in methylene chloride at ambient temperature for 6 days. The measured reaction rate constant was 1.33 × 10−3min−1. The glycidyl cellulose thus obtained with a glycidyl DS of 2.58 was determined by titrating the product with perchloric acid in conjunction with tetrabutylammonium iodide. The 2.58 of glycidyl DS was also confirmed by1H‐NMR integration. Both allyl cellulose and glycidyl cellulose were analyzed and characterized with FTIR,1H‐NMR,13C‐NMR, TGA, and GPC. During epoxidation of allyl cellulose, possible side reaction leading to ester formation was evidenced from the continuous increase ofvCOat 1735 cm−1in FTIR analyses. In addition, a bimodal distribution and a decreased molecular weight for glycidyl cellulose were found from GPC data, which might suggest a possible chain scission at the cellulosic ether linkage. © 1992 John

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301103

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractEthyl α‐hydroxymethylacrylate (EHMA) was polymerized in a 3 mol/L tetrahydrofuran solution at 50°C, using 2–2' azobisisobutyronitrile as initiator. The kinetic behavior indicates a higher polymerization rate for EHMA than for methyl methacrylate (MMA). Copolymerization reaction between MMA and EHMA, under the same experimental conditions, was carried out and values ofrMMA= 1.264 andrEHMA= 1.285 were found for the reactivity ratios. The comparison of triad sequences as determined from Bernouillian statistic to those calculated from the experimental spliting ofO‐methyl and α‐methyl1H‐NMR signals of the copolymers confirm the obtained results. © 1992 John Wi

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301104

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThermal decompositions and pyrolyses ofp‐tert‐butylphenol, 4,4'‐isopropylidenediphenol (BPA), and their acetate and pivalate esters as model compounds for the polyarylate synthesis have been performed. Acetate esters decompose chiefly into phenols and ketene. Pivalate esters, unable to form ketene, are more stable. Acetates and pivalates undergo homolytic cleavage both at ester and alkyl groups. Styrene derivatives stabilize acetate esters, considerably reducing the amount of phenol formed during the decomposition. No intensely colored aromatic compounds were found, although this result is probably an artifact of the methods used. From this study we conclude that ketene is one source of colored materials during polyarylate synthesis. © 1992 John Wiley&Son

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301105

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractIn this work several polyorganosilylenes were synthesized including homo‐and copolymers containing SiMe2and SiPh2units. A Wurtz‐type coupling reaction of the respective dichlorodiorganosilanes with sodium metal, varying the Ph2SiCl2/Me2SiCl2ratio was the chosen synthesis method. Products with different characteristics for solubility, structure (cyclic or linear), composition, and molecular weight distribution could be obtained depending on the comonomer ratios employed. The polysilane derivatives were characterized by infrared spectroscopy (IR), proton nuclear magnetic resonance (1H‐NMR), and gel permeation chromatography (GPC). Valuable information related to the comonomers' reactivities was obtained, such as molecular weight distribution, composition, and relationships between yields of soluble, insoluble, and cyclic materials of each polycondensation reaction. © 1992 John Wiley&Son

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301106

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe synthesis of a series of novel cyano‐containing copolymers is described. Alternating copolymers of acrylonitrile with vinyl esters are obtained by increasing the electrophilic character of the nitrile monomers by complexation with zinc chloride. Copolymers of methyl and ethyl α‐cyanoacrylates with vinyl esters are prepared using radical initiators in the presence of 7% acetic acid as inhibitor for anionic polymerization. The copolymers of methyl α‐cyanoacrylate with the vinyl esters haveTg's above 140°C. Methyl vinylidene cyanide (MVCN) copolymerizes spontaneously with para‐substituted styrenes to yield copolymers with high inherent viscosities and highTg(160°C) and the copolymer of MVCN with vinyl acetate is also synthesized. The pyroelectric constantspfor these polymers were measured and the values ofpfor the copolymers of vinyl acetate with methyl β,β‐dicyanoacrylate, methyl α‐cyanoacrylate, or MVCN were in the same range as the well‐studied vinylidene cyanide/vinyl acetate copolymer. A higher concentration of dipoles generally results in higherTg's and higher pyroelectric coefficients. © 1992

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301107

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe carbonation of the adduct of poly(styryl)lithium with 1,1‐diphenylethylene with gaseous carbon dioxide in benzene proceeds in high yield (>99%) compared to the inefficient functionalizations for poly(styryl)lithium (66%), poly(isoprenyl)lithium (59%), and polybutadienyl)lithium (27%). The quantitative carboxylation of poly(isoprenyl)lithium and poly(butadienyl)lithium requires the presence of larger amounts of Lewis bases such as THF ([THF]/[Li]= 300) or TMEDA ([TMEDA]/[Li]= 46) compared to poly(styryl)lithium in which a ratio of [TMEDA]/[Li]= 12 is effective. © 1992 John Wiley&Sons, I

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301108

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractRandom and block disiloxane‐containing copolyamides were prepared through one‐ and two‐step procedures, respectively, by the low temperature solution polycondensation in chloroform containing triethylamine hydrochloride starting from 1,3‐bis(3‐aminopropyl)tetramethyldisiloxane, an aromatic diamine [3,4'‐diaminodiphenyl ether (ODA) orm‐phenylenediamine], and isophthaloyl chloride. The random copolyamides exhibited composition‐dependent single glass transition temperature (Tg), and gave transparent and tough films by solution casting or hot pressing. The ODA‐based block copolyamides had twoTg's, and the solvent‐cast transparent films exhibited microphase separated morphology. The block copolymers gave better quality films than the single‐phase random copolymers. © 199

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301109

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractBenzyl cation was detected by transient absorption spectroscopy with a spectroscopic multichannel analyzer on pulse excitation (fourth harmonic of Nd:YAG laser, 266 nm; 10 ns fwhm) of benzyl(4‐hydroxyphenyl) methylsulfonium hexafluoroantimonate(BSS) in 1,2‐dichloroethane (EDC). The benzyl cation was long‐lived (lifetime, 59 ms) at room temperature and quenched by a vinyl ether compound. The formation of the benzyl cation as active species on photolysis of BSS is in contrast to the formation of Brønsted acids in other sulfonium salts so far reported. © 1992 John Wiley&So

ISSN:0887-624X    

DOI:10.1002/pola.1992.080301110

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY