摘要:

AbstractThe thermal degradation of poly(vinylfluoride) (PVF) was studied under slow heating conditions to 1000°C with and without the presence of air. The degradation products, classified as low‐boiling volatiles, high‐boiling volatiles, and nonvolatile residues, were analyzed quantitatively by gas chromatography—mass spectrometry and several spectroscopic methods. Initial stages of degradation begin at 420°C with the evolution of HF and benzene and rapidly reach a maximum in sample weight loss by 450°C. One‐third of this weight loss was in the form of hydrofluoric acid (HF) and at least 70 low‐boiling volatile compounds that consisted of substituted aromatics, unsaturated hydrocarbons, and multiple‐ring compounds, many of which contained a fluorine atom. The high‐boiling volatile fraction contained compounds with more aliphatic but less aromatic character than the low‐boiling. The nonvolatile residue retained 4% of the original fluorine content and exhibited strong unsaturated character. In the presence of oxygen HF, CO, and H2O were the major constituents of the low‐boiling volatiles; the organic fraction was essentially unchanged in composition but reduced in overall concentration. The overall weight‐loss process was bimodal in air and produced a thermally resistant residue that degraded by 650°C. A comparison of degradation products from poly(vinylchloride) with this work demonstrates that PVF forms more lower‐molecular‐weight, halogen‐containing compounds, whereas the former produced more HCl and nonvolatile residue conta

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210611

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractCopolymers ofp‐vinyltrifluoroacetophenone (VTFA) with optically active (−)‐menthyl acrylate (MtA) have been prepared by free radical initiation. The values of reactivity ratios (rVTFA= 4.28 andrMtA= 0.26) indicate that counits are inserted substantially at random into the copolymer macromolecules. CD spectra show a couplet typical of exciton splitting in the absorption region of trifluoromethylphenyl (TFA) chromophore. Dependence of ellipticity on composition and sequence distribution suggests that TFA chromophores are in a chiral environment provided by the dissymmetric conformation of the copolymer macromole

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210612

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractAn optically active polypeptide, poly(trans‐5‐ethylproline) (PT5EP) was synthesized and its solution properties were observed to investigate the conformational changes with various conditions. Thetrans‐5‐ethyl substitution on polyproline showed noticeable perturbed effects on the conformations of the polypeptide as well as mutarotation of the polypeptide in solution. Circular dichroism (CD) spectra suggested that the polypeptide existed in a poly(L‐proline) form‐I‐type helix and mutarotated slowly to an intermediate conformation in which some of the amide bonds had rotated to a trans conformation. In trifluoroethanol (TFE) solution the polymer took more than 20 days to change from a form‐I‐type helix conformation, in which CD bands forD‐PT5EP are at 199.5 ± 1.0 (positive), 115.5 ± 0.5 (negative), and around 238 nm (positive), to an intermediate conformation. Upon addition of trifluoroacetic acid (TFA) to a TFE solution, the polymer was transformed to form‐II‐type polymers. Even a greater change in conformation was observed in a solution of TFA or in LiClO4‐TFE. The overall change of the intensity ratioRCDof positive to negative CD bands ofD‐PT5EP was from 0.6–0.7 to 30. Reverse mutarotation toward the original form I was observed whenn‐butyl alcohol, water, or THF was added to a solution containing the form II polymer. A blue shift of the UV spectra and a change in the NMR spectrum also supported the conc

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210613

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractAttempts were made to copolymerizep‐aminostyrene,p‐acetamidostyrene,N‐methyl‐p‐aceta‐midostyrene,N‐(4‐vinylphenyl) phthalimide,N‐vinyl succinimide, andN‐vinyl phthalimide with methyl acrylate complexed with ethyl aluminum sesquichloride. Only reactions involvingN‐(4‐vinylphenyl)phthalimide andN‐vinyl phthalimide yielded alternating copolymers.N‐vinyl succinimide gave nonalternating copolymers insoluble in common solvents and the other monomers did not copolymerize. In some cases, the conventional radical copolymers were prepared for comparison purposes. The reactivity ratios of the free‐radical initiated copolymerization of methyl acrylate (I) withN‐(4‐vinylphenyl)phthalimide (II) werer1= 0.14 andr21.56. The alternating copolymers were studied by1H‐NMR and13C‐NMR spectroscopy. The alternating copolymer ofN‐(4‐vinylphenyl)phthalimide with methyl acrylate was hydrazinolyzed to form the alternating copolymer of methyl acrylate withp‐aminostyrene. Hydrazinolysis of the alternating copolymer of methyl acrylate withN‐vinyl phthalimide removed the phthalimide moiety and generated vinyl amine units which readily cyclized with neighboring methyl acrylate units to form copolymers that contained five‐membered lactam rings. The infrared (IR) spectra of the hydrazinolyzed products contain bands due to amine or amide groups and are devoid of t

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210614

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThe reaction of solid copolymer of vinylidene chloride and vinyl chloride with aqueous sodium or potassium hydroxide solutions in the presence of quaternary ammonium or phosphonium salts as phase transfer catalysts gave dehydrochlorinated products with chlorine‐substituted polyene structure. Among the catalysts used tetrapropylammonium bromide was the best and potassium hydroxide was more active than sodium hydroxide. The activity of quaternary ammonium salts was discussed in terms of hydrophile–lipophile balance. The effects of temperature and the concentration of the bases and catalysts were investigated to obtain the optimum reaction condition. Treatment of the polymer films and solutions in tetrahydrofuran with aqueous bases under two‐phase conditions also produced dehydrochlorinated films and po

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210615

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThe mutarotation between form I and form II of poly(cis‐5‐ethyl‐D‐proline) has been experimentally realized. A number of hydrogen‐bond‐forming solvents have been found effective in initiating the mutarotational process. The rate of mutarotation seems to be proportional to the acidity of the active solvent. The enthalpy of activation energy for the mutarotation is estimated from the first‐order kinetics at the lower conversion by means of the Arrhenius equation to be approximately 16.7 kcal/mol. The solvent‐polymer interactions are proven to be one of the important driving forces for the mutarotation. The specific site at which hydrogen bonding takes place has been determined to be the carbonyl group of the amide by infrared spectroscopic techniques. The molecular reason for the greater susceptibility of poly(cis‐5‐ethyl‐L‐proline) II to the solvent effect than poly(cis‐5‐ethyl‐L‐proline) I can be satisfactorily explained by the relatively more extended structure of form I than form II. The mechanism for the mutarotation undoubtedly involves a cis‐trans isomerization of the amide bond. The conformation of the transient states during the mutarotational process is still evidently helical in nature, probably consisting of long poly(cis

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210616

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractTwo possible conformations for poly(cis‐5‐ethyl‐D‐proline) have been identified and characterized by using combinations of1H‐ and13C‐NMR, CD, and ORD spectroscopic techniques. Both forms have helical conformations similar to those of poly(L‐proline) characterized by different amide bonds (cis and trans). However, the carbonyl group of the amide in poly(cis‐5‐ethyl‐D‐proline) form II (trans) seems to be closer to perpendicular orientation with respect to the helical axis than in poly(L‐proline) form II. The pyrrolidine ring conformation of form I (cis) is probably β+γ−‐puckered, whereas for form II it is probably β+‐puckered in nature. The side‐chain ethyl groups prefer to adopt anti conformations to the C5H bond, or prefer to have χ = 180°, regardless which of the two forms poly(cis‐5‐ethyl‐D‐proline) may like to assume. The experimental results agree well with our previous

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210617

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThe effect of methanethiol (CH3SH) on the radiation chemistry of low‐density polyethylene was examined by using intrinsic viscosity measurements, low‐angle laser light scattering, and infrared spectrophotometry. Radiation‐induced intermolecular linking was found to be almost completely inhibited in low‐density polyethylene by the presence of less than one weight percent of CH3SH during irradiation. The net yield of transvinylene was also reduced, probably by reaction of transvinylenes with methylthiyl radicals (CH3S). The inhibition of radiation‐induced intermolecular linking by CH3SH demonstrates that linking is a relatively slow process involving reactions of alkyl free radicals, and that prompt intermolecular links caused by rapid ionic, ion–molecule, or “hot hydrogen” processes are not significant in the radiation chemistry of low‐den

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210618

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractCopolymers prepared by the bulk copolymerization ofp‐t‐butylstyrene (S) and methyl methacrylate (M) were analyzed by1H‐NMR. The spectra showed fine structure in the δ 2.2–3.6 region similar to that reported for styrene/methyl methacrylate copolymers. Reactivity ratios for S‐M copolymers determined by classical composition measurements differed markedly from the same ratios determined by NMR when it was assumed that NMR peak‐triad assignments could be made by analogy with published styrene/methyl methacrylate assignments. A new set of peak‐triad assignments was proposed that reconciles this difficulty and gives good agreement between triad fractions measured by NMR and those calculat

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210619

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractAromatic bisvinyl ethers, prepared by the condensation of bisphenols with 2‐chloroethyl vinyl ether in the presence of sodium hydroxide, are a new class of thermosetting monomers. These new materials can be polymerized cationically by using diaryliodonium salts as photo and thermal initiators to produce crosslinked resins whose physical and thermal characteristics resemble those of epoxy resin

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210620

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY