摘要:

AbstractThe interdiffusion of polymer chains across a polymer–polymer interface, and subsequent fracture to re‐create the interface is reviewed. In particular, films formed via latex coalescence provide a very large surface area. Of course, latex film formation is a very important practical problem. Healing of the interface by interdiffusion is treated using the de Gennes reptation theory and the Wool minor chain reptation model. The self‐diffusion coefficients of polystyrene and the polymethacrylates obtained by small‐angle neutron scattering, SANS, direct non‐radiative energy transfer, DET, and other techniques are compared. Reduced to 150,000 g/mol and 135°C, both polystyrene and poly(methyl methacrylate) have diffusion coefficients of the order of 10−16−10−17cm2/sec. Variations in the diffusion coefficient values are attributed to the experimental approaches, theoretical treatments and molecular weight distribution differences. An activation energy of 55 kcal/mol was calculated from an Arrhenius plot of all polystyrene data reduced to a number‐average molecular weight of 150,000 g/mol, using an inverse square molecular weight conversion method. Interestingly, this is in between the activation energies for the α and β relaxation processes in polystyrene, 84 and 35 kcal/mol, respectively. Fracture of polystyrene was considered in terms of chain scission and chain pull‐out. A dental burr apparatus was used to fracture the films. For low molecular weights, chain pull‐out dominates, but for high molecular weights, chain scission dominates. At 150,000 g/mol, the energy to fracture is divided approximately equally between the two mechanisms. Above a certain number average molecular weight (about 400,000 g/mol), the number of chain scissions remains constant at about 1024scissions/m3. Energy balance calculations for film formation and film fracture processes indicate that the two processes are partly reversible, but have important components of irreversibility. From the interdiffusion SANS data, the diffusion rate is calculated to be about 1 Å/min, which is nine orders of magnitude slower than the dental burr pull‐out v

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050901

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractMethods for characterising cyclic polymers are illustrated by reference first to dilute solution methods for cyclic poly(dimethylsiloxane) (PDMS) and then to the entrapment of cyclic polymers in networks. Preparative routes to cyclic polymers are then reviewed, including ring‐chain equilibration reactions, coupling and condensation reactions and new methods using polymer‐supported reagents. Some of the properties of cyclic PDMS are discussed, including differences between ring and chain polymer properties such as their melt viscosities and glass transition temperatures. Methods for preparing the first polymeric catenanes are described, using polymer‐supported reagents. Future directions for cyclic polymer chemistry are indicated, including topological polymer chem

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050902

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe fluorescence method was used to study the interdiffusion of polymer chains during annealing of latex above its glass transition temperature (Tg). The latex film was prepared from mixture of naphthalene (N) (donor) and pyrene (P) (acceptor)‐labeled poly(methyl methacrylate) (PMMA) latex particles. Heptane was used as the coalescent agent. A steady‐state fluorescence technique was employed to measure the amount of direct nonradiative energy transfer from N to P during the interdiffusion of polymer chains across the particle–particle junction. Various latex films with different latex contents were used to measure the percentage critical occupation for the reliable steady‐state fluorescence measurements. Diffusions activation energies in these latex films were measured and found to be around 30 kcal/mol, which was attributed to the backbone motion of PMMA

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050903

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractVinylidene chloride copolymers have a number of superior properties, most notably a high barrier to the transport of oxygen and other small molecules. As a consequence, these materials have assumed a position of prominence in the packaging industry. At processing temperatures these copolymers tend to undergo degradative dehydrochlorination. Unsaturation generated via interaction of the polymer with a variety of agents commonly encountered during polymerization or processing introduces an allylic dichloromethylene unit which may function as a major defect (labile) site for the initiation of degradation. Three approaches to the potential stabilization of these materials have been examined. The first involved the addition of agents, e.g. metal formates, capable of converting labile dichlormethylene units into non‐reactive groups which would interrupt propagation of the degradative dehydrochlorination. The second involved the incorporation into the polymer of a commoner capable of scavenging free chlorine atoms. The third involved the preparation of copolymers which contains units capable of reaction with (consumption of) a mole of hydrogen chloride to expose a good free radical stabilizer to scavenge chlorine atom

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050904

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractProperty–structure correlation in proton exchange membranes, prepared by simultaneous radiation grafting of styrene into FEP films and their subsequent sulfonation, was evaluated. The distribution of ionic sites across the membrane matrix was determined by microprobe measurements. The properties of these membranes, such as ion exchange capacity, swelling and ionic resistivity as a function of the degree of grafting, were studied. The thermal stability of membranes was studied using thermogravimetric analysis and ion exchange capacity measurements. Membranes undergo considerable structural changes in terms of the increase in the ionic content, enhanced hydrophilicity and decrease in crystallinity with the increasing degree of grafting. A correlation between some physical properties and stuctural changes occurring during the membrane preparation was establishe

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050905

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThree‐component photopolymers comprising a photoacid generator, a bifunctional vinyl ether monomer and an aqueous base‐soluble polymer as matrix were developed. These photopolymers exhibit either positive‐ or negative‐working character, depending on the prebake temperature and the concentration of the photoacid generator. When the prebake temperature is high, the photo‐polymer film is made insoluble in aqueous base and organic solvents by the formation of crosslinks. However, on exposure to light, the crosslinks are decoupled by the photogenerated acid and the photopolymer layer becomes again soluble in aqueous base, resulting in a positive‐working character. When the concentration of the photoacid generator is low enough, the photopolymer has a negative‐working character due to the cationic polymerization of vinyl ethers. The mechanism of the photochemical reaction of the photopolymers was investigated to elucidate the complic

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050906

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractMethyl 4‐phenylthiophenyl sulfoxide is polymerized to poly(methyl‐4‐phenylthiophenylsulfonium) in poly(phosphoric acid) with a yield higher than 90%. The demethylation of poly(sufonium cation) is examined to control the composition ratio of the thiophenylene unit in the polycation. The polycation is soluble in common solvents due to the alternative structure of phenylene sufide and phenylenesulfonium cation and is easily converted to poly(phenylene sulfide) through the demethylation with a nucleophile. The poly(sulfonium cation) can be applicable as an alkylating agent for phenol, aniline and benzoic acid to the corresponding to anisole, N‐methyl aniline, N,N‐dimethyl aniline and benzoic methyl ester, respectively, with high conversion through the demethylation. These products can be isolated without a complicated purification because poly(phenylene sulfide) is precipitated in the mixture as the side product due to the poor solvent s

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050907

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe cure of a bismaleimide (BMI) neat resin modified with an aromatic diamine and a siloxane elastomer, has been studied by13C solid state nuclear magnetic resonance. Two chemical reactions occur during the cure cycle; at a low temperature, Michael's reaction predominates, while at a high temperature the polymerization of the double bond maleimide creates the network.The degradation of this BMI material was characterized with isothermal and dynamic thermogravimetric analyses in air and in nitrogen. The BMI thermal stability is lower in nitrogen than in air. This behavior is an indication of oxygen participating in reactions at high temperatures.The activation energy (Ea) of thermal degradation was determined from isothermal data using an Arrhenius equation (In V vs. 1/T). The global Eafor the weight loss in air was found to be 91 kJ/mol.The nature and the evolution of the thermal degradation products were the combined analyzed by techniques of pyrolysis, gas chromatography and mass spectrometry. The major thermal decomposition products obtained in the temperature range of 300–700°C are identified as benzene, methyl formamide, aniline, toluene and isocyanate‐derived prod

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050908

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractPrevious work in our laboratory has shown that covalent bonding of a semiflexible polymer in a bis‐imide matrix prior to thermal polymerization is a promising, although structure‐dependent, approach to the synthesis of molecular composites from organic solvents in thermosets. In the present investigation, the focus has been on the rapid amine‐catalyzed anionic polymerization and crosslinking of fluorine‐containing bis‐maleimides. The objective has been to provide physical entrapment of rigid polymer prior to aggregation. Results have shown that gelation of fluorine‐containing bis‐maleimides initiated by tertiary amines in organic solvent can occur in seconds at moderate temperatures, and thus affords a means of preventing aggregation of rigid polymer prior to

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050909

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractGlucan phosphate is a water‐soluble, yeast‐derived, (1 → 3)‐β‐D‐glucopyranose polymer that has been demonstrated to be a potent immune stimulant. Glucan phosphate administration is associated with stimulation of immunity and a concomitant increase in resistance to a variety of experimentally induced disease states. Preclinical safety evaluation indicates that glucan phosphate does not induce mortality or significant toxicity over a wide dose range. Phase I clinical data indicate that glucan phosphate will ameliorate immunosuppression, stimulate immunity, decrease susceptibility to infection and alter ultimate outcome in trauma patients following laparotomy or thoracotomy. This work reviews the development, characterization, preclinal and clinical evaluation of gluc

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050910

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY