摘要:

AbstractA detailed study of the vulcanization of polybutadiene with various combinations of sulphur, tetramethylthiuram disuphide, ZnO, stearic acid, and zinc dimethyldithiocarbamate is reported. Vulcanization was conducted by heating samples at 2.5°C/min in a differential scanning calorimeter. The reaction was stopped at various points along the vulcanization exotherm, the soluble reaction products and residual curatives were extracted and analyzed, and the crosslink density and percentage polysulphidic crosslinks were determined. The overall reaction mechanism was found to be similar to that for polyisoprene, but the reaction, once initiated, was faster than in polyisoprene, the crosslink density was higher, and the percentage polysulphidic crosslinks was lower. These differences are discussed. © 1993 John Wiley&Sons, In

ISSN:0021-8995    

DOI:10.1002/app.1993.070470301

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractMelt viscosity has been investigated for a series of bisphenol‐A type epoxide oligomers with different weight‐average mol wts (M̄w), ranging from 388 to 2640. The temperature dependence of the melt viscosity is described by the Williams–Landel–Ferry (WLF) equation. The melt viscosity η is correlated with both the direct current (dc) conductivity σ and the dielectric relaxation time τ. The two relationships between these three properties, σ·ηκ= const (0.63 ≦ κ ≦ 1.12) and η/τℓ= const (0.73 ≦ ℓ ≦ 1.06), are experimentally derived. Both exponents, κ and ℓ, depend on the M̄wof the oligomer. The lower M̄woligomer has the larger value of κ. The κ value is close to unity for the low M̄woligomer, which agrees with Walden's rule, σ·.η = const, applicable to most low mol wt liquids. The ℓ value is near unity for the epoxide oligomer with higher M̄wthan 2000, which means that the melt viscosity is proportional to the dielectric relaxation time. The low M̄woligomer (M̄w<2000), on the other hand, has a smaller value of ℓ below unity. The result indicates that the melt viscosity is not proportional to the dielectric relaxation time for the low M̄wepoxide oligomer, whose dielectric α‐relaxation is not governe

ISSN:0021-8995    

DOI:10.1002/app.1993.070470302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractA two‐dimensional position‐sensitive detector for real‐time small‐angle light scattering (RTSALS) of polymers is described. The device performs real‐time image analysis of the evolving light‐scattering pattern during crystallization. Such an approach provides a means of simultaneously measuring the rate of spherulite growth and the overall rate of crystallization, allowing calculation of nucleation density and/or rate. Although separation of nucleation effects from growth effects typically requires the application of two different experimental techniques, this device is unique in that it allows these two effects to be easily separated using only time‐dependent light‐scattering data. The device incorporates a CCD camera, a personal computer, and an imaging board as its major hardware components. Software designed specifically for this application performs real‐time analysis of the light‐scattering pattern at a rate of 1–3 images per second, thus allowing study of even moderately rapidly crystallizing polymers. (More recent software modifications have resulted in a speed enhancement to 5 images per s and further improvement is expected.) Intensities at various scattering and azimuthal angles are plotted at each time. In addition, the average spherulite radius is calculated and plotted. Application of the device is illustrated by measuring the spherulite growth rate of poly(ethylene terephthalate) as a function of temperature. © 199

ISSN:0021-8995    

DOI:10.1002/app.1993.070470303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe synthesis of polyacrylonitrile–poly(ethylene oxide) block copolymers was carried out with the use of modified initiator containing azo groups, being a product of reaction between poly(ethylene oxide) (mol wt 6000) with azobisisobutyronitrile. Effects of initiator concentration, temperature, and synthesis time on the yield, composition, and intrinsic viscosity of the copolymers were examined. To confirm the segmental structure of the obtained products, precipitation, fractionation, gel permeation chromatography, infrared, and1H nuclear magnetic resonance methods were used. © 1993 John Wiley&Sons, I

ISSN:0021-8995    

DOI:10.1002/app.1993.070470304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractGraft polymerization of anionic and cationic monomers was performed onto the surface of poly(ethylene terephthalate) (PET) film with a simultaneous UV irradiation method, but using no photo‐sensitizer. To effect graft polymerization, the PET film was immersed in an aqueous solution containing a monomer and periodate (NaIO4) of appropriate concentrations, followed by UV irradiation without degassing. The monomers used were 2‐acrylamide‐2‐methylpropane sulfonic acid and acrylic acid as anionic and N,N‐dimethyl aminopropyl acrylamide and dimethyl aminoethyl methacrylate as cationic monomer. The role of NaIO4at the polymerization was to make the concentration of oxygen dissolved in solution zero by the photochemical reaction with the oxygen. The surface structure of grafted films was characterized by their contact angle, dyeing, X‐ray photoelectron spectroscopy, and zeta potentials. Graft polymerization took place, not merely on the outermost surface, but also within the thin surface region of the PET film without any change in bulk properties. © 1993 John Wil

ISSN:0021-8995    

DOI:10.1002/app.1993.070470305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe relationships between the isothermal physical properties in the glassy state of amorphous thermosetting crosslinked polymers and chemical conversion are anomalous and complex. In this manuscript, a generalized framework for correlating the basic physical properties of a high‐Tgthermosetting amine/epoxy system vs. extent of cure at isothermal temperatures from aboveTgto deep in the glassy state is reported in terms of theTg‐Temperature Property (TgTP) Diagram. The framework arises from consideration of the isothermal shear modulus and the isothermal physical aging rate vs. extent of cure, both of which display maxima and minima throughout a wide range of temperatures belowTg. Use ofTgas a direct measure of conversion results in linearization of the relationships between the temperatures of the maxima and minima of the physical properties and extent of cure in theTgTP Diagram. The anomalous behavior is related to specific phenomena, such as the glass transition (vitrification) and the glassy‐state β‐transition (Tβ), the temperatures of which change with conversion, and also to gelation. The different types of behavior of a property of the material vs. extent of cure correspond to different regions in the diagram. Such simple diagrams are intellectually useful for understanding the properties of materials for both undercured materials (with change of conversion) and fully cured materials (with change of stoichiometric ratio). © 1993 John Wiley

ISSN:0021-8995    

DOI:10.1002/app.1993.070470306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe physical aging behavior of a high‐Tgamine/epoxy thermosetting system has been investigated vs. change of chemical structure induced by cure and vs. aging temperature (Ta) using the Torsional Braid Analysis (TBA) technique. The chemical structure was changed systematically from monomer to highly crosslinked polymer by curing in the equilibrilium state (T>Tg). The aging temperatures ranged from just below the glass transition temperature to deep in the glassy state (Ta>Tg). In the absence of chemical reaction, the physical aging rate at a given temperature,Ta, passes through a minimum with increasing chemical conversion (i.e., change of chemical structure). Analysis of this behavior is simplified by usingTgas an index of measurement of extent of cure. There is a superposition principle for normalizing the physical aging behavior of the thermosetting glasses, which involves a shift ofTg–Taand a shift ofC(Ta) (a function of aging temperature), regardless of chemical structure. Analysis reveals that: (1) this behavior is the consequence of theTgandTβtransitions, (2) the segmental mobility (1/τ) is a function of the deviation from equilibrium (as measured byTg–Tgand the aging time), (3) the segmental mobility, which is involved in the physical aging process in the glassy state, is insensitive to the extreme changes of chemical structure (from monomer, to sol/gel polymer, and to highly crosslinked polymer), and (4) physical aging deep in the glassy state affects both segmental mobility and cohesive energy density. © 1993 John Wiley&S

ISSN:0021-8995    

DOI:10.1002/app.1993.070470307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe cure of a liquid dicyanate ester monomer, which reacts to form a high‐Tg(≈200°C) polycyanurate network, has been investigated using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and a dynamic mechanical technique, torsional braid analysis (TBA). The monomer is cured with and without catalyst. The same one‐to‐one relationship between fractional conversion and the dimensionless glass transition temperature is found from DSC data for both the uncatalyzed and catalyzed systems, independent of cure temperature, signifying that the same polymeric structure is produced.Tgis the parameter used to monitor the curing reactions since it is uniquely related to conversion, is sensitive, is accurately determined, and is also directly related to the solidification process. The rate of uncatalyzed reaction is found to be much slower than that of the catalyzed reaction. The apparent overall activation energy for the uncatalyzed reaction is found to be greater than that of the catalyzed reaction (22 and 13 kcal/mol, respectively) from time–temperature superposition of experimental isothermalTgvs. In time data to form kinetically‐controlled master curves for the two systems. Although the time–temperature superposition analysis does not necessitate knowledge of the rate expression, it has limitations, because if the curing process consists of parallel reactions with different activation energies, as is considered to be the case from analysis of the FTIR data, there should not be a kinetically‐controlled master curve. Consequently, a kinetic model, which can be satisfactorily extrapolated, is developed from FTIR isothermal cure studies of the uncatalyzed reaction. The FTIR data for the uncatalyzed system at high cure temperatures, where the material is in the liquid or rubbery states throughout cure, 190 to 220°C, are fitted by a model of two parallel reactions, which are second‐order and second‐order autocatalytic (with activation energies of 11 and 29 kcal/mol), respectively. Using the model parameters determined from the FTIR studies and the relationship betweenTgand conversion from DSC studies,Tg, vs. time curves are calculated for the uncatalyzed system and found to agree with DSC experimental results for isothermal cure temperatures from 120 to 200°C to even beyond vitrification. The DSC data for the catalyzed system are also described by the same kinetic model after incorporating changes in the pre‐exponential frequency factors (due to the higher concentration of catalyst) and after incorporating diffusion‐control, which occurs prior to vitrification in the catalyzed system (but well after vitrification in the uncatalyzed system). Time–temperature‐transformation (TTT) isothermal cure diagrams for both systems are calculated from the kinetic model and compared to experimental TBA data. Experimental gelation is found to occur at a conversion of approximately 64% in the catalyzed system by comparison of experimental macroscopic gelation at the various curing temperatures and iso‐Tg(iso‐conversion) curves calculated from the kinetic

ISSN:0021-8995    

DOI:10.1002/app.1993.070470308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractDilute polyolefin solutions, respectively based on EPDM and UHMWPE, were reacted with functionalized silanes to prepare coatings for glass fibers. These were found to provide adequate bonding characteristics for both glass and epoxy resin (bisphenol type). Unidirectional composites containing fiber matrix interlayers, using fibers coated with the aforementioned functionalized polyolefins, were found to exhibit much larger tanδ values over the temperature range of 60 to +60°C and greater ductility in flexural tests, albeit at the expense of a reduction in failure stresses. The UHMWPE coatings produced a multiple step fracture mechanism, which was deemed to provide a more efficient crack stopping mechanism than equivalent EPDM coated fibers. © 1993 John Wiley&Sons, I

ISSN:0021-8995    

DOI:10.1002/app.1993.070470309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effect of a crosslinking agent on the formation of porous solids by polymerizing microemulsions formulated with monomers was investigated. Phenomenological studies were carried out to evaluate the possibility of controlling the morphology of the porous polymeric materials by using precursor microemulsions having a distinct microstructure. A microemulsion system, containing methyl methacrylate (MMA), acrylic acid (AA), the crosslinking agent ethyleneglycol dimethacrylate (EGDMA), water, and sodium dodecylsulfate (SDS) as surfactant, was studied. An identical surfactant‐free system, formed using the same monomers, crosslinking agent, and water, but without surfactant, was also studied. Microemulsion samples from both these systems, having a water in oil droplet microstructure and also samples exhibiting bicontinuous microstructural characteristics, were used as precursor systems for polymerization. The morphology of the polymeric solids obtained was examined using scanning electron microscopy and thermogravimetric analysis. The results of this study indicate the possibility of forming porous polymeric solids having specifically tailored morphology and microstructure by the polymerization of monomer containing microemulsions. © 1993 John Wiley&Sons, I

ISSN:0021-8995    

DOI:10.1002/app.1993.070470310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY