摘要:

AbstractCrosslinking chemistry and network formation in hydroxy and carboxy functional acrylic copolymer resins cured with representative melamine‐formaldehyde crosslinking agents have been studied by infrared spectroscopy. Network formation in these systems is dominated by two reactions, the condensation of the hydroxy (or carboxy) functionality of the acrylic resin with melamine alkoxy groups to form acrylic‐melamine crosslinks, and the condensation of melamine hydroxy groups to form melamine‐melamine crosslinks. The extents of these reactions have been studied as functions of acrylic resin composition, melamine type and concentration, and cure time and temperature. For melamines with just methoxy functionality, the extent of formation of acrylic‐melamine crosslinks increased steadily with cure temperature. For melamines with substantial hydroxy functionality, the extent of formation of acrylic‐melamine crosslinks increased rapidly then leveled off with increasing cure temperature. The formation of melamine‐melamine crosslinks increased slowly with increasing cure temperature. From these data and a statistical model, effective crosslink densities were calculated. The crosslink densities correlated well with solvent

ISSN:0098-1273    

DOI:10.1002/pol.1980.180181001

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractIn a previous paper, the extents of reaction of various functional groups in different acrylic copolymer melamine‐formaldehyde crosslinked formulations were measured by infrared spectroscopy. From these data and a statistical model, various network structure parameters could be calculated. One of these, effective crosslink density, was found to correlate well with film solvent resistance. In this paper the effects of the addition of strong acid catalysts on cure chemistry and network structure are determined. Both solvent‐based and water‐based formulations have been studied. In the solvent‐based formulations studied, the addition of acid catalysts greatly enhanced the crosslinking reactions at low temperatures and dramatically lowered the cure temperature. Acid catalysts also lowered the cure temperature of a water‐based formulation based on a high (180°C) cure temperature melamine. In contrast, the addition of acid catalysts had a negligible effect on the cure chemistry of a water‐based formulation crosslinked with a low (130°C) cure temperature melamine. For this case the rate limiting process was found to be the rate of removal of neutralizing amine from the film. Cure temperatures in this system could only be lowered by replacing the amine used with a more v

ISSN:0098-1273    

DOI:10.1002/pol.1980.180181002

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractFrom the integrated intensities of1H NMR bands it has been found that in solutions of styrene (St)‐ethylene dimethacrylate (EDMA) copolymers, a considerable part of the monomer units do not show directly in high‐resolution1H NMR spectra and it is suggested that these monomer units form compact structures, probably acting as cores of microgel‐like particles. In13C NMR spectra all monomer units are shown, including those which are part of the compact microgel structures. From a comparison of1H NMR spectra with other analytical methods (elemental analysis, infrared spectra) it follows that the composition of the copolymer in the core of the microgel is the same as the overall composition of the copolymer. The content of the compact structures in the microgel increases with the content of the EDMA component. The results are discussed from the point of view of structural features and of the motional restrictions of the St/EDMA copolymers in CCl4solution. The consequences for1H NMR analysis of copolymer composition are also disc

ISSN:0098-1273    

DOI:10.1002/pol.1980.180181003

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe phase diagram of poly(p‐benzamide) (PBA) inN,N‐dimethylacetamide/LiCl solutions was determined for two PBA samples having weight‐average molecular weights of about 10,000. The various equilibria were studied using analytical, viscometric, and optical microscope measurements. The phase diagram at 25°C, taking as variables the concentration of polymer (Cp) and LiCl (Cs), involves several equilibria which can be summarized as follows: solid ↔ isotropic solution when 0.75 ≤Cs≤ 2 g/dl, solid ↔ anisotropic solution when 2 ≤Cs≤ 4 g/dl, isotropic solution ↔ anisotropic solution when 2 ≤Cs≤ 4 g/dl, andCp>6 g/dl, and dilute isotropic solution ↔ gel whenCs>4 g/dl. In theCprange in which the isotropic and anisotropic phases coexist, enrichment of the high‐molecular‐weight component of the polymer in the anisotropic phase becomes more marked as the volume fraction of the latter phase is decreased. The two PBA samples exhibit noticeable differences in solubility, absolute viscosity, and in their viscosity‐concentration behavior. The location of the maximum in the latter dependence does not necessarily coincide with the first appearance of the anisotropic phase. In the absence of a flow field, anisotropic solutions exhibit an irreversible increase in viscosity. Inclusion of the equilibria involving the crystalline state furnishes insight into some of the common observations for extended‐chain polymers. A diagram illustrates the superposition of the solubility curves for a crystalline polymer and the liquid‐crystal regions. This indicates that, for the high melting crystalline polymers, the crystalline phase should be stable relative to the concentrated anisotrop

ISSN:0098-1273    

DOI:10.1002/pol.1980.180181004

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractIn deriving a constitutive equation from a molecular model of polymers in concentrated solutions and melts, Doi and Edwards used a mathematical approximation, the “independent alignment approximation,” which has recently been shown to produce significant error in the particular case of stress relaxation following a double‐step strain in opposite direction. In the present paper, in order to examine the approximation in general cases, we derive a new constitutive equation without using the independent alignment approximation. The new equation is a nonlinear integro‐differential equation and is solved numerically for several cases, i.e., steady shear and elongational flows, and the transient flows after the start of shear and elongation. It is found that, in the cases examined here, the new constitutive equation gives nearly the same results as the old one: the rheological functions calculated from the two theories differ no more than 30%. This substantiates the expectation that the independent alignment approximation does not produce drastic error as long as the flow direction is not r

ISSN:0098-1273    

DOI:10.1002/pol.1980.180181005

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe adsorption of linear polystyrenes from cyclohexane solutions onto a chrome plate of 35 (the theta temperature), 40, and 45°C was studied by ellipsometry. The adsorbance decreases with increasing temperature, while the extension of the adsorbed polymer layer increases. The adsorbance is almost independent of the molecular weight at these temperatures. The slope of a double logarithmic plot of extension versus molecular weight is 0.5 at the theta temperature, whereas at the higher temperatures the slope is a little larger. Both the adsorbance and the extension of the adsorbed layer change reversibly over a cycle of temperature change, indicating that a reversible conformational change has occurred. The expansion factor αtof the adsorbed layer is compared with the theoretical predictions of Hoeve and of Jones and Richmond. The expansion factor αtaccording to Hoeve's theory, was smaller than the measured value, whereas the expansion calculated by the Jones–Richmond theory is much larger than the measured value. It is concluded that the tail portions of adsorbed chains predominantly govern the extension of the adsorbed l

ISSN:0098-1273    

DOI:10.1002/pol.1980.180181006

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractWe study the effect of the memory function on the coherent scattering function of a dilute polymer solution, taking into account hydrodynamic interactions among the polymer segments. The line shape, given by a sum of two exponentials, is very accurate numerically forka≳ 3 (withathe length of a polymer segment) and for times such that ω0(k)t≲ 1.5 [with ω0(k) the initial slope]. However, this approximation to the scattering function is not nearly so accurate at the smaller values of ka encountered in light scattering experiments. The amplitudes and relaxation times associated with the two exponentials are found to be markedly dependent on the strength of the hydrodynamic interac

ISSN:0098-1273    

DOI:10.1002/pol.1980.180181007

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe specific concentrationcaof methylene chloride, the zero‐concentration diffusion coefficientD0, and the concentration coefficient γDof the diffusivity in drawn and annealed LDPE were measured. The influence of the drawing rate, of annealing with the ends of the sample free and fixed and the effects of time of standing at room temperature after annealing were investigated. The observed transport properties are in good agreement with the microfibrillar model of fibrous structure, its relaxation during annealing, and the slow crystallization of relaxed tie‐molecules upon standing at room tempera

ISSN:0098-1273    

DOI:10.1002/pol.1980.180181008

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe infrared and Raman spectra of the two polymorphic forms oftrans‐1,4‐poly(isoprene) (TPI) andtrans‐1,4‐poly(2,3‐dimethyl butadiene) (TPDMB) are presented. Infrared spectra of the alpha and beta forms of TPI were obtained by digitally subtracting the amorphous contribution from the corresponding spectra of semicrystalline TPI polymers. Normal coordinate calculations are presented for both polymorphic forms of TPI and TPDMB, and the assignments of the normal modes are

ISSN:0098-1273    

DOI:10.1002/pol.1980.180181009

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe dependence of thermal conductivity λ and heat capacity per unit volumepcpon temperature and pressure for poly(vinyl acetate) has been measured by a transient hot‐wire probe technique. The measurements were made under pressures up to 0.5 GPa over a temperature range of 270–470 K. The temperature coefficient of thermal conductivity (∂ lnλ/∂T)pwas found to increase with pressure for both the liquid and the glassy state. The change in heat capacity per unit volume in the region of the glass‐transition temperature was found to decrease with increasing pressure. The Ehrenfest relation does not explain the variation of the pressure coefficient of the glass‐transitio

ISSN:0098-1273    

DOI:10.1002/pol.1980.180181010

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY