摘要:

AbstractThe polymer decoration method based on the vaporization and condensation‐crystallization of polyethylene (PE) upon the fold surface of polymer crystals has been widely used to study the chain folding behavior of the crystals. When this method was utilized to study solution‐grown high molecular weight poly (ethylene oxide) (PEO) lamellar crystals, the highly anisotropic, low molecular weight fragment PE decorated become oriented parallel to the fold direction and form rods, which can be observed by transmission electron microscopy (TEM) and electron diffraction (ED). The growth sectors were clearly observed. From the ED patterns the {200} planes of the orthorhombic low molecular weight PE rod crystals can be observed, and thec‐axis of these crystals is aligned parallel to the {120} growth planes of the PEO crystals. The decoration results indicate that the major fold orientation of high molecular weight PEO single crystals grown from dilute solution is along the {120} planes. © 1995 John Wiley&Son

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331301

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe network formation process of the triethylamine‐initiated reaction of 1,4‐butanediol diglycidyl ether withcis‐1,2‐cyclohexanedicarboxylic anhydride has been investigated by conventional differential scanning calorimetry and temperature scanning Brillouin light scattering as a new experimental method for the estimation of the reaction's conversion factor. The time‐temperature evolution of the observed quantities (reaction enthalpy in the calorimetric measurements and hypersound velocity in the light scattering) reflects in both sets of experimental data, but results in different kinetic parameters obtained by the assumption of an Arrhenius behavior. These differences are ascribed to the relation of the observed properties with respect to the evolution of the reaction. The enthalpy production of the system observed in the calorimetric experiment is shown to be connected directly to the chemical reaction, whereas the change in the hypersound velocity measured by the light scattering method is sensitive to the solidification of the system. © 1995 John Wiley

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331302

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractA spinning drop tensiometer was used to measure the interfacial tension between the coexisting phases of mixtures of low molecular weight polypropylene glycol,Mw= 1000, and polyethylene glycol,Mw= 300, 400, or 550. Two types of experiments gave concordant interfacial tensions. First, the static analysis of the equilibrium diameter of cylindrical drops according to Vonnegut and, second, Tomotika's dynamic analysis of Rayleigh instabilities caused by a sharp decrease of the angular speed. The end‐pinching process also lead to the break‐up of the drops and it was characterized by a rapid expansion of the hemispherical ends followed by a slower pinching step. The pinching rate increases as the final angular speed decreases while the growth rate of Rayleigh instabilities shows no definite trends in the range 118‐245 rad · s−1. It is shown that the end‐pinching of long cylindrical drops can be analyzed in terms of short fiber retraction to get the interfacial tension. © 1995 John Wile

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331303

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe crystallization of the monotropic liquid crystal forming polyether, poly‐n‐nonyl‐4 4′‐biphenyl‐2‐chloroethane, was investigated using DSC calorimetry and polarizing optical microscopy. The principal theme was the nature of crystallization from the nematic liquid crystalline state, which in the monotropic system could be directly compared with the more familiar crystallization from the isotropic melt using one and the same compound. Novel, polarizing optical structures were observed that combine features of both the usual LCPs (fine “grains”) and those of the conventional crystallizeable polymers (spherulites) with differing degrees of prominence of each according to crystallization conditions. The considerations of such structural observations, combined with the calorimetric results and the newly gained information on the kinetics of the crystallization process, reveal an acceleration of the overall crystallization rate at the stage where liquid crystal formation sets in as assessed by calorimetry but not as registered with the polarizing microscope, leading to wider issues regarding the conception of “amorphous crystalline ratio” and its extension to the liquid crystal state. Beyond polymers, the new findings lead to the more general considerations on metastable phases, specifically to their emergence and competition with the phases of ultimate stability. In this respect the present study on a monotropic LCP provides an illustrative example of a more general treatment presented previously. © 199

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331304

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractPolyamide 6 (PA) and ethylene‐propylene rubber with maleic functionality (EPMA) were blended in a batch mixer. EPMA anhydride groups react with amine chain ends of polyamide and form a grafted copolymer at the interface. The molecular weights of the grafted PA and of the free PA were measured. The molecular weight of the free PA decreases during the processing. This effect is due to the hydrolysis of the PA consecutively to its reaction with anhydride groups. The molecular weight of both grafted and free polyamide decreases during the processing. Moreover, the molecular weight of the grafted PA is lower than that of the free PA. At constant mixing time, a high conversion level produces grafted PA with a higher molecular weight. This is the result of molecular weight segregation for interfacial reaction. Small molecules react faster at the interface than larger ones. If we compare experimental results with model predictions, two segregation regimes are observed. For high shear and low EPMA concentrations, dispersion is very fast; the segregation only depends on molecular elasticity. In this case, the best correlation between model and experiment is obtained for low interfacial thicknesses. For low shear, or for EPMA concentrations close to the phase inversion composition, the segregation is more noticeable, which is mainly due to the diffusion of macromolecules through the brush of already grafted molecules. In this case, there is a clear competition between the compatibilization and the grafting reaction. Molecular weight segregation gives low ratio of the grafted PA molecular weight to the free PA molecular weight. This is detrimental to interfacial properties of the grafted copolymer formed by melt reactivity. Strategies are developed to improve this ratio in order to investigate its influence on the mechanical properties. © 1995 John Wiley&Sons, I

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331305

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractPolyimides with large aromatic rings were prepared from 3,6‐diaminocarbazole (CDA),N‐ethyl‐3,6‐diaminocarbazole (ECDA), 2,7‐diaminofluorene (DAF), 2,7‐diaminofluorenon (DAFO), and dimethyl‐3,7‐diaminodibenzothiophene‐5,5‐dioxide (DDBT) with 2‐bis(2,4‐dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA). Their physical properties, including gas permeability and permselectivity, were investigated in comparison with those of the related polyimides from 1,3‐phenylenediamine (mPD). Glass transition temperatures of the polyimides with large aromatic rings were much higher than those of the mPD‐based polyimides as a result of increased rigidity of the former polymer chains. With changing diamine from mPD to the large aromatic diamines, charge transfer (CT) interaction between the moieties of acid anhydride and diamine seems to be enhanced, judging from the red shift of absorption edge of the polyimide films and the red shift of CT excitation band of the 6FDA‐based polyimides in solution. Fraction of free space (VF) was a little smaller for the polyimides with large aromatic rings except DDBT than for the mPD‐based polyimides, probably because of enhancement in polymer chain‐chain interactions as a result of the increased CT interaction. The DDBT‐based polyimides had largeVFthan the mPD‐based polyimides because of the nonplanar structure of neighboring dibenzothiophene‐5,5‐dioxide and imide rings. For the 6FDA‐based polyimides, permeability coefficients to H2, O2, N2, CO2, and CH4were in the order, DAFO

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331306

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe literature methods for the determination of the mean of the crystallite orientation distribution for thecaxis, that is of the orientation coefficientfc, for poly(ethylene terephthalate) (PET), based on the azimuthal scan of the (105) reflection, are reviewed. These methods appear unsuitable for samples presenting the “tilted orientation”; that is, the molecular chain axis inclined by some degrees with respect to the fiber axis, as frequently occurs for PET fibers. A new method for the determination offcfor PET, also based on the azimuthal scan of the (105) reflection (which can be applied also to samples with “tilted orientation”), is proposed. This method implies as a first step the determination of the tilt angle, for which the complete fiber pattern is required. A possible simplifying assumption, which allows use of the sole azimuthal (105) profile and makes the method also applicable to poorly oriented samples (for which the determination of the tilt angle is not easy), is also discussed. © 1995 John Wiley&S

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331307

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe synthesis of well‐defined, nearly monodispersed, 3‐miktoarm (from the greek word μlkτós meaning mixed) star copolymer of the A2B type is described. A and B is either polystyrene (PS), polybutadiene (PBd), or polyisoprene (PI). The sequential controlled addition of living anionic B and A chains to methyltrichlorosilane leads to narrow molecular weight distribution miktoarm star copolymers with homogeneous composition. Characterization was carried out by size exclusion chromatography, low‐angle laser light scattering, laser differential refractometry, membrane and vapor pressure osmometry, nuclear magnetic resonance and ultraviolet spectroscopy. Analysis of [η],RHandRvof the A2B and one A2B2miktoarm copolymers, suggests that a small expansion of the copolymer occurs either in a good solvent for both species or in a Θ solvent for one of them, as compared with the corresponding star homopolymers. This is in contrast to results obtained on linear block copolymers, and is due to the increased occurrence of heterocontacts in the miktoarm starshaped architecture. © 1995 John Wile

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331308

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe results of heats of mixing experiments on a series of ortho‐substituted phenols with an amide or an ester are described. Substituents were chosen to span a wide range of electronic and steric character. Enthalpy of mixing results do not correlate solely with the acid strength of the phenol, or with a Hammett linear free‐energy analysis. Rather, interactions are favored by the presence of groups with the ability to weaken the base strength of the proton donor while simultaneously increasing its acid strength. Such groups share a combination of electron‐withdrawing ability and/or steric bulk that causes an effective decrease in the electron density about the phenolic oxygen. Trifluoromethyl andtert‐butyl, and to a lesser extent halogen and hydroxy substituents ortho to the phenolic OH, give the highest exothermic enthalpies of mixing and are thus the most effective at promoting intermolecular interactions with weak bases such as amides and esters. These results should be useful in designing miscible or compatible polymer blends in which specific interactions such as hydrogen bonding are important. © 1995 John Wiley&S

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331309

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe morphology and the physical and mechanical properties of graft‐modified polyethylene fibers have been studied. Two types of fibers, with the diameters of 10 μm (1.1 dtex) and 40 μm (7.5 dtex), were modified by radiation‐induced grafting with acrylic acid. The extent of grafting was determined gravimetrically. Confirmation of gravimetrically obtained values was achieved using conductometric titration. The fibers were hydrated at pH 2 and pH 7. The degree of swelling was 120% at pH 2 and 200% at pH 7. The transversal distribution of polyacrylic acid in the fibers was determined. Fibers were stained and observed with an optical microscope. The diffusion of the monomer into the bulk was found to be rather fast. The changes in the total crystalline content and the lamellar thickness distributions in consequence of irradiation and grafting were determined by differential scanning calorimetry analysis. The measurements showed no effects of irradiation on the crystallinity in either type of fiber, whereas a decreasing crystallinity caused by grafting was noticed in the 40 μm fibers. The lamellar thickness distributions narrowed upon irradiation, indicating recrystallization as a result of chain scission. Wide angle x‐ray scattering and Raman analysis of dry and hydrated fibers were conducted to study the behavior of the fibers in an aqueous environment. These results both showed a decreasing crystalline content caused by fiber hydration. Tensile tests were carried out to evaluate how grafting, hydration and Ca2+‐crosslinking of grafts affected the fiber strength. Grafting and Ca2+‐crosslinking, as well as hydration, resulted in a decreasing E‐modulus for the 40 μm fibers, whereas no significant change could be noticed in the 10 μm fibers. © 1995 Joh

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331310

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY