摘要:

AbstractThe synthesis, fractionation, and characterization of poly(diphenylmethyl methacrylate) (PDPMM) are described. Analysis of tacticity by13C nuclear magnetic resonance (NMR) revealed a high (25%) isotactic content. Results of low‐angle light scattering and intrinsic viscosity measurements in toluene indicate that PDPMM chains behave as random coils and that toluene is a thermodynamically good solvent. The characteristic ratio C∞of the chains was determined from viscosity measurements in a near‐theta solvent, 3‐heptanone at 45°C. The corresponding value of C∞= 14.0 is consistent with previous work on poly(triphenylmethyl methacrylate), C∞= 20.3, and poly(benzyl methacrylate), C∞= 10.0, and reflects the bulkiness of the side group and the increase in isotactic content of the chains with increasin

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281101

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThermotropic liquid crystalline random copolyesters, based on terephthalic acid and substituted hydroquinones, display an unusually large heat for the crystal‐nematic transition; this phenomenon is related to their highly ordered structures. To modify the structures, annealing was carried out in the solid state at different temperatures over different times. As the annealing time or temperature is increased, the melting peaks shift to higher temperatures, whereas the heat of fusion shows no significant change or is lowered, respectively. An explanation is offered in terms of crystal perfection and a molecular weight increase. No evidence for a random‐to‐block conversion on annealing is

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281102

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractAn interface is described that is capable of stripping solvent from polymer solutions emerging from an interfaced high‐temperature gel permeation chromatograph. The chemical composition of each solvent‐free polymer fraction is then determined using Fourier transform infrared (FTIR) or other techniques to obtain the composition drift (CD) pattern of the polymer (i.e., variation of chemical composition as a function of molecular weight). The interface consists of a vacuum oven into which an ultrasonic nebulizer and a stepper motor have been incorporated. The stepper motor drives a fraction collector, equipped with a set of KBr plates, onto which the nebulized polymer solution is sprayed. The temperature and pressure of the interface are maintained so as to strip the solvent from the chromatographic effluent as it impinges on the collector substrates. The technique, which had been applied to the % ethylene CD of ethylene‐propylene rubbers, is employed in the analysis of a block copolymer reaction product. In the example given, the CD pattern of the reaction product generated is simulated along with the observed molecular weight distribution pattern to arrive at the approximate composition of the reaction product. For many applications, this approach eliminates the need to carry out tedious solvent/nonsolvent fractionations commonly employed in the characterization of the compositional heterogeneities in block copolymer reaction pro

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281103

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractUtilizing a newly developed apparatus, force‐length measurements were performed on a series of unfractionated random ethylene copolymers having different counit types and a wide composition range. By controling crystallization conditions, crystallinity levels could be varied over wide extremes and a complete repetoire of superstructures was developed. Emphasis was on key mechanical properties such as the initial modulus, yield stress, and the ultimate properties of draw ratio at break and tensile stress. Except for the ethylene‐methacrylic acid copolymers, which behaved in a unique manner, the properties were found to be independent of the chemical nature of the counit and the particular supermolecular structure that was developed. The initial modulus and the yield stress were found to be very dependent on the crystallinity and phase structure. On the other hand, except for the decrease at low counit content, the draw ratio at break was found to be invariant with counit type, crystallinity level, supermolecular structure, and molecular weight. The results are discussed in terms of the molecular constitution of the copolymer and the structure in the crystalline st

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281104

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractIn order to investigate a viscoelastic‐plastic nonlinear constitutive equation for polymer solids, combined tension and torsion tests were performed using polyethylene (PE) hollow cylinders. The experimental data were compared with the numerical results derived from a multiaxial constitutive equation developed from the uniaxial one proposed by Krempl. It is shown that the proposed theory fairly well describes the stress–strain curves of PE up to relatively high strain ranges not only in simple torsion, but also under combined tension–torsion, provided that the current strain is not below the maximum previous s

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281105

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractPlasticization of poly(ethyl methacrylate) (PEMA) by CO2is investigated by dielectric relaxation spectroscopy. The dissipation factor of a dielectric cell containing the film and air gaps is measured as a function of frequency (1–10,000 kHz) and CO2pressure (0–60 atm) over the temperature range 35–115°C. A maximum in the frequency dependence of the dissipation factor, which is attributed to the α relaxation of PEMA, shifts to higher frequency with increasing temperature, pressure, or concentration. The apparent activation energy of the isosteric relaxation decreases from 28 to 23 kcal/mol as the concentration is increased from 0 to 90 cm3(STP)/cm3(polym). The relaxation peak temperature at fixed frequency decreases with increasing concentration. The effect of hydrostatic pressure on the dielectric relaxation is estimated and compared with values for the PEMA‐He and PEMA‐Ar systems. The plasticizing effect of sorbed CO2is discussed on the basis of the rela

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281106

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThermal expansivities along the a, b, and c axes of the orthorhombic unit cell of poly (ether‐ether‐ketone (PEEK) crystals have been determined from 160 to 470 K by wide‐angle x‐ray diffraction. The expansivities along the a and b axes are positive while the expansivity along the c (chain) direction is negative, with values of\[ \alpha _a^c = 11.3 \times 10^{ ‐ 5} {\rm K}^{ ‐ {\rm 1}} ,{\rm }\alpha _b^c = 4.6 \times 10^{ ‐ 5} {\rm K}^{ ‐ {\rm 1}} ,\]and\[ \alpha _\parallel ^c = ‐ 1.4 \times 10^{ ‐ 5} {\rm K}^{ ‐ {\rm 1}}\]at 300 K. The negative α c∥arises from the effective shortening along the chain axis caused by the torsional and bending motions of the chain, whereas the large and positive α caand α cbreflect the weak interactions across the chains. Using a dilatometric technique we have also studied the expansion behavior of isotropic PEEK as a function of crystallinity (X = 0−0.34) and have measured thermal expansivities of oriented PEEK (draw ratio 1–4) parallel and perpendicular to the draw direction. The effects of crystallinity and orientation can be understood by treating semicrystalline PEEK as a composite consisting of crystall

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281107

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractBlock copolymers consisting of long styrene midblocks and much shorter 4‐vinyl pyridine end‐blocks were quaternized withn‐iodo alkanes (2 ≤n≤ 10) to give block ionomers of a novel architecture. The name “bottlebrush” seems appropriate for these materials. A preliminary investigation of the morphology of these systems, prepared by in situ quaternization, is reported here. The morphology is dependent on both the length of the iodo alkane and the relative sizes of the blocks. Even with identical sample histories, two distinct morphologies are seen. One of these is characterized by a single broad SAXS peak, while the other shows a much narrower peak and higher‐order features. The latter morphology is associated with the higher ionic to nonionic ratios and l

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281108

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe viscoelastic properties of a methylmethacrylate–butadiene–styrene (MBS) modifier over the temperature range −140 to 20°C and frequency range 0.01592 (0.1 Rad/s) to 79.62 Hz (500 Rad/s) is represented in terms of a relaxation function proposed by Havriliak and Shortridge to represent the viscoelastic beta process of MBS‐modified and unmodified poly(vinyl chloride) (PVC). The parameters of the expression as well as their temperature dependence were determined from the multiresponse methods developed by Havriliak and Watts. The complex modulus of PVC/MBS modifier blends at 8.26, 10.71, and 13.04 wt % modifier, over a temperature range −140–20°C, and at a frequency of 1 Hz can be represented, nearly within experimental error, in terms of the complex modulus of the neat components, the volume fraction of the modifier, and the blend equations of Uemura and Takayanagi. The small but persistent deviations that are observed are discussed in terms of hydrostatic stresses due to differential coefficients

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281109

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractWhen the density of n‐butyl branches in an ethylene–hexene copolymer increases from 0 to 4.6 butyls/1000 C, the rate of slow crack growth decreases by a factor of 104. The activation energy for the process is nearly independent of branch density and is about 120 kJ/mol. It is the number of tie molecules and whether they are pinned that control the rate of crack growth which involves the disentanglement of the fibrils in the craze. Branching increases the number of tie molecules by decreasing the lamella thickness, while the branches pin some of the tie molecules to prevent them from sliding through the crystal or other points of entanglem

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281110

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY