摘要:

AbstractThe mechanical anisotropy of polyvinyl chloride oriented in two perpendicular directions with different draw ratios has been studied. The results are compared with the anisotropy of uniaxial samples oriented at a common draw ratio. The propagation velocities of ultrasonic pulses have been measured by an immersion technique. Longitudinal wave velocities have been measured in three principal planes over a wide range of propagation directions. The limitations of measuring velocities in the planes containing the draw axes were mitigated by use of a special slicing technique. Measurements were performed at 2 MHzand 25°C. Velocities of the transverse waves were measured for incident wave angles greater than the critical angle. From these measurements, five elastic moduli were calculated for the uniaxially oriented samples, and nine elastic moduli were obtained for the biaxially oriented samples. In biaxially oriented samples, the moduli along the draw axes are directly proportional to the draw ratio in the same direction

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290801

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe relationship between the basic structure parameters of a polycaproamide (PCA) substrate and the structure of grafted polyacrylonitrile (PAN) was studied. The influence of the total degree of crystallinity of the PCA fiber, its crystal modification, and the orientation of crystallites on the PAN structure in the copolymer were analyzed. The structure of PCA‐PAN graft copolymers was studied by infrared spectroscopy (dichroism and ATR), X‐ray structure analysis, nuclear magnetic resonance, and scanning electron microscopy. The development of an oriented isotactic structure was found in PAN grafted to a PCA substrate having a bigh degree of orientation. The type of crystal modification of PCA does not affect the structure formation process in PAN. The oriented structures in PAN arise directly in the course of synthesis rather than on the subsequent rearrangement of the molecular chains under the action of orientation drawing. In contrast to earlier findings, our studies indicate that synthesis under the conditions specified increases the degree of crystallinity of PCA and crystallite size. The grafted PAN chains are presumed to grow epitaxially under the influence of PCA crystalli

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290802

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractPolymer packing density can be conveniently measured by either density‐based measurements (direct or estimated free volume) or wide‐angle X‐ray diffraction (WAXD) spectra. Previously reported diffusivity and permeability values for various polyarylates and polyimides are examined on the basis of the packing density measured by these different techniques. It is shown that in these rigid glassy polymers, the mean intersegmental distance, thed‐spacing, obtained from WAXD provides a better measure of the effect of polymer packing on diffusivity than either direct density measurements or estimated free volumes. It has been possible to correlate previously reported diffusivity and sorption data for various polyarylates and polycarbonate on the basis of the WAXD investigation, using thed‐spacing and the amorphous peak width, respectively. The effect of polyarylate structure ond‐spacing has been studied. A series of polyarylates have been synthesized with different substituents on the bridge carbon. In this series thed‐spacing remains constant while the carbonyl group density and the glass transition temperatures are varied. However, small substituents on the aromatic ring cause significant changes in thed‐spacing. These results can be used to tailor polyarylates with desired intersegmental distances and ch

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290803

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractViscoelastic properties of styrene‐co‐methyl methacrylate random copolymers have been determined over a temperature range covering the glass transition, the rubbery plateau, and the terminal zone and compared with polystyrene and polymethyl methacrylate homopolymers. Nonlinear behavior was observed in the variations of most of the physical and rheological characteristics with the methyl methacrylate content in the copolymer. Results are interpreted in terms of the rupture of polar‐polar intermolecular interactions between ester groups due to the presence of styrene

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290804

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractA systematic investigation of the dynamic mechanical properties of high‐density polyethylene (HDPE)/high‐impact polystyrene (HIPS)/copolymer blends was carried out. Blends of 80/20 weight percent of HDPE/HIPS were prepared in the melt state at 180°C in a batch mixer. Synthesized pure diblock (H77) and tapered diblock (H35) copolymers of hydrogenated polybutadiene (HPB) and polystyrene (PS) were added at different concentrations (1, 3, and 5 wt %), and the dynamic mechanical properties were investigated. The results show that: (1) both the tapered and the pure diblock copolymers enhance the phase dispersion and the interphase interactions; (2) structure and molecular weight are both important parameters in the molecular design of copolymers; (3) important effects occur when only small amounts of copolymer are added (up to the interface saturation concentration SC); (4) a micellar structure formation is possible when the copolymer is in excess in the blend; (5) the effect of the copolymer structure on the SC and the critical micellar concentration (CMC) is more pronounced than the effect of molecular weight. These concentrations are found to be lower for the tapered diblock copolymer. The analysis of the dynamic mechanical thermal analysis (DMTA) results obtained for the 20/80 HDPE/HIPS blend leads to the conclusion that the copolymers also enhance the interactions between heterogeneous phases. Similar conclusions based on electron microscopy were reported in the literature. DMTA shows great potential to relate macroscopic observations to the state of a copolymer in an immiscible b

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290805

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractIn order to obtain useful information about the molecular motion and structure of poly(N‐isopropylacrylamide) (PNiPAM) in aqueous solution, proton spin‐lattice relaxation times, proton spin‐spin relaxation times, and volume changes were measured at pressures from 1 to 400 kg/cm2as a function of temperature. We found that the molecular motion and the structure of water and PNiPAM in PNiPAM/water solution transitionally change at gelation temperature (31°C). The effect of pressure on such transitional changes is studied. It is suggested that application of pressure to the system prevents the ge

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290806

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractIn situ birefringence measurements of the seeded growth in a tubular flow geometry of 0.01 wt% solution of a polyethylene fraction in xylene have been used to determine the flowinduced crystallization kinetics as a function of temperature and flow rate. In contrast to earlier reports on higher molecular weight polyethylene and polypropylene systems, orientational properties of the crystallized fibers do not show a clear correlation with growth conditions (i.e., temperature and flow rate). The combined kinetic data from these experiments and our earlier studies of higher molecular weight polyethylene—xylene and polypropylene—tetralin systems are analyzed in terms of a modified from of the Avrami equation which provides a basis for separately correlating temperature and flow rate effects. The observed temperature dependency of the crystallization process can be interpreted in terms of nucleation and growth models while the flow rate dependency can be interpreted on the basis of entanglement formation arguments. Results showing liquid phase precursor formation in an atactic polystyrene system are also presented to further document the liquidphase separation which can be induced in polymers under f

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290807

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractStoichiometric, completely cured binary or ternary mixtures of the diglycidylether of bisphenol A (DGEBA), isophorone diamine (IPD), and trimethylcyclohexylamine (TMCA) monomers were studied by differential scanning calorimetry. The relations between the glass transition temperatureTgand the structure of the copolymer networks were investigated. Good predictions ofTgcan be obtained on the basis of the following hypothesis: (1) the molar contributionsMiT−1gito the “copolymer effect” of difunctional groups are additive, (2) the crosslinking effect can be expressed by the DiMarzio relation in which the molar contribution of crosslink mers is an increasing function of the stiffness of linear segments. For the seven systems under study, the deviation between calculated and experimentalTgvalues is within experimental sc

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290808

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractInteraction of high‐pressure CO2gas with a silicone elastomer, and to a lesser extent, with a nitrile rubber and a PTFE have been investigated. Sorptive dilations of the polymers were measured with the help of custom‐made piezoelectric ultrasonic transducers under gas pressures of up to ca. 22 MPa at 42°C. The gas mass sorption was determined by a vibrating reed probe. For the silicone elastomer system the dilation isotherm mimics the sorption isotherm. The partial molar volume (PMV) of the absorbed CO2gas in the silicone elastomer has been computed. A significant drop in the PMV value is observed when the CO2gas becomes supercritical. In the transition region, the transmission of ultrasonic signals through the specimen indicated the formation of discrete small (estimated as about 60 μm in diameter) high density zones of CO2in the rubber matrix. The plasticization effects of the absorbed high pressure CO2gas have been identified from the interpretation of the changes in the acoustic longitudinal modulus obtained from ultrasonic transmission measurements. The effects of rapid gas decompression on the structural integrity of the various polymers have also been determined. Significant inflation of certain specimens occur toward the latter stages of the decompression cycle. The initiation and development of internal cracks or bubbles was followed by monitoring the ultrasonic signal attenu

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290809

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractA series of random copolymers of methylmethacrylate and methacryloxypropyltris (trimethylsiloxy) silane were synthesized by free radical polymerization under ultraviolet light. The permeabilities of these copolymers to carbon dioxide, oxygen, and nitrogen were determined and correlated with the packing densities of the polymers. Correlation between the permeability and permselectivity of these copolymers is also addressed.

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290810

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY