摘要:

Syndiotactic polystyrene films were prepared from the melt with different thermal treatments. Amorphous or crystalline films were obtained; x-ray analysis shows that in the crystalline samples two crystalline forms can be present and that the phase composition depends on the thermal conditions. The two forms show a different stability to liquid methylene chloride, one being stable while the other can be dissolved or transformed to a completely different crystalline structure. In all the analyzed samples the study of transport properties of CH2Cl2at low activity indicates that the amorphous component behaves as atactic polystyrene. This allows the determination of the crystallinity in the different samples.

ISSN:0022-2348    

DOI:10.1080/00222348908215234

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Creep crack propagation in high-density polyethylene (HDPE) is observed to occur with an accompanying layer of damage ahead of the crack tip. The crack layer theory, which accounts for the presence of both the damage and the main crack, is applied to the problem. It is observed that the kinetic behavior of HDPE under creep consists of three regions: initial acceleration, constant crack speed, and reac-celeration to failure. Within the first two regions crack propagation appears “brittle,” while in the third region “ductile” behavior is manifested. Ultimate failure occurs via massive yielding of the unbroken ligament. The notion of critical crack length, well defined in many polymers, is shown

ISSN:0022-2348    

DOI:10.1080/00222348908215235

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

This article makes an attempt to deduce the interrelationship between catalytic reaction rate and solubility parameters for a polymer-metal complex catalyst system for hydrogenation of a small molecule substrate based on compatibility of the polymer backbone and the substrates. Using thermodynamic and kinetic principles, a formula is obtained as follows:

ISSN:0022-2348    

DOI:10.1080/00222348908215236

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Polyethers were prepared by condensing the disodium salt of bis(8-hydroxy-5-quinolinylmethylene) sulfide (Na2BHQS), respectively, with 1,4-xylylene dichloride, 4,4'-dichloromethyl diphenyl ether, 4,4'-dichloroacetyldiphenyl, and 4,4'-dichloroacetyldiphenyl ether in dioxane and DMF solvents. The insoluble polyether samples were characterized by infrared spectroscopy and by thermogravimetry. The electrical conductivity was measured in the temperature range from 35° to 250°C.

ISSN:0022-2348    

DOI:10.1080/00222348908215237

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Smectic isotactic polypropylene films were annealed at different temperatures for different times. Density, wide-angle x-ray scattering (WAXS), differential scanning calorimetry, and the transport properties of methylene chloride vapor were used to follow the transformation of the smectic phase into the monoclinic phase. The results of WAXS diffractograms indicate different saturation levels of crystallization with the maximum order attained progressively more quickly at higher temperatures. Density measurements, however, show that, after a first saturation level, a further increase of this parameter occurs after long annealing times; and this second step is lower, the higher the temperature. Sorption and diffusion, analyzed to investigate the amorphous component, show that annealing the smectic phase at 50°C results in a decrease of amorphous fraction without transformation of the smectic phase. The transition from smectic to monoclinic phase occurs at temperatures higher than 60°C. During the annealing at 80°C there is first a decrease of amorphous fraction corresponding to the first saturation level of the density, and then a further decrease of amorphouse phase corresponding to the final increase of density after 24 hr of annealing.

ISSN:0022-2348    

DOI:10.1080/00222348908215238

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Biaxial rolling was carried out on low-density polyethylene, and the rolled samples were studied using various techniques. Scanning electron microscopy and analysis of transport properties were used to obtain structural information, which was correlated to thermomechanical and dynamic-mechanical behavior. Results indicate that the initial morphology is destroyed by rolling and that clumps of molecules, like fibrils, are generated parallel to the rolling plane. The molecular orientation in the plane is mainly radial, with some reinforcement, particularly at high rolling degree, along axes diagonal with respect to the rolling directions. The rolling drastically reduces the molecular mobility in the amorphous component, as indicated by the transport and dynamic mechanical data. The effects induced by rolling present some relevant analogies with the effects induced by monoaxial drawing.

ISSN:0022-2348    

DOI:10.1080/00222348908215239

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0022-2348    

DOI:10.1080/00222348908215240

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor