摘要:

The temperature dependence of the EPR spectrum of randomly oriented nitroxide radicals doped into nitrocellulose, polyurethane, and mixed nitrocellulose-polyurethane systems has been used to measure the temperature dependence of the motional correlation time during the glass-to-rubber transition. The correlation time for motion of the probes is obtained from the inward shift of the extrema lines using theories of slow tumbling, and is shown to follow an Arrhenius temperature dependence. The energy barriers to the motion are estimated.

ISSN:0022-2348    

DOI:10.1080/00222348408219475

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The cross-link density of DCP-cured natural rubber uniaxially deformed to various extension ratios at room temperature was measured. The cross-link density decreased characteristically with increasing extension ratio. A new model for the structure of the network is proposed in order to explain this decrease in cross-link density. The model can give a new interpretation of the stress-strain behavior of rubber vulcanizates. The birefringence of stretched rubber vulcanizates was determined using a polarizing microscope. The observed birefringence, δT, can generally be factored into two parts: One is the birefringence of the amorphous phase, δTa; the other is the birefringence due to the strain-induced crystalline phase, δTc. In the present paper, it has become feasible to separate δT into δTaand δTc.

ISSN:0022-2348    

DOI:10.1080/00222348408219476

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The thermal behavior of a series of poly(α-olefin-co-maleic anhydride) copolymers was studied by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Polymers with side-chain lengths of 16, 18, and 23 carbons were found to have crystallizable side chains. The melting point and heat of fusion of the side chains increased with increasing side-chain length. Glass transition temperatures were observed to be greater than the side-chain melting points. The molecular weight dependence of the Tg's obeyed the Fox-Flory relationship, with Tg∞= 129°C and k = 1.5 × 105. A spectroscopic method to monitor the extent of hydrolysis of the maleic anhydride units was developed, and the hydrodynamic volume in THF was observed to be dependent on the extent of hydrolysis.

ISSN:0022-2348    

DOI:10.1080/00222348408219477

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor