Mean‐square unperturbed dimensions 〈 r2〉0 and their temperature coefficient d ln〈 r2〉0/dT have been calculated for ethylene‐propylene copolymers by means of the rotational isomeric state theory of chain molecules. Conformational energies required in the analysis are shown to be readily obtained from previous analyses of polyethylene and polypropylene, without additional approximations. Results thus calculated are reported as a function of chemical composition, chemical sequence distribution, and stereochemical composition of the propylene sequences. It is shown that 〈 r2 〉0 and d ln〈 r2〉0/dT for these copolymer chains should be most sensitive to chemical sequence distribution in the case where propylene sequences are highly isotactic in stereochemical structure. Calculations carried out using values of these variables thought to be appropriate for ethylene‐propylene polymers experimentally investigated give values of d ln〈 r2〉0/dT which are in good agreement, in general, with those obtained from previousl...

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On the Configurational Statistics of Ethylene-Propylene Copolymers

The dynamic mechanical properties of Eucommia ulmoides (EU) gum with different degree of cross-linking are studied systematically in this article. EU gum displays five dynamic mechanical behaviors with increasing degree of cross-linking. Before elastic critical turning point, EU gum shows two active dynamic mechanical temperature zones with rising of temperature, one is T
 g zone, controlled by glass transition mechanism, the other is T
 m zone, controlled by crystalline melting mechanism, its tan δ values at T
 g zone and T
 m zone during the process of cross-linking obey the dynamic reverse transition law: at the T
 g zone, the peak value of its tan δ is proportional to cross-linking degree inversely proportional to crystallinity degree; at T
 m zone, its tan δ value is proportional to crystallinity degree and inversely proportional to cross-linking degree. In addition, the T
 g, T
 m, and X
 c of the EU gum with different degrees of cross-linking are obtained as well. In terms of temperature, the tan δ ~ T curve of EU gum has two active dynamic mechanical temperature zones. One is T
 g zone controlled by glass transition mechanism; the other is T
 m zone controlled by crystalline melting mechanism. In terms of cross-linking degree, the tan δ ~ T curve of EU gum displays five dynamic mechanical models.

Dynamic mechanical properties of Eucommia ulmoides gum with different degree of cross-linking

https://link-springer-com-443.webvpn.jmu.edu.cn/content/pdf/10.1007%2F978-3-319-68255-6_84.pdf

Polyhydroxyalkanoates: Biodegradable Plastics and Their Applications

The thermoelasticity of natural rubber in torsion

Rubber is an interesting material possessing some remarkable properties, the most important of which is its high elastic extensibility. Ordinary solids, such as metals, nonmetallic crystals, and glasses, can be deformed or strained elastically only to a small extent, corresponding to an extension of the order of 1%. If an attempt is made to apply a greater extension, they either break, as in the case of glass, or deform plastically, like lead.

J. Standen

Papers

Thermoelastic measurements on some elastomers