排序方式: 共有34条查询结果,搜索用时 15 毫秒
31.
Elena Vassileva Francisco J. Balt-Calleja M. Esperanza Cagiao Stoyko Fakirov 《Macromolecular rapid communications》1998,19(9):451-454
Microhardness (H) of gelatin dry cast films was measured in the 100–250°C range. A strong H increase with temperature from 330 MPa up to 450 MPa was observed in the first cycle. The H values reached in the subsequent cycles are higher than those obtained in the preceding ones, surpassing the hardness of all commercial synthetic polymers and soft metals. Results are discussed in terms of crosslinking between side-chain reactive groups. 相似文献
32.
Evidence is presented for chemical healing—healing resulting from chemical reactions between neighboring macromolecules located at the interface surface—which has recently been reported in linear polycondensates. In order to distinguish the contribution of the solid-state reaction from the healing effect, samples (nylon-11, nylon-12, and nylon-6,6) with strongly restricted chain mobility (by crystallization and chemical cross-linking in the amorphous zones) have been used. It has been found that under the same healing conditions the cross-linked samples display better welding than the un-cross-linked ones. The conclusion is drawn that the observed healing effect is due mainly to the solid-state chemical reactions at the contact surfaces and not to the diffusion of macromolecules. The results obtained can be considered as an indication of the existence of “chemically released diffusion” in the solid state, i.e., motion of chain segments owing to the interchain and/or intrachain chemical reactions, mainly of the exchange type. 相似文献
33.
Hua He Stanislav S. Stoyko Arthur Mar Svilen Bobev 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(5):455-459
Dirubidium pentacadmium tetraarsenide, Rb2Cd5As4, dirubidium pentazinc tetraantimonide, Rb2Zn5Sb4, and the solid‐solution phase dirubidium pentacadmium tetra(arsenide/antimonide), Rb2Cd5(As,Sb)4 [or Rb2Cd5As3.00(1)Sb1.00(1)], have been prepared by direct reaction of the component elements at high temperature. These compounds are charge‐balanced Zintl phases and adopt the orthorhombic K2Zn5As4‐type structure (Pearson symbol oC44), featuring a three‐dimensional [M5Pn4]2− framework [M = Zn or Cd; Pn is a pnicogen or Group 15 (Group V) element] built of linked MPn4 tetrahedra, and large channels extending along the b axis which host Rb+ cations. The As and Sb atoms in Rb2Cd5(As,Sb)4 are randomly disordered over the two available pnicogen sites. Band‐structure calculations predict that Rb2Cd5As4 is a small‐band‐gap semiconductor and Rb2Zn5Sb4 is a semimetal. 相似文献
34.
M. Schulze M. Seufert C. Fakirov H. Tebbe V. Buchholz G. Wegner 《Macromolecular Symposia》1997,120(1):237-245
Several cellulose derivatives belong to a special class of polymers called hairy-rod macromolecules which are used to generate well-defined supramolecular architectures by the Langmuir-Blodgett (LB) technique. In particular trimethylsilyl cellulose (TMSC) forms monomolecular films on the Langmuir-trough and is transferred onto hydrophobic substrates with a constant transfer ratio, as it does not undergo chemical changes in the film-building process. Silylated celluloses was regenerated which represents a convenient method for the generation of homogeneous ultrathin films with hydrophilic surfaces. The adsorption of polymers and dyes as well as biomolecules onto regenerated and modified cellulose LB films have been studied. In addition, chemical reactions, such as cycloaddition, desilylation and crosslinking reactions within single monolayers have been performed. 相似文献