Crosslinkage

Since the double bonds in the macromolecules of the copolymer have a much lower activity than that of the vinyl groups in the ISP molecule, crosslinkage occurs in this case at later stages of reaction, i.e., when the monomer conversion exceeds 50%. 

The sign + means that the crosslinking agent was used, i.e. introduced into the spinning solution. Crosslinkage was conducted at 140 °C. Thiuram D tetramethylthiuramdisulfide. 

This serious disadvantage of the above types of modified PAN fibres, which excludes the possibility of their practical utilization, can be removed by subsequent crosslinkage. 

The presence of double bonds in the macromolecule of copolymers creates the necessary conditions for the subsequent implementation of crosslinkage of the fibres obtained. 

It has been shown44 that on heating modified fibres containing ZnO at 150-170 °C, zinc chloride is formed as a result of crosslinkage by interaction of the 3-chloro-2-butenyl groups with ZnO. Under these conditions the nitrile groups of the copolymer molecules do not undergo any chemical conversions. 

These results made it possible to arrive at a sufficiently well-grounded conclusion that the effect of raised heat resistance caused by the formation of intermolecular chemical bonds is not very significant, and that the usually observed considerable increase of heat resistance of PAN fibres as a result of a crosslinkage with bifunctional compounds, is caused not by the formation of intermolecular chemical bonds, as it has usually been thought45, 46, but by cyclization reactions of the nitrile groups with the formation of naphthyridine cycles47. ... 

This drug belongs to the group of alkylating antineo-plastic drugs. Alkylation finally results in covalent crosslinkage of DNA strands that interrupts the... 

In this case, the crosslinking density is the sum of the effective crosslinking density and the secondary cyclization, since both crosslinkages are elastically effective. The calculation conditions are the same as Figure 1 except that the number of secondary cycles formed per effective crosslinkage T) is 20. 

The second step involves coal activation. The relative ability of different media to split reactive crosslinkages of the coal is a crucial factor in obtaining conversion. The reactive crosslinks appear to be primarily ether bonds and aliphatic linkages, with suitably substituted neighboring aromatic centers (.5,6). Work in these laboratories has shown that ZnCl2 is an active catalyst for cleavage of these crosslinks (5,9). Addition of methanol may enhance this activity, whereas excessive solvent appears to dilute the catalyst. 

The many sulphur dyes synthesised via quinonimine intermediates are polymeric products containing numerous disulphide crosslinkages that can be broken by reduction in aqueous sodium sulphide thioether groups survive the reduction process. The smaller thiolate-containing molecules formed are substantive to cellulose. Although the actual structures of such dyes are complex, their essential features can be illustrated in an idealised model (Scheme 6.23), in which X = S, NH or O, and R indicates substituents or annelated rings. 

Tanimizu M, Asada Y, Hirata T (2002) Absolute isotopic composition and atomic weight of commercial zinc using inductively coupled plasma mass spectrometry. Anal Chem 74 5814-5819 Van der Walt TN, Strelow FWE, Verheij R (1985) The influence of crosslinkage on the distribution coefficients and anion exchange behavior of some elements in hydrochloric acid. Solvent Extract Ion Exchange 3 723-740... 

Veis, A., Bhatnagar, R. S. The microfibrillar structure of collagen and the placement of intermolecular covalent crosslinkages. In Chemistry and molecular biology of the intercellular matrix, Vol. 1, pp. 279. Balazs, E. A. (ed.). London, New York Academic Press 1970... 

The chain formed by polymerization of amino acid molecules provides the primary structure of a protein. Together with any covalent crosslinkages and other modifications, this may also be called the... 

Postsynthetic modifications of cytoskeletal microfilaments can also occur. For example, epidermal keratin has been found to contain lanthionine, (y-gluta-myllysine) and lysinoalanine, both presumably arising from crosslinkages.306... 

Crosslinkages reducible with borohydride are characteristic of newly formed collagen but these disappear and are replaced by more stable crosslinks as collagen matures. For example, a 3-hydroxypyridine that joins three triple helices may be formed from the reaction of two ketoamine groupings (with elimination of one glycosylated hydroxylysine residue).636 639 Similar chemistry can also produce pyrrole crosslinks.639... 

---