File talk:Vulcanization of POLYIsoprene V.2.png
Latest comment: 11 years ago by Dirac66
(Response to comment on file page by Cjp24 on 18 November 2012) This is just a schematic not an exact structure of a vulcanizate since n may be either 0 or 1 or 2 or X, indicating again the schematic approach. The number of cross-links per repeating unit depends on the amount of sulfur agents applied. The capture of the drawing should mention the schematic caracter of the drawing. Best regards, --Jue (talk) 13:45, 18 November 2012 (UTC)
- Hallo Jü. Concerning this "example", as already indicated:
- - the position of sulfur atoms relative to the double bonds is not validated;
- - this presentation suggests that the density of cross-links is high (this is a common mistake); usually, about 1 repeating unit per 50 to 100 is cross-linked (for this presentation: 1 per 2).
- In addition, the number of sulfur atoms of a sulfide bridge may vary from 1 to about 10. This does not match with "n = 0, 1, 2, 3 ..." which is written below the presentation and "n may be either 0 or 1 r 2 or X" written on the first line of this discussion.
- Best regards. --Cjp24 (talk) 04:52, 20 November 2012 (UTC)
- The point about the position of sulfur atoms is that the diagram shows 3 sulfurs linked to allylic carbons (S-C-C=C) and 3 others linked to olefinic carbons (S-C=C). Is there such a mixture of C-S bond types in reality? Morrison and Boyd (Organic chemistry, 4th ed, Allyn and Bacon 1983, p.449) say "Cross-linking in rubber ... is brought about by vulcanizing ... which causes formation of sulfur bridges between molecules. This reaction involves reactive allylic positions, and thus depends on the double bond in the polymer." This suggests that the figure should be redrawn with all sulfurs linked to allylic carbons.
- The high cross-link density in the diagram, however, is useful because it helps to make the diagram easy to understand. We can add a note in the figure captions and the article text (in each language) to explain that the true cross-link density is usually lower than shown in the diagram. Dirac66 (talk) 14:54, 22 November 2012 (UTC)
