Talk:Degree of polymerization

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Merge suggestion

Merge. Wikipedia is not a dictionary. There is no room to expand this article beyond a definition. Irene Ringworm 16:40, 26 February 2007 (UTC)[reply]

Oppose to merge: Once again this discussion belongs in talk page polymerization. My general concerns with merges can be found here: User:V8rik#On_mergers. In addition to that, why treat a reader who is interested in degree of polymerization (a phrase used abundantly in polymer chemistry) to a big article in general. It will take the reader much more time to get the information he or she want if it is buried inside the polymerization article (after all the reader did not select to go to polymerization in the fist place.) The iupac Gold book does a better job. If you merge the phrase degree of polymerization will also disappear from the categories, again a disservice to the reader. Energy is better put in expanding the article V8rik 18:05, 26 February 2007 (UTC)[reply]

Agreed. There's no way to work this into the polymerization article without it being buried and merging with molecular weight poses the same problem. Suggestions for expansion? Irene Ringworm 23:39, 26 February 2007 (UTC)[reply]

Fortunately it hasn't been merged. Zitterbewegung ^Talk 18:08, 9 January 2009 (UTC)[reply]

References

Actually the sort of references I'm looking for are vague statements like "For most industrial purposes, lengths in the thousands or tens of thousands are desired." The definition of DP certainly doesn't need a citation as per wiki guidelines but vague references or potentially controversial statements need to be supported with references or deleted. I'll use the fact template in the future to be more clear. Irene Ringworm 23:39, 26 February 2007 (UTC)[reply]

Repeating Unit

I've got a question about the terms "monomer" and "repeating unit". Let's take the glucose-polymer cellulose (β-1,4-linked glucose) as an example. Does the degree of polymerisation in this context refer to the smallest repeating unit after which the orientation of the glycosidic bond is once again the same (thus, cellobiose = two β-1,4-linked glucose-units), or does it refer to the smallest molecule existing in the polymer (thus, glucose), although its orientation changes after each unit? To exeplify, if we take a cellulose-molecule consisting of 30 glucose-units: is the DP 15 or 30? —Preceding unsigned comment added by 213.114.162.54 (talk) 12:03, 9 October 2010 (UTC)[reply]

Good question - usage is inconsistent on this point. The IUPAC Gold Book definition of DP which is referenced in the article says number of monomeric units (30 in your example), as do the books by Cowie J.M.G. ("Polymers: Chemistry and Physics of Modern Materials", 2nd edn Blackie 1991 p.10) and Allcock H.R., Lampe F.W. and Mark J.P. ("Contemporary Polymer Chemistry" 3d edn Pearson Prentice-Hall 2003). [The latter by implication on p.316: "for condensation polymers prepared from two reactants, the average number of repeating units per molecule is one-half of the average degree of polymerization."]

However Fried J.R. "Polymer Science and Technology" (Pearson Prentice-Hall, 2nd edn 2003, p.27) defines DP as number of repeating units (15 in your example). As does Rudin A. "Elements of Polymer Science and Engineering" (Academic Press 1982, p.7), while noting that they are not always identifiable), and that both definitions are used in the literature.

So what should Wikipedia do? When authoritative sources disagree, the article should mention both versions. In this case I think the monomer definition should be mentioned first as it is supported by IUPAC. Neither is completely satisfactory (which is why there is disagreement) - the definition of the "monomer" may depend on the method of synthesis, and the repeat unit may not be identifiable, for example in DNA or in atactic polymers. Dirac66 (talk) 22:53, 9 October 2010 (UTC)[reply]

I have now revised the intro to mention both definitions, and compared them using as example nylon-6,6 which is simpler than cellulose. Dirac66 (talk) 19:29, 22 October 2010 (UTC)[reply]