Talk:Polymer
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[edit] Clean it up
There are a handful of orphaned paragraphs in this article that have nothing to do with their section headings (esp the last two). I'll rewrite when I have time unless someone beats me to it. Irene Ringworm 19:26, 19 January 2007 (UTC)
[edit] Proteins. Polymers or not?
Proteins are not polymers. The amide linkages of protein molecules have pendant groups that do not repeat and as such are not chains of repeating monomer units. The chain lengthening process for polyamides is also far more sophisticated and exact than is the polymerization of monomers. tRNA shuttle amino acids to growing polypeptides according to the template DNA strand, while addition polymerization is governed primarily by statistical considerations and is driven by large concentration gradients. Industrial polymerization catalysts do not offer the fantastic control over the polymer chain sequence that the cellular machinery does over the polypeptide sequence, and likely never will. For these reasons, the classification of proteins (or polypetides) as polymers is misleading and inaccurate.
-KC
That is really a matter of definition. A more broad term sometimes used is macromolecule. Some people prefer to save the term polymer for chains similar to what we can create synthetically and prefer to put species such as proteins and DNA into the larger category of macromolecules. I don't think it is fair to pull proteins out of the polymer category strictly because of their propagation method. Polymeriization includes many different propagation methods, some providing more control over the propagation than others. Certain forms of living polymerization may soon allow us to control specific addition to polymer chains in similar fashion to the protein construction. In fact, a lot of research is going into making our own proteins. I believe that currently it is possibly, but incredibly slow (i.e. a few monomer units per hour). That being said, there are some other reasons to classify non-polymer macromolecules. Exactly what those are is still a good discussion.
TM
Personally I think the analogy between biopolymers and regular polymers is fine. Other biopolymers, such as starches (polymerized sugars) or the isoprenoids (see isoprene for a classic polymeric unit in a biological context), seem neglected in this article and the remarks on proteins are such that the author believes all proteins are enzymes or transport proteins. Not all are. Some are purely structural proteins, and the notion of active region (isn't the more precise term an active site?) versus structural region is meaningless in this context. Of course, structural proteins are often evolutionarily scavenged enzymes (classic example being the crystallins of the eye, which tend to be derived from various and sundry proteases), so maybe it isn't all that important ;) Dwmyers 18:03, 18 Sep 2003 (UTC)
Proteins are polymers, they're just block copolymers with many different monomers, and very small blocks :) TM - we can already synthesise custom polypeptides, eg via the polystyrene tethered approach of the Merrifield synthesis (for which the 1984 Nobel Prize was awarded). Iridium77 00:17, 9 Mar 2004 (UTC)
Although vandalism is bad and I do not like, I must admit I laughed out loud when I read "dog shit is a common polymer that people like to eat". Well done, whoever put that, it was quite funny (at least I thought so) but don't do it on wikipedia please... Borb 22:49, 8 Apr 2005 (UTC)
In my opinion proteins or the DNA are not polymers and the term macromolecule is more suitable because they are not the repetition of units called monomers. I also disagree with the term block-copolymers for proteins because, in my opinion, this term is used for the macromolecules in which every block is a polymer itself, it means it is formed with teh repetition of identical units. Nevertheless nowadays some polypeptides exist as polymers, for expample poly(Glu) or poly(Ala), or even more complex as the elastin-like polymers, (GVGVP)n, or the silk-like polymers.donjavi.
[edit] Nylon
If memory serves correctly the nylon example is inaccurate - the more reactive acid chloride is used and hydrogen chloride gas the byproduct. --ThomasWinwood 00:12, Apr 19, 2005 (UTC)
There are actually different routes to synthesize nylon. The example where the polyamide is synthesized with the acid chloride is called the "Schotten-Baumann" reaction. It's a form of "interfacial polymerization", also known as a "two phase reaction". It's extremely fast - the reaction rate is 104 to 108 times faster than the mechanism suggested on the page. But, acid chlorides are rather expensive, so its usually used when there are no other routes for synthesis available. However, I think the way the reaction is outlined on the page is misleading, and more work can be done in terms of illustrating the displacement and elimination of the small molecule correctly. HappyCamper 04:13, 19 Apr 2005 (UTC)
[edit] Article Improvement Drive
Contact lens is currently nominated to be improved on Wikipedia:Article Improvement Drive. Please support the article with your vote. --Fenice 10:51, 16 January 2006 (UTC)
Branching Information Under the branching section: IPN stands for Inter-penetrating polymer networks, not integrated polymer networks. You might also want to discuss the effects of both short and long chain branching; how one affects the properties like Tm and Tg and the other influences melt properties.
-ASK
http://www.xanga.com/starrydesigns COOL!
[edit] Vandalism
Well of all articles, this one on polymers has been vandalised. Probably by one of the IP addresses on the history page but I don't know enough about wikipedia to be 100% sure. I've removed the vandalism which said this:
"Proteins are polymers of the nigger family... no one likes the proteins cos they are too cool ffor school amino acids" Changed to Proteins are polymers of amino acids. Once again, I have to add that that's probably not true, I'm just here doing a school project, but it's more likely than what's already there. --Calum Smith 13:30, 2 August 2006 (UTC) PLUS THE SWASH MAN STRUCK AGAIN!!!!!
[edit] polymer
WILL POLYMER EFFECT CHEESE AND BREAD WHEN COVEERED IN PLATSIC WRAP? WILL THE POLYMER IN PLASTIC WRAP KEEP THE FOOD FRESH?
Magic Eightball Say: Signs Point To mabye consult your wife . 68.215.226.236
[edit] New Polymer-related article: Polyanhydrides
I have added an article about polyanhydrides. Any feedback on that article would be appreciated. I am in the process of finding pictures or graphics for the page.
Thanks!
[edit] Cleanup time
I have removed some paragraphs from the main article to the talk page for cleanup or reclassification. Feel free to rework and reinsert into the article (in appropriate places). List below: Irene Ringworm 10:13, 24 February 2007 (UTC)
[edit] from the header
Similar monomers can have various chemical substituents. These differences between monomers can affect properties such as solubility, flexibility, and strength. In proteins, these differences give the polymer the ability to adopt a biologically-active conformation. (See self-assembly.) Identical monomers with nonreactive side groups result in a polymer chain that will tend to adopt a random coil conformation, as described by an ideal chain mathematical model. Although most polymers are organic, with carbon-based monomers, there are also inorganic polymers; for example, the silicones, with a backbone of alternating silicon and oxygen atoms and polyphosphazenes.
Rationale for removal: out of place in general introduction. Incoherent. No references.
[edit] from Polymer nomenclature
Polymers are typically classified according to four main groups:
- thermoplastics (linear or branched chains)
- thermosets (crosslinked chains)
- elastomers
- coordination polymers
Polymer signifies a chain of thousands of monomers that are covalently bonded together usually by the carbon atoms of the polymer backbone, but the backbone can consist of other atoms such as silicon. Examples of polymers include substances anywhere from proteins to stiff, high-strength Kevlar fibres. For example, the formation of poly(ethylene) (also called polyethene) involves thousands of ethene molecules bonded together to form a straight (or branched) chain of repeating -CH2-CH2- units (with a -CH3 at each terminal):
Rationale for removal: Doesn't belong in nomenclature section. Redundant. No references.
Proteins are polymers of amino acids. Typically, hundreds of the (nominally) twenty different amino acid monomers make up a protein chain, and the sequence of monomers determines its shape and biological function. (There are also shorter oligopeptides which function as hormones.) But there are active regions, surrounded by, as is believed now (Aug 2003), structural regions, whose sole role is to expose the active regions. (There may be more than one on a given protein.) So the exact sequence of amino acids in certain parts of the chains can vary from species to species, and even given mutations within a species, so long as the active sites are properly accessible. Also, whereas the formation of polyethylene occurs spontaneously under the right conditions, the synthesis of biopolymers such as proteins and nucleic acids requires the help of enzyme catalysts, substances that facilitate and accelerate reactions. Unlike synthetic polymers, these biopolymers have exact sequences and lengths. (This does not include the carbohydrates.) Since the 1950s, catalysts have also revolutionised the development of synthetic polymers. By allowing more careful control over polymerization reactions, polymers with new properties, such as the ability to emit coloured light, have been manufactured.
Rationale for removal: Doesn't belong in nomenclature section. No references. Poorly organized.
[edit] From Constitution of polymers
Copolymerization with two or more different monomers results in chains with varied properties. There are twenty amino acid monomers whose sequence results in different shapes and functions of protein chains. Copolymerising ethene with small amounts of 1-hexene (or 4-methyl-1-pentene) is one way to form linear low-density polyethene (LLDPE). (See polyethylene.) The C4 branches resulting from the hexene lower the density and prevent large crystalline regions from forming within the polymer, as they do in HDPE. This means that LLDPE can withstand strong tearing forces while maintaining flexibility.
A block copolymer is formed when the reaction is carried out in a stepwise manner, leading to a structure with long sequences or blocks of one monomer alternating with long sequences of the other. There are also graft copolymers, in which entire chains of one kind (e.g., polystyrene) are made to grow out of the sides of chains of another kind (e.g., polybutadiene), resulting in a product that is less brittle and more impact-resistant. Thus, block and graft copolymers can combine the useful properties of both constituents and often behave as quasi-two-phase systems.
The following is an example of step-growth polymerization, or condensation polymerization, in which a molecule of water is given off and nylon is formed. The properties of the nylon are determined by the R and R' groups in the monomers used.
The first commercially successful, completely synthetic polymer was nylon 6,6, with alkane chains R = 4C (adipic acid) and R' = 6C (hexamethylene diamine). Including the two carboxyl carbons, each monomer donates 6 carbons; hence the name. In naming nylons, the number of carbons from the diamine is given first and the number from the diacid second. Kevlar is an aromatic nylon in which both R and R' are benzene rings.
Copolymers illustrate the point that the repeating unit in a polymer, such as a nylon, polyester or polyurethane, is often made up of two (or more) monomers.
Rationale for removal: No references. Poorly organized. String of non sequiturs, none of which have anything to do with intended subject heading.
[edit] Mechanical properties of polymers
Low coefficients of friction - In general coefficients of friction for polymers against polymers, metals or ceramics range from 0.15 to 0.6. Composites also retain the low coefficients of friction while having greater stiffness and strength. [1]
Rationale for removal: Reference is a class project from RPI undergrads - not exactly authoritative. There are interesting things worth saying about polymers as lubricants or low-friction materials but this isn't it. Not my area of expertise. Any takers to improve this one? Irene Ringworm 20:22, 25 February 2007 (UTC)
Creep - the application of a constant (time independent) load causes a continuous displacement associated with the diffusion of the atoms or molecules within the material. This response is termed creep, the progressive deformation of a material under a sustained load. In metal alloys, creep becomes a problem at temperatures above approximately 0.6 Tm, where Tm is the melting temperature of the metal. However, in polymers, creep is an even more critical design problem because the polymers can be described as rubbery and viscous at temperatures above the glass transition temperature.
- Ways to resist creep in polymers: In order to make polymers more resistant to creep at room temperature, increasing the degree of cross-linking within the polymer chain will raise the Tg. Therefore, a higher glass transition temperature allows for more resistance to creep. Furthermore, as molecular mass of the polymer increases, the viscosity, η will increase and effectively reduce the rate of creep. Also, the more crystalline the polymer, the more creep-resistant it is compared to entirely glassy polymers.
Rationale for removal: A nicely referenced, well-organized section on polymer creep is already part of Creep. It probably makes sense to summarize this section in the polymer article but leave the details (including the definition of creep) to the main article.Irene Ringworm 20:22, 25 February 2007 (UTC)
J-shaped stress-strain curves - Many biological materials actually display J-shaped stress-strain curves. In other words, the material will initially experience large extensions for small stresses. Then, as the extension gets larger and larger, the material gradually becomes stiffer and more difficult to extend.
A J-shaped stress-strain curve enables biomaterials to be extremely tough. Because the lower part of the curve has large extensions for small stresses, the shear modulus in that region is very low and so any released strain energy can be prevented from contributing to fracture of the material. Furthermore, large extensions of the material require very large stresses, and so these large extensions are likely to occur only infrequently. The J-shaped stress-strain curve does not lead to the elastic instabilities which arise in S-shaped curves.
An example of biological materials with J-shaped stress-strain curves is mammalian skin tissue. If you pinch your earlobe and try to pull it downwards, it is initially easy to stretch, but then at larger extensions it becomes much more difficult to stretch.
Rationale for removal: Nonsequitur - relevant to biological materials but not clear how this relates to polymers.Irene Ringworm 20:22, 25 February 2007 (UTC)
S-shaped stress-strain curves - These occur in lightly cross-linked polymers such as rubber. A material that exhibits an S-shaped stress-strain curve is very is applied to the material, a very large stiffness occurs because at these high loads, the polymer chains are mostly aligned with the applied stress. Therefore, applying even more stress will stretch the strong intramolecular bonds.
Rationale for removal: Needs references.Irene Ringworm 20:22, 25 February 2007 (UTC)
[edit] Physical properties of polymers
- degree of polymerization - The number of structural units in a polymer chain.
- molar mass distribution - The relationship between a polymer fraction and the molar mass of that polymer fraction.
- crystallinity - as well as the thermal phase transitions:
- Tg, glass transition temperature
- Tm, melting point (for thermoplastics).
- Stereoregularity or tacticity - the isomeric arrangement of functional groups on the backbone of carbon chains.
Rationale for removal: Proseline. Expanded and referenced in new edit. Irene Ringworm 19:19, 28 March 2007 (UTC)
[edit] Biological Polymers
Oops. Perhaps I should have read the discussion first before making my addition.
But, under category of organic polymers, I added (back) biological polymers:
polypeptides polysaccharides polynucleotides
They do have the word poly in them. They are synthesized (by biological processes) out of sub units (peptides, saccharides, and nucleotide). I think these remarkably diverse and important compounds deserve a brief mention in this article.
I was also tempted to add fatty acids as polymers, since they are formed by the condensation of acetic acid (in the form of Acetyl-CoA).
Clemwang 21:24, 26 February 2007 (UTC)
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- Addition is fine and consistent with cleanup. I have some additions in the works to expand - I don't think anyone will argue that these are polymers. I'm hoping to have some sort of "polymers in nature" section that can discuss biopolymers in more detail and point folks to the appropriate pages on polypeptides etc. Feel free to help out in any way you can. My expertise is limited to physical polymer chemistry and I'll need other editors to fill in the blanks. Irene Ringworm 22:20, 26 February 2007 (UTC)
[edit] Clean Up?
I dont really think there needs to be any clean up. I mean, its already organized, don't u think? It's pretty fluent, and the pages aren't really too short I added some info to the Polymers in Solution topic. It should be verified though. AznShark 00:59, 14 March 2007 (UTC)
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- I'm doing my best but there are still sections like "chemical properties of polymers" and "physical properties of polymers" which are rambling, unencyclopedic, and sometimes factually incorrect. If you can offer help there it would be appreciated. Irene Ringworm 19:32, 25 March 2007 (UTC)
