I have suggested a new term in polymer science . The term coherent refers to a polymer which has the same polymer chain length i.e PDI=1.00 . On the other side of this material is the polymer chain arranged in the same phase like metal and is there a chance for any polymer to be a conductive material . I would like to ask if there is anyone who has achieved polymerization with a product near to PDI=1.
Yes I agree with you, however this abbreviation refer to distribution of polymer according to GPC measurement
DP refers to degree of polymerization & it is an average. It starts from 2 & proceeds to beyond with no limits. I think that you probably mean weight average molecular mass divided by number average molecular mass which indicates polydispersity. A polymer could be made with polydispersity close to (1) by anionic polymerization which involves living polymer. In such case, the polymeric chains will have nearly equal length & in this sense they are coherent.
You probably mean polydispersity index which is expressed by PDI =Mw/Mn. Generally it is very difficult to obtain the PDI=1, usually you can be close to 1 e.g. (1.07, 1.09 or 1.13) these values are usually obtained by controlled living polymerization (anionic), but also there are specific ones ATRP (atom transfer radical polymerization) or RAFT (reversible-addtition-fragmentation chain-transfer polymerization) of NMP (nitroxy-mediated polymerization) all these provide the PDI obtained from following GPC analysis of polymerization product close to 1.
Yes, sort of (noting PDI/ DP confusion).
PDI values below 1.01 are certainly achievable. The theoretical PDI = 1+ v/(v+1)^2, where v = the kinetic chain length. For a xn =100 (i.e. DP in common use) polymer PDI = 1.01. However, to achieve such dispersities:
a. initation must be much faster then propagation
b. the propagation must proceed without termination or irreversible chain transfer (controlled/ quasi-living radical polymerisation uses reversible chain transfer to suppress radical-radical coupling)
c. the termination reaction must proceed cleanly (e.g. killing an anionic polymerisation with degassed water or methanol rather than oxygen)
Few polymerisation schemes achieve all these completely, and most that do are anionic with a few cationic thrown in for good measure. Controlled radical polymerisations give approximately the same dispersities at lower xn values, but radical couplings, disproportionation etc. reactions still occur at a low rate, broadening the molecular weight distribution, especially at higher MW and conversions.
Of course, to make something narrower than Flory's poisson distribution weirder methodologies are needed, such as French, A. C.; Thompson, A. L.; Davis, B. G. Angew. Chem. Int. Ed. 2009, 48,
1248–1252.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials Chemistry
- Polymer Chemistry