ISSN:
0449-2978
Schlagwort(e):
Physics
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
A polymerization mechanism in which monomers and dimers add to a growing polymer chain with different rate constants and different stereospecificity is considered. A fraction of the dimers are in isotactic placement internally, and low conversion to polymer is assumed. The stereosequence distribution generated by this monomer-dimer model is calculated and found to be non-Markovian in general. A method of determining kinetic parameters of the mechanism from experimentally obtained placement sequence probabilities and related experimental tests for the applicability of the mechanism are also described. A few ramifications of the general monomer-dimer model are then discussed. A case of special interest is the one in which all the dimers have a single internal tacticity, a model recently proposed by Blumstein, et al., for a polymerization involving the surface of certain aluminosilicate minerals. For the case where all dimers are isotactic, it is found that although the propagation of consecutive syndiotactic placements alone is simple Markovian, the overall stereosequence distribution is non-Markovian. Another special case of interest is the limiting case with dimers only in the feed. This case turns out to correspond to a special case of the cyclopolymerization mechanism proposed previously by Reinmöller and Fox. Although the tacticity distribution of the placements created by the head (or tail) monomer units alone of the dimers is Bernoullian, the composite stereosequence distribution is again non-Markovian.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pol.1971.160090405
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