ISSN:
0025-116X
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
About one hundred samples of poly(1,3-cyclopentylenevinylene) (2) were prepared by ring-opening polymerization of norbornene using a variety of metathesis catalysts based mainly on WCl6 or MoCl5, with EtAlCl2, BuLi, Ph4Sn, and (CH2=CHCH2)4Sn as cocatalysts, and with methyl acrylate, diethyl maleate or diethyl fumarate as additives. Ir, Re, V, and Os compounds were also used as catalysts. The double bond pair sequences, trans-trans (tt), trans-cis (tc) etc. were determined from the 13C NMR spectra of these samples and the ratios rt(=tt/tc) and rc(=cc/ct) examined as a function of the fraction of double bonds σc having cis structure. For σc up to 0,35 all polymers showed random distribution of cis and trans structures (rtrc = 1), corresponding to a single type of propagating species. Polymers having σc = 0,35-0,85 invariably gave rtrc ≥ 1, with values greater than 5 in some cases. It is proposed that steric crowding of the active site leads both to high values of σc and to restriction of rotation about the metal-carbene bond of the propagating metalcarbene species, such as to give rise to kinetically distinct conformations which tend to regenerate their own kind on addition of monomer.
Zusätzliches Material:
4 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/macp.1979.021800813
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