<i>Cis‐trans</i> double bond distribution in poly(1,3‐cyclopentylenevinylene); dependence on metathesis catalyst, cocatalyst, and additives

Abstract

Abstract 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 WCl 6 or MoCl 5 , with EtAlCl 2 , BuLi, Ph 4 Sn, and (CH 2 CHCH 2 ) 4 Sn 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 13 C NMR spectra of these samples and the ratios r t (=tt/tc) and r c (=cc/ct) examined as a function of the fraction of double bonds σ c having cis structure. For σ c up to 0,35 all polymers showed random distribution of cis and trans structures (r t r c = 1), corresponding to a single type of propagating species. Polymers having σ c = 0,35–0,85 invariably gave r t r c ≥ 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 σ c 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.