Premium
Endo/Exo Reactivity Ratios in Living Vinyl Addition Polymerization of Substituted Norbornenes
Author(s) -
Tsai Steven D.,
Register Richard A.
Publication year - 2018
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.201800059
Subject(s) - norbornene , chemistry , copolymer , polymerization , reactivity (psychology) , polymer chemistry , monomer , substituent , double bond , ethylene , living polymerization , cyclopentadiene , cycloaddition , polymer , radical polymerization , organic chemistry , catalysis , medicine , alternative medicine , pathology
Substituted norbornenes may be enchained by vinyl addition polymerization (VAP), through the norbornene double bond. Such monomers are generally prepared by Diels–Alder cycloaddition of cyclopentadiene and the corresponding olefin, which leads to a mixture of endo and exo stereoisomers with potentially very different reactivity, but these differences have not previously been quantified (e.g., as copolymerization reactivity ratios r endo and r exo ). A living Pd‐based VAP initiator is employed and the consumption of endo and exo monomers to high conversions is measured to determine r endo and r exo ; since the polymerization is living, the products are gradient copolymers. For norbornenes bearing n ‐butyl, norbornyl, or methylhexafluoroisopropanol substituents, r exo = 1–4, and r exo r endo = 0.2–0.8, indicating only moderate deviations from ideal copolymerization behavior. By contrast, for norbornene bearing a pentamethyldisiloxane substituent, r endo is indistinguishable from zero, indicating that the endo isomer is effectively incapable of homopropagation. However, since the polymerization is living, propagation resumes (and chain extension proceeds) when additional exo monomer is charged.