posted on 2020-01-09, 19:41authored byEvgeniya V. Bermesheva, Alyona I. Wozniak, Fedor A. Andreyanov, Gleb O. Karpov, Mikhail S. Nechaev, Andrey F. Asachenko, Maxim A. Topchiy, Elizaveta K. Melnikova, Yulia V. Nelyubina, Pavel S. Gribanov, Maxim V. Bermeshev
We studied the addition
polymerization of readily available bifunctional norbornene derivatives,
5-alkylidene-2-norbornenes, in the presence of modified Pd complexes
with N-heterocyclic carbene ligands activated by borates. The Pd–N-heterocyclic
carbene complex/phosphine/borate systems selectively catalyze the
addition polymerization of 5-methylene-2-norbornene and 5-ethylidene-2-norbornene
with the participation of the endocyclic norbornene double bond, whereas
the exocyclic double bond remained intact. The catalysts exhibited
extremely high activity and durability: the activity was higher than
1 × 108 gpolymer/(molPd·h)
and some catalysts were active at a very high monomer/Pd molar ratio
of 2 × 107 or at a Pd complex concentration of 5 ×
10–6 mol %. The structure–catalytic activity
relationships were established for Pd–N-heterocyclic carbene
complexes: the Pd complexes bearing five-membered heterocyclic rings
and/or less sterically hindered aryl groups at nitrogen atoms in carbene
ligands exhibited the highest activity. The polymerization can be
performed in an atmosphere of air and in wet solvents. The resulting
polymers are amorphous and high-molecular-weight products consisting
of rigid saturated main chains and reactive side groups. Thus, they
can be considered as promising intermediates in the production of
polymeric materials with high glass-transition temperatures and desired
properties by targeted modifications.