Novel Pd Catalysts with β-Diketiminates for Homopolymerization of Functionalized Norbornene Derivatives in Water/Organic Mixed Solvents

Abstract

Polynorbornenes prepared by vinyl addition pathway are known to have some desirable characteristics for wider application but they have some critical drawbacks such as brittleness, poor solubility and adhesion. In order to improve these drawbacks, extensive research for the successful homo-and copolymerization of polar functionalized norbornene with olefin has been carried out. Even though considerable advance has been achieved in the polymerization of polar functionalized monomers, successful catalytic systems for the homopolymerization of polar functionalized norbornene are rare. In this study, a novel successful catalytic system for the polymerization of polar functionalized norborene is proposed. This system employs Pd β-diketiminate/borate cocatalyst in water/organic mixed solvents and it is unique due to introduction of water as a component of solvents. Polymers obtained in this study show high Mw with narrow PDI. Effects of several reaction parameters to the polymer activity and properties are investigated and optimal catalytic system are proposed.

Switchable Polymerization of Norbornene Derivatives by a Ferrocene‐Palladium(II) Heteroscorpionate Complex

“…A large discrepancy was found between the experimental and theoretical values of the molecular weights, suggesting a poorly controlled polymerization process, with the PDI (PDI = M w / M n ) values ranging from 1.5–3.6. A similar wide distribution of PDI values is observed in the literature for the polymerization of norbornenes by group 10 metals , , , , , . The polymerization activity for palladium complexes toward norbornene is largely dependent on the coordination environment around the metal center and the substituents on the monomer and can vary greatly from just a few numbers to several millions , , , .…”

“…Modifying the norbornene monomers with functional groups increases the solubility of the resulting polymers and improves their processability . The substitution of norbornenes, typically at the 5‐position, can be achieved via a Diels–Alder reaction, in some cases, directly from dicyclopentadiene and a dienophile . Polymers obtained from the substituted monomers show improved adhesive and mechanical properties while retaining similar optical properties as the unsubstituted polynorbornenes , , …”

Synthesis of Novel Palladium Complexes Containing β‐Diketonate and NHC Ligands and their Catalytic Ability for Addition Polymerizations of the Functional Norbornenes

“…All norbornenes with polar and nonpolar groups were prepared by following the modified procedure of the literature …”

“…reported improved performances with Pd complexes with NHC ligands . By employing this idea to the new Pd catalytic system, successful homo polymerization of polar functional norbornene have been shown . However, the molecular weights of obtained polymers were less than 20 000 g/mol and rather wide PDIs are reported.…”

“…For the enhancement of catalytic activity to achieve desired polymers, several ligands such as β‐ketoiminates and β‐diketonates have been investigated . Among these ligands, NHC ligands have recently drawn much attention due to possible subtle change of steric and electronic effects at the metal center, which may also help to study mechanism of polymerization.…”