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The Effect of Ligand Molecular Weight on Copper Salt Catalyzed Oxidative Coupling Polymerization of 2,6-Dimethylphenol
The Effect of Ligand Molecular Weight on Copper Salt Catalyzed Oxidative Coupling Polymerization of 2,6-Dimethylphenol
Polyphenylene oxide (PPO) was prepared
via oxidative coupling polymerization of 2,6-dimethylphenol
(DMP) catalyzed by copper salt. The ligand was a
novel series of random copolymers (PSVP) of styrene and
4-vinylpyridine prepared by reversible addition-fragmentation
chain transfer (RAFT) copolymerization. The copolymers
with well-controlled molecular weight (MW) were
used to study the effects of ligand molecular weight on
the catalytic activity and selectivity. It was found that the
catalytic activity increased with the molecular weight but
there existed an upper MW limit above which no further
increase in activity could be achieved. With PSVP of
FvPy ¼ 0.39, the critical MW was about 5000 g/mol. The
mechanism involved in the successive complexation of
copper ions and PSVP was elucidated and the equilibrium
constants were estimated by pH titration. It was found
that the macromolecular ligand was in favor of bridging
CuII ions that formed catalytically active dinuclear copperamine
complexes. However, the catalytic selectivity
was almost independent of the ligand MW. VC
