Al(III)/K(I) Heterodinuclear Polymerization Catalysts Showing Fast Rates and High Selectivity for Polyester Polyols

Low molar mass, hydroxyl
end-capped polymers, often termed “polyols,”
are widely used to make polyurethanes, resins, and coatings and as
surfactants in liquid formulations. Epoxide/anhydride ring-opening
copolymerization (ROCOP) is a controlled polymerization route to make
them, and its viability depends upon catalyst selection. In the catalysis,
the polyester polyol molar masses and end-groups are controlled by
adding specific but excess quantities of diols (vs catalyst), known
as the chain transfer agent (CTA), to the polymerizations, but many
of the best current catalysts are inhibited or even deactivated by
alcohols. Herein, a series of air-stable Al(III)/K(I) heterodinuclear
polymerization catalysts show rates and selectivity at the upper end
of the field. They also show remarkable increases in activity, with
good selectivity and control, as quantities of diol are increased
from 10–400 equiv. The reactions are accelerated by alcohols,
and simultaneously, their use allows for the production of hydroxy
telechelic poly/oligoesters (400 < Mn (g mol–1) < 20,400, Đ < 1.19). For example, cyclohexene oxide (CHO)/phthalic anhydride
(PA) ROCOP, using the best Al(III)/K(I) catalyst with 200 equiv of
diol, shows a turnover frequency (TOF) of 1890 h–1, which is 4.4× higher than equivalent reactions without any
diol (Catalyst/Diol/PA/CHO = 1:10–400:400:2000, 100 °C).
In all cases, the catalysis is well controlled and highly ester linkage
selective (ester linkages >99%) and operates effectively using
bicyclic
and/or biobased anhydrides with bicyclic or flexible alkylene epoxides.
These catalysts are recommended for future production and application
development using polyester polyols.