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Isocyanates have been in use for some time as cross-linking agents for polyester
and polyether polymers. These form three-dimensional network polymers on crosslinking
and are familiar commercial materials. This cross-linking system has the
merit that it is possible to produce a wide range of materials from a given isocyanate
or polyester by varying the reaction proportions, catalysts and so on. In addition,
these materials possess a useful range of physical properties. In the present work
the chemical basis of cross-linking epoxide resins with isocyanates has been investigated.
Previous work on the subject has been largely empirical and though certain
workers have produced cross-linked polymers by this means, the precise nature of
the cross-linking process has not been established. As an initial step it was decided
to investigate the nature of the link between the two types of compound, using monofunctional
model compounds. These were phenyl glycidyl ether (2-3 epoxy propyl
phenyl ether), and phenyl isocyanate. Phenyl glycidyl ether resembles in structure
the active part of the epoxide resin molecule, and phenyl isocyanate is similar to
toluene di-isocyanate, which is frequently used in isocyanate cross-linking
mechanisms.
A reaction has been found to take place giving a crystalline material which is a
one-to-one addition compound of the two reagents, together with a red oil, which may
be a mixture of alkyl anilides. The structure of the crystalline material has not been
fully proved, but is believed to be a 2-oxazolidone. |
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