The present invention provides a process for the photopolymerization of vinyl compounds in the presence of a photoinitiator.
Photopolymerization has many useful technical applications as, for example, for the curing of lacquers and coatings, in the manufacture of printing plates and in letter press printing.
Photopolymerization is also useful in the dental field. Photopolymerizable materials are used in the preparation of dental fillings and sealings, of crowns and bridges and artificial teeth and dentures (see, for example, British Pat. No. 569,974, DE-OS No. 31 36 484.5 corresponding to U.S. Ser. No. 413,804 filed Sept. 1, 1982, GB No. 1 428 672, U.S. Pat. No. 4,243,578, U.S. Pat. No. 4,267,133 and GB No. 2 018 666A).
British Pat. No. 1 408 265 described photopolymerizable materials which contain as a photoinitiator a mixture of:
(a) at least one photosensitizer of the formula ##STR1## where X is CO, C(R.sup.1)(R.sup.2) or C(R.sup.3)(OR.sup.4), R.sup.1,R.sup.2,R.sup.3,R.sup.4, which may be the same or different, are hydrogen or hydrocarbyl groups; n is 0 or 1; and the groups A, which may be the same or different, are hydrocarbyl or substituted hydrocarbyl groups, and in which the groups A may be further linked together by a direct link or by a divalent hydrocarbyl group, or in which the groups A together may form a fused aromatic ring system, the groups A being aromatic or substituted aromatic when n is 1 and X is C(R.sup.1)(R.sup.2) and when n is 0, and PA0 (b) at least one reducing agent capable of reducing the photosensitizer when the photosensitizer is in an excited state and having the structure ##STR2## where M is an element of Group V B of the Periodic Table and the units R, which may be the same or different, are hydrogen atoms, hydrocarbyl groups, substituted hydrocarbyl groups or groups in which two units R together with the element M for a cyclic ring system, no more than two of the units R being hydrogen atoms or substituted hydrocarbyl groups and where element M is attched directly to an aromatic group R, at least one of the other units R has a ##STR3## group attached to M. PA0 (a) at least one photosensitizer of the formula ##STR4## wherein X is selected from CO, C(R.sup.1)(R.sup.2) or C(R.sup.3) (OR.sup.4), R.sup.1, R.sup.2, R.sup.3, R.sup.4 are each selected from a hydrogen atom or a hydrocarbon radical; PA0 (b) at least one reducing agent selected from compounds of formula I and II: ##STR5## wherein R is selected from the group consisting of a halogen atom, an alkyl radical, an aryl radical, an alkoxy radical and an aryloxy radical, which radicals may be substituted;
The resulting mixtures can be cured by exposure to visible or ultraviolet light. Examples of the photosensitizers include biacetyl, benzil, p,p'-dialkoxybenzil, benzoin and camphorquinone. Reducing agents include propylamine, dimethylaminoethyl methacrylate, N,N'-dimethylaniline and piperidine.
German patent application No. P 31 36 484.5 discloses a method for the photopolymerization of vinyl compounds in the presence of ketones as photosensitizers and cyclic or heterocyclic compounds, particularly 5-substituted barbituric acids, which are used as reducing agents.
It is an object of the present invention to provide a method of photopolymerizing vinyl compounds which results in rapid curing of the vinyl compounds. The resulting polymers produced according to the present invention have excellent color fastness.