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FIELD OF THE INVENTION
The present invention relates to a polymerization process and composition employing ultraviolet(UV) light. More particularly, the polymerization process and composition of the present invention includes at least one unsaturated compound
containing a charge transfer complex and a cationic photoinitiator.
BACKGROUND OF THE INVENTION
Commercialization of radiation polymerizable coatings, inks and films requires the reactants be cured quickly and completely.
Typically, such photopolymerizable compositions contain a photosensitive monomeric and/or polymeric material along with a photoinitiator and adjuvant materials which provide desired properties for the end product coating or film.
If the cure of the reactants is not complete, the residues of unreacted starting materials migrate out of the coating following cure. This is disadvantageous since such residues cause contamination of the environment or otherwise render the
coating unsuitable for use in connection with products having direct food contact. As a result, efforts have been made to develop UV curable coating compositions that cure as quickly and completely as possible.
It has been found that photopolymerization of a charge transfer complex composition may be achieved with ultra-violet light and without the need for addition of a photoinitiating compound. More particularly, U.S. Pat. No. 5,446,073 to Jonsson
et al. describes charge transfer complexes obtained from at least one unsaturated compound that has an electron donor group and an electron withdrawing group. In a preferred embodiment, the specific electron donating material is a vinyl ether and the
electron withdrawing compound is a maleamide. These compositions cure in the
absence of a photoinitiator upon subjecting the composition to ultra-violet light having a defined wavelength.
More recently, ultra-violet curing of vinyl ether maleate systems have been developed which incorporate free radical photoinitiators. For example, EP 0 322 808 B1 to Friedlander et al. discloses a film or liquid radiation curable composition
comprising an ethylenically unsaturated polyester component and ethylenically unsaturated polyester oligomer component in a nonpolymerized vinyl ether component together with the free radical photoinitiator.
A similar vinyl ether maleate system is disclosed in PCT/NL97/00017 to Jansen whereby the radiation curable binder comprises an unsaturated compound containing at least one maleate and an unsaturated compound comprising at least one vinyl ether
together with the free radical photoinitiator.
While the above systems provide a modest increase in cure time for the reactants, each falls far short of the cure rates required for purposes of commercialization. Further, a substantial quantity of unreacted vinyl ether and polyester remain
following irradiation notwithstanding the use of a free radical photoinitiator. It has been observed that as much as 20% to 40% of unreacted vinyl ether or unsaturated polyester remains un-crosslinked in the resultant polymeric films.
It is known to employ a cationic catalyst or photoinitiator for copolymerization of vinyl ethers and unset polyesters. A small amount of a Lewis Acid catalyst such as Sn Co.sub.4 will readily polymerize vinyl monomers such as styrene butadiene,
vinyl alkyl ethers or the like. For example, U.S. Pat. No. 4,423,136 to Crivello provides a cationic photoinitiator in connection with ultra-violet cure of unsaturated polyesters including vinyl ethers.
In view of the above, a need has existed in the art for an improved photopolymerization process and composition having increased cure rates and conversion of the reactants with a reduction in the release of volatiles.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a photopolymerization process and composition employing a charge transfer complex wherein the starting materials include at least one mono or polyunsaturated basic compound in the presence of
cationic photoinitiator and in an alternative embodiment, in the presence of both a cationic photoinitiator and free radical photoinitiator.
It is another object of the present invention to increase cure times, reduce volatiles and improve polymerization of the starting materials.
A further object of the present invention is to provide a photopolymerization process and composition that will not contribute to contamination of the environment and will provide coatings and plastics that are suitable for use in connection with
products having direct contact with food.
Yet a further object of the present invention is to provide cationic cure in the presence of mono or polyunsaturated nitrogen containing compound.
In summary, the present invention relates to a radiation curable coating composition comprising a charge transfer complex, the charge transfer complex comprising at least one electron withdrawing reactant component and at least one electron
donating reactant component that is free radically reactive therewith, the electron withdrawing reactant component comprising an unsaturated nitrogen containing compound and the electron donating reactant component comprising an unsaturated compound
having at least one vinyl ether group, the electron donating reactant component may be separate from or structurally incorporated within the electron withdrawing reactant component and an effective amount of a cationic photoinitiator, the cationic
photoinitiator may be combined with a free radical photoinitiator.
The present invention also relates to a photopolymerization process comprising the steps of providing a radiation curable coating composition comprising a charge transfer complex and effective amount of cationic photoinitiator, the charge
transfer complex comprising at least one electron withdrawing reactant component and at least one electron donating reactant component free radically reactive therewith, the electron withdrawing reactant component comprising an unsaturated nitrogen
containing compound and the electron donating reactant component comprising an unsaturated compound having at least one vinyl ether group, the electron donating reactant component at least one of separate from or structurally incorporated within the at
least one electron withdrawing reactant component, applying the radiation curable coating composition to a substrate to be coating and, subjecting the applied radiation curable coating composition to ultraviolet light for a period of time sufficient to
polymerize the charge transfer complex.
These and other objects of the present invention will be apparent from the following detailed description and examples of the invention which follow.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates conversion rates for vinyl ether and maleiates when employing a cationic catalyst in the absence of a free radical photoinitiator; and
FIG. 2 illustrates the conversion rates for vinyl ether and maleiates when employing a blend of free radical photoinitiator together with a cationic photoinitiator.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Charge transfer complex according to the present invention generally refers to the combination of a monounsaturated compound which includes an electron accepting (withdrawing) group i.e. having electron depleted double bonds, with compounds
having an electron donor properties i.e. having electron enriched double bonds. A charge transfer complex is thereby formed by combining each of the above-identified monounsaturated compounds or, in the alternative, may be formed from a single
bi-functional compound which includes both the donor and the acceptor groups.
When the charge transfer complex compounds or compound is subsequently exposed to ultra-violet radiation it will polymerize and cure in the presence of a photoinitiator. Charge transfer complex compounds are taught in assignee's prior U.S. Pat. No. 5,446,073 the relevant portions of which are incorporated herein by reference.
It is within the scope of the present invention to provide multiple unsaturated compounds, each of which contain an electron donor group and an electron withdrawing group or, as noted above, one unsaturated compound containing both the electron
donor and the electron withdrawing groups. A composition of the present invention is typically liquid and capable of being cured by application of actinic light and in particular ultra-violet light.
In a preferred embodiment of the present invention, the reactants of the charge transfer complex comprises: an unsaturated compound comprising at least one maleate, fumarate, itaconate, citraconate, mesaconate group, and an unsaturated compound
comprising at least one vinyl ether group which may be separate from or structurally incorporated within the first unsaturated component.
In a preferred embodiment, the unsaturated compound comprising at least one maleate, fumarate, itaconate, citraconate or mesaconate group is an unsaturated polyester resin. The unsaturated (ethylenically unsaturated) polyester resin can be an
unsaturated polyester polymer, an unsaturated polyester oligomer or a mixture thereof. As used herein, the term "unsaturated polyester" is meant to be distinguished from unsaturated alkyd resins and the like.
Unsaturated polyesters of the present invention are esterification products of ethylenically unsaturated carboxylic acids and organic polyhydric alcohols. An unsaturated carboxylic acid having an acid functionality of at least two, more
particularly a dicarboxylic acid or its anhydride, is utilized as a starting reactant. The unsaturated polyester resins according to the present invention is prepared by heating the carboxyilic component, an organic polyol component together for about 1
to 10 hours to temperature from about 165.degree. C. to about 250.degree. C. with water formed during the esterification being distilled off using a sparge of an inert gas such as nitrogen. Examples of unsaturated dicarboxylic acids and anhydrides
forming unsaturated compounds according to the present invention are maleic acid, maleic anhydride, fumaric acid, itaconic acid, citraconic acid, mesaconic acid.
Specific examples of unsaturated compounds having an electron accepting group include N-alkyl maleimides, mono-and di-cyanofumarates, maleic acid anhydride, fumaronitril, fumaric and maleic mono and diamide derivatives. In particular, these
compounds include N-phenyl-maleimide, N-2-ethylhexylmaleimide, N-cyclohexyl-maleimide, fumaronitril, fumaramide, dicyanofumarate diethylester, the di-butylester of monocyano fumarate, maleic acid anhydride, the di-butylamide of fumaric acid and maleic
acid di(ethylamide). These compounds may be attached to or incorporated within an oligomer or a polymer such as the polyester component noted earlier polyacrylates, polyethers, polyurethanes and polyolefins.
In a preferred embodiment the monounsaturated compound is a polymer or oligomer comprising at least one maleate, fumarate, itaconate, citraconate or mesaconate group.
The unsaturated polyester according to the present invention is an ordinary unsaturated polyester having a molecular weight between about 800 to about 5,000. These polyesters are based upon one or more diacids and one or more diols, the diacids
are at least in part ethylenically unsaturated diacids. As noted above, suitable diacids include maleic acid (anhydride), fumaric acid, itaconic acid (anhydride), citraconic acid (anhydride), mesaconic acid, phthalic acid (anhydride), adipic acid,
terephthalic acid, isophthalic acid, malonic acid, succinic acid, glutaric acid, sebacic acid, and 1,4-cyclohexane dicarboxylic acid and Diels Alder products thereof.
Representative diols include, for example, ethyleneglycol, butanediol, neopentylglycol, hexanediol, 1,4-cyclohexane diol, 1,4-cyclohexanedimethanol, propyleneglycol, diethylene glycol, alkoxylated bisphenol-A, and alkoxylated hydrogenated
bisphenol-A.
The diacids and diols may be combined with mono-, tri- or tetra-functional alcohols or acids. Suitable compounds include ethylenol, butenol, 2-ethylhexanol, saturated and unsaturated fatty acids, trimellitic acid, trimetholypropane glycerol
pentaerythritol and the like.
Separately or in combination with the unsaturated polyesters, the unsaturated compound having the electron accepting group may be an oligomer or a monomer. In the preferred embodiment, a maleate of fumarate end-capped oligomer is used with one
or more unsaturated groups. In addition, monomeric species such as, for example, dioctylmalate can be used or various other maleate or fumarate functional compounds. Thus, the type of unsaturated compound in general will have a molecular weight higher
than about 140, preferably higher than 200 and will have a molecular weight lower than about 5,000 and preferably lower than 3,000 depending upon the commercial application.
The unsaturated compound having the electron donor property according to the present invention is a compound having a vinyl ether component or group and includes polymers, oligomers or monomers, the polymer, oligomer or monomer having between
about 1 to about 10 vinyl ether groups.
The molecular weight of the vinyl ether compound is in general higher than about 90 and preferably higher than about 100. Generally speaking, the molecular weight is lower than about 5,000 and preferably lower than about 3,000.
The vinyl ether groups of the unsaturated compound containing the at least one vinyl ether group is different from and cocurable with the ethylenically unsaturated moieties in the backbone of the unsaturated compound forming the electron
accepting group. By cocurable it is meant the vinyl ether groups are reactive with ethylenic unsaturation derived from the unsaturated polyester following exposure of the composition of the present invention to ultra-violet light. It will be understood
that when a composition of the present invention is to be cured utilizing ultra-violet light a photoinitiator and preferably two photoinitiators will be combined with the composition of the present invention either prior to or at the time of UV curing
and in the manner as will be further explained below.
Suitable examples of mono- and divinyl ether compounds include butylvinyl ether, cyclohexyldi-methanol-divinyl ether, butyldivinyl ether, triethylene glycol-divinylether and hydroxbutylvinyl ether among others.
Suitable oligomers and polymers are polyurethanes having a polyester, polyether or polycarbonate backbone and a vinylether end group, made by reaction of hydroalkylvinylether, a polyisocyanate and a hydroxy functional oligomer. This oligomer
being a polyester, polyether or polycarbonate having a molecular weight between about 200 and 2,000.
As noted earlier, the unsaturated compound containing the electron accepting group may also include the electron donor group. Thus, the unsaturated compound comprising at least one maleiate, fumarate, itaconate, citraconate or mesaconate group
and the unsaturated compound comprising at least one vinyl ether group can be combined into a single molecule. For example, a vinyl ether N-polyurethane can be used which has an hydroxyfunctional unsaturated polyester as a backbone. Dual function
monomers include the following, a hydroxy functional vinyl ether such as hydroxybutyl vinyl ether can be reacted with an organic diisocyanate such as isophorone diisocyanate in a stoichiometric ratio to provide a half-capped isocyanate adduct.
Thereafter, residual isocyano functionality of the half-capped diisocyanate can be reacted with hydroxyl functionality provided by an unsaturated polyester polyol so as to structurally incorporate an average vinyl ether functionality of at least two in
the unsaturated polyester component. Examples of unsaturated carboxylic acids and unsaturated carboxylic acid anhydrides as well as organic polyols suitable for preparing hydroxyl-functional unsaturated polyester resins include those described herein
previously. Examples of organic diisocyanates include: toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, and mixtures thereof; diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate and mixtures thereof; para-phenylene diisocyanate;
biphenyl diisocyanate; 3,3'-dimethyl-4,4'-diphenylene diisocyanate; tetramethylene-1,4-diisocyanate; hexamethylene-1,6-diisocyanate; 2,2,4-trimethylhexane-1,6-diisocyanate; lysine methyl ester diisocyanate; bis(isocyanatoethyl)fumarate; isophorone
diisocyanate; ethylene diisocyanate; dodecane-1,12-diisocyanate; cyclobutane-1,3-diisocyanate; cyclohexane-1,3-diisocyanate, cyclohexane-1,4-diisocyanate and mixtures thereof; methylcyclohexyl diisocyanate; hexahydrotoluene-2,4-diisocyanate,
hexahydrotoluene-2,6-diisocyanate and mixtures thereof; hexahydrophenylene-1,3-diisocyanate, hexahydrophenylene-1,4-diisocyanate and mixtures thereof; perhydrodiphenylmethane-2,4'-diisocyanate, perhydrodiphenylmethane-4,41-diisocyanate and mixtures
thereof. The resulting unsaturated polyester component (also now containing urethane moieties), and having an average vinylether functionality of at least two, usually is free of unreacted NCO groups.
Optionally, a liquid, radiation curable composition of the invention additionally may contain other ethylenically unsaturated monomers or oligomers examples of which include: other vinyl monomers such as vinyl acetate, styrene, vinyl toluene,
divinyl benzene, methylvinyl ether, ethylvinyl ether and butylvinyl ether; acrylic and methacrylic esters such as methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)
acrylate, 2-hydroxyethyl (meth)acrylate, glycidyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, glycerol di(meth)acrylate, glycerol tri(meth)acrylate, 1,3-propylene glycol
di(meth)acrylate, dipropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate,
1,2,4-butanetriol tri(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,4-cyclohexanediol di(meth)acrylate, 1,4-benzenediol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, 1,5-pentanediol di(meth)acrylate, trimethylolpropane
di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate, isobornyl (meth)acrylate and tetrahydrofurfuryl (meth)acrylate; (meth)acrylates derived from aromatic glycidyl ethers such as
bisphenol-A-diglycidyl ether and aliphatic glycidyl ethers such as butanediol diglycidyl ether, specific examples of which include 1,4-butanediol diglycidylether di(meth)acrylate, bisphenol,-A-diglycidylether di(meth)acrylate and neopentylglycol
diglycidylether di(meth)acrylate; and acrylic or methacrylic amides such as (meth)acrylamide, diacetone (meth)acrylamide, N(beta-hydroxyethyl) (meth)acrylamide, N,N-bis(beta-hydroxyethyl) (meth)acrylamide, methylene bis(meth)acrylamide, 1,6-hexamethylene
bis(meth)acrylamide, diethylenetriamine tris(meth)acrylamide, bis(gamma-(meth)acrylamidepropoxy) ethane and beta-(meth)acrylamide ethylacrylate.
Charge transfer complex compounds within the scope of the present invention further include those taught in International Application No. WO 98/11151 and Application No. WO 98/11152 both applications of which are incorporated herein by reference.
For example, the present invention includes a polymerizable composition, characterized by at least one compound selected among the polymers functionalized by maleimide groups and consisting of products obtained by reaction of at least one maleic
anhydride represented by formula: (I): ##STR1## wherein each of R.sup.1 and R.sup.2 represents independently H, a C.sub.1 -C.sub.12 alkyl group such as methyl, or a halogen such as chlorine; at least one compound (II) having at least one --NH.sub.2
function and at least another function selected among --OH, --NH.sub.2, --NH--, --COOH and --COOR.sup.3, R.sup.3 representing a C.sub.1 -C.sub.5 alkyl group; and at least one compound (III) selected among polyols, mono- or polyfunctional epoxy,
polyisocyanates and polyamines; the compound (II) having reacted first with the maleic anhydride in order to open maleic anhydride rings, among others, in order to form maleamic acid functions by opening the maleic anhydride rings by the primary amine
function of compound (II), the maleamic acid functions having then being at least partially closed again into maleimide rings by heating; the maleimides so produced having reacted with the compound(s) (III) and/or with at least one polyacid and/or one
cyclic anhydride (IV), added to the reaction medium after opening of the maleic by anhydride compound (II), and the chain of the polymer having been formed by polycondensation and/or polyaddition reactions having involved the compound(s) (III) and the
compound(s) (IV) as added, and/or in case where it would be remained an excess of the maleic anhydride (I) after opening of compound (I) by (II), the excess of maleic anhydride (I), and the uncyclized products being also entered into the composition of
the chain; the compounds (III) involved being furthermore selected among: in case where they are intended to react with an anhydride (IV) and/or with the excess of anhydride (I): at least one polyol and/or at least one mono- or polyfunctional epoxy
and/or at least one polyamine, and possibly at least one polyisocyanate; in case where they are intended to react with a diacid (IV): at least one polyol and/or at least one mono- or polyfunctional epoxy and/or at least one polyamine, and possibly at
least one polyisocyanate; or at least one polyisocyanate; and in case where the compound (II) includes a --COOR.sup.3 function: at least one polyol.
Preferably, the anhydride of formula (I) is maleic anhydride.
The compounds (II) are especially selected among the compounds represented by the formulas H.sub.2 N--A--OH, H.sub.2 N--A--COOH, H.sub.2 N--A--COOR.sup.3 and H.sub.2 N--A--NH.sub.2, wherein A represents a straight, branched or cyclic alkylene
group, or an arylene group, it being possible for the groups to be interrupted by oxygen or sulfur atoms, or by --NR.sup.4 -- groups, wherein R.sup.4 represents hydrogen or alkyl. Examples of the compounds (II) include aminoalcohols, such as
ethanolamine, propanolamine, isopropanolamine, 2-(2-aminoethoxy)ethanol, N-(2-amino-ethyl)ethanolamine; aminoacids, such as valine, p-amino-benzoic acid, alanine, 2-aminohexanoic acid, 6-aminohexanoic acid, 7-aminoheptanoic acid, 2-aminoisobutyric acid;
methyl or ethyl esters of the abovementioned aminoacids; diamines, such as ethylenediamine, 2-methyl-1,5-pentamethylenediamine, hexamethylenediamine, 2,2,4- and/or 2,4,4-trimethylhexamethylenediamine, dodecamethylenediamine, 5-methylnonamethylenediamine,
decamethylenediamine, isophoronediamine, bis(4-aminocyclohexyl)methane, bis(3-methyl-4-aminocyclohexyl)methane, bis(3-methyl-4-amino-5-ethylcyclohexyl)methane, 1,2-bis(4-aminocyclohexyl)-ethane, 2,2'-bis(4-aminocyclohexyl)propane,
2,2'-bis(3-methyl-4-aminocyclohexyl)propane, 4,7-dioxadecane-1,10-diamine, 4,9-dioxadodecane-1,12-diamine, 4,7,10-trioxatridecane-1,13-diamine; and polyoxyethylenated and/or polyoxypropylenated di- or triamines sold under the tradename "Jeffamine.RTM.".
Trifunctional compounds (II) such as L-serine, 3-hydroxy 4-amino benzoic acid and 3-amino 4-hydroxy benzoic acid and other triamines such as N-(2-aminoethyl)-1,2-ethanediamine and N-(3-aminopropyl)-1,3-propanediamine, are also included.
The polyols (III) are preferably diols or triols, it is within the scope of the present invention for polyols of higher functionality (pentaerythritol for example) to be present in small amounts. As examples of diols or triols, propylene glycol,
dipropylene glycol, diethylene glycol, ethylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, triethylene glycol, tripropylene glycol, butylene glycol, glycerol, trimethylol propane, 1,6-hexanediol, 1,4-cyclohexane diol, 1,4-cyclohexane
dimethanol, 2-methyl-1,3-propane diol, 2-butyl-2-ethyl-1,3-propane diol, 1,2-bis(hydroxyethyl)cyclohexane, 4'-(2-hydroxyethoxy)-2,2-dimethyl-2-hydroxyacetophenone, 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate, dibromoneopentylglycol can
be mentioned. Monoalcohols may be added in small amounts.
The epoxy compounds (III) are generally mono- and diepoxy compounds, among which epichlorhydrine, 7-oxa-bicyclo[4.1.0]heptane, 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate, bisphenol A diglycidyl ether, 1,2-epoxyhexadecane,
3,3,3-trichloropropylene oxide and allyl glycidyl ether.
The polyisocyanates (III) are, above all, diisocyanates, such as 4,4'-diphenylmethane diisocyanate, trimethylhexamethylene diisocyanate, toluene diisocyanate, isophoronediisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate,
4,4'-dicyclohexylmethane diisocyanate, 2,2,4-trimethylhexamethylene-1,6-diisocyanate, triphenylmethane-4,4',4"-triisocyanate, polymethylene polyphenylisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 1,5-naphthalene diisocyanate,
naphthalene-1,4-diisocyanate, diphenylene-4,4'-diisocyanate, 3,3'-bi-tolylene-4,4'-diisocyanate, 1,4-cyclohexylene dimethylene diisocyanate, xylylene-1,4-diisocyanate, xylylene-1,3-diisocyanate, cyclohexyl-1,4-diisocyanate and
3,3'-dimethyldiphenylmethane-4,4'-diisocyanate.
Preferably, the polyamines (III) are diamines, such as ethylene diamine, 2-methyl-1,5-pentamethylene diamine, trimethylhexane-1,6-diamine, hexamethylenediamine, 2,2,4- and/or 2,4,4,-trimethylhexamethylenediamine, dodecamethylenediamine,
trimethylhexamethlenediamine, 5-methylnonamethylenediamine, decamethylenediamine, isophoronediamine, bis(4-aminocyclohexyl)methane, bis(3-methyl-4-aminocyclohexyl)methane, bis(3-methyl-4-amino-5-ethylcyclohexyl)methane, 1,2-bis(4-aminocyclohexyl)ethane,
2,2'-bis(4-aminocyclohexyl)propane and 2,2'-bis(3-methyl-4-aminocyclohexyl)propane.
As primary examples of polyacids (IV) and as noted earlier, diacids, such as maleic, fumaric, chloromaleic, citraconic, metaconic, itaconic, tetraconic, orthophthalic, isophthalic, terephthalic, succinic, methylsuccinic, adipic, sebacic,
tetrabromophthalic, tetrachlorophthalic, glutaric, pimelic acids or the like, are within the scope of the present invention.
The cyclic anhydrides (IV) employed, which are unsaturated or saturated, may be selected among maleic anhydride, succinic anhydride, phthalic anhydride, trimellitic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, chlorinated
anhydrides such as chlorendic anhydride, tetrachlorophthalic anhydride and tetrabromophtalic anhydride, methyltetrahydrophthalic anhydride, nadic anhydride, methyl nadic anhydride, itaconic anhydride, citraconic anhydride, and glutaric anhydride. Maleic
anhydride and succinic anhydride are particularly mentioned. An anhydride including a photoinitiator moiety, such as 3,3',4,4'-benzophenonetetracarboxylic anhydride, may be used in some applications. The polymerizable composition characterized by at
least one compound selected among the polymers functionalized by maleimide groups have a number average molecular weight between about 350 and about 5000, and especially between about 500 and about 3000 (as measured by GPC, polystyrene standard).
Furthermore, they include generally about 0.02 to about 5 maleimide functions, especially 0.2 to 2 maleimide functions, by kg of polymer (mass).
Preparation of the polymers functionalized by maleimide groups according to the present invention can be carried out generally as follows. At least one compound (I), at least one compound (II) and at least one compound (III), the compounds (I),
(II) and (III), are reacted under conditions that permit compound (II) to react first with the maleic anhydride (I), thereby opening the maleic anhydride rings, among others, in order to form maleamic acid functions by opening the maleic anhydride rings
by the primary amine function of the compound (II), then to close again at least partially the maleamic acid functions into maleimide rings, by heating, the maleimides so formed reacting with the compound(s) (III) and/or with (IV) at least one polyacid
and/or one cyclic anhydride which are added to the reaction medium after opening of (I) by (II), and the chain of the polymer thereby being formed by polycondensation and/or polyaddition reactions involving the compound(s) (III) and said compound(s) (IV)
as added and/or, in case where it would remain an excess of maleic anhydride after opening of (I) by (II), the excess of maleic anhydride (I) and with the uncyclized products also entering into the composition of the chain.
According to this process, in a first step, at least one maleic anhydride (I) is reacted with at least one compound (II) in a polar solvent medium in order to open the anhydride rings. In the second step, a ring forming reaction is conducted by
heating the reaction medium obtained at the end of the first step, possibly in the presence of at least one cyclic anhydride (IV), wherein the ring forming reaction results in at least partly closing the anhydride rings which were opened in the previous
step, in order to give a product of at least partly ring forming reaction which comprises maleimides N-substituted by groups functionalized by --OH or --COOH or --COOR.sup.3 or --NH.sub.2 or --NH-- according to the compound (s) (II) used, in case whe | | |
