Epoxy-terminated polyoxazolidones and process for the preparation thereof

Epoxy-terminated polyoxazolidone having from about 5 to about 30 weight percent of the isocyanate content are described. These polyoxazolidone are prepared by a process in which various process parameters are controlled in a targeted manner to give a product having from about 50 to about 100 percent of isocyanate groups converted to oxazolidone rings and from about 0 to about 50 percent of the isocyanate groups converted to isocyanurate rings. These epoxy terminated polyoxazolidones exhibit high glass transition temperatures and high resistance to chemicals when cured. They are useful for the preparation of electrical laminates, particularly laminates used in the preparation of electrical circuit boards.

BACKGROUND OF THE INVENTION 
The present invention relates to isocyanate modified epoxy resins 
(epoxy-terminated polyoxazolidones) having from about 5 to about 30 weight 
percent of the isocyanate content wherein from about 0 to about 50 percent 
of the isocyanate groups are converted to isocyanurate rings and from 
about 50 to about 100 percent of the isocyanate groups are converted to 
oxazolidone (commonly referred to in the past as "2-oxazolidinone") rings 
and a process for the preparation thereof. The present invention also 
relates to epoxy resin varnish compositions containing these isocyanate 
modified epoxy resins and electrical laminates prepared therefrom. 
The synthesis and properties of isocyanate modified epoxy compounds which 
are copolymers of polyisocyanates and polyepoxides have attracted a great 
deal of interest in recent years. Various isocyanate modified epoxy 
compounds are described as promising engineering materials for the 
manufacture of a wide variety of useful products including rigid foams, 
thermoplastics, coatings, adhesives and elastomers. 
During the reaction of a polyepoxide with a polyisocyanate there is 
competition between formation of 2-oxazolidone rings and isocyanurate 
rings. The crosslinking density and branching of the formed polymer 
compound increases with increased content of isocyanurate rings and 
thereby the glass transition temperature (Tg) of the polymer is raised. 
Many studies have shown that many factors such as reaction temperature, 
nature of the catalyst, relative amounts of the reactants and solvents 
employed, influence the reaction and formation of 2-oxazolidone rings and 
isocyanurate rings. See, for example, Kinjo et al, Polymer Journal Vol. 
14, No. 6, 505-507 (1982); Sandler, S. R., Journal of Polymer Science, A 
1-5, 1481 (1967); Sayigh and Ulrich, J. Chem. Soc., 1961, 3148-51; Uribe 
and Hodd, Polym. Sci. Technical, 31, 251-73 (1985); Kordomenos et al, 
Macromolecules, 14, 1434-37 (1981); Kitayana et al, Rubber Chemistry and 
Technology, Vol. 53, 1-6 (1980); Herweh et al, Tetrahedron Letters, No. 
12, 809-812 ( 1971); Dileone, J. Polymer Sci., A 1-8, 609-615 (1970); 
Herweh et al, J. Org. Chem., Vol. 33, 1409-23 (1968) and Sandler, J. 
Polym. Sci., A1-5, 1481 (1967). For convenience most of this fundamental 
studies were conducted with model compounds in dilute solutions 
particularly in dimethylformamide (DMF). 
In general it has been found that epoxides promote formation of 
isocyanurate rings at low temperature. It has been shown that isocyanurate 
rings are formed from the isocyanate groups by the catalytic effects of 
nucleophilic compounds at temperatures below 100.degree. C. and are 
converted into oxazolidone rings at temperature above 110.degree. C. in 
the presence of DMF solvent. It has been disclosed that the usual reaction 
temperature to form oxazolidone rings is about 150.degree. C. to 
160.degree. C. (boiling temperature of DMF solvent). 
There are three end products which can be obtained in the condensation 
reaction of polyisocyanates with polyfunctional epoxides. The reactants' 
stoichiometry (ratio of epoxide groups to isocyanate groups) determines 
the various end products, their remaining end groups and their possible 
uses. These condensation products are conventionally referred to as 
polyoxazolidones. 
Isocyanate-terminated polyoxazolidones, are prepared using a stoichiometric 
excess of the polyisocyanate (isocyanate/epoxide ratio greater than 1) in 
the presence of a suitable catalyst. The following catalysts have been 
reported to promote the formation of isocyanate-terminated 
polyoxazolidones: quaternary ammonium salts, diethylzinc, zinc 
chloride/trimethylamine complex and organoantimony iodide. See, for 
example, Sander, J. Polym. Sci., A 1-5, 1481 (1967); Kordomenos et al, 
Journal of Coating Technology, 55, No. 700, pp. 49 and 59 (1983); U.S. 
Pat. No. 4,022,721 to Mitsubishi; and PCT Patent Application WO/US 
86/06734 to Dow. Isocyanate-terminated polyoxazolidones are reported to be 
suitable for use as resins, elastomers, paints and adhesives. The 
isocyanate-terminated polyoxazolidones can be further cross-linked via the 
catalytic trimerization of the terminal isocyanate groups to isocyanurate 
rings. 
Linear high molecular weight polyoxazolidones are prepared using 
stoichiometric amounts (isocyanate/epoxide ratio=1) of a diepoxy compound 
and diisocyanate compound. 
Another class of resins (often referred to as "ISOX" resin) contain both 
isocyanurate and oxazolidone rings but the isocyanurate rings are 
predominant. The mechanical properties of ISOX resins can be varied from 
hard to flexible by changing equivalent ratio of isocyanate and epoxide 
groups. See, for example, Kinjo et al, Polymer Journal, Vol. 14, No. 6, 
505-507 (1982). This reference describes preparation of a series of 
thermosetting ISOX resins in which diphenylmethane-4,4'-diisocyanate (MDI) 
was reacted with different diepoxides in the presence of ethyl-methyl 
imidazole as a catalyst and as a curing agent. ISOX resin is low viscosity 
liquid at room temperature before curing. Compared with other conventional 
heat resistant solventless varnishes, ISOX resin are reported to have 
greater mechanical strength at elevated temperatures, and goods heat, 
electrical, chemical and moisture resistance properties. 
U.S. Pat. No. 4,070,416 (Hitachi Ltd.) describes a process for producing 
thermosetting resins by mixing one equivalent or more of polyfunctional 
isocyanate per one equivalent of a polyfunctional epoxide in the presence 
of a tertiary amine, morpholine derivatives or imidazole as catalysts. The 
catalyst is used within a range of 0.1 to 2 weight percent, based on the 
combined weight of the reactants. The reaction temperature of 130.degree. 
C. or lower is said to result in the formation of mainly isocyanurate 
rings, whereas it is assumed that oxazolidone rings should be mainly 
formed at temperature above 130.degree. C. The produced resins are said to 
exhibit excellent electrical and mechanical properties and high thermal 
stability. The produced resins are said to have various applications as 
heat resistance insulation varnishes, casting resins, impregnation resins, 
molding resins for electrical parts, adhesives, resins for laminating 
boards, resins for printed circuits etc. 
Epoxy-terminated polyoxazolidones are prepared by reacting an epoxy resin 
with a polyisocyanate compound using stoichiometric excess of epoxy resin 
(isocyanate/epoxide ratio lower than 1). The following catalysts have been 
described in the literature to promote formation of epoxy-terminated 
polyoxazolidones: quaternary ammonium salts, HEXA 
(hexamethylenetetramine), diazabicyclooctane (sold by Air Product under 
the trademark DABCO), diethylzinc and organoantimony iodide. See, for 
example Sander et al, J. Appl. Polymer Sci., 9, 1984-1996 (1965); Uribe et 
al, Polym. Sci. Technical, 31, 251-73 (1985); Kordomenos et al, Journal of 
Coating Technology, 55, No. 700, pp. 49 and 59 (1983); and PCT Patent 
Application WO/US 8606734. The epoxy-terminated polyoxazolidones can be 
cured with conventional epoxy hardeners. The cured epoxy resin exhibit 
very good thermal properties and solvent stability and have generally good 
impact properties. The epoxy-terminated polyoxalidones are reported to be 
useful for the preparation of coatings resins and adhesives. 
European Patent Application No. 0113575A discloses powder coating 
compositions comprising epoxy-terminated polyoxazolidone resins prepared 
by reacting a diepoxide and a diisocyanate in amounts which provide a 
ratio of epoxide equivalents to isocyanate equivalents of from about 1.1:1 
to about 10:1 and curing agents. The polyoxazolidone resins are said to 
have comparatively high glass transition temperatures and provide coatings 
of improved resistance to cathodic disbandment. The coating composition 
are applied by fluidized bed sintering or electrostatic spray methods. 
Self thermosetting compositions of polyisocyanates and polyepoxides are 
described in U.S. Pat. Nos. 4,564,651 and 4,631,306 (both to Markert et 
al) which discloses a method for the preparation of reaction resin molded 
materials and molded materials for insulating components, respectively 
containing oxazolidone and isocyanurate rings by mixing a polyepoxide and 
a polyisocyanate to from a resin mixture having a viscosity up to 7000 
mPa.s at 25.degree. C. and the mole ratio of epoxy to isocyanate groups of 
from about 1:1 to about 5:1; reacting the resin mixture in the presence of 
an imidazole or tertiary amine catalyst at elevated gelling temperature of 
from 80.degree. C. to 130.degree. C. to form a cross-linked polymer; and 
heating the cross-linked polymer to from about 130.degree. C. to about 
200.degree. C. to cause posthardening and produce a molded material. The 
molded materials are reported to exhibit improved mechanical properties. 
U.S. Pat. No. 3,334,110 (Schramm) discloses a method for preparing 
epoxy-terminated polyoxazolidones by reacting a polyisocyanate with a 
polyepoxide in the presence of a catalyst mixture comprising an alcohol 
and tertiary amine or a quaternary ammonium salt. The epoxy-terminated 
polyoxazolidones can be cured with epoxy curing catalysts or reacted with 
epoxy hardeners to give a variety or products useful in the fields of 
coatings, laminating, bonding, molding, foams etc. 
U.S. Pat. No. 4,066,628 (Ashida et al) discloses a process for preparing 
polyoxazolidones by reacting an organic isocyanate with an epoxide in the 
presence of dialkyl zinc, zinc carboxylate, organozinc chelate compound or 
trialkyl aluminum as the catalyst. Polyoxazolidones prepared by this 
process are useful starting materials for the manufacture of a wide 
variety of products including foams, coatings, adhesives, elastomers and 
the like. 
Although numerous processes for the preparation of polyoxazolidones are 
described in the literature and various catalysts are used in these 
processes, only polyoxazolidones having fixed product specifications are 
produced. None of the known processes allows for the preparation of 
epoxy-terminated polyoxazolidones in controlled manner by manipulating 
various process parameters. None of the known processes provides for 
producing epoxy-terminated polyoxazolidones which will have particularly 
desired physical and mechanical properties by controlling the content of 
the oxazolidone and isocyanurate rings incorporated in the 
epoxy-terminated polyoxazolidone in order to accommodate desired end use 
of the polyoxazolidone. Furthermore, none of the known art discloses nor 
suggests that imidazole compounds would be useful as catalysts in a 
process for the preparation of epoxy-terminated polyoxazolidones. 
Moreover, there is no disclosure nor suggestion in the known art that 
epoxy-terminated polyoxazolidones would be useful materials for the 
preparation of electrical laminates and in particular, for the preparation 
of electrical circuit boards. 
Heretofore electrical laminates have been conventionally prepared from 
bisphenol A based epoxy resins advanced with either bisphenol A or 
tetrabromobisphenol A and cured with a biguanide such as dicyanodiamide. 
However, for many applications, such as multilayered printed circuit 
boards, the glass transition temperature (Tg) of the cured epoxy resins is 
undesirably low, for example, less than 135.degree. C. and the chemical 
resistance of the cured epoxy resins is also undesirably low, for example, 
N-methylpyrrolidone pick-up is greater than 0.5 weight percent. Although 
in many applications these physical properties are acceptable, for many 
applications it is desirable to have cured epoxy resins which have glass 
transition temperature above 135.degree. C. and chemical resistance such 
as N-methylpyrrolidone pick-up of less than 0.1 weight percent. There are 
available specialty epoxy resins and other resinous products which meet 
the desired higher standards but their use is limited due to the 
economics. In particular, the cost associated with these resins precludes 
them from being used in the most of the applications associated with 
electrical circuit boards. 
There is a need in industry for a process which will allow for the 
preparation or epoxy-terminated polyoxazolidones in a targeted manner by 
controlling various process parameters to obtain materials having physical 
and mechanical properties targeted to specific, desired end uses of such 
materials. 
There is also a great need for engineering materials which will have the 
desired physical and mechanical properties (particularly, sufficiently 
high Tg's and chemical resistance properties) and still be inexpensive 
enough to be used in the most of the electrical laminate applications, 
particularly in electrical circuit board applications. 
The present invention provides such engineering materials which materials 
have physical and mechanical properties targeted to specific end uses. 
Moreover, the present invention provides a process for the preparation of 
these engineering materials which process can be controlled in a targeted 
manner by manipulating various process parameters. 
SUMMARY OF THE INVENTION 
The present invention concerns a process for the preparation of an 
epoxy-terminated polyoxazolidone (isocyanate modified epoxy resin) which 
process comprises reacting a polyepoxide compound with a polyisocyanate 
compound in the presence of a catalyst for the reaction of the epoxy and 
isocyanate groups at an elevated temperature, said process being 
characterized by 
(A) adding (1) from about 5 to about 30, preferably from about 5 to about 
20, most preferably from about 10 to about 20, weight percent of the 
polyisocyanate compound within a period of time of from about 3 about 90, 
preferably from about 15 to about 60, most preferably from about 20 to 
about 45, minutes to (2) a mixture comprising (a) from about 70 to about 
95, preferably from about 80 to about 95, most preferably from about 80 to 
about 90, weight percent of the polyepoxide compound and (b) from about 
0.01 to about 2, preferably from about 0.02 to about 1, most preferably 
from about 0.02 to about 0.1, weight percent of the catalyst, said weight 
percentages being based on the combined weight of the polyepoxide compound 
and polyisocyanate compound; and 
(B) heating the reaction mixture obtained in step A to a temperature of 
from about 110.degree. C. to about 200.degree. C., preferably from about 
120.degree. C. to about 180.degree. C., most preferably from about 
140.degree. C. to about 160.degree. C., for a period of time from about 5 
to about 180, preferably from about 30 to about 120, most preferably from 
about 60 to about 90, minutes; and further characterized in that the 
conversion of isocyanate groups to the oxazolidone and isocyanurate rings 
is controlled in any of the following manner: 
(i) by increasing the reaction temperature at a given amount of the 
catalyst and a given amount of the polyisocyanate compound used when 
higher conversion to oxazolidone rings is desired; or 
(ii) by increasing the amount of the catalyst at a given reaction 
temperature and a given amount of the polyisocyanate compound used when 
higher conversion to oxazolidone rings is desired; or 
(iii) by increasing the amount of the polyisocyanate used at a given amount 
of the catalyst and a given reaction temperature when higher conversion to 
isocyanurate rings is desired; or 
(iv) by increasing the rate of addition of the polyisocyanate compound at a 
given reaction temperature, given amount of the catalyst and given amounts 
of the polyepoxide and polyisocyanate compounds when higher conversion to 
isocyanurate rings is desired; whereby the epoxy-terminated 
polyoxazolidone having from about 50 to about 100 percent of the original 
isocyanate groups converted to oxazolidone rings and from about 0 to about 
50 percent of the original isocyanate groups converted to isocyanurate 
rings is obtained. 
In another aspect, the present invention concerns the epoxy-terminated 
polyoxazolidone having from about 5 to about 30 preferably from about 5 to 
about 20, most preferably from about 10 to about 20 weight percent of the 
isocyanate content and having from about 50 to about 100 percent of the 
original isocyanate groups converted to oxazolidone rings and from about 0 
to about 50 percent of the original isocyanate groups converted to 
isocyanurate rings whenever prepared according to the aforementioned 
process. 
Yet in another aspect, the present invention concerns an epoxy resin 
varnish composition comprising an epoxy resin, a hardener for the epoxy 
resin, an organic solvent, an accelerator and, optionally, other 
conventional adjuncts, characterized in that said epoxy resin is the 
epoxy-terminated polyoxazolidone prepared by the process described 
hereinbefore. 
Still in another aspect, the present invention concerns a process for 
preparing electrical laminates comprising the steps of: 
(a) impregnating a reinforcing web with an epoxy resin varnish comprising 
an epoxy resin, a hardener for the epoxy resin, an organic solvent and an 
accelerator; 
(b) heating the so prepared prepreg to a temperature sufficient to 
partially react the epoxy component of the varnish with the hardener 
component; and 
(c) laminating one or more layers of the prepreg with an electrically 
conductive material and heating the so formed laminate at an elevated 
pressure and to elevated temperatures, characterized in that the epoxy 
resin varnish is the aforementioned epoxy resin varnish composition in 
which the epoxy component is the epoxy-terminated polyoxazolidone having 
from about 5 to about 30, preferably from about 5 to about 20, most 
preferably from about 10 to about 20, weight percent of the isocyanate 
content and having from about 50 to about 100 percent of the original 
isocyanate groups converted to the oxazolidone rings and from about 0 to 
about 50 percent of original isocyanate groups converted to isocyanurate 
rings. 
Yet in another aspect, the present invention concerns an electrical 
laminate prepared according to the above process. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The polyepoxide compound useful in the practice of the present invention is 
suitably a compound which possesses more than one 1,2-epoxy group. In 
general, the polyepoxide compound is saturated or unsaturated aliphatic, 
cycloaliphatic, aromatic or heterocyclic compound which possesses more 
than one 1,2-epoxy group. The polyepoxide compound can be substituted with 
one or more substituents which are non-reactive with the isocyanate groups 
such as lower alkyls and halogens. Such polyepoxide compounds are well 
known in the art. Illustrative polyepoxide compounds useful in the 
practice of the present invention are described in the Handbook of Epoxy 
Resins by H. E. Lee and K. Neville published in 1967 by McGraw-Hill, New 
York and U.S. Pat. No. 4,066,628. 
Particularly useful polyepoxide compounds which can be used in the practice 
of the present invention are polyepoxides having the following general 
formula 
##STR1## 
wherein R is substituted or unsubstituted aromatic, aliphatic, 
cycloaliphatic or heterocyclic polyvalent group and n has an average value 
of from greater than about 1 to less than about 5. The preferred 
diepoxides include diglycidyl ether of 2,2-bis(4-hydroxyphenyl) propane 
(generally referred to as bisphenol A) and diglycidyl ether of 
2,2-bis(3,5-dibromo-4-hydroxyphenyl) propane (generally referred to as 
tetrabromobisphenol A). Mixtures of any two or more polyepoxides can also 
be used in the practice of the present invention. 
The polyisocyanate compound useful in the practice of the present invention 
is represented by the following general formula: 
##STR2## 
wherein R' is substituted or unsubstituted aliphatic, aromatic or 
heterocyclic polyvalent group and m has an average value of greater than 
about 1 to less than about 5, preferably from about 1.5 to about 4, most 
preferably from about 2 to about 3. Examples of suitable polyisocyanates 
include 4,4'-methylene bis(phenylisocyanate) (MDI) and isomers thereof, 
higher functional homologs of MDI (commonly designated as "polymeric 
MDI"), toluene diisocyanate (TDI) such as 2,4-toluene diisocyanate and 
2,6-toluene diisocyanate, m-xylylene diisocyanate, hexamethylene 
diisocyanate (HMDI) and isophoronediisocyanate. Mixtures of any two or 
more polyisocyanates can also be used in the practice of the present 
invention. Other suitable polyisocyanate compounds are described in U.S. 
Pat. Nos. 3,313,747; 4,066,628 and 4,742,146. 
Preferred polyisocyanate compounds are 4,4'-methylene bis(phenylisocyanate) 
(MDI) and isomers thereof, polymeric MDI and toluene diisocyanate (TDI). 
The most preferred polyisocyanate compounds are 4,4'-methylene 
bis(phenylisocyanate), isomers thereof and polymeric MDI. 
A suitable catalyst is employed in the practice of the present invention to 
facilitate reaction of the polyepoxide compound with the polyisocyanate 
compound. Examples of suitable catalysts include zinc carboxylate, 
organozinc chelate compound, trialkyl aluminum, quaternary phosphonium and 
ammonium salts, tertiary amines and imidazole compounds. The preferred 
catalysts are imidazole compounds. Particularly, preferred catalysts are 
2-phenylimidazole 2-methylimidazole, 1-methylimidazole, 
2-ethyl-4-methylimidazole and 
4,4'-methylene-bis(2-ethyl-5-methylimidazole). 
The catalyst is generally employed in an amount of from about 0.01 to about 
2; preferably from about 0.02 to about 1, most preferably from about 0.02 
to about 0.1, weight percent based on the combined weight of the 
polyepoxide compound and polyisocyanate compound used. 
In the practice of the present invention, an epoxy-terminated 
polyoxazolidone containing from about 50 to about 100 percent of the 
isocyanate groups converted to oxazolidone rings and from about 0 to about 
50 percent of the isocyanate groups converted to isocyanurate rings is 
produced by reaction of the polyisocyanate compound with the polyepoxide 
compound in the presence of a suitable catalyst at elevated temperatures. 
The polyisocyanate compound is employed in an amount of from about 5 to 
about 30, preferably from about 5 to about 20, most preferably from about 
10 to about 20, weight percent, the weight percent being based on the 
combined weight of the polyepoxide and polyisocyanate reactants. 
The polyepoxide compound is employed in an amount of from about 70 to about 
95, preferably from about 80 to about 95, most preferably from about 80 to 
about 90, weight percent, the weight percent being based on the combined 
weight of the polyepoxide and polyisocyanate reactants. 
The reaction of the polyepoxide with the polyisocyanate is conducted at a 
temperature of from about 110.degree. C. to about 200.degree. C. 
Preferably, the reaction is conducted at a temperature of from about 
120.degree. C. to about 180.degree. C. Most preferably, the reaction is 
conducted at a temperature of from about 140.degree. C. to about 
160.degree. C. 
In the practice of the present invention the catalyst is added to the 
reaction vessel containing the polyepoxide prior to the start of the 
addition of polyisocyanate compound. The catalyst can be dissolved in a 
suitable solvent prior to the addition to the polyepoxide to improve 
homogenization if desired. The temperature at which the catalyst is added 
is not critical. In general the catalyst is added at a temperature lower 
than the reaction temperature. The temperature is then raised and the 
reaction temperature maintained while the controlled addition of the 
polyisocyanate to the mixture of the catalyst and the polyepoxide is 
started. The polyisocyanate is added to the reaction vessel within a 
period of time of from about 3 to about 90, preferably from about 15 to 
about 60, most preferably from about 20 to about 45, minutes while 
maintaining the reaction temperature. The reaction temperature is 
maintained after the complete addition of the polyisocyanate for a period 
of time of from about 5 to about 180, preferably from about 15 to about 
120, most preferably from about 30 to about 90 minutes. 
In general, the reaction of the polyepoxide compound and the polyisocyanate 
compound according to the process of the present invention is conducted 
neat, that is, in the absence of a solvent or other liquid reaction 
diluent. 
In the practice of the present invention it has been surprisingly found 
that the conversion of the isocyanate groups can be controlled in a 
targeted manner to obtain the epoxy-terminated polyoxazolidone having from 
about 5 to about 30, preferably from about 5 to about 20, most preferably 
from about 10 to about 20, weight percent of the isocyanate content and 
having from about 50 to about 100 percent of the original isocyanate 
groups converted to oxazolidone rings and from about 0 to about 50 percent 
of the original isocyanate groups converted to isocyanurate rings in any 
of the following manner: 
(i) at a given amount of the catalyst and a given amount of the 
polyisocyanate, higher conversion of the isocyanate groups to oxazolidone 
rings (up to about 100 percent conversion) is achieved by increasing the 
reaction temperature; or 
(ii) at a given amount of the polyisocyanate and a given reaction 
temperature, higher conversion of the isocyanate groups to oxazolidone 
rings (up to about 100 percent conversion) is achieved by increasing the 
amount of the catalyst; or 
(iii) at a given amount of the catalyst and a given reaction temperature, 
higher conversion of the isocyanate groups to isocyanurate rings (up to 
about 50 percent conversion) is achieved that is, in the absence of a 
solvent or other liquid reaction diluent. 
In the practice of the present invention it has been surprisingly found 
that the conversion of the isocyanate groups can be controlled in a 
targeted manner to obtain the epoxy-terminated polyoxazolidone having from 
about 5 to about 30, preferably from about 5 to about 20, most preferably 
from about 10 to about 20, weight percent of the isocyanate content and 
having from about 50 to about 100 percent of the original isocyanate 
groups converted to oxazolidone rings and from about 0 to about 50 percent 
of the original isocyanate groups converted to isocyanurate rings in any 
of the following manner: 
(i) at a given amount of the catalyst and a given amount of the 
polyisocyanate, higher conversion of the isocyanate groups to oxazolidone 
rings (up to about 100 percent conversion) is achieved by increasing the 
reaction temperature; or 
(ii) at a given amount of the polyisocyanate and a given reaction 
temperature, higher conversion of the isocyanate groups to oxazolidone 
rings (up to about 100 percent conversion) is achieved by increasing the 
amount of the catalyst; or 
(iii) at a given amount of the catalyst and a given reaction temperature, 
higher conversion of the isocyanate groups to isocyanurate rings (up to 
about 50 percent conversion) is achieved by increasing the amount of the 
polyisocyanate; or 
(iv) at a given reaction temperature and given amounts of the polyepoxide 
compound, polyisocyanate compound and catalyst, higher conversion of the 
isocyanate groups to isocyanurate rings (up to about 50 percent 
conversion) is achieved by increasing the rate of addition of the 
polyisocyanate compound. 
The relation between the various reaction parameters influencing conversion 
of isocyanate groups into oxazolidone rings can be expressed as follows: 
EQU % Oxazolidone=-3.17i+0.135c-2.126t+8.685r+0.0142t.sup.2 -0.184r.sup.2 
wherein i is weight percent of polyisocyanate, c is amount of catalyst (in 
ppm), t is reaction temperature (.degree.C.) and r is addition time of 
polyisocyanate (in min.). 
Using the above equation, reaction parameters can be selected and the 
reaction conducted so as to obtain an epoxy-terminated polyoxazolidone 
having the desired content of oxazolidone rings (a margin of error: .+-.15 
percent). 
It should be understood that if the number obtained in the above equation 
is 100 or greater it represents 100 percent conversion of isocyanate 
groups into oxazolidone rings. 
The process of the present invention provides for the preparation of the 
epoxy-terminated polyoxazolidone which have specific properties linked to 
the particular ratio of oxazolidone and isocyanurate rings. 
The epoxy-terminated polyoxazolidones prepared according to the process of 
the present invention, when cured, are found to have unexpectedly high 
glass transition temperatures (up to about 175.degree. C. and higher) and 
surprisingly high solvent resistance properties (for example 
N-methylpyrrolidone pick-up of less than about 0.05 percent). The 
epoxy-terminated polyoxazolidones of the present invention, when cured, 
consistently have glass transition temperatures greater than about 
135.degree. C. and N-methylpyrrolidone pick-up of less than about 0.5 
percent. These properties make the epoxy-terminated polyoxazolidones of 
the present invention particularly advantageous for use in the electrical 
laminate applications, especially printed circuit board uses, in which 
high glass transition temperatures and high solvent resistance properties 
are highly sought after properties in the materials. 
Laminates used in the preparation of electrical circuit boards, have been 
conventionally produced by impregnating a supporting or reinforcing web 
with a resin composition, by passing the impregnated mat through a heated 
chamber where the resin composition is partially cured and laminating one 
or more layers of the resin mat with a layer such as copper foil under the 
application of heat and pressure. The resin composition employed for 
impregnating, in general, is referred to as "varnish", and the impregnated 
resin mat, conventionally, is referred to as "prepreg". The electrical 
laminate, is processed into circuit boards in known manner. 
A typical epoxy resin composition for the electrical laminating 
applications comprises a brominated epoxy resin prepared from a diglycidyl 
ethers of bisphenol A and a tetrabromobisphenol A, dicyandiamide as a 
hardener, an organic solvent such as acetone, and an accelerator. 
Unfortunately, the glass transition temperature of a cured epoxy resin 
prepared from this varnish composition is undesirably low, for example 
from about 110.degree. C. to about 135.degree. C. which causes problems in 
the subsequent processing steps used to prepare the printed circuit 
boards. 
An alternative varnish composition for application to a reinforcing web 
used in the production of electrical laminates, comprises a blend of a 
diglycidyl ether of bisphenol A and either bisphenol or 
tetrabromobisphenol A and a dicyandiamide as a hardener. The diglycidyl 
ether of bisphenol A is reacted in situ with bisphenol A and/or 
tetrabromobisphenol A and dicyandiamide during impregnation of the 
reinforcing web and the partial cure of the resin (see for example U.S. 
Pat. No. 3,738,862). Unfortunately, this varnish composition also exhibit 
undesirably low glass transition temperatures (less than 135.degree. C.). 
The present invention solves the problem experienced in the art by 
providing an epoxy resin varnish composition comprising an epoxy resin, a 
hardener, an organic solvent, an accelerator and, optionally, another 
standard adjuncts characterized in that the epoxy resin is the 
epoxy-terminated polyoxazolidone having the isocyanate content of from 
about 5 to about 30 weight percent and having from about 50 to about 100 
percent of the isocyanate groups converted to oxazolidone rings and from 
about 0 to about 50 percent of the isocyanate groups converted to 
isocyanurate rings. 
The epoxy-terminated oxazolidones are prepared according to the process 
described hereinbefore. 
When cured, the epoxy resin varnish compositions of the present invention 
exhibit surprisingly excellent physical and mechanical properties. In 
particular the cured epoxy-terminated polyoxazolidones exhibit 
substantially higher glass transition temperatures, for example, about 
175.degree. C. and higher, than the conventional epoxy resins cured with 
dicyandiamide. In addition, the cured epoxy-terminated polyoxazolidone 
exhibit surprisingly high resistance to attack by various chemicals as 
demonstrated by the N-methylpyrrolidone pick-up of less than about 0.1 
percent. 
The organic solvents suitably employed for the epoxy resin varnish 
compositions of the present invention are those organic liquids in which 
the epoxy-terminated polyoxazolidone and the hardener are soluble and 
which are sufficiently volatile such that they escape from the varnish 
composition before and/or during the partial cure and/or before the final 
cure. Illustrative examples of such organic liquids are various glycol 
ethers such as ethylene or propylene glycol monomethylether and the esters 
thereof such as ethylene glycol monomethylether acetate; ketones such as 
methylisobutyl ketone, methylethyl ketone, acetone and methylisopropyl 
ketone; and aromatic hydrocarbons such as toluene and xylene or mixtures 
thereof. Of such organic liquids, those preferably used as the solvent in 
the epoxy resin composition of the present invention are the ketones, 
particularly acetone, methyl ethyl ketone and methyl isobutyl ketone, or 
mixtures of these ketones with each other or with one or more of the other 
solvents. Other solvents that can be used are dimethyl sulfoxide (DMSO), 
N-methylpyrrolidone and dimethylformamide. 
The amount of solvent most advantageously employed in the varnish 
composition of the present invention will vary depending on a variety of 
factors including the particular solvent, hardener and epoxy resin 
employed, desired properties of the epoxy resin composition (for example, 
desired viscosity of the varnish composition and the desired resin 
"pick-up" of this composition by the reinforcing web). Advantageously, the 
composition exhibits a viscosity from about 50 to about 1000 milliPascal 
seconds (mPa.s) measured using a Brookfield viscometer, Type RVT, 20 rpm 
and the appropriate spindle at 25.degree. C. In general, the amount of 
solvent will range from about 20 to about 60, preferably from about 25 to 
about 50 weight percent, based on the total weight of the varnish 
composition, the remainder comprising non-volatiles components (amount of 
the total solids other than the solvents). More preferably, the epoxy 
composition will contain from about 20 to about 45 weight percent of the 
solvent and from about 55 to about 80 weight percent non-volatiles. 
The hardener useful in the present invention is capable of curing the 
epoxy-terminated polyoxazolidone and is soluble in the solvent employed. 
The hardener useful in the epoxy resin varnish composition of the present 
invention is suitably dicyandiamide system, bisphenols such as bisphenol A 
and tetrabromobisphenol A, and multifunctional novolacs. 
The amount of the hardener in the epoxy resin varnish composition of the 
present invention is dependent on a variety of factors including the 
specific hardener and the epoxy resin employed and the desired properties 
of the varnish composition. In general, the amount of the hardener is 
selected to give the cured epoxy-terminated polyoxazolidone composition 
the maximum glass transition temperature. Conveniently, from about 1 to 
about 8, preferably from about 2 to about 6, most preferably from about 3 
to about 5, phr of the dicyandiamide system are employed in the present 
invention. In general, the polyhydric phenolic hardener is employed in 
amounts such that the epoxy resin varnish composition comprises from about 
0.5 to about 1.5 preferably from about 0.75 to about 1.2, most preferably 
from about 0.9 to about 1.1, phenolic hydroxyl groups per epoxy group. 
The epoxy resin varnish compositions of the present invention will also 
contain an accelerator. Illustrative examples of accelerators include the 
stannous salts of monocarboxylic acids, such as stannous octoate and 
stannous laurate, various alkali metal salts such as lithium benzoate, 
certain heterocyclic compounds such as the imidazole and benzimidazole 
compounds and salts thereof, tertiary amine borates and tertiary amines. 
Preferred accelerators are the benzyldimethylamine and imidazoles, 
particularly the alkyl-substituted imidazole and phenyl-substituted 
imidazoles. The most preferred accelerators are 2-methyl imidazole and 
2-phenyl imidazole. Additional accelerators that can be used in the 
present invention are described in U.S. Pat. No. 3,738,862 (Klarquist et 
al). 
In general, if employed, the accelerator is used in an amount sufficient to 
catalyze the reaction. The accelerator is generally used in amounts of 
from about 0.01 to about 2 weight percent based on the combined weight of 
the epoxy resin and hardener. Preferably, the accelerator is employed in 
an amount of from about 0.02 to about 1 weight percent based on the 
combined weight of the epoxy resin and hardner. 
The epoxy resin varnish compositions can optionally contain adjuncts such 
as pigments, fillers, dyes and the like. The adjuncts employed in the 
practice of the present invention are well-known in the art and reference 
is made thereto for the purpose of this invention. 
The epoxy resin varnish compositions of the present invention are 
particularly useful in impregnating weaves, webs, fabric and cloth of 
variety of different materials including glass, quartz and synthetic 
fibers such as aramid. In the preparation of electrical laminates, a glass 
web is conventionally employed. 
In the process of the present invention for preparing electrical laminates, 
the varnish composition is applied to the reinforcing web in a desired 
amount and the web subsequently heated to advance and/or cure the 
epoxy-terminated polyoxazolidone. Although the amounts of the epoxy resin 
varnish composition which are applied to the reinforcing web will vary 
depending on the specific web and epoxy resin varnish composition employed 
and the desire properties of the impregnated cloth and electrical 
laminates prepared therefrom, the epoxy resin varnish composition of the 
present invention is generally applied to the reinforcing web in 
conventional amounts; which amounts vary from about 30 to about 70 weight 
percent, based on the total weight of the impregnated web. 
The impregnated web or prepreg is subsequently processed using conventional 
techniques. Such techniques involve advancing and/or curing the epoxy 
resin by heating the impregnated web to an elevated temperature such as 
from about 100.degree. C. to about 200.degree. C. Subsequently, the 
prepreg is fabricated into laminates by laminating one or more prepregs, 
commonly cut to a predetermined size, with thin layers of an electrical 
conductive material such as copper foil using elevated temperatures and 
pressures. Conventionally, the laminating temperature vary from about 
130.degree. C. to about 230.degree. C., with pressures varying from about 
34 kPa to about 6.9 MPa. 
The present invention is further illustrated by the following examples in 
which the formation of oxazolidone and isocyanurate rings is confirmed by 
infrared (IR) spectrum. The percent conversions of isocyanate groups to 
oxazolidone and isocyanurate rings is calculated from the relative 
intensities of oxazolidone and isocyanurate IR bands. 
Various terms and designations used in the examples are explained 
hereinbelow. 
Epoxy Resin A stands for a diglycidyl ether of bisphenol A having an epoxy 
equivalent weight between 177 and 189 sold by The Dow Chemical Company 
under the trademark D.E.R. 330. 
Epoxy resin B stands for an epoxidized phenolformaldehyde novolac resin 
having an EEW between 176 and 181 with functionality of 3.6 sold by The 
Dow Chemical Company under the trademark D.E.N. 438. 
Epoxy resin C stands for a diglycidyl ether of tetrabromobisphenol A having 
an EEW between 325 and 375 sold by The Dow Chemical Company under the 
trademark D.E.R. 542. 
Epoxy resin D stands for triglycidyl ether of this (hydroxyphenyl)methane 
having an EEW between 145 and 175 sold by The Dow Chemical Company under 
the trademark TACTIX 742. 
Epoxy resin E stands for diglycidyl ether of bisphenol A having an EEW of 
400-475 sold by The Dow Chemical Company under the trademark D.E.R. 652 
A75. 
Epoxy resin F stands for brominated bisphenolic epoxy resin having an EEW 
of 480 to 560 and bromine content of 20.5 to 22.5 weight percent, sold by 
The Dow Chemical Company under the trademark D.E.R. 512 A75. 
TBBA stands for tetrabromobisphenol A. 
TDI stands for toluenediisocyanate 
Isocyanate A stands for MDI sold by The Dow Chemical Company under the 
trademark ISONATE M 143. 
Isocyanate B stands for polymeric MDI sold by The Dow Chemical Company 
under the trademark VORANATE M 220. 
Isocyanate C stands for 20/80 isomer mixture of TDI. 
DICY stands for dicyandiamide. 
NMP stands for N-methylpyrrolidone. 
The following analytical methods are used for various measurements in the 
examples. 
The standard wet titration method was used to determine Epoxy Equivalent 
Weight. 
The solids content was calculated from the difference of weight of a sample 
(approximately 1 g) before and after heating in an aluminium dish on a hot 
plate at 150.degree. C. for an hour and then for a further hour in a 
vacuum oven at 150.degree. C. 
The viscosity of the resin was measured according to ASTM D445 method using 
a Cannon Fenske Viscometer at 25.degree. C. Reactivity of the resins was 
measured according to the following method: The resin solution was blended 
with 0.1 phr 2-methylimidazole based on solid. 2-methylimidazole was first 
dissolved in acetone to form a 10 percent solution. The mixture was then 
reacted on the surface of a hot plate held at 175.degree. C. The 
reactivity was reported as elapsed time required for gelation. 
The glass transition temperature was measured on film prepared from the 
varnish formulation used for reactivity measurement. The film were cured 
on a hot plate at 175.degree. C. for 90 min. Samples were run at 
10.degree. C/min. from 38.degree. C. using a METTLER TA.TM. 2000 DTA. 
The glass transition temperature of the laminate was measured directly on 
the cured laminate according to the method for measuring glass transition 
temperature on film. 
The melt viscosity was measured according to the ASTM D445 method using an 
ICI cone and plate viscosimeter. 
To measure the chemical resistance, three pieces of etched laminates 6 
cm.times.1.5 cm were cut, weighed and dipped for 30 minutes in 
N-methylpyrrolidone solvent at 23.degree. C. The pieces were dried and 
then weighed; the solvent pick up was taken as the gain in weight. 
To measure the moisture resistance, twelve pieces of etched laminates 6 
cm.times.1.5 cm were placed in a pressure cooker in water for 30, 60 or 90 
minutes at 120.degree. C. Then, after being dried were dipped (20 seconds) 
in a tin solder bath (260.degree. C.), to determine resistance to 
blistering due to moisture absorption. 
The binding strength between the copper and the epoxy resin was determine 
through the strength needed to peel off the copper from a laminate. 
The volatile determination of the prepreg was done as follows: 
A sample of prepreg approximately 10 cm.times.10 cm was weighed to the 
nearest 0.001 gram (W.sub.1). The sample is placed in a circulating air 
oven at 163.degree. C. for 15 minutes and on removal it was placed 
immediately in a desiccator to cool. When cooled, the sample was reweighed 
and the weight recorded as W.sub.2. The volatile content is calculated 
from: 
##EQU1## 
In the following examples, all parts and percentages are by weight unless 
otherwise expressly indicated. 
PREATION OF THE EPOXY-TERMINATED POLYOXAZOLIDONES

EXAMPLE 1 
10% Polyisocyanate/90% Epoxy Resin 
To a 1000 ml 3-neck flask equipped with pneumatic stirrer water cooled 
condenser, inlet for nitrogen padding, a thermocouple, temperature 
controller, heating mantle and an attached addition funnel, was added 
Epoxy Resin A (450 g; EEW=180). The flask was heated up to about 
145.degree. C. to 150.degree. C. while stirring and was padded with 
nitrogen. 2-Methylimidazole (0.15 g; 0.03 percent) was then added to the 
flask and the resultant mixture was heated to 160.degree. C. At that time, 
of Isocyanate A (50 g) was placed in the addition funnel. Isocyanate was 
added dropwise to the mixture of Epoxy Resin A and 2-methylimidazole at 
160.degree. C. within a period of 30 minutes. The reaction mixture was 
maintained at a temperature of 160.degree. C. for additional 15 minutes 
after completion of the addition of Isocyanate A. 
The IR spectrum of the sample of the product showed the presence of the 
characteristic absorption band of oxazolidone J (C.dbd.O) at 1755 
cm.sup.-1. The characteristic absorption bands of isocyanate J (C.dbd.O) 
at 2250 to 2270 cm.sup.-1 and isocyanurate J (C.dbd.O) at 1700 cm.sup.-1 
were not present. This indicates 100 percent conversion of isocyanate 
groups into oxazolidone rings. 
The obtained epoxy-terminated polyoxazolidone has an EEW of 222 and 
viscosity of 600 mPa.s at 80.degree. C. This product is referred to as 
Resin 1 hereinafter. 
EXAMPLE 2 
20% Polyisocyanate/80% Epoxy Resin 
To a 100 ml 3-neck flask equipped as in Example 1, was added Epoxy Resin A 
(400 g; EEW=180). The flask was heated to about 135.degree. C. to 
140.degree. C. while stirring and was padded with nitrogen. 
2-Phenylimidazole (0.11 g; 0.022 percent) was added to the flask and the 
resultant mixture heated to 150.degree. C. Then, Isocyanate A (100 g) was 
placed in the addition funnel and added dropwise to the flask within a 
period of time of 30 minutes while maintaining the reaction temperature at 
150.degree. C. Samples were taken periodically after the end of addition 
of Isocyanate A and analyzed by titrating for residual epoxide and by 
infrared analysis. 
The IR spectrum of the sample of the product taken at 60 minutes after the 
end of the addition of Isocyanate A showed the presence of characteristic 
absorption bands of oxazolidone J(C.dbd.O) at 1753 cm.sup.-1 and of 
isocyanurate J(C.dbd.O) at 1709 cm.sup.-1 with approximately the same 
absorption intensities. The isocyanate band was not present, which 
indicates that about 50 percent of isocyanate groups was converted to 
oxazolidone rings and 50 percent was converted to isocyanurate rings. 
The obtained epoxy-terminated polyoxazolidone is a solid at 25.degree. C., 
has an EEW of 253 and viscosity of 460 mPa.s at 150.degree. C. This 
product is referred to as Resin 2 hereinafter. 
EXAMPLE 3 
9.4% Polyisocyanate/90.6% Epoxy Resin Advanced with Bisphenol A 
A. To a flask equipped as in Example 1 was added 532 g of Epoxy Resin A 
(EEW=180). While stirring, the flask was heated to about 85.degree. C. to 
90.degree. C. and padded with nitrogen. At about 90.degree. C., 1.89 of 
tetraphenylphosphonium bromide was added to the flask and the resultant 
mixture heated to about 150.degree. C. Then, 64.7 g of Isocyanate A was 
placed in the addition funnel and added dropwise to the flask within a 
period of 3 minutes. The temperature of the reaction mixture was raised by 
exothermic reaction to about 195.degree. C. Approximately 10 minutes after 
the end of addition of Isocyanate A, a sample was taken and analyzed by 
titrating for residual epoxide, and by infrared analysis. The product 
obtained is a semi-solid at room temperature. This product has an EEW of 
234 and melt viscosity of 9280 mPa.s at 60.degree. C. 
B. The above semi-solid product (254.8 g) was added to another flask and 
heated to about 85.degree. C. to 90.degree. C. and the flask padded with 
nitrogen. At about 90.degree. C., bisphenol A (40.5 g) was added to the 
flask while stirring and the temperature of the reaction mixture raised by 
the exothermic reaction to about 187.degree. C. A sample was taken 45 
minutes after the addition of bisphenol A and titrated. The reaction was 
complete and the EEW of the product advanced in molecular weight is 416. 
This product is referred to as Resin 3 hereinafter. 
EXAMPLE 4 
30% Polyisocyanate/70% Epoxy Resin 
To a flask equipped as in Example 1 was added 350 g of Epoxy Resin A 
(EEW=180). While stirring, the flask was heated to about 165.degree. C. to 
170.degree. C. and padded with nitrogen. At about 170.degree. C., 0.25 g 
(0.05 percent) of 2-phenylimidazole was added to the flask and the 
resultant mixture heated to 180.degree. C. Then, 150 g of Isocyanate A was 
added dropwise to the mixture during a period of 45 minutes while the 
reaction temperature increased from 180.degree. C. to 190.degree. C. 
Samples were taken periodically and analyzed by tritration and infrared 
spectroscopy. The reaction mixture was maintained at 180.degree. C. for 
additional 60 minutes. 
The IR spectrum of the sample taken 60 minutes after the end of addition of 
Isocyanate A showed the presence of the characteristic absorption band of 
oxazolidone J(C.dbd.O) at 1752 cm.sup.-1. The characteristic band of 
isocyanate and isocyanurate were not present. 
This product is a solid material at room temperature and has an EEW of 588. 
The product is referred to as Resin 4 hereinafter. 
EXAMPLE 5 
20% Polyisocyanate/80% Epoxy Resin 
To a flask equipped as in Example 1 was added 400 g of Epoxy Resin A 
(EEW=180). While stirring the content, the flask was heated to about 
145.degree. C. to 150.degree. C. and padded with nitrogen. 
2-Phenylimidazole (0.175 g; 0.035 percent) was added to the flask and the 
resultant mixture heated to 160.degree. C. Then, Isocyanate A (100 g) was 
added dropwise to the mixture within a period of 45 minutes. The 
temperature was raised by the exothermic reaction to about 180.degree. C. 
to 185.degree. C. Sample of the product was taken 15 minutes after the end 
of addition of Isocyanate A and analyzed by titrating for residual epoxide 
and infrared spectroscopy. The characteristic absorption band of 
oxazolidone J(C.dbd.O) at 1750 cm.sup.-1 was present. The isocyanate and 
isocyanurate absorption bands were not present. This indicates 100 percent 
conversion of isocyanate groups to oxazolidone rings. The product obtained 
is a solid at room temperature and has an EEW of 330 and viscosity of 580 
mPa.s at 150.degree. C. This product is referred to as Resin 5 
hereinafter. 
EXAMPLE 6 
14% Polyisocyanate/86% Epoxy Resin 
To a flask equipped as in Example 1 were added Epoxy Resin A (245 g) and 
Epoxy Resin C (185 g). While stirring the content, the flask was heated to 
about 145.degree. C. to 150.degree. C. and padded with nitrogen. 
2-phenylimidazole (0.2 g dissolved in 0.2 g methanol) was added to the 
flask and the resultant mixture heated to about 155.degree. C. Then, 
Isocyanate B (70 g) was added dropwise to the mixture within a period of 
30 minutes. The temperature of the reaction mixture was raised by the 
exothermic reaction to about 175.degree. C. to 180.degree. C. A sample of 
the product was taken 30 minutes after the end of the addition of 
Isocyanate B and analyzed by titrating for residual epoxide and infrared 
spectroscopy. The infrared spectroscopy showed the presence of oxazolidone 
band J(C.dbd.O) at 1752 cm.sup.-1. No isocyanate and isocyanurate bands 
were present. This indicates 100 percent conversion of isocyanate groups 
to oxazolidone rings. 
The product obtained is a solid at room temperature and has an EEW of 356 
and viscosity of 900 mPa.s at 150.degree. C. This product is referred to 
as Resin 6 hereinafter. 
EXAMPLE 7 
7.5% Polyisocyanate/92.5% Epoxy Resin Advanced with TBBA 
(A) To a flask equipped as in Example 1 was added Epoxy Resin A (307.6 g; 
EEW=177) and the flask was heated to about 135.degree. C. to 140.degree. 
C. and padded with nitrogen while the content was stirred. 
2-Ethyl-4-methylimidazole (0.276 g; 0.08 percent) was added to the flask 
and the resultant mixture heated to about 145.degree. C. Then, Isocyanate 
A (37.4 g) was added dropwise to the mixture within a period of 25 
minutes. The temperature of the reaction mixture was kept at 160.degree. 
C. The reaction temperature was kept at 160.degree. C. and 20 minutes 
after the end of the Isocyanate A addition a sample of the product was 
taken and analyzed by titrating for residual epoxide and by infrared 
spectroscopy. This product is a semi-solid at room temperature and has an 
EEW of 224. 
(B) While the reaction temperature was kept at 160.degree. C., 
tetrabromobisphenol A (155 g) was added to the flask containing the 
product of above paragraph for the advancement in molecular weight of the 
product. The reaction temperature was then lowered to 150.degree. C. and 
the advancement reaction continued at that temperature for about 30 
minutes. The advanced product has an EEW of 567. This product is referred 
to as Resin 7 hereinafter. 
EXAMPLE 8 
19% Polyisocyanate/81% Epoxy Resin 
To a flask equipped as in Example 1 was added Epoxy Resin A (405 g; 
EEW=177). While stirring the content the flask was heated to about 
145.degree. C. and padded with nitrogen. 2-Phenylimidazole (0.175 g; 0.035 
percent) was then added to the flask and the resultant mixture heated to 
about 155.degree. C. Isocyanate B (95 g) was added dropwise to the mixture 
within a period of 30 minutes. A sample of the product was taken 60 
minutes after the end of the Isocyanate B addition and analyzed by 
titration for residual epoxide and by infrared spectroscopy. The 
characteristic absorption band of oxazolidone J(C.dbd.O) at 1752 cm.sup.-1 
was present. The isocyanate and isocyanurate absorption bands were not 
present. This indicates 100 percent conversion of isocyanate groups to 
oxazolidone groups. The product obtained has an EEW of 320 and melt 
viscosity of 840 mPa.s at 150.degree. C. 
EXAMPLE 9 
7.5% Polyisocyanate/92.5% Epoxy Resin 
To a flask equipped as in Example 1 was added Epoxy Resin C (4625 g; 
EEW=330). While stirring the content, the flask was heated to about 
150.degree. C. and padded with nitrogen. 2-Phenylimidazole (0.25 g/0.05 
percent) was then added to the flask and the resultant mixture heated to 
about 160.degree. C. Then, Isocyanate B (37.5 g) was added dropwise to the 
mixture within a period of 30 minutes. A sample of the product was taken 
60 minutes after the end of Isocyanate B addition and analyzed by 
titrating for residual epoxide and by infrared spectroscopy. The 
characteristic absorption band of oxazolidone J(C.dbd.O) at 1752 cm.sup.-1 
was present. The isocyanate and isocyanurate bands were not present. This 
indicates 100 percent conversion of isocyanate groups to oxazolidone 
rings. The product obtained has an EEW of 440 and melt viscosity of 920 
mPa.s at 150.degree. C. 
EXAMPLE 10 
10% Polyisocyanate/90% Epoxy Resin 
To a flask equipped as in Example 1 was added Epoxy Resin D (450 g; 
EEW=160). While stirring the content, the flask was heated to about 
150.degree. C. and padded with nitrogen. 2-Phenylimidazole (0.175 g/0.035 
percent) was then added to the flask and the resultant mixture heated to 
about 160.degree. C. Then, Isocyanate A (50 g) was added dropwise to the 
mixture within a period of 30 minutes and the reaction temperature 
maintained at 160.degree. C. after the end of the Isocyanate addition for 
60 minutes. At that time a sample of the product was taken and analyzed by 
titrating for residual epoxide and by infrared spectroscopy. The 
characterized absorption band of oxazolidone J(C.dbd.O) at 1752 cm.sup.- 
was present. The absence of isocyanate and isocyanurate bands indicates 
100 percent conversion of isocyanate groups to oxazolidone rings. 
EXAMPLE 11 
15% TDI/85% Epoxy Resin 
To a 1000 ml 3-neck flask equipped with pneumatic stirrer water cooled 
condenser, inlet for nitrogen padding, a thermocouple, temperature 
controller, heating mantle and an attached addition funnel, was added 
Epoxy Resin A (425 g; EEW=180). The flask was heated up to about 
150.degree. C. while stirring and was padded with nitrogen. 
2-Phenylimidazole (0.15 g; 0.03 percent) was then added to the flask and 
the resultant mixture was heated to 160.degree. C. At that time, of 
Isocyanate C (75 g) was placed in the addition funnel. Isocyanate was 
added dropwise to the mixture of Epoxy Resin A and 2-phenylimidazole at 
160.degree. C. within a period of 30 minutes. The reaction mixture was 
maintained at a temperature of 160.degree. C. for additional 60 minutes 
after completion of the addition of Isocyanate C. 
The IR spectrum of the sample of the product taken at 60 minutes after the 
end of the addition of Isocyanate C showed the presence of characteristic 
absorption bands of oxazolidone J(C.dbd.O) at 1753 cm.sup.-1 and of 
isocyanurate J(C.dbd.O) at 1709 cm.sup.-1 with approximately a ratio 85/15 
absorption intensity. The isocyanate band was not present, which indicates 
that about 85 percent of isocyanate groups was converted to oxazolidone 
rings and 15 percent was converted to isocyanurate rings. 
The obtained epoxy-terminated polyoxazolidone is a solid at 25.degree. C., 
has an EEW of 315 and viscosity of 440 mPa.s at 150.degree. C. This 
product is referred to as Resin 11 hereinafter. 
EXAMPLE 12 
10% Polyisocyanate/90% Epoxy Resin 
To a 1000 ml 3-neck flask equipped with pneumatic stirrer water cooled 
condenser, inlet for nitrogen padding, a thermocouple, temperature 
controller, heating mantle and an attached addition funnel, was added 
Epoxy Resin A (450 g; EEW=177). The flask was heated up to about 
130.degree. C. while stirring and was padded with nitrogen. 
2-Phenylimidazole (0.15 g; 0.03 percent) was then added to the flask and 
the resultant mixture was heated to 140.degree. C. At that time, of 
Isocyanate A (50 g) was placed in the addition funnel. Isocyanate was 
added dropwise to the mixture of Epoxy Resin A and 2-phenylimidazole at 
140.degree. C. within a period of 30 minutes. The reaction mixture was 
maintained at a temperature of 140.degree. C. for additional 15 minutes 
after completion of the addition of Isocyanate A. 
The IR spectrum of the sample of the product showed the presence of the 
characteristic absorption band of oxazolidone J (C.dbd.O) at 1755 
cm.sup.-1. The characteristic absorption bands of isocyanate J (C.dbd.O) 
at 2250 to 2270 cm.sup.-1 and isocyanurate J (C.dbd.O) at 1700 cm.sup.-1 
were not present. This indicates 100 percent conversion of isocyanate 
groups into oxazolidone rings. 
The obtained epoxy-terminated polyoxazolidone has an EEW of 288 and 
viscosity of 600 mPa.s at 80.degree. C. This product is referred to as 
Resin 12 hereinafter. 
EXAMPLE 13 
10% Polyisocyanate/90% Epoxy Resin 
The reaction conditions were the same as Example 12, except the amounts of 
2-phenylimidzole used was (0.075 g; 0.015 percent). The reaction mixture 
was maintained at a temperature of 140.degree. C. for additional 120 
minutes after completion of the addition of Isocyanate A. 
The IR spectrum of the sample of the product taken at 120 minutes after the 
end of the addition of Isocyanate A showed the presence of characteristic 
absorption bands of oxazolidone J(C.dbd.O) at 1753 cm.sup.-1 and of 
isocyanurate J(C.dbd.O) at 1709 cm.sup.-1 with approximately the same 
absorption intensities. The isocyanate band was not present, which 
indicates that about 50 percent of isocyanate groups was converted to 
oxazolidone rings and 50 percent was converted to isocyanurate rings. 
The obtained epoxy-terminated polyoxazolidone is a semi-solid at 25.degree. 
C., has an EEW of 204 and viscosity of 610 mPa.s at 80.degree. C. This 
product is referred to as Resin 12 hereinafter. 
EXAMPLE 14 
10% Polyisocyanate/90% Epoxy Resin 
The reaction conditions were the same as Example 12, except the Isocyanate 
A was added dropwise to the mixture of Epoxy Resin A and 2-phenylimidazole 
at 140.degree. C. within a period of 10 minutes (instead of 30 minutes). 
The reaction mixture was maintained at a temperature of 140.degree. C. for 
additional 60 minutes after completion of the addition of Isocyanate A. 
The IR spectrum of the sample of the product taken at 60 minutes after the 
end of the addition of Isocyanate A showed the presence of characteristic 
absorption bands of oxazolidone J(C.dbd.O) at 1754 cm.sup.-1 and of 
isocyanurate J(C.dbd.O) at 1708 cm.sup.-1 with approximately the same 
absorption intensities. The isocyanate band was not present, which 
indicates that about 50 percent of isocyanate groups was converted to 
oxazolidone rings and 50 percent was converted to isocyanurate rings. 
The obtained epoxy-terminated polyoxazolidone is a semi-solid at 25.degree. 
C., has an EEW of 212 and viscosity of 1960 mPa.s at 80.degree. C. This 
product is referred to as Resin 14 hereinafter. 
EXAMPLE 15 
15% Polyisocyanate/85% Epoxy Resin 
To a 1000 ml 3-neck flask equipped with pneumatic stirrer water cooled 
condenser, inlet for nitrogen padding, a thermocouple, temperature 
controller, heating mantle and an attached addition funnel, was added 
Epoxy Resin A (425 g; EEW=180). The flask was heated up to about 
150.degree. C. while stirring and was padded with nitrogen. 
2-Phenylimidazole (0.15 g; 0.03 percent) was then added to the flask and 
the resultant mixture was heated to 160.degree. C. At that time, of 
Isocyanate A (75 g) was placed in the addition funnel. Isocyanate was 
added dropwise to the mixture of Epoxy Resin A and 2-phenylimidazole at 
160.degree. C. within a period of 30 minutes. The reaction mixture was 
maintained at a temperature of 160.degree. C. for additional 15 minutes 
after completion of the addition of Isocyanate A. 
The IR spectrum of the sample of the product showed the presence of the 
characteristic absorption band of oxazolidone J (C.dbd.O) at 1755 
cm.sup.-1. The characteristic absorption bands of isocyanate J (C.dbd.O) 
at 2250 to 2270 cm.sup.-1 and isocyanurate J (C.dbd.O) at 1700 cm.sup.-1 
were not present. This indicates 100 percent conversion of isocyanate 
groups into oxazolidone rings. 
The obtained epoxy-terminated polyoxazolidone has an EEW of 258 and 
viscosity of 260 mPa.s at 120.degree. C. This product is referred to as 
Resin 15 hereinafter. 
EXAMPLE 16 
15% Polyisocyanate/85% Epoxy Resin 
To a 1000 ml 3-neck flask equipped with pneumatic stirrer water cooled 
condenser, inlet for nitrogen padding, a thermocouple, temperature 
controller, heating mantle and an attached addition funnel, was added 
Epoxy Resin A (425 g; EEW=180). The flask was heated up to about 
130.degree. C. while stirring and was padded with nitrogen. 
2-Phenylimidazole (0.15 g; 0.03 percent) was then added to the flask and 
the resultant mixture was heated to 160.degree. C. At that time, of 
Isocyanate A (75 g) was placed in the addition funnel. Isocyanate was 
added dropwise to the mixture of Epoxy Resin A and 2-phenylimidazole at 
140.degree. C. within a period of 30 minutes. The reaction mixture was 
maintained at a temperature of 140.degree. C. for additional 60 minutes 
after completion of the addition of Isocyanate A. 
The IR spectrum of the sample of the product taken at 60 minutes after the 
end of the addition of Isocyanate A showed the presence of characteristic 
absorption bands of oxazolidone J(C.dbd.O) at 1754 cm.sup.-1 and of 
isocyanurate J(C.dbd.O) at 1707 cm.sup.-1 with approximately the same 
absorption intensities. The isocyanate band was not present, which 
indicates that about 55 percent of isocyanate groups was converted to 
oxazolidone rings and 45 percent was converted to isocyanurate rings. 
The obtained epoxy-terminated polyoxazolidone has an EEW of 234 and 
viscosity of 330 mPa.s at 120.degree. C. This product is referred to as 
Resin 16 hereinafter. 
EXAMPLE 17 
20% Polyisocyanat/80% Epoxy Resin 
To a 100 ml 3-neck flask equipped as in Example 1, was added Epoxy Resin A 
(400 g; EEW=180). The flask was heated to about 150.degree. C. while 
stirring and was padded with nitrogen. 2-Phenylimidazole (0.15 g; 0.03 
percent) was added to the flask and the resultant mixture heated to 
160.degree. C. Then, Isocyanate A (100 g) was placed in the addition 
funnel and added dropwise to the flask within a period of time of 30 
minutes while maintaining the reaction temperature at 160.degree. C. 
Samples were taken periodically after the end of addition of Isocyanate A 
and analyzed by titrating for residual epoxide and by infrared analysis. 
The IR spectrum of the sample of the product taken at 60 minutes after the 
end of the addition of Isocyanate A showed the presence of characteristic 
absorption bands of oxazolidone J(C.dbd.O) at 1753 cm.sup.-1 and of 
isocyanurate J(C.dbd.O) at 1709 cm.sup.-1 with approximately a ratio of 
70/30 absorption intensity. The isocyanate band was not present, which 
indicates that about 70 percent of isocyanate groups was converted to 
oxazolidone rings and 30 percent was converted to isocyanurate rings. 
The obtained epoxy-terminated polyoxazolidone is a solid at 25.degree. C., 
has an EEW of 284 and viscosity of 280 mPa.s at 150.degree. C. This 
product is referred to as Resin 17 hereinafter. 
EXAMPLE 18 
15% Polyisocyanate/85% Epoxy Resin 
To a 100 ml 3-neck flask equipped as in Example 1, was added Epoxy Resin A 
(400 g; EEW=180) and Epoxy Resin B (25 g; EEW 185). The flask was heated 
to about 150.degree. C. while stirring and was padded with nitrogen. 
2-Phenylimidazole (0.1 g; 0.02 percent) was added to the flask and the 
resultant mixture heated to 160.degree. C. Then, Isocyanate A (75 g) was 
placed in the addition funnel and added dropwise to the flask within a 
period of time of 30 minutes while maintaining the reaction temperature at 
160.degree. C. Sample was taken 60 minutes after the end of addition of 
Isocyanate A and analyzed by titrating for residual epoxide and by 
infrared analysis. 
The IR spectrum of the sample of the product showed the presence of the 
characteristic absorption band of oxazolidone J (C.dbd.O) at 1755 
cm.sup.-1. The characteristic absorption bands of isocyanate J (C.dbd.O) 
at 2250-2270 cm.sup.-1 and isocyanurate J (C.dbd.O) at 1700 cm.sup.-1 were 
not present. This indicates 100 percent conversion of isocyanate groups 
into oxazolidone rings. 
The obtained epoxy-terminated polyoxazolidone has an EEW of 263 and 
viscosity of 50 mPa.s at 150.degree. C. This product is referred to as 
Resin 18 hereinafter. 
Preparation of Varnishes and Laminates 
Using procedures described in the Examples hereinbefore, Resins 1 to 7 and 
9 were prepared in larger quantities in a 10 liter stainless steel 
reaction. After the completion of the reactions which was indicated by the 
absence of the isocyanate band in the IR spectra of the samples taken, 
each reaction mixture was cooled to about 130.degree. C. and diluted with 
methylethylketone to give a solution of from 70 to 80 percent solids 
content. 
Epoxy Resin varnishes are prepared by mixing solution of an 
epoxy-terminated polyoxazolidone of this invention, a hardener, a solvent 
and an accelerator at room temperature in a container equipped with a 
stirrer according to the proportions (based on solid resins) indicated in 
Table 1 below. Approximately 15 kg of each Epoxy Resin Varnish were 
prepared. 
The resulting varnishes were used to impregnate a glass cloth (Marglass 
7628 finish 782). This cloth is an industrial glass silk fabric having 
equal warp and weft (plain weave) of electrical grade glass treated with 
finish 782. The glass silk fabric was impregnated with the varnish on the 
horizontal pilot plant size Caratsch treater. 
The varnish was applied to a glass silk fabric by pulling the glass silk 
fabric through a resin bath containing the varnish and then through a 
doctor bar set at about 0.5 to 1.3 mm and then through three air heated 
zones to a temperature of from 150.degree. C. to 170.degree. C. The total 
length of all three heating zones was 3 meters. The glass silk fabric 
passed through the resin bath and heating zones at a rate of 0.5 to 2.5 
m/min. 
The treater parameters were adjusted to produce prepreg with the following 
characteristics: 
______________________________________ 
Test method 
______________________________________ 
Rest gel time at 175.degree. C. 
100-200 sec 
NEMA LI 1-12.19 
Flow at 170.degree. C. 
12-20% NEMA LI 1-14.32 
Volatile &lt;1% 
Resin content 40-44% NEMA LI 1-12.16 
______________________________________ 
except for Examples III and XII, in which the parameters were adjusted to 
produce the following characteristics: 
Rest gel time at 170.degree. C.--60-100 sec 
Flow at 170.degree. C.--10-25% 
The prepregs were then fabricated into "FR-4" and "G-10" type electrical 
laminates by placing 8 plies of prepreg between 2 sheets of copper foil 
and pressing in a laboratory press (LAUFFER) following the press cycle: 
0-30 min. low pressure (14 kg/cm.sup.2) R.T. to 170.degree. C. 
30-120 min. high pressure (45 kg/cm.sup.2) at 170.degree. C. 
120-150 min. cooling (by water) 170.degree. C. to R.T. 
The press was loaded at room temperature. 
Composition of the epoxy resin varnishes and various physical and 
mechanical properties of the cured resins, prepregs and laminates are set 
out in Table I below. 
TABLE I 
__________________________________________________________________________ 
COMPOSITIONS - CURED RESINS, PREPREGS AND LAMINATES 
PROPERTIES 
__________________________________________________________________________ 
Varnish 
and 
Laminate XII 
Examples 
I II III IV V VI VII VIII 
IX X XI (2) 
__________________________________________________________________________ 
VARNISH 
COMPO- 
SITION 
(parts by 
weight) 
RESINS 
(parts 
based on 
solid) 
Resin 1 80 
Resin 2 75.9 58.4 
91.3 
Resin 3 100 
Resin 4 100 
Resin 5 100 72.4 
67.4 
Resin 6 100 
Resin 7 100 
Resin 9 100 
DER* 542 32.6 
HARD- 
ENERS 
DICY so- 
53.3 
25 
50.7 
28 40 45.3 53.3 
26.7 
60 44 
lution (1) 
Bisphe- 8.7 
nol A 
TBBA 24.1 27.6 31 
__________________________________________________________________________ 
Examples 
I II III IV V VI VII VIII 
IX X XI XII 
__________________________________________________________________________ 
Phenolic 10.6 
Novolac 
CATALYSTS 
2-methyl- 
0.08 
0.1 
0.08 
0.11 
0.07 
0.075 
0.1 
0.05 
0.1 
0.08 
0.066 
0.06 
imidazole 
SOLVENTS 
Methyl-ethyl- 
20 67 
33 33.3 
33.3 
38.3 25 33.3 
33.3 
33.3 
25 33 
ketone 
RESIN 
PROPERTIES 
Geltime, 
256 215 
240 205 146 272 230 250 221 218 167 279 
175.degree. C., sec. 
Tg of film, 
168 170 
175 148 164 139 168 150 175 152 150 193 
deg C. 
(cure: 90 
min, 175.degree. C.) 
Viscosity 27 34 60 45 56 25 65 41 20 
(Ford Cup #4, 
sec.) 
PREPREG 
PROPERTIES 
% Resin 42 42.5 
45 41 40.5 
41 42 41 46 
content 
% Volatiles 0.1 0.2 
NA NA NA NA NA 0.38 
0.2 
Geltime, 88 65 91 103 152 105 103 60 101 
175 C., sec. 
% Flow 16.5 18.7 
NA 23 8.1 
17.7 
19.8 
24.4 11.3 
LAMINATE 
PROPER- 
TIES 
Tg, deg C. 168 164 136 168 149 175 146 147 190 
Chemical 0.1 0.06 
0.3 0.03 
0.75 
0.03 
0.34 
0.09 
0.1 
Resistance 
(% NMP 
pick-up) 
Blister 120 60 60 120 90 120 90 60 120 
Resistance 
(P.T.C., 
min.) 
Copper peel 15 14.2 
15 14.4 
18.8 
14.8 
13.8 
12.6 14.8 
Strength 
(N/cm.) 
__________________________________________________________________________ 
(1) DICY solution: 
Dicyandiamide 7.5% 
Propylene glycol monomethyl ether 69.9% 
Dimethylformamide 22.6% 
(2) Pressure cycle: RT 
175.degree. C. Low pressure 15 min. 
175.degree. C. High pressure 60 min. 
175.degree. C. to 30.degree. C. pressure 15 min. 
Laminates produced from standard commercial grades of NEMAG-10 (Non 
Brominated) and NEMA FR-4 (Brominated) resins have properties set out in 
Table II below. 
TABLE II 
______________________________________ 
Standard Laminate Properties 
Laminate Type* 
NEMA G-10* NEMA FR-4* 
______________________________________ 
St. Resin Type 
Epoxy Resin E* 
Epoxy Resin F* 
Tg .degree.C. 110 127 
Chemical 2.0 1.6 
Resistance 
(% NMP Pick-up) 
______________________________________ 
*Not an example of the present invention. 
Note: 
The resins are cured according to standard practice in the industry with 
dicyandiamide. 
The data in Table I and Table II clearly demonstrate surprisingly improved 
properties of the laminates incorporating the epoxy-terminated 
polyoxazolidones of the present invention, especially the improved heat 
resistance (Tg) and chemical resistance (percent NMP pick-up) properties.