Photocurable compositions based on acrylate polyester urethanes

Provided are processes for preparing compositions useful in photopolymerizable compositions, which processes comprise: PA0 A. reacting a polyether diol and an acrylic acid in about equal molar proportions; and PA0 B. PA1 1. reacting a polyether diol and an acrylic acid in about equal molar proportions and PA1 2. reacting the product of step B1, a hydroxyalkylacrylate and an organic diisocyanate in about equal molar proportions. Also provided are the products of these processes. These products are useful in photopolymerizable compositions which may typically contain, in addition to said products, N-vinyl-2-pyrrolidone and a photoinitiator.

BACKGROUND OF THE INVENTION 
Compositions which polymerize when exposed to light or other forms of 
radiation have become increasingly useful and popular in the field of 
coatings for various substrates. Such photopolymerizable coating 
compositions have several advantages over coatings which must either be 
applied in molten form or as a solution in a suitable solvent followed by 
removal of the solvent. Since the photopolymerizable compositions do not 
require heating, either in their application or in a drying process, they 
can provide substantial energy savings. Likewise, since they do not 
require solvent removal, pollution problems can be minimized. 
SUMMARY OF THE INVENTION 
This invention relates to processes for preparing compositions which are 
useful in photopolymerizable compositions and the products of such 
processes. More particularly, the processes of this invention comprise 
Process A 
reacting a polyether diol and an acrylic acid in about equal molar 
proportions, and 
Process B 
1. reacting a polyether diol and an acrylic acid in about equal molar 
proportions; and 
2. reacting the product of step 1, a hydroxyalkyl acrylate and an organic 
diisocyanate in about equal molar proportions. 
The compositions produced by the processes of this invention are 
particularly useful in photopolymerizable compositions which require 
relatively low viscosity, such as in coating compositions which must have 
the ability to flow readily and uniformly over the surface of a substrate. 
Generally, the photopolymerizable compositions prepared from the 
compositions produced by the processes of this invention will have 
viscosities below about 50 poise, preferably in the range of about 20 to 
about 50 poise. Such photopolymerizable compositions also possess 
excellent stability at elevated temperatures, e.g. up to about 70.degree. 
C., and good flexibility when cured. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The processes of this invention comprise: 
Process 1 
reacting a polyether diol and an acrylic acid in about equal molar 
proportions, and 
Process 2 
A. reacting a polyether diol and an acrylic acid in about equal molar 
proportions; and 
B. reacting the product of step A, a hydroxyalkyl acrylate and an organic 
diisocyanate in about equal molar proportions. 
The polyether diols useful in the processes of this invention are polymers 
whose backbones contain the repeating units --R--O-- where R is alkylene, 
and have free hydroxyl groups attached to their terminal repeating unit, 
i.e. the polymers are terminated at each end by a --R--OH group. The 
hydroxyl group may be a primary or secondary hydroxyl, although the 
primary hydroxyl groups are preferred. The polyether diols are preferably 
hydroxy-terminated polypropylene glycols having molecular weights in the 
400-800 range and having Hydroxyl Nos. from about 145 to about 265. 
Examples of the polyether diols include, but are not limited to, 
hydroxy-terminated adducts of propylene oxide to dipropylene glycol having 
an average molecular weight of about 425 and a Hydroxyl No. of about 263 
(NIAX PPG 425, sold by Union Carbide Corp.), hydroxy-terminated adducts of 
propylene oxide to dipropylene glycol having an average molecular weight 
of about 725 and a Hydroxyl No. of about 147, (NIAX PPG 725, sold by Union 
Carbide Corp.), polypropylene glycol end-capped with ethylene oxide groups 
and having an average molecular weight of about 650 and an Hydroxy No. of 
about 173 (POLYG 55-173, sold by Olin Corp.), polypropylene glycol 
end-capped with ethylene oxide and having an average molecular weight of 
about 775 and a Hydroxy No. of about 150, polypropylene glycol end-capped 
with ethylene oxide and having an average molecular weight of about 425 
and a Hydroxyl No. of about 265, and the like. Other useful polyether 
diols include hydroxy-terminated poly(1,4-butanediol) (derived from 
tetrahydrofuran) and hydroxy-terminated copolymers of 1,4-butanediol and 
ethylene oxide. A particularly preferred polyether diol is POLY-G 55-173 
which has the formula: 
##STR1## 
(avg. molecular weight approximately 650) 
The acrylic acids useful in the processes of this invention include acrylic 
acid and alkyl acrylic acids such as methacrylic acid and the like. As 
used herein the phrase "an acrylic acid" is intended to represent both 
acrylic acid and the alkyl acrylic acids. 
The hydroxyalkyl acrylates which may be used in the processes of this 
invention are compounds having the formula: 
##STR2## 
where R.sup.1 is C.sub.2 to C.sub.3 alkylene. Examples of the hyroxyalkyl 
acrylates include, but are not limited to, 2-hydroxyethyl acrylate, 
2-hydroxypropyl acrylate and the like. 2-hydroxyethyl acrylate is 
particularly preferred. 
The organic diisocyanates used in the processes of this invention have the 
formula: 
EQU OCN-R.sup.2 -NCO 
where R.sup.2 is a divalent, organic radical such as alkylene, arylene, 
alkarylene or aralkylene. Examples of organic diisocyanates useful in this 
invention include, but are not limited to, isophorone diisocyanate; 
2,4-tolylene diisocyanate; 2,6-tolylene diisocyanate; hexamethylene 
diisocyanate; trimethyl hexamethylene diisocyanate; dicyclohexylmethane 
diisocyanate and the like. The preferred diisocyanates are the aliphatic 
diisocyanates which impart improved properties such as light stability, 
stain resistance and flexibility to the cured photopolymerizable 
compositions made from them. 
The following reaction schemes illustrate the processes of this invention: 
##STR3## 
The above reaction scheme illustrates a typical composition produced when a 
polyether diol and acrylic acid are reacted in about equal molar 
proportions. The reaction depicted is based on a statistical 
approximation, assuming the hydroxyl groups are equally reactive. It is 
estimated that the product contains about 50% Hemi-acrylate, about 27% 
Di-acrylate and about 23% Polyether diol. 
In Process 2, the product of the above reaction is further reacted with a 
hydroxyalkyl acrylate acid and an organic diisocyanate as illustrated 
below. 
##STR4## 
where X represents the polyether backbone of the Polyether diol. 
It will be apparent to one skilled in the art that other side reactions may 
occur which are not illustrated above. Thus, it should be emphasized that 
the above reaction scheme is presented for illustrative purposes only and 
is not intended to limit this invention in any manner. 
The reaction of the polyether diol and an acrylic acid (Process 1) may be 
carried out by mixing the polyether diol and acrylic acid in any suitable 
vessel together with an effective amount of catalyst, e.g. methane 
sulfonic acid, sulfuric acid, toluene sulfonic acid and the like, and a 
polymerization inhibitor such as, for example, phenothiazine, MEHQ and the 
like. The resulting reaction mixture is then heated, preferably at reflux 
temperature to remove water formed during the reaction, until the 
acrylation is complete. The resulting reaction product may then be shaken 
with a 20% Na.sub.2 CO.sub.3 solution until the acid number of the product 
is below about 1.0. 
In Process 2, the product of Process 1, a hydroxyalkyl acrylate and an 
organic diisocyanate are blended together in a suitable vessel. More 
preferably the product of Process 1 and the hydroxyalkyl acrylate are 
blended together and the organic diisocyanate is added slowly over the 
course of the reaction. (This slow addition of the organic diisocyanate 
prevents premature or possibly violent reaction of the reaction mixture.) 
Also blended into the reaction mixture are an effective amount of 
catalyst, e.g. dibutyl tin dilaurate, and, if desired, additional 
polymerization inhibitor (the total amount of polymerization inhibitor in 
Process 2, whether carried over from Process 1 or added during Process 2 
should be about 75-300 ppm). The reaction may be conducted under an inert 
atmosphere, e.g. nitrogen, if desired. The reaction is begun by heating 
the reaction mixture to about 60.degree. C. to about 90.degree. C., 
preferably about 60.degree. C. to about 70.degree. C., and such hearing is 
maintained until the isocyanate content of the reaction mixture drops to 
about 1.0% or less. 
The compositions produced by the processes of this invention generally have 
viscosities in the range of about 20 to about 30 poise, preferrably about 
25 poise, and average molecular weights of less than about 1500. 
The compositions produced by the processes of this invention may be 
employed in photopolymerizable compositions, i.e. compositions which are 
capable of polymerizing or curing upon exposure to actinic radiation, e.g. 
ultraviolet radiation or electron beam. Generally, they may be blended in 
any convenient manner with the other ingredients commonly employed in such 
photopolymerizable compositions. Thus, for example, the photopolymerizable 
composition may contain the composition of this invention, a 
photoinitiator, a polymerization inhibitor and other additives as may be 
desirable.

The preparation of the compositions of this invention is illustrated by the 
following examples in which all parts are by weight unless otherwise 
indicated. 
EXAMPLE 1 
To a suitable vessel fitted with a drop funnel, thermometer and condenser 
is added 1287.6 g of a polyether diol which is a hydroxy-terminated adduct 
of propylene oxide to dipropylene glycol having an average molecular 
weight of about 725 and a Hydroxy No. of about 147 (NIAX PPG 725, sold by 
Union Carbide Corp.), 3.32 g of methane sulfonic acid catalyst, 0.25 g 
phenothiazine and 351.45 g toluene. The resulting mixture is heated to 
about 68.degree. C. and 144.12 g of acrylic acid is added to the vessel 
via the drop funnel over a period of about 1 hour during which time the 
temperature of the mixture rises to about 124.degree. C. About 100 cc of 
toluene is added to the mixture and a slow reflux is begun. The reflux is 
maintained for a period of time sufficient to remove water which is formed 
during the reaction. When the reaction is completed the resulting product 
is shaken with a 20% solution of Na.sub.2 CO.sub.3 until the acid number 
of the mixture is below about 1.0. The product is recovered by filtering 
and removing the toluene by distillation. 
EXAMPLE 2 
To a 2 liter, 4 neck round bottom flask equipped with a stirrer, condenser, 
thermometer, N.sub.2 inlet and condenser are added 500 g of the product of 
Example 1, 88 g 2-hydroxyethyl acrylate, and 0.12 g dibutyl tin dilaurate. 
The mixture is stirred, blanketed with N.sub.2 and slowly heated to about 
60.degree. C. for about 1 hour during which time 201 g of dicyclohexyl 
methane diisocyanate is added to the reaction mixture. Heating is 
maintained for an additional 1.5 hours. The reaction mixture is analyzed 
periodically for isocyanate content (by titration with amine) and the 
reaction is continued until the isocyanate content drops to about 1-1.1%. 
The resulting product has a density of 1.11 and a viscosity of 26.1 
poises. 
EXAMPLE 3 
A photopolymerizable composition is prepared by blending together 70 parts 
of the product of Example 1, 15 parts of N-vinyl-2-pyrrolidone, and 4 
parts of a photoinitiator (CG 184 sold by Ciba Geigy). The resulting 
composition is coated onto polycarbonate, paper and primed aluminum 
substrates and exposed under a nitrogen atmosphere by a mercury lamp in a 
Radiation Polymer Company processor at a rate of about 20 feet per minute. 
The coating cures completely and has excellent physical properties. 
EXAMPLE 4 
A photopolymerizable composition is prepared by blending together 70 parts 
of the product of Example 2, 15 parts of N-vinyl-2-pyrrolidone, and 2 
parts of a photoinitiator (CG 184 sold by Ciba Geigy). The composition is 
coated onto paper and polycarbonate substrates and exposed under air 
atmosphere by a mercury lamp in a Radiation Polymer Company processor. The 
composition is also coated onto a primed aluminum substrate and exposed in 
the same manner except that a nitrogen atmosphere is employed. All 
coatings cure completely and have excellent physical properties. 
Other features, advantages and specific embodiments of this invention will 
become readily apparent to those exercising ordinary skill in the art 
after reading the foregoing disclosures. These specific embodiments are 
within the scope of the claimed subject matter unless otherwise expressly 
indicated to the contrary. Moreover, while a few specific embodiments of 
this invention have been described in considerable detail, variations and 
modifications of these embodiments can be effected without departing from 
the spirit and scope of the invention as disclosed and claimed.