Process for making hydroxyl terminated liquid polymers

Hydroxyl terminated reactive liquid polymers are prepared by reacting ethylene oxide, in presence of an amine catalyst, with a carboxyl terminated reactive liquid polymer serum which contains, in addition to the carboxyl terminated liquid polymer, a solvent, an initiator, other reaction products formed during the reaction, and any unreacted reactants; adding a strong acid to form water-soluble amine salts; water-washing; coagulating; separating; drying; and recovering a shelf stable product.

BACKGROUND OF THE INVENTION 
Hydroxyl terminated reactive liquid polymers can be made in a number of 
different ways. They can be made from olefinic polymers by initially 
converting a portion of the olefinic bonds of the polymer to ozonide 
linkages and then cleaving the ozonide linkages to produce a hydroxyl 
terminated liquid polymer. Liquid polymers prepared in this fashion do not 
achieve hydroxyl functionality at each end of the polymer chains and as a 
result, the final terminal hydroxyl functionality is generally 
considerably less than 2, on the order of 1.6 to 1.8. For most efficient 
use of the reactants and best overall properties, it is desirable to have 
final terminal hydroxyl functionality as close to 2 as possible or greater 
than 2. 
The desired terminal hydroxyl functionality is made more attainable by the 
use of a process wherein a carboxyl terminated reactive liquid polymer is 
converted to the corresponding hydroxyl terminated liquid polymer. 
Terminal functionality of practically 2 can be achieved by this process 
which is essential if higher polymers are to be produced by the subsequent 
curing reactions with suitable materials. 
The carboxyl terminated liquid polymers for the conversion reaction can be 
made by the process disclosed in U.S. Pat. No. 3,285,949. Pursuant to this 
process, a suitable monomer is polymerized in a solvent such as tertiary 
alkanol and/or acetone in presence of an aliphatic azodicarboxylate 
initiator such as 4,4'-azobis(4-cyanovaleric acid) radical initiator to 
form unrefined carboxyl liquid polymer that is washed with water, 
coagulated, separated by decantation, dried and drummed for storage. 
The conversion to the corresponding hydroxyl liquid polymer is made by 
reacting a carboxyl terminated liquid polymer with a stoichiometric or an 
excess amount of ethylene oxide, per 100 parts of the carboxyl liquid 
polymer, in presence of 0.01 to 3 parts of a tertiary amine catalyst. 
Amount of ethylene oxide is generally 3 to 10 parts per 100 parts of the 
liquid polymer. The product is then dried by vacuum treatment to remove 
unreacted catalyst and ethylene oxide and drummed for storage, as 
disclosed in U.S. Pat. No. 3,712,916. 
A process has now been discovered for preparing hydroxyl terminated liquid 
polymers from corresponding carboxyl terminated liquid polymers that 
eliminates the steps of coagulating, separating, drying and drumming of 
carboxyl terminated liquid polymers. Furthermore, impurities originating 
with ethylene oxide and the amine catalyst can be easily removed by 
addition of a strong acid and subsequent water washing. 
SUMMARY OF THE INVENTION 
The inventive process comprises reacting unrefined carboxyl terminated 
liquid polymer with ethylene oxide to produce unrefined hydroxyl 
terminated liquid polymer and refining the liquid polymer by water 
washing, coagulating, separating and drying. 
DETAILED DESCRIPTION OF THE INVENTION 
The invention described herein relates to a process for reacting carboxyl 
terminated liquid polymer serum, or unrefined carboxyl terminated liquid 
polymer, with 3 to 10 parts of ethylene oxide in the presence of 0.01 to 3 
parts of a tertiary amine catalyst, per 100 parts of the carboxyl 
terminated liquid polymer. Generally, stoichiometric or an excess amount 
of ethylene oxide is used. The serum is defined as the functionally 
terminated liquid polymer in unrefined condition still in the original 
reaction medium which can contain a solvent, initiator, other reaction 
products formed during reaction, and any unreacted reactants. The crude 
hydroxyl terminated liquid polymer is then refined by the steps of water 
washing, coagulating, separating and drying. The refined product is 
drummed for storage. 
Carboxyl terminated polymers of butadiene, butadiene-acrylonitrile and 
alkyl acrylates can be produced, for example, by the process taught in 
U.S. Pat. No. 3,285,949. Preferably, the desired monomers are placed in a 
solvent with a low chain transfer potential, preferably tertiary butanol, 
and/or acetone and a radical initiator, preferably 
4,4'-azobis-(4-cyanovaleric acid), is added. Polymerizations are run at 
70.degree.-90.degree. C. Product polymer is coagulated with a solvent such 
as methanol or water, separated by decantation and dried under vacuum. The 
carboxyl terminated liquid polymers normally have molecular weights in the 
range of about 400 to 8,000 and viscosities in the range of about 500 to 
1,000,000 cps, determined by Brookfield Viscometer type RVT. 
The carboxyl terminated liquid polymers can have copolymerized therein at 
least one other olefinically unsaturated monomer, more preferably at least 
one other vinylidene monomer (i.e., a monomer containing at least one 
terminal CH.sub.2 .dbd.C&lt;group per molecule) in the polymeric backbone. 
Preferred vinylidene comonomers in the polymeric backbone include (a) 
dienes containing 4 to 10 carbon atoms such as butadiene-1,3, (b) vinyl 
nitriles such as acrylonitrile and methacrylonitrile, (c) other acrylates 
having the formula 
##STR1## 
wherein R.sup.1 is hydrogen or an alkyl radical containing 1 to 3 carbon 
atoms and R.sup.2 is hydrogen or an alkyl radical containing 1, 2 or 11 to 
18 carbon atoms, or an alkoxyalkyl, alkylthioalkyl, or cyanoalkyl radical 
containing 2 to 12 carbon atoms, preferably 2 to 8. Alternately, R.sup.1 
can be an alkyl group of 1 to 3 carbon atoms and R.sup.2 an alkyl group of 
3 to 10 carbon atoms. 
Other suitable vinylidene comonomers include (d) vinyl aromatics such as 
styrene, methyl styrene, and the like; (e) vinyl and allyl esters of 
carboxylic acids containing 2 to 8 carbon atoms such as vinyl acetate, (f) 
vinyl and allyl ethers of alkyl radicals containing 1 to 8 carbon atoms 
such as vinyl methyl ether, allyl methyl ether, and the like; and (g) 
monoolefins containing 2 to 14 carbon atoms, more preferably 2 to 8 carbon 
atoms, such as ethylene and propylene. 
Examples of liquid carboxyl terminated polymers are carboxyl terminated 
polyethylene, polybutadiene, polyisoprene, poly(butadiene-acrylonitrile), 
poly(butadiene-styrene), poly(butadiene-acrylonitrile-acrylic acid), 
poly(ethyl acrylate), poly(ethyl acrylate-n-butyl acrylate), poly(n-butyl 
acrylate-acrylonitrile), poly(butyl acrylate-styrene), and the like. 
The reaction medium can be any solvent that will dissolve the carboxyl 
terminated liquid polymer and the hydroxyl terminated liquid polymer that 
is formed. Acetone, tertiary butanol, methyl ethyl ketone, cyclohexanone, 
cyclohexanol, tetrahydrofuran, and dioxane are typical solvents that can 
be used. Optionally, the reaction can be carried out in a mass or a bulk 
system with no solvent being employed. In such instances, ethylene oxide 
can be used in excess to insure fluidity and accomplish satisfactory heat 
transfer. 
When a liquid carboxyl terminated polymer is reacted with ethylene oxide, 
the oxirane ring of ethylene oxide is opened up by reaction with terminal 
carboxyl groups on a chain to form terminal hydroxyl groups. Pendant 
carboxyl groups, if present, can likewise be reacted with ethylene oxide. 
The hydroxyl terminated liquid polymers produced include polybutadiene, 
copolymers of butadiene containing in excess of 50% by weight of butadiene 
with remainder being at least one copolymerizable olefinically unsaturated 
monomer, such as acrylonitrile, and polyalkyl acrylates containing 
polymerized in excess of 65% by weight, preferably in excess of 85%, of at 
least one alkyl acrylate of 3 to 10, preferably 3 to 8 carbon atoms. The 
polymeric backbone of a hydroxyl terminated liquid polymer can have 
copolymerized therein at least one other olefinically unsaturated monomer, 
preferably a vinylidene monomer, already described in connection with 
carboxyl terminated liquid polymer reactants. Molecular weight, viscosity 
and other similar properties of the hydroxyl terminated liquid polymers 
will generally be the same as the carboxyl terminated liquid polymers from 
which the hydroxyl liquid polymers are made, however, in a preferred 
embodiment, molecular weight of the hydroxyl terminated liquid polymers is 
in the range of 1500 to 4000. 
This process is made possible by the fact that an epoxide will react with a 
carboxylic acid much faster than it will with alcohol or water under 
certain conditions. It is, therefore, possible to manufacture hydroxyl 
terminated liquid polymers by reacting ethylene oxide with carboxyl 
terminated liquid polymer serum. 
A number of significant advantages are realized by this process when 
compared to the prior art process. These include elimination of some of 
the post polymerization process steps, reduction in labor costs since the 
reaction can be carried out in one reactor, and carrying out the reaction 
in a low viscosity medium which facilitates handling, charging and 
agitation. Another even more significant advantage resides in the fact 
that a cleaner product is obtained. In the prior art process, impurities 
originating from ethylene oxide or the amine catalyst were difficult to 
remove by vacuum treatment. In the process disclosed herein, however, 
water washing and coagulating operations immediately follow the reaction 
between a carboxyl terminated liquid polymer and ethylene oxide. Thus, the 
impurities, such as ethylene glycol, can be removed readily. 
Removal of the amine catalyst is especially important for promoting shelf 
stability of hydroxyl terminated liquid polymers. Elimination of the amine 
catalyst by vacuum treatment is very difficult due to formation of an 
amine salt with the residual carboxylic acid. In this process, the amine 
catalyst can be readily removed by adding equal or excess amounts of a 
strong organic or inorganic acid to the serum after reaction between a 
carboxyl terminated liquid polymer and ethylene oxide. Ionization constant 
of the strong acid should be higher than that of 
4,4'-azobis-(4-cyanovaleric acid), preferably in the range of about 
1.times.10.sup.-3 to 1.times.10.sup.-1. Examples of suitable strong acids 
include phosphoric, sulfuric, hydrochloric, pyrophosphoric, sulfurous, and 
trichloroacetic acids. The strong acid forms water soluble amine salts 
instead of the amine salts with a carboxylic acid, that are sparingly 
soluble in water. Thus, the water soluble amine salts can be easily 
removed during the water washing step. 
Shelf stability of hydroxyl terminated liquid polymers prepared by the 
process described herein is vastly superior to shelf stability of the 
corresponding liquid polymers prepared by the prior art process. Whereas 
viscosity of hydroxyl terminated liquid polymers prepared conventionally 
deteriorates in 1 to 2 months of storage at 60.degree. C., the liquid 
polymers prepared pursuant to the process described herein can show less 
than 10% increase in viscosity at accelerated aging conditions of 
60.degree. C. for one month. An example of how badly can viscosity 
deteriorate of conventionally prepared liquid polymer is a hydroxyl 
terminated butadiene liquid polymer that had original viscosity at 
60.degree. C. of 4880 cps that increased to 25,476 cps on standing for 30 
days at 60.degree. C. Since hydroxyl terminated liquid polymers prepared 
as described herein have less heat history, this would contribute to a 
lower product viscosity which should lead to a more shelf stable product.

A number of experiments are presented below to demonstrate the 
herein-claimed invention in greater detail. 
EXAMPLE 1 
This example demonstrates preparation of a carboxyl terminated 
poly(butadiene-acrylonitrile) reactive liquid polymer containing 25% 
acrylonitrile. 
Polymerization of 76 parts by weight of butadiene and 24 parts of 
acrylonitrile was carried out at 85.degree. C. for 18 hours in 100 parts 
by weight acetone in presence of 13 parts by weight of 
4,4'-azobis-(4-cyanovaleric acid). A portion of acrylonitrile and the 
radical initiator was added incrementally. After completing the 
polymerization reaction, excess butadiene was vented and about an equal 
amount of water, i.e. 200 parts, was added with stirring to coagulate the 
liquid polymer. After settling, the water-acetone layer was decanted and 
the polymer was then dried in an evaporator to constant weight. The 
resulting carboxyl terminated liquid polymer had Brookfield viscosity of 
324,000 cps at 27.degree. C., and COOH/ephr of 0.065. The contraction ephr 
stands for equivalents per 100 parts of rubber. 
EXAMPLE 2 
This example demonstrates preparation of hydroxyl terminated liquid polymer 
by the prior art procedure. 
The liquid polymer used in this experiment was carboxyl terminated 
poly(butadiene-acrylonitrile) containing 25% acrylonitrile, with a 
viscosity of 324,000 cps at 27.degree. C., and ephr of 0.065, as defined 
in Example 1, above. 
200 grams or 0.130 equivalent of the carboxyl terminated liquid polymer was 
reacted with 9.75 milliliters or 0.195 equivalent of ethylene oxide in 
presence of 500 ppm trimethylamine catalyst. The reaction was carried out 
at 90.degree. C. for 7 hours until residual acid of 0.005 ephr was 
reached. 
EXAMPLE 3 
This example demonstrates preparation of a hydroxyl terminated liquid 
polymer by the process disclosed herein. 
Serum for this experiment was obtained by polymerizing butadiene and 
acrylonitrile, as described in Example 1, through the step of venting 
unreacted butadiene but prior to the coagulating step. 250 grams of the 
serum containing 0.173 equivalent of carboxyl terminated 
poly(butadiene-acrylonitrile) liquid polymer of Example 1, above, was 
reacted with 10.7 milliliters or 0.214 equivalent of ethylene oxide in 
presence of 3000 ppm of trimethylamine catalyst as a 25% aqueous solution. 
Temperature of the reaction was 90.degree. to 95.degree. C. and its 
duration was 11 hours. Progress of the reaction was monitored by measuring 
the acid content. The reaction was completed when acid content of about 
0.002 ephr was reached following which, the hydroxyl terminated liquid 
polymer serum was treated by an identical procedure used for refining 
carboxyl terminated liquid polymers. This procedure involved coagulation, 
washing with 200 ml of water, separation, and drying at 130.degree. C. in 
vacuum. The physical properties of hydroxyl terminated liquid polymers 
prepared by the prior art process and the new process described herein are 
nearly identical, as is apparent from the table below. 
TABLE A 
______________________________________ 
Prior 
Art New 
Process Process 
______________________________________ 
Viscosity @ 27.degree. C., cps 
242,000 190,000 
OH Number 34.5 38.4 
Residual Acid, ephr 
0.005 0.003 
______________________________________ 
Gel permeation chromatography further corroborated that nearly identical 
hydroxyl terminated liquid polymers were obtained by the prior art process 
and the new process described herein. The GPC results are given in the 
table below in terms of polystyrene. 
TABLE B 
______________________________________ 
Prior 
Art New 
Process Process 
______________________________________ 
Mn 7030 7260 
Mw 14,700 16,400 
Mw/Mn 2,10 2.26 
Peak 8930 10,300 
______________________________________ 
Accelerated aging tests were conducted at 60.degree. C. on the hydroxyl 
terminated liquid polymer prepared in this example pursuant to the process 
described herein. Initial viscosity thereof was 273,000 cps measured at 
27.degree. C. which increased to 290,000 cps after two weeks and to 
300,000 cps after one month at 60.degree. C. Viscosity of hydroxyl 
terminated liquid polymers prepared by the prior art procedure had initial 
viscosity of 277,000 cps that increased to 290,000 cps after two weeks and 
to 307,000 cps after one month at 60.degree. C. The relatively slight 
viscosity increase from 277,000 cps to 307,000 cps was unexpected since 
hydroxyl terminated liquid polymers prepared by the prior art process 
normally suffer unacceptable viscosity increase on storage. For instance, 
a hydroxyl terminated polybutadiene liquid polymer prepared in a 
conventional way had original viscosity of 36,000 cps at 27.degree. C. 
that increased to 62,400 cps at 27.degree. C. after aging for 30 months at 
ambient conditions. The relatively slight increase in viscosity of the 
hydroxyl terminated reactive liquid polymer, noted above, is probably due 
to more efficient and longer drying, and higher vacuum when compared to 
such liquid polymers prepared in the plant.