Preparation of monohydroxy-containing polymers

A method for preparing hydroxyl-containing polymers comprising polymerizing at least one free radical-polymerizable monomer in the presence of at least one monohydroxy-containing chain transfer agent and at least one hydroxy-containing free radical initiator. The method results in monohydroxy-functional polymers in yields in excess of 90%.

BACKGROUND OF THE INVENTION 
This invention relates to the preparation of monohydroxy-functional 
polymeric materials. Such compounds have been widely used in adhesive, 
coating and molding compositions, as plasticizers, leveling agents, melt 
index modifiers, solvents and to modify properties of other chemical 
compositions, particularly other and different polymers, with which they 
may be partially or wholly incompatible. 
In their use as polymer modifying materials, monohydroxyl-containing 
polymers have been employed as blend materials or, in an attempt to 
improve compatibility, they have been interpolymerized with other and 
different compounds to form copolymeric products. Such copolymers are 
random ABABA . . . type, block AB type or block ABA type. 
Monohydroxy-functional polymers can be produced by using 
monohydroxyl-functional chain transfer agents. However, yields of 
monohydroxy-functional polymers are less than 90%, typically around 80%. 
Some polymer chains are formed having no hydroxyl functionality. On the 
other hand, if hydroxy-functional initiators are used, dihydroxy terminal 
polymers are produced. 
The object of the present invention is to improve yields in the formation 
of monohydroxy-functional polymers. 
SUMMARY OF THE INVENTION 
In the present invention, monohydroxy-functional polymeric materials are 
made by reacting at least one ethylenically unsaturated monomer in the 
presence of at least one monohydroxy-functional chain transfer agent and 
at least one hydroxy-functional free radical polymerization initiator. 
Surprisingly, rather than producing substantially a di-hydroxy functional 
polymer, the method of the invention yields more than 90% 
monohydroxy-functional polymers. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The ethyleneically-unsaturated monomers which are polymerized in accordance 
with the preferred embodiment of this invention can be substantially any 
monoethylenically-unsaturated monomer which can be polymerized via a free 
radical polymerization mechanism. Examples of such polymerizable monomers 
include methyl acrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, 
decyl acrylate, lauryl acrylate, stearyl acrylate, cyclopentyl acrylate, 
cyclohexyl acrylate, the corresponding methacrylates, acrylamide, 
acrylonitrile, monoesters and diesters of maleic and fumaric acids, vinyl 
chloride, vinyl bromide, vinylidiene chloride, methacrylonitrile, vinyl 
acetate, vinyl propionate, vinyl benzoate, vinyl methyl ether, vinyl 
isobutyl ether, styrene, alphamethyl styrene, vinyl toluene, p-ethyl 
styrene, 2,4-methyl styrene, o-chloro styrene and 2,5-dichloro styrene. 
Mixtures of such monoethylenically unsaturated monomers can be employed. 
Chain transfer agents which can be employed in this invention contain one 
hydroxy group, thereby insuring that the resulting polymer of 
ethylenically unsaturated monomer will have a single terminal 
hydroxyl-containing moiety. Suitable chain transfer agents include 
2-mercaptoethanol, thiopropylene glycol, 2-ethylhexyl thioglycolate and 
2-mercaptopropanol, with 2-mercaptoethanol being currently preferred. 
Bifunctional chain transfer agents such as bis-(4-hydroxy phenyl) 
disulfide, which disassociate into two monofunctional chain transfer 
segments, can also be employed in the practice of this invention. The term 
"monohydroxy functional chain transfer agent" as used herein is intended 
to include dihydroxy functional chemicals which disassociate in this 
manner such that each dissociated segment acts as a monohydroxy functional 
chain transfer agent. 
The polymerization initiator for the free radical polymerization of the 
monoethylenically unsaturated monomer contain at least one free hydroxy 
group. While the reaction is not completely understood, the hydroxy group 
of the polymerization initiators employed in the present invention appears 
to direct and drive the reaction to a higher level of completion with 
respect to forming polymers having only one terminally located hydroxy 
functional group. The use of the hydroxy functional polymerization 
initiators in combination with the monohydroxy functional chain transfer 
agents insures that at least 90% of the polymer product will have a single 
hydroxy group on the individual polymer molecules, with less than 10% of 
such polymer molecules having no hydroxy groups. This is in contrast to 
prior art systems which employ polymerization initiators such as benzoyl 
peroxide or azobisisobutyronitrile in combination with chain transfer 
agents such as 2-mercapto ethanol, which provide polymer products wherein 
not more than about 80% of the individual molecules have a monohydroxy 
group. Representative free radical polymerizations which can be employed 
in the practice of this invention include hydroxy alkyl peroxides, and 
hydroxy alkyl alkyl peroxides. Representative of such peroxides are 
1-hydroxy-n-butyl peroxide, bis-(1-hydroxy cyclohexyl) peroxide, 
12-hydroxy peroxy stearic acid, di(4-hydroxy 
butyl)-2,2'-azobisisobutyrate, di(3-hydroxy propyl)-2,2'-azobisiosbutyrate 
and di(2-hydroxy ethyl)-2,2'-azobisisobutyrate. Although no free radical 
initiators containing two hydroxy groups, such as the hydroxy alkyl 
peroxides, are currently commercially available, it is anticipated that 
the availability of such initiators could provide products in which 
substantially all of the polymer product would contain the desired 
monohydroxyl functionality. 
The amount of the chain transfer agent to be employed in the polymerization 
mixtures in accordance with the present invention is within the range of 
0.001 to 5% by weight, preferably 0.005 to 2% by weight based on the 
monomer or monomers charged into the polymerization reactor. The amount of 
the polymerization initiator will be in the range of 0.001 to 5%, and 
preferably 0.01 to 1% by weight based on the monomer or monomers charged 
into the polymerization reactor. 
The polymerization process can be carried out by bulk polymerization, 
solution polymerization, suspension polymerization, emulsion 
polymerization, continuous bulk/solution polymerization and the like, with 
solution polymerization being currently preferred. Polymerization reaction 
temperatures can be any at which the polymerization reaction takes place, 
e.g., 0.degree. C. or less to 150.degree. C. or more, and preferably from 
50.degree.C. to about 100.degree.C. Basically, the reaction time varies 
with quantity of reactant as well as the life of the free radical 
initiator employed, however, basically the reaction time can be any time, 
e.g., from about 5 minutes or less to 2 hours or more. Those skilled in 
the art can readily determine the appropriate reaction time and 
temperatures through routine experimentation. 
The hydroxy-functional polymers of monoethylenically unsaturated monomers 
which are produced in accordance with this invention are particularly 
adapted for the preparation of block copolymers of the ABA variety by 
reacting the monohydroxy polymers of this invention with a polymer which 
has at least two moieties which are reactive with hydroxyl functionality. 
The following example will serve to illustrate the invention.

EXAMPLE 1 
Preparation of Hydroxyl Functional Styrene Acrylonitrile Polymer 
A reaction vessel was charged with 900 grams styrene, 300 grams 
acrylonitrile, 6 grams phenylazophenyl acrylate, 12 grams 
2-mercaptoethanol and 12 grams of 50% active 
1,1-dimethyl-3-hydroxybutylperoxy-2-ethyl hexanoate and 300 grams of 
toluene. 
This solution was pumped continuously at a rate of 10 cc per minute into a 
second reactor equipped with a mechanical stirrer, thermometer and heating 
bath. The reactor temperature was raised to 90.degree.C. and maintained at 
that temperature .+-.1.degree.C. After 3 hours, the entire contents of the 
first vessel had been transferred to the second reactor. Heating was 
contained for another 30 minutes to give syrup containing 56% by weight of 
polymer. 
The syrup was freed of volatile components by heating in a vacuum oven at 
75.degree.C. for 20 hours. Size exclusion chromatographic analysis of the 
polymer product showed that it had a weight average molecular weight of 
6700 and a number average molecular weight of 2825 compared against 
polycarbonate standards. More than 90% of the individual polymer chains 
contained only one hydroxyl group with less than 10% of the individual 
polymer molecules being nonfunctional. 
It is understood that the above is merely a preferred embodiment and that 
various changes and alterations can be made without departing from the 
spirit and broader aspects of the invention.