Hydroxyl containing liquid polymers
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of my copending application Ser. No. 045,899, filed June 6, 1979, now abandoned; a continuation-in-part of my copending application Ser. No. 931,234, filed Aug. 7, 1978, now abandoned, that was a division of my application Ser. No. 782,104, filed Mar. 28, 1977, now U.S. Pat. No. 4,120,766. 
    
    
     BACKGROUND OF THE INVENTION 
     Thermal polymerization of styrene is known using a disulfide modifier in the presence of azoisobutyronitrile initiator (Pierson et al, 17 J. Polymer Science 221-246, 1955). Alkyl disulfides were found in the latter reference to be relatively ineffective compared to aryl disulfides in incorporating end groups into polystyrene. U.S. Pat. No. 3,470,146 discloses improved polystyrene beads produced by thermal polymerization of styrene in the presence of a finely divided phosphate suspending agent, a water soluble sulfite or precursor, and certain water soluble organic sulfides. None of the above references discloses liquid polymers or a process for preparing them, let alone hydroxyl-containing liquid polymers having an aliphatic polymer backbone and sulfide linkages near the terminal portions of the polymer molecule, and the use of ultraviolet radiation to prepare the polymers. Such new hydroxyl-containing liquid polymers and a process for preparing them are desired. 
     SUMMARY OF THE INVENTION 
     Hydroxyl-containing liquid polymers are prepared having the formula 
     
         HO--X--S--D--S--X--OH 
    
     wherein S is a sulfide linkage; X is (CH 2  O) m  (CH 2 ) n  or ##STR1## m is an integer from 0 to 10; n is an integer from 1 to 10; and D is an aliphatic backbone containing polymerized units of at least one vinylidene monomer having at least one terminal CH 2  ═C&lt; group. The hydroxyl-containing liquid polymers are prepared by polymerizing said monomer(s) together with at least one hydroxyl-containing disulfide in the presence of ultraviolet radiation. The disulfide has the formula ##STR2## wherein m is an integer from 0 to 10, and n is an integer from 1 to 10. 
     DETAILED DESCRIPTION 
     By the process of this invention, hydroxyl-containing liquid polymers can be produced having an aliphatic polymeric backbone and sulfide linkages near the terminal portions of the polymeric molecules. The polymers have terminal groups of the structure ##STR3## and provide polymers of the structure ##STR4## wherein m is an integer from 0 to 10, more preferably 0 to 4, and n is an integer from 1 to 10, more preferably 1 to 4. Excellent results are obtained when m is 0 and n is 2. D is a carbon to carbon backbone comprising polymerized units of vinylidene monomers having at least one terminal CH 2  ═C&lt; group, for example, butadiene-1,3 and comonomers therewith, and esters of acrylic acid and comonomers therewith. 
     The hydroxyl-containing liquid polymers contain an average from about 1.1 to about 4 hydroxyl groups per molecule, more preferably from about 1.5 to about 2.5 hydroxyl groups per molecule. Average functionalities lower than 2 are accounted for by the fact that not all polymer chain ends need be terminated by hydroxyl groups. Average functionalities higher than 2 are explained by the fact that some hydroxyl groups may be pendant from the polymeric backbone, e.g., when a hydroxyl-containing comonomer such as 2-hydroxyethyl acrylate or vinyl benzyl alcohol is used. Alternatively, a carboxylated comonomer such as acrylic acid may be used, and after polymerization is complete, some or all of the carboxyl groups may be reacted with ethylene oxide, butanediol or the like to produce hydroxyl groups. Such pendant hydroxyl groups giving average functionalities higher than 2 may be useful where higher crosslink density is desired from a subsequent crosslinking reaction, e.g., using polyisocyanates or the like. 
     The hydroxyl-containing liquid polymers may have Brookfield viscosities (measured using a Brookfield RVT viscometer at 27° C.) from about 500 cps. to about 2,500,000 cps., more preferably from about 500 cps. to about 1,200,000 cps. The hydroxyl-containing liquid polymers may have hydroxyl equivalent weights (gram molecular weight per hydroxyl group) from about 200 to about 10,000 more preferably from about 400 to about 5,000. 
     The hydroxyl-containing liquid polymers can be produced by reacting at least one of selected vinylidene monomers with at least one hydroxyl-containing disulfide in the presence of ultraviolet radiation. The vinylidene monomer contains at least one terminal CH 2  ═C&lt; group and may be, for example, monoolefins containing 2 to 14 carbon atoms, more preferably 2 to 8 carbon atoms, such as ethylene, propylene, isobutylene, 1-butene, 1-pentene, 1-hexene, 1-dodecene and the like; dienes containing 4 to 10 carbon atoms, more preferably 4 to 8 carbon atoms, such as butadiene, isoprene, 2-isopropyl-1,3-butadiene, and the like; vinyl alkyl ketones such as vinyl methyl ketone, vinyl ethyl ketone, methyl isopropenyl ketone and the like; 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 acrylic acids and acrylates having the formula ##STR5## wherein R is hydrogen or an alkyl or hydroxyalkyl radical containing 1 to 3 carbon atoms, and R 1  is hydrogen or an alkyl or hydroxyalkyl radical containing 1 to 18 carbon atoms, more preferably 1 to 8 carbon atoms, or an alkoxyalkyl, alkylthioalkyl, or cyanoalkyl radical containing 2 to 12 carbon atoms, more preferably 2 to 8 carbon atoms. Even more preferably R 1  is hydrogen or an alkyl or hydroxyalkyl radical containing 1 to 8 carbon atoms. Examples of suitable acrylates include ethyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, 2-hydroxyethyl acrylate, methoxyethyl acrylate, butoxyethyl acrylate, hexylthioethyl acrylate, β-cyanoethyl acrylate, chloroethyl acrylate, bromopropyl acrylate, cyanooctyl acrylate, methyl methacrylate, ethyl methacrylate, octyl methacrylate and the like. Often two or more types of these polymerized monomeric units are contained in the polymer backbone. 
     More preferred liquid polymers contain polymerized units of a diene containing 4 to 10 carbon atoms, more preferably 4 to 8 carbon atoms or acrylic acids and acrylates having the formula ##STR6## wherein R is hydrogen or an alkyl or hydroxyalkyl radical containing 1 to 3 carbon atoms, and R 1  is hydrogen or an alkyl or hydroxyalkyl radical containing 1 to 18 carbon atoms, more preferably 1 to 8 carbon atoms, or an alkoxyalkyl, alkylthioalkyl, or cyanoalkyl radical containing 2 to 12 carbon atoms, more preferably 2 to 8 carbon atoms. Even more preferably R 1  is hydrogen or an alkyl or hydroxyalkyl radical containing 1 to 8 carbon atoms. Excellent results were obtained with dienes containing 4 to 10 carbon atoms, more preferably 4 to 8 carbon atoms, including butadiene. Excellent results were also obtained with alkyl and hydroxyalkyl acrylates wherein the alkyl or hydroxyalkyl group contained 1 to 8 carbon atoms including ethyl acrylate, 2-hydroxyethyl acrylate, and butyl acrylate. 
     The monomers described above may be polymerized readily with from 0% to about 40% by weight, more usually from 0% to about 30% by weight, of at least one other copolymerizable ethylenic monomer. Suitable comonomers include those selected from the group consisting of vinyl aromatics having the formula ##STR7## wherein R 2  is hydrogen, halogen or an alkyl or hydroxyalkyl radical containing 1 to 4 carbon atoms, such as styrene, chlorostyrene, vinyl toluene, vinyl benzyl alcohol, and the like; α-methyl styrene vinyl nitriles having the formula ##STR8## wherein R 3  is hydrogen or an alkyl radical containing 1 to 3 carbon atoms, such as acrylonitrile, methacrylonitrile and the like; acrolein and methacrolein, divinyls and diacrylates such as divinyl benzene, divinyl ether, diethylene glycol diacrylate, and the like; diethyl fumarate, diethyl maleate, amides of α,β-olefinically unsaturated carboxylic acids containing 2 to 8 carbon atoms such as acrylamide, methacrylamide, N-methylol acrylamide, and the like; methallyl chloride; itaconic acid; vinyl and allyl esters of carboxylic acids containing 2 to 8 carbon atoms such as vinyl acetate, vinyl propionate, vinyl benzoate, allyl acetate and the like; vinyl halides including vinyl chloride, vinyl bromide, vinylidene chloride and the like; vinyl chloroacetate, allyl chloroacetate, vinyl crotonate, vinyl cyclohexane, vinyl ethyl fumarate, nitro styrene, methoxy styrene, chloroprene, vinyl naphthalenes, vinyl piperidines, vinyl pyridines, N-vinyl pyrrolidines, vinyl stearate, vinyl sulfanilic acid, methyl vinyl sulfone, vinylidene cyanide, chloroethyl vinyl ether, vinyl benzylchloride, alkyl alkaacrylates as methyl methacrylate, β-chloroethyl vinyl phosphonate, diacetone acrylamide, and other copolymerizable vinylidene monomers well known to those skilled in the art may be used to make these hydroxyl-terminated liquid polymers. 
     More preferred comonomers may be selected from the group consisting of vinyl aromatics wherein R 2  is hydrogen, halogen, or an alkyl or hydroxyalkyl radical containing 1 to 4 carbon atoms; and wherein R 3  is hydrogen or an alkyl radical containing 1 to 3 carbon atoms, such as acrylonitrile and methacrylonitrile. 
     Examples of useful liquid polymeric backbones comprising carbon-carbon linkages include polyethylene, polyisobutylene, polyisoprene, polybutadiene, poly(vinyl ethyl ether), poly(ethylacrylate) and poly(butylacrylate) as well as copolymers of butadiene and acrylonitrile; butadiene and styrene; butadiene, butyl acrylate and acrylonitrile; vinyl acetate and isoprene; vinyl ethyl ether and diallyl ether; vinyl ethyl ether and α-methyl styrene; methyl acrylate and butadiene; methyl acrylate and ethyl acrylate; methyl acrylate and butyl acrylate; methyl acrylate and 2-ethylhexyl acrylate; ethyl acrylate and ethylene; ethyl acrylate and isobutylene; ethyl acrylate and isoprene; ethyl acrylate and butadiene; ethyl acrylate and butyl acrylate; ethyl acrylate and vinyl acetate; ethyl acrylate and styrene; ethyl acrylate, styrene and butadiene; ethyl acrylate and n-butyl acrylate; ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate; ethyl acrylate and 2-ethylhexyl acrylate; ethyl acrylate and acrylic acid; ethyl acrylate and acrylamide; ethyl acrylate and allyl alcohol; butyl acrylate, styrene and isoprene; butyl acrylate and 2-hydroxyethyl acrylate; butyl acrylate, ethyl acrylate, and 2-hydroxyethyl acrylate; butyl acrylate and styrene; butyl acrylate, ethyl acrylate and acrylonitrile; butyl acrylate and vinyl benzyl alcohol; and the like. Excellent results were obtained in producing a backbone comprising copolymerized linkages of butadiene and acrylonitrile; ethyl acrylate and butyl acrylate; butyl acrylate and 2-hydroxyethyl acrylate; and butyl acrylate, butadiene and acrylic acid, wherein following polymerization the acrylic acid backbone units were reaced further with ethylene oxide to introduce further hydroxyl groups into the polymer molecule. 
     Hydroxyl-containing disulfide suitable for use in the process of this invention have the formula ##STR9## wherein m is an integer from 0 to 10, more preferably from 0 to 4, and n is an integer from 1 to 10, more preferably from 1 to 4. Examples of suitable hydroxyl-containing disulfides include 2-hydroxyethyl disulfide, 3-hydroxypropyl disulfide and the like. Excellent results were obtained using 2-hydroxyethyl disulfide. The disulfide acts both as a polymerization initiator and also as a polymerization modifier. The amount of hydroxyl-containing disulfide will vary according to the desired polymeric molecular weight but typically is from about 1 to 20 weight percent, more preferably from 1 to 10 weight percent, based upon total monomeric weight. 
     At least one vinylidene monomer defined heretofore is reacted together with at least one hydroxyl-containing disulfide in the presence of ultraviolet (UV) radiation having a wavelength from about 1,850 Å to about 6,000 Å, more preferably from about 2,400 Å to about 4,000 Å. Common sources of UV radiation include mercury lamps and arcs, carbon arcs and hydrogen discharge tubes. The vessel in which the polymerization is conducted may be transparent to light of the desired wavelength, with the UV light source located external to the vessel so that light can pass through the sides of the vessel. Suitable glasses are available commercially and include borosilicates (&#34;Pyrex&#34;), &#34;Vycor&#34; or soft glass. Alternatively, the UV light source may be placed within the reaction vessel, either directly above the surface of the reaction mixture or within the mass of the reaction mixture. In some cases a sensitizer may be useful in catalytic amounts to accelerate the photopolymerization, including ketones such as acetone, benzophenone and the like. 
     The photopolymerization may be conducted by any method known to the art, including bulk, solution, suspension and emulsion methods. Solvents for the monomer and/or polymer can be used during polymerization, including benzene, aliphatic hydrocarbons such as hexane and heptane, and alcohols such as methanol, ethanol, t-butanol and the like. Well-known suspension techniques comprise suspending the monomeric material, preferably already mixed with the hydroxyl-containing disulfide, in the form of small particles in a non-solvent liquid such as water, together with a suspending agent to aid in maintaining the particles separate from one another during polymerization. Suitable suspending agents include starch, carboxymethylcellulose and the like. Emulsion polymerization is similar, except that emulsifiers are used to produce much smaller particles, and the end product is a stable aqueous emulsion of the polymer. Suitable emulsifiers include sodium or potassium fatty acid soaps, sodium alkaryl sulfonates, and the like. 
     Air or oxygen has an inhibiting effect on the reaction and preferably is excluded from the reaction vessel. Therefore, the reaction vessel desirably is flushed with nitrogen before the vessel is charged, and a nitrogen purge may be continued if necessary to exclude air during polymerization. The reaction generally is conducted with stirred at room temperature, with cooling provided if necessary. The polymerization rate may be monitored by withdrawing reaction mixture samples at periodic intervals for total solids analysis. The reaction can be run to 100% conversion, but it generally is more economical to run to about 70-90% conversion and recover unreacted monomer for reuse. The hydroxyl-containing liquid polymer may be purified by vacuum distillation or by washing with a solvent such as a benzenemethanol mixture in order to remove the unreacted hydroxyl-containing disulfide, followed by drying the polymer. The structure of the hydroxyl-containing liquid polymer can be confired by infrared analysis, together with well-known wet chemical methods for determination of hydroxyl and sulfur content. Number average molecular weights (M n ) can be measured using vapor pressure osometry, gel permeation chromatography or the like. 
    
    
     The following examples illustrate the present invention more fully. 
     EXAMPLES 
     The following examples demonstrate preparation of hydroxyl-containing liquid polymers having aliphatic carbon-carbon backbone linkages, together with sulfide linkages near the terminal portions of the polymeric molecule. Brookfield viscosity, employing an LVT model viscometer and a #4 spindle, was run at 27° C. on the freshly prepared polymers. Polymeric number average molecular weight (M n ) were measured using vapor pressure osmometry and toluene as the solvent. The instrument was calibrated using azobenzene or biphenyl. Weight percent hydroxyl and weight percent sulfur were measured by wet chemicals analysis. 
     Hydroxyl functionality (Functionality OH ) was calculated as follows: ##EQU1## Sulfide functionality (Functionality S ) was calculated as follows: ##EQU2## 
     EXAMPLES 1-5 
     In each of examples 1 to 5, butadiene, acrylonitrile, 2-hydroxyethyl disulfide and t-butanol solvent were charged to a clean, 16 oz. pop bottle reactor which had been flushed with nitrogen and equipped with a magnetic bar stirrer. The bottle was capped with a three-hole metal cap having a neoprene rubber liner and placed on a magnetic stirrer. An ultraviolet radiation source (GE &#34;Circline&#34; fluorescent lamp equipped with a &#34;Black-lite&#34; #FE 12T10-BL bulb) was placed next to the bottle and turned on, and stirring was begun. It was found that when the UV lamp was turned off, polymerization ceased until the lamp was turned back on. Total reaction time and % conversion for each of examples 1 to 5 is set forth in Table I. 
     After a given reaction time the reactor was cooled, and unreacted monomer was vented through a syringe needle inserted through a cap hole. Venting was continued until bubbling ceased in the reactor. The metal cap was removed and the reaction mixture transferred to a round-bottom flask. The flask was connected to a rotary evaporator, which was used to remove solvent and residual unreacted monomer. The reaction products were analyzed using the test methods described heretofore. In each of examples 1-5, sulfur functionality was somewhat higher than hydroxyl functionality. This may be explained at least in part by the fact that different wet chemical analytical techniques were used. Test results are summarized in Table I. 
     
                       TABLE I                                                     
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Example      1       2       3     4     5                                
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Polymerization Recipe                                                     
Butadiene, grams                                                          
             160     160     160   170   170                              
Acrylonitrile, grams                                                      
             40      40      40    30    30                               
2-Hydroxyethyl                                                            
             12      8       4     8     12                               
Disulfide, grams                                                          
t-Butanol, grams                                                          
             24      16      8     32    48                               
% Conversion after                                                        
24 hours     23      21      15    15    17                               
48 hours     42      34      24    40    54                               
69 hours     55      45      31    --                                     
96 hours     65      52      34    --    --                               
195 hours    --      --      --    --    --                               
Polymer Test Data                                                         
Brookfield Viscosity                                                      
             75,000  106,000 220,000                                      
                                   35,000                                 
                                         19,300                           
at 27° C., cps                                                     
M.sub.n      1,410   1,636   --    1,409 1.140                            
Wt. % Hydroxyl                                                            
             1.52    1.16    0.92  1.70  2.00                             
Content                                                                   
Ephr.sub.OH  0.0894  0.0682  0.0541                                       
                                   0.100 0.118                            
Hydroxyl Equivalent                                                       
             1,119   1,466   1,848 1,000 847                              
Weight                                                                    
Functionalty.sub.OH                                                       
             1.3     1.1     --    1.4   1.4                              
Wt. % Sulfur Content                                                      
             3.52    2.57    2.64  3.66  4.58                             
Ephr.sub.S   0.116   0.080   0.083 0.114 0.143                            
Functionalty.sub.S                                                        
             1.6     1.3     --    1.6   1.6                              
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     EXAMPLES 6-13 
     In each of examples 6-9 and 11-13, n-butyl acrylate, ethyl acrylate, 2-hydroxyethyl disulfide and t-butanol solvent (where used) were charged to a clean 16 oz. pop bottle reactor which has been flushed with nitrogen and equipped with a magnetic bar stirrer. The bottle was capped as in the previous examples and placed on a magnetic stirring plate. In example 10 a flask and pneumatic stirrer was used, with the flask being sealed after purging and charging was complete. An ultraviolet radiation source (GE &#34;Circline&#34; fluorescent lamp equipped with a &#34;Black-Lite&#34; #FE 12T10-BL bulb) was placed next to the bottle and turned on, and stirring was begun. After the time listed in Table II for each example, each polymer was recovered as described in the previous examples. The polymers were all clear and colorless. Polymerization data is summarized in Table II. 
     
                                           TABLE II                                
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Example          6  7  8  9  10 11 12 13                                  
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Polymerization Recipe                                                     
n-Butyl Acrylate, grams                                                   
                 70 730                                                   
                       70 70 280                                          
                                140                                       
                                   140                                    
                                      140                                 
Ethyl Acrylate, grams                                                     
                 30 30 30 30 120                                          
                                60 60 60                                  
2-Hydroxyethyl Disulfide, grams                                           
                 6  2+ 4  2  24 8  20 16                                  
t-Butanol, grams -- -- -- -- 30 8  20 50                                  
+Number of UV Lamps Used                                                  
                 2  2  2  2  2  1  1  1                                   
Total Polymerization Time, hours                                          
                 1.0                                                      
                    1.0                                                   
                       1.0                                                
                          1.0                                             
                             2.0                                          
                                5.0                                       
                                   6.0                                    
                                      6.0                                 
% Conversion     50.6                                                     
                    65.5                                                  
                       54.2                                               
                          44.6                                            
                             75.2                                         
                                56.1                                      
                                   57.8                                   
                                      45.6                                
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 +One gram 2hydroxyethyl disulfide was charged together with other        
 reactants, and the second gram was charged 30 minutes after polymerizatio
 began.                                                                   
 
    
     The hydroxyl-containing liquid polymers of this invention are useful as rocket propellant binders, adhesives, sealants, caulking compounds, polyurethane prepolymers, and the like. An elastomeric polyurethane may be prepared for example by taking 1 mol of the polymer of example 2, heating it to about 100° C. and mixing therewith by stirring in 2 mols of p,p&#39;diphenylenemethane diisocyanate and 1 mol of ethylene glycol, heating until the mixture solidifies, and cooling. A useful polyurethane prepolymer is prepared by reacting 1.1 moles of a diisocyanate, for example tolylene diisocyanate, with 1 mole of any of the polymers of the examples, and heating to form the prepolymer, which may thereafter be further reacted with difunctional crosslinking agents including diamines, glycols, and the like as is well known in the art to form an elastomer. Useful pressure sensitive adhesives may be prepared from any of the polymers of the examples by mixing any of the liquid hydroxyl-terminated polymers with a prepolymer of an isocyanate terminated polyether or polyester glycol, for example, a prepolymer of polytetramethylene ether glycol and tolylene diisocyanate and the hydroxyl terminated polymer of example 8. A specific example of such prepolymer has a molar weight of about 1300 and contains 6 weight percent NCO groups. The ratio of reactants used of OH/NCO, equivalent ratio, may be from about 2.5 to 3. After the two polymers are mixed, they are spread on the substrates to be adhered together and heated to about 100° C. to 150° C. for three minutes. These materials have excellent tack and adhesion.