Abstract:
Ester compositions based on blends of the mono- and dibenzoates of 2,2,4-trimethyl-1,3-pentanediol and containing a minimum of 87 weight percent of the dibenzoate are novel and exhibit viscosities that are unexpectedly high relative to the benzoates of other mono- and polyfunctional alcohols. These viscosities are not exhibited at lower concentrations of the dibenzoate.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to novel benzoate ester compositions. More particularly, this invention relates to the benzoates of a particular branched diol. This benzoate composition exhibits an unexpectedly high viscosity, making it particularly unique and useful as a plasticizer or other type of additive for one- and two part polymer compositions. 
         [0002]    This invention also relates to one- and two-part polymer compositions containing one of the present benzoate ester compositions as a plasticizer. 
       BACKGROUND OF THE INVENTION 
     Description of the Prior Art 
       [0003]    Esters of both aliphatic and aromatic carboxylic acids with mono- and polyfunctional alcohols are widely used as plasticizers and other types of additives for a variety of polymers. The viscosities of liquid benzoic acid esters derived from 1) mono- and difunctional alcohols, 2) glycols containing from 2 to 4 carbon atoms or 3)oligomers of these glycols are typically no higher than about 150 centipoises at 25° C., measured using a Brookfield LVT viscometer. Unless otherwise specified all viscosity values in this specification and the accompanying claims refer to values measured at 25° C. using this viscometer. 
         [0004]    All of the aforementioned benzoic acid esters are employed as plasticizers and other types of modifiers and additives in a variety of organic polymer compositions. 
         [0005]    The viscosities of liquid compositions containing both the mono- and dibenzoates of either 1) a diol or a glycol such as ethylene and propylene glycols or 2) an oligomeric ethylene or propylene glycol typically do not increase substantially as the relative concentration of the dibenzoate is increased up to 100 weight percent. The viscosities of these ester compositions are typically less than 150 centipoises. 
         [0006]    Some monomeric phthalic acid esters derived from a) monofunctional alcohols and b) half esters and glycols containing from 2 up to about 8 carbon atoms typically exhibit viscosities of up to about 1200 centipoise, however health and/or environmental regulations limit the use of phthalates in certain end use applications. 
         [0007]    A commercially available product referred to in the literature as the dibenzoate of 2,2,4-trimethyl-1,3-pentanediol, hereinafter referred to as TMPDB, is actually a mixture of this ester with monobenzoate and degradation products. The viscosity of this mixture is about 400 centipoise. 
         [0008]    The present invention is based on the discovery that as the percent by weight of TMPDB in this commercially available product is increased from 85 to 100 percent its viscosity increases dramatically, reaching about 1200 centipoise. Mixtures containing more than 85 weight percent of the dibenzoate have not heretofore been disclosed and are considered novel. 
       SUMMARY OF THE INVENTION 
       [0009]    This invention provides a liquid benzoate ester composition comprising the general formula 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    and at least one monobenzoate of a formula selected from the group consisting of 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    and mixtures thereof, wherein R 1  is alkyl or H, and mixtures thereof, and the concentration of the dibenzoate is effective for imparting the liquid benzoate ester composition with a viscosity of from about 425 to about 1200 centipoise, measured at 25° C. using a Brookfield LVT viscometer, to said composition. 
         [0010]    The concentration of dibenzoate is effective for providing a viscosity of about 550 to about 1200 centipoise, measured at 25° C. using a Brookfield LVT viscometer, to said composition. In an important aspect, the dibenzoate is from about 87 to about 100 weight percent of the composition. In another aspect, the dibenzoate ester composition is provided with from about 5 to about 95 weight percent of an additional liquid or solid. Liquid and solid components may include polymers, other plasticizers, liquid carriers, solvents, pigments, fillers, catalysts, curing agents, adhesion promoters, cure retarders and deaerators. 
         [0011]    In another aspect, the benzoate ester composition includes 5 weight percent or less, based on the total weight of the benzoate ester composition, of monobenzoate. The benzoate ester composition can also contain 5 weight percent or less, based on the total weight of the benzoate ester composition, of unesterified diol, such as for example 2,2,4-trimethyl-1,3-pentanediol (HOCH 2 C(CH 3 ) 2 CH(OH)CH(CH 3 )CH 3 ). In the aspect where the benzoate ester composition includes an unesterified diol, the viscosity of the benzoate ester composition will be at least about 900 centipose. 
         [0012]    This invention also provides one- and two-part polymer compositions containing an ester composition of this invention as a plasticizer. 
         [0013]    In this aspect, a plasticized polymer composition is provided that includes the liquid benzoate ester and at least one organic polymer. Organic polymers that may be utilized include polysulfides, homopolymers and copolymers of vinyl chloride, acrylic polymers, polyesters, polyurethanes, elastomeric copolymers of styrene, and mixtures thereof. The liquid benzoate ester may be from about 5 weight percent to about 95 weight percent of the plasticized polymer composition. 
         [0014]    In another aspect, a two-part curable polymer composition is provided that includes a cross-linkable polymer and at least one plasticizer as a first part and the liquid benzoate ester as a second part. The second part may also include a catalyst for cross-linking the cross-linkable polymer. Cross-linkable polymers that may be used include polysulfides, polyurethanes, acrylic polymers, and mixtures thereof. The plasticizer may include esters of benzoic acid and monohydric alcohols, esters of benzoic acid and diols, esters of benzoic acid with at least one glycol containing from 2 to 4 carbon atoms, esters of benzoic acid with oligomers of said glycol, and mixtures thereof. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The uniqueness of the present benzoate ester compositions resides in their unexpectedly high viscosity relative to other non-polymeric esters of benzoic acid, including the aforementioned commercially available product identified as the dibenzoate of 2,2,4-trimethyl-1,3-pentanediol. The viscosity of the commercially available product is typically 400 centipoise at 25° C. and the hydroxyl number, a measure of the monobenzoate content, is about 12. 
         [0016]    The viscosities of the present ester compositions are directly proportional to the dibenzoate concentration. What distinguishes the present ester compositions from other mixtures of mono- and dibenzoates is not only the magnitude of the viscosity of these compositions, but also the unexpectedly large percentage increase in viscosity observed at dibenzoate concentrations above about 87 weight percent. 
         [0017]    The ester compositions of this invention can be prepared using conventional methods for preparing other esters of benzoic acid. In accordance with this method the esterification reaction is continued until a conversion to diester of greater than 87 percent is achieved. It is at this level that the greatest percentage increase in viscosity is observed. Methods for achieving this level of dibenzoate content and for determining the extent of conversion to dibenzoate by measuring the concentration of unreacted carboxylic acid and hydroxyl groups in a reaction mixture are known to those skilled in the art. 
         [0018]    Substituted benzoic acids such as toluic acid can be used in place of benzoic acid. 
         [0019]    Suitable catalysts for the esterification reaction include but are not limited to compounds of the elements in groups IVA and IVB of the periodic table. 
         [0020]    Methods for isolating and purifying mixtures of mono- and dibenzoates from reaction mixtures used to prepare them are known in the art and are not part of the present invention. 
         [0021]    The unexpectedly high viscosity of the present dibenzoate compositions make them particularly useful plasticizers in two part polymer compositions containing a cross-linkable polymer in one part and a cross-linking agent and/or a catalyst in a second part. Including a high viscosity benzoate ester composition of the present invention as a plasticizer in the second part of these polymer compositions increases the viscosity of this part to a level comparable to that of the first part containing the polymer, thereby facilitating blending of the two parts to form a homogeneous curable composition. 
         [0022]    In the past increasing the viscosity of the non-polymer portion of a 2-part composition was typically achieved using high viscosity phthalic acid esters of monohydric alcohols or by adding thickening agents, fillers, or other viscosity modifiers that could adversely affect the properties of the cured polymer. A disadvantage of phthalates is that they either cannot be used in certain applications or require warning labels. 
         [0023]    The high viscosities of the plasticizers of this invention reduces separation of these plasticizers from other components, resulting in increased storage stability of the compositions. Storage stability is the lack of settling or separation of the solid and/or liquid components of the composition. 
         [0024]    Polymers particularly suitable for use with the high viscosity benzoate ester compositions of this invention include but are not limited to polysulfides, homo- and copolymers of vinyl chloride, polyesters, polyurethanes, acrylic polymers, epoxide polymers and elastomeric polymers including but not limited to those derived from styrene. 
         [0025]    The present benzoate ester compositions can also be used in the same manner as other esters of benzoic acid, namely 1) as plasticizers, viscosity modifiers, and other types of additives and carriers in non-aqueous polymer compositions, 2) in aqueous adhesives containing polyvinyl esters and 3) to adjust the viscosity of curable and foamable polymer compositions. 
         [0026]    Uses of polymer compositions containing the benzoate esters of the present invention include but are not limited to paints, coatings, adhesives, construction and automotive sealants, including insulating glass sealants, inks, elastomers, foams and films. 
         [0027]    The benzoate ester compositions of this invention can be used in combination with known benzoate esters to achieve desired properties in specific polymer compositions. For example, it has now been found that when the benzoate ester composition of this invention is blended with glycol benzoate(s) such as dipropylene glycol dibenzoate the resultant polymer composition becomes softer and more pliable. This is particularly desirable when the polymer composition is intended for use as a sealant. The benzoate ester composition and glycol benzoates are blended in an amount effective for providing a depression of Shore A Hardness of about 15 to about 22%, an increase in % elongation of about 33 to about 140%, and a depression of Break Stress of about 9 to about 20%. In this aspect, the benzoate ester composition may be blended with up to an equal amount of the glycol benzoate. 
         [0028]    The following examples describe the preparation of a preferred benzoate ester composition of this invention and the performance of this composition as a plasticizer in the non-polymer portion of a two-part curable polysulfide composition. 
         [0029]    Unless otherwise specified all parts and percentages are by weight and properties were measured at 25° C. Viscosities were measured using a Brookfield model LVT viscometer. 
       EXAMPLE 1 
       [0030]    This example describes the preparation of a preferred benzoate ester composition of this invention. 
         [0031]    An esterification reaction mixture was prepared by blending benzoic acid, 2,2,4-trimethyl-1,3-pentanediol and an effective amount of a suitable esterification catalyst in a reactor typical of those used for esterification reactions. The reactor included means for measuring the temperature of the reaction mixture and removing the water formed as a by-product of the reaction. The molar ratio of acid to diol was 2.2:1.0 
         [0032]    The resultant mixture was heated with stirring to a temperature sufficient to distill the water formed as a by-product of the esterification reaction. Heating was continued until OH number of the reaction mixture was 8. The reaction mixture was purified using known techniques to isolate the desired ester composition. 
         [0033]    The viscosity of the final ester composition was 900 centipoise. 
       EXAMPLE 2 
       [0034]    This example demonstrates the use of the benzoate ester described in Example 1 as the replacement for a high-viscosity phthalate ester plasticizer in the non-polymer portion of a 2-part curable polysulfide composition. 
         [0035]    Part A of the composition was prepared using the following ingredients: 
         [0000]    100 parts of a liquid polysulfide polymer available as Thiopolast® G 21 from Akzo Nobel
 
35 parts of one of four different plasticizers: butyl benzyl phthalate, referred to hereinafter as A1; dipropylene glycol dibenzoate, referred to hereinafter as A2 (Benzoflex® 9-88); a 6.6:17.4:4.3 weight ratio mixture of dipropylene glycol dibenzoate: diethylene glycol dibenzoate:triethylene glycol dibenzoate, referred to hereinafter as A3 (Benzoflex 2088); and propylene glycol dibenzoate, referred to hereinafter as A4 (Benzoflex 284).
 
1.2 parts of gamma-glycodioxypropyl trimethoxy silane
 
155 parts of ground calcium carbonate and
 
32.5 parts of precipitated calcium carbonate
 
         [0036]    Procedure for preparing part A: 
         [0000]    All of the liquid ingredients were blended to homogeneity;
 
Ground calcium carbonate was added to liquid ingredients and blended in;
 
One half of precipitated calcium carbonate was added and blended in;
 
Remaining precipitated calcium carbonate was blended in;
 
Resulting mixture blended sufficiently to achieve a rating of 4 using a Hegmann grind gauge.
 
         [0037]    Part B was prepared using the following ingredients: 
         [0000]    100 parts of one of two different plasiticizers;
 
64.9 parts of manganese (IV) oxide;
 
21 parts of carbon black
 
7.1 parts of 1,1,3,3-tetramethyl guanidine
 
         [0038]    The two plasticizers evaluated in part B were: 
         [0000]    The benzoate ester of Example 1, referred to hereinafter as B1;
 
as B2, 2,2,4-trimethyl-1,3-pentanediol isobutyrate(1) benzylphthalate(3), referred to hereinafter as TMPDIBBP, exhibiting the formula
 
         [0000]      CH 3 CH(CH 3 )C(O)OCH 2 C(CH 3 ) 2 CHXCH(CH 3 ) 2    
         [0000]      X=—OC(O)PhC(O)OCH 2 C 6 H 5    
         [0000]    B2 was evaluated for comparative purposes.
 
Part B was prepared using the following procedure:
 
40 percent of the plasticizer being evaluated was blended with the remaining ingredients to homogeneity;
 
the resultant mixture was ground using a 3-roll mill with a 0.10 mm gap to a rating of between 4 and 5 on the Hegmann grind gauge;
 
the remainder of the plasticizer was added and the composition blended to homogeneity.
 
         [0039]    Curable compositions were prepared by blending parts A and B in a 10:1 volumetric ratio. The resultant mixtures were degassed by passing them through a 3-roll mill with a gap of 0.2 mm. Test samples were prepared for the evaluation of tensile properties and hardness (durometer measurement) by placing the resultant mixtures into polyethylene terephthalate molds measuring 5 inches (12.7 cm.) in length, ¾ inch (1.9 cm.) in width and 1/16 inch (0.16 cm) in depth. Five samples were prepared from each of the compositions. 
         [0040]    The test samples were cured for 3 days under ambient conditions followed by 4 hours at 70° C., following which the samples were allowed to cool for 4 hours under ambient conditions. The thickness of each sample was measured following which the hardness of the samples was determined using ASTM test procedure D2240 and the tensile strengths measured using ASTM test procedure D-638. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Shore A Hardness 
                 Tensile Strength 
               
             
          
           
               
                 Plasticzers 
                 Initial 
                 10 Second 
                 % Elongation 
                 Break Stress (psi) 
               
               
                   
               
               
                 A1, B2* 
                 40 
                 40 
                 49 
                 136 
               
               
                 A2, B1 
                 36 
                 34 
                 96 
                 124 
               
               
                 A3, B1 
                 44 
                 42 
                 40 
                 143 
               
               
                 A4, B1 
                 46 
                 44 
                 72 
                 155 
               
               
                   
               
               
                 *Evaluated for comparative purposes 
               
             
          
         
       
     
         [0041]    The data in Table 1 indicate that the combination of plasticizers A2 and B1 would be preferred in those instances when a softer, more compliant polymer composition is desired. 
         [0042]    The maximum shear stress and peak load values for each of the cured compositions on aluminum and glass were measured using the Lap Shear test described in ASTM test procedure C 961-01. These values are recorded in Table 2. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Max. Shear Stress (Lb/in 2 ) 
                 Peak Load (Lb · f) 
               
             
          
           
               
                 Plasticizers 
                 Aluminum 
                 Glass 
                 Aluminum 
                 Glass 
               
               
                   
               
               
                 A1, B2* 
                 3 
                 3 
                 51 
                 50 
               
               
                 A2, B1 
                 5 
                 3 
                 49 
                 50 
               
               
                 A3, B1 
                 3 
                 3 
                 56 
                 64 
               
               
                 A4, B1 
                 3 
                 4 
                 54 
                 72 
               
               
                   
               
               
                 *Evaluated for comparative purposes 
               
             
          
         
       
     
         [0043]    All of the failures resulted from cohesive splitting within the body of the polymer compositions and not from adhesion failure to the glass or aluminum substrate. 
       EXAMPLE 3 
       [0044]    This example demonstrates the effect of TMPD dibenzoate content in the plasticizer on the stability of the composition described as part B of in the preceding example 2. A prior art plasticizer, the mixed isobutyl/benzylphthalyl ester referred to hereinbefore as TMPDIBBP, was also evaluated as a comparison. 
         [0045]    Samples weighing approximately 60 grams of compositions containing the ingredients of component B in the preceding Example 2 were weighed into a centrifuge tube using a 4 point balance and the weight recorded. The tube was then centrifuged at 4000 rpm for 60 min. The tube was then removed from the centrifuge and the separated liquid was removed from the surface of the sample using a Pasteur Pipette. The liquid was then weighed using a 4 point balance. The percent weight loss (based on total sample weight) was calculated and is recorded in Table 3. 
         [0000]                                                            TABLE 3                   B Component Stability by Centrifuge                Viscosity of       Weight %           plasticizer   Weight %   Plasticizer           (cps)   *TMPDDB   loss                            **TMPDIBBP   920   0   19.60           TMPDB 1     400   84.5   28.94           TMPDB 2     537   87   20.63           TMPDB 3     680   90.5   19.60           TMPDB 4     794   93.4   18.92           TMPDB 5     909   96.2   21.74                       *TMPDB = Dibenzoate of 2,2,4-trimethyl 1,3-pentanediol           **2,2,4-trimethyl-1,3-pentanediol isobutyrate(1) benzylphthalate(3)           TMPDB 1-5  = Various Benzoate Ester compositions containing stated amounts of TMPDB            
The data in Table 3 demonstrate the improved stability of the compositions containing an elevated dibenzoate concentration over the composition containing 84.5% dibenzoate.