2-Methylpropenyl-terminated polyisobutylene-polydimethyl-siloxane compositions

Abstract: An antifoam composition is disclosed comprising (A) a polydimethylsiloxane having a viscosity greater than 2 mm 2 /s (cS) at 25°C; and (B) a polyisobutylene oligomer having a number average molecular weight of 200 to 2,300 and having at least one end terminated with a 2-methylpropenyl group.

Description: The present invention relates to an antifoaming composition comprising a blend of a polydimethylsiloxane oil and a polyisobutylene oligomer having at least one end terminated with a 2-methylpropenyl group. Polydimethylsiloxane oils, particularly when formulated with a silica powder, are known for their ability to reduce frothing or foaming in aqueous systems. There are also examples in the art where organic formulations have been used to control foam in such systems. These antifoaming or defoaming agents find utility in many industrial processes, some of which would be highly impractical if the agent were not available. The US-A-5152925 describes the use of hydroxyalkyl acrylate/vinyl copolymers as defoaming agents. Antifoam agents containing both organic and silicone components are also known. For example, US-A-3,959,175 discloses a defoamer based on a mixture of polyisobutylene and a high melting hydrophobic component, such as fatty amide, fatty acid or tri-glyceride, or a mixture of the polyisobutylene and a hydrophobic material such as treated silica powder. Combinations of the above three ingredients are also taught therein. This patent incorrectly includes silicone oil as a member of the aforementioned "high melting" component which is said to have a melt point above 40°C. Rather, the typical melting point of a polydimethylsiloxane oil is actually -40°C. This patent also includes examples wherein silicone oil is used, albeit at levels of no more than 0.5 percent. The viscosity of the silicone oil used is not stated and no criticality thereof is suggested. Likewise, the polyisobutylene taught therein is shown to have particular end groups of the formula -CH 2 C(CH 3 )=CH 2 , and there is no suggestion to alter this group. We have found that certain blends of polydimethylsiloxane (PDMS) oils and polyisobutylene (also referred to as polybutene or PIB) have antifoaming activity which is superior to either of these individual components. Our blends, wherein the polyisobutylene has at least one terminal 2-methylpropenyl group of the structure -HC=C(CH 3 ) 2 in its molecule, have been found to be significantly better antifoams for aqueous detergent systems than comparable blends wherein both terminal groups are saturated hydrocarbon groups, such as those having the structure -C(CH 3 ) 3 or -CH 2 CH(CH 3 ) 2 . The former structure is that normally present on one terminus of the PIB as typically available in commerce. The latter structure is almost identical with that of the end group taught by US-A 3,959,175. It is surprising that such a subtle change in end groups can result in the enhanced defoaming performance of our blends wherein the polyisobutylene has a 2-methylpropenyl end group. The synergistic antifoam activity observed when our blends are used to defoam an aqueous foaming system may be further augmented by the incorporation of a fine silica powder. This further serves to reduce the concentration of antifoam agent required to defoam a particular foaming system. The present invention therefore relates to an antifoam composition comprising: (A) a polydimethylsiloxane having a viscosity greater than 2 mm 2 /s (cS) at 25°C; and (B) a polyisobutylene oligomer having a number average molecular weight of 200 to 2,300 and having at least one end terminated with a 2-methylpropenyl group of the structure -HC=C(CH 3 ) 2 , wherein the weight ratio of (A) to (B) is 1:99 to less than 50:50 or said ratio is greater than 55:45 to 99:1. Our invention further relates to a method for defoaming a foaming system using the above described composition. The polydimethylsiloxane (A) of our invention is a homopolymer or copolymer having a viscosity at 25°C. which is greater than 2 mm 2 /s (cS) wherein up to 15 mole percent of diorganosiloxane units may be copolymerized with the dimethylsiloxane units. It has been found that when the viscosity of the polydimethylsiloxane is ≤2 mm 2 /s (cS) the antifoam activity of the instant blends is not enhanced over the corresponding polydimethylsiloxane polymer itself. On the other hand, when the viscosity of this component is more than 2 mm 2 /s (cS), a synergistic effect is obtained whereby the antifoaming activity of our composition is superior to either the pure polydimethylsiloxane or the pure PIB components. There is no critical upper limit of the polydimethylsiloxane viscosity and it is only limited by practical mixing considerations, but is preferably no more than 100,000 mm 2 /s (cS). The organic groups of the above mentioned diorganopolysiloxane units are independently selected from alkyl radicals having 1 to 16 carbon atoms, phenyl radical or halogenated alkyl radicals having 3 to 6 carbon atoms or alkylene oxide groups, such as ethylene oxide, propylene oxide or copolymeric combinations thereof. The nature of the terminal groups on the polydimethylsiloxane component (A) is not critical for the purposes of the present invention. These may be inert groups, such as trimethylsiloxy, dimethylphenylsiloxy and diethylphenylsiloxy. They may also be illustrated by groups such as dimethylvinylsiloxy, dimethylhexenylsiloxy, dimethylhydroxysiloxy, dimethylhydrogensiloxy, dimethylalkoxysiloxy, methyldialkoxysiloxy and trialkoxysiloxy, wherein the alkoxy groups are preferably methoxy. Most preferably, component (A) is a polydimethylsiloxane homopolymer having trimethylsiloxy terminal units. Component (A) is well known in the art and is generally available commercially. Component (B) of our invention is a polyisobutylene oligomer having a number average molecular weight (MWn) of 200 to 2,300, preferably 200 to 800 and most preferably 300 to 400. The polyisobutylene oligomer must have at least one 2-methylpropenyl terminal group of the structure -HC=C(CH 3 ) 2 . Again, the specific polymers and oligomers described above can be prepared by methods known in the art. Such oligomers are known in the art and many are available commercially in a variety of molecular weights from the Amoco Chemical Company under the trade name Indopol™, and are referred to as "vinyl" terminated in the company's literature. For this invention, the weight ratio of component (A) to component (B) is such that the antifoam activity of the blend of (A) and (B) is greater than that of either (A) or (B) alone, as determined by the percent foam drop in a simple shake test, described more completely in the examples. Generally, this ratio is between 1:99 and 99:1, with the exception of a narrow region in which the improved antifoam activity is not observed. Thus, the improved antifoam activity is observed when the PDMS/PIB weight ratio is 1:99 to less than 50:50 or when this ratio is greater than 55:45 to 99:1. Preferably, the weight ratio of (A) to (B) is 10:90 to 40:60 or it is 60:40 to 90:10. Most preferably, the weight ratio of (A) to (B) is 10:90 to 30:70 or 70:30 to 90:10. In addition to components (A) and (B), the instant compositions preferably also contain (C), a fine powdered silica component. The addition of silica further augments the antifoam activity of our compositions. Component (C) can be a precipitated or fumed silica that is treated with, e.g., a silane or siloxane agent to render it hydrophobic as commonly practiced in the art. Examples of such treating agents include hexamethyldisiloxane, trimethylchlorosilane and low molecular weight silanol-terminated polydimethylsiloxane, preferably hexamethyldisilazane. Preferably, this component is a silica having a surface area in the range of 50 to 400 m 2 /gram, most preferably 50 to 150 m 2 /gram. The silica can be pre-treated or treated in-situ. To prepare our antifoam compositions, components (A), (B) and, optionally, component (C) are blended to form a homogeneous mixture. Any suitable means for mixing such systems may be used (e.g., low shear mixers, vortex mixer) and the order of addition is not critical. Typically, components (A) and (B) are added to component (C) and the latter is then uniformly dispersed in the combination of (A) and (B). In our method, the above antifoam composition is then added to a foaming system, preferably an aqueous foaming system, in an amount sufficient to reduce foaming, as determined by routine experimentation. Typically, the amount used of our antifoam composition is approximately 1 to 14,000 parts per million (ppm) based on the weight of the foaming system. When silica (C) is not included in our composition, this range is preferably 400 to 8,000 ppm, and most preferably 800 to 4,000 ppm. When silica (C) is added in our compositions, the region of exclusion (i.e., wherein improved antifoam activity is not observed) is not generally found. In this case, the antifoam activity of blends containing (A), (B) and (C) is generally superior to that of blends of only (A) and (C) or blends of (B) and (C) over the full range of (A):(B) weight ratios (i.e., 1:99 to 99:1). The silica, when added, is preferably present at a level which results in a silica concentration of no more than 140 ppm (by weight) in the foaming system, preferably no more than 130 ppm. Preferably, up to 50%, more preferably up to 35% and most preferably up to 3%, of the total weight of components (A), (B) and (C) is present as silica. It has been found that the addition of greater amounts of silica in foaming systems does not enhance the efficiency of our antifoam composition beyond that of only PDMS-silica mixtures. Thus, for example, when the total concentration of our antifoam composition is more than 4,000 ppm, the silica content is preferably no more than 3% based on the combined weight of components (A) and (B) and (C). For the preferred range of antifoam concentration in a foaming system, the silica is preferably used at a level of up to 1 percent based on the total weight of (A), (B) and (C). The skilled artisan can readily determine the optimum amount of silica by routine experimentation. In a preferred embodiment, the foaming system comprises aqueous surfactant media, such as aqueous detergents encountered in laundry and dishwashing applications. Our compositions are also suitable as antifoams in pulp and paper production. Additionally, our method may also be used to defoam other foaming systems, such as found in petroleum and petrochemical processing, solvent-based inks and paints and in chemical processing. EXAMPLES The following examples are presented to further illustrate the composition and method of this invention. All parts and percentages in the examples are on a weight basis and all measurements were obtained at a temperature of 25°C., unless indicated to the contrary. The activity of our antifoam compositions were determined by a shake test as follows. An aqueous detergent stock solution was prepared by adding 20 drops (0.45 gram) of DAWN™ Original Scent Dishwashing Liquid (Proctor & Gamble, Cincinnati, OH) to 345 ml of warm tap water and mixing thoroughly. Twenty ml (19.7 g) aliquots of the stock solution were placed into 35.2 ml (9.5 dram) vials, filling each vial about half way. An antifoam composition was added to each vial at the level indicated in the tables below. In each shake test series at least one vial did not contain antifoam agent and this served as a control for the series. In the shake test procedure a vial was lifted to a position above the operator's ear and then shaken by extending the arm in a "throwing" motion (approximately a 0.61 m (2 foot) extension), then returning to the initial position. Ten such shake cycles were used in each case, with a slight pause between cycles, all within a span of 5 seconds. After shaking, the vial was placed on a laboratory bench top and observed as a function of time, as shown in the tables. The activity of a given antifoam composition after a given time interval was obtained according to the following formula: % drop in foam height = 100 (T - F)/(T - L). wherein T = 8.4 cm = maximum height of liquid plus foam in the vial (i.e., when empty portion of vial is completely filled with foam) F = liquid plus foam height at a given time L = liquid height = 4.4 cm From this above formula it is seen that, when foam fills the empty portion of the vial, as in the case of the controls immediately after shaking, T = F and the % drop is zero. Likewise, when all the foam has collapsed after a given time interval, F = L and the % drop is 100%. Thus, a larger value of the % drop (for a given time of rest after shaking) indicates improved defoaming activity. The values of F obtained herein represent an average of three measurements, each taken at a different location around the vial. Series 1 Polysynlane™ PIB and trimethylsiloxy-terminated PDMS having a viscosity of 350 cS (350 mm 2 /s) were blended in the ratios shown in the first column of Table 1a to form comparative antifoam agents and these were evaluated according to the above shake test. Polysynlane™ is described as a saturated polyisobutylene having a number average molecular weight of 320 (MWn = 380 by gel permeation chromatography) and having one terminal group of the formula the other terminal group being of the formula -C(CH 3 ) 3 . It is a product of Polyesther Corporation, Southhampton, NY. The measured total concentration of the antifoam blend (or pure PIB or PDMS) in the foaming system is shown in the second column of Table 1a (ppm = parts per million). The % drop in foam height at three different times is reported in the last three columns. For the purposes herein, the term "immediate" indicates measurement within 10 seconds. (no silica) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) ---- 0 0 25 100/0 4023 22 27 60 0/100 4162 0 0 33 90/10 4112 21 22 51 70/30 4114 14 14 50 50/50 4132 22 23 49 30/70 4208 19 19 51 10/90 4036 14 15 58 From Table 1a it is seen that the antifoam activity of these blends is generally lower than that of the pure PDMS component (i.e., weight ratio = 100/0) for all times. Similar results were obtained when this series was repeated, in this case the total antifoam composition level ranging from 3,890 to 4,069 ppm. This series also included evaluation of the above compositions wherein 3% of each blend was replaced with QUSO™ WR55 FG silica powder. QUSO™ WR55 FG is described as a synthetic, amorphous, precipitated, PDMS-treated silica having a typical surface area of 90 m 2 /g and marketed by Degussa Corporation, Dublin, OH. The results are presented in Table 1b. (3% silica in antifoam composition) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 25 100/0 4061 97 98 100 0/100 4086 38 40 100 90/10 4079 95 97 100 70/30 4135 95 97 100 50/50 4081 95 95 100 30/70 4137 95 95 100 10/90 4059 93 93 100 From Table 1b it is again seen that the antifoam activity of these comparative blends is generally lower than that of the pure PDMS component. In this case, however, the introduction of silica results in good performance for most of the compositions. Series 2 The comparative evaluations using the Polysynlane™ PIB and PDMS of Series 1 were repeated wherein the total concentration of the antifoam blend was reduced, as indicated in Tables 2a and 2b. (no silica) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 26 100/0 736 23 28 57 0/100 822 0 0 8 90/10 736 0 0 39 70/30 756 11 13 49 50/50 731 0 0 25 30/70 761 4 7 44 10/90 741 0 0 29 (3% silica in antifoam agent) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 26 100/0 726 84 86 100 0/100 777 11 16 100 90/10 716 67 70 100 70/30 761 85 86 100 50/50 746 75 78 100 30/70 771 79 81 100 10/90 746 76 78 100 From Tables 2a and 2b it is seen that the same general trend as found in Series 1 was obtained at the lower antifoam concentrations (i.e., the addition of this PIB to PDMS generally detracts from the antifoam performance of the latter for all time intervals under consideration). Series 3 Antifoam agents of the present invention were prepared as described in Series 1 using Indopol™ L-14 PIB in place of the Polysynlane™. Indopol™ L-14 is described as a vinyl-terminated polyisobutylene oligomer having a number average molecular weight of 320 and is a product of the Amoco Chemical Company, Chicago, IL. One terminal group of this oligomer has the vinyl-like structure -HC=C(CH 3 ) 2 (i.e., 2-methylpropenyl) and the other terminal group has the formula -C(CH 3 ) 3 . The results of the shake test using antifoam concentrations similar to those of Series 1a are presented in Table 3a. (no silica) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 0 100/0 4059 18 23 49 0/100 4079 0 0 29 90/10 4162 33 35 76 70/30 4096 45 48 70 60/40 4112 27 28 61 55/45 4102 10 16 48 50/50 4102 18 19 47 45/55 4117 21 23 60 40/60 4162 19 22 58 30/70 4127 28 28 84 10/90 4132 25 29 68 Table 3 demonstrates that the compositions of our invention have greater antifoam activity than either pure PDMS or pure PIB. This enhancement is observed either immediately, or at longer time intervals, within certain proportions of the two components. In this particular case, the improvement is generally observed when the two components are combined, with the exception of a narrow region in which the PDMS/PIB weight ratio is greater than 45:55 to less than 55:45. This can be better appreciated from the graphical representation of the data of Table 3a in Figure 1. Figure 1 is a plot of the percent foam drop at 24 hours as a function of polydimethylsiloxane content in blends of polydimethylsiloxane and 2-methylpropenyl-terminated polyisobutylene. In this graph, the percent foam drop (at 24 hours) is plotted against the weight percent of the PDMS component, the dotted line at 49% being indicative of the pure PDMS antifoam activity. The compositions of Series 3a were modified with 3% silica, as described in Series 1b. Evaluation of these antifoams is reported in Table 3b. (3% silica in antifoam composition) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 28 100/0 4264 97 98 100 0/100 4340 64 68 100 90/10 4225 98 100 100 70/30 4256 98 98 100 50/50 4257 98 98 100 30/70 4239 98 98 100 10/90 4244 97 97 100 From Table 3b it is seen that the antifoam activity of the blends is not better than that of the PDMS alone when each system is modified with silica at this total level of antifoam composition. Series 4 Antifoam compositions of the invention based on the PDMS and PIB used in Series 3 were again evaluated and the results are presented in Table 4. (no silica) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 1 19 100/0 3823 9 12 37 0/100 4580 0 0 23 99/1 3856 5 5 51 90/10 3984 31 33 63 70/30 3952 24 26 50 50/50 4058 0 3 36 30/70 3987 4 7 54 10/90 3916 0 1 43 1/99 3853 1 1 51 0/100 3890 0 0 28 Again, it is seen that the blends of the invention had enhanced antifoam activity, either immediately or at longer time intervals, except at the PDMS/PIB ratio of 50/50. Series 5 Evaluation of antifoam compositions similar to those of Series 3 and Series 4 were repeated wherein the total concentration of the antifoam blend in the foaming system was reduced, as indicated in Tables 5a and 5b. (no silica) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 13 100/0 786 27 29 54 0/100 848 0 0 39 90/10 787 22 24 60 70/30 771 33 35 62 50/50 807 29 33 59 30/70 832 16 18 63 10/90 843 5 7 82 (3% silica in antifoam agent) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 13 100/0 731 87 88 100 0/100 863 43 45 100 90/10 761 95 95 100 70/30 756 95 95 100 50/50 782 95 95 100 30/70 802 95 95 100 10/90 833 90 91 100 From Table 5a it is seen that, at this lower total antifoam level, the improvement in activity of our blends over either PDMS or PIB is deminished. However, when silica is added, our enhancement over PDMS/silica blends is apparent. This trend was observed at still lower total antifoam levels (approximately 200 ppm). Series 6 The effect of the viscosity of trimethylsiloxy-terminated PDMS component on the antifoam performance was determined using the PIB of Series 3, this PDMS viscosity is indicated in the second column of Table 6. In this series of experiments the total antifoam agent concentration was in the range of 4213 to 4508 ppm. (no silica) Weight Ratio of PDMS/PIB Viscosity of PDMS (mm 2 /s) Drop in Foam Height (%) Immediate 4 Hours 24 Hours 0/0 (Control) -- 0 0 26 0/100 -- 0 0 33 100/0 2 22 28 58 90/10 2 22 31 61 100/0 50 5 6 40 90/10 50 32 35 58 100/0 100 24 28 51 90/10 100 23 30 61 100/0 350 47 49 71 90/10 350 53 57 89 100/0 1,000 53 55 78 90/10 1,000 62 63 89 100/0 30,000 48 50 95 90/10 30,000 64 67 98 From Table 6a it is seen that the antifoam activity of blends based on PDMS having a viscosity of 2 mm 2 /s (cS) is not improved by the addition of the 2-methylpropenyl-terminated PIB, whereas blends of our invention containing PDMS oil having a viscosity of greater than 2 mm 2 /s (cS) show improved performance relative to the corresponding pure PDMS component, either immediately or after longer periods. The above results were repeated using compositions containing 0.5% of the above described silica and the results of testing at a total antifoam agent concentration of 4239 to 4467 ppm are shown in Table 6b. (0.5% silica) Weight Ratio of PDMS/PIB Viscosity of PDMS (mm 2 /s) Drop in Foam Height (%) Immediate 4 Hours 24 Hours 0/0 (Control) -- 0 0 26 0/100 -- 23 28 100 100/0 2 74 91 100 90/10 2 76 93 100 100/0 50 79 88 100 90/10 50 86 90 100 100/0 100 80 84 100 90/10 100 88 90 100 100/0 350 84 85 100 90/10 350 90 93 100 100/0 1,000 90 90 100 90/10 1,000 95 96 100 100/0 30,000 93 95 100 90/10 30,000 95 97 100 It is again seen that the enhanced antifoam activity is only obtained when the viscosity of the polydimethylsiloxane is greater than 2 mm 2 /s (cS). At this total antifoam level, a PDMS viscosity of greater than 1,000 mm 2 /s (cS) does not seem to result in improved activity over the PDMS/silica blend. Similar results were obtained when the silica was present at 0.5% and the total antifoam composition was used at a level of 350 ppm. Series 7 Compositions were prepared and tested as above wherein the PDMS had a viscosity of 60,000 mm 2 /s (cS) and the PIB was the same as used in Series 3. The results are shown in Table 7a and 7b (without silica and with 0.5% silica, respectively). (no silica) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 28 100/0 355 19 22 47 90/10 421 18 18 33 100/0 4558 29 29 58 90/10 4528 50 52 100 (0.5% silica in antifoam agent) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 28 100/0 406 73 75 100 90/10 411 75 75 100 100/0 4695 90 93 100 90/10 4523 89 91 100

Claims: An antifoam composition comprising (A) a polydimethylsiloxane having a viscosity greater than 2 mm 2 /s (cS) at 25°C; and (B) a polyisobutylene oligomer having a number average molecular weight of 200 to 2,300 and having at least one end terminated with a 2-methylpropenyl group of the structure -HC=C(CH 3 ) 2 , wherein the weight ratio of said polydimethylsiloxane (A) to said polyisobutylene (B) is 1:99 to 99:1, with the proviso that the antifoam activity of the blend of (A) and (B) is greater than that of either (A) or (B) alone. The composition of claim 1 further comprising (C) a silica powder, wherein up to 50 percent of said silica is present based on the total weight of components (A), (B) and (C). The composition according to claims 1 or 2 wherein said polydimethylsiloxane (A) has trimethylsiloxy terminal groups and has a viscosity of ≥50 mm 2 /s (cS) at 25°C. The composition of claims 1 or 2 wherein the weight ratio of said polydimethylsiloxane (A) to said polyisobutylene (B) is 1:99 to less than 50:50 or said ratio is greater than 55:45 to 99:1. The composition of claims 1 or 2 wherein the number average molecular weight of said polyisobutylene (B) is 300 to 400. The composition of claims 1 or 2 wherein the weight ratio of said polydimethylsiloxane (A) to said polyisobutylene (B) is 60:40 to 90:10. The composition of claims 1 or 2 wherein the weight ratio of said polydimethylsiloxane (A) to said polyisobutylene (B) is 10:90 to 30:70. The composition according to claim 2 wherein up to 3 percent of said silica powder is present based on the combined weight of said polydimethylsiloxane, said polyisobutylene and said silica powder. A method for defoaming a foaming system comprising adding to said foaming system the composition of claims 1 - 8.

Inventors: GENTLE THOMAS MATTHEW, HAUENSTEIN DALE EARL, KENNAN LINDA DENISE, POPA PAUL JOSEPH, GENTLE, THOMAS MATTHEW, HAUENSTEIN, DALE EARL, KENNAN, LINDA DENISE, POPA, PAUL JOSEPH
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1995
Main classification: B01D19
IPC codes: C08L83, B01D19, C08L23