GB2052539A - Process for the Continuous Manufacture of Diorganopolysiloxane Polymers - Google Patents
Process for the Continuous Manufacture of Diorganopolysiloxane Polymers Download PDFInfo
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- GB2052539A GB2052539A GB8018106A GB8018106A GB2052539A GB 2052539 A GB2052539 A GB 2052539A GB 8018106 A GB8018106 A GB 8018106A GB 8018106 A GB8018106 A GB 8018106A GB 2052539 A GB2052539 A GB 2052539A
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
- C08G77/04—Polysiloxanes
- C08G77/32—Post-polymerisation treatment
- C08G77/34—Purification
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
- C08G77/04—Polysiloxanes
- C08G77/06—Preparatory processes
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
- C08G77/04—Polysiloxanes
- C08G77/14—Polysiloxanes containing silicon bound to oxygen-containing groups
- C08G77/16—Polysiloxanes containing silicon bound to oxygen-containing groups to hydroxyl groups
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Abstract
The polymerization reaction, wherein cyclic dimethyl polysiloxane monomers are treated with a basic catalyst, takes place in a static mixer (i.e. one having static mixing elements), which provides plug flow conditions (i.e. all portions of the mixture have essentially the same residence time). The efficiency of the static mixer may be maintained by the early introduction of water as chainstopper. Preparation of other polysiloxane fluids utilizing triorganosiloxy chainstoppers is also disclosed.
Description
SPECIFICATION
Process For the Continuous Manufacture of Siloxane Polymers
This invention relates to a process for continuously manufacturing diorganopolysiloxane polymeric materials wherein it is possible to control the efficiency of the process by the judicious application of an appropriate chainstopping agent. Siloxane polymers and copolymers have long been prepared by batch polymerization methods wherein silogane monomers are catalyzed with acids or bases to produce polymers and copolymers having a wide range of average molecular weights. These polymeric products may be varied from low viscosity fluids to high viscosity gums.
The average molecular weight of the polymer may be controlled by the degree of polymerization and the addition of a chainstopping agent. As the polymerization reaction proceeds, monomers add to the end of the polymeric chain forming longer and longer polymers. The chainstopping agent halts the polymerization reaction and thereby limits the average molecular weight. The chainstopping agent may variously employ trialkylsiloxy-, alkoxy-, or silanol-groups or combinations' thereof. The choice of chainstopper is made upon consideration of the end use of the polymeric product.For example, when water is used as a chainstopper, the diorganopolysiloxane polymer will terminate at each end with silianol groups (Si-OH). Furthermore, a silanol-stopped diorganopolysiloxane will have different properties than.a polymer which is alkoxy- or trialkylsiloxy-stopped.
A typical polymeric product could be silanol-stopped dimethylpolysiloxane which has the following general formula:
wherein R=lower saturated and unsaturated alkyl and aryl groups including methyl-, ethyl-, propyl-, vinyl-, phenyl-, etc. And wherein X=approximately 50 to approximately 2000.
Prior to the present invention, such a polysiloxane polymer was ordinarily prepared by batch processes as follows: Siloxane cyclic monomers such as dimethyl tetramer were charged to a polymerization vessel and dried by distillation or by refluxing the siloxane vapors through a molecular sieve column. The temperature of the dry monomers was then adjusted to about 1 550C and sufficient potassium hydroxide polymerization catalyst was added in the form of a ground slurry in methyl tetramer to give a potassium hydroxide concentration of approximately 20 ppm. The polymerization reaction was allowed to proceed with agitation until a highly viscous polymer was obtained, typically within 30+10 minutes.Then, water was added as a chainstopper to the polymer to restrict further viscosity increase and agitation was continued at about 1 55or. Three more water additions were made at approximately 25 minute intervals, and agitation was continued for approximately 30 minutes after the last water addition,
The polymer was then sampled and tested for completion of the polymerization reaction and to determine the viscosity of the polymer. The potassium hydroxide catalyst was neutralized by adding an equal molar quantity of phosphoric acid and agitating for 1 to 1-1/2 hours to complete the neutralization reaction. The polymer was again sampled and'tested for acid/base concentration. Its stability to elevated temperatures was also tested.
Finally, the polymer could be stripped of unreacted monomers by distillation at pressures of 5 to 10 mm Hg and a temperature of approximately 1 60 C. The resultant silanol-stopped siloxane polymer made by the above reaction would have a viscosity of approximately 3500 cs at 250C and would contain less than approximately 2% unreacted monomer.
The production of large volumes of polymers by the above-described batch processing method is curnbersome and expensive and is subject to significant variations typical of batch processing.
The present invention is directed toward a process for the continuous manufacture of polysiloxane polymeric products. Preheated and degassed monomeric starting material and the polymerization catalyst could be fed to a mechanical mixer to establish a uniform concentration of catalyst. The polymerization reaction, which starts immediately, could be carried out in any of several classical continuous reactor systems. Some examples of such continuous reactor systems are (1 ) a series of continuous stirred tank reactors; (2) a continuous mixer consisting of a long cylinder with mechanical agitation throughout its length; (3) a continuous cylindrical reactor in which mixing and converging are accomplished by one or more rotating screws; or (4) an open pipe continuous reactor.
Each of these devices variously exhibit poor residence time distribution, required residence times in excess-of the theoretical minimum, slow response to process variables, and elaborate and expensive construction. The shortcomings of an open pipe continuous reactor, for example, are discussed in detail below.
Therefore, in the present invention, the polymerization reaction is carried out in a static mixer which consists of a long pipe containing static mixing elements. Such a mixer allows plug-type flow, i.e., any portion of the reaction mixture entering the static mixer receives essentially the same residence time therein as any other portion of the composition. Other types of flow may exhibit disadvantageous fluid velocity profiles resulting in varying degrees of mixer residence time, inefficient mixing and non-uniform products. This plug flow condition ensures the production of a consistent and uniform product.
It has been found that it is also necessary to maintain the efficiency of a static mixer when one is used in place of a mechanical mixer. That is to say, plug flow must be substantially maintained within the static mixer. This object has been achieved in the present invention by the early introduction of a chainstopping agent. It has been discovered that the mixing efficiency of a static mixer is maintained by the introduction of an effective amount of chainstopping agent into what is essentially the beginning of the polymerization reaction zone, thus maintaining near plug flow conditions in the static mixer.
The present invention is also able to produce diorganopolysiloxane polymers on a continuous basis whereas previously such polymers were only available through batch processing which was, as described above, inherently cumbersome, inefficient and inconsistent.
The continuous polymerization process of the present invention can be carried out under a wide range of process variables. For example, the degassing temperature can range from, approximately, 120 to 1 730C and the polymerization temperature ranges from, approximately 150 to 2100C.
The catalyst concentration can be from about 5 ppm to about 500 ppm of Equivalent KOH. The
KOH I equivalency of potassium silanolate ranges from, approximately, 0.05% to 6.0% KOH by weight; and the phosphoric acid equivalency of silyl phosphate ranges from, approximately, 1% to 20% H3PO4 by weight.
When water is selected as the chainstopping agent, the first water addition near the front of the polymerizer section will contain, approximately, 50 to 500 ppm water as compared to the monomer.
Subsequent water additions can total approximately 0 to 2500 ppm water, however, the water added at any single point along the polymerizer section should not exceed approximately 1000 ppm.
The monomer feed rate is determined by the amount of residence time required for polymerization as well as the volume of the polymerizer section.
Residence time required is deterinined by the desired degree of completion of the polymerization and the rate of polymerization (controlled primarily by temperature and secondarily by catalyst concentration). In typical practical application, the desired degree of polymerization completion is specified and a desired production rate is known. With this information, along with the knowledge of the volume of the polymerization section, the residence time can be calculated and a polymerization temperature and catalyst concentration selected within limits to produce the desired polymer.The relationship between polymerization completion and residence time is given by the 1 st order reversible kinetic equation
m-12
log =-Kt 100-12 where m=weight % monomer in polymer, K=polymerization rate constant (minutes -1), and t=polymerization residence time (minutes). The value of K is determined by temperature and catalyst concentration. Good practice resulting in maximum performance is to select combinations of temperature and catalyst concentrations such that at the residence time involved, active polymerization will be taking place over the entire length of the polymerizer section.
The present invention will be further described by way of example only, with reference to the accompanying drawing which shows in schematic form a flow diagram for the process of the present invention.
Referring to the drawing, a starting material such as dimethylcyclic siloxane monomer 11 is introduced into the polymerization process through feedline 12 to a monomer preheater 13. The monomer preheater 13 raises the temperature of the monomers to at least 1 400C but maintains the temperature below the boiling point of the monomer. In one embodiment of the present invention, the monomer preheater utilizes steam 14 to heat the monomer.
The preheated monomers flow through feedline 1 5 to a degassing tank 16 which is a gas-liquid separating tank having a float controlled air valve 17 at the top for discharge of gases. At atmospheric pressure the preheated monomers are only partly degassed in this separating chamber, and leave the degassing tank through feedline 20.
A chemical proportioning pump 21 feeds the preheated degassing monomer through a feedline 22 at a constant adjustable rate. The pump discharge pressures are ordinarily approximately 170 to 200 psig.
The preheated partly degassed monomer is heated again by a second preheater 23. The second preheater 23 utilizes hot oil 24 to heat the monomer to a temperature desired for the polymerizer stage.
From feedline 25 the monomer enters a two-stage mechanically driven in-line mixer 26 which has a volume of 0.25 gallons per stage. The hot monomer within the two-stage in-line mixer is mixed with a basic catalyst. For example, potassium silanolate catalyst 33 may enter the first stage of the inline mixer 26 through feedline 35 at a constant adjustable rate which is controlled by a chemical proportioning pump 34. The use of a mechanical in-line mixer is a preferred but not essential item in the practice of the present invention, and serves the primary purpose of providing back-mixing at the start of the polymerization process so that the catalyst-monomer solution is of more uniform composition with time.
The hot catalyzed monomer passes through feedline 36 into a static mixer 40 which constitutes the reaction zone of the manufacturing process. In apparatus for practising one embodiment of the present invention, the polymerization section consists of a 1 56 inch long pipe containing static mixer elements throughout its entire length and has a jacket containing recirculating hot'oil for temperature control. Such a static mixer provides the plug flow required for the practice of the present invention so that essentially all elements of the hot catalyst monomer have the same residence time within the static mixer.
A chemical proportioning pump 42 feeds the first water chainstopper 41 at a constant adjustable rate through feedline 43 to point 44 at the front section of polymerizer section 40. This early introduction of water chainstopper maintains the mixing efficiency of the static mixer even though the viscosity of the material within the static mixer reaction zone 40 is increasing with time. It should be noted, however, that water is used as a chainstopper when it is desired to produce a silanoi-stopped polydiorganosiloxane polymer and that other chainstopping agents may be selected depending upon the desired end product.
Alternatively, the first water chainstopper 41 can be introduced earlier or later in the process. For example, the water chainstopper 41 could be introduced through feedline 44A into the first stage of the two-stage in-line mechanical mixer 26.
If additional chainstopping activity is necessary, a second chemical proportioning pump 52 is utilized for feeding the second water chainstopper 51 at a constant adjustable rate through feedline 53 into the polymerizer section 40. This is done at a point sufficiently upstream from the end of the polymerizer section to provide for complete mixing of the water with the polymer and which provides approximately at least two minutes additional residence time for reaction of the water into the polymer.
Such an upstream point Is indicated by feedline 53.
The polymer next passes through feedline 54 into a short length small diameter static mixer 55
wherein a neutralizing agent is introduced from a chemical proportioning pump 57 through feedline 58
into the small static mixer so as to neutralize the catalyst. When potassium silanolate is used as the
catalyst, a suitable neutralizing agent is silyl phosphate 56. The small static mixer 55 provides for
thorough mixing of the silyl phosphate neutralizer with the polymer. Note that the silyl phosphate
neutralizer can be added at a controlled constant rate.
The neutralizing reaction takes place in a long pipe containing static mixer elements throughout
its entire length. This static mixer 63 is the neutralization reaction zone and has a jacket containing
recirculating hot oil for temperature control. Alternatively, static mixer 55 can be replaced with a
mechanically driven in-line mixer at this point to eliminate the pressure drop characteristic of a static
mixer and yet still provide for thorough mixing of the silyl phosphate neutralizer with the polymer.
The neutralized polymer leaves the neutralization zone through feedline 64 to a back pressure
regulating valve 65 which is used to control the system pressure at approximately 1 70 psig.
A heat exchanger 66 heats the polymeric product. Circulating hot oil 67 may be utilized as the
heat exchange medium and the heated polymer then leaves the heat exchanger through feedline 68.
Note that instruments for indicating and/or controlling the temperatures, pressures and flow rates are appropriately used throughout the process.
The polymer is then passed into a liquid-vapor entrainment separator 73 wherein the neutral
polymer is devolatized. Evaporation takes place within separator 73 and an absolute pressure of
approximately 5-10 mm Hg is maintained therein. The devolatized polymer 77 is removed from the
bottom of the vapor liquid separator through feedline 74 by a pump 75 whereupon the polymer product 77 exiting feedline 76 is ready for use or storage. Meanwhile, the monomer vapors are
removed from the top of the separator through feedline 81 and condensed by a water-cooled condense
82.
The monomer can be collected in a monomer surge tank 84 and can be removed through feedline
86 by monomer discharge pump 87. Preferably, the collected monomer can be recycled through feedline 88 for further use in the polymerization process.
Suitable monomeric starting materials can be any of several cyclic polysiloxanes. Although
dimethyl tetramer (octamethylcyclotetrasiloxane) is a suitable choice, it is also possible to utilize
pentamers, hexamers, heptamers, and equivalents as well as mixtures thereof. Note also that it is not
essential for the production of diorganopolysiloxanes that the organic substituents be methyl radicals.
Although methyl radicals are common substituents, other saturated and unsaturated alkyl and aryl
substituents and mixtures thereof are suitable, depending on the intended use of the end product.
Linear polysiloxane starting materials, however, are not ordinally suitable for the practice of the present invention.
The continuous polymerization process of the present invention can be carried out as follows: DimethVl cyclic siloxane monomer is partially degassed by heating the monomer to a
temperature of at least 140 C but not higher than the boiling of the gases are
separated from the monomer in a gas-liquid separating chamber at atmospheric pressure. The
degassed monomere are then pumped at a desired constant rate through a heat exchanger in order to
raise the temperature of the degassed monomers to atemperature which is compatible with residence
time in the polzmerization reactor. Suitable temperatures can be from approximately 160 C to
approximatelt 200 C.
The lot monomer is then mixed with a basic catalyst in a mechanically driven in-line mixer.
Suitable basic catalysts include cesium hydroxide, potassium hydroxide, sodium hydroxide,
lithium hydroxide and their analogurs cesium silanolate, potassium silanolate, sodium silanolate and
lithium silanolate. These various catalyzing agents have different relative reactivities with respect to the
present polymerization process and accordingly, compensation must be made for them. For example,
sodium hydroxide is a weak base and will catalyse the polymerization relatively slowly than the
others, and therefore the reaction takes longer at any given temperature.On the other hand, cesium
hydroxide reacts very quikly and may be less suitable for the reason that the polymerization reaction
could run to completion before there is any opportunity to control the viscosity of the product or the
efficiency of the process by the practice of the present invention. Thus, cesium hydroxide may be an
effective catalyst when a strong required, as for example, when the temperature of the
polymerization reaction zone is low.
It has been found that the preferred basic catalyst is potasium silanolate which is an active form
of potassium hydroxide and which is also very soluble in a monomer solution such as
octamethylsiloxane. The relatively great solubility of this catalyst in the starting material is a very
advantageous characteristic which greatly increases the efficiently of this continuous polymerization
process. If a less soluble catalyst such as potassium hydroxide were utilized it would be necessary to
provide an agitated chamber having sufficient residence time to dissolve the potassium hydroxide by
reaction with the siloxane monomer to form potassium silanolate. In the practice of the present
invention, it is preferred that the potassium silanolate be prepared beforehand in sufficient quantities
that it may be continuously added to the polymerization process.
ha potassium silenolate is pumped into the in-line mixer by a constant rate pump. As noted
above, the in-line mixer is preferred but not essential and serves the primary purpose of providing back
mixing at the start of the process so at the the catalyst monomer solution has a more uniformly
consistent composition with time. A secondary benefit of the in-line mixer is to ensure rapid and
uniform solution of the potassium silanolate catalyst in the monomer.
The hot catalyzed monomer is then passed into a static mixer which is kept at an essentially
constant temperature of approximately 150 C to approximately 200 C and more preferably
approximately 180 C to approximately 190 C. A preasure slightly greater than the vapor pressure of
water at the polymerization temperature is maintained within the static mixer. Typically, 170 psi gauge
pressure for a polymerization temperature of 190 C is suitable.
The volume of the static mixer is chosen so that sufficient residence time can be provided in order
to obtain the desired degree of polymerization and so that the polymerization reaction can proceed
continuously at a predetermined rate. Normal practice is to obtain a polymer containing less than 16%
of the unreacted monomer. It is recognized, however, that when the monomer is dimethyl cyclic
siloxane the equilibrium monomer content is approximately 12 %.
It is essential that the polymerization section of the processor be a static mixer in order that plug
flow is obtained. Plug flow means that each element of the fluid monomer entering the polymerizer
section will have essentially the same residence time as any other element of the monomer. The use of
a static mixer in the polymerization stage is particularly essential due to the rapid increase in viscosity
with increasing degree of polymerization. For example, if a static mixer is not used, a polymerizer
section composed of an open pipe would exhibit the typical parabolic velocity profile of liquids flowing
through pipes ndert laminar flow conditions. The liquid near the wall pf pipe would move at a lower
velocity than the liquid in the center of the pipe, resulting in residence times varying according to radial
position in the pipe.This variation of residence time quikly result in the formation of a higly
viscous polymer near pipe wall moving at extremely low velocities and a stream of very low
viscosity partly polymerized material rapidly down the center of the pipe. Adverse effects of
this situation are eliminated by installing the static mixer elements inside the pipe so that there exists
constant radial mixing of the fluid. Thus, a substantially uniform velosity profile resulting nearly
constant residence times will be obtained.
The mixing efficiency of the static mixer is maintained by controlling the viscosity increase of the
polymeric product. The viscosity is controlled by an early introduction of a chainstopping agent. For a
silanol-stopped polymer, water chainstopper is pumped into the polymerizer at a rate such that a
polymer of the desired average molecular weight and viscosity will be produced. It is essential for the practice of this continuous polymerization process that at least approximately 100 ppm water and not more than approximately 500 ppm water be added at the front section of the polymerizer to provide sufficient chainstopping activity to limit the viscosity of the polymer formed at this point and, more particularly, to limit the viscosity of polymer formed early in the polymerization process.
This early introduction of water chainstopper into the process is necessary due to the decreasing mixing efficiency of static mixers as the viscosity ratio of the materials being mixed increases. (The viscosity ratio is defined as: viscosity of the most viscous polymer/viscosity of unreacted monomer).
For example, complete mixing of liquids at a 10,000 to 1 viscosity ratio requires a static mixer length equal to 8 to 12 diameters, whereas increasing the viscosity ratio to 1,000,000 to 1 increases static mixer length to 1 5 to 20 diameters. For purposes of the present invention, it is more relevant to recognize that as the viscosity ratio increases, the rate of mixing within the static mixer decreases. At the same time, there exists within the hydraulic channels of the static mixer, a fluid velocity profile whereby fluid in the center of the channel is moving at a relatively greater velocity than fluid adjacent to the wall, as described above for an open pipe reactor.The increased residence time of the fluid adjacent the walls of the hydraulic channels results in a higher degree of polymerization and increased viscosity which, in turn, further reduces velocity. Thus, a situation develops in which segregation into high and low viscosity polymerizing masses occurs at a rate higher than the rate of mixing by the static mixers. This segregation destroys the plug flow characteristic of the static mixer, creates channeling inside the polymerizer, and results in incomplete polymerization.
The above-described condition relating to the velocity profile of a fluid within the hydraulic channel of a static mixer is completely eliminated by the procedure of the present invention wherein sufficient water chainstopper is introduced into the process at essentially the start of the polymerization section in order to limit the viscosity of the polymer and to limit the viscosity range of polymer within the static mixer. Thus, the rate of mixing remains equal to or greater than the rate of segregation and plug flow conditions are maintained. The preferred location of water introduction is the inlet of the static mixer, but it may alternatively be added at the first or second stage of the in-line mixer or at any point before approximately the first 1/6 of the static mixer.
For the manufacture of polymers requiring more than the above 100 to 500 ppm water chainstopper, a second stream of water is later introduced at a controlled flow rate at a point sufficiently upstream from the end of the polymerizer section to provide for complete mixing of the water with the polymer plus approximately 2 minutes residence time for reaction of the water with the polymer. The viscosity of the silanol end-stopped polymer is controlled by the proportion of water to polymer, with the water proportion being the sum of the two streams.
The polymer next passes into a short length of small diameter static mixer wherein a suitable neutralizing agent is introduced.
The neutralizing agents utilized in practicing the present invention may be any mild acids effective for neutralizing the basic catalyst. Such neutralizing agents can include phosphoric acid, trischlorethylphosphite, or more preferably, silyl phosphate which is particularly effective because it is quite soluble in siloxane polymers and allows for rapid neutralization.
Silyl phosphate may be pumped into the static mixer to neutralize the potassium silanolate catalyst. A small diameter static mixer is employed at this point to provide thorough mixing of the silyl phosphate with the polymer. An alternate approach involves the use of a mechanically driven in-line mixer at this point to eliminate the pressure drop of a small static mixer. The flow rate of silyl phosphate is controlled so that the equivalent of approximately one mole equivalent of phosphoric acid is added for every mole equivalent potassium hydroxide in the polymer.
The polymer containing silyl phosphate neutralizer then enters a larger diameter static mixer which provides additional residence under plug flow conditions for completion of the reaction between the potassium silanolate catalyst and the silyl phosphate neutralizer.
The neutralized polymer is then discharged through a back-pressure regulating valve that controls the system pressure.
The neutral polymer is then devolatilized by passing through a preheater where heating and evaporation take place. The mixed liquid-vapor passes into a vapor-liquid entrainment separatior maintained at an absolute pressure of 5 to 10 mm Hg. The devolatized polymer is removed from the bottom of the vapor-liquid separator by a pump while the monomer vapors are removed from the top of the separator, condensed by a water-cooled condenser and pumped out of the evaporator. The monomers, of course, may be collected in a suitable storage tank, or more preferably, recycled to the monomer feedline entering the polymerizer section.
In the following example, the potassium silanolate catalyst is a dimethylpolysiloxane containing potassium hydroxide in the form of potassium silanolate groups (Si-OK) and is a siloxane soluble potassium hydroxide catalyst. Workable and practicable potassium silanolate may contain up to approximately 5% by weight of equivalent potassium hydroxide.
The neutralizing agent, silyl phosphate, is a dimethylpolysiloxane containing phosphoric acid in the form of silyl phosphate groups and is a siloxane soluble form of phosphoric acid. In this example, silyl phosphate containing 12.0% of equivalent H3PO4 was prepared and then diluted for convenience to a 7:1 weight ratio with octomethylcyclotetrasiloxane to give a solution containing the equivalent of 1.50% by weight H3PO4.
The following examples are illustrative of a process for the continuous polymerization of silanol terminated diorganopolysiloxane polymers having a viscosity varying from 500 to 500,000 centipoise at250C.
Example 1
The monomer preheater heated the monomer to a temperature of approximately 1 450C. The chemical proportioning pump fed the monomer into the system at a pressure of approximately 170 to approximately 200 psig. The two-stage mechanically driven in-line mixer had a volume of 0.25 gallons per stage.
In this example, the polymerization section consisted of a 1 56 inch long pipe containing static mixer elements throughout its entire length. This polymerization section had an internal diameter of 3.26 inches. A suitable static mixer for the practice of the present invention and the one utilized with the present example is a type "BY" static mixer having a 1/4 inch layer height which is manufactured by the Koch Engineering Company of Witchita, Kansas. This static mixer had a jacket containing recirculating hot oil for temperature control.
The second static mixer was a 9-374 inch long by 1 inch diameter static mixer providing a 1/8 inch layer height such as a type "CY" static mixer manufactured by Koch Engineering.
The neutralizing section consists of a 3.26 inch internal diameter of 78 inch long pipe containing static mixer elements of the type described above for the polymerizing section. This neutralizing section also has a jacket containing recirculating hot oil for temperature control.
The back-pressure regulating valve controls the system pressure at about 1 70 psig.
Octomethylcyclotetrasiloxane monomer containing approximately 60 ppm water was polymerized to a silanol-stopped polymer under the following conditions:
Monomer Feed Rate: 110 Ibs/hour Degassing Temperature: 1 550C Feed Pump Pressure: 174+1 psig.
Preheat Temperature: 2070C
Potassium Silanolate Feed Rate: 82.5 gms/hour
Equivalent KOH Concentration of
Potassium Silanolate: 1.93% by weight
First Water Feed Rate: 12.7 ml/hour
Ratio of First Water to Monomer
Content: 254 ppm Water to Monomer
Second Water Feed Rate: 37.6 ml/hour
Ratio of Second Water to Monomer: 752 ppm Water to Monomer
Second Water Feed Location: 52 inches from end of polymerizer
section (feedline 53)
Silyl Phosphate Feed Rate: 184 gms/hour
Equivalent H3PO4 Concentration
of Silyl Phosphate: 1.50%
Polymerizer Pressure: 1 70 psig
Measured KOH Concentration: 28.5 ppm (sampled from end of
polymerizer section)
Residence Time Within Polymerizer: 1 7.8 minutes
Run Time: 12 hours
Polymer Product:
Residual Monomer Content: 15.1% Average (13 samples;
Range 14.1 to 16.0%)
Viscosity at 250C of Polymer
Product: 1798 cs (Avg. of 13 samples
ranging from 1460 cs to
2225 cs)
Acid-Base Content: 2 ppm base (equivalent KOH) to
2 ppm acid (equivalent HCI)
Example 2
The equipment used in this example was identical to that used in Example 1.
Octomethylcyclotetrasiloxane monomer containing approximately 50 ppm water was
polymerized to a silanol-stopped polymer under the following conditions:
Monomer Feed Rate: 83.5 Ibslhr.
Degassing Temperature: 1 550C Feed Pump Pressure: 1 80 psig.
Preheat Temperature: 212do Polymerizer Temperature: 1 80.50C Potassium Silanolate Feed Rate: 70 gms./hour
Equivalent KOH Concentration of
Potassium Silanolate: 1.94% KOH by weight
First Water Feed Rate: 16 ml/hour
Ratio First Water to Monomer: 442 ppm water to monomer
First Water Feed Location: Front face of static mixer
Second Water Feed Rate: 0 - Second Water Unnecessary
Silyl Phosphate Feed Rate: 144 gms./hour Equivalent H3PO4 Concentration of
Silyl Phosphate: 1.50%
Polymerizer Pressure: 170 psig.
Measured KOH Concentration: 30 ppm (sampled from end of
polymerization section)
Polymerization Residence Time: 23.5 minutes
Run Time: 60 minutes
Polymer Product:
Residual Monomer Content: 14.7% Average (5 samples;
Range 13.216.2%) Viscosity at 250C: 10,700 cs (Avg. of 5
samples ranging from 10,500 cs
to 1 1,100cs) With only two modifications to the above-described procedure, the process of the instant invention is also useful for the preparation of triorganosilyldiorganopolysiloxane polymers having a viscosity from approximately 10 to approximately 1,000,000 centipoise at 250C which are chainstopped with triorganosiloxy groups. First, the cyclic siloxane monomer must be dried in order to avoid the formation of a silanol-stopped polymer.Second, the triorganosiloxy chainstopper should be in the form R3Si[OR2Si]XSiR3, where x is three or greater and R=monovalent hydrocarbon radicals.
This second requirement is necessary so that the triorganosiloxy chainstopper will be incorporated into the polymer as rapidly as the diorganosiloxy monomer thus resulting in uniform chainstopping and a desirable molecular weight distribution in the finished polymer. Typically, trimethylsiloxy chainstoppers are suitable. It is required that all of this R3Si-[OR2Si]x-SiR3 chainstopper be fed into the two-stage mechanical in-line mixer (through feedline 44A). In all other respects, the procedures for producing a silanol-stopped diorganopolysiloxane polymer are followed.
Example 3
The equipment used in this Example is identical to that used in Example 1.
Octamethylcyclotetrasiloxane monomer containing less than 20 ppm water is polymerized to a trimethylsiloxy-chainstopped polymer under the following conditions. The trimethylsiloxy chainstopper is provided by a siloxane polymer of the general formula (CH3)3Si-[O Si(CH3)2jnSi(CH3)3 where n is substantially three (3) or more. A typical useful chainstopping polymer rich in trimethylsiloxy units is a mixture having the following composition:
Value ofn Weight % Value of n Weight %
0 0.1 5 13.2
1 0.7 6 5.1
2 3.9 7 1.6
3 41.7 8 0.5
4 27.9 9 0.2
This mixture contains approximately 35.9% by weight of trimethylsiloxy units. The balance of the mixture consists of cyclic polysiloxanes having 4 to 7 dimethylsiloxy units per cyclic molecule.
Monomer Feed Rate: 133 Ibs./hour
Degassing Temperature: 1 550C Feed Pump Pressure: 102+1 psig
Preheat Temperature: 2050C
Polymerizer Temperature: 1 900C Potassium Silanolate Feed Rate: 94 gms/hr.
Equivalent KOH Concentration of
Potassium Silanolate: 1.93% by weight
Rate of Chainstopper Feed: 1.94 Ibs/hr.
(CH3)3SiO"2 Content of Chainstopper: 35.9%
Location of Chainstopper Feed: First Stage of in-line mixer
(feed line 44A)
Silyl Phosphate Feed Rate: 211 gms/hr.
Equivalent H3PO4 Concentration of
silyl phosphate: 1.50%
Polymerizer Pressure: 100 psig
KOH Concentration: 30 ppm Residence Time within Polymerizer: 14.7 minutes
Polymer Product
Residual Monomer 14% by weight
Viscosity at 250C 2,100 centistokes
It will be seen from the foregoing that the present invention provides a novel process for continuously manufacturing diorganopolysiloxane polymers. This novel process results in a uniquely
uniform polymeric product which has properties that exhibit a remarkable degree of consistency and ensures uniformity of performance unavailable to products made by prior art processes.
Additionally, the ability to produce a uniform product on a continuous basis results in a process which is more efficient than those of the prior art.
Claims (21)
1. A process for the continuous polymerization of silanol terminated diorganopolysiloxane polymers having a viscosity varying from 500 to 500,000 centipoise at 250C comprising:
(a) mixing degassed and preheated cyclopolysiloxanes with an effective amount of a basic catalyst:
(b) passing the mixture of the polysiloxane and catalyst into a static mixer maintained under pressure and providing sufficient residence time for completion of the polymerization wherein in the initial part of the static mixer reaction zone there is introduced from 100 to 500 parts per million of water as a chainstopper;
(c) mixing into the reaction mixer an effective amount of a neutralizing agent to neutralize the basic catalyst; and
(d) passing the solution of the neutralizing agent and reaction mixture through a mixer providing sufficient residence time for completion of the neutralization.
2. A process as claimed in Claim 1, further comprising the step of adding an effective amount of additional water chainstopper near the terminal end of the static mixer reaction zone to produce a polymer of the desired viscosity.
3. A process as claimed in Claim 1 or Claim 2 wherein the basic catalyst is cesium hydroxide, potassium hydroxide, sodium hydroxide, cesium silanolate, potassium silanolate or sodium silanolate.
4. A process as claimed in Claim 3 wherein the basic catalyst is potassium silanolate.
5. A process as claimed in any one of the preceding claims wherein the static mixer reaction zone is maintained at a pressure slightly greater than the vapour pressure of water at the reaction zone temperature.
6. A process as claimed in Claim 5 wherein the reaction zone pressure is at least 1 70 psig.
7. A process as claimed in any one of the preceding claims wherein the static mixer reaction zone temperature is 1 600C to 2000C.
8. A process as claimed in any one of the preceding claims wherein the preferred temperature is from 1800Cto 1900C.
9. A process as claimed in any one of the preceding claims wherein the residence time of the hot catalyzed monomer within the static mixer reaction zone is sufficient to give the desired degree of polymerization and wherein less than approximately 1 6% unreacted monomer remains after the polymerization reaction.
10. A process as claimed in any one of the preceding claims wherein the neutralizing agents are silyl phosphate and/or trischloroethyl phosphite.
11. A process as claimed in Claim 10 wherein the neutralizing agent is silyl phosphate.
12. A process as claimed in any one of the preceding claims wherein one mole equivalent of neutralizing acid is added for each mole equivalent of catalytic base utilized in the polymerization reaction.
13. A process as claimed in any one of the preceding claims wherein the neutralization reaction takes place in a static mixer providing sufficient residence time for completion of the neutralization reaction.
14. The process for the continuous polymerization of triorganosilyldiorganopolysiloxane polymers having a viscosity ranging from 10 to 1,000,000 centipoise at 250C comprising:
(a) mixing dried degassed and preheated cyclopolysiloxanes with an effective amount of a basic catalyst;
(b) passing the mixture of the polysiloxane and catalyst into a static mixer maintained under pressure and providing sufficient residence time for completion of the polymerization, wherein in the initial part of the static mixer reaction zone there is introduced a low molecular weight triorganosilyldiorganopolysiloxane as a chainstopper, and where the organo group is a monovalent hydrocarbon radical;
(c) mixing into the reaction mixture an effective amount of a neutralizing agent so as to neutralize the basic catalyst; and
(d) passing the solution of the neutralizing agent and reaction mixture through a static mixer providing sufficient residence time for completion of the neutralization.
1 5. A process as claimed in Claim 14 wherein the basic catalyst is cesium hydroxide, potassium hydroxide, sodium hydroxide, cesium silanolate, potassium silanolate or sodium silanolate.
16. A process as claimed in Claim 1 5 wherein the basic catalyst is potassium silanolate.
17. A process as claimed in any one of Claims 14 to 16 wherein the triorganosilyldiorganopolysiloxane chainstopper has the general formula
(CH3)3 Si-[O Si(CH3)2]nSi(CH3)3 wherein n is a positive integer of 3 or more.
1 8. A process for the continuous polymerization of silanol terminated diorganopolysiloxane as claimed in Claim 1 substantially as hereinbefore described in Example 1 or Example 2.
1 9. A silanol terminated diorganopolysiloxane when produced by a process as claimed in any one of Claims 1 to 13 and 18.
20. A process for the continuous polymerization of triorganosilyldiorganopolysiloxane as claimed in Claim 14 substantially as hereinbefore described in Example 3.
21. A triorganosilyldiorganopolysiloxane when produced by a process as claimed in any one of
Claims 14 to 17 and 20.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8018106A GB2052539B (en) | 1980-06-03 | 1980-06-03 | Process for the continuous manufacture of diorganopolysiloxane polymers |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8018106A GB2052539B (en) | 1980-06-03 | 1980-06-03 | Process for the continuous manufacture of diorganopolysiloxane polymers |
Publications (2)
Publication Number | Publication Date |
---|---|
GB2052539A true GB2052539A (en) | 1981-01-28 |
GB2052539B GB2052539B (en) | 1984-06-20 |
Family
ID=10513785
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB8018106A Expired GB2052539B (en) | 1980-06-03 | 1980-06-03 | Process for the continuous manufacture of diorganopolysiloxane polymers |
Country Status (1)
Country | Link |
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GB (1) | GB2052539B (en) |
Cited By (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0108208A2 (en) * | 1982-09-10 | 1984-05-16 | General Electric Company | Solventless silicone controlled release compositions |
EP0129318A1 (en) * | 1983-06-15 | 1984-12-27 | Dow Corning Corporation | Neutralization of alkali metal catalysts in organopolysiloxanes |
GB2154596A (en) * | 1984-02-27 | 1985-09-11 | Gen Electric | Continuous production of silicone gums |
EP0266076A2 (en) * | 1986-10-27 | 1988-05-04 | Dow Corning Corporation | Method of producing polydiorganosiloxane gum |
EP0299634A2 (en) * | 1987-07-10 | 1989-01-18 | Dow Corning Corporation | Silicone polymer termination |
EP0515081A1 (en) * | 1991-05-20 | 1992-11-25 | Dow Corning Corporation | Base-catalyzed preparation of polyorganosiloxanes with controlled low-levels of hydroxy substitution |
EP0546747A1 (en) * | 1991-12-05 | 1993-06-16 | General Electric Company | Polymerisation process |
CN112142976A (en) * | 2020-09-18 | 2020-12-29 | 湖北兴瑞硅材料有限公司 | Continuous preparation method of electronic-grade methyl silicone oil |
-
1980
- 1980-06-03 GB GB8018106A patent/GB2052539B/en not_active Expired
Cited By (14)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0108208A3 (en) * | 1982-09-10 | 1984-07-18 | General Electric Company | Solventless silicone controlled release compositions |
EP0216376A1 (en) * | 1982-09-10 | 1987-04-01 | General Electric Company | Process for making solventless release diorganopolysiloxane composition |
EP0108208A2 (en) * | 1982-09-10 | 1984-05-16 | General Electric Company | Solventless silicone controlled release compositions |
EP0129318A1 (en) * | 1983-06-15 | 1984-12-27 | Dow Corning Corporation | Neutralization of alkali metal catalysts in organopolysiloxanes |
GB2154596A (en) * | 1984-02-27 | 1985-09-11 | Gen Electric | Continuous production of silicone gums |
EP0266076A3 (en) * | 1986-10-27 | 1989-06-14 | Dow Corning Corporation | Method of producing polydiorganosiloxane gum |
EP0266076A2 (en) * | 1986-10-27 | 1988-05-04 | Dow Corning Corporation | Method of producing polydiorganosiloxane gum |
EP0299634A2 (en) * | 1987-07-10 | 1989-01-18 | Dow Corning Corporation | Silicone polymer termination |
EP0299634A3 (en) * | 1987-07-10 | 1990-01-24 | Dow Corning Corporation | Silicone polymer termination |
EP0515081A1 (en) * | 1991-05-20 | 1992-11-25 | Dow Corning Corporation | Base-catalyzed preparation of polyorganosiloxanes with controlled low-levels of hydroxy substitution |
EP0546747A1 (en) * | 1991-12-05 | 1993-06-16 | General Electric Company | Polymerisation process |
US5519158A (en) * | 1991-12-05 | 1996-05-21 | General Electric Company | Method and apparatus for desiccant drying of fluorosilicones |
CN112142976A (en) * | 2020-09-18 | 2020-12-29 | 湖北兴瑞硅材料有限公司 | Continuous preparation method of electronic-grade methyl silicone oil |
CN112142976B (en) * | 2020-09-18 | 2022-07-15 | 湖北兴瑞硅材料有限公司 | Continuous preparation method of electronic-grade methyl silicone oil |
Also Published As
Publication number | Publication date |
---|---|
GB2052539B (en) | 1984-06-20 |
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