Classifications

• • 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
  • C08G2/00—Addition polymers of aldehydes or cyclic oligomers thereof or of ketones; Addition copolymers thereof with less than 50 molar percent of other substances
  • C08G2/08—Polymerisation of formaldehyde
• • 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
  • C08G10/00—Condensation polymers of aldehydes or ketones with aromatic hydrocarbons or halogenated aromatic hydrocarbons only
  • C08G10/02—Condensation polymers of aldehydes or ketones with aromatic hydrocarbons or halogenated aromatic hydrocarbons only of aldehydes
• • 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
  • C08G2/00—Addition polymers of aldehydes or cyclic oligomers thereof or of ketones; Addition copolymers thereof with less than 50 molar percent of other substances
  • C08G2/06—Catalysts

Definitions

• the present invention relates to a process for the production of polyoxymethylene by the polymerization of formaldehyde in the presence of a quaternary ammonium salt initiator and an aliphatic anhydride.
• High molecular weight polyoxymethylene also known as polyacetal
• polyacetal is a well-known commercial product. It can be made, for example, according to the process described in U.S. patent 2,994,687, which involves passing dry, gaseous formaldehyde into an agitated hydrocarbon solvent containing an initiator (typically a quaternary ammonium salt) and small amounts of a molecular weight control agent, typically methanol.
• the polymer is isolated and its hydroxyl end groups, arising from chain transfer by reaction with methanol and adventitious water, are capped by reaction with an aliphatic anhydride such as acetic anhydride to stabilize the polymer against depolymerization and provide sufficient thermal stability to allow the polymer to be melt-processed.
• an aliphatic anhydride such as acetic anhydride
• R 1 is an aliphatic or olefinic hydrocarbon group containing about 18 to about 25 carbon atoms
• R 2 , R 3 , and R 4 are each methyl, ethyl, and/or propyl, such that the total number of carbon atoms in R 2 , R 3 , and R combined is between 3 and 7
• X " is an organic anion.
• Gaseous formaldehyde is preferably added to a highly-agitated hydrocarbon solvent containing a quaternary ammonium salt initiator and an aliphatic anhydride.
• the reaction temperature is preferably about 50 to about 90 0 C or, more preferably, about 60 to about 70 0 C and the reaction pressure is preferably less than about 2 atm.
• the polymerization initiator is a quaternary ammonium salt of the formula:
• R is an aliphatic or olefinic hydrocarbon group containing about 18 to about 25 carbon atoms
• R 5 R , and R are each methyl, ethyl, and/or propyl, such that the total number of carbon atoms in R 2 , R 3 , and R 4 combined is between 3 and 7
• X " is an organic anion.
• R 1 is preferably behenyl.
• X " is preferably an alkanoate anion or alkoxide. Examples of alkanoate anions include formate, acetate, propionate, butyrate, heptanoate, decanoate, oleate, palmitate, and stearate.
• alkoxides examples include methoxide, 1-propoxide, 2-propoxide, 1-butoxide, and 1-hexoxide.
• Preferred anions acetate, formate, or propionate.
• a preferred initiator is behenyltrimethylammonium acetate.
• the initiator will preferably be used at about 20 to about 3000 ppm, or more preferably about 100 to about 1000 ppm, or yet more preferably at about 200 to about 300 ppm, relative to the total weight of polymer produced.
• the aliphatic anhydride may be any that can serve both as a molecular weight control agent and endcapping agent for the polyoxymethylene.
• a preferred aliphatic anhydride is acetic anhydride.
• the hydrocarbon solvent may be a single hydrocarbon or a mixture of two or more hydrocarbons.
• hydrocarbons include aliphatic hydrocarbons such as hexane, cyclohexane, heptane, octane, 2-methylhexane, and aromatic hydrocarbons such as benzene, toluene, and xylene.
• aliphatic hydrocarbons such as hexane, cyclohexane, heptane, octane, 2-methylhexane
• aromatic hydrocarbons such as benzene, toluene, and xylene.
• Preferred is heptane or mixtures of heptane and up to 15 weight percent toluene.
• the process of the present invention may be carried out in polymerizer comprising a double loop arrangement as shown in Figure 1.
• Continuous pumping through the loops agitates a slurry of polymer in hydrocarbon solvent in the polymerizer.
• Formaldehyde is introduced through line 5 at the top of reactor 3.
• the aliphatic anhydride and hydrocarbon solvent are added through line 6, while the polymerization initiator is added to the bottom of the reactor through line 4 to loop 10, which includes pump 1.
• Spray loop 9 includes pump 2.
• Unpolymerized formaldehyde is vented through line 7.
• the polymer is recovered through line 8.
• Polymerization experiments were performed in two slightly different laboratory polymerizers.
• a schematic diagram of the polymerizers is shown in Figure 1.
• Polymerizer B has the same configuration as polymerizer A, but is three times taller with essentially three times the reacting polymer-solvent slurry volume and thus three times the circulation time. Circulation time is defined as the slurry volume divided by the pumping rate through pump loop 9. All experiments begin with a polymer-solvent slurry containing 42 weight percent seed polymer content, and this initial slurry charge is three times larger for polymerizer B than for polymerizer A.
• the circulation time for polymerizer B is similar to that used in commercial plant scale polymerizers, and therefore this larger laboratory polymerizer is used to study initiator reactivity or formaldehyde conversion as discussed below.
• the smaller polymerizer A is better suited to measure particle size performance since proportionately less seed polymer is used, meaning that particle size measurements are made predominately on polymer that is produced in the polymerizer, rather than introduced as seed polymer.
• DHTA Dihydrogenated tallow dimethylammonium acetate
• BTMA Behenyltrimethylammonium acetate
• Polymer particle size is measured by standard mechanical sieve separation.
• Particle size is defined as the median size determined by interpolation of the weight fractions of polymer collected on sieve screens with 420, 250, 150, 75 and 44 micrometer opening sizes after vigorous shaking.
• IV intrinsic viscosity
• Comparative Example 1 To polymerizer A was added 1000 mL heptane, and 500 grams of seed polyoxymethylene polymer with a median particle size of 290 microns. With vigorous agitation maintained by the dual pumping loops 9 and 10, a continuous flow of purified formaldehyde monomer, solvent, acetic anhydride and dihydrogenated tallow dimethylammonium acetate (DHTA) initiator was started. Monomer flow rate was about 300 grams/hr, solvent flow was about 410 grams/hr, and acetic anhydride addition rate was 0.62 grams/hr and DHTA was added at a rate equivalent to 180 parts per million parts of produced polymer.
• DHTA dihydrogenated tallow dimethylammonium acetate
• the temperature was maintained at 62-65 0 C by a cooled water bath on one of the reactor pumping loops. After 3.3 hours of continuous operation, with intermittent sampling to maintain a constant slurry volume in the reactor, a total of 990 grams of polymer was produced with an unacceptable median particle size of 130 microns and an inherent viscosity in hexafluoroisopropanol of 1.78.
• Comparative Example 2 For this experiment, formaldehyde polymerization with DHTA initiation was first established in polymerizer A with methanol injection before transitioning to acetic anhydride. Heptane was again used with same solvent and seed charge as in Comparative Example 1. DHTA was added at a rate equivalent to 360 parts per million parts of produced polymer and, methanol was added at 0.19 grams/hr. After one hour of continuous operation, the polymer particle size was 400 microns. Methanol injection was then stopped and acetic anhydride was added at a rate of 0.65 grams/hr for the remaining two hours of the three hour experiment. The final product median particle size had decreased to an unacceptable 148 microns with an inherent viscosity of 1.82.
• Example 1 was run using the same procedure as Comparative Example 1, but using behenyltrimethylammonium acetate (BTMA) as the initiator.
• the initiator was added at a rate equivalent to 140 parts per million parts of produced polymer.
• the acetic anhydride addition rate was 0.67 grams/hr.
• the temperature was maintained at about 58 0 C for 1 hour and was then increased to greater than 68 0 C for another 2.3 hours. After the first hour the resulting polymer had a median particle size of about 560 micrometers and after the additional 2.3 hours, the polymer had an acceptable median particle size of greater than 420 micrometers.
• Example 2 was run using the same procedure as Example 1, again using BTMA as the initiator.
• the hydrocarbon solvent used was Citgo Special Naphtholite, a paraffinic solvent.
• the initiator was added at a rate equivalent to 260 parts per million parts of produced polymer.
• the acetic anhydride addition rate was 0.60 grams/hr.
• the temperature was maintained at about 75 0 C for 2 hours and was then lowered to 65 0 C for another 2.5 hours.
• the median polymer particle size was 176 micrometers after the first 2 hours and an acceptable 300 micrometers at the end of the polymerization.
• Comparative Example 3 was run using the same procedure as Example 2, except that methanol was used as the chain transfer agent instead of acetic anhydride. The initiator was added at a rate equivalent to 500 parts per million parts of produced polymer. The methanol addition rate was 0.18 grams/hr. The temperature was maintained at about 75 0 C for 1 hour. The median polymer particle size was acceptable at greater than 400 micrometers, but the polymerization rate was relatively slow at 190 grams/hr. Comparative Example 4
• Comparative Example 4 was run using the procedure of Comparative Example 1, except that Isopar® E, a paraffinic solvent available from Exxon, was used as the hydrocarbon solvent.
• the initiator was added at a rate equivalent to 150 parts per million parts of produced polymer.
• the acetic anhydride addition rate was 0.70 grams/hr.
• the temperature was maintained at about 60 0 C for 1.25 hours and was then increased to 80 0 C for another 1.42 hours.
• the median polymer particle size was 220 micrometers after the first 1.25 hours and an unacceptable 140 micrometers at the end of the polymerization.
• Example 3 was run using the procedure of Comparative Example 4, except that BTMA was used as the initiator.
• the initiator was added at a rate equivalent to 440 parts per million parts of produced polymer.
• the acetic anhydride addition rate was 0.60 grams/hr.
• the temperature was maintained at about 66 0 C for 1.33 hours and was then increased to 80 0 C for another 1 hour.
• the median polymer particle size was 325 micrometers after the first 1.33 hours and an acceptable 290 micrometers at the end of the polymerization.
• Formaldehyde conversion is specifically characterized by the residual formaldehyde content of the solvent sampled through line 8 of pump loop 9, where higher formaldehyde content corresponds to poorer conversion of formaldehyde to polymer.
• Lower formaldehyde conversion is problematic in commercial scale polymerizers where solvent is evaporated from the spray loop to remove the heat of polymerization. This additional formaldehyde is flashed off with the solvent and can cause excessive fouling in downstream condensers that in turn reduces plant uptime.
• the conversion per pass behavior of a plant scale polymerizer was simulated in polymerizer B.
• the circulation time defined as the volume of the slurry contained in the reactor divided by the volumetric flow rate in spray loop 9 as shown in Figure 1, was similar to a typical circulation time in a commercial reactor.
• Initiator (DHTA in the case of Comparative Examples 5 and 6 and BTMA in the case of Examples 4-7) was added at the rates shown in Table 2.
• Solvent was added at a rate of 410 grams/hr and chain transfer agent (methanol followed by acetic anhydride in the case of Comparative Example 5 and acetic anhydride in the cases of Examples 4-7) was added at the rates given in Table 2.
• the reaction temperature was maintained at 60 0 C by the use of a cooling water bath on one of the pumping loops.
• the slurry solvent was sampled for residual formaldehyde content at line 8 as shown in figure 1 by simultaneously quenching the sample in excess methanol and filtering the solids through a syringe filter.
• Formaldehyde content was measured by titration in sodium sulfite solution. In this case, excess sodium sulfite in aqueous solution at pH 9.4 was used to convert dissolved formaldehyde to titratable base.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Polyoxymethylene Polymers And Polymers With Carbon-To-Carbon Bonds (AREA)

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• 2005
  • 2005-06-10 US US11/150,679 patent/US7476718B2/en not_active Expired - Fee Related
  • 2005-06-30 JP JP2007519535A patent/JP5291339B2/ja not_active Expired - Fee Related
  • 2005-06-30 WO PCT/US2005/023814 patent/WO2006007596A1/en not_active Ceased
  • 2005-06-30 KR KR1020067027850A patent/KR101228673B1/ko not_active Expired - Fee Related
  • 2005-06-30 CN CN2005800216645A patent/CN1976966B/zh not_active Expired - Fee Related
  • 2005-06-30 DE DE602005022444T patent/DE602005022444D1/de not_active Expired - Lifetime
  • 2005-06-30 EP EP05769124A patent/EP1765896B1/en not_active Expired - Lifetime

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