U.S. patent number RE39,182 [Application Number 09/998,276] was granted by the patent office on 2006-07-11 for process for the preparation of thermally stable polyoxymethylene copolymers.
This patent grant is currently assigned to Ticona GmbH. Invention is credited to Robert M. Gronner, Karl-Friedrich Muck, Horst Roschert, Satyajit Verma, Michael G. Yearwood.
United States Patent |
RE39,182 |
Muck , et al. |
July 11, 2006 |
Process for the preparation of thermally stable polyoxymethylene
copolymers
Abstract
A process for the preparation of polyoxymethylene copolymers,
wherein 1,3,5-trioxane is polymerized with generally known
comonomers in the presence of a strong protonic acid initiator and
in the presence of a formaldehyde dialkyl acetal, and wherein the
initiator is dissolved in the formaldehyde dialkyl acetal before
admixing to the trioxane and the comonomers.
Inventors: |
Muck; Karl-Friedrich
(Wiesbaden, DE), Roschert; Horst (Ober-Hilbersheim,
DE), Gronner; Robert M. (Corpus Christi, TX),
Verma; Satyajit (Corpus Christi, TX), Yearwood; Michael
G. (Bishop Nueces, TX) |
Assignee: |
Ticona GmbH
(DE)
|
Family
ID: |
22531829 |
Appl.
No.: |
09/998,276 |
Filed: |
November 30, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
09149795 |
Sep 8, 1998 |
05994455 |
Nov 30, 1999 |
|
|
Current U.S.
Class: |
524/745; 524/713;
524/792; 528/241; 528/244; 528/249; 528/250; 528/248; 528/242;
528/232; 524/730; 524/706; 524/701 |
Current CPC
Class: |
C08G
2/24 (20130101); C08G 4/00 (20130101); C08G
2/06 (20130101) |
Current International
Class: |
C08K
5/41 (20060101); C08G 4/00 (20060101) |
Field of
Search: |
;528/232,241,242,244,248,249,250 ;524/701,706,713,730,745 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
4431794 |
February 1984 |
Sadlowski et al. |
5144005 |
September 1992 |
Sextro et al. |
|
Foreign Patent Documents
|
|
|
|
|
|
|
3147757 |
|
Jul 1982 |
|
DE |
|
31 47 757 |
|
Jul 1982 |
|
DE |
|
3147757 |
|
Jul 1982 |
|
DE |
|
0080656 |
|
Jun 1982 |
|
EP |
|
0 080 656 |
|
Jun 1983 |
|
EP |
|
0347119 |
|
Dec 1989 |
|
EP |
|
0 347 119 |
|
Dec 1989 |
|
EP |
|
6-92475 |
|
Aug 1992 |
|
JP |
|
Primary Examiner: Acquah; Samuel A.
Attorney, Agent or Firm: Connolly Bove Lodge & Hutz
LLP
Claims
We claim:
1. A process for the preparation of polyoxymethylene copolymers
exhibiting a reduced amount of unstable terminal end groups
comprising, polymerizing 1,3,5-trioxane with at least one cyclic
ether .[.and.]. .Iadd.or .Iaddend.acetal comonomer with the aid of
a strong protonic acid or Lewis acid initiator and in the presence
of a formaldehyde dialkyl acetal, the improvement comprising
dissolving the initiator in the formaldehyde dialkyl acetal before
introducing the same to the trioxane and the comonomers.
2. The process according to claim 1, wherein the strong protonic
acid initiator is selected from the group consisting of
trifluoromethanesulfonic acid and anhydrides,
pentafluoroethylsulfonic aicd and anhydrides,
heptafluoropropylsulfonic acid and anhydrides, nonafluorobutyl
sulfonic acid and anhydrides, and perfluoroheptylsulfonic acid,
anhydrides, and mixutres thereof and the Lewis acid is selected
from the group consisting of phosphorus pentafluoride, silicon
tetrafluoride, boron trifluoride, boron trifluoride eatherates,
tintetrachloride, arsenic pentafluoride, triphenylmethyl
hexafluorophosphate, and mixtures thereof.
3. The process according to claim 2, wherein the strong protonic
acid initiator is trifluoromethanesulfonic acid and the Lewis acid
is boron trifluoride.
4. The process according to claim 3, wherein the strong protonic
acid or Lewis acid initiator is present in an amount of from about
0.01 to about 1 ppm, based on the total amount of trioxane and
comonomers.
5. The process according to claim 4, wherein the formaldehyde
dialkyl acetal is selected from the group consisting of
formaldehyde dimethyl acetal, formaldehyde diethyl acetal,
formaldehyde dipropyl acetal, formaldehyde dibutyl acetal, and
mixtures thereof.
6. The process according to claim 5, wherein the formaldehyde
dialkyl acetal is formaldehyde dimethyl acetal.
7. The process according to claim 6, wherein the formaldehyde
dialkyl acetal is present in an amount of from about 3.4 to about
34 mmol per kg of trioxane and comonomers.
8. The process according to claim 2, wherein the formaldehyde
dialkyl acetal containing the dissolved strong protonic acid
initiator is added to the comonomers before admixing to the
trioxane.
Description
Process for the preparation of thermally stable polyoxymethylene
copolymers
The present invention relates to a process for the preparation of
thermally stable polyoxymethylene (POM) copolymers wherein the
initiator is distributed within the monomers through prior
dissolution in a formaldehyde dialkylacetal.
Thermoplastic molding materials of POM homopolymers and copolymers
have long been frequently used as versatile materials of
construction, particularly in engineering and manufacturing. In
many cases they can be used as a substitute for metals on account
of their outstanding mechanical properties, such as high rigidity,
hardness and strength and the fact that it is possible to produce
moldings and molded parts to strict tolerance limits, and their
good resistance to many chemicals.
It is known that, by copolymerizing trioxane with cyclic ethers or
cyclic acetals, copolymers can be obtained in which the sequence of
the --CH.sub.2--O-- groups is interrupted by randomly distributed
comonomer units such as --CH.sub.2CH.sub.2--O--,
--(CH.sub.2).sub.4--O-- or
--CH.sub.2--CH.sub.2--O--CH.sub.2--CH.sub.2--O-- (G. W. Becker/D.
Braun, Kunststoff-Handbuch, Vol. 3/1, p. 303, Munich-Vienna, 1992).
The comonomers are normally used in a weight proportion of 0.2 to
20%. Suitable initiators used in the present invention are strong
protonic acids selected from the group consisting of
trifluoromethanesulfonic acid and anhydrides,
pentafluoroethylsulfonic acid and anhydrides,
heptafluoropropylsulfonic acid and anhydrides, nonafluorobutyl
sulfonic acid and anhydrides, perfluoroheptylsulfonic acid and
anhydrides, and mixtures thereof Suitable initiators are also Lewis
acids selected from the group consisting of phosphorus
pentafluoride, silicon tetrafluoride, boron trifluoride, boron
trifluoride etherates, tintetrachloride, arsenic pentafluoride,
triphenylmethyl hexafluorophosphate, and mixtures thereof
At the end of the polymerization reaction the crude POM polymer
still contains a certain amount of unconverted monomers and
unstable terminals which have to be eliminated to stabilize the
final product.
In order to be able to form such a polymer from the melt, as it is
customary for thermoplastics, it is necessary to deactivate the
polymerization initiator, to remove the adhering monomer residues
from the polymer and to break down the unstable fractions.
Thus, it is known that the deactivation of the initiator is carried
out in the aqueous phase or in an organic solvent, subsequent
filtration, washing and drying steps being required. The
deactivation of the initiator with the addition of different
deactivators can also be effected in the melt (DE 3703790). The
deactivation step is often carried out in combination with the
demonomerization and the elimination of unstable chain ends (DE 37
38 632 and EP 0 137 305). EP 0673 955 describes a process in which
crude polymer is treated with a steam which also contains small
amounts of volatile base. In this way, unconverted residual monomer
is removed and the initiator is deactivated. JP 05059255 states
that the initiator is deactivated by adding alkali metal or
alkaline earth metal oxides to the polymer melt.
The elimination of unstable terminal groups, which usually remain
in the crude polymer after the polymerization and in particular
lead to chain degradation when the polymer is heated, is also a
usual process step in the preparation of POM copolymers. The
unstable hemiacetal end groups in trioxane copolymers can be
selectively broken down, for example, by hydrolysis, i.e. by
treating the copolymer at temperatures of from 120 to 220.degree.
C. with pressurized water comprising alkaline material, especially
trialkylamines, and optionally with the addition of organic
solvents, especially lower alcohols, trioxane or dioxolane
(Kunststoff Handbuch, p. 316). After the hydrolysis, the polymer
must be precipitated again, washed and dried.
The object of the invention therefore is to develop a process which
makes it possible economically to prepare stable copolymers of
1,3,5-trioxane in a continuous process while avoiding the
deficiencies of the known processes.
It has now been found that thermally stable POM polymers can be
obtained if the initiator, which in general is a strong protonic
acid, is first dissolved in a formaldehyde dialkylacetal, a
substance which usually is known to regulate the molecular weight
of the POM polymer, and then added to the reaction mixture. The
invention eliminates the need to utilize an organic solvent
carrier, an unnecessary component in the reaction mechanism, for
the introduction of the protonic or Lewis acid into the reaction
mixture.
The present invention accordingly relates to a process for
preparing polyoxymethylene copolymers, wherein 1,3,5-trioxane is
polymerized with generally known comonomers in the presence of a
strong protonic acid initiator and in the presence of a
formaldehyde dialkyl acetal, and wherein the initiator is dissolved
in a portion of the formaldehyde dialkyl acetal before admixing the
same with trioxane and the comonomers.
In the prior art process of the production of POM polymers,
generally formaldehyde dialkyl acetals are used as molecular weight
regulators. Generally, the use of use a molecular weight regulator
has not been known to produce high molecular weight polymers.
The advantage of the process according to the invention is,
however, that through initial dissolution of the initiator in a
formaldehyde dialkylacetal it is possible to add a very low
quantity and controlled amount of the initiator in a perfectly
dispersed state to the monomer mixture thereby controlling the
reaction rate. Due to the very low quantity of initiator in the
reaction mixture it is possible to also produce high molecular
weight material although there is a small amount of molecular
weight regulator present in the reaction mixture. According to the
invention, it is possible to avoid contamination of the monomers
and resulting polymer with substances which are critical to the
polymerization process. For example, it is no longer necessary to
add an agent to deactivate the initiator. In principle, it is also
no longer necessary to perform hydrolysis to the crude polymer.
However, to further reduce the content of unstable terminal groups
in the polymer, it is advantageous to perform hydrolysis
thereto.
In the process according to the invention, the initiator can be
dissolved in a part of or in the total amount of formaldehyde
dialkyl acetal used. The formaldehyde dialkyl acetal comprising the
dissolved initiator usually is added to the mixture of trioxane and
comonomers, i.e. the reaction mixture. A further predetermined
amount of formaldehyde dialkyl acetal can be directly added to the
reaction mixture before or after admixing the formaldehyde dialkyl
acetal and dissolved initiator solution therewith.
In another working example, the formaldehyde dialkyl acetal
containing the dissolved initiator is premixed with the comonomers
before admixing the same with the trioxane. Optionally, a further
predetermined amount of formaldehyde dialkyl acetal may be added to
the reaction mixture afterwards.
In the process according to the invention strong protonic acids, in
particular heteropoly acids, perchloric acid and
perfluoroalkanesulfonic acids, can be used as initiator.
Trifluoromethanesulfonic acid is the preferred initiator. The
amount of the initiator generally is at least about 0.01 to about
1.0 ppm, based on the total amount of trioxane and comonomers.
Preferably the amount of the initiator is from about 0.03 to about
0.4 ppm, and preferably from about 0.05 to about 0.2 ppm, based on
the total amount of trioxane and comonomers.
Suitable formaldehyde dialkyl acetals used according to the
invention are formaldehyde dimethyl acetal, formaldehyde diethyl
acetal, formaldehyde dipropyl acetal, and formaldehyde dibutyl
acetal. Formaldehyde dimethyl acetal, i.e. methylal, is preferred.
The amount of formaldehyde dialkyl acetal, generally, is from about
3.4 to about 34 mmol per total kg of trioxane and comonomers.
Suitable comonomers of the present invention are generally known
and may be selected from the group consisting of ethylene oxide,
1,3-dioxolane, 1,3-trioxepane, diethylene glycol formal,
1,4-butanediol formal, 1,3-dioxane, propylene oxide, trimethylene
oxide, butadiene oxide, o-xylene glycol formal, thiodiglycol
formal, 1,3-oxthiolane, and mixtures thereof. Particularly
preferable comonomers are ethylene oxide, 1,3-dioxolane, diethylene
glycol formal, and 1,4-butanediol formal. The amount of the
comonomer utilized herein may range from about 0.2 to about 10% by
weight, preferably from about 0.4 to about 5% by weight, based on
the total amount of trioxane and comonomers.
The polymerization process according to the invention can be
performed in any polymerization reactor or combination of reactors
known for the production of POM polymers.
Further, antioxidants, acid acceptors, lubricants, waxes, UV
stabilizers, nitrogen-containing co-stabilizers and other products
known in the art for POM may be used as stabilizers and additives,
either individually or in combination.
All fillers and reinforcing materials customary and known for
plastics, in particular polyacetal copolymers, may be used as
fillers and reinforcing materials.
EXAMPLES
Example 1
In a batch reactor operated at a temperature of about 80.degree. C.
and a pressure of about 1 atms., 96.6% by weight of trioxane was
mixed with 3.4% by weight of dioxolane to form a monomer mixture.
To this mixture 0.2 ppm of trifluoromethanesulfonic acid (TFMSA)
dissolved in 500 ppm of formaldehyde dimethyl acetal (Methylal)
were added, the quantities in ppm being based on the total weight
of the monomer mixture. After an induction period of about 30
seconds the polymerization started. The obtained crude polymer was
quenched in a water/triethylamine mixture and subsequently
hydrolyzed at 170.degree. C. in a water/methanol (10/90) mixture
from which it was precipitated at room temperature. From the dried
product the melt viscosity ratio (MVR) value and, through the
measurement of the formaldehyde formation during 1 hour at
170.degree. C. under alkaline conditions, the content of unstable
terminal groups was determined (for data, cf. Table 1).
Examples 2 and 3
The procedure in Example 1 was utilized herein and additional
amounts of methylal were added to the monomer mixture. The MVR and
percent of unstablized terminal groups are shown (for data, cf.
Table 1).
Comparative Examples 4 through 6
Utilizing the procedure of Example 1, 96.6% by weight of trioxane
was mixed with 3.4% by weight of dioxolane to form the monomer
mixture. To this mixture 50 ppm of BF.sub.3 gas and 0 ppm, 400 ppm
or 1000 ppm of formaldehyde dimethyl acetal (Methylal) were added,
respectively, to the monomer mixture of Examples 4,5 and 6, the
quantities in ppm being based on the total weight of the monomer
mixture and being adjusted to obtain products having the same MVR
values as in Examples 1-3, respectively. After an induction period
of 30 seconds the polymerization started. The obtained crude
polymer was quenched in a water/triethylamine mixture and
subsequently hydrolyzed at 170.degree. C. in a water/methanol
(10/90) mixture from which it was precipitated at room temperature.
The dried product was analyzed as in Examples 1-3.
TABLE-US-00001 TABLE 1 TFMSA in Additional Total Unstable Thoxane
Dioxolane BF.sub.3 Methylal Methylal Methylal MVR terminals Example
% b.w. % b.w. ppm ppm/ppm ppm ppm m/10 cm % 1 96.6 3.4 0.2/500 0
500 2.5 0.04 2 96.6 3.4 0.2/500 500 1000 9 0.035 3 96.6 3.4 0.2/500
1000 1500 27 0.03 4 96.6 3.4 50 0 0 2.5 0.25 5 96.6 3.4 50 400 400
9 0.20 6 96.6 3.4 50 1000 1000 27 0.18
In accordance with the data shown in Table 1, after the MVR values
were adjusted in Examples 3, 4, and 5 to be equal to those of
Examples 1, 2 and 3, the percentage of unstable terminal end groups
of the polymers were dramatically reduced (see Examples 1, 2 and 3)
wherein small amounts of trifluoromethanesulfonic acid dissolved in
methylal were added to the reaction mixture.
* * * * *