Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-08-12
2001-02-27
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C523S332000
Reexamination Certificate
active
06194503
ABSTRACT:
DESCRIPTION
This invention describes a new, advanced process for converting polytetrahydrofuran (PTHF) and copolymers of tetrahydrofuran with alkylene oxides into products with a narrow molecular weight distribution by means of a solvent-mixture treatment. The solvent mixture consists of methanol, an alicyclic compound and water.
Polytetrahydrofuran (PTHF) is, eg, an important intermediate in the production of polyurethanes or polyesters with soft segments, and is discussed in the monograph “Polytetrahydrofuran” by P. Dreyfus, Gordon and Breach Science Publishers, New York, London, Paris 1982. PTHF is normally obtained by way of cationic polymerization, with a fairly broad molecular weight distribution that usually deviates from the Gaussian distribution.
The polydispersity of a polymer is characterized by the quotient M
w
/M
n
, where M
w
is the weight-average molecular weight and M
n
is the number-average molecular weight. The quotient M
w
/M
n
is usually determined as the result of a gel permeation chromatography (GPC) measurement compared with the distribution of calibrating substances. The quotient can also be derived from the empirical formula M
vis
/M
n
, as is described in German patent No. 2453114. In this formula, log M
vis
=0.483 log viscosity (at 40° C. in poise) +3.0646. This relation is connected with the fact that the viscosity of polymers with a broad molecular weight distribution increases exponentially with the molecular weight.
Polymeric end products based on PTHF and having a narrow molecular weight distribution have altogether better mechanical properties than their counterparts with a broad molecular weight distribution. Accordingly, it is to advantage if products exhibiting a narrow molecular weight distribution are obtained already at the polymerization stage, or at least if, by way of a subsequent treatment, the molecular weight distribution is narrowed down afterwards.
According to the teaching of Canadian patent application No. 800 659, polymers with a relatively narrow molecular weight distribution can be obtained by stopping the polymerization reaction before equilibrium is reached. According to the German patent No. 2 453 114, the polydispersity can be reduced by partially degrading the polymers with acidic cation exchangers. Other patent applications, such as the U.S. Pat. No. 4,510,333 or the German patent No. 4 205 984, describe a polymerization which, to narrow down the molecular weight distribution, is conducted at stepped reaction temperatures. These measures are tedious, technically complicated, costly, and usually of limited effectiveness. Exact reproducibility with the method described is practically impossible, which means that the quotient M
w
M
n
is subject to constant fluctuations. However, a highly reproducible polydispersity M
w
/M
n
is indispensable for many PTHF and THF-copolymer applications, especially with regard to desired product properties.
In the U.S. Pat. No. 3,478,109, a process for removing low-molecular fractions by extraction of polymeric glycols with methanol or methanol and water is described. However, the low-molecular fractions are only removed satisfactorily if the polymeric glycols are subjected to the extraction as a solution in a hydrocarbon. Only in the case of a continuous or multistage discontinuous extraction of polymeric glycols does this method provide the diols suitable for the production, for example, of spandex fibers. The process described in the Japanese laid-open patent application No. 60-42421 for preparing THF polymers with a narrow molecular weight distribution likewise produces unsatisfactory results, as too does that according to the teaching of Japanese patent application No. 215 111/83. Especially where copolymers are required that have a narrow molecular weight distribution and contain more than 5 wt. % ethylene or propylene oxide, these methods are not particularly suitable. This also applies to the method described in the U.S. Pat. No. 4,762,951, which is based on a complicated three-phase system but which doesn't work for copolymers with a high alkylene oxide content (>30 wt %).
In the U.S. Pat. No. 4,933,503, an extractive procedure is described for preparing PTHF polymers of narrow molecular weight distribution. In this process, a polymer freed from low-molecular components by means of short-path distillation at a temperature of 200-260° C. and a pressure of <
0
.
3
mbar is mixed with a hydrocarbon, methanol and water. However, this process does not yield satisfactory results unless a three-phase system is formed. With the process of the present invention, by contrast, polymers with a highly desirable range of properties are already obtained on the basis of the simpler two-phase system.
All these processes are based on a complex, usually three-phase system, necessitating complicated apparatus and extremely careful process control.
One object of this invention was thus to provide a technically simple and economically efficient process for producing PTHF polymers with a narrow molecular weight distribution, the process allowing the separation of commercially available polymers into narrowly distributed fractions, each of which is suitable for a practical application, and there being no limitations in respect of molecular weight or copolymer content.
A further object of the invention was to provide a process for narrowing down the molecular weight distribution, with which, in the absence of appreciable losses, polymers especially in the technically interesting molecular weight range from 500 to 5000 Daltons are obtained that are not contaminated by catalysts. In addition, contamination of the polymers of the invention by crown ethers should, at the most, be very slight.
These objectives are established according to the invention by a process for fractionating tetrahydrofuran polymers or tetrahydrofuran-alkylene-oxide-copolymers, which is characterized in that one
(a) mixes the starting polymer with a cycloalkane (a), methanol (b) and water (c) at a temperature in the range from 0° C. to 40° C. and
(b) separates the different phases formed during mixing at a temperature in the range from 40° C. to 80° C.
The process of the invention is suitable, on the one hand, for fractionating tetrahydrofuran polymers. Such polymers are normally synthesized by the cationic, ring-opening polymerization of tetrahydrofuran (THF), with the formation of polyethers. These are also often referred to as polytetramethylene glycols (PTMG), polytetramethylene glycol ethers (PTMEG) or polytetramethylene oxide (PTMO). The process of the invention is also suitable for fractionating copolymers of tetrahydrofuran with alkylene oxides. Random or block copolymers are used with preference. It is to advantage if the alkylene oxide is one with 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms or, especially preferable, 2 to 5 carbon atoms. It is most preferable if the copolymer contains ethylene oxide and/or propylene oxide units.
The proportion of THF and alkylene oxide groups in the copolymer is generally 1:99 to 99:1 (in mol %), preferably 10:90 to 90:10 (in mol %) or, especially preferable, 20:80 to 80:20 (in mol %). The process of the invention is especially useful for fractionating copolymers with a high alkylene oxide content of ≧20 %, preferably ≧30% and, especially preferable ≧40%.
According to the invention, the starting polymer is mixed with a cycloalkane, methanol and water at a temperature in the range from 0° C. to 40° C. This step is referred to in the specification as step (a), or as the mixing step. In principle, every cycloalkane is suitable for the process of the invention, although it is to advantage if the cycloalkane is liquid within the temperature range indicated. Preference is given to a cycloalkane with 3-20, better 3-10 and best of all 5-7 carbon atoms. The carbon atoms can constitute part of the ring structure or part of the hydrocarbon substituents on the ring structure. Use is made preferably of cycloalkanes with a C3-C8 or, even better, C3-C6 ring struc
Cain Edward J.
Fulbright & Jaworski LLP
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