Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
1996-11-27
2001-06-05
Acquah, Samuel A. (Department: 1207)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S180000, C528S181000, C528S194000, C528S195000, C528S206000, C528S212000, C528S272000, C528S279000, C528S283000, C528S302000, C528S308000, C528S308600
Reexamination Certificate
active
06242558
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to polytrimethylene terephthalate. In one aspect, the invention relates to the production of modified polytrimethylene terephthalate which has a reduced tendency to form acrolein when heated in air.
Polytrimethylene terephthalate is a polyester useful in fiber applications in the carpet and textile industries. The manufacture of high molecular weight polytrimethylene terephthalate commonly involves the melt condensation polymerization of 1,3-propanediol and terephthalic acid (or an alkyl ester thereof) to a low molecular weight polymer, followed by solid-state polymerization to produce a high molecular weight polyester. The 1,3-propanediol can be derived from either acrolein or ethylene oxide, but in each case the product 1,3-propanediol typically contains carbonyl-containing by-products in amounts from 50 ppm to more than 1000 ppm.
The inventor has found that when polytrimethylene terephthalate is heated in air at temperatures greater than about 100° C., such as just prior to solid-state polymerization or when the finished polymer is being dried, acrolein is slowly formed. It would be desirable to produce polytrimethylene terephthalate and other 1,3-propanediol-based polyesters having a reduced tendency to generate acrolein when heated in air.
It is therefore an object of the invention to provide a modified 1,3-propanediol-based polyester. In a specific aspect, it is an object of the invention to provide polytrimethylene terephthalate having a reduced tendency to generate acrolein when heated in air.
SUMMARY OF THE INVENTION
According to the invention, a 1,3-propanediol-based polyester composition is provided which includes polyester molecules having at least one terminal group of the formula
in which R is a C
1-12
alkyl group including methyl, ethyl, isopropyl, t-butyl, t-amyl, 2-phenyl-2-propyl and the like; x is an integer from 1 to 4; at least one R group is ortho to the phenolic hydroxyl group; R′ is —(CH
2
)— or alkyl-substituted methylene; and y is an integer from 1 to about 20.
Such a modified 1,3-propanediol-based polyester composition has the advantage of generating less acrolein when heated in air than the corresponding unmodified polyester.
According to a further aspect of the invention, a modified 1,3-propanediol-based polyester composition is prepared in a process comprising:
preparing a polymerization reaction mixture comprising 1,3-propanediol, an aromatic diacid or an alkyl ester thereof, and a hindered phenolic ester/acid of the formula
in which R is a C
1-12
alkyl group; x is an integer from 1 to 4; at least one R is ortho to the phenolic hydroxyl group; R′ is —(CH
2
)— or alkyl-substituted methylene; y is an integer from 1 to about 20; G is oxygen or nitrogen; z is an integer from 1 to about 4; and R″ is a direct bond, H or C
1-30
hydrocarbyl or heterocarbyl,
and maintaining said reaction product mixture at a temperature within the range of about 180 to about 300° while removing byproduct water, for a time sufficient to produce a polyester composition of intrinsic viscosity at least about 0.8.
The process produces a polyester composition which generates less acrolein when heated in air than an unmodified 1,3-propanediol-based polyester.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, “1,3-propanediol-based aromatic polyester” refers to a polyester prepared by reacting at least one diol with at least one aromatic diacid (or alkyl ester thereof) in which at least 50 mole percent of the diol is 1,3-propanediol, and “polytrimethylene terephthalate” (“PTT”) refers to such a polyester in which at least 50 mole percent of the aromatic diacid is terephthalic acid (or an alkyl ester thereof). Other diols may include, for example, ethylene glycol, bis(3-hydroxypropyl)ether and 1,4-butanediol, and other diacids may include, for example, isophthalic acid and 2,6-naphthalene dicarboxylic acid. The condensation polymerization of polytrimethylene terephthalate usually generates as much as about 4 mole percent of the bis(3-hydroxypropyl)ether which, in effect, becomes a comonomer and is incorporated into the polyester chain. The modified 1,3-propanediol-based polyester of the invention, including polyesters and copolyesters, is formed in part of oligomeric or polymeric chains in which the phenolic residuum of a hindered phenolic acid or ester is bonded to one or both ends of the polymer chain via an ester linkage.
Such a modified polyester can be prepared by incorporating a hindered phenolic acid or ester in a polymerization reaction mixture containing 1,3-propanediol and an aromatic diacid (or alkyl ester thereof) and permitting the polymerization reaction to proceed until a polymer of desired molecular weight is achieved. One class of such polyesters can be represented by the formulas
in which n is about 4 to about 2500, preferably about 40 to about 250. One specific embodiment of this class can be represented by the formula
in which the polytrimethylene terephthalate composition includes polyester chains endcapped at one end with a specific hindered phenolic group.
It is not necessary that every polymer chain of the composition include a hindered phenolic group for the 1,3-propanediol-based polyester to exhibit reduced acrolein generation. On average, it is expected that advantageous results are achieved with about 0.000002 to about 2, preferably about 0.00002 to about 1.0, hindered phenolic terminal group per polymer molecule. For fiber-grade polytrimethylene terephthalate, the average number of hindered phenolic endgroups per polymer molecule will be within the range of about 0.001 to about 0.01, or about 1 out of every 100 to 1000 polymer molecules.
Numerous processes are known to prepare polyesters. Such processes may be batch or continuous and employ one or multiple stages. The currently preferred process is a two-stage condensation polymerization process which involves melt polymerization followed by solid-state polymerization. The first stage, melt polycondensation, includes two steps, a “pressure step” followed by a “vacuum step.” In the pressure step, a molar excess of the diol(s) is reacted with the aromatic diacid(s) (or alkyl ester(s) thereof), usually in the absence of added catalyst in the case of diacid reactions, at a temperature within the range of about 230 to about 300° C., preferably about 240 to about 270° C., under elevated pressure, preferably under nitrogen gas, within the range of about 20 to about 200 psi, preferably about 50 psi. Water is produced as a byproduct and is removed by suitable means such as overhead distillation. The polymerization conditions are selected so as to produce a relatively low molecular weight polyester having an intrinsic viscosity (i.v.) as measured in hexafluoroisopropanol of less than about 0.3, usually within the range of about 0.05 to about 0.25.
For the vacuum step of the melt polymerization stage, the pressure is reduced and a polycondensation catalyst such as a titanium or tin compound is added. The preferred catalyst is a titanium alkoxide such as titanium butoxide typically present in an amount within the range of about 10 to about 200 ppm titanium, based on the weight of the polyester.
The low molecular weight product of the first step is heated at a temperature within the range of about 240 to about 300° C. under less than atmospheric pressure for a time effective to increase the intrinsic viscosity of the starting material to at least about 0.5. During the reaction, additional water is produced as a byproduct and is removed overhead along with the excess diol.
In order to impart to the polyester maximum resistance to acrolein generation, the hindered phenolic acid or ester is added to the polymerization reaction mixture in the pressure step of the melt polymerization process. Alternatively, the hindered phenolic acid/ester can be added in the vacuum step or to the polymer melt prior to solid-stating, but addition under high vacuum conditions can result in a lower degree of modification of the polyester, particularly with th
Acquah Samuel A.
Shell Oil Company
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