Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-04-23
2003-01-21
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S285000, C528S286000, C528S302000, C528S308600
Reexamination Certificate
active
06509438
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to 1,3-propanediol-based polyesters such as polytrimethylene terephthalate. In one aspect, the invention relates to polytrimethylene terephthalate which exhibits an excellent combination of ease of dyeability of PTT fabrics and fibers and stability under oxidative conditions which can reduce the need for adding stabilizers. More particularly, the invention relates to a new polytrimethylene terephthalate composition which can be made by a new all-melt process which is a unique composition which has an optimum level of dipropylene glycol units.
BACKGROUND OF THE INVENTION
Polytrimethylene terephthalate (PTT) is primarily a linear aromatic polyester which can be prepared from the condensation polymerization of 1,3-propanediol (PDO) and terephthalic acid (TPA). It is useful for carpet and textile fiber applications. For such commercial applications, it is desired to produce a product which has an intrinsic viscosity greater than about 0.70 dl/g, preferably greater than 0.8 dl/g, and good color stability. It is also desired to produce polytrimethylene terephthalate from PDO and TPA which has low tendency to generate acrolein when the polymer is heated in air, as it commonly is during downstream processing such as spinning into fibers. It is known that this instability can be controlled with additives such as hindered phenols such as described in copending, commonly assigned U.S. patent application Modified Polytrimethylene Terephthalate, Ser. No. 09/756,595, filed Dec. 7, 1998). It would be desirable, however, to produce polytrimethylene terephthalate (PTT) having an inherent stability against acrolein generation, i.e., having a lower dipropylene glycol (DPG) content, and which also is easy to dye when used to make fibers and fabrics. The tendency to produce acrolein is related to the amount of dipropylene glycol produced in the polymer during polymerization. DPG affects the dyeing of PTT and generally for that reason, the DPG level in the polymer has to be controlled within a narrow range (e.g. +/−0.1%) so that the polymer will dye consistently from lot to lot. DPG is used here to mean the residual unit [—OCH
2
CH
2
CH
2
OCH
2
CH
2
CH
2
O—] in the polymer chain. The following formula shows how the DPG units are copolymerized into the polymer to form a random copolyester (and how some end groups, such as allyl, carboxyl, methyl ester, may be incorporated):
comprising units A and B connected randomly to each other by ester bonds and wherein E is an endgroup attached to the diol end and consisting of either H or the residuum of a hindered phenol (defined herein), E′ is an endgroup attached to the carboxyl end and consisting of a PDO [—OCH
2
CH
2
CH
2
OH], a DPG [—OCH
2
CH
2
CH
2
OCH
2
CH
2
CH
2
OH], an allyl [—OCH
2
CH═CH
2
] group, a hydroxy [—OH] or, in the case when terephthalate diesters are used, alkoxy [—OR] group, such as methoxy [—OCH
3
], and where the average (or overall) molar proportion of DPG units to the total diol units, including endgroups, is the ratio of the sum of y+E′ (where E′ is the DPG endgroups only) to the sum of x+y+E′ (where E′ is the diol endgroups, including allyl, but excluding the hydroxy and alkoxy endgroups) and is in the range of from 0.006 to 0.02. The average degree of polymerization is x+y and is greater than about 50 and preferably greater than 80, typically greater than 100. The average number of endgroups E+E′ is 2 or less relative to x+y.
PTT made by prior art processes with dimethyl terephthalate (DMT), such as described in Japanese published patent application 51-142097 or U.S. Pat. No. 5,340,909, is inherently oxidatively stable (as shown in the comparative examples below) and does not form very much acrolein because the milder, less acidic DMT process reaction conditions form very little DPG (as shown in the examples below, 0.55 mole percent or less) but the polymer made this way is difficult to process. These DMT polymers are not as dyeable as the polymers of the present invention.
Current commercial processes for making PTT using TPA by polycondensation and solid state polymerization produce PTT, hereinafter referred to a “TPA PTT,” with higher levels of DPG (thus exhibiting an increased capacity to produce acrolein in downstream processing), i.e., generally in the range of 2 to 4 mole percent. These polymers are not as dyeable as the polymers of the present invention.
BRIEF SUMMARY OF THE INVENTION
According to the invention, a polytrimethylene terephthalate is provided having less than about 2 mole percent based on diol units, preferably 0.6 to 1.9 mole percent, more preferably 1.0 to 1.8 mole percent, dipropylene glycol monomer units copolymerized into the polymer. Total diol units also includes endgroups such as allyl, PDO, and DPG. Such compositions have a reduced tendency to generate acrolein when heated in air. These PTT polymer compositions exhibit improved and enhanced dyeability as compared to PTT made by the DMT processes and the TPA polycondensation/solid state polymerization processes.
DETAILED DESCRIPTION OF THE INVENTION
The invention compositions are prepared by the reaction of a molar excess of 1,3-propanediol (PDO) and terephthalic acid (TPA) by esterification followed by polycondensation, with the important proviso that the reaction conditions include maintenance of relatively low concentration of PDO and TPA in the melt reaction mixture. The condensation polymerization of polytrimethylene terephthalate can generate as much as about 2 to 4 mole percent of dipropylene glycol which, in effect, becomes a comonomer and is incorporated into the polyester chain. The all-melt process by which the PTT of this invention can be made dramatically decreases the amount of DPG generated (and hence also decreases the tendency for generation of acrolein during polymer processing) while maintaining a desired (for dyeability) minimum amount of DPG of 0.6 to less than 2.0, preferably 0.6 to 1.9, most preferably 1.0 to 1.8, mole percent based on total diol units. This PTT is referred to as “all-melt PTT.” One could adjust the DPG level by adding DPG monomer to the polymerization mixture or by treating the PDO with acid before polymerization (as shown in the examples).
As used herein, “1,3-propanediol-based aromatic polyester” refers to a polyester prepared by the condensation polymerization reaction of one or more diols with one or more aromatic diacids or alkyl esters thereof (herein referred to collectively as “diacid”) in which at least 80 mole percent of the diol(s) is 1,3-propanediol. “Polytrimethylene terephthalate” refers to such a polyester in which at least about 80 mole percent of the diacid(s) is terephthalic acid. Other diols which may be copolymerized in such a polyester include, for example, ethylene glycol, diethylene glycol, 1,4-cyclohexane dimethanol, and 1,4-butanediol; and other aromatic and aliphatic acids which may be copolymerized include, for example, isophthalic acid and 2,6-naphthalane dicarboxylic acid.
The preparation of the invention composition can be conveniently described by reference to an esterification step, a prepolymerization step, and a polycondensation step. The process can be carried out in batch or continuous mode. Each step can be carried out in multiple stages in a series of reaction vessels if desired for optimum efficiency in the continuous mode or for product quality. Each step is preferably carried out in the absence of oxygen. The following will describe the process in terms of the preferred continuous mode.
In the process, which will be described below in terms of the reaction of terephthalic acid and 1,3-propanediol to prepare polytrimethylene terephthalate, careful regulation of conditions in the esterification step is critical to the production of a high intrinsic viscosity (IV) PTT without the necessity of a solid state polymerization step. The important conditions are believed to be the ins
Brown Houston Slade
Dangayach Kailash
Kelsey Donald Ross
Reitz Hans
Scardino Betty Marrou
Haas Donald F.
Ribar Travis B
Seidleck James J.
Shell Oil Company
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