Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-11-22
2002-07-02
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C528S302000, C528S306000, C528S308000, C528S308600, C525S445000
Reexamination Certificate
active
06414085
ABSTRACT:
TECHNICAL FIELD
The present invention pertains to the field of unsaturated polyester resins and to molding compositions containing these unsaturated polyester resins and a copolymerizable unsaturated monomer.
BACKGROUND ART
Unsaturated polyester resins (“UPR”) are well known items of commerce with a myriad of uses, for example as matrix resins for fiber reinforced composites, fillers for autobody repair, molding of plastic parts, and in sheet molding compound (SMC). Unsaturated polyester resins have a polyester backbone which incorporates or is modified to contain reactive ethylenic unsaturation. These unsaturated polyester resins are most often admixed with styrene or other unsaturated co-monomers such as alkylmethacrylates to produce the ultimate molding resin, which is also frequently termed an unsaturated polyester resin despite the presence of considerable amounts of styrene. In the present invention, the term “UPR” refers to the unsaturated polyester resin only, i.e., the styrene-free resin. UPR should be distinguished from thermoplastic polyester molding resins prepared from saturated monomers, which are moldable solids useful for polyester fibers, sheet goods, and beverage bottles.
The majority of UPR are derived from a “saturated” aromatic dicarboxylic acid or acid anhydride containing no ethylenic unsaturation, i.e., isophathalic acid and/or phthalic anhydride; a glycol or mixture of glycols, i.e., ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, or neopentylglycol; and a fumarate precursor, i.e., maleic anhydride. The choice of diol is often important for the end use. For example, UPR prepared with propylene glycol tend to have both lower water absorbtion properties as well as higher hydrolytic stability than those prepared from primary diols such as ethylene glycol and diethylene glycol.
A variety of processes have been proposed for manufacture of UPR. However, the conventional process involves a first reaction of the aromatic dicarboxylic acid with glycol to produce a diol-terminated polyester oligomer of the desired molecular weight, followed by reaction with maleic anhydride (“two stage process”). One stage reactions are not generally possible due to poor resin performance. The second stage is typically concluded by allowing sufficient time at elevated temperatures to convert maleate unsaturation to fumarate unsaturation. An example of UPR production may be found in U.S. Pat. No. 5,880,225, herein incorporated by reference.
As in other industrial processes, numerous factors are important in dictating the economics and performance of UPR. For example the process time in preparing UPR is desirably as short as possible. From both a cost, and performance standpoint, would be highly desirable to employ terephthalic acid as the aromatic dicarboxylic acid in UPR production, as terephthalic acid has significant economic benefits due to its widespread use in manufacture of polyethylene terephthalate (PET), and also exhibits excellent high temperature characteristics. However, UPR based on terephthalic acid, although commercially available, constitute only a very small portion of commercial UPR despite these cost and performance benefits. Several factors dictate this result.
First, polyesterification when employing terephthalic acid is very slow. Thus, high temperatures, which require pressurized reactors, and the use of transition metal esterification catalysts are generally necessary. The use of catalysts such as tin and transition metal compounds are particularly effective in lowering reaction time and temperature; however, the UPR product generally exhibits loss of corrosion resistance due to the residual catalyst content. Reaction at high temperatures over extended periods of time frequently leads to highly colored products, particularly in the presence of metal salts, and the pressurized reactors necessary for high temperature production are expensive both from capital and operational standpoints. Second, terephthalic acid is insoluble in the starting glycol, especially when propylene glycol is used, and is only sparingly soluble in the initially produced polyester oligomers as well. This insolubility is well documented. For example, in the production of saturated polyesters for polyester fibers, as disclosed in U.S. Pat. No. 5,916,677, the starting terephthalic acid and diol are slurried together.
Of the diols which have been used in polyester production, ethylene and propylene glycols have been the most dominant. Diethylene glycol is also used to a considerable extent. Neopentyl glycol, like ethylene glycol and diethylene glycol is a primary glycol, hence it has also been used in polyesters. Diols such as 1,4-cyclohexanediol and particularly cis- and trans 1,4-cyclohexanedimethanol have been touted as being suitable for high temperature and high strength saturated polyester molding resins. However, these diols are not inexpensive, thus limiting their use. Moreover, terephthalate-based polyesters prepared from diols such as ethylene glycol, diethylene glycol, and neopentyl glycol are generally not sufficiently soluble in styrene to be useful as casting, sheet molding, and matrix resins for fiber reinforced products.
One diol which has seen only limited use is 2-methyl-1,3-propanediol. This diol is commercially available as MPDiol® from the Lyondell Chemical Company, and has been suggested for use as a diol in preparing thermoplastic (saturated) polyester resins. In U.S. Pat. No. 4,381,379, mixtures of 2-methyl-1,3-propanediol and polytetramethylene ether glycol (“PTMEG”) are suggested for use with terephthalic acid as a thermoplastic molding resin. However, the patentees caution against use of more than 25% by weight of 2-methyl-1,3-propanediol/terephthalate moieties. U.S. Pat. No. 4,415,727 teaches modified polyethyleneterephthalate thermoplastic molding resins prepared from a glycol mixture of ethylene glycol and up to 15 mol percent 2-methyl-1,3-propanediol. The preparation requires in excess of 8 hours even when catalyzed by tetralkoxytitanium compounds. U.S. Pat. No. 4,436,896 similarly prepared thermoplastic terpolyesters from diol mixtures of two low molecular weight diols, 2-methyl-1,3-propanediol and 1,6-hexanediol, and a high molecular weight polyoxyalkylene ether glycol. U.S. Pat. No. 5,380,816 discloses linear polyester diols prepared by the monobutyl tin oxide catalyzed reaction of 2-methyl-1,3-propanediol and mixtures of aromatic and aliphatic dicarboxylic acids, for coatings employing aminoplast crosslinking resins. U.S. Pat. Nos. 4,396,746 and 5,614,299 both disclose thermoplastic polyester molding resins employing, as the diol component, mixtures of 2-methyl-1,3-propanediol and cyclohexanedimethanol.
Seldom has 2-methyl-1,3-propanediol been used in terephthalate-based unsaturated polyester resins, and then only in minor amounts, and always in catalyzed reactions. For example, U.S. Pat. No. 5,373,058 employs mixtures of 2-methyl-1,3-propanediol and 40 mol percent ethylene glycol in a catalyzed polyesterification to produce an intermediate acid-functional oligomer which is then reacted with glycidylmethacrylate to produce a methacrylate-terminated polyester. Addition of styrene and considerable quantities of low profile additives is said to provide sheet molding compound having low shrinkage. However, glycidyl methacrylate is an expensive component. The Lyondell Chemical Co. and the former ARCO Chemical Co. have touted MPDiol™ for use in unsaturated polyesters prepared by the conventional, catalyzed esterification of phthalic anhydride and isophthalic acid, for many years. However, these aromatic dicarboxylic acids are much more reactive than terephthalic acid.
DISCLOSURE OF INVENTION
It would be desirable to produce terephthalate-based UPR in short cycle times, but without employing a catalyst. It would be further desirable to prepare UPR in a one pot process, where aromatic dicarboxylic acid, glycol, and unsaturated dicarboxylic acid anhydride are simultaneously present. It would be further desirable to prepare UPR which e
Karas Lawrence J.
Puckett Paul M.
Acquah Samuel A.
Arco Chemical Technology L.P.
Brooks & Kushman P.C.
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