Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-09-05
2002-12-10
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S271000
Reexamination Certificate
active
06492487
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for making unsaturated polyester resins. In particular, the invention is a process for improving the reactivity of polyester resins based on 2-methyl-1,3-propanediol.
BACKGROUND OF THE INVENTION
Unsaturated polyester resins (UPR) are condensation polymers of glycols and aromatic dicarboxylic acid derivatives, particularly phthalic anhydride, isophthalic acid, or terephthalic acid. An unsaturated dicarboxylic acid derivative, usually maleic anhydride, is included to enable crosslinking of the resin with vinyl monomers, especially styrene.
Many glycols (e.g., ethylene glycol, propylene glycol, neopentyl glycol) have been incorporated into UPR. A welcome addition has been 2-methyl-1,3-propanediol (MPD), which became available in commercial quantities only within the last decade. MPD offers significant process advantages to resin producers because it is an easily handled liquid, it has a high boiling point, and it has two primary hydroxyl groups for rapid condensations.
Reactive resins are needed for environmentally demanding uses such as corrosion-resistant storage tanks and gel coats. Resin reactivity (with the crosslinking monomer) is linked to the content of maleic anhydride-derived fumarate groups in the resin. Resins with high fumarate contents (>85%) react faster and cure more thoroughly to give more highly crosslinked thermosets with better physical properties, particularly resistance to water or aqueous mixtures. Traditionally, high fumarate contents have been induced by preparing resins at high temperature or by heating resins to isomerize maleate groups to fumarates. Unfortunately, higher reaction temperatures inevitably produce resins with high color. For many applications, including gel coats and cultured marble, a resin with high color is unacceptable.
Polyester resins produced from MPD using conventional condensation polymerization have relatively low fumarate contents (60-70%), and simply increasing the reaction temperature to promote isomerization causes the color problems noted above. Ideally, resins with high reactivity could be made from MPD without the need for a high-temperature isomerization step.
In the case of UPR produced from terephthalic acid (or dimethyl terephthalate) and MPD, there is another problem. Styrene solutions of MPD-based terephthalate resins are usually cloudy. This turbidity is undesirable because it intereferes with thixotropic additives and causes sedimentation upon storage of the resin.
In sum, the UPR industry needs a better way to make reactive MPD-based unsaturated polyester resins, i.e., ones having fumarate contents greater than about 85%. Preferably, the process would provide resins that cure rapidly and thoroughly with vinyl monomers to give thermosets with an excellent balance of physical properties, especially good water resistance. Ideally, the process would provide these reactive resins while maintaining good clarity and low color, attributes that are valuable for gel coats, cultured marble, and other end-uses.
SUMMARY OF THE INVENTION
The invention is process for making reactive unsaturated polyester resins from 2-methyl-1,3-propanediol. The process comprises two steps. First, an aromatic dicarboxylic acid derivative reacts with 2-methyl-1,3-propanediol at a temperature within the range of about 175° C. to about 225° C. to produce an ester diol intermediate. In a second step, the intermediate reacts with maleic anhydride and from about 15 to about 40 mole percent, based on the total glycol requirement, of propylene glycol at a temperature within the range of about 185° C. to about 215° C. The resulting unsaturated polyester resin has a fumarate content greater than about 85%.
We surprisingly found that shifting a portion of the glycol to the second step of the process, and substituting propylene glycol for 2-methyl-1,3-propanediol in that second step, enable the preparation of unsaturated polyester resins having fumarate contents greater than 85%. The high fumarate content helps the resins cure quickly and thoroughly with vinyl monomers, giving the resulting thermosets excellent water resistance. Especially high fumarate contents are achieved using the “T5 method,” in which the propylene glycol is added during the later stages of the second step, i.e., in the last hours of the polymerization. In sum, the invention provides a better way to make highly reactive, low-color, MPD-based unsaturated polyester resins.
DETAILED DESCRIPTION OF THE INVENTION
In the first step of the process of the invention, an ester diol intermediate is prepared by reacting 2-methyl-1,3-propanediol with an aromatic dicarboxylic acid derivative.
Suitable aromatic dicarboxylic acid derivatives are well known in the UPR industry, with their annual productions often measuring in the billions of pounds. They include at least one aromatic ring and two carboxy functional groups (acids, esters, acid halides, anhydride). Examples include unsubstituted and substituted phthalic anhydrides, isophthalic acids, terephthalic acids, dialkyl terephthalates, and the like. Particularly preferred, because of their low cost and commercial availability are phthalic anhydride, isophthalic acid, terephthalic acid, and dimethyl terephthalate. Suitable aromatic dicarboxylic acid derivatives also include recycled polyesters, especially thermoplastic polyesters such as polyethylene terephthalate (PET) or polybutylene terephthalate (PBT).
2-Methyl-1,3-propanediol (MPD) can be obtained from any suitable source. Commercially available MPD (sold as MPDiol® glycol by Lyondell Chemical Company) can be used in the process of the invention without further purification. The amount of MPD used is from about 1.4 to about 2.6 equivalents based on the amount of aromatic dicarboxylic acid derivative. A more preferred range is from about 1.6 to about 2.4 equivalents; most preferred is the range from about 1.9 to about 2.1 equivalents.
The aromatic dicarboxylic acid and MPD are reacted at a temperature within the range of about 175° C. to about 225° C. A more preferred range is from about 185° C. to about 215° C.; most preferred is the range from about 195° C. to about 210° C.
The reaction is conveniently performed by combining the reactants and heating until the condensation proceeds to the desired degree. Preferably, the reaction is performed under an inert atmosphere to minimize oxidative side-reactions. A steam-jacketed condenser (see Example 1) allows the water-of-reaction to evaporate but keeps glycols and molten aromatic dicarboxylic acid derivatives in the reactor.
Optionally, an esterification or transesterification catalyst is used in the first step to accelerate formation of the ester diol intermediate. This catalyst also facilitates further condensation in the subsequent reaction with maleic anhydride. The catalyst is often used to reduce the total reaction time required. Suitable esterification and transesterification catalysts are well known. Examples include organotin and organozinc compounds. Preferred organozinc compounds are zinc carboxylates such as zinc acetate, zinc propionate, or the like. Suitable organotin compounds are oxides, hydroxides, and mixed hydroxide oxides of tin. They include, for example, butyltin oxide hydroxide, dibutyltin oxide, phenyltin oxide hydroxide, and the like. A preferred catalyst is Fascat 4100, a product of Atochem, which is butyltin hydroxide oxide. When an esterification or transesterification catalyst is used, it is preferably used in an amount within the range of about 1 to about 5000 ppm, preferably from about 1 to about 500 ppm, based on the amount of finished polyester resin.
The esterification catalyst provides unanticipated benefits for MPD-terephthalates. For example, we produced an unsaturated terephthalate polyester resin with low color (APHA<100) and good clarity with butyltin oxide hydroxide as a catalyst (Example 1). Ideally, the resin will have no observable turbidity and will have an APHA color less than about 100, preferably less than about 90. These attributes a
Baylis Edmund
Gosset Patrice
Yang Lau S.
Arco Chemical Technology, l.p.
Boykin Terressa M.
Schuchardt Jonathan L.
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