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
2002-03-18
2003-04-29
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, C525S437000, C525S445000
Reexamination Certificate
active
06555623
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the preparation of unsaturated polyesters from 2-methyl-1,3-propanediol (MPD). In particular, the unsaturated polyester prepared has a high fumarate content.
BACKGROUND OF THE INVENTION
Unsaturated polyesters are condensation polymers with a polyester backbone formed from a glycol and an unsaturated diacid. Commonly used unsaturated diacids are maleic acid, fumaric acid, and maleic anhydride. Even though fumaric acid offers many advantages in production of unsaturated polyesters, it is seldom used because it is expensive. Saturated diacids are often used with the unsaturated diacid to control the degree of unsaturation and to modify the physical properties of the resulting polyester. For instance, the inclusion of phthalic anhydride reduces the tendency of the unsaturated polyester to crystallize and thereby improves its solubility in styrene.
Unsaturated polyesters are crosslinked, through the unsaturation, with ethylenic monomers such as styrene. To cure well with styrene, the unsaturated polyester needs a high degree of fumarate unsaturation (fumarate/maleate ratio greater than 90/10). Maleate-containing polyesters do not readily cure with styrene. However, most unsaturated polyesters are commercially made from maleic anhydride. Thus, it is crucial to effectively isomerize maleate to fumarate during the condensation polymerization.
Many glycols are used for making unsaturated polyesters. Examples are ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, and neopentyl glycol. The degree of isomerization of maleate to fumarate largely depends on the glycol used. In general, the use of a primary glycol leads to a low degree of isomerization, while the use of a secondary glycol leads to a high degree of isomerization. For instance, the esterification of maleic anhydride with neopentyl glycol, ethylene glycol, and propylene glycol gives fumarate/maleate ratios of 50/50, 75/25, and 93/7, respectively. See
Ind. Eng. Chem. Prod. Res. Dev.
3(3), 218 (1964). Although propylene glycol gives a high fumarate content, it has lower reactivity toward condensation and the resultant unsaturated polyester often has a dark color and poor appearance.
2-Methyl-1,3-propanediol (MPD) became commercially available only within the last decade. It is an easily handled liquid, it has a high boiling point, and it has two primary hydroxyl groups for rapid condensation. However, like other primary glycols, MPD disadvantageously gives unsaturated polyesters having low fumarate/maleate ratios (60/40 to 70/30). Many efforts have been made to increase the fumarate content of unsaturated polyesters made from MPD. One approach is to increase the polymerization temperature. However, increasing reaction temperature often causes color problems in the product.
Co-pending application Ser. No. 09/946,326 teaches a process for making unsaturated polyesters from MPD that have fumarate/maleate ratios greater than 85/15. However, the process requires the use of propylene glycol to boost the isomerization of maleate to fumarate in a late stage of the polymerization. In sum, a better way to make a MPD-based unsaturated polyester is needed. Ideally, the unsaturated polyester would have a high fumarate content.
SUMMARY OF THE INVENTION
The invention is a process for making unsaturated polyesters from 2-methyl-1,3-propanediol (MPD). The process comprises two steps. First, one equivalent of an aromatic dicarboxylic acid derivative reacts with about two equivalents of 2-methyl-1,3-propanediol (MPD) to produce an ester diol.
Second, one equivalent of the ester diol reacts with from about 1.1 to about 1.9 equivalents of maleic anhydride. We surprisingly found that the resultant unsaturated polyester has a fumarate/maleate ratio of 90/10 or grater, which is significantly higher than the conventional unsaturated polyester prepared from MPD.
The invention also provides a novel unsaturated polyester. The unsaturated polyester consists essentially of recurring units of MPD, an aromatic dicarboxylic acid, maleic acid, and fumaric acid. It has a fumarate/maleate ratio of 90/10 or greater. The unsaturated polyester gives its thermoset polymer improved heat resistance.
DETAILED DESCRIPTION OF THE INVENTION
The process of the invention comprises two steps. The first step involves reacting one equivalent of an aromatic dicarboxylic acid derivative with about two equivalents of 2-methyl-1,3-propanediol (MPD) to produce an ester diol. Suitable aromatic dicarboxylic acid derivatives 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).
The aromatic dicarboxylic acid and MPD are preferably reacted at a temperature within the range of about 175° C. to about 225° C., more preferably from about 185° C.to about 215° C., and most preferably from about 195° C. to about 210° C. One advantage of the invention is that a high reaction temperature is not needed in the first step because MPD has two primary hydroxyl groups that react rapidly with the aromatic dicarboxylic acid derivatives. Lower reaction temperature gives a product with lighter color and better appearance.
Preferably, the reaction is performed under an inert atmosphere to minimize oxidative side-reactions. This is particularly important when the reaction temperature is relatively high. Preferably, a steam-jacketed reflux condenser is used. Such a condenser allows an efficient removal of water or other volatile products from the reaction mixture but keeps MPD and other reactants in the reactor. The use of a steam-jacketed reflux condenser also helps to avoid a high temperature, which otherwise is often needed to drive water out of the reaction mixture.
Optionally, an esterification or transesterification catalyst is used in the first step to accelerate the formation of the ester diol. Suitable catalysts include organotin compounds and zinc salts such as zinc acetate, zinc propionate, butyltin oxide hydroxide, dibutyltin oxide, and phenyltin oxide hydroxide. The catalyst can be used in an amount up to about 5,000 ppm based on the amount of the unsaturated polyester. Preferably, the catalyst is used in an amount from about 1 to about 500 ppm.
The equivalent ratio of MPD/aromatic dicarboxylic acid derivative is about 2/1 so that the ester diol has a low acid number. The ester diol preferably has an acid number less than about 15 mg KOH/g, more preferably less than about 10 mg KOH/g and most preferably less than about 5 mg KOH/g. The ester diol so produced has little or no color.
In the second step, one equivalent of the ester diol reacts with from about 1.1 to about 1.9 equivalents of maleic anhydride to produce an unsaturated polyester. Preferably, the equivalent ratio of maleic anhydride/ester diol is within the range of about 1.1/1 to about 1.8/1. More preferably, the ratio is from about 1.2/1 to about 1.5/1. While a sufficient amount of maleic anhydride is needed to introduce a high degree of unsaturation, using too much maleic anhydride reduces the fumarate/maleate ratio and thereby adversely reduces the reactivity of the unsaturated polyester (see Comparative Example 7).
The second step may be performed under essentially the same conditions as the first step. The reaction temperature is preferably within the range of about 175° C. to about 225° C., more preferably from about 185° C. to about 215° C., and most preferably from about 195° C. to about 210° C. Conventional processes for making unsaturated polyesters from MPD often need an “over-cooking”, i.e., heatin
Albano Paul A.
Armstead Diandre
Karas Lawrence J.
Puckett Paul Malcolm
Yang Lau S.
Acquah Samuel A.
Arco Chemical Technology L.P.
Guo Shao
LandOfFree
Preparation of unsaturated polyesters does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Preparation of unsaturated polyesters, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Preparation of unsaturated polyesters will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3094318