Unsaturated polyester-modified flexible copolymers for use in sheet molding compositions

#This invention relates to compatible saturated polyester polymer blocks having terminal alkylene maleate end blocks formulated into an unsaturated polyester or vinyl ester resin composition. These saturated polyester blocks may also have small amounts of aromatic diacids in their polymer backbone. The incorporation of these saturated polyesters, which have a lower Tg than the unsaturated polyesters, gives the composition higher strain to failure or crack values while maintaining high modulus, good molded part surface quality, and low in-mold shrinkage. These compositions are generally used in highly filled, fiber reinforced molded parts.

#Unsaturated polyester resins are well-known and useful materials for making molding compositions with a broad application in the manufacture of automotive and other products. One of the main deficiencies of cured unsaturated polyesters and fiber reinforced polyesters (FRP's) made from them is the inherent brittleness of the polymer matrix. Cracking at room and elevated temperatures is a principal cause of failure in production and in service of the molded parts.

#Improvements in crack resistance in resin materials for SMC's have been reported by the incorporation of flexible ethers (diethylene glycol) or acids (adipic acid) in the unsaturated polyester. This approach using the so-called flexible polyesters has been only moderately successful, since the modulus and high temperature properties of the molded composite significantly decline with increasing amounts of these materials, and frequently they are faulted as sacrificing too much in their mechanical properties and dimensional stability.

#FIGS. 1, 2, and 3 compare the stress/strain curves of an unsaturated polyester control composition and formulation f, which substitutes on an approximately 20 weight percent basis a hydroxypropylmaleate terminated poly(propylene adipate) polymer for a 20 weight percent portion of the polyester resin, low profile additive, styrene, and divinylbenzene in the control composition. FIG. 1 shows the flexural stress/strain curves at 23.degree. C. of the two formulations. FIG. 2 shows the Flexural stress/strain curves at 150.degree. C. of the two formulations. FIG. 3 shows the tensile stress/strain curves at 150.degree. C. of the two formulations.

#The B portion of the block copolymers of the present invention can generally be any flexible polymer. Such flexible polymers are generally defined as any polymer which has a Tg of about 0.degree. C. or less and preferably below minus 20.degree. C. often are liquid, and are readily known in the art and to the literature, including the preparation thereof.

#A preferred class of the B block flexible polymers is the various saturated polyesters made from aliphatic dicarboxylic acids or aliphatic anhydrides and glycols, and such are well known to the art and to the literature, as is the preparation thereof, and are commercially available. The aliphatic dicarboxylic acids and anhydrides have from 1 to 10 carbon atoms, with specific examples including carbonic acid, malonic acid, succinic, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, the anhydride counterparts thereof, and the like, with adipic acid generally being preferred. Optionally included within the above aliphatic dicarboxylic acids are minor amounts, that is up to 40 percent by weight based upon a total weight of the acids, of an aromatic diacid such as phthalic acid, isophthalic acid, terephthalic acid, and the like. Mixtures of all of the above acids can be utilized as well. The glycols generally have from 2 to 15 carbon atoms with specific examples including ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, pentane diol, hexane diol, cyclohexanedimethanol dipropylene glycol, diethylene glycol, pinacol, and the like. Preferred glycols include diethylene glycol or a mixture of propylene glycol with ethylene glycol.

#The polyester or A block is generally an unsaturated polyester having an average molecular weight of between 100 or 500 to 2,000 or 5,000 and has one, or less desirably two, functional end groups thereon such as hydroxyl, carboxyl, or amine. The polyesters are made by the copolymerization of generally cyclic ethers typically containing 2 or 3 carbon atoms in the ring and an unsaturated anhydride, as well as optional saturated anhydrides using double metal complex cyanide catalysts. Generally any cyclic oxide can be utilized such as 1,2-epoxides, oxetanes, and the like, with the cyclic ether having a total of up to 18 carbon atoms, as for example 2 carbon atoms in the ring and up to 16 carbon atoms in the side chains. Such cyclic oxide monomers can also contain one or more aliphatic double bonds and preferably only contain one aliphatic carbon to carbon double bond. Examples of suitable cyclic oxides include ethylene oxide (1,2-epoxy ethane), 1,2-propylene oxide, 1,2-butene oxide, 1,2-hexene oxide, 1,2-dodecane monoxide, isobutylene oxide, styrene oxide, 1,2-pentene oxide, isopentene oxide, 1,2-heptene oxide, allyl gylcidyl ether, isoheptene oxide, 1,2-octene oxide, methyl glycidyl ether, ethyl glycidyl ether, phenyl glycidyl ether, butadiene monoxide, isoprene monoxide, styrene oxide, tolyl glycidyl ether, 1,2-pentadecene oxide, epichlorohydrin, glycidoxypropyltrimethoxysilane, and the like. Generally, ethylene oxide, propylene oxide, and butylene oxide are preferred.