Abstract: An anti-shrink additive for unsaturated polyester resins of the formula: ##STR1## wherein, R is the remainder of a triol or tetrol,x is 3 or 4,z is .gtoreq.1,R' is the remainder of the radical of the product carrying the acid function, andn and n' being such that the molecular weight of the non-acidified propoxylated compound is preferably between 1,000 and 3,000.The invention also comprises the method of making such additive and unsaturated polyester resins containing such additive.

Abstract: This invention relates to an unsaturated polyester resin containing from about 1.5 .times.10.sup.-3 to 1.5.times.10.sup.-2 ether group per gram of resin and having a viscosity of from about 6 to 20 poise measured at 20.degree. C. on a 60% by weight solution thereof in styrene, comprising the condensation reaction product of at least one dibasic acid or corresponding anhydride, at least one of which is a polyol and at least one of which is a saturated linear ether alcohol containing at least one ether group; preimpregnated materials comprising said resin; and to the methods of making such resin.