Abstract: A low-profile unsaturated polyester resin composition, consisting essentially of (A) an unsaturated polyester, (B) a monomer copolymerizable with the unsaturated polyester, and (C) an A-B type block copolymer comprising an A segment which is a product using vinyl acetate and butyl acrylate as raw materials and a B segment which is a product solely of styrene or a product using styrene and a monomer copolymerizable with styrene as raw materials.

Abstract: A plastic lens which has high hardness and excellent scratch resistance and can form a transparent and uniform reflection preventing film through vacuum deposition, is produced by mixing(a) diethylene glycol bis(allyl carbonate) with(b) at least one of organic peroxides having a decomposition temperature at selected half-life value for ten hours of not higher than 80.degree. C. and(c) at least one of organic peroxides having a decomposition temperature at selected half-life value for ten hours of 90.degree.-110.degree. C., which have no copolymerizability to the diethylene glycol bis(allyl carbonate) (a), as a polymerization initiator, and polymerizing and casting the resulting mixture in a desired lens-forming mold.

Abstract: Disclosed herein is a low shrinkable unsaturated polyester resin composition consisting of (A) 20-70% by weight of an unsaturated polyester, (B) 28-60% by weight of a monomer polymerizable with the above unsaturated polyester, and (C) 2-20% by weight of a block copolymer mixture. The mixtures of the monomer (B) and the block copolymer mixture (C), and a mixture of the polyester (A), the monomer (B), and the block copolymer mixture (C) are in a non-aqueous dispersion state. The block copolymer mixture is obtained by polymerizing either one of the monomers defined below in (a) and (b) with a polymerization initiator a polymeric perioxide represented by the formula: ##STR1## in which R.sub.1 represents a divalent branched hydrocarbon group having 10-30 carbons, and R.sub.2 and R.sub.

Abstract: An unsaturated polyester resin composition comprising an unsaturated polyester resin, a polymerizable monomer and a mixture of block copolymers having acid groups prepared by first copolymerizing in a first copolymerization reaction a polymeric peroxide with a monomer A or B, or with an unsaturated acid together with monomer A or B, thereby obtaining a copolymer having peroxy bonds in the molecule thereof, which copolymer is further copolymerized in the second copolymerization reaction with each of monomers A or B or the unsaturated acid which were excluded in the first copolymerization reaction to give the block copolymer mixture, which composition shows no segregation of the low shrinkage agent on thickening by a thickener and the said composition gives cured moldings of reduced shrinkage which are excellent in many characteristics.