VINYl. COPOLYMER IN THE COSMETIC COSMOS 295 CH2:CH I c1 Vinyl Chloride CH I CH2:C i c=() () R Methacrylate Esters F gure 5.--Typical Comonomers Hardening. The most important factor determining the plasticizing efficiency is the length of the sidegroup R attached to the comonomer. The longer the R group, the greater the chain separation and therefore the plasticizing effect. Because the plasticizer is an integral part of the backbone we have perma- nent and nonmigratory plasticizing. Many internallyplasticized polyvinyl acetates show specific adhesion compared with conventionally plasticized homopolymers. It is also possible to harden the polymer through the use of selective comonomers which bring the polymer chains closer together. Two typical comonomers, vinyl chloride and the lower alkyl methacrylates, are shown in Fig. 5. The resultant copolymer will reflect the personality of the par- ticular comohomer used. For example, if we take a 50-50 vinyl chloride --acetate copolymer, it will adhere to vinyl chloride plastic (which acetate ordinarily does not) and to many polar surfaces such as metal, glass, wood, cloth, etc. (which chloride ordinarily does not). The chloride would also. bolster the heat and chemical resistance of the acetate. Of equally great importance in polymer pyrotechnics is the introduction of polar chemical groups such as amide, carboxyl and cyano into the back- bone. These modifications improve adhesion to more polar surfaces as well as provide a site for further chemical reaction. The carboxyl group is particularly sensitive to alkaline materials and thus provides soap solubility. CH_=CH I C=O NH= Acrylamide CH--C00H HOOC--CH Fumaric Ac d where R is Methyl Through Butvt• Acrylic Acid Maleic Acid (or Anhydride) CH•--CH:CH CH•=C--CH• COOH HOOC COOH Crotonic Acid Iraconic Acid Figure &--Addition of Polar Chemical Groups. CH2:CH CH--C00H C00H CH--C00H

296 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Up to now the material (Resyn 28-.1310) has been referred to simply as a polyvinyl acetate copolymer. More accurately, it is a polyvinyl acetate copolymer containing carboxyl groups through its copolymerization with one of the reactive acids shown in Fig. 6. The copolymei contains less than 2{) per cent by weight of the comonomer. Figure 7 is a picture of the beads as they are supplied. Figure 7.--Beads of National's Resyn 28-1310, polyvinyl acetate copolymer. Figure 8 shows the molecular configuration of a typical carboxyl co- polymer. Due to the presence of the carboxyl groups an unusual balance of prop- erties is present. The resin is soluble both in solvents and in water, a property possessed by a limited number of polymers. The solvents which may be used for the preparation of solutions are the alcohols, alcohol- ethers, ketones, esters, halogenated aliphatic hydrocarbons--in short, practically all of the common solvents, except the aliphatics such as hexane and heptane and aromatics such as toluene. Water solutions may be obtained by partial or complete neutralization of the carboxyl groups with ammonia or stronger alkalis. One group of coinpounds which performs an especially useful function is the aminohydroxys. The reaction product with the vinyl copolymer is a water soluble salt. One aminohydroxy in particular, AMPD, which is 2-amino-2-methyl-l,3-propanediol, offers permament neutralization with-