The physical and morphological properties of heterogeneous mixtures of polystyrene with styrene: butadiene copolymers were determined. A mechanism of ultimate failure is proposed which permits the qualitative rationalization of the effects of copolymer composition, structure, and concentration upon certain physical properties of the mixture.

SynopsisBlock copolymers were prepared by anionic polymerization and their dynamic mechanical properties and thermal stability were compared with those of random copolymers and mechanical blends of similar composition. The block copolymers were prepared by means of Na-naphthalene as the initiator, under conditions leading in most cases to almost complete absence of contaminating homopolymers. The composition, structure, and molecular weight of the block copolymers were determined by ( a ) molecular weight determinations of the polymers before and after addition of the second monomer to the preformed polymeric anions, and ( b ) by fractionation and chemical analysis of the resulting fractions. The block copolymers prepared were of the type: poly(a-methyl styrene)polystyrenepoly( a-methylstyrene), polystyrenepoly( a-methylstyrene)-polystyrene, poly( methyl methacrylate)-polystyrene-poly( methyl methacrylate), and poly(ethy1ene oxide)-polystyrene-poly(ethy1ene oxide). The various block copolymer systems showed considerable differences in dynamic mechanical properties among themselves; they also had properties differing from those of copolymers and blends. 417

synopsisPolybutadiene rubbers of well-defined and varying molecular weight were prepared by anionic polymerization and used in the preparation of mass-polymerized polystyrene blends. The particle size of the dispersed rubber phase was varied by (1) controlling the relative viscosity, at phase inversion, of the two liquid phases composed of polystyrene and polybutadiene in styrene monomer; (2) by varying the intensity of mixing, ahd (3) by adding preformed polystyrene to the prepolymer, prior to phase inversion. The mechanical and dynamic properties of the resulting blends are found to be determined mainly by the particle size of the dispersed rubber phase, independently from the method used to obtain such size. The weight fraction of rubber phase, rather than the weight fraction of rubber charged, is found to correlate with the blend modulus and may also affect its level of toughness. Low molecular weight rubbers are found capable of efficient blend reinforcement, if the excessively small rubber particle size obtaihed by conventional processes is enlarged by incorporation of preformed polystyrene prior to phase inversion.

synopsisSaturated rubbers composed of ethylene-propylene or ethylene-vinyl acetate copolymers and terpolymers were used in the mass polymerization of high-impact styrene or styrene-acrylonitrile polyblends. Conventional polymerization procedures lead to blends of inferior mechanical properties. The cause for the poor performance was traced to the inability of the rubber-phase particles to preserve the desired size and particularity during processing.Polymeric blends of saturated rubbers having mechanical properties comparable to those obtainable with polybutadiene rubbers are prepared by (1) cohtrolling the rubberparticle size during prepolymerization and (2) preserving such size by crosslinking and grafting of the rubber following phase inversion. Extensive crosslinking of the rubber in the final blend must take place prior to processing to resist rubber particle deformation and disintegration during mechanical working. Rubber vulcanization is realized by the presence of peroxides in the final stages of polymerization; pendant unsaturation in the rubber is also needed or helpful. The reactivity and number of unsaturated groups in the rubber must be controlled to avoid excessive grafting prior to phase inversion and to permit efficient crosslinking following phase inversion.

SynopsisAnionic block polymerization of styrene onto polystyrene anions was found to be a useful diagnostic method which can readily reveal when the chosen polymerization conditions are conducive to complete catalyst consumption and quantitative block polymerization. With Na-naphthalene as initiator, it was shown that under the proper polymerization conditions (a) the initiator is essentially completely consumed in the first polymerization step, thus avoiding initiation of new chains in the following polymerization steps, ( 6 ) in each block polymerization step, styrene adds quantitatively to the preformed live anions, and ( c ) essentially no termination is observed throughout the successive block polymerization steps. The ratio of monomer to initiator greatly affects the efficiency of initiator consumption. The rate of agitation is also considered to play a dominant role.