Sever Serban

Bromination of some styrene-diene block copolymers

Abstract The bromine addition at the polydiene block double bonds of a radial styrene-butadiene (SBS) and a linear styrene-isoprene (SIS) block copolymer (thermoplastic elastomers), in tetrahydrofurane solution at 0 °C, has been investigated by IR spectroscopy. In both cases the bromine reacts exclusively with the polydiene middle block double bonds; the polystyrene blocks are unaffected. The bromine reacts preferentially with the 1,4-type (cis and trans) double bonds of the polybutadiene block of SBS. At low bromination level (below 5%) the bromine reacts mainly with the 1,4-cis type double bonds of polyisoprene block of SIS, while at higher bromination level the bromine presents the same reactivity towards the 1,4-type (cis and trans) and vinylic (3,4-type) double bonds.

Mechanical properties of some brominated styrene–diene block copolymers

Abstract The mechanical properties of a brominated radial styrene–butadiene (SBS) and a linear styrene isoprene (SIS) block copolymer are investigated as a function of bromination level. The brominated SBS has been investigated by dynamic mechanical analysis (DMA). The mechanical properties of brominated styrene diene block copolymers indicate that the central (polyisoprene or polybutadiene) soft block loses some elasticity becoming harder. On the other hand, the miscibility of polystyrene hard blocks with the central soft blocks increases with increasing degree of soft block bromination. Consequently, mainly the tensile strength and the true tensile strength decrease with increasing bromine content. Bromination affects the mechanical properties of the SIS material more than those of the SBS.

HOMOPOLYMERIZATION AND COPOLYMERIZATION OF VINYL ACETATE IN NON-IONIC ICROEMULSIONS. I. A STUDY OF HOMOGENEITY DOMAINS

Abstract The homogeneity ranges of the systems consisting of the monomer (vinyl acetate or vinyl acetate + di-2-ethyl hexil maleate), cosurfactant (ethanol, n-propanol, n-butanol), surfactant (nonylphenol ethoxylate with 25 moles of ethylene oxide) and water were studied. Addition of the more hydrophobic comonomer requires utilization of a more hydrophobic cosurfactant. The increase of surfactant concentration entails the widening of the homogeneity range. The effect of the cosurfactants mentioned is accounted for by the modification of the cluster structure of water. Therefore the refractive indexes and the signals of protons in NMR spectra vary non-linearly with the composition of homogeneous systems. DSC analysis of the systems obtained has come out with two crystallization temperatures of water undercooled to −60°C in systems of concentrations close to those of organic and aqueous phases. The results plead for the existence of a structure which differs from that of the ideal solutions of the systems s...

Notes: Polymer-Water Interaction in Emulsion Copolymerization of Vinyl Acetate

Abstract In the case of copolymer latexes of vinyl acetate with maleic diesters, the amount of water bound to particles decreases with the increase of comonomer hydrophobicity. Increasing the concentration of bound water for more polar polymers determines a decrease of free water concentration. Therefore, the concentration of free surfactant and initiator in free water is higher and results in an increase of decomposition rate of potassium persulfate initiator. The increase of more polar copolymers hydration results in the increase of latex particle size. Abstract published in “Proc-Working Party on Polymer Reaction Engineering”, Thessaloniki, September 1996.