Joginder Lal

Effect of Crosslink Structure on Properties of Natural Rubber

Abstract Natural rubber-sulfur-diphenylguanidine vulcanizates were allowed to react with triphenylphosphine under nitrogen to convert polysulfidic crosslinks principally to di- and monosulfidic cro...

Novel thermoplastic elastomers via selective modification of conjugated diene block copolymers

Abstract A new class of amorphous thermoplastic elastomers, potentially important commercially and scientifically, was synthesized from conjugated dienes only by first synthesizing polyisoprene–polybutadiene–polyisoprene (IBI) block copolymers with 1,4-structures with alkyl lithium anionic initiators and subsequently selectively cyclizing polyisoprene blocks with different cationic catalysts. The resulting, essentially gel-free products, consisting of poly(cyclized isoprene-b-butadiene-cyclized isoprene), IcBIc, exhibited heterophase domains of Ic in the polybutdiene matrix. They exhibited stress–strain properties typical of polystyrene–polybutdiene–polystyrene, SBS, thermoplastic elastomers, for instance, Shell Oil Companys Kraton D-1101, but with improved tear strength and superior tensile strength versus temperature profile. This is because the Ic block has higher Tg by about 15°C than displayed by the polystyrene block. The best thermoplastic elastomers were obtained from IBIs containing 35–45 polyisoprene.

Effect of Sulfur during Radiation Curing of Poly(Vinyl Ethyl Ether) and Ethylene-Propylene Rubber

Abstract A study was made of the effect of sulfur, during radiation curing, on the physical properties of poly(vinyl ethyl ether) and an ethylene/propylene copolymer containing HAF carbon black. The presence of sulfur enabled the attainment of higher maximum tensile strength and generally higher crosslink density than when sulfur was omitted. Furthermore, the maximum tensile strength of the sulfur-containing samples was obtained at a lower radiation dose than in the corresponding control experiments. For a given swelling ratio, a higher tensile strength was generally obtained for samples irradiated in the presence of sulfur. For a given dose of radiation, the per cent elongation-at-break values of poly(vinyl ethyl ether) samples decreased as the amount of sulfur in the recipe was increased. In contrast, in the ethylene/propylene rubber the presence of sulfur resulted in an increase in the elongation values. The per cent sol values were also quite high for the ethylene/propylene vulcanizates as compared to...

The Microstructure of Cyclized Polyisoprene

The modification of polyisoprene by treatment with strong acid dates, in the case of natural rubber, to at least the late 18th century.1 It has been accepted for some time now that the resinification and loss of unsaturation accompanying such treatment are due, in most instances, to acid-catalyzed cyclization. The earlier work on such cyclization has been reviewed thoroughly1–6 and only a brief overview of the main aspects will be given here.