Synthesis of nanosize polyisoprene and isoprene copolymer by microemulsion polymerization and their diimide hydrogenation

Abstract

The synthesis of nanosized polyisoprene (PIP) latex was carried out by differential microemulsion polymerization using 2, 2’-Azoisobutyronitrile (AIBN) as initiator. The main effects on PIP particle size were the amount of initiator, reaction temperature and stirring speed. The optimum conditions gave highest monomer conversion of 90% and average particle size of PIP of 27 nm. Chemical modification of unsaturated PIP has been an attractive process for preparation or improvement of polymeric materials. The graft copolymerization of methyl methacrylate (MMA) or styrene (ST) onto nanosized PIP was carried out by using cumene hydroperoxide (CHPO) and tetraethylene pentamine (TEPA) as redox initiators. The optimum conditions of methyl methacrylate graft on polyisoprene (MMA-g-PIP) synthesis gave high grafting efficiency (GE = 77%) and average particle size of MMA-g-PIP of 49 nm. For styrene graft on polyisoprene (ST-g-PIP) synthesis, the optimum condition gave high GE (75.9%) and monomer conversion (90%). While hydrogenation of nanosized PIP latex via diimide reduction was accomplished by using hydrazine hydrate/hydrogen peroxide and Cu2+ as catalyst and 75% hydrogenation was achieved. The nanosized PIP with smaller particle size gave higher rate constant than that of large particle size. Moreover, nanosized PIP and ST-g-PIP could be used as colloid stabilizer for pre-vulcanized natural rubber (NR) latex. Tensile strength, elongation at break and hardness of rubber blends were reduced by addition of nanosized PIP and ST-g-PIP. From ageing test, the retentions of tensile strength and elongation of compounds was high compared with NR. Morphology studies of the compounds showed that the addition of nanosized PIP and ST-g-PIP has changed the fracture surface behavior from ductile behavior to brittle type.