Preparation and characterization of poly(stearyl methacrylate) grafted natural rubber in latex stage

- DPNR-graft-PSMA was successfully prepared by the graft-copolymerization of SMA onto DPNR in latex stage.
- The highest conversion of 95 mol% and grafting efficiency of 62 mol% were obtained.
- The melting temperature, Tm and degree of crystallinity, w/w% increased after graft-copolymerization.
- The nanomatrix structure was formed and the highest stress at break of 13 MPa was achieved.
- The abrupt increase in the stress at strain 3 may be due to the nucleating effect of the crystallizable stearyl groups.
- The strain-induced crystallization of the DPNR-graft-PSMA is promoted by the effect of the PSMA.

An attempt to prepare graft copolymer of natural rubber, NR and poly(stearyl methacrylate), PSMA, was made to improve mechanical properties of NR, since the grafted PSMA was composed of crystallizable stearyl groups as a nucleating agent and methacrylate units. The graft-copolymerization of stearyl methacrylate (SMA) onto deproteinized natural rubber (DPNR) was performed in latex stage with tert-butylhydroperoxide (TBHP)/tetraethylenepentamine (TEPA) as an initiator, after purifying the rubber with urea and sodium dodecyl sulphate followed by centrifugation. The optimal conditions for the graft-copolymerization were determined as follows: 3.3 × 10−2 mol/kg-rubber of initiator, 1.5 mol/kg-rubber of monomer and 30 w/w% of dry rubber content (DRC). The conversion and grafting efficiency of SMA were 95 mol% and 60 mol%, respectively. After graft-copolymerization, the melting temperature of PSMA increased from 304.1 K to 306.2 K. The morphology showed that the DPNR particles, which were about 1 μm in average diameter, were well dispersed in PSMA nanomatrix. The stress at break increased about three times, i.e. 13 MPa, as high as that of DPNR. The increase in the mechanical properties was promoted by the nucleating effect of stearyl group of PSMA.

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