Application of the SSA calorimetric technique to characterize LLDPE grafted with diethyl maleate

Abstract

A linear low density polyethylene (LLDPE) was functionalized with diethyl maleate (DEM) using different amounts of a peroxide as initiator. The modified polymers were characterised by means of FTIR and 1H NMR spectroscopy and the percentage of grafted DEM was determined. When the initiator concentration is increased from 0.44 to 0.88 g per 100 g of polymer, the degree of functionalization also increases from 0.47 to 0.8 mol-% of grafted DEM per ethylene unit. The results gathered here indicate that in this case, the grafting reaction preferentially occurs on the secondary carbons of LLDPE. Such a result was inferred by the use of the DSC based successive self-nucleation and annealing technique (SSA). The ability of SSA to induce molecular segregation during crystallisation and annealing proved to be very useful to characterise the functionalized polyolefins prepared here. When the amount of initiator was further increased to 1.76 wt.-%, the degree of functionalization only increased marginally to 0.84 mol-%. Combined results by SSA, capillary rheometry and FTIR indicated that secondary reactions occur when only part of the initiator is used in the grafting reactions. Such secondary reactions most probably produce long chain branching in the grafted polymer as indicated by the alterations in the melt flow behaviour of this sample and the modifications of its FTIR spectrum.