OLIGOMERIC FUNCTIONALIZATION OF POLYETHYLENE WITH POLYACRYLAMIDE GRAFTS (HDPE-co-PAAm) AND WITH DIETHYLMALEATE UNITS (HDPE-co-PAAm-g-DEM): CHARACTERIZATION BY FTIR AND THERMAL FRACTIONATION SSA

Abstract

This work presents the solution-based functionalization of high-density polyethylene (HDPE) in one stage with acrylamide (AAm) and in two sequential stages: with AAm (1st stage) (HDPE-co-PAAm) and with diethylmaleate (DEM) (2nd stage) (HDPE-co-PAAm-g-DEM). The degrees of functionalization (GF) were high (up to 10 mol %) when the HDPE was functionalized with AAm (a stage). The study of the variables: HDPE/monomer feed ratio, reaction time, monomer and initiator concentration in the functionalization of  HDPE with AAm, resulted in all cases in high GF, estimated experimentally by means of by Fourier Transform Infrared spectroscopy FTIR, agreeing with a oligomeric functionalization of PAAm grafts in HDPE. The Differential Scanning Calorimetry (DSC) analyzes allowed us to observe that the melting temperature (Tf) of the HDPE did not vary with the functionalization, however variations were detected in the degrees of crystallinity (Xc) reached in the HDPE-co-PAAm, demonstrating that the grafts joined at few carbons of the HDPE chains. FTIR spectroscopy showed the formation of final vinyl groups, which were postulated as the binding points to generate HDPE-co-PAAm. Fractionation by Successive Self-nucleation and Annealing (SSA) demonstrated that the most influential variable in the oligomeric functionalization with AAm was the reaction time, since it was the only condition in which an SSA profile different from that of pure HDPE was found, a product of high GF and gelation as a competitive collateral reaction by increasing the reaction time from 1 to 3 h. The functionalization using the two monomers (AAm and DEM) in sequential stages turned out to be effective, to incorporate the isolated DEM units in the 2nd stage, according to the results obtained by DSC and SSA, generating a polyethylene with ester groups that did modify the length of the ethylene sequences: PEAD-co-PAAm-g-DEM. In summary, all the analyzes carried out (FTIR, DSC and SSA) indicated that the functionalization modified the apolar character of the HDPE by incorporating PAAm grafts and units isolated from the DEM esters, potentially increasing the capacity of the HDPE to interact with polar materials.