Study of the synthesis of graft copolymers by a reactive process. Influence of the copolymer structure on the adhesion of polypropylene onto poly(vinylidene fluoride)

The synthesis of graft copolymers by a “grafting onto” process using a reaction in the molten state is described. Amine or alcohol functionalized oligomers were grafted onto maleic anhydride grafted polypropylene. The grafting yields obtained with hydroxyl terminated oligomers were almost zero. Increasing the temperature from 180 °C to 200 °C or increasing the molecular weights of the oligomers did not show any significant increase in grafting rate. This result is contradictory with those obtained in the case of simple molecules where some grafting was observed. The cyclisation of the hemiester to give the anhydride was observed and the grafting rate was low in comparison with that reached in the case of amine terminated oligomers where grafting was observed. This result was confirmed by FTIR and elemental analysis. Experimental grafting rates were close to theoretical ones. These copolymers were characterized by SEM and DSC and tested as adhesion promoters of PVDF film onto PP film. It was shown that the use of these graft copolymers allowed the adhesion of the two polymers and improvement by a factor 15 of the peeling forces in respect to the adhesion without promoters was observed. This adhesion was correlated to the length of the grafts and the higher the polydispersity indexes, the better the peeling forces.