PAmXD,6/PP-g-MA blends. I. Compatibilization

This work deals with the study of PAmXD,6/PP-g-MA blends [poly(meta-xylylene adipamide)] and (maleic-anhydride-functionalized-polypropylene) blends. Compatibilization occurs during the blending of the components in a Brabender plastograph at 265 ± 5°C and at a mixing rate of 45 rpm. Kinetic data from the literature indicate that the rate of amine/anhydride reaction is much faster than the rate of amide/anhydride reaction. This interpretation is confirmed by the use of model systems constituted of PAmXD,6 and pyromellitic dianhydride or of PP-g-MA and meta-xylylene diamine. Infrared analyzes of extracted nodules of PAmXD,6/PP-g-MA blends also confirm the extent of the imidization and show that the length of the PAmXD,6 blocks is lower than the free PAmXD,6 one. Segregation mechanisms during the compatibilization are discussed to explain this observation. The structure of the copolymers was deduced from those results and from the previous characterizations of PP-g-MA and PAmXD,6. It consists in a block of PP linked with some blocks of PAmXD,6. The average number of PAmXD,6 blocks depends on the average length of the poly(maleic anhydride) functionality carried on by PP-g-MA. © l997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 901–915, 1997     

Molecular weight segregation induced by interfacial melt reactivity in polyamide 6/reactive rubber blends

Polyamide 6 (PA) and ethylene-propylene rubber with maleic functionality (EPMA) were blended in a batch mixer. EPMA anhydride groups react with amine chain ends of polyamide and form a grafted copolymer at the interface. The molecular weights of the grafted PA and of the free PA were measured. The molecular weight of the free PA decreases during the processing. This effect is due to the hydrolysis of the PA consecutively to its reaction with anhydride groups. The molecular weight of both grafted and free polyamide decreases during the processing. Moreover, the molecular weight of the grafted PA is lower than that of the free PA. At constant mixing time, a high conversion level produces grafted PA with a higher molecular weight. This is the result of molecular weight segregation for interfacial reaction. Small molecules react faster at the interface than larger ones. If we compare experimental results with model predictions, two segregation regimes are observed. For high shear and low EPMA concentrations, dispersion is very fast; the segregation only depends on molecular elasticity. In this case, the best correlation between model and experiment is obtained for low interfacial thicknesses. For low shear, or for EPMA concentrations close to the phase inversion composition, the segregation is more noticeable, which is mainly due to the diffusion of macromolecules through the brush of already grafted molecules. In this case, there is a clear competition between the compatibilization and the grafting reaction. Molecular weight segregation gives low ratio of the grafted PA molecular weight to the free PA molecular weight. This is detrimental to interfacial properties of the grafted copolymer formed by melt reactivity. Strategies are developed to improve this ratio in order to investigate its influence on the mechanical properties. © 1995 John Wiley & Sons, Inc.