Multifunctional crosslinking agents based on substituted cyclic phosphazenes and their application as coupling agents in reactive processing and coatings formulations
Various amino-, alkoxy-, aryloxy-, and siloxy-substituted cyclic phosphazenes were synthesized and characterized. These phosphazenes were incorporated into coatings formulations as UV- and sol-gel-curable network formers. By changing the identity of the substituents on the phosphonitrilic template, the hydrophobicity/hydrophilicity of the coatings were systematically varied. Hexa(allylamino)cyclotriphosphazene (HAP) was grafted onto polypropylene (PP) in the presence of a peroxide via reactive extrusion. This grafting was able to offset some of the mechanical property degradation of PP due to peroxide-induced β-scission. In addition to increasing the z-average molecular weight and improving the impact strength and tensile strength over that of the peroxide control extrudates, it was observed that these crosslinks served as nucleation sites for crystallization. Furthermore, the crosslinks enhanced the ability of the PP chains to form crystalline stacks, facilitating the crystallization of PP at a higher temperature. To enhance the low temperature impact strength of PP, it was blended with ethylene-propylene-2-methylene-5-norbornene terpolymer (EPDM). Reactive processing of these two polymers in the presence of peroxide and a phosphonitrilic coupling agent generated a PP/EPDM copolymer in situ, which improved the dispersion of EPDM within the PP matrix and reduced the interfacial tension between the two components.