Chemical Modification of Molten Polypropylene by Thermolysis of Peroxidic Compounds

• Published in: Macromolecules Vol. 36; no. 20; pp. 7469 - 7476
• Main Authors: Saule, Myriam, Navarre, Sébastien, Babot, Odile, Maslow, Wasil, Vertommen, Luc, Maillard, Bernard
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 07.10.2003
• Subjects: Applied sciences; Chemical modifications; Chemical reactions and properties; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Peracetal; Radical catalyst; Chemical modification; Functionalization; Thermal decomposition; Propylene polymer; Priming activity; Perester; Reaction mechanism; Growth from melt; Experimental study; Free radical reaction
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma0342325

The modification recently developed for polyethylene, based on the thermolysis of peroxyketals and peroxy esters in the molten polymer, was applied to atactic and isotactic polypropylene. The grafting of an ester function onto the backbone of these polyolefins was much less efficient in this case than for the former. The thermal decomposition of such peroxides in polyethylene and isotactic and atactic polypropylenes was analyzed by DSC. These studies showed that the physical state of the polyolefin cannot account for the difference encountered in the functionalization yields. The analysis of the reaction products, generated in the thermolysis of a cyclic peroxy ketal, was realized on the extracts by GC and on the bulk by 1H NMR and DOSY spectroscopies. This led one to conclude that the difference in efficiencies in the chemical modification of the various polyolefins is related to the chemical reactivity of the hydrogens toward 1,1-dimethylethyloxy radicals. Surprisingly, it was found that hydrogen abstraction hardly occurs with polypropylene (either isotactic or atactic) despite the presence of thermodynamically more labile tertiary hydrogen atoms than the ones present in polyethylene. This was attributed to the steric hindrance of the methyl present on the backbone of this polyolefin.