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.

Liquid chromatography-electrospray ionization-tandem mass spectrometry (LC−ESI−MS2) was employed for the characterization of three poly(n-butyl acrylate)s. These polymers were produced at high temperature using the same initiator, tert-butyl peroxy-3,5,5-trimethylhexanoate, but in different solvents, viz. pentyl propionate, xylene and butyl acetate. Exact mass experiments performed on these polymers in an Orbitrap instrument supplied valuable information on the end group structures. Study of the data allowed identification of many reactions during the polymerization such as beta-scission and chain transfer to solvent or radical transfer to solvent from the initiator. Different fragmentation pathways were observed from the same precursor mass on MS/MS experiments, indicating the presence of isomers. The comprehensive assignment of the peaks in the LC−MS data allowed us to describe the end group distribution in a semiquantitative way. The results clearly show that the relatively reactive solvents used for polymerization have strong influences on the polymer composition.

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