Three different heteroaromatic ring derivatives (coagents) were used to adjust the melt radical reaction of polypropylene (PP). From the results of high temperature 1H NMR and high-temperature size-exclusion chromatography (HT-SEC), all the coagents could quickly convert the tertiary PP macroradicals into resonance stabilized macroradicals and effectively restrain the β-scission of PP macroradicals. Long chain branched structures, without significant bimodal distribution of molecular weight, could be introduced into coagents-functionalized PP samples. Effect of chemical structures of heteroaromatic rings and electron-attracting groups on the molecular structures and melt properties of modified PP samples was studied. The possible reactions of coagents-functionalized PP samples in different theoretical molar ratio of coagent to alkoxy radical were also proposed according to the results of 1H NMR, torque curves, rheological measurements and HT-SEC coupled with laser light scattering detector.

Heteroaromatic ring derivatives with the CC bond conjugated with different five-membered heteroaromatic rings were used to adjust melt reaction of polypropylene (PP). The effect of heteroatoms in the five-membered rings and electron-attracting groups connecting with CC bond on restricting the β-scission of PP macroradicals and promoting the branching reaction between PP and trimethylol propane triacrylate (TMPTA) was studied. From the analysis of the results concerning molecular structures and melt properties, it was found that the electron density of the CC bond determined the reaction rate between PP macroradicals and heteroaromatic ring derivatives. 2-cyano-3-(furan-2-yl)-2-propenoic acid ethyl ester (CFA) and 2-(furan-2-ylmethylene)malononitrile (FN) had CC bonds with lower electron density, therefore they can quickly convert the tertiary PP macroradicals into resonance stabilized macroradicals. As a result, the β-scission of PP macroradicals and the homopolymerisation of TMPTA were restrained to some extent. Modified PP samples containing TMPTA, peroxide and CFA (or FN), which had the lower grafting degree of TMTPA, showed the most obvious change on the relaxation behaviour of polymer chains.