Synthesis of Long-Subchain Hyperbranched Polypropylene Using Thermally Degraded Products as Precursor

A new strategy to access long-subchain hyperbranched polypropylene (LHB-PP) has been established, starting from the thermally degraded polypropylene (PP) possessing two-terminal vinylidene double bonds of isopropenyl end groups (PP-TVD). PP-TVD reacts with hydrogen bromide (HBr) with high efficiency, followed by a substitution reaction with sodium azide to yield azide-terminated PP (PP-N3). Finally, the highly efficient click reaction between PP-N3 and 1,3,5-triethynylbenzene (TEB) affords the unprecedented LHB-PP, of which the molecular weight and topologic microstructure are well controlled by tuning the (PP-N3)-to-TEB molar ratios. Compared to the linear PP with a similar molecular weight, the solution of this newly obtained LHB-PP has a lower intrinsic viscosity and a smaller hydrodynamic radius. Simultaneously, the LHB-PP melt presents a higher zero shear viscosity and a more apparent shear-thinning phenomenon. For solid properties, there are γ crystalline components in the LHB-PP, and the lamellar thickness of LHB-PP is much smaller than that of linear PP. This work paves a new avenue for upgrading the recycled PP to new products with hyperbranched topology and improved properties.