Unlike linear polypropylene (PP), PP with long-chain branches (LCB-PP) has been known to have high value in polymer processing that requires high melt strength characteristics, such as thermoforming, foaming, and blow molding. In this study, LCB-PP is prepared utilizing the C–H insertion capability of an azidoformate (AF) group. A small molecule with two AF groups at both ends, tri(ethylene glycol) di(azidoformate) (GDAF), is synthesized, where the AF groups are thermally activated to afford nitrene intermediates to interconnect PP chains. Propylene/1-butene copolymer is employed as a dispersant of GDAF, which is first melt-blended with each other at 100 °C to afford a master batch. Then, the mixture is reactive melt mixed with PP at 165 °C to thermally activate the AF groups of GDAF to afford LCB-PP. The amount of branches is controllable by adjusting the GDAF loadings. Due to the branched chain architectures, investigation of rheological characteristics reveals more elastic and strain hardening melt behaviors of the resulting LCB-PPs with higher GDAF loadings, which demonstrates a simple and scalable melt mixing procedure to afford value-added polyolefins.