The introduction of long-chain branches within linear semicrystalline polymers enhances overall crystallization by promoting homogeneous nucleation

Long-chain branches (LCBs) are primarily introduced within linear chains to enhance their melt strength and rheological performance. However, the influence of LCBs on crystallization has received comparatively little attention. This review reports recent results on isotactic polypropylene (iPP) and poly(lactic acid) (PLA) as representative semicrystalline polymers in which the effect of LCBs on nucleation and crystal growth has been extensively studied. A consistent trend emerges: LCBs accelerate nucleation, as indicated by higher nucleation densities, faster nucleation rates, and notable increases in crystallization temperatures. However, LCBs decrease spherulitic growth due to restricted chain mobility. Despite these opposing contributions, the overall crystallization kinetics are enhanced, underscoring the dominant role of primary nucleation. The long-standing belief that branching points serve as heterogeneous nuclei has recently been challenged, with fast scanning calorimetry (FSC) showing that LCBs instead promote nucleation through conformational stabilization and homogeneous nucleation pathways. While FSC has been vital in uncovering these mechanisms, further studies, using FSC and complementary techniques, are still needed to fully determine the molecular origins of LCB-induced crystallization across different polymer families. • Long-chain branches enhance nucleation rate and density, thus increasing T c . • Spherulitic growth slows as branching restricts the mobility of the chains. • Even with slower growth, nucleation dominates, so overall crystallization is faster. • FSC results show that LCBs provoke homogeneous nucleation • LCBs barely shift T m and T g , but strongly govern crystallization pathways.