Perspective: rethinking polymer crystallization pathways-two decades after Strobl's mesomorphic-to-granular-to-lamellar model.

The 2000 perspective article by Gert Strobl, "From the melt via mesomorphic and granular crystalline layers to lamellar crystallites: A major route followed in polymer crystallization?", proposed a revolutionary multistep mechanism for polymer crystallization from the quiescent melt, fundamentally challenging the dominant single-step models of the time. Two decades later, this perspective revisits Strobl's conceptual framework to assess its legacy, its limitations, and its continuing relevance to modern polymer science. We examine the three-stage pathway-mesomorphic layer formation, cooperative transition to a granular crystalline layer, and block merging into lamellar crystallites-through the lens of subsequent experimental, theoretical, and simulation advances. While the model's central premise of intermediate states has stimulated extensive research, key elements remain debated. The distinction between crystal-fixed and crystal-mobile polymers has emerged as a critical factor, reinterpreting the stabilization phenomena Strobl observed and challenging the universality of his proposed pathway. Simulation studies have provided complementary insights into precursor states; yet, the direct detection of the granular crystalline layer and the mesomorphic precursor remains elusive. We identify open questions regarding the molecular origins of early stage ordering, the factors determining lamellar thickness, and the universality of granular crystalline states. Strobl's model was important not because it provided definitive answers, but because it forced the field to confront its assumptions and inspired a generation of research that continues to advance our understanding of polymer crystallization.