Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush

Grafting density is an important structural parameter that impacts the physical properties of architecturally complex polymers. The physical consequences of varying the grafting density (z) were studied in the context of block polymer self-assembly. Well-defined block polymers spanning the linear, comb, and bottlebrush regimes (0 ≤ z ≤ 1) were prepared via grafting-through ring-opening-metathesis polymerization (ROMP). Small-angle X-ray scattering (SAXS) experiments demonstrate that these graft block polymers self-assemble into long-range-ordered lamellar structures. For seventeen series of block polymers with variable z, the scaling of the lamellar period with the total backbone degree of polymerization (d* ~ N_bb^α) was studied. The scaling exponent α monotonically decreases with decreasing z and exhibits an apparent transition at z ≈ 0.2, suggesting significant changes in the backbone and side chain conformations. A model is proposed in which the characteristic ratio (C_∞), a proxy for the backbone stiffness, scales with N_bb as a function of the grafting density: C_∞ ~ N_bb^f(z). Understanding the scaling behavior provides valuable insight into conformational changes with grafting density, thereby introducing new opportunities for block polymer and materials design.