Effect of GraftingDensity on Self-Assembled LamellarPhases of Core–Shell Bottlebrushes

This report examines the melt self-assembly behaviors of core–shell bottlebrush polymers (csBBs), in which a single AB diblock copolymer decorates each backbone repeat unit. To access these nonlinear polymer architectures, four norbornyl end-functionalized, symmetric composition poly(ε-decalactone)-<i>block</i>-poly(<i>rac</i>-lactide) (<b>DL</b>) diblock copolymers (<i>M</i>_n = 5.9–7.6 kg/mol, <i>Đ</i> = 1.20–1.29, with <i>f</i>_L = 0.49–0.51) were first synthesized by sequential ring-opening polymerizations (ROPs). Living ring-opening metathesis polymerization (ROMP) of these DL macromonomers produces narrow dispersity csBBs (<i>Đ</i> = 1.02–1.18) with backbone degrees of polymerization <i>N</i>_bb = 6–37. For csBBs of a given <b>DL</b> macromonomer, small-angle X-ray scattering (SAXS) analyses reveal that the order-to-disorder transition temperatures (<i>T</i>_ODT’s) of their microphase-separated lamellar mesophases increase with increasing <i>N</i>_bb. From these data, the dependence of the critical macromonomer arm segregation strength for microphase separation (χ<i>N</i>_arm)_ODT on <i>N</i>_bb is identified. Comparisons of these results with reports on related nonlinear block polymers suggest that the csBB architecture reduces the free energy penalty for chain arrangement into the self-assembled lamellar morphology, while brush grafting density directs the extent of side chain stretching, with implications for microphase-separated melt stability and the observed domain (<i>d</i>) spacings.