Anionic Copolymerization Enables the Scalable Synthesis of Alternating (AB)_<i>n</i> Multiblock Copolymers with High Molecular Weight in <i>n</i>/2 Steps

Based on the highly disparate reactivities of isoprene (I, <i>r</i>_I = 25.4) and 4-methylstyrene (4MS, <i>r</i>_4MS = 0.007) in the anionic copolymerization in nonpolar media, a general strategy for the rapid and scalable synthesis of tapered multiblock copolymers with an extremely steep gradient has been developed. A repetitive addition strategy of a mixture of isoprene and 4MS leads to a tapered diblock in each case, giving access to linear alternating multiblock copolymers of the (AB)_<i>n</i> type with up to 10 blocks. All multiblock copolymers showed narrow molecular weight distributions (dispersity <i>Đ</i> = 1.04–1.12). High molecular weights in the range of 80 to 400 kg mol^–1 were achieved. Due to the incompatibility of PI and P4MS segments, the multiblock copolymers exhibit nanophase separation, manifested by separate glass transitions for both constituents. Stress–strain measurements revealed extraordinary toughness and elongations up to 1150% strain at break, even at a 50/50 molar ratio I/4MS (i.e., 37 wt% isoprene). Our synthesis permits access to a wide range of tapered multiblock copolymer architectures with rigid (P4MS, high glass transition, <i>T</i>_g) and flexible (low <i>T</i>_g) chains, in <i>n</i>/2 steps, while keeping overall dispersity low