Complex Star Architectures of Well-Defined Polyethylene-Based Co/Terpolymers

Well-defined polyethylene (PE)-based 3-miktoarm star copolymers (PI)2PE-OH, PI2(PI′-b-PE)-OH and terpolymer PI2(PS-b-PE)-OH (PI: polyisoprene, PS: polystyrene), bearing a functional group (−OH) at the PE chain end, were synthesized by combining anionic polymerization, polyhomologation, and linking reaction with a “bridge” molecule, BF3OEt2. 4-(Dichloromethylsilyl)diphenylethylene was first synthesized and linked with anionically prepared linear PI, through titration, to afford the “living” star precursors. Subsequently, boron-linked macroinitiators were synthesized through linking reaction with BF3OEt2 for the polyhomologation of dimethylsulfoxonium methylide to produce novel PE-based miktoarm star polymers. All intermediates and final products were characterized by high-temperature size exclusion chromatography, proton nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. The microdomain morphologies of the samples were elucidated by transmission electron microscopy imaging of microtomed sections as well as small-angle and wide-angle X-ray scattering as a function of the sample temperature. Depending on the relative degree of segregation (varying with the block molecular weight and the interaction parameter between blocks) versus the crystallization temperature of the PE block, both crystallization-driven microphase separation and segregation-driven order–disorder microphase separation can take place, resulting in various domain morphologies.