Structurally Well-defined Polyolefin Block Copolymers: Design, Synthesis And Self-assembly

The design and synthesis of polyolefin block copolymers with polar polymer segment is of great significance in broadening the application scope of polyolefin and is one of hot topics in the functionalization of polyolefin in recent years. Herein well-defined PM-b-PtBA diblock copolymers and PM-b-PtBA-b-PS triblock copolymers based on polymethylene were synthesized via the combination of living polymerization of ylides and atomic transfer radical polymerization (ATRP). Amphiphilic diblock copolymers PM-b-PAA were obtained via hydrolysis of PM-b-PtBA.Firstly, hydroxyl terminated polymethylene (PM-OH) was synthesized via living polymerization of ylides followed by oxidation. The structure of PM segment was studied by the high temperature 1H-NMR, FT-IR and high temperature gel permeation chromatography. The ratio of hydroxyl terminated polymethylene is-100% in all polymethylene. The molecular weight distributions (Mw/Mn)of hydroxyl terminated polymethylenes were under 1.10 when their molecular weights were controlled in the range of 1000-10000 g/mol. The macroinitiator (PM-MI) was obtained by the reaction of PM-OH and 2-bromo-2-methylproplonyl bromide, then initiated the ATRP of tert-butyl acrylate to obtain PM-b-PtBA diblock copolymers. Subsequently, PM-b-PtBA-b-PS triblock copolymers were prepared using ATRP of styrene. Amphiphilic diblock copolymers PM-b-PAA were obtained via hydrolysis of PM-b-PtBA diblock copolymers.The self-assembly behavior of such block copolymers was studied. It found that the amphiphilic block copolymers PM-b-PAA self-assembled to form spherical micelles and the average diameter of micelles is about 250 nm. Porous films of such diblock and triblock copolymers were fabricated via breathe-figure method with chloroform and carbon disulfide as solvent, respectively. The morphology of such porous film was observed by scanning electron microscopy (SEM). The effects of PS segment and temperature on the morphology of porous film were investigated.