Precise preparation, microstructures, micromechanical behavior and morphology of well-defined PS-b-PS/Bd-b-PS triblock copolymers via RAFT seeded miniemulsion polymerization

Abstract

Reversible addition-fragmentation transfer (RAFT) miniemulsion polymerization was one of the prominent controlled/“living” radical polymerization (CLRP) techniques with environmental friendly, energy saving and high efficient characteristics. The well-defined Polystyrene-block-Polystyrene/butadiene-block-Polystyrene (PS-b-PS/Bd-b-PS) triblock copolymers with uniform, tapered or gradient and pure polybutadiene compositions distribution in the middle block were precisely controllably prepared via RAFT seeded miniemulsion polymerization, in which number-average molecular weigh (Mn) t was from 60.00 ~ 82.00 kg/mol with narrow distribution and substantially the similar PS volume fraction about 0.64 ~ 0.65 and 0.80. The copolymers microstructures were characterized by gel permeation chromatography (GPC), fourier translation infrared spectroscopy (FT-IR) and hydrogen nuclear magnetic resonance spectroscopy (1H-NMR). The GPC traces indicated that type curves remained nearly symmetrical, unimodal molecular weight distribution in the whole PS-b-PS/Bd-b-PS triblock copolymers preparation. FT-IR and 1H-NMR results showed that microstructures of the copolymers were mainly 1, 4-trans butadiene with about 10% content of 1, 2-units. Microphase morphology, micromechanical behavior and thermal property of the copolymers were identified by transmission electron microscopy (TEM), tensile testing and differential scanning calorimetry (DSC). The fracture mechanisms of thin layer yielding and cavitation deformation were corresponding to the lamellar and cylindrical morphology in micromechanical behaviors, respectively. It was indicated that microphase morphologies, micromechanical properties and thermal properties were identical to their molecular microstructures, composition profiles distribution, toughening mechanisms and microphase separation strength.