Investigation on Viscoelasticity of Waterborne Polyurethane with Azobenzene-containing Pendant Groups under Ultraviolet and Visible-light Irradiation

In this study,a novel waterborne polyurethane(WPU)with azobenzene-containing(azo-containing)pendant groups was synthesized by isophorone diisocyanate,long-chain diol of polycaprolactone,2-ethyl-2-methyl-butanoic acid(2,2-dimethylolpropionic acid),10-(4-(phenyldiazenyl)phenoxy)decyl-3-hydroxy-2-(hydroxymethyl)-2-methylpropanoate,and N,N-diethyl-ethanamine(triethylamine).Moreover,the influence of ultraviolet and visible(UV-Vis)light irradiation on the viscoelasticity of azo-containing WPU film in terms of the reversible trans-cis photoisomerization of azo-containing pendant groups was investigated by UV-Vis light spectroscopy,atomic force microscopy,and dynamic thermomechanical analysis.The results revealed that the adhesion of azo-containing WPU with single crystal silicon atomic force microscope probe was about 13 n N when irradiated by 450 nm Vis light for 60 s at 25°C.Subsequently,the adhesion increased to 82 n N after irradiation with 365 nm UV light for 60 s at 25°C.In addition,the azo-containing WPU presented a photo-induced reversible transition of tensile modulus and tanδin the range from about 2 MPa to 22 MPa and 6000 to 0.35 with UV-Vis light cyclic irradiation for 120 s at 25°C,respectively.

Synthesis of Isotactic Polystyrene-block-Polyethylene by the Combination of Sequential Monomer Addition and Hydrogenation of 1,4-Trans-polybutadiene Block

Herein, we demonstrate the synthesis of a well-defined diblock copolymer consisting of isotactic polystyrene （iPS） and linear polyethylene, isotactic polystyrene-block-polyethylene （iPS-b-PE）, by the combination of sequential monomer addition and hydrogenation. Isospecific living polymerization of styrene and living trans-1,4-polymerization of 1,3-butadiene were catalyzed by 1,4-dithiabutandiyl-2,2＇-bis（6-cumenyl-4-methylphenoxy） titanium dichloride （complex 1） activated by triisobutyl aluminum modified methylaluminoxane （MMAO） at room tempera^xre to provide highly isotactic polystyrene （iPS） and 1,4-trans-polybutadiene （1,4-trans-PBD） with narrow molecular weight distribution. Furthermore, the iPS-b-I,4- trans-PBD was synthesized via sequential monomer addition in the presence of complex 1 and MMAO. The hydrogenation of the 1,4-trans-PBD block was promoted by RuC12（PPh3）3 used as a catalyst to produce iPS-b-PE.

Crystallization-driven Self-assembly of Isotactic Polystyrene in N,N-Dimethylformamide

Herein we demonstrate crystallization-driven self-assembly ofisotactic polystyrene （iPS） with high isotacticity and narrow molecular weight distribution and crystallization-induced switching of the morphology of iPS aggregates in N, N-dimethylformamide （DMF）. The formation and morphology switching of the self-assembled aggregates of iPS are investigated by means of dynamic light scattering （DLS）, scanning electron microscopy （SEM）, differential scanning calorimetry （DSC） and wide angle X-ray diffraction （WXRD）. The results reveal that cooling DMF solution of iPS promotes iPS chains to self-assemble into spherical aggregates with a gelled core cross-linked by microcrystals, which is surrounded by solvent-swollen corona. Furthermore, crystallization induces the deformation of iPS aggregates from spherical to plate-like or nest-like.