Synthesis, Characterization and Physical Properties of Amphiphilic Rod-Coil DEH-PPV-b-PNIPAM Block Copolymers

• Main Authors: Hsin-Chieh Tsai, 蔡欣潔
• Other Authors: 林唯芳
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/52102796872976217358

碩士 === 國立臺灣大學 === 高分子科學與工程學研究所 === 101 === A series of poly(diethylhexyloxy-p-phenylenevinylene)-b-poly(N-isopropylacylamide) (DEH-PPV-b-PNIPAM) amphiphilic block copolymers were synthesized using Siegrist polycondensation and atom transfer radical polymerization (ATRP) followed by “click” chemistry. Theses copolymers are well-defined with PNIPAM block volume fraction from 0.40-0.72 and low polydispersity (< 1.2), as determined by 1H NMR and GPC. Due to the amphiphilic property of PNIPAM, these copolymers can be easily dissolved in polar solvent. The copolymers with all volume fractions of fPNIPAM are completely soluble in methanl and in water with fPNIPAM > 0.55. In both solutions, the copolymers show slightly blue shift of absorption (UV-Vis) and strong quenching of emission (PL), indicating H-aggregations occurred. These copolymers in polar solution were self-organized into lamellar structures with same width (6-8 nm) regardless the fPNIPAM according to the TEM studies. The average aspect ratio of these lamellae is increased from 6.5 to 13.8 when the fPNIPAM is decreasing from 0.72 to 0.48. These results suggest that the nanostructure of these copolymers is mainly dominated by the PPV block. The lower critical solution temperature (LCST) of block copolymers is increased with increasing hydrophobic DEH-PPV block ratio, since χ value between DEH-PPV and PNIPAM segment is weak to reduce the real thermo-responsive length of PNIPAM. The variation of the micelle size with temperature was judged to be similar from both TEM and DLS measurement. In bulk state, nanostructure and phase transition of the DEH-PPV-b-PNIPAM amphiphilic rod-coil block copolymers were experimentally investigated via SAXS, TEM, POM, and DSC to map the phase diagram. At low coil fraction (fPNIPAM<0.48), the DEH-PPV rods are organized smectic-lamellar structure. However, as coil fraction increases, DEH-PPV pack into hexagonal structure. Upon heating the low coil fraction copolymer exhibit a series of clear transition of smectic-lamellar to nematic to isotropic phase. Similarly, in high coil fraction copolymer, the transitions from smectic-hexagonal to nematic to disorder could be observed clearly. In addition, the order to microphase disorder transition (ODT) and nematic-to-isotropic (NI) transition temperature are decreased with increasing coil fraction. These results suggest that the phase transition of DEH-PPV-b-PNIPAM amphiphilic rod-coil block copolymer shows the weak segregation strength behavior.