Synthesis And Rheological Properties Of Polybiphenylenevinylenes And Polyquinacrinones

Electrorheological fluid (ERF) is a novel type of smart materials, which is of remarkable academic interest and extensive potential application. It has become one of the most active research fields in functional materials. In this dissertation, the nature of the ERF and its theoretical model as well as its development and application has been extensively reviewed. Two types of novel conjugated polymers and two dispersing-medium materials were designed and synthesized according to the molecular design principles. The ER properties of these novel smart materials have been intensively studied. The relationship between the ER effect of these novel materials and their related properties was discussed. In the synthesis of the conjugated polymers precursors, 2-methoxyl-5-octyloxy-1,4-dichloromethylbenzene and 4,4'-bischloromethyl-1,1'-biphenyl, the reaction conditions of chloromethylation reaction were thoroughly investigated. Meanwhile, 4,4'-diformyl-1,1'-biphenyl and 4,4'-dicyanomethyl-1,1'-biphenyl were synthesized and the reaction conditions were optimized. The conjugated polymer, polybiphenylenevinylene (PBPV) was synthesized based on the self-condensation reaction of 4,4'-bischloromethyl-1,1'–biphenyl via Gilch method; Poly(2-methoxyl-5-octyloxylphenylene-1,4-vinylene-biphenylene-4,4'-vinylene) (PMOBPV) was synthesized based on the "one-pot method "of 2-methoxyl-5-octyloxy-1,4-dichloromethylbenzene with 4,4'-diformyl-1,1'-biphenyl via Wittig reaction; Polybiphenylene-4,4'-vinylene-1-cyano (CNPBPV) was synthesized based on the Knoevenagel reaction of 4,4'-diformyl-1,1'-biphenyl with 4,4'-dicyanomethyl-1,1'-biphenyl. All polymer synthetic conditions were optimized; the molecular structure, thermal properties, morphology and dielectric properties of these resulting polymeric particles were characterized. Plane ladder-like polymers, polyquin (2,3-b) acridine-7,14 (5,12) dione (PTQA) or polyquin (2,3-b) acridine-12,14 (5,7) dione (PCQA) was synthesized based on the condensation reaction of 1,4-phenylenediamine or 1,3-phenylenediamine with dimethyl 2,5-dioxocyclohexane-1,4-dicarboxylate, subsequently cyclization and dehydrogenation. The reaction conditions were thoroughly investigated. The molecular structure, thermal properties, morphology and dielectric properties of the resulting polymers were characterized. Bromochlorotoluene (BCT) was synthesized based on the bromonization reaction of chlorotoluene with Br2; Bromodiphenylmethane (BDPM) was synthesized based on the Friedel-Crafts reaction of bromobenzene with chlorobenzyl. The molecular structure and physical properties related to the ER effect were characterized. The stability and rheological properties of the PBPV, PMOBPV or CNPBPV suspensions in silicon oil were intensively investigated. The results show that, due to proper conductivity and dielectric properties of the dispersed materials, these polymeric suspensions can be polarized to form fabricated chains under electric field, which leads to good ER activity with low current density: The yield stress reaches up to 802.3 Pa (2kV/mm), 1354.2 Pa (3kV/mm) and 1919.2Pa (3kV/mm) under the current density of only 100 μA/cm2 (2kV/mm), 28.7 μA/cm2 (3kV/mm)and 34 μA/cm2(3kV/mm) respectively for 30 wt.% polymer-based ER fluids at room temperature; the yield stress of these suspensions increases with the electric field strength, and shows the relationship as τy ∝E n, where n equals to 1.88,1.9,1.58 respectively for PBPV, PMOBPV and CNPBPV-based systems; The yield stress linearly increases with the particle concentration, and has a maximum as increasing the employed temperature. The apparent viscosity of the ER fluids increases with the electric field strength, while decreases with the shear rate, i.e., shear-thinning effect. The results also show that the difference in molecule structure of the dispersed materials leads to the difference in ER activity. The conductivity of the dispersed materials has only effect on the current density of the ER Fluid. Moreover, it is the difference in dielectric constant of the dispersed-phase materials that contributes to the difference in yield stress of the ER fluids. The rheological properties of the suspensions of PTQA and PCQA in BDPM were also studied. The results show that, these systems exhibit excellent ER activity under electric field. Under 3kV/mm electric field, the yield stress of 30 wt% PTQA and PCQA suspensions reaches up to 6.0 and 4.0 kPa under the current density of only 21.7 and 14.3 μA/cm2 respectively at room temperature. The yield stress linearly increases with squared electric field strength and the particle concentration, has a maximum as increasing the employed temperature.The apparent viscosity of the ER fluids increases with the electric field strength, while decreases with the shear rate, i.e., shear-thinning effect. The excellent ER activity and the difference in these two systems are attributed to the novel molecular structure as well as the difference in the molecular regularity. The influence of the dispersing phase on the stability and rheological properties of PTQA-base suspension was investigated. The results show that, the sedimentation rate of the ERF depends on the density difference between the dispersing particles and the medium, as well as the viscosity of the medium. The yield stress of the ERF is proportional to the dielectric constant of the medium which is in well agreement with the dielectric loss model.