Hirokazu Okamura

Thermosensitive properties of a novel poly(methyl 2-acetamidoacrylate-co-methyl acrylate)

Abstract Copolymerizations of methyl 2-acetamidoacrylate (MAA) with methyl acrylate (MA) were carried out at 60 °C in chloroform. MAA-rich copolymers are soluble in water and MAA-poor copolymers insoluble. Among water-soluble copolymers obtained, only one (HP-77) which contains 77% of MAA units was thermosensitive. Thermal properties of HP-77 were investigated in the presence or absence of inorganic salts. The cloud point of aqueous HP-77 solution depended on polymer concentration: The cloud point decreased exponentially with an increasing concentration of the polymer. The cloud point of HP-77 was also affected significantly by the type and concentration of salts. The effectiveness of salts to reduce the cloud point is NaBr≈KBr 2 SO 4 ≈K 2 SO 4 . The salting-out coefficients were evaluated as 2.45 l/mol for sodium chloride and 14.56 l/mol for sodium sulfate, respectively, from the relationship (Setschenows equation) between logarithm of the solubility of HP-77 and salt concentration. The salting-out coefficient of sodium sulfate is larger than that of sodium chloride.

A Novel Thermosensitive Poly(methyl 2-acetamidoacrylate)

The thermosensitive properties of aqueous poly(methyl 2-acetamidoacrylate) (PMAA) solutions were investigated in the absence or presence of sodium sulfate. Poly(methyl 2-acetamidoacrylate) with a molecular weight of 23,000 (PMAA-1) exhibited the cloud point. On heating the PMAA-1 solution, the transmittance began to decrease from near 34 °C and increased again after the minimum value was shown at 36.0 °C. The minimum transmittance increased linearly with an increasing concentration of the polymer although the minimum-transmittance temperature did not depend on polymer concentration. The minimum transmittance was affected by the pH and the 1-butanol added. This finding suggests that the cloudiness is controlled by a delicate balance of hydrophilicity and hydrophobicity and by intra- and/or inter-molecular hydrogen bonding. Poly(methyl 2-acetamidoacrylate) with a molecular weight of 15,000 (PMAA-2) did not exhibit cloudiness in distilled water. However, the addition of sodium sulfate caused cloudiness to appear. The cloud point of a PMAA-2 solution depended on concentrations of polymer and salt added. It decreased with an increase in polymer and salt concentrations. The salting-out constants were determined from the relationship between the cloud point and concentrations of polymer and salt.

CHAIN BEHAVIOR IN MODEL HOMOGENEOUS ER FLUIDS DEPENDING ON TEMPERATURE

Water-soluble urethane-modified polyethers were prepared by addition of poly(ethylene oxide)-co-poly(propylene oxide) and aromatic isocyanate compounds. These polymers were found to dissolve in water at lower temperature and separate from solution upon heating. The temperature showing this unusual solubility change is called lower critical solution temperature (LCST). These chemical structures of thermo-responsive polymers were similar to those of urethane-modified ER active polymers containing poly(tetramethylene oxide) and aromatic urethane moiety. The thermo-responsive and ER polymers may have various intra- and intermolecular interactions through the urethane moiety. It is considered that both thermo-responsivility and ER effect are dependent on the conformational stability of the polymers under different conditions possibly related to these stimuli-responsivility through the molecular interactions. In order to clarify molecular motion of thermo-responsive polymers near the LCST, 1H-NMR spin-lattice relaxation time (T1) was measured in D2O. The result indicated that hydrophobic interaction of terminal urethane moiety would strongly affect the LCST behavior.

Preparation and Property of Model Homogeneous ER Fluids Having Urethane Groups

Urethane modified polyether liquids composed of hard and soft segments exhibit either positive or negative ER effect depending on the structure. Here some model compounds of the urethane polymers were synthesized, and the influence of chemical structure, e.g. displacement of hard and soft segments and existence of branches, on the ER effect was studied. It was found that negative ER effect is enhanced by introducing a branched structure in the polyether main-chain or a hard segment at center of the linear polyether.

Copolymerization of methyl 2-acetamidoacrylate and styrene in the presence of stannic chloride

Abstract Continuous variation method in UV revealed that methyl N-acetylaminoacrylate (MNA) and SnCl4 formed the 1:1 complex. The copolymerization of MNA with styrene in tetrahydrofuran was carried out at 50 °C in the presence of SnCl4. The resulting monomer reactivity ratios decreased with an increasing concentration of SnCl4 added. This finding suggests that SnCl4 participates in the propagation step of the copolymerization. Therefore, the copolymerization was analyzed by assuming terpolymerization of free MNA (M1), complexed MNA (M2), and styrene (M3). The absolute copolymerization parameters were obtained as follows: k11/k12=0.165, k11/k13=3.04, k22/k21=0.32, k22/k23=0.103, k33/k31=0.058, k33/k32=0.001, Q1=6.03, e1=0.52, Q2=88.57, and e2=2.23. The complexed MNA is more reactive to polymer radicals with free MNA and styrene as the terminal unit than the free MNA. Very small values of k22/k23 and k33/k32 suggests that the copolymerization of the complexed MNA and styrene proceeds alternatingly.

NMR Analysis of Molecular Motion of Polyurethane Fluid

Urethane modified polyethers having hard-soft-hard structure were prepared as simple model compounds for homogeneous ER fluids. The NMR relaxation analysis was applied to these polyurethane ER fluids, and the molecular motions and interactions were studied with a series of the data of spin-lattice relaxation time T1 and the spin-spin relaxation time T2. Two hard-soft-hard urethanes, which showed opposite ER effects, were found to have similar relaxation behaviors under no electric field. The temperature dependence of T1 indicated existence of significant intermolecular interaction and the concentration dependence of T2 suggested that the molecular interaction mainly occurs at the polyether main-chain.

ELECTRIC-FIELD RESPONSE OF THE STRUCTURE AND RHEOLOGICAL PROPERTY OF SILICONE/POLYETHER BLENDS

The ER effects were studied for various immiscible blends composed of urethane-modified polyethers and sillicones. Some polyethers and silicones were prepared from polypropylene glycol (PPG) and modified poly(dimethyl siloxane) having terminal hydroxyl groups, respectively. The influence of blend composition on the ER effects were examined for some binary and ternary blends based on these materials. The ER effects of these blends varied with the modification of polyethers and silicones, and also with the blend composition. In particular, the response of viscosity on applying or removing an electric field was found to vary with the blend composition, which should reflect some time-dependent change in the phase structure during the application and removal of the electric field. The variety of field response are discussed on the basis of the miscibility of the blend components.