Rheology of Styrene–Butadiene Diblock Copolymers in Selective Solvent: Mechanisms of Thixotropy and Thermally Induced Rheological TransitionWatanabe, Hiroshi; Kotaka, Tadao
doi: 10.1295/polymj.15.337pmid: N/A
Styrene-rich butadiene–styrene (BS) diblock copolymers dispersed in dibutyl phthalate (DBP) formed micelles with B cores and S cilia. As the concentration was increased, these micelles arranged themselves on a macrolattice, and the system began to show plasticity and also thixotropy. When the temperature was raised, the system underwent a transition from plastic to viscoelastic behavior. This rheological transition was found to be associated with disordering of the macrolattice. The mechanism was interpreted as follows. With increasing temperature, the S and B blocks intermix more extensively in the interphase, making the interphase more diffuse. The mobility of the B–S junctions in the diffuse interphase increases, and hence, the stability of the macrolattice is reduced. This interpretation is supported by the following two findings: no transition occurred when the micelle cores were crosslinked in order to prevent intermixing of the B and S blocks and to anchor the junctions tightly on the cores; no plastic behavior was observed for DBP solutions of tapered block copolymers (tBS) with the characteristics comparable to those of the BS/DBP micellar solutions. In such a tBS solution, micelles with a diffuse BS interphase were formed, and the macrolattice became unstable. Thixotropy of the system having a macrolattice was apparently caused by breakage of the macrolattice but not necessarily that of the micelles. In fact, the macrolattice system of BS micelles with crosslinked B cores exhibited thixotropy, while random suspensions of the micelles were neither plastic nor thixotropic.
Syntheses and Properties of Periodic CopolymersYokota, Kenji; Kougo, Takanori; Hirabayashi, Tadamichi
doi: 10.1295/polymj.15.349pmid: N/A
A2B-type periodic copolymers with the structure, –[–CH2CH2–CH2CH2–CH2CXY–]– were synthesized by hydrogenating various alternating butadiene–acrylic copolymers. Substituents X, Y were Cl, COOCH3; H, COOCH3; CH3, COOC2H5; CH3, COOCH(CH3)2; CH3, COOC6H5; CH3, COOCH2C6H5; and H, CN. Identification of the structure and tensile properties of the copolymers are described. A periodic copolymer was compared with a random copolymer of the same composition. The periodic copolymer showed crystalline melting and higher glass-transition temperatures and was a harder and less extensible material than the random copolymer.
Effect of Substituent Groups on Hydrogen Bonding of Polyhydroxystyrene DerivativesNakamura, Kunio; Hatakeyama, Tatsuko; Hatakeyama, Hyoe
doi: 10.1295/polymj.15.361pmid: N/A
Poly(2-hydroxystyrene) (PoHS), poly(3-hydroxystyrene) (PmHS), poly(4-hy-droxystyrene) (PpHS), and their acetylated polymers were prepared. Attention was directed to the effect of substituent groups and sorbed water on the molecular motion of the polyhydroxystyrene derivatives. The glass transition temperature (T
g) of these polymers and the phase transition of water sorbed on the polymers were studied by differential scanning calorimetry (DSC). Bound water content was calculated from total amounts of sorbed water and crystallization enthalpy of water. The T
g of each polymer increases linearly with increasing mole fraction of hydroxystyrene (HS). It was clarified that the T
g increase is dependent on the replacement of acetoxyl groups with hydroxyl groups, since formation of hydrogen bonding occurs through the hydroxyl groups of the polymers. It was also found that the hydroxyl group of PmHS located at the 3-position of each aromatic ring formed hydrogen bonds the most readily, while that located at the 4-position did so second to this. The OH group of PoHS located at the 2-position formed hydrogen bonds with difficulty. Two exothermic peaks for the crystallization of water sorbed on each of the above polymers were observed on a DSC curve: one was a sharp peak (Peak I) of free water observed at about 255 K, and the other, a broad small peak (Peak II) of freezing bound water observed at about 230 K. Judging from the amounts of water calculated from the crystallization enthalpy of water sorbed on each polymer, there seems to be non-freezing water which does not crystallize. The bound water content of each polymer increased with increasing mole fraction of HS. The increase in bound water content of PmHS was highest with increasing mole fraction of HS.
Osmotic Pressure of Semidilute Solutions of Branched PolymersHigo, Yuji; Ueno, Noboru; Noda, Ichiro
doi: 10.1295/polymj.15.367pmid: N/A
Osmotic pressures for branched polymers in a good solvent were measured over a wide range of concentrations. Two types of branched polymers, star-shaped poly(α-methylstyrene)s having three branches and comb-shaped polystyrenes having 15—16 branches, were studied. The data were analyzed using the scaling law. The difference in the reduced osmotic pressure between star-shaped polymers having three branches and the corresponding linear polymers results from the difference in radii of gyration. In branched polymers having many branches, there is a region from which the segments of other molecules are excluded as a result of high segment density.
Dielectric and Dynamic Mechanical Behaviour of Poly(vinylchloride) Containing Small Amounts of Cholesterol, Cholesteryl Chloride, and Cholesteryl BenzoateDeshpande, D D; Tiwari, V K
doi: 10.1295/polymj.15.377pmid: N/A
Poly(vinyl chloride) (PVC) containing small amounts of cholesterol (Ch), cholesteryl chloride (ChCl), and cholesteryl benzoate (ChBz) were studied by dielectric and dynamic mechanical spectrometry. Dielectric data were fitted to the WLF equation. Using the C1C2 constants obtained for pure PVC, PVC+additive systems fitted well the WLF curve by an appropriate choice of reference temperature, T
0. T
0 of PVC+additives were lower than that of pure PVC. α- and β-peaks in PVC+additives occurred at temperatures lower than those in pure PVC. β-Peak intensities in DMA spectra decreased on adding Ch and ChBz. This may be ascribed to the possible specific interactions of C-Cl dipoles in PVC with OH from Ch or aromatic protons from ChBz. Such a suppression of β-peak is described as antiplasticization by earlier workers. The behaviour of these additives with PVC differed from that with poly(vinyl acetate) or poly(butyl methacrylate) due to differences in apparent enthalpy of activation (ΔH
a) for the α-process.
Synthesis of Living Cationic Poly(N-vinylcarbazole) with Low Molecular WeightHigashimura, Toshinobu; Deng, Yun-Xiang; Sawamoto, Mitsuo
doi: 10.1295/polymj.15.385pmid: N/A
Living cationic polymers of N-vinylcarbazole (NVC) with controlled low molecular weight (Mn=103–104) and narrow molecular weight distribution (Mw/Mn∼1.2) were synthesized with iodine initiator at −78°C in methylene chloride containing a common-ion salt (nBu4NI). The polymerization was carried out at low NVC concentration (20—60 mM; [I2]0=1.0 mM; [nBu4NI]=0.50 mM) by the successive addition of small amounts of the monomer to a completely polymerized solution. At each stage of the monomer addition, the reaction was rapid and quantitative (completed within 5 min), and the number-average molecular weight (Mn) of the polymers was proportional to the total amount of added NVC. In salt-free methylene chloride solvent, on the other hand, such living polymerization did not take place; the Mn of the total polymer decreased with further monomer addition. At higher temperatures (−30 and −15°C), no living polymers were obtained even in the presence of the added salt.
Triple Helix and Random Coil of Scleroglucan in Dilute SolutionYanaki, Toshio; Norisuye, Takashi
doi: 10.1295/polymj.15.389pmid: N/A
Eleven sonicated samples of a polysaccharide scleroglucan (chemically identical with but different in biological origin from schizophyllan) in 0.01N sodium hydroxide (NaOH) and dimethylsulfoxide (DMSO) at 25°C were studied by light scattering, viscometry, and ultracentrifu-gation. Data for the radius of gyration 〈S
2〉1/2, the intrinsic viscosity [η], and the sedimentation coefficient s
0 as functions of weight-average molecular weight Mw, combined with those for the ratio Mw (0.01N NaOH)/Mw (DMSO), showed that scleroglucan dissolves in DMSO as a single randomly coiled chain very similarly to that of schizophyllan in the same solvent, while it dissolves in 0.01N NaOH as a rodlike trimer or higher aggregates, depending on whether Mw (DMSO) is lower or higher than 2×105. From ‹S
2›, [η], and s
0 for samples with Mw (DMSO)≲1×105 in 0.01N NaOH, the contour length per main chain residue and the diameter of the scleroglucan trimer rod were found to be 0.30±0.03 and 2.6±0.5 nm, respectively, which agree with the reported pitch (per residue) and diameter of the schizophyllan triple helix. Thus, it was concluded that the scleroglucan trimer has essentially the same triple helical structure as that of the schizophyllan trimer. Evidence was obtained showing that the higher aggregates in 0.01N NaOH consist of trimers as building units.