Tadao Kotaka

A hierarchical structure and properties of intercalated polypropylene/clay nanocomposites

Abstract We have prepared the intercalated nanocomposites of polypropylene (PP)/clay (PPCNs) successfully using maleic anhydride modified PP (PP-MA) and organophilic clay via melt extrusion process. The hierarchical structure of the PPCNs from the structure of confined PP-MA chains, in the space a few nanometer width between silicate galleries to crystalline lamellae of 7–15xa0nm thickness and spherulitic texture of 10xa0μm diameter, were probed using a wide-angle X-ray diffraction, small-angle X-ray scattering, transmission electron microscope, polarizing optical microscopy and light scattering. After crystallization had taken place at 80°C, the PPCNs formed rod-like crystalline texture in the 10xa0μm length scale which consisted of the inter-fibrillar structure including γ-phase crystallite caused by the reduction of the PP-MA chains mobility due to the intercalation of the PP chains in the space between silicate galleries and the narrow space surrounded by the dispersed clay particles. The intercalated PPCNs showed an enhancement of moduli compared with PP matrix without clay. The necessity of the intercalating degree of PP-MA chains on the enhancement of the mechanical properties are discussed.

Synthesis and structure of smectic clay/poly(methyl methacrylate) and clay/polystyrene nanocomposites via in situ intercalative polymerization

Via in situ intercalative free-radical polymerization, we prepared clay/poly(methyl methacrylate) (PMMA) and clay/polystyrene (PS) nanocomposites from lipophilized smectic clays. The intercalation spacing in the nanocomposites and the degree of dispersion of these composites were investigated with X-ray diffraction and transmission electron microscopy, respectively. Under some conditions, the intercalative nanocomposites exhibited flocculation because of the hydroxylated edge–edge interaction of silicate layers. The nanocomposites had higher storage modulus and higher Tg compared to without clay systems.

DISPERSED STRUCTURE CHANGE OF SMECTIC CLAY/POLY(METHYL METHACRYLATE) NANOCOMPOSITES BY COPOLYMERIZATION WITH POLAR COMONOMERS

Abstract Via in situ free-radical copolymerization of methyl methacrylate (MMA) with a small amount of polar comonomers such as N,N-dimethylaminopropyl acrylamide (PAA), N,N-dimethylaminoethyl acrylate (AEA) and acrylamide (AA), we synthesized clay/copolymer-based nanocomposites from lipophilized smectic clay (SPN). The degree of dispersion and the intercalation spacing of these nanocomposites were investigated by using a transmission electron microscope (TEM) and X-ray diffraction (XRD), respectively. The introduction of the polar comonomers affected the features of both aggregation and flocculation (edge–edge) interactions. On incorporation of the PAA comonomer, a much stronger flocculation took place owing to the edge–edge interaction of the silicate layers. In contrast, the AA comonomer played an important role in delaminating the layers. Especially in the PMMA-AA (1xa0mol%)/SPN system, the ordered intercalated nanocomposite was formed as revealed by XRD and TEM. Each copolymer matrix nanocomposite showed a larger enhancement of moduli compared with the PMMA/SPN nanocomposite due to the large aspect ratio of the dispersed clay particles in the copolymer matrices.

Dispersed structure and ionic conductivity of smectic clay/polymer nanocomposites

Abstract We examined the correlation between the internal structure and the ionic conductivity behavior of lipophilized smectic clay (SPN)/polymer nanocomposites having various dispersed morphology of the clay layers. Both polystyrene (PS)/SPN and poly(methyl methacrylate) (PMMA)- co -acrylamide (AA) (99/1xa0mol rate)/SPN intercalated nanocomposites, which have finer dispersion of the clay layers, exhibited higher ionic conductivity rather than the other systems such as PMMA/SPN nanocomposite with stacking layer structure. The finer the dispersed morphology the higher was the conductivity of the nanocomposites.

Phase separation and homogenization in poly(ethylene naphthalene-2,6-dicarboxylate)/poly(ethylene terephthalate) blends

Abstract Competitive domain-structure development and homogenization under annealing were investigated via time-resolved light scattering and 1H n.m.r. in melt-quenched blends of partially miscible poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) and poly(ethylene terephthalate) (PET) loaded with/without PEN-PET random copolymer as a compatibilizer. In the early stage the domain structure formation took place presumably by demixing via spinodal decomposition (SD). In the intermediate stage, the domain growth was retarded by transesterification between the two polyesters through the domain interphase, and the whole system was gradually homogenized due to the miscibility enhancement by the produced PEN-PET multiblock copolymer species, as revealed by 1H n.m.r. analysis. Incorporation of the random copolymer also suppressed the domain growth and resulted in acceleration of the homogenization.

Structure and properties of polyaniline films prepared via electrochemical polymerization. I: Effect of pH in electrochemical polymerization media on the primary structure and acid dissociation constant of product polyaniline films

Abstract Electrochemical polymerization of aniline was conducted in constant current mode at different pH ranging from 0.2 to 3.7 in an ITO glass electrode-quartz cell assembly for in situ monitoring of the changes in potential, amount of charge passed through, and u.v.-visible absorption (u.v.-Vis) spectra during polymerization. u.v.-Vis spectra of product polyaniline (PAn) films were determined in different pH solutions to evaluate the apparent acid dissociation constants (pKa)app from plots of log { (Abs HAX − Abs obs ) (Abs obs − Abs A ) versus pH, where Absobs, AbsHAX, and AbsA are the observed absorption strength and those of the fully protonated and deprotonated species, respectively, for a given wavelength light. In PAn films prepared at low pH ( 1.5), PAn chains with short conjugation length were produced and later deteriorated as the polymerization proceeded, because the polymerization potential eventually exceeded a critical value (+ 0.8 V) beyond which degradation of produced PAn chains took place.

Structure development in polyaniline films during electrochemical polymerization. II: Structure and properties of polyaniline films prepared via electrochemical polymerization

Abstract Structure development in polyaniline (PAn) films was followed during the electrochemical polymerization in 1 M HCl solution via a constant potential mode at + 0.76 ± 0.03 V and pH = 0.2 by using several in situ and/or out of situ techniques including UV-visible spectrometry, chronoamperometry, cyclic voltammetry, Rayleigh scattering and atomic force- and optical microscopy. As the polymerization proceeded from the initial nucleation stage I (where the polymerization current density varies as I ∝ t0) to the intermediate stages IIa and IIb (I ∝ t3 → t2) and the final stage III (I ∝ t4), the gross morphology changed from grainy to fibrillar texture. The fibrils were aggregates of the grains with the size unchanged from that formed in the early stage. This difference between the grainy and fibrillar structures is due to the difference in the state of aggregation of the initially formed grains. In the later stages, however, the fibrils began to form branches, accelerating the rate of polymerization. The branched fibrils grew toward the vertical direction, keeping their horizontal structural size virtually unchanged.

Effect of counter ions in electrochemical polymerization media on the structure and responses of the product polyaniline films. III. Structure and properties of polyaniline films prepared via electrochemical polymerization

Abstract Using polymerization solutions containing 0.1 M aniline and 1 M HCl or 1 M HC104, which happened to give the same pH (0.2), we investigated the effects of different counter-anions on the primary and higher order structures as well as on electrochemical responses of the obtained polyaniline (PAn) films. From time developments of polymerization current and u.v.-visible absorption spectra as well as the results of atomic force microscopic (AFM) observation, we found that in both media the higher order structure of the PAn films developed in almost the same manner from grainy to fibrillar texture and finally to bundles of the fibrils. The primary structures as judged from the spectra were not very different, but the structural size was somewhat larger for the films prepared in HC104 than the ones prepared in HCl. The apparent acid dissociation constants of the resulting PAn films were again not so different, reflecting little differences in their primary structures. However, the electrochemical responses of the former were much slower than those of the latter, especially when the transition from the oxidation to reduction form was compared, reflecting differences especially in the structural size and compactness of their higher order structures.

Elongational flow and birefringence of low density polyethylene and its blends with ultrahigh molecular weight polyethylenet

Via elongational flow opto-rheometry (EFOR), simultaneous measurements of tensile stress σ(t) and birefringence Δn(t) were conducted on a low density polyethylene (LDPE) melt and its blends with an ultra-high molecular weight polyethylene (UHMWPE) at 140°C under transient elongational flow with constant tensile strain rate ʵ0. The transient elongational viscosity nE(t)σ0 of LDPE melt first gradually increases with time t following the linear viscoelasticity rule in that ηE(t) is 3 times the shear viscosity development. 3η(t), at low shear rate γ up to a certain critical strain, beyond which ηE(t) tended to increase rapidly with t. The behaviour was often referred to as strain-induced hardening. For LDPE melt both σ(t) and Δn(t) versus tensile strain ɛ(t) (=ɛ0 t)curves were dependent on ɛ0 in such a manner that the stress optical coefficient C(t) ≡ Δ(t)/σ(t)) was independent either of ɛ0, ɛ(t), ɛ(t) or σ(t). Addition of UHMWPE up to 10 wt% to LDPE melt increased the levels of both σ(t) and Δn(t), but the tendency of strain-induced hardening was reduced. The C(t) was again independent either of ɛ0, ɛ(t) or σ(t) and also essentially independent of molecular weight (MW) and its distribution (MWD) or the blend ratio. For both LDPE and the blends the C(t) value roughly agreed with that (= 2.2 × 10−9 Pa−1) reported for shear flow experiments, thus confirming the val dity of the so far established stress optical rule.

Elongational flow-induced morphology change of block copolymers. 2. A polystyrene-block-poly(ethylene butylene)-block-polystyrene triblock copolymer with cylindrical microdomains

Abstract Elongational flow behavior of a polystyrene-block-poly(ethylene butylene)-block-polystyrene (SEBS) triblock copolymer melt with cylindrical morphology is investigated by elongational flow opto-rheometry (EFOR), transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The SEBS film is first roll-processed to align the PS cylinders in a preferred direction. The uniaxial elongation is applied either parallel (denote Case I) or perpendicular (Case II) to the cylinder axis. Transient tensile stress σ( ϵ 0 ;t) and birefringence Δ n( ϵ 0 ;t) are measured with a constant Hencky strain rate ϵ 0 ranging from 0.01 to 1.0xa0s−1 at various temperatures between PS glass transition, Tg(PS), and the order–disorder transition, TODT, of the SEBS. The data suggest that either the PS or PEB domains is preferentially elongated in the early stage of elongation, depending on the initial alignment of the cylinder phase. On further elongation, the elongational viscosity of the Case I melt exhibits strain-induced softening behavior in the final stage of elongation, whereas that of the Case II melts clearly displays strain-induced hardening behavior. The TEM and SAXS data of the samples elongated with a ϵ 0 =1.0 s −1 show that the cylinders are mostly inclined approximately by 40–50° to the direction of elongation, whereas they are mostly aligned, parallel to the elongation direction on slower elongation. The morphology of highly elongated SEBS melts is governed by the applied strain rate and temperature, regardless of the initial orientation of the cylinders.