Shinichi Yamazaki

Morphology Control of Aromatic Polymers in Concert with Polymerization

Morphology control methods of aromatic polymers in concert with polymerization reaction are described in this review. Many attractive methods have been developed including reaction-induced phase separation of oligomers, epitaxial polymerization, shear-induced chain orientation during gelation, template-based polymerization, suspension polycondensation, solid-state polycondensation and liquid-liquid interfacial precipitation and so on. Among them, the reaction-induced phase separation of oligomers, in which there are two modes of crystallization and liquid-liquid phase separation, possess practically high potentiality to create novel polymer materials since it can control not only the morphology but also the molecular chain orientation. Ultimate goal is the embodiment of the nature system in a flask, that is, the control of the materials from primary structures to super structures. The morphology control methods by using polymerization reaction afford the valuable methodology for the three-dimensional structure architecture.

Second-order phase transition of high isotactic polypropylene at high temperature

Abstract A second-order phase transition of α2 form isotactic polypropylene (iPP) is found at high annealing temperature (T a =159.3 ° C ) by means of X-ray diffraction method. Although the lattice shape and the space group keep the same as those of the α2 form, i.e. monoclinic and P 2 1 / c , with increase of T a , it has been revealed that there are discontinuous increases in the slopes of the lattice constants a and b against T a plots, while the c and the β keep almost constant. As a result, the slope of the unit cell volume V versus T a plot also shows a discontinuous increase at T a =159.3 ° C , indicating the occurrence of the second-order phase transition. In order to distinguish the two phases, the phase above the transition temperature is named α2′ phase and the transition temperature is denoted T α2–α2′ . These facts suggested that the α2′ form is a mobile phase where the molecular chains would become loosely packed and mobile, promoting the better chain sliding diffusion. A fast lamellar thickening process has been confirmed in the higher temperature region than T α2–α2′ , which was reported in the precedent paper. General significance is proposed that mobile phases possibly exist at high temperature, close to the melting temperature and accelerate lamellar thickening, which improves physical properties of polymers.

Direct Evidence of Nucleation During the Induction Period of Polyethylene Crystallization by SAXS

Direct evidence that nuclei are formed during the induction period of crystallization is obtained for the first time by means of small-angle X-ray scattering (SAXS). Polyethylene (PE) was used as a model crystalline polymer. The nucleating agent was mixed with PE in order to increase the scattering intensity I x from nuclei as large as 104 times bigger than usual. I x increased soon after quenching to the crystallization temperature from the melt and saturated after some time. A new theory is proposed to estimate the size of the nuclei N, the number density distribution of nuclei with N at time t, f(t,N), and the induction time τ i, by analyzing the SAXS scattering intensity. The volume-averaged size of the nuclei was nearly the same as that of critical nuclei and does not change so much with time during the induction period. Lamellae start stacking much later than nuclei start forming.

Molecular weight dependence of equilibrium melting temperature and lamellar thickening of isotactic polypropylene with high tacticity

Molecular weight (M) dependence of the equilibrium melting temperature of isotactic polypropylene (iPP) with high tacticity ([mmmm]=99.6%) was studied. Four fractionated iPPs with M n=23×103, 64×103, 94×103, and 263×103 were used. was obtained by using an improved method based on the Gibbs–Thomson plot proposed in previous papers. The effect of “melting kinetics” on melting temperature (T m) was eliminated by observing isothermal melting of spherulites. The effect of lamellar thickening on T m during T m measurement at high temperature was also eliminated by observing thick lamellae formed at high crystallization temperatures (T c=148∼166°C). With increase of M, increased significantly. The empirical equation, (°C), was obtained. The molecular weight dependence of the α2–α2′ transition was observed. The transition temperature (T α2–α2′) also increased with increase of M. The ΔT dependence of lamellar thickness was concluded to be controlled by that of lamellar thickening.

Nucleation and Morphology of Polyethylene Under Shear Flow

Effect of the shear flow (γ˙=0.5∼5 s−1) on the nucleation and on the morphology of polyethylene (PE) during crystallization from the melt was studied by means of polarizing optical microscopy and small angle X-ray scattering. In order to analyze the results by the nucleation theory, we observed the effect of shear flow on the equilibrium melting temperature The under shear flow and that under quiescent state are almost the same, Therefore, the shear flow does not affect the The “heterogeneous” primary nucleation rate (I) and the induction onset time of nucleation (τ onset) of the isolated crystals under shear flow are also almost the same as those under quiescent state. The heterogeneous primary nucleation means that isolated nuclei are sporadically generating from the melt with the aid of heterogeneities such as nucleating agents. After the generation of primary nuclei, the “shish” were generated independent of the primary nucleation. We found that the shish were formed by the chain elongation caused by the velocity difference between polymer chains and dust particles, etc. After that, we observed that the “kebabs” were formed on the shish. It was found that the nucleation from the melt after melting of the “shish-kebabs” (at melt annealing temperature T max=160°C for 5 min) was accelerated compared with the ordinary melt crystallization after melting of folded chain crystals. This indicates that the “solid memory effect” of the former solid is significant. This is because of the low entanglement density within the melt of shish kebabs.

Improvement of Adhesion Between Liquid Crystalline Polyester Films by Plasma Treatment

Surface modification of thermotropic liquid crystalline aromatic polyester (LCP) films was carried out by low-pressure plasma treatment to improve the initial adhesion as well as the long-term adhesion reliability, a measure of durability between the LCP films used as substrates for printed circuit boards. Plasma irradiation was carried out in various plasma gases with different plasma modes such as reactive-ion-etching, and direct-plasma (DP) with pressures ranging from 6.7 Pa to 26.6 Pa. The introduction of polar groups on the film surface such as phenolic hydroxyl groups and carboxyl groups enhanced the initial adhesion by increased chemical interaction. However, if the concentration of polar groups became too high, the longterm adhesion reliability estimated by the pressure cooker test was degraded due to the acceleration of the penetration of water molecules into the interface. A large surface roughness was also effective in preventing the decrease in the long-term adhesion reliability. However, too much increase in surface roughness decreases the long-term adhesion reliability. The DP-treatment in the O2 atmosphere at a gas pressure of 6.7 Pa was found to be the best plasma condition for both the initial adhesion as well as the long-term adhesion reliability between the LCP films.