Structure changes around the crack tip of natural rubber vulcanizates filled with carbon-black were investigated after a cycle of stretch-retraction. On the extension line of the crack, formation of a valley-like dent was newly found. The depth of the dent was about 10 μm. By the diffraction mapping using the micro X-ray beam, localization of crystals of paraffin, which has been mixed as plasticizer, along the valley-like dent was disclosed. These findings indicate the occurrence of large-scale mass transfer which leads to three-dimensional transformation and segregation of the low molecular weight material along with the strain-induced crystallization around the crack tip.

The 100% modulus measured by a tensile test for crosslinked poly (butyl acrylate-acrylic acid) random copolymer (P (BA-AA)) as pressure-sensitive adhesive showed the clear tensile rate dependence, whereas that for vulcanized isoprene rubber (IR) never showed the dependence. To clarify this reason, the crosslinking structure of both systems was compared in terms of the molecular weight between crosslinking points (M_c) values determined via equilibrium swelling, dynamic mechanical analysis and tensile tests. There are two kinds of crosslinking points: the chemical crosslinking points and the entanglement points of polymer chains. It was found that the proportion of entanglement points was far greater in the crosslinked P (BA-AA). The entanglement points can readily disentangle with a stress relaxation in response to slow deformation. This is the reason why only the crosslinked P (BA-AA) showed the tensile rate dependence. The glass transition temperature (T_g) was higher for the crosslinked P (BA-AA) than for the vulcanized IR. From the ¹H pulse nuclear magnetic resonance analysis, the restriction of molecular mobility by the intermolecular interaction was found to be larger in the crosslinked P (BA-AA) than in the vulcanized IR. Therefore, the crosslinked P (BA-AA) shows higher T_g.

Polyurethane elastomers (PUEs) are one of the most popular polar polymers. The PUEs are usually composed of soft segment formed with polymer glycol and hard segment done with diisocyanate and curing agent. The properties of the PUEs are strongly dependent on chemical structure, molecular weight and polydispersity of soft segment or hard segment components, weight fraction of both components and so on. However, the quantitative contribution of physical cross linkages to rubber elasticity and the direct observation of micro phase separation have not been done yet. The molecular design factors for high performance PUEs and origin of rubber elasticity are discussed by chemical analysis of crosslinks and observation of the micro phase-separated structure of the PUEs using AFM.

Some of the pioneering works on polymer nanotechnology by our group have been illustrated with basic concepts and several experimental evidences. They are developments of;

1) Real time pulsed NMR system using personal computer and software for analysis to calculate spin-spin relaxation time, spin-lattice relaxation time, and spin-lattice relaxation time in the rotating frame. At the same time signal intensity for multiple relaxation time component can be analyzed. The system has been applied to study crystallization of crystalline polymers, phase separation process of polymer blends, gellation process, and so on.

2) Digital image analysis system using video-recorder, personal computer, large scale computer center and optical microscope or electron microscope to analyze images from polymeric materials quantitatively. Some examples are 2 dimensional Fourier transformation and its power spectrum calculation during phase separation and so on.

3) Polymer material oriented energy filtered three dimensional transmission electron microscope using computer tomography. By this system, we can analyze microphase separated block copolymers, nano-composites, poly mer alloys and so on in three dimension.

4) Nano-mechanical property evaluation system based on atomic force microscopy. By this system, we can do nano-mechanical mapping of multiphase polymers and even nano-fishing of a single polymer chain.

The future developments in this field is also described in this paper.