The structural analyses of silicon-based polymers such as polysilanes and poly[(phenylsilylene) ethynylene-1, 3-phenyleneethynylene] (abbreviated by MSP) by solid-state NMR were reviewed. As an example for polysilanes, the structure of solid polymethyiphenylsilane over a wide range of temperatures has been successfully elucidated by solid-state NMR combined with FPT-CNDO/2 MO method. On the other hand, for MSP thermosetting mechanism has been elucidated. The intermolecular cross-linking reactions owing to 1) the Diels-Alder reaction and 2) the hydrosilylation reaction occur at above 150°C, and a very highly thermally stable structure is formed. It has been demonstrated that solid-state NMR is a very useful tool to study the structure and dynamics of silicon-based polymers.

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Positron annihilation lifetime spectroscopy (PALS) has recently been applied successfully to the detectection of free volumes in solid state polymers. Positrons injected into polymers from radioisotopes such as ²²Na lose energy through interaction with atoms and molecules. After loosing the energy, positrons with a few hundred eV make the terminal spurs, which consist of ions, electrons and positrons, and then the positrons form a hydrogen like atom, positronium (Ps). Ps diffuses in polymers until it is trapped in intermolecular spaces. Ps decays in these spaces and the size can be measured by the long lifetime (τ₃) of ortho-Ps. Thus Ps is considered to be a nanometer probe of the inter-molecular spaces. The intensity (I₃) of o-Ps is influenced by characteristics of polymers such as chemical structure (electronegativity), polymer structure (crystallinity, polymerization, softening points) and movement of molecules and segments. Hence I₃ is a good probe for studying the molecular motion and other charactristics of polymers.
In this article, free volumes of several epoxy resins have been studied. The shift of the size of free volumes was observed when a THPM epoxy resin absorbed water. Polymerization of bisphenol A dicyanate was examined using PALS and the increase in the specific volume was observed with the increase in the degree of polymerization. Also, the relaxation of polymer structures was discussed using PALS. After quenching the novolac epoxy resins to liquid nitrogen temperature, the large intermolecular spaces were observed, which would be formed by combining several small spaces due to the stress among polymer chains.
Although PALS is considered to be a useful method to detect nm size spaces, this will be more important methology by the comparison of other analytical methods, which is now under investigation.

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Photo-probe technique using photophysical or photochemical process as a probe is one of the most useful technique to characterize microstructure of amorphous polymer solids. It has advantages giving information both of molecule-size scale and of nano-second time scale. The concept and examples of fluorescent probes and photoreactive probes are presented. Fluorescent probes are classified into microenvironment probes, molecular motion probes, and microstructure probes. Photoreactive probes are used for investigating local free-volume size distribution and fluctuation arising from various thermal relaxation of matrices. In the present review, photo-probe technique is applied mainly to crosslinked polymers.

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Principles of characterization of polymer surface structure and surface molecular motion have been presented. Also, the characterization techniques of surface molecular motion of polymeric solids have been summarized. Temperature dependent X-ray photoelectron spectroscopy (TDXPS) was utilized for the characterization of surface molecular motion of symmetric diblock copolymers. The activation of surface molecular motion at the surface was also confirmed by TDXPS. Dynamic secondary ion mass spectroscopy (DSIMS) was employed for the depth profiling of the chemical composition of end-labelled polystyrene (PS) film and the end group segregation at the air/solid PS interface was verified by DSIMS. Scanning viscoelasticity microscopy (SVM) was developed for studying of the surface mechanical properties of polymeric solids. It was revealed that the molecular motion at the surface of glassy polystyrene (PS) was fairly activated compared with that of bulk one due to the surface segregation of chain end groups. These results indicate that surface glass transition temperature is depressed due to the increase in free volume near surface region. The two-dimensional mapping of the surface mechanical properties for the polymer blend ultrathin films was carried out on a nanometer scale by using SVM.

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This review describes the characterization of network polymers by ESR, mainly focusing on the following two points : (1) Generation of the inhomogeneity of network structure, which was discussed by pursuing the accumulation and spectral change of growing polymer radical and pendant radical generated in the radical crosslinking polymerization of multivinyl compounds. (2) Evaluation of the micro-Brownian motion of polymer and generation of the inhomogeneization of the resulting network structure with the progress of crosslinking, which were pursued by using spin probes and/or labels.

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The mechanical properties of gels obtained by the cationic crosslinking of poly (ethylene glycol allenyl methyl ether) were examined both in the dried and swollen states. Relatively high elastic properties were observed in the dried state. The storage modulus (E′) and loss modulus (E″) were evaluated as a function of the cationic crosslinking conditions. In most cases, E″was much smaller than E'. The number of elastically effective crosslinking points (n_e) and the molecular weight between two crosslinking points (M_c) were estimated from the storage modulus (E′) in a linear viscoelastic region. The maximum value of ne and the minimum value of M_c was observed for the dried gel produced by the reaction in CH₂Cl₂ (20wt%) with 1.2mol% of BF₃·OEt₂. Thus, the effectiveness of the crosslinker was found to be dependent upon the cationic crosslinking conditions.

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