The effects on the mechanical properties and cross-linking reaction as well as on the heat fusion properties of silicone rubber (PDMS) with/without polysilane (PMPS) were investigated. First, as a result of uniaxial tensile test and dynamic viscoelasticity measurement, although no change was observed in the cross-linking structure itself, the value of the molecular weight between the cross-linking points increased with the increase in the amount of PMPS added. On the other hand, regarding the cross-linking reaction process, the exothermic peak temperature during the cross-linking reaction decreased with PMPS content though, the enthalpy of the reaction did not change. Regarding the heat-fusion properties, it was found that although neat PDMS did not heat-fuse, both the PMPS-added PDMS sample and the solvent-extracted PDMS sample showed heat fusion characteristics. The reasons are as follows: 1. In the PMPS-added PDMS sample, many large network structures and free-ended chains are present when the cross-linked structure is formed, and these favor the entanglement of the PDMS molecular chains during heat fusion. 2. PMPS has the effect of improving the motility of PDMS molecules, and since the activation energy of diffusion in PDMS was as low as 11.3 kJ･mol^-1, PMPS diffused at the fusion interface.

Zero shear viscosity η₀ and steady state compliance J _e ⁰ are significant rheological parameters. Shear creep measurement could bring us these parameters. Meissner et al. reported their excellent procedure using the principle of Boltzmann’s superposition and the Ninomiya’s protocol. In this article the author revisited this procedure using industrial high density polyethylene. It was concluded that the Meissner’s procedure could give us stress independent (linear) values of the η₀ and the J _e ⁰ more properly than the traditional. The proposed η₀ was correlated with M _w ^4.5 (M _z/M _w). And theJ _e ⁰ had a reasonable relationship with MWD (molecular weight distribution), J _e ⁰ ∝(M _z/M _w)⁵ (M _n : the number averaged molecular weight, M _w : the weight averaged molecular weight and the M _z : the z-averaged molecular weight).

Currently, to pursue the international slogan of sustainable development goals (SDGs), both industry and academic researchers have devoted themselves for creation of sustainable materials. Usually, polymeric cross-linked materials have been suffered from the lack of recyclability due to the formation of covalent bonded cross-links with permanent life time. To overcome this issue, incorporation of dynamic covalent bonds into network structures is admitted as a useful option, which provides sustainable functions, such as recyclability and healability, with cross-linked materials. Recently, a new type of dynamic covalent bonds has been developed, in which the associative bond exchange without distinct steps of bond dissociation and reassociation are operated. Such materials have been termed vitrimers and nowadays attracted great attention due to the potential of the sustainable materials. In this article, we describe the features and useful functions realized by the vitrimer concept. In the last section, one simple application way of vitrimer concept into commodity plastic is demonstrated based on our recent research, where three distinct steps of decomposition (i.e., hydrolysis), epoxy opening reaction, and trans-esterification are evolved in the present unusual cross-linking mechanism.

In engineering uses of polymeric materials, heterogeneous polymer systems are applied to various parts or products as polymer blends and composites. Several useful topics on fundamental materials technology for the heterogeneous polymer systems will be introduced in the series of this special lecture, concerned with R&D activities in materials development & processing, product manufacturing & use, product retirement (end of life) and materials recycling. In this partⅠ, static fatigue of rubbery polymers under constant stress or strain conditions is mainly focused to obtain a basic understanding of the failure mechanism for pure and carbon black-filled rubber vulcanizates on the basis of a phenomenological theory of a stochastic process. The scattering in the lifetime of the pure vulcanizate reflects the inherent characteristics of the polymer, showing a random failure. Furthermore, influences of rubber-filler interactions, crosslink density and size of hard domains dispersed in the rubber matrix on the failure mechanism are discussed how to interrupt an unstable failure for the pure rubber vulcanizate.

When natural rubber (NR) with low cross-linking density is quickly stretched to high draw ratio, occasionally, stable strain-induced crystals form, resulting in a “shape memory” state in which elongation is maintained even when the rubber is released from tension. X-ray analysis showed that the crystalline part of the shape-memory NR is not so different from the usual NR. On the other hand, the melting behavior of the shape-memory NR suggested that the contraction force of the stretched amorphous chains decreases the melting temperature of the strain-induced crystals. Based on this idea, the free energy change of the melting of shape memory NR was formulated. The relationship between the factors used in this formulation was compared with the experimental results. A correlation was found between the experimental crystallinity and the crystallinity calculated using the other factors.