The mechanism of low‐temperature relaxations in bisphenol‐A‐type epoxide resins cured with aliphatic diamines, with aliphatic diamines in the presence of salicylic acid as an accelerator, and with tertiary amines was investigated to compare the dynamic mechanical properties and the chemical structure of these networks. Mechanical relaxations are observed at about −140 and −60°C. The former relaxation is denoted the γ relaxation and the latter the β relaxation. The β relaxation of the cured epoxide resins containing hydroxyether groups is a sum of contributions from the relaxation of these groups and of other parts of the network structure. A new relaxation due only to the motion of the hydroxyether group can be estimated from the difference of tanδ curves between the aminecrosslinked and ether‐crosslinked systems. The γ relaxation is attributed to the motion of a polymethylene sequence consisting of at least four carbon atoms.

SynopsisThe shrinkage and internal stress of bisphenol-type epoxide resins cured with aliphatic a,w-diamines, H&(CHz),,,,-NH2 (m' = 2,4,6, and 12), were investigated by measuring the change of density and the strain of the steel ring embedded in the cured resins. Internal stress was found to be induced by the shrinkage occurring in the cooling process from the glass transition temperature (T,) to room temperature. Shrinkage and internal stress increased with increase in the concentration of network chains and Tg of the cured systems, and then with a decrease in m' of the curing agents.It appears that the reductions in the concentration of network chains and T, were necessary to reduce the shrinkage and internal stress caused by the curing.

SYNOPSISThe mechanism for the occurrence of internal stress in the curing cycle of four-functional epoxide resins was investigated in detail. The internal stress in this system was generated at the vitrification point in the course of curing, because the modulus of samples was rapidly increased at this point. After the vitrification point, the internal stress was increased with an increase of the shrinkage in the curing and cooling processes.Moreover, the magnitude of the internal stress in the four-functional resin systems depended on the chemical structure of aromatic diamines used as curing agents. This was explained by the difference of curing shrinkage after vitrification in each system.

Static and dynamic mechanical properties of cured epoxide resins based on ester bonds, ether bonds, or a mixture of ester and ether bonds were investigated. Their network structures were estimated from the results of gel content before and after saponification, and conversion of functional groups. It was found that cured epoxide resins based on a mixture of ester and ether bonds indicate intermediate properties between the resins based on ester bonds and the resins based on ether bonds. Both dynamic and static mechanical properties were strongly affected by their network density and their segmental structures suggested in this paper.

SynopsisMechanisms for low-temperature relaxations of three spiro-ring-type epoxide resin systems with and without methoxy branches were investigated by comparison with those of a bisphenol A-type resin system. In the spiro-ring-type epoxi.de resin systems, two well-defined relaxation peaks, denoted as the 8 and 8' relaxations, and a shoulder peak were observed a t about -70, + 60, and OOC, respectively. The magnitude of the relaxation was decreased by the introduction of methoxy branches on the phenylene group. This phenomenon could be interpreted as a result of the formation of hydrogen bonds between the hydroxy-ether group and methoxy branch.Moreover, it was concluded that the 8' relaxation and the shoulder peak are due to the motion of the p-phenylene group adjacent to the spiro-ring and of the hydroxy-ether group blocked by the hydrogen bond, respectively. that the p' relaxation, which is observed from +50 to + 100°C, is due to the motion of the phenylene group in the n e t w~r k . '~*~ In this paper the effect of the epoxide resin structure on the low-temperature relaxation of cured resins is studied by comparing the relaxation behavior of a bisphenol A-type and three spiro-ring-type resins. The relaxation mechanisms for the cured spiro-ring-type epoxide resins are discussed in detail.