With a small amount of isocyanate-terminated polysulfide (NCO-PSF-NCO) as additive, the commercial polysulfide-based sealant had significant improvement in mechanical properties. The test results showed that 5% of NCO-PSF-NCO could help to rise 50% in the tensile strength and 27% in the ultimate elongation of the polysulfide sealant. The adhesive strength to substrates such as steel, epoxycoated or polyurethane-coated surface also increased significantly. Dynamic mechanical thermal analysis and differential scanning calorimetry analysis revealed that formed polysulfide polythio-urethane-urea (polysulfide-urea) contributed to a slight increase in the T g of the polysulfide sealant. It might be due to the domains of polysulfide-urea, which had effects of physical crosslinking and chain-extending on the polysulfide sealant. However, the introduction of polysulfide-urea structures had no appreciable influence on oil resistance of the polysulfide sealant.

Highly branched poly(urethane-imide)-epoxy (AHBPUI-EP) cross-linked copolymer was prepared by the reaction of epoxy resin (EP) with amino-terminated highly branched poly(urethane-imide) via A 2 + B 3 approach. The structure and properties of the AHBPUI-EP cross-linked copolymers were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal gravimetric analysis, tensile tests, and X-ray diffraction, respectively. It has been found that the increasing of the Tg of the cross-linked copolymer was resulted from the high density of crosslinking. The thermal stability was enhanced after introducing both imide and epoxy. The initial degradation temperature was up to 332.68°C. Moreover, the mechanical properties changed with changing the content of EP, imide and the ratio of [A 2 ]/[B 3 ].

The curing process of a polysulfide (PSF) with a triacrylate crosslinker in the presence of an amine catalyst at room temperature is a rapid Michael addition. This reaction was monitored by real‐time infrared spectrum (RTIR). The results of the RTIR show that the consumptions of thiol and acrylate are stoichiometric until 80% conversion, indicating the characteristics of a “click” reaction. Dielectric analyzer (DEA) and dynamic mechanical analyzer (DMA) were employed to investigate the curing kinetics from which the activation energies of this curing reaction were obtained and shown to correlate with each other. In addition, the influences of the types and amount of amine catalyst, the different molecular weights of PSFs, and the triacrylate crosslinkers were discussed. Copyright © 2011 John Wiley & Sons, Ltd.

In this work, in situ dielectric analysis (DEA) was employed for the first time to the best of our knowledge, to monitor the curing process of polysulfide (PSF) sealant using manganese dioxide (MnO 2 ) as the curing agent, where the gel point and ending point were determined. The obtained results were verified by rheological tests of dynamic mechanical analysis and tensile strength tests. It showed a significant difference between this curing process and those of usual thermosetting materials. The influences of the pH value of the samples and curing temperature were investigated and discussed in detail. Also, activation energies of the curing reaction of the samples with different pH values were calculated. The results proved DEA as a reliable and useful method for in situ monitoring PSF-MnO 2 curing process.

Trimethylolpropanetriacrylate (TMPTA) was added to the polysulfide‐manganese dioxide (PSF‐MnO2) liquid mixtures as a crosslinker to improve their crosslinking capability. The samples were cured at room temperature for different times and the crosslinking degree was characterized by extraction and swelling tests. Mechanical properties of the cured samples including tensile, compression (stress relaxation, permanent set, and cyclic compression), and dynamic mechanical behaviors were investigated. The results indicated that the TMPTA crosslinker significantly increased the crosslinking degree and the homogeneity of the formed PSF networks. As a result, the tensile and compression stress and relaxation performances of the cured PSF rubber were dramatically improved. This result was also consistent with the results from the swelling, cyclic compression, and dynamic mechanical measurements. Interestingly, the tensile strength of the TMPTA cured samples did not show apparent change when the curing time was longer than 14 days, whereas their compression stress and relaxation performance were growing remarkably from 14 to 60 days. The improved performances were attributed to the high efficiency of thiol‐acrylate Michael addition reaction for the crosslinking. It promoted the curing rate, resulting in good compression properties in a much shorter curing time.POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers