Shape-memory polyurethanes (PUs) were synthesized by 4,4 -diphenylmethane diisocyanate (MDI), 1,4-butanediol (BD), and poly(tetramethyl oxide)glycol (PTMO). The morphology of PUs was studied using DSC, DMA, and TEM. The results indicated that the PUs would show different morphology by changing the mol ratio of MDI and BD (hard segment). The specimens would show the shape-memory behavior that was fixing and recovering the deformation at different operating temperature ranges. These results demonstrated that the shape-memory behavior of the PUs would be affected by the morphology and the modulus ratio that was defined as E T g 020ЊC /E T g /20ЊC in DMA analysis. The amount of the hard-segment-rich phase would affect the ratio of recovery, that is, the low content would lead to the recovery of the deformed specimen being incomplete. The recovering rate would be influenced by the modulus ratio and the size of the dispersed phase in the micromorphology. On the other hand, the shape-memory behavior of PUs could be enhanced by the training process.

Polyurethanes (PUs) of a suitable molar ratio of monomers were found to have shape-memory behavior. In this study, four series of PUs were synthesized by 4,4-diphenylmethane diisocyanate (MDI), 1,4-butanediol (BD), and various molecular weights of poly(tetramethylene oxide)glycol (PTMO) to study the influence of the soft segment (PTMO) on the shape-memory behavior of PUs. The investigation on thermal and dynamic mechanical properties was performed using DSC and DMA; then, the morphology of the PUs was directly observed by TEM. At the range of the individual glass transition, a similar recovering behavior was found from the deformed specimen that contained the same composition but different molecular weights of PTMO. However, the phase separation between the soft and the hard segments of the PUs would influence their shape-memory behavior. On the other hand, a large number of the dispersed phase of the PUs would delay the recovery rate of the deformed specimens using a high molecular weight PTMO.

A series of shape-memorized crosslinked ester-type polyurethanes (PUs), based on different compositions of 4,4Ј-diphenyl methane diisocyanate (MDI), poly(butylene adipate) glycol (PBAG) with different molecular weight (MW) and trimethylol propane (TMP), were synthesized. The morphology of samples was investigated by using DSC, WAXD, and dynamic mechanical analysis (DMA). It was found that the morphology of the soft segment, which was PBAG with a different MW, was in an amorphous state and no crystalline domain was found. By increasing the crosslinked density (varying the content of TMP) or decreasing the length of the soft segment (MW of PBAG), the glass transition temperature of studied samples increased. But the range of transition broadened and the modulus ratio EЈ (T g Ϫ20°C) /EЈ (T g ϩ20°C) also decreased. The shape-memory behavior was studied by the bending test method adopted from the shape-memory alloy. The sample with high T g showed not only a high recovered temperature (T r ) but also a high recovered rate (V r ) with a high modulus ratio. By introducing the chemical crosslinked structure, the deformed samples completely recovered their original shape and rendered shape-memory behavior under the complex deformation. The shape-memorized crosslinked ester-type PUs can be applied at different operating temperatures. A mechanical viscoelastic model is discussed for the shape-memory behavior of PUs, and the modified Bonart's viscoelastic model properly describes the mechanism of the shape memory of PUs.

Effects of temperature (15/10, 25/20, 30/25, and 35/30 °C) and drought stresses on the expression of granule-bound starch synthase I (GBSSI) gene were examined in rice (Oryza sativa L.) seedlings. The GBSSI expression was higher at the low temperature (15/10 °C), and the transcript level decreased at temperatures higher than 30 °C. Protein phosphorylation was involved in the low temperature-stimulated signal transduction of GBSSI regulation. The expression of GBSSI in rice seedling was reduced under a drought stress. Even though exogenous ABA played a role to reduce the GBSSI transcript accumulation under non-stress condition, the reducing of GBSSI expression by drought stress appeared to be mediated by an ABA-independent pathway.

To understand the kinetic of synthesis of polyamide‐imide (PAI) via p‐chlorophenol‐(PCP) blocked 4,4′‐diphenyl methane diisocyanate (MDI) with trimellitic anhydride (TMA), a series of reactions of blocked MDI with excess phthalic anhydride (PA) and benzoic acid are designed. PCP‐blocked phenyl isocyanate (BPI) which also released isocyanate at higher temperatures was used as a model compound for BMDI. The dissociation constants of BPI and BMDI in the presence of excess PA or BA was measured by collecting the evolved CO2. The effect of the catalyst concentration and temperatures were combined by a Hostettler equation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1703–1710, 1997