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Thermal properties of polymer are very important to the understanding of morphology and shape memory effect of shape memory polymers (SMPs). In this article, the thermal properties of shape memory polyurethane nanofibrous nonwoven are investigated systematically from the morphology of nanofibers, crystalline structure, isothermal crystallization behavior, and thermal-dependent strain recovery. The results indicate that the thermal properties of shape memory polyurethane nanofibrous nonwoven are influenced greatly by the electro-spinning and the recrystalline condition. The crystal melting temperature ( T) decreases as the crystallization temperature ( T) decreases, while the relative degree of crystallinity ( X) increases with the decrease of T within the temperature range of 20 to −30 °C. In particular, when the annealing temperature is higher than 150 °C, the T shifts to higher value and the X decreases significantly with the increase of T. Finally, temperature-dependent strain recovery curves show that the shape memory polyurethane nanofiber tends to have a lower recovery temperature as compared with the SMPU bulk film due to their ultrafine diameter. [ABSTRACT FROM AUTHOR]

In this paper, we developed a photo-thermo staged-responsive shape-memory polymer network which has a unique ability of being spontaneously photo-responsive deformable and thermo-responsive shape recovery. This new type of shape-memory polyurethane network (A-SMPUs) was successfully synthesized with 4,4-azodibenzoic acid (Azoa), hexamethylenediisocyanate (HDI) and polycaprolactone (PCL), followed by chemical cross-linking with glycerol (Gl). The structures, morphology, and shape-memory properties of A-SMPUs have been carefully investigated. The results demonstrate that the A-SMPUs form micro-phase separation structures consisting of a semi-crystallized PCL soft phase and an Azoa amorphous hard phase that could influence the crystallinity of PCL soft phases. The chemical cross-linking provided a stable network and good thermal stability to the A-SMPUs. All A-SMPUs exhibited good triple-shape-memory properties with higher than 97% shape fixity ratio and 95% shape recovery ratio. Additionally, the A-SMPUs with higher Azoa content exhibited interesting photo-thermo two-staged responsiveness. A pre-processed film with orientated Azoa structure exhibited spontaneous curling deformation upon exposing to ultraviolet (UV) light, and curling deformation is constant even under Vis light. Finally, the curling deformation can spontaneously recover to the original shape by applying a thermal stimulus. This work demonstrates new synergistically multi-responsive SMPUs that will have many applications in smart science and technology. [ABSTRACT FROM AUTHOR]

Supramolecular polymers are attractive in recent years. In this article, a series of pyridine containing polyurethanes (PUPys) with various pyridine contents and various MDI-BDO contents were synthesized from 1,6-hexamethylene diisocyanate (HDI), 1,4-butanediol (BDO), N, N-bis(2-hydroxylethyl) isonicotinamine (BINA) and diphenylmethane diisocyanate (MDI). Thereafter, the moisture absorption of PUPys was mainly investigated systematically from the effect of temperature, relative humidity (RH), pyridine content, MDI-BDO content, the mechanism, and the kinetic of moisture absorption. Results show that the moisture absorption process of PUPys matches with Fick's second law in the initial stage. The moisture absorption is dependent on the content of N, N-bis(2-hydroxylethyl) isonicotinamine (BINA), e.g., the moisture absorption decreases with the increase of MDI-BDO content as well as the decrease of BINA content. In addition, the moisture absorption increases with the increase of temperature and relative humidity (RH). Accordingly, the moisture absorption process of PUPy45 at RH = 65% and T = 25° can be expressed with the equation: ln M = 8.88-2975(1/ T) + 0.5lnt. On the basis of the moisture absorption, the shape recovery process of PUPys film under the moisture condition support that PUPys show excellent moisture-responsive shape memory effects. [ABSTRACT FROM AUTHOR]

Shape memory polymers are attractive for both science and industrial application. In this article, a series of pyridine-containing supramolecular shape memory polyurethanes (Py-SMPUs) with various diphenylmethane diisocyanate-butanediol (MDI-BDO) contents are synthesized from the 1,6-hexamethylene diisocyanate (HDI), N, N-bis(2-hydroxylethyl) isonicotinamide (BINA), BDO, and MDI. Then, they are investigated systematically using FT-IR, DSC, DMA, WAXD, and shape memory testing. The results show that the addition of MDI-BDO segment improves the strength of hydrogen bonding of Py-SMPUs. It promotes the formation of hard domains, but not influences the phase-separation structure, the intensity, and distribution of physical netpoints. In addition, the MDI-BDO segment improves the rubber modulus and drops the energy loss of Py-SMPUs. However, it does not influence the shape memory behaviors which are mainly influenced by the BINA content. If the BINA content is beyond 30 wt%, good shape memory effect can be achieved in the BINA-HDI-BDO-MDI system; and high shape recovery force can be obtained by increasing the MDI-BDO segment. [ABSTRACT FROM AUTHOR]

This work aimed at elucidating the influence of zwitterionic hard segments on the structures and properties of shape memory polyurethanes (SMPUs). A series of zwitterionic SMPUs was successfully prepared with N-methyldiethanolamine (MDEA), 1,3-propanesultone (1,3-PS), 1,6-hexamethylene diisocyanate (HDI) and polyethylene glycol (PEG6000). The influence of MDEA-PS-based zwitterionic hard segment on structure, morphology, thermal property, shape memory property and cytocompatibility were systematically investigated. The results demonstrated that the PEG-based zwitterionic SMPUs (PEG-ZSMPUs) formed phase separation structure consisting of crystalline soft phase and amorphous hard phase. The MDEA-PS zwitterionic segments showed a tendency to form ionic clusters in hard segments, which served as reinforced net points. Shape memory analysis showed that zwitterionic PEG-ZSMPUs containing a high content of zwitterionic segments had thermal-induced shape memory effects. Finally, cytotoxic assays demonstrated that MDEA-PS zwitterionic segment improved the biocompatibility of PEG-ZSMPUs. The zwitterionic PEG-ZSMPUs could thus have a promising application in smart biomedical fields. [ABSTRACT FROM AUTHOR]