Study On Hyperbranched Polyurethane Materials For Energy Storagy And Shape Memory

Hyperbranched polymer has become one of the research focuses in polymer research field and attracted much attention in recent years because of its unique structure and properties. In the past decades, the research in hyperbranched polymers has been developed from synthesis, chemical and physical properties to molecular theory, functionality and utilities. Recently, the polymeric material scientists have found growing interest in synthesis and properties of hyperbranched polyurethane. Among them, the research on the synthesis, structure and the relationship between structure and properties of hyperbranched polyurethane for energy storage and shape memory is a novel one and meaningful in scientific research and potential applications.Two kinds of hyperbranched polyurethanes for energy storage and shape memory based on hyperbranched polyester end-capped with hydroxyl groups were prepared by a two-step method in this study. The detailed research was focused on the synthesis, structure and the relationship between structure and properties of the hyperbranched polyurethane. The following works were carried out in this thesis:1. Studies on Solid-solid Phase Change Heat Storage Hyperbranched Polyurethane Based on Hyperbranched PolyesterThis study was focused on the synthesis of a novel solid-solid phase change heat storage hyperbranched polyurethane (HB-PUPCM) based on hyperbranched polyester. FT-IR, DSC, WAXD, DTG, SEM and AFM were used to study the structure characterization, phase change behavior, heat storage property, aggregation structure and phase change mechanism.The result indicated the HB-PUPCM has good thermal properties: great transition enthalpy, suitable phase transition temperature, good thermal stability, no liquid leakage in the phase transition process, great phase transition reversibility, the enthalpy of positive process and reverse process is close, and the direction is only depended on the temperature; reasonably good stability throughout the cycling process. It can be considered as promising PCMs.Polarization Microscope (POM), Wide Angle X-ray Diffraction (WAXD) investigations indicated that the soft segment of HB-PUPCM was crystalline and the crystal structures were spherulites, but the spherulites size were much smaller than those of PEG since the soft segment PEG's crystallization in HB-PUPCM was confined by the hard segment. The heat storage mechanism is indeed the transition process of the soft segment of HB-PUPCM from crystalline state to amorphous one. The energy is mainly obtained from the heat coursed by entropy change between the low entropy crystal state and high entropy amorphous state. The hard segment has no contribution to the phase change heat storage, but it acts as "physical cross-links" and restricts PEG's free movement, so HB-PUPCM still remains its solid state without free movement even when it is heated to the temperature 30-40°C above PEG's melting point.Polyurethane with solid-solid phase change heat storage properties has two essential conditions: one is the soft domain is crystalline with high melting enthalpy(AH) and suitable melting temperature, another is the hard domain can bind themselves via hydrogen bonding, becoming the fixed point to keep HB-PUPCM in solid state above phase change temperature. The result indicates that the soft segment was not able to crystallize until its average molecular weight was above 2000, and the hard segment was not able to form sufficient domains until its content reaching 10wt%.The enthalpy (AH) and transition temperature of HB-PUPCM whose soft segment molecular weight was above 2000 were depressed with the decreasing of soft segment content due to the restriction of hard segment. The enthalpy of HB-PUPCM with the same soft segment content but different soft segment molecular weight was increasing with the soft segment molecular weight's increasing. When the soft segment molecular weight reached over 10000, the enthalpy started to drop slightly. And the transition temperature was also increasing with the soft segment molecular weight's increasing, when the soft segment molecular weight reached 10000, the trend of increasing become slowly.2. Studies on Shape Memory Hyperbranched Polyurethane Based on Hyperbranched PolyesterThis study was focused on the synthesis of shape memory hyperbranched polyurethane based on hyperbranched polyester. FT-IR, DSC, DTG, WAXD, SEM and AFM studies characterized this hyperbranched polyurethane, and the shape memory behaviors were discussed here, such as shape fixity, shape recovery etc, and the tensile properties were also discussed in order to investigate some significant questions, such as the raw materials for soft segments selecting principle of HB-SMPU.It was found that the hard segment content affected the morphological structure of HB-SMPU. While the hard segment content was less than 40 wt.%, PBAG soft segments in HB-SMPU were in a crystalline state. However, the PBAG segments were in an amorphous state in the HB-SMPU with 40 wt.% hard segments. Crystallinity of soft segments in the HB-SMPU decreased with increasing hard segment content. 96-98% shape recovery could be obtained for the HB-SMPU with 15-35 wt.% of hard segment. In a word, the content of hard segments in HB-SMPU played an important role in determining their physical and chemical properties.The results of raw materials selecting study showed that HB-SMPU with bigger molecular weight soft segment showed more excellent shape memory behaviors and tensile properties than that with smaller molecular weight soft segment. At the same time, it was found that the chain segment was longer, the shape memory properties was more excellent even in the same poly(adipate) type glycol system. For example, the poly(hexaylene adipate) glycol (PHAG) was the low-cost soft segment raw material, and the HB-SMPU synthesized by PHAG also had an excellent shape memory behaviors.In this paper, the experimental results showed the functional hyperbranched polyurethane was a kind of novel matrix of functional polymer materials, which possessed good and comprehensive properties. It was supposed that this kind of hyperbranched polyurethane could become a kind of polymeric materials with excellent performance and wide applications through effective modifications and detailed investigations.