Maleated trans -1,4-polyisoprene from Eucommia ulmoides Oliver with dynamic network structure and its shape memory property

Effect of alkali metal cations on network rearrangement in polyisoprene ionomers

The effects of cations, Li⁺, Na⁺, and Cs⁺, on the structure of ionic aggregates and network rearrangement in carboxylated polyisoprene (PI) ionomers were studied. We found that network rearrangement via interaggregate hopping of metal carboxylates is improved with a decrease in cation size, even though density functional theory (DFT) calculation indicated the increase in the attractive interaction between metal carboxylates. At the same time, we also found that as the size of the cation decreases, the inclusion of the PI segment in the ionic aggregate increases. The DFT calculation suggested the cation-π interaction between the cation and double bonds in the PI segment as the cause for the inclusion. The inclusion of the PI segment with a low glass transition temperature (T_g) plasticizes the ionic aggregate and would sterically hinder the attractive interaction between metal carboxylates. In fact, the electron spin resonance measurement revealed a decrease in the T_g of the ionic aggregate with a decrease in cation size. Based on our findings, we proposed that the inclusion of PI segments in the ionic aggregate is the possible cause for the enhancement of network rearrangement in the carboxylated PI ionomers with a decrease in the cation size.

Influence of functionalized core-shell structure on the thermodynamic and shape memory properties of nanocomposites

Filler/matrix interfacial cohesion exerts a straightforward effect on stress transfer at the interface in composite structures, thereby significantly affecting their integrated mechanical properties. Thus, controlling the interface interaction of polymers/fillers is essential for the fabrication of high-performance polymer composites. In this work, a functionalized core-shell structured hybrid was prepared via charge attraction and applied as a novel filler in the trans-1,4-polyisoprene matrix to improve the interfacial interaction of the filler/matrix. A series of tests on the micro- and macroscale was performed to investigate its thermal, mechanical and shape memory performances. The obtained results show that while guaranteeing the shape memory properties of the composites, the utilization of the core-shell structured hybrid not only improved the heat resistant performance, but also contributed to better mechanical properties. This provides solid evidence for the potential of the innovative method presented herein, which may shed some light on the improvement of the interface design strategy and the development of composites with high performances.

Multidirectional Triple-Shape-Memory Polymer by Tunable Cross-linking and Crystallization

Medical fixing is one of the very important applications of the shape-memory polymer material, and the two important properties of the medical fixing material are that it perfectly fits the body during the fixing and easily detaches after being used. As the fixing and detachment are triggered by two independent stimuli in two opposite directions, it is necessary to develop multidirectional triple-shape-memory polymers. In this research, a series of polymer materials composed of trans-polyisoprene (TPI) and paraffin were prepared by melt blending and compression molding, and then the TPI was cross-linked by vulcanization. As a result of the large difference in the melting temperature and crystallization temperature between TPI and paraffin, the obtained polymer materials exhibit a triple-shape-memory behavior. According to the analysis of crystal behavior, microscopic morphology, and mechanical properties of the materials with different paraffin contents and TPI cross-linking density by differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and dynamic mechanical thermal analysis, the shape-memory behavior of the obtained materials was tunable by the cross-linking density of TPI and the crystallization degree of TPI or paraffin. Compared with the traditional triple-shape-memory material, our samples are prepared in a more facile way and can recover at human body temperature (37 °C). Moreover, our TPI/paraffin material can realize more flexible multidirectional recovery, as well as can be reprogramed and used multiple times. To the best of our knowledge, there are few polymer materials reported, which can realize multidirectional recovery. These unique multidirectional and reprogramable properties will enable the application of this polymer material, especially in the medical fixing materials.

Shape Memory Behavior of Natural Eucommia ulmoides Gum and Low-Density Polyethylene Blends with Two Response Temperatures

A series of shape memory blends of natural Eucommia ulmoides gum (EUG) and low-density polyethylene (LDPE) with a bicontinuous cross-linked structure were prepared by a physical blending method, which could be used in the field of thermal response with two different temperatures. We report the shape memory properties of these blended materials with two response temperatures for the first time. The mechanical, curing, thermal and shape memory properties of the blends were studied in this manuscript. Schematic diagrams are proposed to illustrate the dual shape memory behaviors of the EUG/LDPE blends. Our study focused on observing the relationship between the shape memory behavior and the microscopic crystalline phase states in the blends. In the blends, both the cross-linked network and the LDPE crystalline regions could act as fixed domains, while the crystalline regions of LDPE or EUG could act as the reversible domain. The shape memory properties were mainly determined by the components of the fixed and reversible domains. We focused on the shape memory behavior of blends at 60 °C and 130 °C in this manuscript. The results showed that when the peroxide dicumyl peroxide (DCP) dosage was 1.0 phr, the blends exhibited acceptable shape behavior at 60 °C (R_1f = 74.8%, R_1r = 63.3%). At the same time, when DCP dosage was 0.4 phr, the shape memory behavior of the blends at 130 °C was good and much better than that at 60 °C (R_2f = 91.1%, R_2r = 89.4%).

Bioinspired shape-memory graphene film with tunable wettability

Functional materials with specific surface wettability play an important role in a wide variety of areas. Inspired by nature's Nepenthes pitcher plant, we present a novel slippery film with tunable wettability based on a shape-memory graphene sponge. The porous graphene sponge coated with shape-memory polymer was used to lock in inert lubricants and construct slippery surfaces to repel different liquids. The superelasticity and high strength, together with good electrical conductivity, of the graphene sponge imparted the graphene/polymer hybrid films with fast recoverable shape-memory properties. Various droplets could slip on the compressed film with a lubricant-covered surface, but the droplets would be pinned when the shape-memory graphene film rebounded due to electrical stimulation, which caused the penetration of the infused lubricant into the pores and the exposure of rough topography film surfaces. The electrothermally dynamic tuning approach was stable and reversible; thus, the shape-memory graphene film was imparted with controlled slippery properties and functions that would be amenable to a variety of applications, such as liquid handling for microplates.

Gene coexpression network for trans-1,4-polyisoprene biosynthesis involving mevalonate and methylerythritol phosphate pathways in Eucommia ulmoides Oliver

Eucommia ulmoides, a deciduous dioecious plant species, accumulates trans-1,4-polyisoprene (TPI) in its tissues such as pericarp and leaf. Probable TPI synthase (trans-isoprenyl diphosphate synthase (TIDS)) genes were identified by expressed sequence tags of this species; however, the metabolic pathway of TPI biosynthesis, including the role of TIDSs, is unknown. To understand the mechanism of TPI biosynthesis at the transcriptional level, comprehensive gene expression data from various organs were generated and TPI biosynthesis related genes were extracted by principal component analysis (PCA). The metabolic pathway was assessed by comparing the coexpression network of TPI genes with the isoprenoid gene coexpression network of model plants. By PCA, we dissected 27 genes assumed to be involved in polyisoprene biosynthesis, including TIDS genes, genes encoding enzymes of the mevalonate (MVA) pathway and the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway, and genes related to rubber synthesis. The coexpression network revealed that 22 of the 27 TPI biosynthesis genes are coordinately expressed. The network was clustered into two modules, and this was also observed in model plants. The first module was mainly comprised of MEP pathway genes and TIDS1 gene, and the second module, of MVA pathway genes and TIDS5 gene. These results indicate that TPI is likely biosynthesized by both the MEP and MVA pathways and that TIDS gene expression is differentially controlled by these pathways.

Robust Vacuum-/Air-Dried Graphene Aerogels and Fast Recoverable Shape-Memory Hybrid Foams

New graphene aerogels can be fabricated by vacuum/air drying, and because of the mechanical robustness of the graphene aerogels, shape-memory polymer/graphene hybrid foams can be fabricated by a simple infiltration-air-drying-crosslinking method. Due to the superelasticity, high strength, and good electrical conductivity of the as-prepared graphene aerogels, the shape-memory hybrid foams exhibit excellent thermotropical and electrical shape-memory properties, outperforming previously reported shape-memory polymer foams.