Cai-Li Huang

Self-healable and recyclable triple-shape PPDO–PTMEG co-network constructed through thermoreversible Diels–Alder reaction

Based on Diels–Alder reaction, linear bisfuranic terminated poly(tetramethylene oxide) and poly(p-dioxanone) were crosslinked by tris(2-maleimide ethyl)amine; this process was fully reversible under moderate conditions. All of the results indicate that the co-network possesses the typical advantages of chemical and physical crosslinking, peculiar thermal invertibility, shape memory effect and self-healability.

Poly(butylene succinate)-poly(ethylene glycol) multiblock copolymer: Synthesis, structure, properties and shape memory performance

Thermally-induced shape memory multiblock poly(ether-ester)s (PBSEGs) comprising crystallisable poly(butylene succinate) (PBS) hard segments and poly(ethylene glycol) (PEG) soft segments, were synthesized by polycondensation from succinic acid, 1,4-butanediol and PEG diol. The copolymers were characterized by 1H-NMR, GPC, DSC and DMA. DSC analysis revealed that all PBSEGs prepared in this work are double-crystalline copolymers which ensure it to form separated crystalline domain determined the permanent shape and temporary shape respectively. The Tm of PEG segment (Tm,PEG) of the PBSEGs ranging from 27.54 to 51.04 °C, acting as the transition temperature (Ttrans), was controllable by varying the chain length of soft segment. The DMA test indicated that a large difference in modulus below and above the Ttrans of PBSEGs endows it with sufficient deformability at high temperature and high capacity for keeping deformation at low temperature. The mechanical properties of the copolymer films were assessed by tensile strength measurement. It showed that the copolymers were ductile which enabled remarkable reversible deformation. The shape memory properties of PBSEGs were evaluated by bending test, as expected, most copolymers possessed excellent shape memory effect. The contact angle tests demonstrated that the copolymers were more hydrophilic with the introduction of PEG segment, suggesting this biodegradable PBSEG multiblock copolymer with excellent shape-memory properties has great potential in application for biomaterials.

A facile method to produce PBS-PEG/CNTs nanocomposites with controllable electro-induced shape memory effect

A facile method to develop electro-induced shape memory polymer composites with good location- and process-controlled shape recovery performance is proposed. The poly(butylene succinate) (PBS)–poly(ethylene glycol) (PEG) multiblock copolymer (PBSEG), which has excellent flexibility, was chosen as the matrix of the composites. The conducting medium, carbon nanotubes (CNTs), was introduced to this copolymer by in situ polycondensation. The fine dispersion of CNTs in the PBSEG matrix, which was confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations, enabled it to form a percolation network when only 0.5 wt% filler was loaded. DSC analysis revealed another important role played by CNTs in this system, as a nucleating agent for both PBS and PEG segments, and it caused an increase in crystallization temperature and crystallinity of both segments. The tensile properties test showed that the nanocomposite still exhibits good ductility with the addition of no more than 1 wt% CNTs, which allows it to undergo large deformation during shape programming. The electrical actuation shape memory performance was evaluated by a bending test, and the recovery process was recorded with a camera and an infrared video camera. The effect of CNTs loading, segment content and chain length upon the fixity ratio, recovery ratio and speed was studied, and the temporary shape control and localized shape memory response were also investigated. The results showed that the PBSEG/CNTs nanocomposites possess good shape memory performance with high shape fixity (more than 93.77%) and recovery ratio (more than 97.04%), and the shape recovery process can be adjusted by tailoring the polymer chain structure, the content of CNTs and the mode of how the samples are put in a circuit. In present work, we successfully achieved an electro-induced shape memory device which can be well controlled to remain at any stage during the recovery process and respond at any local position.

Fractional crystallization and homogeneous nucleation of confined PEG microdomains in PBS-PEG multiblock copolymers.

Fractional crystallization, homogeneous nucleation of poly(ethylene glycol) (PEG) segment, and self-nucleation behavior of PEG segment within miscible double crystalline poly(butylene succinate)-poly(ethylene glycol) (PBSEG) multiblock copolymers with different composition and segment chain length were studied by differential scanning calorimetry (DSC). Surface morphology of PBSEG10K with different PEG content was investigated by atomic force microscope (AFM). Different from di- or triblock copolymers, the microstructure and confinement of PEG dispersed phase in PBS matrix phase highly depends on chain length and sequence as well as segment content. The transition point of the PEG segment content from heterogeneous to homogeneous nucleation mechanism decreased from 50 to 39 wt % with PEG segment chain length increasing from 1000 to 2000 g/mol. When PEG segment chain length increased further to 6000 and 10000 g/mol, homogeneous nucleation phenomenon took place at much lower PEG content and fractional crystallization was observed at 29 and 24 wt %, respectively. Homogeneous nucleation mechanism of PBSEG(1K-36), PBSEG(2K-26), PBSEG(6K-19), and PBSEG(10K-12) was evidenced by the large supercoolings needed for crystallization, as well as first-order crystallization kinetics obtained. Self-nucleation behaviors of PEG segment still rely on the composition of PBSEGs. In the case of heterogeneous nucleation crystallization, self-nucleation behaviors of PEG segment showed standard self-nucleation behavior with classical three self-nucleation domains. When the crystallizable chains were confined into isolated microdomains, however, self-nucleation domain (domain II) disappeared. The absence of III(A) was observed in PBSEG(2K-39), while PBSEG(6K-29) had both III(A) and III(SA). Furthermore, AFM morphology studies still indicated the confined degree of PEG segment by previous PBS crystals was profoundly influenced by segment fraction. The confinement of the PEG segment by previous PBS edge-on lamellae was observed in the sample which displays a homogeneous nucleation crystallization behavior.

Composition dependence of physical properties of biodegradable poly(ethylene succinate) urethane ionenes

To obtain an excellent comprehensive performance of poly(ethylene succinate) (PES), we have synthesized a series of poly(ethylene succinate) (PES) urethane ionenes (PESUIs) with various content of urethane ionic group by the chain extension reaction of dihydroxyl-terminated poly(ethylene succinate) and diethanolamine hydrochloride with hexamethylene diisocyanate as a chain extender, and we systematically investigated the composition dependence of the physico-chemical properties of PESUI through a series of characteristic techniques. The results of thermal and crystallization behaviors suggest that the incorporation of urethane ionic group slightly affects the glass transition temperature, melting temperature, and thermal stability, and significantly accelerates the crystallization rate of PES without changing the crystallization mechanism. The fastest crystallization rate was reached with the incorporation of 4 mol% urethane ionic groups. Spherulitic morphology observation indicates that nucleation density significantly increased, while spherulitic growth rate gradually decreased with increase in urethane ionic group content. Both complex viscosity and storage modulus initially increased and then decreased with increase in urethane ionic group content, and their maximum values were observed for the sample with 4 mol% of urethane ionic group. Mechanical properties slightly varied with urethane ionic group content.

Thermal Degradation, Crystallization, and Rheological Behavior of Biodegradable Poly(p-dioxanone)/Synthetic Hectorite Nanocomposites

Biodegradable poly(p-dioxanone) (PPDO)/synthetic hectorite nanocomposites were successfully prepared by in-situ ring-opening polymerization of p-dioxanone (PDO) in the presence of organomodified synthetic hectorite (OSHEC). Attachment of poly(ester-ether) chains around the exfoliated clay sheets was found. Influence of clay content on thermal behavior was studied. OSHEC accelerated the thermal degradation of the ester group in the polymer chains. Exfoliated organoclay layers, to some extent, acted as a hindrance to the growth rate of the spherulites instead of as nucleating agents. Inorganic clay played an important role in enhancing the shear viscosity of nanocomposites due to its unique structure and the reasonable interaction between the clay and PPDO matrix.