Xiaolie Luo

Thermally stimulated shape-memory behavior of ethylene oxide-ethylene terephthalate segmented copolymer

A series of ethylene oxide—ethylene terephthalate segmented copolymers (EOET) with different long soft segments and different hard-segment contents were synthesized. The thermally stimulated shape-memory behavior of EOET segmented copolymer is characterized by the maximum recovery (Rf), the recovery temperature (Tr), and the recovery speed (Vr) or the temperature (TM) of the maximum deformation recovery rate against temperature and the maximum recovery speed (VM). These parameters show that the features of thermally stimulated shape-memory effects of EOET segmented copolymers are following: The crystallinity of soft segments determines the temperature Tr and TM, and the parameters Rf, Vr, and VM depend on the stability of the physical crosslinks formed by the hard segments, which at the same time are influenced by the length of soft segment. Rf, Vr, and VM decrease with prolongation of the keeping time (tk) and increasing stretching ratio.

Dynamic mechanical behavior in the ethylene terephthalate-ethylene oxide copolymer with long soft segment as a shape memory material

Abstract Several ethylene terephthalate-ethylene oxide segmented copolymers with long soft segments, in which poly(ethylene oxide) (PEO) chains serve as soft segments while poly(ethylene terephthalate) (PET) chains serve as hard segments, were investigated by dynamic mechanical analysis (DMA). The PET-PEO copolymers show three distinguishable relaxation processes, α-, β- and γ-relaxation, within the examined concentration range of PET in the copolymers, and α-relaxation was associated with the glass transition of PEO segments in amorphous phase. Both longer PEO segments and higher PET content would tend to decrease the α-relaxation temperature (Tα). The intensity of tan δ for α-relaxation reduced with the increase of soft segment length, and increased with PET content in the PET-PEO segmented copolymer. DMA measurements were carried out on the samples containing 2000, 4000, 6000 and 10,000 PEO segments, respectively. Relations between the intensity of tan δ for α-relaxation and the maximum shape recovery (Rf) were also discussed. Experiments revealed that small energy dissipation and high physical crosslinking effects supplied by the PET component in the copolymer would be favorable for the material to show a good shape recovery.

Compositional heterogeneity, thermostable, and shape memory properties of ethylene oxide-ethylene terephthalate segmented copolymer with long soft segment

Ethylene oxide-ethylene terephthalate segmented copolymers (EOET) with long PEO segment or high PET content have showed an obvious compositional heterogeneity. The EOET copolymers with compositional heterogeneity could be separated into soluble and insoluble fractions by extraction with chloroform. 1 H-NMR measurements showed that the former contains much lower PET content than the average content value, and the latter is in reverse. DSC results revealed that PET segments in the latter would crystallize more easily, but in the former PEO segments exhibits more intensive melting peak. The thermogravimetric behaviors of EOET copolymers were between PEO and PET homopolymers. The EOET copolymers with serious compositional heterogeneity showed two stages of weight loss. TGA was sensitive to indicate the compositional heterogeneity in EOET copolymers. The compositional heterogeneity could impart a great influence on the shape memory behavior of EOET copolymers. The recovery curve of EOET copolymers with serious compositional heterogeneity also can exhibit two stages of deformation recovery. Generally, the component with worse memory behavior in EOET copolymer is an unfavorable factor, and the addition of EOET copolymer with better memory behavior into the blend is a favorable factor for the blend system.

Miscibility of the segmented polyurethane blends with chlorinated poly(vinyl chloride)

Abstract The miscibility of a series of segmented polyurethane (SPU) blends with chlorinated poly(vinyl chloride) (CPVC) was investigated by differential scanning calorimetry (DSC) and Fourier-transform infrared (FTIR) spectroscopy. The segmented polyurethanes based on p , p -diphenylmethane diisocynate (MDI) with 1,4-butanediol (BDO) were synthesized by a two-step, solution polymerization method. DSC results demonstrated that the polyester polyurethane blend with CPVC formed a miscible system, whereas the polyether polyurethane–CPVC blend was an immiscible one. Increasing the molecular weight of the glycol can decrease the miscibility due to the crystallizability of the soft segment. FTIR spectroscopic results showed a strong interaction between CPVC and the polyester soft segment. In addition, it was found that the miscibility of SPU and CPVC decreased upon increasing the hard segment content.

Transesterifications of poly(bisphenol A carbonate) with caprolactone segments in copolyester and poly(ε-caprolactone) homopolymer

Abstract Transesterification of poly(bisphenol A carbonate) with caprolactone segments in ethylene terephthalate–caprolactone copolyester was investigated using 1H and 1H–1H nuclear magnetic resonance (NMR) spectroscopy and a model compound. It was found that during annealing process, transesterification took place between poly(bisphenol A carbonate) and caprolactone segments and resulted in the formation of bisphenol A-caprolactone ester unit. On the basis of the results, we separately examined the interchange reaction of poly(bisphenol A carbonate) with poly(e-caprolactone) homopolymer by 1H and 13C nuclear magnetic resonance spectroscopy. It was shown that in the presence of Ti compound catalyst, transesterification mainly occurred and gave rise to three different kinds of linkage patterns: bisphenol A-caprolactone ester unit, bisphenol A-caprolactone carbonate unit and caprolactone–caprolactone carbonate unit. However, the resultant aliphatic carbonate units were stable under the reaction conditions; the evidence of decarboxylation was not obtained from NMR measurements. The characteristics of the transesterification behavior will be discussed in this paper.

Multiple melting endotherms from ethylene terephthalate—caprolactone copolyesters

Abstract The melting behaviour of ethylene terephthalate (ET)—caprolactone (CL) random block copolyesters (TCLs) crystallized from the melt were studied by differential scanning calorimetry (d.s.c.). The TCLs with high ET contents showed three melting endotherms. Peaks I and II can be attributed to the melting of crystallites formed during primary and secondary crystallization processes respectively, and peak III is the fusion of crystals recrystallized during the d.s.c. heating scan process. For TCL having relatively lower ET content, another melting endotherm, corresponding to the fusion of crystallites of the CL segments, was observed, which indicated that the segregation occurred during the annealing process because of the non-uniformity of the chemical composition and sequence length distribution of the ET and CL segments in TCL copolyesters.

Miscibility of polyhydroxy ether of bisphenol-A with ethylene terephthalate-caprolactone copolyesters

Blends of the polyhydroxyether of bisphenol-A (Phenoxy) and a series of ethylene terephthalate (ET)-caprolactone (CL) random copolyesters (TCL) having different ET contents were examined mainly by differential scanning calorimeter (DSC). A miscibility limit specified by the ET content was obtained and estimated to be about 90 wt%. When the ET content is less than this limit, the Phenoxy and copolyesters are miscible with each other. A relatively stronger specific intermolecular interaction between Phenoxy and copolyester was detected by Fourier Transform infra-red (FTIR) spectroscopy, and it may be an important factor which affects the miscibility in these blends. Based on the miscibility behaviour of Phenoxy/TCL copolyester blends, the factors which affect the miscibility of Phenoxy with polyester was discussed.