Dezhu Ma

Miscibility of epoxy resins/poly(ethylene oxide) blends cured with phthalic anhydride

Abstract Epoxy resins (EP)/poly(ethylene oxide) (PEO) blends cured with phthalic anhydride were studied by differential scanning calorimetry and dynamic mechanical analysis. Single glass transition temperatures were observed for all blends before and after curing, indicating a high degree of miscibility. At the same time, a marked deviation from the empirical equation (e.g. the Fox equation) was noticed after curing. This is ascribed to the dilution effect of the PEO component and participation of PEO in the cure reaction resulting in incomplete crosslinking, i.e. the formation of imperfect crosslinking network structures. Fourier transform infra-red spectroscopy provided strong evidence that there is a specific interaction between the EP and PEO molecules.

FTIR studies on the compatibility of hard-soft segments for polyurethane-imide copolymers with different soft segments

The polyurethane–imide (PUI) copolymers with different soft segments (polyethylene-co-propylene adipates, polyethylene glycol, or polypropylene-oxide) were studied. FTIR spectroscopy shows the different absorption bands of imide-I groups and reveals the different intermolecular interactions due to hydrogen bonding in these PUI copolymers. FTIR results suggest there is a good compatibility between hard and soft segments in either polyester–PUIs or polyether–PUIs having short soft segments. On the other hand, DSC analysis reveals that the glass transition temperature for hard segments (Tgh) of polyether–PUIs is higher than that of polyester–PUIs, and it increases with the soft segment length in PUIs consisting of the same type soft segments, which further supports the conclusions drawn from the FTIR data.

Nonisothermal crystallization kinetics: poly(ethylene terephthalate)-poly(ethylene oxide) segmented copolymer and poly(ethylene oxide) homopolymer

Abstract The nonisothermal crystallization behavior of polyethylene oxide (PEO) in poly(ethylene terephthalate)–poly(ethylene oxide) (PET–PEO) segmented copolymer and PEO homopolymer has been studied by means of differential scanning calorimetry, as well as transmission electron microscope. The kinetics of PEO in copolymer and PEO homopolymer under nonisothermal crystallization condition has been analyzed by Ozawa equation. The results show that Ozawa equation only describes the crystallization behavior of PEO-6000 homopolymer successfully, but fails to describe the whole crystallization process of PEO in copolymer because the secondary crystallization in the later stage could not be neglected. Due to the constraint of PET segments imposed on the PEO segments, a distinct two stage of crystallization of PEO in copolymer has been investigated by using Avrami equation modified by Jeziorny to deal with the nonisothermal crystallization data. In the case of PEO-6000 homopolymer, good linear relation for the whole crystallization process is obtained owing to the secondary crystallization does not occur under our experimental condition.

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.

H-bond and conformations of donors and acceptors in model polyether based polyurethanes

Abstract The molecular mechanics (MM) method with COMPASS force field was used to study the H-bonds in the polyether based polyurethane model molecules. Availability of the calculation was firstly verified in comparison of some H-bonded model molecules, which were studied by using ab initio calculation, and those calculated by MM. Based on a urethane model molecule 1,3-dimethylcarbamate, which can be donor or acceptor and behaves in various conformations, it is reasonable to have a large number of H-bond interactions between various conformational donors and acceptors. For examining all the possible interaction patterns, we studied 57H-bond complexes. This systematic modeling covers well-known four types of interaction patterns, such as NH⋯OC (Type I), NH⋯O–CO (Type II), NH⋯NH (Type III), NH⋯COC (Type IV) in the system. Obtained H-bond energies were used to analyze the probabilities of the complexes. For the interaction within the hard segments, or Type I, Type II and Type III, a predominant H-bond complex has been found in the present study, which belongs to Type I. For the interaction between the hard segment and the soft segment, two conformations of Type IV were calculated to be existed.

Relationship between miscibility and chemical structures in reactive blending of poly(bisphenol A carbonate) and poly(ethylene terephthalate)

Abstract Commercial poly(bisphenol A carbonate) (PC) and poly(ethylene terephthalate) (PET) were directly melt mixed without adding any catalyst. The changes of miscibility and chemical structures during reactive blending were detected by high-field nuclear magnetic resonance spectroscopy and differential scanning calorimetry, respectively. It was found that transesterification significantly improved the miscibility between PC and PET. About 5% reaction extent was sufficient to change the blend system from initial immiscibility to miscibility. The single glass transition temperature of the miscible product did not change with further increasing extent of reaction. However, excessive exchange reaction caused severe decarboxylation and thus introduced a number of aromatic–aliphatic ether moieties into the products. As a result of the homogenization, both exchange and decarboxylation reactions were subsequently speeded up. The quantitative analysis provided a possibility to design the resultant chemical structures while producing miscible PC/PET alloy.

Double cold crystallization peaks of poly(ethylene terephthalate)—1. Samples isothermally crystallized at low temperature

In this work, the cold crystallization peak in DSC analysis is used as a probe to study the structure in amorphous regions of poly(ethylene terephthalate) (PET). The appearance of double cold crystallization peaks for PET samples properly treated at low temperature reveals the co-existence of two kinds of amorphous regions: interlamellar amorphous regions with some order and complete amorphous regions between spherulites.

Nonisothermal crystallization kinetics of ethylene terephthalate-ethylene oxide segmented copolymers with two crystallizing segments

The nonisothermal crystallization behavior of ethylene terephthalate-ethylene oxide segmented copolymers has been studied by means of differential scanning calorimetry (DSC). The kinetics of ET-EO segmented copolymer under nonisothermal crystallization conditions has been analyzed by the Ozawa equation. During the crystallization of the high-T-m segments (PET), the low-T-m segments (PEO) act as a noncrystalline diluent, the crystallization behavior of PET obeys the Ozawa theory. When the PEO segments begin to crystallize, the PET phase is always partially solidified and the presence of the spherulitic microstructure of PET profoundly influences the crystallization behavior, which results in that the overall crystallization process does not obey the Ozawa equation

Degree of microphase separation in segmented copolymers based on poly(ethylene oxide) and poly(ethylene terephthalate)

Abstract Microphase separation effects in segmented copolymers based on poly(ethylene oxide) and poly(ethylene terephthalate) (EOET) were studied with differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and optical microscopy. The PEO segments in a segmented EOET copolymer showed a higher glass transition temperature ( T g ), and lower melting temperature ( T m ) and crystallinity ( X c ) than the corresponding PEO homopolymer. Experimental results revealed that both long PEO segments and high PET content in the copolymers lead to a high degree of microphase separation. Both T g and T m of the PEO segments can be used to evaluate the degree of microphase separation in the EOET copolymer.

The comparison of the ringed spherulite morphology of PCL blends with poly(vinyl chloride), poly(bisphenol A carbonate) and poly(hydroxyether of bisphenol A)

The crystallization and ringed spherulite morphology of poly(e-caprolactone) (PCL) in the miscible blends of PCL/poly(vinyl chloride) (PVC), PCL/poly(hydroxyether of bisphenol A) (phenoxy resin) and PCL/poly(bisphenol A carbonate) (PC) were investigated by differential scanning calorimetry (DSC) and polarized light microscopy (PLM). Through the comparison of the PCL crystalline morphology with the interaction energy density B between the miscible components in these blends, it was found that the addition of the non-crystallizable component had great effect on the regularity of the ringed spherulite, which was coincided with the change of the interaction energy density B. To grow regular ringed spherulites in the PCL miscible blends, it was most important that the crystallization rate of PCL in the blends must be matched with the diffusion rate of the non-crystallizable component. Such a matching relation in the process of the ringed spherulite growth was a most important condition for the regular twisting of PCL lamellae.