Jue Cheng

Thermomechanical and shape-memory properties of epoxy-based shape-memory polymer using diglycidyl ether of ethoxylated bisphenol-A

A series of epoxy-based shape-memory polymers (SMPs) was prepared by using diglycidyl ether of ethoxylated bisphenol-A containing two oxyethylene units and the curing agents iso-phorone diamine and Jeffamine D230. The thermal properties, dynamic mechanical properties, mechanical properties and shape-memory properties of the epoxy-based SMPs were systematically studied by DSC, DMTA, universal tester and fold-deploy experiments, respectively. The results showed that as the content of D230 increased, the glass transition temperature of the SMPs decreased from 77.5 ± 1.1 to 40 ± 0.7 °C according to DSC, the rubber modulus decreased gradually according to DMTA, and the tensile strength at room temperature (RT) decreased from 58.5 ± 0.3 to 27.0 ± 3.3 MPa according to tensile tests. Tensile tests above RT showed that the tensile stress and elongation at break depended heavily on the experimental temperature, and fold-deploy experiments showed that these SMPs had shape retention ratios higher than 95% and shape recovery ratios close to 100%.

Thermal, mechanical and shape memory properties of an intrinsically toughened epoxy/anhydride system

A series of intrinsically toughened shape memory epoxy resins (SMEPs) were prepared by curing two bisphenol-A type epoxy resins containing two and six oxyethylene units (DGEBAEO-2 and DGEBAEO-6) with hexahydrophthalic anhydride in the presence of tris-(dimethylaminomethyl) phenol. The thermal, thermomechanical, mechanical and shape-memory properties of these SMEPs were systematically investigated by DSC, DMTA, tensile test and fold-deploy shape memory test, respectively. DSC and DMTA experiments showed that as the concentration of the DGEBAEO-6 increased, the glass transition temperature and storage modulus in the rubbery plateau of the SMEPs decreased gradually. The tensile stress at yield also decreased with increase in the relative content of DGEBAEO-6 and all the SMEPs exhibit a ductile fracture feature with the appearance of yielding, according to the uniaxial tensile test. The fold-deploy shape memory test showed that all the SMEPs showed a good shape memory effect with a combination of relatively high shape fixity and shape recovery.

Effects of the furan ring in epoxy resin on the thermomechanical properties of highly cross-linked epoxy networks: a molecular simulation study

Two highly cross-linked epoxy networks based on two epoxy resin model compounds with similar structures, 2,5-bis[(2-oxiranylmethoxy)-methyl]-furan (BOF) and 2,5-bis[(2-oxiranylmethoxy)methyl]-benzene (BOB), and the same curing agent PACM were constructed by using molecular dynamic simulations. Several thermomechanical properties of these two systems including glass transition temperatures, coefficients of thermal expansion, Youngs moduli, and Poissons ratios were calculated. The simulated values were compared with the available experimental results, and good agreements were obtained. This consistency proved the validity of the atomistic models. The changes of aromatic structures in the epoxy monomers from phenyl to furyl lead to a higher glassy Youngs modulus of the cross-linked epoxy network. This phenomenon can be illustrated by the reduced mobility of the polymer chains arising from the increased packing efficiency. These changes are considered to be induced by the higher van der Waals energy within the furan-based epoxy.

Influence of cross-linking density on the structure and properties of the interphase within supported ultrathin epoxy films

Supported polymer film models based on epoxy resin networks with four different cross-linking densities and silica substrates have been established using molecular dynamics simulations. Van der Waals forces in the form of Lennard-Jones 9-6 are applied in calculating the interfacial interactions between the polymer and substrate. The existence of the interphase adjacent to the substrate surface was confirmed by carrying out density profile. Detailed analyses including mean square displacement and radial distribution functions of the structural properties of interphases for the four models were performed and compared. It was found that, with increasing the cross-linking density, the polymer sticks to the substrate more tightly, accompanied by stronger interactions arising from more hydrogen bonds formed between them. Furthermore, the mechanical properties of the interphase were found to be enhanced with the conversion by carrying out tensile deformation. This research regarding the interphase region within supported ultrathin epoxy films will be helpful in understanding the effect mechanism of nanofillers in the epoxy nanocomposites.

Synthesis, characterization, and cure kinetics analysis of high refractive index copolysiloxanes

Two kinds of high refractive index of polysiloxane compounds containing both pendent and terminal vinyl groups were successfully synthesized through a cohydrolysis-condensation method based on alkoxy silanes in the presence of acids and anionic ring-opening copolymerization of methylphenycyclosiloxane (Dn) and octamethylcyclotetrasiloxane (D4), respectively. Their structures were confirmed by Fourier-transformed infrared and nuclear magnetic resonance spectra (1H NMR and 29Si NMR). The curing kinetics of the silicone resin (MPSR) in the presence of phenylvinyl silicone oil (MPSO) as reactive diluent and T-shaped hydrosiloxane (TPHS) as crosslinking agent was studied by non-isothermal differential scanning calorimeter at different heating rates. The kinetic parameters of the curing process were determined by Friedman and Šesták–Berggren method. A comparison of the results calculated with the experimental data showed that Šesták–Berggren equation was found to be the most adequately selected to describe the cure kinetics of the studied silicone resin, and the experimental data had a great coherence with that theoretically calculated. It would give a valuable guide for the curing process of silicone resin. In addition, TG curves showed that the cured MPSR/MPSO/TPHS system exhibited much higher heat resistance and thermal stability compared to MQ resin/PMVS/PHVS blends.

Epoxy/polysiloxane intimate intermixing networks driven by intrinsic motive force to achieve ultralow-temperature damping properties

The preparation of highly incompatible interpenetrating polymer network systems with a high extent of phase mixing has been a challenging task because the thermodynamics of phase separation are so powerful. Here, we propose a facial strategy to design a ‘forced’ intermixing epoxy/polysiloxane network by utilizing a novel epoxy/polysiloxane monomer (SH-EP) in a one-pot synthesis. The relationship between the structure and properties is systematically investigated using FTIR spectrometry, rheology, SEM, and DMA. Impressively, the epoxy and polysiloxane networks can be driven to closely interpenetrate by their intrinsic motive force derived from the ‘forced’ sites in SH-EP, which in turn, may easily give rise to a bicontinuous morphology. In addition, the gelation time is systematically controlled by varying the polysiloxane content and pre-curing temperature. By tuning the gelation time, the extent of phase mixing and the degree of phase separation can be further regulated. The result is striking: for the first time, these highly incompatible epoxy/polysiloxane intermixing networks exhibit ultralow-temperature damping properties (tan δ > 0.3) over a very broad temperature range of 217 °C (from −114 °C to 103 °C). This finding may revolutionise the frontiers of materials knowledge.

Synthesis and properties of segmented polyurethanes with hydroquinone ether derivatives as chain extender

Two series of 4, 4′-diphenylmethane diisocyanate (MDI) type polyurethanes based on poly(tetramethyleneoxide) glycol (PTMO) and polybutylene adipate glycol (PBA) as soft segments were synthesized by one-step bulk polymerization process. Various hard segments were obtained from hydroquinone ether derivatives with or without ether oxygen structure bonded with the aromatic units in main chain, including hydroquinone (HQE), hydroquinone bis(b-hydroxyethy) ether (HQEE), and 4-hydroxyethyl ethyl oxygen-1-hydroxy ethyl benzene ether (HQEE-L) as chain extenders. The effect of chain extender structure on aggregation structure, thermal and mechanical properties was studied. ATR-FTIR suggested that hydrogen bonding interactions were significantly changed in the presence of flexible ether oxygen structure in hard segment. HQEE-based polyurethanes and HQEE-L-based polyurethanes displayed microphase separation and microphase mixing behavior respectively based on DMA and DSC results. XRD curves confirmed that flexible ether oxygen chain bonded with the rigid aromatic units played a balancing role in the steric effect caused by aromatic chain extender. Thermal properties of polyurethanes were affected mainly by the hard segment packing while mechanical properties were influenced by both phase separation and phase mixing which possess strong hydrogen bonding interactions. The excellent elongation in PTMO/HQEE-L and the high ultimate tensile strength in PBA/HQEE-L can be attributed to the phase mixing with strong hydrogen bonding interactions presented in HQEE-L-based polyurethanes.

A facile method for fabrication of titanium-doped hybrid materials with high refractive index

This paper presents a facile route to prepare a series of high refractive index and homogeneous hybrid resins with titanium in the backbone by a non-hydrolytic sol–gel process. The confirmation of the condensation reaction and the formation of Si–O–Ti hetero-metal bonds in the hybrid resins were conducted by FT-IR spectroscopy, FT-Raman spectroscopy and liquid state 29Si-NMR spectroscopy. In addition, the molecular weight and molecular size of the hybrid resin were characterized by MALDI-TOF MS and small-angle X-ray scattering (SAXS), respectively. These results show that the content of Si–O–Ti bridges, condensation degree of precursors and molecular weight and size of these hybrid resins increase depending on the TPT content from 0 to 30%. Moreover, the refractive index of the hybrid resin varied from 1.57 to 1.62 with increasing TPT content and the hybrid resin was thermally cured by hydrosilylation in the presence of a Pt catalyst to fabricate a transparent TSR hybrid film. These experimental results demonstrated that the physical and chemical properties of these hybrid films, such as visible transparency, surface roughness and surface energy, dielectric constant, thermal stability and glass transition temperature were investigated as a function of the chemical composition.

Comparative curing kinetics of 1,4-bis (4-diaminobenzene-1-oxygen) n-butane and 4,4′-bis-(diaminodiphenyl) methane with tetraglycidyl methylene dianiline systems

Aromatic amine curing agent with flexible unit in backbone, 1,4-bis (4-diaminobenzene-1-oxygen) n-butane (DDBE), was synthesized, and the structure was confirmed by FT-IR and 1H NMR. The curing kinetics of tetraglycidyl methylene dianiline (TGDDM, or AG80) using DDBE and 4,4′-bis-(diaminodiphenyl) methane (DDM) as curing agents, respectively, were comparatively studied by non-isothermal DSC with a model-fitting Málek approach and a model-free advanced isoconversional method of Vyazovkin. The dynamic mechanical properties and thermal stabilities of the cured materials were investigated by DMTA and TG, respectively. The results showed that the activation energy of AG80/DDBE system was slightly higher than that of AG80/DDM system. Šesták-Berggren model can generally simulate well the reaction rates of these two systems. DMTA measurements showed that the storage modulus of cured AG80/DDBE is similar to that of cured AG80/DDM at the temperature below glass transition temperature (Tg) and lower than that of cured AG80/DDM at the temperature above glass transition temperature, while Tg of cured AG80/DDBE is lower than that of cured AG80/DDM. TG showed that the thermal stabilities of these two cured systems are similar.

Preparation of thermal plastic polyurethane-polystyrene block copolymer via UV irradiation polymerization

A facile method is described for preparing thermal plastic polyurethane-polystyrene (PUPS) block copolymer. 2-Hydroxy-2-methyl-1-phenyl-1-propanone (HMPP)-capped polyurethane was synthesized and used as macrophotointiator to prepare PUPS by ultraviolet (UV) irradiation polymerization of styrene. The polymerization process of PUPS block copolymer was monitored by real-time FTIR, 1H NMR, and GPC, which confirmed the conversion of styrene and formation of PUPS block copolymer. The influence of reaction temperature on styrene conversion was investigated and the results demonstrated the feasibility of preparation of PUPS block copolymer by UV polymerization at ambient temperature. The DSC and TG data revealed a new glass transition temperature and degradable step respectively for PUPS block copolymer induced by polystyrene block compared with neat polyurethane and polyurethane macrophotoinitiator, which further clarified the formation of PUPS block copolymer. The properties measurements showed that the prepared PUPS block copolymer exhibited better tensile strength, hardness and water-resistance than neat polyurethane.