Broad Glass Transition Temperature Research Articles

Programmable shape memory bismaleimide composite claw with two-way grabbing function

• A series of shape memory polymers (SMPs) based on bismaleimide (BMI) were synthesized. The BMI-based polymers are made of a 4,4'-bismaleimidodiphenylmethane (BDM) matrix and chain extender polyether diamine poly(propyleneglycol) bis(2-aminopropylether) (D400). Then crosslinking agent 2,4-tolylene diisocyanate (TDI) was added to form a crosslinking network. Last, it was toughened by adding liquid nitrile rubber (ETBN). • These BMI-based SMPs achieved wide T g ranges of 170-200 °C. This property allows these SMPs to remember two pre-deformed shapes. By designing the second pre-deformed shape similar to the original shape, the 2W-SME can be achieved. • Carbon fabric reinforced BMI-based shape memory composites (SMPCs) were prepared. By exploring the preparation process, the claw structure was formed with this BMI-based SMPC. The composite claw realizes the motion of reach out and grab 250g items. Functional polymer materials with a two-way shape memory effect (2W-SME) have attracted great interest recently. Herein, by introducing 2,4-tolylene diisocyanate (TDI) into the bismaleimide (BMI) network, the shape memory polymers we synthesized are a series thermosetting polymers with adjustable T g and triple-shape memory effect(triple-SME), and realized two-way behavior by programming. Those shape memory polymers (SMPs) were toughened by acrylonitrile-butadienerubber (ETBN) and reinforced with carbon fabric to make composites. The cured network with varying transition temperatures and flexibility was synthesized by varying the cyanate ester and rubber concentration in the system. Polymers with a broad glass transition temperature ( T g ) range can achieve triple-SME. Due to the complex cross-linked structure, the two-way behavior demonstrated above for BMI-based SMPs stem from its broad T g ranges. Select two temperatures higher and lower than T g as the switching temperature, and fix the pre-deformed shape in the opposite direction at these two temperatures to achieve the two-way behavior. These BMI-based SMPs could grab objects through the design of the structure. Results indicated that the above BMI-based SMPs with two-way function have excellent thermal stability and mechanical properties, which provides the basic attempts for the further development of thermosetting SMPs and their composite materials.

Dynamic heterogeneity and nanophase separation in rubber-toughened amine-cured highly cross-linked polymer networks

Solid state nuclear magnetic resonance (NMR) spectroscopy and small-to wide-angle X-ray scattering (SWAXS) methods were used to characterize the heterogeneous dynamics and polymer domain structure in rubber modified thermoset materials containing the diglycidyl ether of bisphenol A (DGEBA) epoxy resin and a mixture of Jeffamine reactive rubber and 4,4-diaminodicyclohexylmethane (PACM) amine curing agent. The polymer chain dynamics and morphologies as a function of the PACM/Jeffamine ratio were determined. Using dipolar-filtered NMR experiments, the resulting networks are shown to be composed of mobile and rigid regions that are separated on nanometer length scales, along with a dynamically immobilized interface region. Proton NMR spin diffusion experiments measured the dimensions of the mobile phase to range between 9 and 66 nm and varied with the relative PACM concentration. Solid state 13C magic angle spinning NMR experiments show that the highly mobile phase is composed entirely of the dynamically flexible polyether chains of the Jeffamine rubber, the immobilized interface region is a mixture of DGEBA, PACM, and the Jeffamine rubber, with the PACM cross-linked to DGEBA predominantly residing in the rigid phase. The SWAXS results showed compositional nanophase separation spanning the 11–77 nm range. These measurements of the nanoscale compositional and dynamic heterogeneity provide molecular level insight into the very broad and controllable glass transition temperature distributions observed for these highly cross-linked polymer networks.

Renewable Castor-Oil-based Waterborne Polyurethane Networks: Simultaneously Showing High Strength, Self-Healing, Processability and Tunable Multishape Memory.

Materials with multifunctionality or multiresponsiveness, especially polymers derived from green, renewable precursors, have recently attracted significant attention resulting from their technological impact. Nowadays, vegetable-oil-based waterborne polyurethanes (WPUs) are widely used in various fields, while strategies for simultaneous realization of their self-healing, reprocessing, shape memory as well as high mechanical properties are still highly anticipated. We report development of a multifunctional castor-oil-based waterborne polyurethane with high strength using controlled amounts of dithiodiphenylamine. The polymer networks possessed high tensile strength up to 38 MPa as well as excellent self-healing efficiency. Moreover, the WPU film exhibited a maximum recovery of 100 % of the original mechanical properties after reprocessing four times. The broad glass-transition temperature of the samples endowed the films with a versatile shape-memory effect, including a dual-to-quadruple shape-memory effect.

Synthesis of Polycarbonate Block Terpolymers Using Robust Cobalt Catalyst Systems

This contribution reports an efficient approach for preparing polycarbonate block terpolymers by immortal stepwise copolymerization of CO2 with different epoxides in the presence of enol chain transfer, mediated by robust cobalt catalyst systems consisting of the fluorine substituted salenCo(III)NO3 or biphenol-linker bimetallic Co(III) complex in conjunction with an ionic cocatalyst, PPNX (PPN = bis(triphenylphosphine)iminium, X = NO3− or 2,4-dinitrophenoxide). Various polycarbonate block terpolymers were obtained in perfectly unimodal distribution of their molecular weights with narrow polydispersity. They all possessed only one broad glass transition temperature, which could be adjusted by altering the length of different polycarbonate segments.

Polyurethane networks based on disulfide bonds: from tunable multi-shape memory effects to simultaneous self-healing

With the prompt development in intellectualization nowadays, the smart materials with multifunctionality or multi-responsiveness are highly expected. But it is a big challenge to integrate the different actuating units into a single system in a synergy pattern. Herein, we put forward a new strategy to develop the polyurethane networks which can present shape-memory effect and self-healing effect in independent way as well as simultaneous acting mode. To realize this goal, poly(tetremethylene ether) glycol was chosen as the soft segment to ensure the polymer chains a good mobility, and disulfide bond as the dynamic covalent bond was embedded in the backbone of polyurethane to endow it with desirable self-healing capacity under mild condition. Moreover, a rational control of the architecture of the networks by adjusting the content of disulfide bond and the degree of cross-linking, a broad glass transition temperature ( T g) was achieved, which enabled the network a versatile shape-memory effect, covering from dual-, triple- so far as to quadruple-shape memory effect. More importantly, the shape recovery and healing process can be realized simultaneously because of the highly matched actuating condition in this system.

Photonic Shape Memory Polymer with Stable Multiple Colors.

A photonic shape memory polymer film that shows large color response (∼155 nm) in a wide temperature range has been fabricated from a semi-interpenetrating network of a cholesteric polymer and poly(benzyl acrylate). The large color response is achieved by mechanical embossing of the photonic film above its broad glass transition temperature. The embossed film, as it recovers to its original shape on heating through the broad thermal transition, exhibits multiple structural colors ranging from blue to orange. The relaxation behavior of the embossed film can be fully described using a Kelvin–Voigt model, which reveals that the influence of temperature on the generation of colors is much stronger than that of time, thereby producing stable multiple colors.

The F···H Hydrogen Bonding Effect on the Dynamic Mechanical and Shape‐Memory Properties of a Fluorine‐Containing Polybenzoxazine

A fluorine‐containing difunctional benzoxazine is synthesized by hydrosilylation of a monofunctional benzoxazine based ono‐allylphenol andp‐fluoroaniline. Besides the intramolecular and intermolecular hydrogen bonding associated with the nitrogen and oxygen atoms in the oxazine ring, specific self‐complementary intermolecular ArF···HO hydrogen bonding is formed in the polymerization of the benzoxazine, which leads to the resultant polybenzoxazine possessing a broad glass transition temperature range and showing two not well‐separated transitions. Based on the two glass transition temperatures, the polybenzoxazine exhibits triple‐shape‐memory behaviors by manipulating temperature and strain in the shape fixing process under tensile and bending modes. The dynamic mechanical and shape‐memory properties of the polybenzoxazine are influenced by the combined effect of the cross‐linking density and the ArF···HO hydrogen bonding.image

Tunable Shape Memory Polymers from α-Amino Acid-Based Poly(ester urea)s

The thermal shape memory behavior of poly(ester urea)s (PEUs) composed of varying α-amino acids and linear diols has been explored. The thermal, mechanical, and shape memory properties of PEUs are shown to be controlled by changing the amino acid and diol components of the polymer, without negatively affecting the shape memory performance of the polymer in most cases. These materials display triple-shape memory behavior and temperature memory properties due to a broad glass transition temperature interval. The versatility of the shape memory behavior of PEUs was explored by demonstrating shape transformations of thin films, salt leached scaffolds, and larger constructs. Overall good shape memory behavior in combination with the tunable properties of PEU materials makes them prime candidates for use as shape memory materials in biomedical applications.

The Influence of Biobased Olegomeric Diisocyanate on Thermal and Mechanical Properties of Poly(3‐hydroxybutyrate)

SummaryIn the present work, poly (3‐hydroxybutyrate) (PHB) blends were prepared by melt blending with biobased oligomeric diisocyanate synthesised from hexamethelene diisocyanate (Tolonate XFLO100 (TXF100)). PHBTXF100 blends with four different weight fraction (10, 15, 20 and 25 phr) of TXF100 were prepared and characterized for mechanical, thermal and thermomechanical properties. Strain at break and tensile toughness of PHBTXF10025 blend were improved by 200% and 193%, respectively. PHBTXF100 blends showed a broad glass transition temperature with a decreased onset temperature compared to PHB. PHBTXF100 blends exhibited low crystallinity than PHB, and was further decreased with an increased weight fraction of TXF100. Elastic and storage moduli PHBTXF100 blends were decreased compared to PHB, and correlated to their low degree of crystallinity. The changes in mechanical properties of PHBTXF100 blends were mainly due to efficient weakening of intermolecular interactions in the amorphous regions of PHB, and also a slight decrease in crystalline order of PHB.

High performance multiple-shape memory behaviors of Poly(benzoxazole-co-imide)s

High temperature triggered multiple-shape memory poly(benzoxazole-co-imide)s with adjustable properties were prepared via facile random copolymerization 3,3′,4,4′-biphenyltetracarbolylic dianhydride (BPDA) with two different diamine of 4,4′-oxydianiline (ODA) and 5-amino-2-(4-aminobenzene) benzoxazole (BOA). The effect of polybenzoxazole on the molecular packing, physical properties and shape memory behaviors of poly(benzoxazole-co-imide)s was investigated systematically. The incorporation of polybenzoxazole into polyimides endows better mechanical properties, higher chain packing, broad glass transition temperature and excellent tunable dual-shape memory behaviors with shape fixity above 98% and shape recovery up to 98%. Besides, multiple-shape memory effects with high switching temperature are first achieved in poly(benzoxazole-co-imide)s, and the multiple-shape memory could be adjusted by choosing the two different switching temperatures. Lastly, the potential mechanism of multiple-shape memory behaviors of poly(benzoxazole-co-imide)s are suggested.

Relating structure and chain dynamics to ballistic performance in transparent epoxy networks exhibiting nanometer scale heterogeneity

The ballistic performance was examined for a series of broad glass transition temperature epoxy formulations consisting of a di-epoxy monomer crosslinked with bi-modal mixtures of both a rigid, low molecular weight diamine and a flexible, high molecular weight diamine. Interestingly, the resins did not macro-phase separate during cure, but exhibited structural and dynamic heterogeneity on a length scale of a few nanometers, as confirmed by X-ray scattering, dynamic mechanical analysis, modulus-mapped atomic force microscopy, and broadband dielectric spectroscopy. The nano-structured resins were optically transparent and demonstrated a nearly 300% increase in ballistic energy dissipation relative to the neat resins, as well as when compared to epoxy formulations composed of similar bi-modal blends that exhibited a macro-phase separated structure. The ballistic performance is found to be insensitive to sub-glass transition temperature (Tg) relaxations, but appears to be dependent on both the nano-structure and the Vogel temperature of the high Tg component. The study demonstrates a new class of transparent protective materials composed of rigid and flexible components with a fine scale heterogeneous structure.

Shape memory property of microcrystalline cellulose–poly(ε-caprolactone) polymer network with broad transition temperature

Preparation of shape memory polymers (SMPs) with broad transition temperature was an effective method to realize multishape memory effect. In this study, a novel SMP with a broad glass transition temperature (Tg) based on microcrystalline cellulose was prepared. The structure of the SMP was analyzed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance, which can prove the successful synthesis of the material. The thermal properties were investigated with differential scanning calorimetry and dynamic mechanical analysis (DMA). The dual- and multishape memory effects were also quantificationally analyzed by DMA. Further, the influence of programming temperature within Tg on dual-shape memory effect was investigated, and a 1D model was built to explain their relationship.

Synchronized Tandem Catalysis of Living Radical Polymerization and Transesterification: Methacrylate Gradient Copolymers with Extremely Broad Glass Transition Temperature.

Gradient copolymers with differential sequences linearly changing from methyl methacrylate (MMA) to dodecyl methacrylate (DMA) were efficiently synthesized by a concurrent tandem catalysis in the ruthenium-catalyzed living radical (co)polymerization coupled with the in situ transesterification of MMA with 1-dodecanol assisted by titanium isopropoxide [Ti(Oi-Pr)4]. The key is to perfectly synchronize the two reactions throughout the tandem catalysis by using molecular sieves (MSs), which facilitates the MMA transesterification into DMA by removing the resulting methanol. The MMA/DMA gradient copolymers had an extremely broad glass transition temperature range (i.e., hardly detectable by differential scanning calorimetry (DSC)), in sharp contrast to the random and the block counterparts of similar compositions.

Structure, Viscoelastic Properties and Damping Mechanisms of Reactive Butadiene-nitrile Rubber/Epoxy Polymer Blends

Carboxyl-terminated butadiene acrylonitrile (CTBN) rubber/ epoxy (diglycidyl ether of bisphenol-A) / diamino diphenyl methane polymer blends with 60 wt% of CTBN were formulated to evaluate the viscoelasticity and the damping properties. When the blend resins had micro-phase separated morphologies composed of epoxy-rich dispersed phases larger than 500 nm in diameter surrounded by a rubber-rich continuous phase, the loss factors (η) of the steel laminates adhered with the resin significantly depended on the environmental temperature and the resonant frequencies. The resins with epoxy-rich phases smaller than 200 nm in diameter had broad glass-transition temperature range that resulted in the high loss factor (η > 0.1) of the steel laminates in the broad temperature range. Inhomogeneous nano-gel structures with 20∼30 nm sizes were observed in more compatible resins by scanning probe microscopy, although appreciable micro-phase separation was detected by none of SEM and TEM. Pulse NMR suggested that the fraction of interfacial phase in the resins increased with increasing the compatibility of the blends. The large interfacial phase in the inhomogeneous nano-gel structures seems to play an important role in the damping mechanisms.

Gradient copolymers with broad glass transition temperature regions: Design of purely interphase compositions for damping applications

AbstractGradient copolymers with gradients in composition along the chain lengths are synthesized by controlled radical polymerization, and their damping behaviors are compared to those of random and block copolymers. The effect of comonomer incompatibility is studied by comparing behaviors of strongly segregating styrene/4‐hydroxystyrene (S/HS) and moderately segregating styrene/n‐butyl acrylate (S/nBA) copolymers. The effect of composition gradient steepness is studied by designing “constant” or “increasing” gradients via the comonomer addition rate during semibatch polymerization. Dynamic mechanical analysis (DMA) is used to compare the temperature dependences of the storage modulus (E′), loss modulus (E″), and tan δ of the materials. A glass transition breadth (ΔTg) is defined by a temperature range over which E′ decreases from 109 Pa to 108 Pa. The gradient copolymer ΔTgs are at least four times larger than the random copolymer ΔTgs. The S/nBA gradient copolymers show strong effects of gradient steepness on ΔTg, with ΔTg being much larger for the increasing gradient than for the constant gradient. DMA data are compared to predictions by Hashimoto et al. for tapered block copolymers in the limit where the taper extends across the entire chain. The shapes of their calculated temperature dependences of E′ and E″ correspond well to the gradient copolymers with large ΔTg values, providing strong support for symmetric gradient copolymers forming nanoscale, ordered domains with sinusoidal composition profiles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 48–58, 2008

Evaluation of a new visco-elastic foam for automotive applications

The geometry and mechanical characteristics of the automotive seat greatly influences the occupant kinematics in rear-end collisions. The head restraint is important particularly with respect to soft tissue neck injuries. While several studies analysed the effect of geometrical properties of head restraints, little is reported on the potential to reduce such injury by changing the material of the head restraint padding, i.e. the underlying foam. This study investigates whether the head restraint foam alone can be tailored to reduce whiplash injury. A newly developed visco-elastic (VE) foam was chosen, because advanced energy absorption properties are expected to produce beneficial effects on the occupant motion. The behaviour of the visco-elastic foam was evaluated by performing impact pendulum tests. The most important novel property of the foam thereby consists of its broad temperature range over which it keeps its advantageous visco-elastic deformation properties, while sustaining the ability to dissipate energy. The tests indicated in particular a broad glass transition temperature resulting in a stable impact behaviour over a temperature range of 5°C to 35°C. Applying this foam as a head restraint padding material, several sled tests using a standard car seat were performed. The tests were conducted to mimic rear-end collisions with a delta-v of 16 km/h. A BioRID dummy was used as a human surrogate. For the seat tested, the change of the foam resulted only in minor changes at room temperature, while the standard foam exhibited adequate performance. Additional changes of the head restraint geometry were shown to have a larger beneficial influence on the occupant kinematics.

Phase Behavior and Segmental Mobility in Binary Blends of Polystyrene and Poly(vinyl methyl ether)

The phase behavior and segmental mobility in binary blends of polystyrene (PS) and poly(vinyl methyl ether) (PVME) were investigated. Two nearly monodisperse PSs having weight-average molecular weights (Mw) of 57 000 and 95 000 with polydispersity indexes (PDI) of 1.06 and 1.09, respectively, and PVME having Mw = 99 000 with a PDI of 2.13 were used for this study. Two sets of PS/PVME binary blends with varying compositions were prepared by solvent casting from toluene. Thermograms from differential scanning calorimetry showed that each blend has a single, yet very broad glass transition temperature. Cloud point measurements via He−Ne laser light scattering were taken to determine phase equilibria in each blend, which exhibited lower critical solution temperature (LCST) behavior. Solid-state nuclear magnetic resonance (NMR) spectroscopy was used to examine segmental mobility and component domain sizes. 1H T1ρ experiments were run at temperatures ranging from −40 to 140 °C. We observed only small differences in 1H T1ρ values of PS and PVME at temperatures below 45−80 °C (depending on blend composition) and a large divergence of 1H T1ρ values at higher temperatures. 13C T1ρ and wide-line separation (WISE) experiments were run at room temperature on untreated and heat-treated samples. WISE experiments revealed that heterogeneities from 3.5 nm to greater than 30 nm existed within the blends, depending on the temperature of heat treatment. Since it has been found that 1H T1ρ measurements can give ambiguous domain information, 1H-NOESY NMR was used to examine several blend compositions at 100 °C. We conclude from this study that nanoheterogeneities exist in these PS/PVME blends at temperatures below the binodal curve determined by cloud point measurements and that a broad, single glass transition should not be construed as evidence of miscibility at the molecular level. It has been shown that nanoheterogeneities exist on a segmental level and that there are large changes in mobility at temperatures above 45−80 °C. However, the blend does not phase separate until the critical temperature (LCST), determined by cloud point measurements, is reached.

Synthesis and properties of two kinds of nonlinear optical interpenetrating polymer networks

Two kinds of interpenetrating polymer networks (IPNs) containing 4-(4'-nitrophenylazo)aniline chromophore groups were synthesized. A polyacrylate network was prepared by polymerization of Dispersed Red-19 (DR-19) diacrylate, whereas an epoxy resin network was formed by reaction of Bisphenol A-type epoxy resin E44 with 4(4'-nitrophenylazo)-3-amino aniline. A polyurethane network was synthesized by reaction between (β-hydroxyl propyl acrylate-DR-1 methacrylate) copolymer and phenol-capped isocynate-terminated DR-19. IPNs based on polyacrylate/epoxy resin and IPNs based on polyurethane/epoxy resin were obtained by carrying out two corresponding kinds of reactions simultaneously. Both kinds of IPNs were characterized by gel content, IR spectra, and DSC. The first kind of IPNs exhibits two glass transition temperatures at 122 and 165°C, while the second kind of IPNs showed one broad glass transition temperature at 172°C. Thin and transparent poled films of both IPNs were prepared by spin-coating, followed by thermal curing and corona poling at 160°C for 1 h. The second-order nonlinear optical properties of the poled films were studied by a visible light absorbance measurement according to the one-dimensional rigid oriented gas model. The polyurethane/epoxy resin IPNs were more stable in dipole alignment than were the polyacrylate/epoxy resin IPNs at temperature higher than 120°C

Synthesis, properties and photocuring behaviour of poly(2-acrylamido-anthraquinone)

Poly(2-acrylamidoanthraquinone) has been prepared by free radical polymerization using a peroxide catalyst. Confirmation of polymer formation is obtained using 1H-FT NMR, gel permeation chromatography, thermal analysis and Fourier transform i.r. spectroscopy. The yellow-orange coloured polymer was highly soluble in chloroform with a number-average molecular weight of 3230 (Polystyrene standard). Using a polarizing microscope, solvent-cast films were found to be essentially amorphous and, from thermal analysis, there is a broad glass transition temperature range with a maximum at 128°C and a broad-weak melting point peak over the range 180–200°C. Absorption maxima and extinction coefficients are slightly lower than those of the corresponding monomer. In terms of its photoinitiator properties, it was found to exhibit the same photoactivity as the monomer in a mixed vinyl urethane-dimethacrylate prepolymer system as well as being more soluble. Both systems were also more effective as visible sensitizers than camphotquinone at an equivalent mol%.

Dynamic Mechanical Properties and Adhesive Joint Strengths of Emulsion Polymers Produced by Power Feed Technique. III. Adhesive Joint Strengths of Grafted Power Feed Copolymer

Abstract Power feed copolymers were synthesized using styrene and n-butyl acrylate through non-uniform feeding emulsion polymerization. Poly(vinyl alcohol) (PVA) was used as a protective colloid, onto which vinyl monomers were grafted. Power feed copolymer had a very broad glass transition temperature compared with random copolymer, even if grafting and/or crosslinking were introduced to the system. This tendency was almost the same as the non-grafted power feed copolymer where only low molecular weight surfactant was used. Adhesive joint strengths of power feed copolymers were evaluated compared with random copolymers. In the case of usual linear power feed copolymer, the adhesive joint strengths were not higher than those of random copolymer, which was considered to be due to the lower film strengths of the power feed copolymer. Power feed copolymer having grafting showed slightly higher adhesive joint strengths over a wide range of temperatures than random copolymer. When crosslinking was introduced to the system, power feed copolymer showed much higher adhesive joint strengths over a wide temperature range.