Miscibility with a linear Tg–composition relationship was proven for blend of poly(butylene adipate-co-butylene terephthalate) [P(BA-co-BT)] with poly(4-vinyl
phenol) (PVPh). In comparison to the blends of PBA/PVPh and poly(butylene terephthalate) (PBT)/PVPh, the Kwei’s Tg model fitting on data for the P(BA-co-BT)/PVPh blend yields a q value between those for the PBA/PVPh and PBT/PVPh blends. The q values suggest that the interaction strength in the P(BA-co-BT)/PVPh blend is not as strong as that in the PBT/PVPh blend.
Upon mixing the PVPh into the immiscible blend of PBA and PBT, the ternary PBA/PBT/PVPh blends only exhibits partial miscibility.
Full-scale ternary miscibility in whole compositions is not possible owing to the significant ∆χ effect (χij – χik). The wavenumber shifts of the hydroxyl IR absorbance band indicates that the H-bonding strength is in decreasing order—PBT/PVPh
> P(BA-co-BT)/PVPh > PBA/PVPh—and shows that the BA segment in the copolymer tends to defray interactions between P(BA-co-BT)
and PVPh in blends. 相似文献
Poly(l-lactide) (PLLA) was melt-blended with poly(p-vinyl phenol) (PVPh) using a two-roll mill, and the miscibility between PLLA and PVPh and degradation of the blend films were investigated. It was found that PLLA/PVPh blend has miscibility in the amorphous state because only single Tg was observed in the DSC and DMA measurements. The Tg of the PLLA/PVPh blend could be controlled in the temperature range from 55 °C to 117 °C by changing the PVPh weight fraction. In alkaline solution, degradation rate of PLLA/PVPh blends was faster than that of neat PLLA because PVPh could dissolve in alkaline solution. The surface morphology of degraded PLLA and PLLA/PVPh blend were observed by SEM. The surface morphology of degraded PLLA/PVPh blend was finer than that of PLLA. Young's modulus of PLLA/PVPh blend increased with increasing PVPh content. Yield stress of PLLA/PVPh blends whose PVPh content was less than 30 wt% kept the level of about 55 MPa and that of PLLA/PVPh blend whose PVPh content was 40 wt% is much lower than that of neat PLLA. 相似文献
The isothermal time–temperature-transformation (TTT) cure diagram is developed in this article to investigate the effect of
thermoplastic toughening agent on glass transition temperature (Tg) and cure kinetics of an epoxy carbon fiber prepreg, Cycom 977-2 unidirectional (UD) tape. The glass transition temperature
was measured using differential scanning calorimetry (DSC) over a wide range of isothermal cure temperatures from 140 to 200 °C.
Times to gelation and vitrification were measured using shear rheometry. The glass transition temperature master curve was
obtained from the experimental data and the corresponding shift factors were used to calculate the activation energy. The
kinetic rate model was utilized to construct iso-Tg contours using the calculated activation energy. It was observed that the iso-Tg contours did not follow the behavior of the neat epoxy resin, since they deviated from the gel time curve. This deviation
was believed to be the effect of the thermoplastic toughening agent. The behavior of the neat epoxy resin in 977-2 was shown
by constructing the iso-Tg contours using the activation energy obtained from gel time modeling. 相似文献
The fracture behavior of a core-shell rubber (CSR) modified cross-linkable epoxy thermoplastic (CET) system, which exhibits high rigidity, highTg, and low crosslink density characteristics, is examined. The toughening mechanisms in this modified CET system are found to be cavitation of the CSR particles, followed by formation of extended shear banding around the advancing crack. With an addition of only 5 wt.% CSR, the modified CET possesses a greater than five-fold increase in fracture toughness (GIC) as well as greatly improved fatigue crack propagation resistance properties, with respect to those of the neat resin equivalents. The fracture mechanisms observed under static loading and under fatigue cyclic loading are compared and discussed. 相似文献
Previously, poly(methyl methacrylate) (PMMA) was found to be almost immiscible with poly(vinyl acetate) (PVAc) regardless of tacticity of PMMA and casting solvent. Poly(vinyl phenol) (PVPh) was found successful previously in making immiscible atactic PMMA/PVAc miscible. In this investigation, tacticity effect of PMMA on a ternary composed of PMMA, PVAc and PVPh was studied. Isotactic PMMA ternary was shown to be miscible in all the studied compositions on the basis of single Tg observation. However, syndiotactic PMMA ternary demonstrated immiscibility at ca. 25% PVPh and miscibility was observed at higher PVPh concentrations. A modified Kwei equation based on the binary interaction parameters was proposed to describe the experimental Tg of the miscible ternary almost quantitatively. 相似文献
Thiol‐click reactions lead to polymeric materials with a wide range of interesting mechanical, electrical, and optical properties. However, this reaction mechanism typically results in bulk materials with a low glass transition temperature (Tg) due to rotational flexibility around the thioether linkages found in networks such as thiol‐ene, thiol‐epoxy, and thiol‐acrylate systems. This report explores the thiol‐maleimide reaction utilized for the first time as a solvent‐free reaction system to synthesize high‐Tg thermosetting networks. Through thermomechanical characterization via dynamic mechanical analysis, the homogeneity and Tgs of thiol‐maleimide networks are compared to similarly structured thiol‐ene and thiol‐epoxy networks. While preliminary data show more heterogeneous networks for thiol‐maleimide systems, bulk materials exhibit Tgs 80 °C higher than other thiol‐click systems explored herein. Finally, hollow tubes are synthesized using each thiol‐click reaction mechanism and employed in low‐ and high‐temperature environments, demonstrating the ability to withstand a compressive radial 100 N deformation at 100 °C wherein other thiol‐click systems fail mechanically.
A series of hot-melt processable thermosetting compositions was prepared by blending N,N,N′,N′-tetraglycidyl-4,4′ -diaminodiphenyl-methane/4,4′-diaminodiphenylsulfone (TGMDA/DDS) epoxy resin and thermoplastic polymer powders with average particle size below 30 μm. The basic thermoplastic polymers were either a high Tg amorphous cardo polyimide (Tg=350°C) or commercial semicrystalline PA6 and PA12 polyamides. The resulting heterogeneous mixtures showed viscosity values below 5000 cps suitable for prepregging process. After cure, phase-separated morphologies were maintained with a rather limited interphase miscibility as demonstrated by thermomechanical analysis. Scanning electron microscope examination of fracture surfaces pointed out a strong adhesion between the powder particles and the surrounding polyepoxy network, particularly for the potentially reactive polyamide structures. Moreover, as shown by differential scanning calorimeter analysis, the crystallinity ratio of the PA6 and PA12 powders was lowered due to melting during thermal polymerization. The fracture toughness properties of the powder-containing materials were compared with those of a fully miscible cardo polyimide–TGMDA/DDS blend coming from an homogeneous resin composition. The best improvement in fracture energy was obtained for the powder-modified resins. The most effective composition filled with 16 wt% of powdered polyimide exhibited a fourfold increase in GIC (388 J/m2 versus 100 J/m2) without compromising the epoxy thermomechanical stability (Tg=227°C versus 223°C). 相似文献
Suitable as highly effective polymerization catalysts is the new class of donor/acceptor metallocenes in which the rotation of the two π ligands is restricted through the formation of a dative D+→A− bond (see picture). Specifically optimized substitution patterns yield excellent properties for the synthesis of high-melting, highly crystalline thermoplastic materials, amorphous thermoplastic materials with high glass transition temperatures as well as polyolefin elastomers with low glass Tg. 相似文献
The creep behavior of a series of fully cured epoxy resins with different crosslink densities was determined from the glassy compliance level to the equilibrium compliance Je at temperatures above Tg and at the glassy level below Tg during spontaneous densification at four aging temperatures, 4,4-diamino diphenyl sulfone DDS was used to crosslink the epoxy resins. The shear creep compliance curves J(t) obtained with materials at equilibrium densities near and above Tg were compared at their respective Tgs. Tgs from 101 to 205°C were observed for the epoxies which were based on the diglycidyl ether of bisphenol A. Creep rates were found to be the same at short times, and equilibrium compliances Je were close to the predictions of the kinetic theory of rubberlike elasticity. Time scale shift factors determined during physical aging were reduced to Tg. At compliances below 2 × 10?10 cm2/dyn, Andrade creep, where J(t) is a linear function of the cube root of creep time, was observed. The time to reach an equilibrium volume at Tg was found to be longer for the epoxy resin with lower crosslink densities. The increase of density during curing is illustrated for the epoxy resin with the highest crosslink density. 相似文献
Thin films of 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexane carboxylate were UV irradiated (1.1 J cm-2) under isothermal conditions ranging from 0 to 50°C. Under these conditions the polymerization advanced quickly but only
to a conversion level of less than 10% before the reaction rate slowed by more than an order of magnitude. This drop off in
rate was not caused by the glass transition temperature, Tg, reaching or exceeding the reaction temperature, Trxn, since the epoxide's Tg remained at least 40°C below Trxn. Raising the sample temperature above 60°C caused a sharp increase in the conversion level. At 100°C conversion exceeds 80%
and the ultimate Tg approaches 190°C. The addition of 10 mass% 1,6-hexanediol, HD, to the epoxy caused the conversion at room temperature to
quintuple over the level obtained without the alcohol present. The heat liberated from this alcohol epoxy blend during cure
on a UV conveyor belt system caused the sample's temperature to increase by about 100°C above ambient whereas the epoxy alone
under these conditions only experienced a modest temperature rise of about 26°C. If the amount of HD in the blend is increased
above 10% the heat of reaction at 23°C decreases due to HD being trapped in a nonreactive crystalline phase. Boosting reaction
temperatures above 50°C melts the HD crystals and yields significantly improved conversion ratios. As the level of alcohol
blended with the epoxy is raised its ultimate Tg is lowered and when the concentration of alcohol in the blend nears 30 mass%Tg drops below room temperature.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献