Wide-angle X-ray Diffraction Results Research Articles

Synthesis and Rheological Analysis of Non-Isocyanate Polyurethanes Blended with Poly(vinyl alcohol)

This study investigated the blending of non-isocyanate polyurethanes (NIPUs) with poly(vinyl alcohol) (PVA) at various ratios, with specific emphasis on ratios such as 20%, 50%, 80%, and 100% NIPU content. Focus has been made on assessing their rheological behaviour, mechanical performance, and thermal stability. As the NIPU content surpassed 50%, a shear-thickening trend emerged, suggesting a highly interwoven molecular structure. Rheological studies demonstrate viscosity variations dependent on blend composition and shear rate, with pure NIPU solution exhibiting shear thickening behaviour suggestive of network formation facilitated by the application of shear. Dynamic modulus analysis revealed viscoelastic properties in blends containing 50% and 100% NIPU. Thixotropic analysis showcased a remarkable structural recovery of 99% in solutions with over 20% NIPU, emphasizing the resilience of NIPU-rich blends to shear-induced alterations. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) demonstrate thermal stability and crystallinity, with blends exhibiting intermediate behaviour and reduced crystallinity compared to pure PVA due to NIPU incorporation. Blends exceeding 10% PVA displayed reduced consistency and diminished PVA crystallization ability, corroborated by DSC and wide-angle X-ray diffraction (WXRD) results. Thermal stability increased with NIPU integration, and blends demonstrated intermediate thermal behaviour between the pure polymers. Notably, the PU2PVA8 blend demonstrates the highest miscibility and a unique combination of amorphous and crystalline nature, showcasing its potential for tailored material design with enhanced structural and thermal properties.

The role of nanoclay in processing immiscible polypropylene and poly (ethylene terephthalate) waste blends using twin screw extrusion

Polypropylene and poly(ethylene terephthalate) waste were blended with different types of nanoclay (cloisite Na+, cloisite 20A and CT4270) to understand the role of nanoclay in immiscible polymer blends. The blend morphology was investigated using scanning electron microscopy, the dispersion of the nanoclay was characterized using wide angle x-ray diffraction (WAXD) and rheology. WAXD results showed partial exfoliation for cloisite Na+ and intercalation for cloisite 20A and CT4270. It was predicted that cloisite Na + settled in the PET phase while cloisite 20A settled at the interface of PP and PET. Morphology analysis showed that increasing the concentration of nanoclay in the blend decreased the droplet size. The nanoclay was shown to inhibit coalescence of the droplets causing a decrease due to its rigidity.

In situ study on the tensile deformation in high-density polyethylene/hexagonal boron nitride composite

Tensile deformation in the post processing of polymer plays a critical role in determining its mechanical properties. In this work, we investigated the structure evolution of high-density polyethylene/hexagonal boron nitride (HDPE/h-BN) composite during stretching in a wide temperature range from 25 °C to 100 °C in order to reveal the suitable post processing temperature of HDPE/h-BN composites fiber. The structure transition of HDPE crystal and the distribution of h-BN were investigated by in-situ small-angle X-ray scattering (SASX), in-situ wide-angle X-ray diffraction (WAXD) measurements, and scanning electron microscopy (SEM). The result shows that the parent HDPE crystal would be broken and recrystallize into highly oriented daughter crystal along the tensile direction when the tensile temperature (Tten) is in the range from 70 °C to 100 °C, though the recrystallization rate is low at high Tten. When Tten is low (25 °C), the crystallinity decreases continuously as no recrystallization takes place. In addition, the h-BN migrates accompany with the HDPE matrix and becomes oriented during the tensile direction. Combining the result of WAXD, SAXS, and the SEM measurement, it is concluded that the temperature of 70 °C is suitable for post processing of the HDPE/h-BN composite fiber.

An efficient β-nucleating agent with high lattice matching rate for plate-like crystallization of polypropylene random copolymer.

It is challenging to naturally produce large amounts of β-crystals by directly adding a commercial β-nucleating agent (β-NA) into polypropylene random copolymer (PPR) at present. In this work, a novel rare earth β-NA WBN-28 was directly introduced into PPR to prepare β-PPR with high β-crystal conversion. The results of differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) indicated that it is an efficient β-NA for PPR. The β-conversion rate (β-CR) could surpass 85% when the nucleating agent content was mere 0.05%. With the further increment of nucleating agent, the β-CR increased gradually, which could reach 89.5% and 86.9% respectively calculated by DSC and WAXD when the addition amount was 0.4%. The incredible high β-CR delayed the βα-recrystallization in isothermal crystallization. The fusion peak of α-crystal was unobserved below the isothermal crystallization temperature of 122 °C when the addition amount was more than 0.2%. Furthermore, there was a highly ordered structure in WBN-28 with the periodicity of 12.89 Å, which was approximately twice of the unit cell parameter in the c direction of β-PP, indicating a high lattice matching rate between them. Intuitively observed by polarizing optical microscope (POM), the crystal grains of the blends with β-NA were more refined and finally crystallized in a plate-like shape. The forming process of the plate-like β crystalline regions were proposed by scanning electron microscope (SEM) and POM.

Rationally designed fluorinated aromatic polyamide membrane for stable air dehumidification

Membrane based dehumidification technology has attracted wide attention. The anti-hydrolytic property of the membrane holds a significant role in its long-term operation in a wet environment. Herein, a series of fluorinated aromatic polyamides (FPA) are first proposed for stable air-dehumidification. Amide bond offers superior hydrolytic stability over chemical bond in the present dehumidification membrane. The deliberately introduced bulky fluorinated group (-CF3) increases the water permeability and enhances the anti-hydrolytic property of the FPA membranes. The membrane separation performance and membrane stability are further tuned by adjusting the molar ratio of para- and meta-amide groups to optimize the intermolecular forces and polymer chain arrangement, which is verified by the refractive index data and wide-angle X-ray diffraction results. The obtained co-FPA membranes exhibit tunable gas and water vapor permeation properties. With increasing para-amide group content, the gas and water vapor permeability of copolyamides gradually decreases and the selectivity of H2O/N2 increases. Meanwhile, the hydrolytic stability of the co-FPA membranes increases with the increase of TPC content as verified by 1H NMR, GPC, and mechanical property tests. Among these co-FPA membranes, the co-FPA-70 membrane exhibits the most excellent hydrolytic stability. The membrane shows almost no change in 1H NMR spectra and 97% retention of tensile strength after 5000 h of hydrolysis reaction. In the meanwhile, it shows excellent separation stability with a water vapor permeability retention of 74% during long-term hydrolysis aging operation. This study demonstrates the great potential of polyamide for the fabrication of dehumidification membranes with high hydrolysis resistance.

Crystallization with Nodular Aggregation near the Glass Transition Temperature for Syndiotactic Polypropylene

The isothermal crystallization from the melt state of syndiotactic polypropylene (sPP) has been studied by wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), and optical microscopy. The WAXD and SAXS results show the crystallization mechanism near the glass transition temperature in which the crystalline and mesomorphic nodules cover the entire sample with the formation of aggregation regions. For the SAXS analysis, the scattering function for the three-component system has been suggested. Furthermore, to analyze the growth kinetics of the aggregation region for sPP, the time-dependent structure factor combined with the homogeneous and inhomogeneous nucleation-and-growth kinetics has been suggested. The analysis shows that the growth kinetics of the aggregation region for sPP is the homogeneous nucleation-and-growth. The growth velocity of the aggregation region is a natural extrapolation of that of spherulite to the high supercooling region. These results might indicate that the crystallization with the nodular aggregation is a fundamental crystallization process near the glass transition temperature for polymers.

Kinetics of Polymer Crystallization with Aggregating Small Crystallites.

The isothermal crystallization near the glass transition temperature from the melt state of poly(trimethylene terephthalate) has been studied by wide-angle x-ray diffraction (WAXD), small-angle x-ray scattering (SAXS), and optical microscopy. The SAXS and WAXD results show the crystallization mechanism in which the crystalline nodules cover the entire sample with the formation of aggregation regions. The analysis of the SAXS results using Kolmogorov-Johnson-Mehl-Avrami theory indicates that the formation kinetics of the aggregation regions is of three-dimensional homogeneous nucleation type. The analysis of the SAXS profiles using Sekimoto's theory provides the growth velocity and the nucleation rate of the aggregation region. The temperature dependence of the growth velocity of the aggregation region is a natural extrapolation of that of spherulite to the high supercooling region. The temperature dependence of the nucleation rate of the aggregation region is also represented by the parameters of the spherulitic growth rate. The result of the growth velocities of the aggregation region and the spherulite suggests the existence of precursors at the front of the crystal growth.

Novel intercalation mechanism of cationic surfactants modified muscovite

Intercalation of cationic surfactants cetyltrimethylammonium bromide (CTAB) into the interlayer space of muscovite by the ion-exchange process was investigated. Changes in the surface and structure of the muscovite modified with CTAB were characterized using Wide angle X-ray diffraction (WAXD), Fourier-transform infrared spectroscopy (FTIR) and Transmission electron microscopy (TEM). As revealed by WAXD results, the basal spacing of CTAB-muscovite increased from 0.99 nm to 2.82 nm, indicating the formation of an intercalated structure. Through this intercalated structure, the CTA+ ions in the muscovite interlayer space were arranged in a paraffin complex that may ease the process of intercalation within the polymer matrices. FTIR spectra indicated new absorption bands at 2922 and 2855 cm−1, which signified the presence of a long alkyl chain, verifying the incorporation of CTAB into the muscovite structure. The TEM images showed separation within the muscovite layers was more intense, given their flat morphology. These micrographs demonstrate that CTAB addition had expanded the basal spacing in the muscovite layers. The present study concludes that the intercalation of CTAB-modified muscovite has a potential for polymer intercalation that can be tailored to a specific purpose.

Phenol functionalized high‐density polyethylene as compatibilizer of high‐density polyethylene/graphene nanocomposites toward enhanced mechanical and interfacial adhesion

AbstractIn this work, the methodology to obtain high‐density polyethylene (HDPE) and graphene (G) nanocomposites using phenol‐modified graphene and phenol‐modified HDPE as compatibilizer obtained from the reaction of malleated polyethylene (HDPE‐g‐MA) with phenol, is described. Six different methods were used to obtain these composites, resulting from the combination of melt and solution mixing with three different procedures to functionalize either graphene or HDPE‐g‐MA with phenol. Nanocomposites were characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), wide angle X‐ray diffraction (WAXD), dynamic mechanic analysis (DMA) and tensile properties. The FTIR results evidenced the occurrence of an esterification reaction between HDPE‐g‐MA and phenol groups serving as compatibilizer. The SEM and WAXD results showed that the addition of this compatibilizer agent had a positive effect on graphene dispersion, which promoted greater stiffness in these composite materials, presenting higher storage modulus. In addition, a noticeable enhancement in dimensional stability at high temperatures was observed according to Tan Delta measurements. These results indicated a good interfacial adhesion between graphene and the polymer matrix by using this compatibilizer agent. It was observed that the composites obtained by solution mixing method showed better performance and stronger interfacial adhesions than the composites produced by melt mixing methods. The use of this phenol modified HDPE compatibilizer offers a new option to enhance the final performance of HDPE/graphene composites with better mechanical and thermal properties to be used in materials for various applications, such as automotive industry, electrical and electronics, construction, aerospace, and other engineering applications.

An FTIR and X‐ray diffraction study of the crystal phase transition in isotactic polybutene‐1

The nature of crystal transformation in the industrially important polyolefin isotactic polybutene-1 (iPB-1) with excellent mechanical properties has not been well understood. We investigated the crystal structure transition of iPB-1 via wide-angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR) after crystallization at 78°C from the melt at 200°C. The total crystallinity index based on the WAXD results and the evolutions of form I and form II according to FTIR spectroscopy were analyzed. It was found that the total crystallinity increases with the transition time, and the time to detect the initiation of the form I is about 20 h but the time for the initiation of the decrease in the form II content is about 50 h. The result indicates that the increase of the crystallinity during the transition originates from the direct formation of the form I rather than the transformation of the form II. These results provide valuable insight into the structure evolution of the iPB-1 crystal phase transition.

Effect of Organoclay on the Rheology, Morphology, Thermal and Mechanical Properties of Nanocomposite Fibers Based on Polypropylene/Poly(Trimethylene Terephthalate)/Organoclay

Modification of the rheological and thermal properties of polypropylene (PP) was accomplished through the in-situ generation of PP/poly(trimethylene terephthalate) (PTT) nanocomposites fibrils containing organoclay via a melt spinning process. The development of the fibrillar structures in the fibers during the melt spinning and a subsequent hot drawing process was confirmed by scanning electron microscopy; the lowest mean diameter of the nano-fibrils was 74 nm for the hot drawn nanocomposite fibers consisting of 10 wt.% of PTT and 1 wt.% organoclay in the PP. The results of wide-angle X-ray diffraction and differential scanning calorimetry indicated that the presence of the 10 wt.% of PTT and 1 wt.% organoclay in the nanocomposite fibers led to an approximately 16% increase in the crystallinity of the PP, compared to pure PP fibers. The distribution of the organoclay in the nanocomposites was investigated using transmission electron microscopy and small-angle X-ray scattering.

Structure and property of comb-like polyolefins derived from highly Stereospecific homo-polymerization of higher α-olefins

A series of comb-like polyolefins possessing ultrahigh absolute molecular weight (Mw = 0.32–3.83 × 106), relatively narrow molecular weight distributions (PDIs ≤ 1.78) and high isotacticity were synthesized via the homopolymerization of higher α-olefins, from 1-octene to 1-eicosylene, by (pyridyl-amido)hafnium catalyst combined with very low loading of [Ph3C][B(C6F5)4] and Al (iBu)3, with surprisingly high catalytic activities (0.81–2.78 × 107 gpolymer/molHf·h). More noteworthily, comprehensive structure-property relationships of the resultant comb-like polyolefins were systematically investigated for the first time. The thermogravimetric analysis (TGA) characterizations demonstrated that increasing the side chain length led to the higher thermal stability of the polymers. The results of differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) measurements together confirmed that the poly (α-olefin)s became more crystalline with lengthening the side chain. Moreover, as the side-chain length increased, the poly (α-olefin) materials became stronger and more brittle.

Crystal polymorphism of polylactide and its composites by X-ray diffraction study

Polylactide (PLA) exhibits various types of crystal modifications depending on the preparation conditions, including the components. To solve the open question, a reliable calculation method for crystallinity, crystal forms, and composition in neat PLA and PLA composites was developed on the basis of temperature-dependent synchrotron wide-angle X-ray diffraction results. The relative composition of amorphous, α-form, and α’-form phases of PLA and its composites filled with halloysite nanotubes during heating was successfully obtained. It was found that only 47–56% of α’-form crystals transform into α-form crystals during a 2 °C/min heating process for PLA with a molecular weight of 54,300 g/mol. The loading of halloysite nanotubes decreases the cold crystallization and starting transition (α’ crystals transform into α-form crystals) temperatures of PLA. The crystallinity and the main diffraction peak intensity as a function of temperature were also analyzed. These results suggest that the α’-to-α form transition is a solid-solid phase transition. Polylactide (PLA) exhibits various types of crystal modifications depending on the preparation conditions, including the components. To solve the open question, a reliable calculation method for crystallinity, crystal forms and composition in neat PLA and PLA composites was developed on the basis of temperature-dependent synchrotron wide-angle X-ray diffraction results. The relative composition of amorphous, α-form, and α’-form phases of PLA and its composites filled with halloysite nanotubes during heating was successfully obtained.

Effects of pure and intercalated halloysites on thermal properties of phthalonitrile resin nanocomposites

In this work, composite materials with different halloysite nanotubes (HNTs) content as fillers were prepared by using phthalonitrile resin with alkyl center as matrix. In order to improve the dispersibility of HNTs in the polymers, phenylphosphonic acid (PPA) was used to treat HNTs. The results of Wide-angle X-ray Diffraction (WAXD), Fourier Transform Infrared spectroscopy (FTIR), Thermogravimetric Analysis (TGA) and Scanning Electron Microscope (SEM) showed that when the mass ratio of PPA to HNTs was 2:1, the intercalation rate of HNTs was the highest. The thermomechanical properties, thermal stability and thermal oxidation stability of the composite were tested by Dynamic Mechanical Analysis (DMA) and Thermogravimetric analysis (TGA). The results indicated that the polymers with intercalated HNTs as fillers have better thermomechanical properties than those with pure HNTs as fillers. When the modified HNTs content was 7%, the storage modulus of the polymer increased by 16.52% and 15.43% at 30 °C and 380 °C, respectively. With the increase of fillers, the thermal stability of polymers with pure HNTs as fillers increased, while that of polymers with modified HNTs as fillers increased first and then decreased. On the other hand, the limit oxygen index (LOI) of the polymers also increased to some extent. The degradation and control of the nanocomposites at high temperature were discussed. SEM was used to observe the cross-section morphology and found that pure HNTs would agglomerate in the polymer. The thermal properties of the phthalonitrile resin were improved by using the wide source HNTs as fillers.

Recrystallization of biaxially oriented polyethylene film from partially melted state within crystallite networks

Recrystallization behavior and the final crystallite orientation of biaxially oriented polyethylene (BOPE) film from different melted states have been studied by using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD), respectively. WAXD result shows that two kinds of crystallites (1 and 2) with different orientations are aligned around the transverse direction (TD) of the film plane. When BOPE film is annealed in the temperature range of 110~125 °C, the residual crystallites 1 are still aligned along the TD, while the residual crystallites 2 are gradually rotated and aligned along the machine direction (MD). Recrystallization of BOPE film from the partially melted states is enhanced and the maximum crystallization peak shifts to higher temperature by 7 °C. The newly formed crystallites after recrystallization are aligned along the TD and MD, respectively. When annealing temperature attains to 128 °C, a trace amount of residual crystallites 1 persists along the TD. The newly formed crystallites after recrystallization are also aligned the TD. When the storing temperature range is in 130–150 °C, the melt memory effect occurs in BOPE film, and it influences crystallization kinetics and the crystallite orientation.

Enzymatic Degradation of Acrylic Acid-Grafted Poly(butylene succinate-co-terephthalate) Nanocomposites Fabricated Using Heat Pressing and Freeze-Drying Techniques.

Biodegradable acrylic acid-grafted poly(butylene succinate-co-terephthalate) (g-PBST)/organically modified layered zinc phenylphosphonate (m-PPZn) nanocomposites were effectively fabricated containing covalent bonds between the g-PBST and m-PPZn. The results of wide-angle X-ray diffraction and transmission electron microscopy revealed that the morphology of the g-PBST/m-PPZn nanocomposites contained a mixture of partially exfoliated or intercalated conformations. The isothermal crystallization behavior of the nanocomposites showed that the half-time for crystallization of 5 wt % g-PBST/m-PPZn nanocomposites was less than 1 wt % g-PBST/m-PPZn nanocomposites. This finding reveals that increasing the loading of m-PPZn can increase the crystallization rate of nanocomposites. Degradation tests of g-PBST/m-PPZn nanocomposites fabricated using the heat pressing and the freeze-drying process were performed by lipase from Pseudomonas sp. The degradation rates of g-PBST-50/m-PPZn nanocomposites were significantly lower than those of g-PBST-70/m-PPZn nanocomposites. The g-PBST-50 degraded more slowly due to the higher quantity of aromatic group and increased stiffness of the polymer backbone. The degradation rate of the freeze-drying specimens contained a more extremely porous conformation compared to those fabricated using the heat pressing process.

Probing the structural evolution in deformed isoprene rubber by in situ synchrotron X-ray diffraction and atomic force microscopy

Developing a better understanding of the structural evolution in deformed polymers is key to designing new materials and structures that achieve superior mechanical properties. Here, we used in situ synchrotron wide-angle X-ray diffraction (WAXD) and atomic force microscopy (AFM) nanomechanical mapping (AFM-NM) to assess the strain-induced crystallization (SIC) and the associated structural evolution and mechanical properties of peroxide vulcanized isoprene rubber (IR) as a function of crosslink density (ν) and strain. The WAXD and AFM-NM results show agreement in the onset strain of SIC. Crystalline reflections appears in the WAXD while a nanofibrillar structure is found by AFM-NM. The higher ν, the smaller is the onset strain of a steep upturn in the stress-strain curves, the smaller is the onset strain of SIC, the higher is the crystallinity as evidenced in the WAXD, and the larger is the amount of nanofibrils seen by AFM-NM. Both WAXD and AFM-NM results show the SIC occurs rapidly at high strains while most chains remain in the amorphous state. The elastic modulus of the formed nanofibrils that range in diameter from several to a hundred nanometers, is two times higher than that of the amorphous regions. From the WAXD and AFM-NM results, a schematic model of structural evolution is proposed and used to illustrate the self-reinforcement mechanism in IR.

Synthesis, Structure and Properties of Poly(1-trimethylsilyl-1-propyne) Obtained with NbBr5- and TaBr5-Based Catalytic Systems

In this work, the polymerization of 1-trimethylsilyl-1-propyne [TMSP] using catalytic systems based on pentabromide Nb(V) and Ta(V) with organometallic cocatalysts Ph3Bi, Ph4Sn, Bu4Sn, Ph3SiH, and Et3SiH was investigated. The use of NbBr5-based catalytic systems has strongly marked cis-stereospecificity and gives highly cis-enriched poly(1-trimethylsilyl-1-propyne) [PTMSP] (content of cis-units above 70%), whereas the use of TaBr5-based catalytic systems leads to the formation of PTMSP with mixed cis-/trans-composition (content of cis-units from 50 to 65%).With increasing cis-content, solvent resistance of PTMSP increases significantly. PTMSP with a content of cis-units above 70% obtained on NbBr5-containing systems in cyclohexane acquires resistance to aliphatic and aromatic hydrocarbons, and cis-regular PTMSP obtained on NbBr5-based systems in toluene is totally insoluble in any of the organic solvents. The results of wide-angle X-ray diffraction indicate an increase in the packing density of the polymer during the transition from a mixed configuration to a cis-regular one. Durable PTMSP film membranes exhibit ultra-high permeability coefficients for individual gases (e.g., $${{P}_{{{{{\text{O}}}_{{\text{2}}}}}}}$$ = 8500–11000 barrer, $${{\alpha }_{{{{{\text{O}}}_{{\text{2}}}}{\text{/}}{{{\text{N}}}_{{\text{2}}}}}}}$$ = 1.5–1.9). According to the low-temperature Ar sorption, PTMSP synthesized with NbBr5- and TaBr5-based catalytic systems has high BET surface areas in the range of 870–1050 m2/g, high intrinsic microporosity, and higher gas permeability coefficients of PTMSP correlate with BET surface area growth.

Studies on thermo-mechanical and thermal degradation properties of bio-based polyurethanes synthesized from vanillin-derived diol and lysine diisocyanate

Novel bio-based polyurethane (PU) was synthesized using vanillyl alcohol (VA) and lysine diisocyanate (LDI) by one-step solution polyaddition process with 1,4-butanediol (BD) as a co-monomer. The ratios of VA/BD were varied in the PU synthesis, and the properties of the obtained PUs with different vanillin contents were characterized. The molecular weights of PUs ranged from 32 to 44 kDa, and slight decreases of the molar masses were found as VA contents increased due to lower reactivity of phenolic-OH in VA structure with respect to aliphatic BD. The low VA contents in the PU provided flexible material with high elongation up to 600%, while the PU with high VA contents presented stiff characteristics with high glass transition temperature (Tg) of 70 °C and Young's Modulus of 1.8 GPa. Furthermore, thermo gravimetrical analysis (TGA) revealed lower thermal degradation temperature for the PU with higher VA contents, suggesting weaker thermal stability of the urethane bond connected with VA unit. Pyrolysis-gas chromatography/mass spectrometry and nuclear magnetic resonance were employed for the investigation of thermal degradation manner of the PU, which detected the formation of urea compound during the thermal degradation via scission of the urethane bond at benzyl-side accompanied by the elimination of carbon dioxide. Based on these findings, the effect of vanillin-derived diol structure on thermal properties for the resulted PUs was studied by using modified diols of diphenol (methoxyhydroquinone, MHQ) and stilbene-type bisphenol (vanillin-derived stilbene, VS). TGA, differential scanning calorimetry and wide angle X-ray diffraction results indicate that the modified diphenol and stilbene structure improve thermo-mechanical properties of the obtained PU. The introduction of the modified diols into PU increased thermal degradation temperature up to 220 °C. The VS-based PU showed highest Tg of approximately 120 °C due to the stiff structure and strong interaction of the stilbene.

Thermal, soluble, and hydrophobic properties of polyimides derived from 4-(4-diethylamino)phenyl-2,6-bis(4-(4-aminophenoxy)phenyl)pyridine

A novel aromatic diamine monomer, 4-(4-diethylamino)phenyl-2,6-bis(4-(4-aminophenoxy)phenyl)pyridine (EPAPP), containing pyridine ring units, ether linkage moieties and diethylaminophenyl pendent groups, has been designed and synthesized through three-step methods, and then used to prepare for a series of polyimides with commercial aromatic dianhydrides via two-step solution polycondensation. The resulting polyimides showed good solubility in common polar solvents, such as NMP, DMF, DMSO. They exhibited high thermal stability with the glass transition temperature (Tgs) more than 254 °C, and the temperature of 10% weight loss over 544 °C with more than 64% residue at 800 °C under nitrogen. They presented excellent hydrophobic properties with the contact angle in the range of 81.9–91.9°. In addition, the results of Wide-angle X-ray Diffraction (WAXD) indicated that these polymers revealed an amorphous structure.