Weight Loss Temperatures Research Articles

Lipase-catalyzed synthesis and characterization of medium-long-medium (MLM) type structured triacylglycerols from peony seed oil

Structured triacylglycerols (STAGs) with medium-chain fatty acids (FAs) at sn-1,3 positions and long-chain FAs at the sn-2 position are known as medium-long-medium (MLM) type STAGs. They can not only provide energy immediately and control weight effectively, but may also provide essential or beneficial FAs to meet the human needs. In this study, MLM type STAGs were synthesized from lipase-catalyzed acidolysis of peony seed oil (PSO) with octanoic acid (OcA) and decanoic acid (DA) as medium-chain FAs in solvent-free systems. Optimal reaction conditions were 1:8 (PSO to OcA/DA), 40 °C and 24 h. The OcA content and DA content at sn-1,3 of two STAGs were 81.1% and 82.5%. The total essential FA (α-linolenic acid and linoleic acid) contents at sn-2 reached 61.5% and 57.2%, and long-chain unsaturated FA contents reached 93.3% and 87.4%. Infrared absorptions of two STAGs were weaker than those of PSO at 723 cm−1 [-(CH2)n-rocking] and 3011 cm−1 [ = CH (cis) stretching]. The end melting temperature and maximum weight loss temperature of STAG rich in DA were higher than those of STAG rich in OcA. This study is conducive to the deep processing of PSO and provides a new and promising substrate for MLM type STAG synthesis.

Fabrication of antibacterial food packaging from polyvinyl alcohol/sodium caseinate composite films cross‐linked with lactic acid

AbstractIn this study, Polyvinyl Alcohol (PVA)/Sodium Caseinate (NaCAS) were cross‐linked by mixing with Lactic acid (LA) in different proportions (0.5%, 1%, 2%, and 4%). Composite films were obtained from the prepared solutions using the solution casting method. The obtained composite films were appeared as slightly opaque and lightly yellowish, but mostly transparent. As the amount of LA increased, the polarized microscope surface images of the composite films became rougher. It was explained that cross‐linking occurred with the aldehyde groups (CHO) determined in the Fourier transform infrared spectroscopy (FTIR) analysis. The increasing 5% weight loss temperature of the films because of cross‐linking also increased the thermal strength. In X‐ray diffraction analysis (XRD), the 2θ peak intensity of the 2% LA‐added film, which had the highest cross‐link density, was indicated to be the lowest. It was reported that 4% and above the LA contribution rate negatively affects the physical and mechanical properties of the PVA/NaCAS matrix. The pure PVA/NaCAS film had 30.08 MPa tensile strength and 1.49% tensile strain. The film with 2% LA added showed the tensile strength value closest to the pure film with 23.89 MPa. With a 6.52% value, the film containing 2% LA showed the lowest moisture retention behavior. Pure PVA/NaCAS film, which has a hydrophilic structure with a contact angle of 57°, gained hydrophobic ability with the addition of LA. The 1% LA‐added film exhibited the highest hydrophobic behavior with a contact angle value of 99°. With the LA additive, an increase in the contact angle values of the composite films was observed between approximately 61% and 74%. In addition, the water vapor permeability (WVTR) with 582.37 g/m2 day value of pure PVA/NaCAS composite film decreased after the addition of LA. It was degraded to 322.72 g/m2 day WVTR value in the 1% LA‐added film. 100% antibacterial activity against both E. coli and S. aureus was observed in composite films containing 1% or more LA additive. The resulting films were suggested to be used as active food packaging with antibacterial effects.Highlights LA can be used as a crosslinking agent for PVA/NaCAS blends. 2% LA contribution has shown the highest cross‐linking density. 4% LA and higher LA contribution would negatively affect the mechanical properties of the matrix. High antibacterial activity was obtained against both E. coli and S. aureus in films containing 1% or more LA.

Trifluorovinyl-ether (TFVE) substituted side-chain polynorbornene for preparing crosslinked polymer with high performance

Characteristics and properties of polynorbornene can be regulated through side-chain engineering. In this contribution, a linear polynorbornene (PNI-TFVE) containing trifluorovinyl-ether (TFVE) side groups was synthesized via ring-opening metathesis polymerization. This linear polynorbornene was soluble in common organic solvents and showed good film-forming ability. Upon thermal post-polymerization, this linear PNI-TFVE can be easily transformed into crosslinked polynorbornene (PNI-PFCB) with perfluorocyclobutyl linkers. The resulted PNI-PFCB exhibited outstanding thermal stability with ultra-high glass transition temperature above 350 °C and a 5 % weight loss temperature of 479 °C. Due to the high crosslinking density and high fluorine content of PFCB, crosslinked PNI-PFCB also exhibited low thermal expansion of 73 ppm °C−1, as well as favourable storage modulus and hydrophobicity.

Preparation and thermal insulation properties of lightweight high-strength polyimide aerogels containing benzoazole structures

Polyimide (PI) aerogels, serving as thermal insulation materials in extreme environments, stand out for their exceptional high temperature stability and superb thermal insulation properties, rendering them ideal for aerospace, transportation, and specialized equipment industries. However, conventionally synthesized PI aerogels suffer from significant drawbacks in mechanical properties and thermal stability, limiting their practical applications. To overcome this challenge, we successfully synthesized polyimide aerogels using biphenyl-3,3,4,4′-tetracarboxylic dianhydride (BPDA), 5-amino-2-(4-aminophenyl)benzimidazole (PABZ), and 5-amino-2-(4-aminophenyl)benzoxazole (APBO) followed by supercritical carbon dioxide drying. These synthesized PIs exhibit remarkable thermal stability, with high thermal weight loss temperatures (Td5 %=595–611℃) and high glass transition temperatures. Additionally, these novel PI aerogels demonstrate exceptional thermal insulation properties, high specific surface area, and extremely small pore size. Furthermore, boasting a low dielectric constant (ε=1.72), these newly developed PI aerogels offer along with excellent mechanical properties, holding substantial promise for applications in the forthcoming generation of advanced aerospace and specialized equipment materials.

Thermal stability and luminescence of zinc and lanthanide(Tb3+ and Ce3+) coordination polymers with pyridine-2,5-dicarboxylic acid by the WASSR method

Two sorts of inorganic-organic coordination polymers (Tb2Zn(2,5-PDC)4・10H2O(I), Ce2Zn2(2,5-PDC)5・2H2O(II))constructed by lanthanide(TbIII 、CeIII) and ligand of the pyridine-2,5-dicarboxylate have been prepared by the soft chemical synthesis method(WASSR method). The purpose of this study was to investigate optic property, thermal stability and dehydration/hydration behavior. The experimental results indicated Tb compound(I) show stronger red phosphor than Ce compound(II), but framework of crystal structure is weaker than Ce compound(II) on account of XRD patterns comparison between dehydrated compound and re-hydrated compound. The thermal stability of Ce compound(II) is better than Tb compound(I) owing to the first weight loss temperature is high to Tb compound about 200 °C.

Synthesis and Characterization of Negative-Tone Photosensitive Polyimides with Low Coefficient of Thermal Expansion for Packaging Applications.

Negative-tone photosensitive polyimides (PSPIs) with a low coefficient of thermal expansion (CTE) were prepared by dissolving polyimide precursor-poly(amide ester) (PAE) resins, photoinitiators, photocrosslinkers and other additives in organic solvents. Using triamine as a monomer and dianhydride and diamine as polycondensates, tri-branched structure PAE resins with different molecular weights named PAE-1~5 were prepared. A series of corresponding PSPI films named PSPI-1~5 were prepared from PAE-1~5 resins with the same formulation, respectively. The PSPI-1~5 films prepared from resins of this structure have excellent mechanical, thermal and electrical properties after being thermally cured at 350 °C/2 h in nitrogen. The PSPI-1~5 films' coating solution also show good photolithographic performance and are able to obtain photolithographic patterns with a resolution of about 10 μm after homogenization, exposure and development. Among the PSPI-1~5 films, PSPI-2 has the most excellent lithographic properties with a weight average molecular weight (Mw) of 2.9 × 104 g/mol, a CTE of 41 ppk/°C, a glass transition temperature (Tg) of 343 °C and a 5% weight loss temperature (Td5) of 520 °C, making it suitable for industrial scale-up. The mechanical properties of elongation at breakage of 42.4%, tensile moduli of 3.4 GPa and tensile strength of 153.7 MPa were also measured.

Frequency-Dependent Dielectric Permittivity and Water Permeability in Ordered Mesoporous Silica-Grafted Fluorinated Polyimides.

Polymers with a low dielectric constant (Dk) are promising materials for high-speed communication networks, which demand exceptional thermal stability, ultralow Dk and dissipation factor, and minimum moisture absorption. In this paper, we prepared a series of novel low-Dk polyimide films containing an MCM-41-type amino-functionalized mesoporous silica (AMS) via in situ polymerization and subsequent thermal imidization and investigated their morphologies, thermal properties, frequency-dependent dielectric behaviors, and water permeabilities. Incorporating 6 wt.% AMS reduced the Dk at 1 MHz from 2.91 of the pristine fluorinated polyimide (FPI) to 2.67 of the AMS-grafted FPI (FPI-g-AMS), attributed to the free volume and low polarizability of fluorine moieties in the backbone and the incorporation of air voids within the mesoporous AMS particles. The FPI-g-AMS films presented a stable dissipation factor across a wide frequency range. Introducing a silane coupling agent increased the hydrophobicity of AMS surfaces, which inhibited the approaching of the water molecules, avoiding the hydrolysis of Si-O-Si bonds of the AMS pore walls. The increased tortuosity caused by the AMS particles also reduced water permeability. All the FPI-g-AMS films displayed excellent thermooxidative/thermomechanical stability, including a high 5% weight loss temperature (>531 °C), char residue at 800 °C (>51%), and glass transition temperature (>300 °C).

Study on the synthesis and properties of a new fluorine‐containing copolyarylate

AbstractA range of new fluorine‐containing copolyarylates were successfully produced through interfacial polymerization using hexafluorobisphenol A (BPAF) featuring a symmetric trifluoromethyl group structure, bisphenol B (BPB), and two acyl chloride monomers as raw materials. The results indicated that the synthesized amorphous copolyarylates exhibited good solubility, with number average molecular weights (Mn) of 19,000–44,000 g/mol, weight average molecular weights (Mw) of 66,000–159,000 g/mol, and intrinsic viscosities of 0.66–1.19 dL/g. The thermal stability of copolyarylates increased with the increase of BPAF monomer content (0~100%), which was manifested by the linear increase of glass transition temperature (Tg) from 201.6 to 237.1°C, and the increase of 5% thermogravimetric weight loss temperature (T5%) from 474.1 to 491.5°C. The tensile strength of copolyarylates ranged from 52.63 to 59.93 MPa, the tensile modulus ranged from 1102.08 to 1502.84 MPa, and the elongation at break ranged from 32.0 to 75.5%. In addition, the copolyarylates had good dielectric properties with a dielectric constant of 2.58–3.75 at 107 Hz and a dielectric loss tangent of 0.021–0.028.

Effects of the Introduction of Tertiary Amino Linkages on the Properties of Phenothiazine Derivatives as Delayed Emission Fluorophores

AbstractTwo phenothiazine‐based electroactive compounds were synthesized by Buchwald‐Hartwig cross‐coupling reaction. The compounds consist of pyridine‐ or benzonitrile accepting moiety and phenothiazine donor fragments linked through tertiary amino linkage. The resulting electroactive compounds showed high thermal stability with 10 % weight loss temperatures of 270 and 308 °C. Both the compounds showed reversible oxidation after repeated scans of cyclic voltammetry. Experimental results in combination with the outcomes of TD‐DFT calculations, were employed to examine the emission nature of the target compounds. By demonstrating the correct choice of acceptor moiety and linking topology, the synthesized compounds were found to be emitters exhibiting efficient RTP. With emission lifetime reaching 26.04 ms and spin‐orbit coupling value of the triplet states with the singlet ground state of 18.72 cm−1, the radiative recombination of the triplet state is ensured. Having lifetimes of 26 ms and strong sensitivity to oxygen, the benzonitrile‐containing phenothiazine derivative demonstrated fast oxygen response with the quenching constant of 4.97*10−4 ppm−1 at low oxygen concentrations that is comparable to the corresponding characteristics of reported RTP‐based sensors.

Effect of MWCNTs surface functionalization on the characterization of PVA/MWCNTs nanocomposites

The present study aims to put forward the role of surface functionalization of multi-walled carbon nanotubes (MWCNTs) on the enhancement thermal and hydrophilicity properties of new nanocomposite based poly(vinyl alcohol)/surface functionalized MWCNTs (PVA/MWCNTs), prepared by a facile phase inversion process. In this study, the fabrication of PVA/MWCNTs nanocomposites is carried out using functionalized MWCNTs (f-MWCNTs) with different functional groups (–OH, –COOH, –NH2). The structural, morphological, thermal, hydrophilicity and physico-chemical properties of PVA/MWCNTs nanocomposites are characterized by XRD, FE-SEM, FT-IR, TGA and contact angle measurement. The FT-IR results confirm the formation of a hydrogen bond between MWCNTs and PVA chain. XRD analysis indicates an improvement in the crystallinity of the PVA/MWCNTs nanocomposite. TGA results reveal that the PVA/f-MWCNTs nanocomposites show higher thermal stability than pure PVA. It is revealed that PVA/MWCNTs nanocomposites based functionalized MWCNTs remarkably increase the degradation temperature, and thus enhancing the thermal properties. The highest weight loss (30.7 wt%) and degradation temperature (520 °C) values are obtained with PVA/f-MWCNTs(0.5 wt%). The contact angle measurement confirms that the hydrophobic properties of pure PVA became hydrophilic because of the functional groups of MWCNTs. The hydrophilicity of PVA/MWCNTs nanocomposites is increased with the increase in wt% of MWCNTs embedded in the nanocomposite.

Effect of outdoor ageing on pyrolytic characteristics and kinetics of different organic components in waste photovoltaic panels

Pyrolysis is a potential approach for volume reduction and utilization of organic components in waste photovoltaic panels. During a usage period of 20–25 years, the physical and chemical properties of photovoltaic panels might undergo ageing and deterioration, thereby affecting their thermal decomposition characteristics. The characteristics of samples before and after ageing were studied using Fourier transform infrared spectroscopy, scanning electron microscopy, elemental analyzer, and thermogravimetry-Fourier transform infrared spectroscopy-mass spectrometry. There were certain differences in the weight loss temperature, time, residual mass, and activation energy of the samples in the pyrolysis reaction. After ageing, the production of acetic acid and methane in ethylene vinyl acetate pyrolysis products increased, while the production of CO2 decreased. After ageing, Tedlar-Polyethylene Terephalate-Tedlar mainly produced water, carbon dioxide, and fluorocarbon compounds, and the percentage of harmful fluorocarbon compounds in the human body increased. Cyclosiloxane, CO2, and hydrocarbons containing C-H bond were detected in each weight-loss stage of aged silica gel. As the heating rate changed, the amount of pyrolysis products also changed. Controlling the sample's heating rate would help to lessen the quantity of hazardous pollutants that were produced. The influence of ageing on the weight loss of mixed samples was discussed. This study seeks to give a fundamental understanding of the physicochemical properties, pyrolysis behaviour, and volatiles of samples before and after ageing, thus providing helpful insights for the final disposal or recovery of waste photovoltaic panels through pyrolysis.

Fully Aromatic Thermotropic Copolyesters Based on Vanillic, Hydroxybenzoic, and Hydroxybiphenylcarboxylic Acids.

Several series of new polymers were synthesized in this study: binary copolyesters of vanillic (VA) and 4'-hydroxybiphenyl-4-carboxylic (HBCA) acids, as well as ternary copolyesters additionally containing 4-hydroxybenzoic acid (HBA) and obtained via three different ways (in solution, in melt, and in solid state). The high values of logarithmic intrinsic viscosities and the insolubility of several samples proved their high molecular weights. It was found that the use of vanillic acid leads to the production of copolyesters with a relatively high glass transition temperature (~130 °C). Thermogravimetric analysis revealed that the onset of weight loss temperatures of ternary copolyesters occurred at 330-350 °C, and the temperature of 5% mass loss was in the range of 390-410 °C. Two-stage thermal destruction was observed for all aromatic copolyesters of vanillic acid: decomposition began with VA units at 420-480 °C, and then the decomposition of more heat-resistant units took place above 520 °C. The copolyesters were thermotropic and exhibited a typical nematic type of liquid crystalline order. The mechanical characteristics of the copolyesters were similar to those of semi-aromatic copolyesters, but they were much lower than the typical values for fully aromatic thermotropic polymers. Thus, vanillic acid is a mesogenic monomer suitable for the synthesis of thermotropic fully aromatic and semi-aromatic copolyesters, but the processing temperature must not exceed 280 °C.

Polybenzoxazines containing borosiloxane structures as high-temperature resistance (T g > 300 °C) and environment-friendly flame-retardant materials

A series of borosiloxane structures-containing polybenzoxazines (PBZs) with intrinsic environment-friendly flame-retardant properties and high-temperature resistance are investigated in this study. Initially, borosiloxane structures-containing benzoxazine macromonomers (BZ-BSiO-X) were synthesized through a condensation reaction between silicon ethoxy groups-containing benzoxazine monomers (P-mdes), boric acid (BA) and diphenyldimethoxysilane (DPDMS) with varying feed ratios. Subsequently, the benzoxazine groups in BZ-BSiO-X underwent ring-opening polymerization at elevated temperatures to produce poly(BZ-BSiO-X). The properties of poly(BZ-BSiO-X) were evaluated using Dynamic Mechanical Analysis, Thermogravimetric Analysis and an Oxygen Index instrument. The results show that the heat resistance of poly(BZ-BSiO-X) is enhanced by the cross-linking structures formed by the P-mdes segment and B-N coordination interaction, leading to their glass transition temperatures (T g, tan δ) exceeding 300 °C. The thermal stability and flame-retardant properties of poly(BZ-BSiO-X) are reinforced via the borosiloxane structures formed through DPDMS and BA, resulting in a 5% weight loss temperatures (T d5) around 400 °C and limiting oxygen index (LOI) values above 30. These polymers, containing environment-friendly flame-retardant boron (B) and silicon (Si) elements, exhibit potential as alternatives to halogen- or phosphorus-containing flame-retardant materials and are expected to be used in various fields as environment-friendly flame-retardant materials.

Improvement of heat resistance in silicone rubber by Fe-doped TiO2 nanoparticles prepared via flame spray pyrolysis

In recent years, the development of heat-resistant silicone rubber has been a research hotspot. In this paper, a kind of Fe doped TiO2 nanoparticles (Fe-TiO2) was prepared via flame spray pyrolysis, which can significantly improve the high temperature resistance of silicone rubber. The results show that, on the one hand, the prepared Fe-TiO2 can inhibit the breakage of Si-O main chain; on the other hand, because Fe is doped into the lattice of TiO2, it causes the change of TiO2 crystal phase and produces more oxygen vacancies, which is more beneficial to capture free radicals in silicone rubber matrix, so that Fe-TiO2 can effectively inhibit the excessive cross-linking of silicone chain caused by methyl oxidation on the side of silicone rubber. TGA results showed that after adding Fe-TiO2, the 5 % thermal weight loss temperature of methyl vinyl silicone rubber increased from 392.8 °C to 435.6 °C.

Structure-property relationships in dicyanopyrazinoquinoxalines and their hydrogen-bonding-capable dihydropyrazinoquinoxalinedione derivatives.

Presented here is the design, synthesis, and study of a variety of novel hydrogen-bonding-capable π-conjugated N-heteroacenes, 1,4-dihydropyrazino[2,3-b]quinoxaline-2,3-diones (DPQDs). The DPQDs were accessed from the corresponding weakly hydrogen-bonding dicyanopyrazinoquinoxaline (DCPQ) suspensions with excess potassium hydroxide, resulting in moderate to good yields. Both families of compounds were analyzed by UV-vis and NMR spectroscopy, where the consequences of hydrogen bonding capability could be assessed through the structure-property studies. Conversion of the DCPQs into hydrogen-bonding capable DPQDs results in modulation of frontier MO energies, higher molar extinction coefficients, enhanced crystallinity, and on-average higher thermal stability (where in some cases the 5% weight loss temperature is increased by up to 100 °C). Single crystal X-ray diffraction data could be obtained for three DPQDs. One reveals pairwise hydrogen bonding in the solid state as well as a herringbone packing arrangement rendering it a promising candidate for additional studies in the context of organic optoelectronic devices.

Fine extraction of cellulose from corn straw and the application for eco-friendly packaging films enhanced with polyvinyl alcohol

Biomass materials substituting for petroleum-based polymers occupy an important position in achieving sustainable development. Cellulose, a typical biomass material, stands out as the primary choice for producing eco-friendly packaging materials. However, it is still a challenge to efficiently utilize cellulose from waste biomass materials in practice. Herein, cellulose-based films were prepared by pretreating waste corn straw, separating straw husk, straw pith and straw leaf, and extracting cellulose through alkali and sodium chlorite treatment to improve its mechanical properties using the cross-linked polyvinyl alcohol (PVA) method in this work. The prepared composite films were characterized by Fourier transform infrared spectrometer (FTIR), X-ray diffraction instrument (XRD), Scanning electron microscopy (SEM), Thermogravimetric (TG) and mechanical properties. The results indicated that corn straw husk exhibited the highest cellulose content of 31.67 wt%, and obtained husk cellulose had the highest crystallinity of 52.5 %. Compared to corn straw, the crystallinity of husk cellulose, pith cellulose and leaf cellulose increased by 19.5 %, 16.4 % and 44.1 %, respectively. Husk cellulose/PVA composite films were the most thermally stable, with a maximum weight loss temperature of 346.8 °C. In addition, the husk cellulose/PVA composite film had the best tensile strength of 37 MPa. Meanwhile, the composite films had good UV shielding, low water vapor transmission rate and biodegradability. Therefore, this work provides a fine utilization route of waste corn straw, and as-prepared cellulose based films have potential application in eco-friendly packaging materials.

Synthesis and Oxidative Degradation of Leucine-Based Poly(diacylhydrazine).

Diacylhydrazine is thermally and chemically stable, and it remains inert to oxygen even at high temperatures. However, it is rapidly oxidized by sodium hypochlorite, leading to its decomposition into carboxylic acid and nitrogen gas. In the synthesis of a novel poly(diacylhydrazine) as an oxidatively degradable polymer, L-leucine methyl ester is acylated by terephthaloyl chloride. Subsequent hydrazination yields a bishydrazide monomer. The oxidative coupling polymerization of this monomer produces poly(diacylhydrazine). The molecular structures of the products are confirmed by an 1H NMR analysis. A polymodal molecular weight distribution and a large polydispersity index are observed by GPC in all cases. A 10% weight loss temperature is noted at 286 °C in air by TGA. The obtained polymer is not oxidized by oxygen. No glass transition is observed below the decomposition temperature. Upon the treatment of the poly(diacylhydrazine) with sodium hypochlorite solution, decomposition occurs rapidly, resulting in monomeric carboxylic acid and nitrogen gas. The L-leucine-based poly(diacylhydrazine) serves as a novel on-demand degradable polymer with high levels of thermal and chemical stability during usage.

Preparation and characterization of stannous phosphate glass – polytetrafluoroethylene composites

Abstract A low-T g SnO–MgO–P2O5 (SMP) glass was mixed with polytetrafluoroethylene (PTFE) to form composites by a sintering route. Effects of SMP:PTFE ratio and sintering temperature (350 °C–430 °C) on the microstructure and the bonding ability to a low thermal-expansion glass substrate were investigated. The onset softening temperatures of SMP and PTFE are close (328 °C and 313 °C), which are much lower than the onset temperature of weight loss of PTFE (381 °C). This is important for the sintering of SMP–PTFE composites. After sintering, pure SMP glass was not able to bond to the low thermal-expansion 1737® glass substrates. However, SMP–PTFE composites were able to bond to 1737® after sintering at appropriate temperatures. A possible mechanism for the enhancement of bonding by adding PTFE is discussed.

Synthesis of transparent polymer hybrids consisting of gelatin, as a natural polymer, and zinc oxide

Abstract Gelatin and zinc oxide (ZnO) polymer hybrids were prepared via the sol–gel reaction of zinc acetate dihydrate in the presence of gelatin. When the gelatin/ZnO ratio was 9/1, a transparent polymer hybrid was obtained. This hybrid contained no phase separations consisting of organic and inorganic phases. Microscopic or submicroscopic aggregations and separations between gelatin and ZnO were clearly observed in the sample with a high inorganic content. The results of thermal analysis showed that the yield of ceramic decreased as ZnO content increased, and a 10% weight loss temperature increased as gelatin content increased. FT-IR measurements suggested the formation of intermolecular interactions, thought to be hydrogen bonds, between gelatin and ZnO. Furthermore, the results of XRD measurements revealed that the hybrid with a ZnO content of 10% is amorphous.

Synthesis and characterization of high Tg and colorless polyamide-imide films derived from amide-containing diamines with different trifluoromethyl substitution

Four new diamines (3TFDABA, 2TFDABA, 22TFDABA and TFAPTA) were successfully synthesized to investigate the effect of different trifluoromethyl (CF3) substitution position on poly(amide-imide)s (PAIs) properties. High-performance PAIs were prepared from high-temperature polycondensation of these diamines with 6FDA dianhydride. All the PAI films exhibited good heat resistance with glass-transition temperatures (Tgs) of 311–392 °C, good 5% weight loss temperatures (Td5%s) of 480–510 °C in nitrogen, and excellent optical transparency with T450 ranging from 52% to 84%. According to the monomer structural design, a high heat resistant and colorless poly(amide-imide) film (PAI-2-6FDA), with excellent optical properties (T450 of 82%), outstanding thermal properties (Td5% of 499 °C and Tg of 392 °C), and good mechanical properties (tensile strength of 123 MPa, tensile modulus of 4.4 GPa) was achieved. A comprehensive structure-to-property relationship study revealed that the CF3 in ortho-position of the amino group effectively inhibited the rotation between imide ring and benzene, thus improved the heat resistance of the film. Moreover, it could also weaken the generation of charge transfer complexes through strong electron-withdrawing ability, which is beneficial for the synthesis of colorless polyimides.