Fluorinated high-performance polymers: Poly(arylene ether)s and aromatic polyimides containing trifluoromethyl groups

Investigation of the degradation of pitch-based carbon fibers properties upon insufficient or excess thermal treatment

To overcome the disadvantages of discontinuous conventional batch extruders, a continuous screw extruder is introduced to manufacture pitch-based carbon fibers. For a carbon fiber preparation process, an oxidation time of 8 h was determined to be optimal for obtaining desirable mechanical properties of the fibers acquiring employing the screw extruder. It is hypothesized that the differences in the properties of the carbon fibers fabricated utilizing the batch and screw extruders originate from the melt spinning time; therefore, a combined equation for the total amount of heat treatment from the pitch precursor through the oxidation process is established in this study. The crystallinity of the carbon fibers is confirmed to correspond to the differences in mechanical properties as the oxidation time increases. The poor mechanical properties of the carbon fibers that are insufficiently oxidized are a result of irregular oxidation from the sheath to the core of the fiber cross section. However, the over-oxidized carbon fibers also show poor mechanical properties than the optimal fibers. This result further affirms that excessive oxidation times cause unstable chemical bonding, which interrupts the formation of stable crystal structures after carbonization.

Synthesis and characterization of novel fluorinated pyridine-based polyimides derived from 4-(4-trifluoromethylphenyl)-2,6-bis(4-aminophenyl)pyridine and dianhydrides

A series of new fluorinated pyridine-based polyimides (PIs) was synthesized by polycondensation of 4-(4-trifluoromethylphenyl)-2,6-bis(4-aminophenyl)pyridine with various aromatic dianhydrides in N, N-dimethylacetamide (DMAc) via the conventional two-step method. The inherent viscosities of the resulting poly(amic acid)s and PIs were 0.54–0.94 and 0.58–0.88 dLg−1, respectively. The obtained PIs were predominantly amorphous and soluble in polar solvents such as N-methyl-2-pyrrolidone, N, N-dimethylformamide, and DMAc at room temperature or upon heating at 70°C. They also displayed good thermal stability with the glass transition temperature of 324–416°C, the temperature at 5% weight loss of 546–584°C, and the residue of 58–69% at 750°C under nitrogen, as well as outstanding mechanical properties with tensile strengths of 69132 MPa, tensile moduli of 1.1–2.0 GPa, and elongations at break of 7–27%. Meanwhile, these PI films had dielectric constants of 2.95–3.22 (1 MHz), low water uptake 0.44–0.71%, and high optical transparency with the ultraviolet cutoff wavelength in the 388–406 nm range and the wavelength of 80% transparency in the range of 550–680 nm.

The influence of organosoluble (co)polyimides side functionalization and drawing parameters on the optical fibre coatings formation and properties

A series of the copolyimides have been synthesized by one-step high-temperature method in m-cresol solution to explore their effect on the optical fibre coatings formation and properties. The following parameters that influence the coating quality and properties have been estimated: the viscosity of the polymer solution, drawing technological parameters, polyimide (PI) structure and molecular weight. It was found that copolyimides bearing side hydroxyl and carboxyl groups formulate the coatings with good adhesion without additional coupling agent. The fibres with elaborated PI coatings have high thermal stability. For some of them, 20% reduction of the fibre’s bending strength takes place only after heating for 24–72 h at 300°C.

A strategy for preparing spirobichroman dianhydride from bisphenol A and its resulting polyimide with low dielectric characteristic

The high performance polyimide, SBC-DDM, exhibits a large free volume, leading to outstanding organo-solubility and a low dielectric constant.

Hybrid formation of graphene oxide–POSS and their effect on the dielectric properties of poly(aryl ether ketone) composites

Covalent functionalization of graphene oxide with aminopropylisobutyl polyhedral oligomeric silsesquioxane efficiently reduced the dielectric constant of the polymer matrix.

Preparation and properties of a novel graphene fluoroxide/polyimide nanocomposite film with a low dielectric constant

A novel graphene fluoroxide/polyimide nanocomposite film with a low dielectric constant is prepared with excellent mechanical and thermal properties.

High performance polyimides with good solubility and optical transparency formed by the introduction of alkyl and naphthalene groups into diamine monomers

Highly soluble and optically transparent polyimides with excellent thermal stability were prepared by the introduction of alkyl and naphthalene groups into a single diamine monomer under microwave-assisted polymerization.

A spiro-centered thermopolymerizable fluorinated macromonomer: synthesis and conversion to the high performance polymer

A new spiro-centered thermopolymerizable fluorinated macromonomer is reported here.

Multi-shape memory effect of polyimides with extremely high strain

Polyimides exhibited high strain and multi-shape memory properties with the synergistic effects of physical and chemical crosslinks.

Synthesis and properties of fluorinated polyimides with multi-bulky pendant groups

A new family of fluorinated polyimides with four pendant trifluoromethylphenyl groups was prepared. The incorporation of multi-bulky pendant fluorinated groups and large noncoplanar structures brought about great improvement for their properties.

Optically transparent and organosoluble poly(ether imide)s based on a bis(ether anhydride) with bulky 3,3′,5,5′-tetramethylbiphenyl moiety and various fluorinated bis(ether amine)s

Novel optically transparent and organosoluble poly(ether imide)s (PEIs) were prepared from 4,4′-bis(3,4-dicarboxyphenoxy)-3,3′,5,5′-tetramethylbiphenyl dianhydride and various fluorinated bis(ether amine)s via chemical or thermal imidization. The effects of fluorinated groups and the imidization method on the properties of PEIs were investigated. Fluorinated PEIs prepared by the chemical imidization method exhibited essentially colorless characteristic with cutoff wavelengths lower than 380 nm, and yellowness index (b* values) ranging from 5.2 to 7.3, which are close to that of transparent polyarylate polymer (b* = 3.3). In addition, all fluorinated PEIs showed excellent solubility in common organic solvents. The thermal decomposition temperature at 10% weight loss is higher than 490°C, and the glass transition temperatures are in the range of 245–315°C. The fluorinated PEI series also exhibited low dielectric constants of 2.95–3.29 (1 MHz) and low moisture absorption in the range of 0.17–0.86 wt%, which are lower than the analogous nonfluorinated series.

Electrochromic and electrofluorochromic polyimides with fluorene-based triphenylamine

A series of novel polyimides (PIs) based on N,N-di(4-aminophenyl)-2-amino-9,9-dimethylfluorene and various dianhydrides were synthesized. These PIs were amorphous and readily soluble in many solvents. They displayed outstanding thermal stability and high glass transition temperatures (269–374°C). The polymer films showed reversible electrochemical redox and satisfactory electrochromic performance with long-term stability, high coloration efficiency, and acceptable switching times. The PI derived from 1,2,4,5-cyclohexanetetracarboxylic dianhydride exhibited maximum fluorescence at 400 nm with quantum yields up to 28.1%. Furthermore, the fluorescence can be effectively electroswitched between “on” and “off” states, exhibiting a high contrast ratio of 75.

Insights into the Mechanism and Kinetics of Thermo-Oxidative Degradation of HFPE High Performance Polymer

The growing requisite for materials having high thermo-oxidative stability makes the design and development of high performance materials an active area of research. Fluorination of the polymer backbone is a widely applied strategy to improve various properties of the polymer, most importantly the thermo-oxidative stability. Many of these fluorinated polymers are known to have thermo-oxidative stability up to 700 K. However, for space and aerospace applications, it is important to improve its thermo-oxidative stability beyond 700 K. Molecular-level details of the thermo-oxidative degradation of such polymers can provide vital information to improve the polymer. In this spirit, we have applied quantum mechanical and microkinetic analysis to scrutinize the mechanism and kinetics of the thermo-oxidative degradation of a fluorinated polymer with phenylethenyl end-cap, HFPE. This study gives an insight into the thermo-oxidative degradation of HFPE and explains most of the experimental observations on the thermo-oxidative degradation of this polymer. Thermolysis of C-CF3 bond in the dianhydride component (6FDA) of HFPE is found to be the rate-determining step of the degradation. Reaction pathways that are responsible for the experimentally observed weight loss of the polymer is also scrutinized. On the basis of these results, we propose a modification of HFPE polymer to improve its thermo-oxidative stability.

Photomediated Controlled Radical Polymerization and Block Copolymerization of Vinylidene Fluoride

This review summarizes recent research on novel photochemical methods for the initiation and control of the polymerization of main chain fluorinated monomers as exemplified by vinylidene fluoride (VDF) and for the synthesis of their block copolymers. Such reactions can be carried out at ambient temperature in glass tubes using visible light. Novel, original protocols include the use of hypervalent iodide carboxylates alone or in conjunction with molecular iodine, as well as the use of photoactive transition metal carbonyls in the presence of alkyl, fluoroalkyl, and perfluoroalkyl halides. An in-depth study of the reaction parameters highlights the use of dimethyl carbonate as a preferred polymerization solvent and outlines the structure-property relationship for hypervalent iodide carboxylates and halide initiators in both the free radical and iodine degenerative transfer controlled radical polymerization (IDT-CRP) of VDF. Finally, the rational selection of metal carbonyls that are successful not only as IDT mediators but, more importantly, in the quantitative activation of both PVDF-CH2-CF2-I and PVDF-CF2-CH2-I chain ends toward the synthesis of well-defined PVDF block copolymers is presented.

Poly(2-cycloalkyl-2-oxazoline)s: high melting temperature polymers solely based on Debye and Keesom van der Waals interactions

The synthesis of new 2-cycloalkyl-2-oxazoline monomers, namely 2-cyclobutyl (cBuOx), 2-cyclopentyl (cPentOx) and 2-cyclohexyl-2-oxazoline (cHexOx) is described. Polymers thereof are semi-crystalline and reveal unexpectedly high melting transitions.

Synthesis of trifluoromethylated isoxazoles and their elaboration through inter- and intra-molecular C–H arylation

We report conditions for the preparation of a range of trifluoromethylated isoxazole building blocks through the cycloaddition reaction of trifluoromethyl nitrile oxide and their subsequent derivatisation.

Synthesis and characterization of blue light emitting redox-active polyimides bearing a noncoplanar fused carbazole–triphenylamine unit

Photoactive organosoluble polyimides containing a fused triphenylamine–carbazole group were synthesized. These polyimides demonstrated significant potential for optoelectronic devices.

Design and preparation of silica tube/poly(aryl ether ketone) composites with low dielectric constant

Low dielectric constant porous composites in which uniform nanosized silica tubes are covalently bonding onto fluoropoly(aryl ether ketone) are prepared.