Synthesis and characterization of novel fluorinated polyimides derived from 4,4?-[2,2,2-trifluoro-1-(3-trifluoromethylphenyl)ethylidene]diphthalic anhydride and aromatic diamines

Research progress of low dielectric constant polymer materials

The advent of high frequency communication era presents new challenges for further development of dielectric polymer materials. In the field of communication, efficient signal transmission is critical. The lower the dielectric constant of the dielectric material used, the lower the signal delay and the higher the signal fidelity. The preparation of polymer materials with low dielectric constant or reduce the dielectric constant of polymer materials becomes a key research topic. Summarizing past progress and providing perspective, this paper primarily discusses the intrinsic low dielectric polymers, fluorine doped low dielectric polymers, and microporous low dielectric polymers, while predicting the research trend of low dielectric materials.

Sustainable radical approaches for cross electrophile coupling to synthesize trifluoromethyl- and allyl-substituted tert-alcohols

Trifluoromethylated molecules have gained privileged recognition among the medicinal and pharmaceutical chemists. Sustainable photoredox- and electrochemical processes were employed to facilitate the relatively less explored radical cross-electrophile coupling to access trifluoromethyl- and allyl-substituted tert-alcohols. Reactions proceed through trifluoromethyl ketyl radical and allyl radical intermediates, which undergo challenging radical-radical cross-coupling. The developed transformations are mild and chemo-selective to give cross-coupled products and deliver a wide range of valuable trifluoromethyl- and allyl-containing tertiary alcohols. Both processes can also be applied for the synthesis of amine variant containing trifluoromethyl and allyl moiety, which is considered as amide bioisostere.

Synthesis and characterization of new polyimides from diphenylpyrene dianhydride and ortho methyl substituted diamines

Three new polyimides were synthesized via one-step polycondensation from 3,8-diphenylpyrene-1,2,6,7-tetracarboxylic dianhydride (DPPD) with two diamines with ortho methyl substitution (MBDAM and HFI) and one diamine without ortho substituents (BAPHF). The effect of diamine structure in DPPD based polyimides' physical, thermal, mechanical and gas transport properties has been studied. The polyimide structure was confirmed by FTIR and ¹H NMR. All polymers show high thermal stability with decomposition temperatures above 493 °C, and glass transition temperatures above 336 °C. Changes in packing density of polyimide membranes were assessed by wide angle X-ray diffraction and correlated to fractional free volume FFV. Polyimides based on rigid DPPD dianhydride exhibited an improved gas permeability and selectivity when ortho methyl substituents are present in the diamine used for polyimide synthesis. DPPD-MBDAM polyimide showed the best gas productivity values with 565 barrer CO₂ permeability and a selectivity of 16 for CO₂/CH₄.

Three new polyimides were synthesized from 3,8-diphenylpyrene-1,2,6,7-tetracarboxylic dianhydride (DPPD) with two diamines with ortho methyl substitution (MBDAM and HFI) and one diamine without ortho substituents (BAPHF).

Synthesis and Properties of Novel Meltable Fluorinated Aromatic Oligoimides Endcapped with 4-Phenylethynylphthalic Anhydride

A series of phenylethynyl-endcapped fluorinated aromatic oligoimides with calculated molecular weights of 1250—10000 were prepared by thermal polycondensation of an aromatic dianhydride, 4,4'oxydiphthalic anhydride (ODPA), with aromatic diamine mixtures of 1,4-bis(4-amino-2-trifluoromethylphenoxy)-benzene (1,4,4-6FAPB) and 3,4'-oxydianiline (3,4'-ODA) in the presence of 4-phenylethynylphthalic anhydride (PEPA) as reactive endcapping agent. Effects of chemical compositions and molecular weights of the aromatic oligoimides on their meltability as well as the thermal and mechanical properties of the thermal-cured polyimide resins were systematically investigated. The phenylethynyl-endcapped fluorinated aromatic oligoimides could be completely melted in the temperature range of 250—350 °C to give low viscosity fluids. The melt viscosity of the oligoimide increased with increasing molecular weight. After thermally curing at 371 °C, the thermoset polyimide resins produced showed good combination of thermal and mechanical properties. For example, the glass transition temperature ( Tg) as high as 300 °C by differential scanning calorimetry, flexural strengths of > 135.5 MPa, flexural moduli of > 3.1 GPa, tensile strength of > 65.7 MPa and elongation at break of > 3.9% were obtained.

Synthesis and Characterization of Organosoluble Polysiloxaneimides Derived from Siloxane-containing Aliphatic Dianhydride and Various Aromatic Diamines

A new siloxane-containing monomer, 5,51- exo-(1,1,3,3,5,5-hexamethyl-trisiloxane -1,5-diyl) bisbicyclo[2,2,1]heptene-2,3- endo-dicarboxylic anhydride (3) was synthesized by the hydrosilylation reaction of 1,1,3,3,5,5-hexamethyl-trisiloxane (1) and cis-5-norbornene- endo-2,3-dicarboxylic anhydride (2). A series of organosoluble polysiloxaneimides (PI 5a-e) was prepared from the dianhydride 3 and several aromatic diamines 4 by a one-step high-temperature polycondensation method and the structures were characterized by IR and NMR. The effects of the main chain siloxane groups on the properties of PIs were evaluated by solubility, thermal stability and dielectric properties in addition to optical and water adsorption. The PIs were readily soluble in polar aprotic solvents such as NMP, DMAc and CHCl 3 at room temperature, except PI 5a, which was only soluble in polar amide type solvents at elevated temperature. PIs 5a-e had glass transition temperatures between 138 and 251°C in N2 and the 5% weight loss temperature ranged from 460 to 470°C under air. The PIs could be cast into flexible and tough films from DMAc solution. The films had tensile strengths of 44—52 MPa, tensile moduli of 0.56—0.68 GPa and elongations at break from 5.8—7.9%. The PI films exhibited good optical UV-vis transparency with wavelength cutoff of 269—289 nm and transmittances over 90% at 400 nm, and dielectric constants of about 2.76—2.65 with low water adsorption (0.3—0.4%).

Synthesis and Characterization of Soluble Polyimides Derived from the Polycondensation of 2,6-bis(4-amino-2-trifluoromethylphenoxy-4'-benzoyl)pyridine with Some Aromatic Dianhydrides

A new aromatic diamine monomer containing both pyridine and fluorine, 2,6-bis(4-amino-2-trifluoromethylphenoxy-4 '-benzoyl)pyridine (BAFP), was successively synthesized by the nucleophilic substitution reaction of 2,6-bis(4,4'-dihydroxybenzoyl)pyridine with 2-chloro-5-nitro-trifluoromethylbenzene in the presence of k2CO 3 in N, N-dimethylacetamide, and followed by reduction with SnCl2 and HCl in ethanol. The polycondensation of BAFP with four aromatic dianhydrides afforded a series of novel aromatic polyimides containing both pyridine and fluorine. The reaction was conducted by the one-step thermal imidization method. The resulting polyimides were characterized for inherent viscosity, solubility, and thermo-oxidative stability. The polyimides exhibited excellent solubility in various solvents such as N-methyl-2-pyrrolidone (NMP), N, N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO) and chloroform. The glass-transition temperatures ( Tg) were in the range of 206—227°C. The polyimides displayed good thermal stability, e.g. the temperatures at the 5% weight loss range were at 487—543°C in nitrogen and 463—521°C in air, respectively. Wide-angle X-ray diffraction measurements revealed that the polyimides were predominantly amorphous.