Synthesis and properties of novel fluorinated epoxy resins

Bio-based Low-k Polymers at High Frequency Derived from Anethole: Synthesis and the Relationship between the Structures and the Properties

Bio-based polymers have been widely investigated as sustainable low dielectric (low-k) materials in past decades. Nevertheless, a few of the polymers with excellent comprehensive properties have been achieved to satisfy the requirements of high-frequency communication application. In this paper, two fluorinated monomers (BCB-F and 2BCB-F) have been designed and successfully prepared from biomass anethole. The thermal-cross-linkable benzocyclobutene and polyfluorobenzene groups were introduced in order to obtain low-k polymers with good comprehensive properties. A control monomer C1 was prepared from the estragole, the isomer of anethole, to study intensively the effect of structures on properties. Among the thermally cured polymers, cured BCB-F with higher fluoride content shows a comparable dielectric constant (Dk) of 2.62 and lower dielectric loss (Df) of 1.31 × 10-3 at a frequency of 10 GHz, as well as better hydrophobic properties with a water uptake of 0.18%. Such good hydrophobic properties enable it to maintain the good dielectric properties even after being soaked in boiling water for 96 h. Cured 2BCB-F with bifunctional benzocyclobutene groups displays excellent heat resistance with a high glass transition temperature (Tg) of 408 °C and a low coefficient of thermal expansion (CTE) of 52 ppm/°C in the temperature range 30-300 °C. Cured 2BCB-F also shows good dielectric properties with a Dk of 2.61 and a Df of 2.60 × 10-3 at a frequency of 10 GHz. The good comprehensive properties reveal that the anethole-based polymers are suitable candidates as matrix or encapsulation resins for application in electronics and microelectric fields.

Comparison of the Properties of Epoxy Resins Containing Various Trifluoromethyl Groups with Low Dielectric Constant

A series of epoxy resins containing various trifluoromethyl groups were synthesized and thermally cured with diaminodiphenylmethane (DDM) and aminophenyl sulfone (DDS). All epoxy resins exhibited excellent thermal stability with the glass transition temperatures of above 128 °C and 5% weight loss temperatures of above 300 °C. DDS-cured epoxy resins possessed higher thermal stability than that of DDM-cured epoxy resins, while DDM-cured epoxy resins showed better mechanical, dielectric, and hydrophobic properties. Additionally, DDM-cured epoxy resins with different locations and numbers of trifluoromethyl groups showed flexural strength in the range of 95.55~152.36 MPa, flexural modulus in the range of 1.71~2.65 GPa, dielectric constant in the range of 2.55~3.05, and water absorption in the range of 0.49~0.95%. These results indicate that the incorporation of trifluoromethyl pendant groups into epoxy resins can be a valid strategy to improve the dielectric and hydrophobic performance.

Nature of halogen-centered intermolecular interactions in crystal growth and design: Fluorine-centered interactions in dimers in crystalline hexafluoropropylene as a prototype

The wide occurrence of halogen-centered noncovalent interactions in crystal growth and design prompted this study, which includes a mini review of recent advances in the field. Particular emphasis is placed on providing compelling theoretical evidence of the formation of these interactions between sites of positive electrostatic potential, as well as between sites of negative electrostatic potential, localized on the electrostatic surfaces of the bound fluorine atoms in a prototypical system, hexafluoropropylene (C₃ F₆ ), upon its interaction with another same molecule to form (C₃ F₆ )₂ dimers. The existence of σ- and π-hole interactions is shown for the stable dimers. Even so, weakly bound interactions locally responsible in holding the molecular fragments together cannot and should not be overlooked since they are partly responsible for determining the overall geometry of the crystal. The results of combined quantum theory of atoms in molecules, molecular electrostatic surface potential, and reduced density gradient noncovalent interaction analyses showed that these latter interactions do indeed play a role in the stability and growth of crystalline C₃ F₆ itself and the (C₃ F₆ )₂ dimers. A symmetry adapted perturbation theory energy decomposition analysis leads to the conclusion that a great majority of the (C₃ F₆ )₂ dimers examined are the consequence of dispersion (and electrostatics), with nonnegligible contribution from polarization, which together competes with an exchange repulsion component to determine the equilibrium geometries. In a few structures of the (C₃ F₆ )₂ dimer, the fluorine is found to serve as a six-center five-bond donor/acceptor, as found for carbon in other systems (Malischewski and Seppelt, Angew. Chem. Int. Ed. 2017, 56, 368). © 2019 Wiley Periodicals, Inc.

Toughening of POSS-MPS composites with low dielectric constant prepared with structure controllable micro/mesoporous nanoparticles

In this work, we developed a modified calcination and extraction method to obtain controllable micro/mesoporous nanoparticle samples POSS–MPS, which were synthesized through glycidyl polyhedral oligomeric silsesquioxane (G-POSS) grafting with aminopropyl-functionalized mesoporous silica (AP-MPS). The POSS–MPS was introduced into the cyanate ester (CE) matrix to optimize the dielectric properties and enhance the toughness of the POSS–MPS/CE nanocomposite. The structure of the hybrid was characterized by FTIR and SEM. The dispersion properties, mechanical properties, dielectric properties and thermal performance were also studied. The results showed that both the C-POSS–MPS and E-POSS–MPS uniformly distribute in the CE matrix with the content of 0.5–4 wt%. The impact strength increased 52% and 60% separately with 2 wt% C-POSS–MPS and E-POSS–MPS addition respectively. The introduction of E-POSS–MPS particles can significantly decrease the dielectric loss value of the POSS–MPS/CE composites to 0.00498, which is of potential in wave transparent composites and structures.

A promising method to improve the performance of CE composites via combining advantages of POSS and MPS.

Advanced studies on synthesis and cure reaction of fluorinated epoxy resin

Fluorinated epoxy resins (FERs) were extensively studied for applications in electronic packaging, optical waveguides, and antifouling coatings. This research focuses on the synthesis and characterization of FER following a polycondensation reaction between fluorinated bisphenol and epichlorohydrin. Cure reaction was monitored using dispersive Raman spectroscopy and by calculation of the oxirane groups conversion. After one short postcuring stage, the decomposition temperatures of fluoroepoxy showed increased values with 28–35°C for the samples cured at 50°C. The resultant materials showed excellent fracture morphology, while the presence of fluorine was revealed by energy-dispersive X-ray and X-ray photoelectron spectroscopic techniques. Hydrophobic surface was evidenced through the surface energy resulted from contact angle measurements.

Toughening of cyanate resin with low dielectric constant by glycidyl polyhedral oligomeric silsesquioxane

In this article, a high-performance hybrid material was prepared by melt blending from glycidyl polyhedral oligomeric silsesquioxane (G-POSS) and bisphenol-A cyanate ester (CE), using triethylamine as the curing agent. The structure of the hybrid was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy (SEM), and the transparency properties, mechanical properties, dielectric properties, thermal performance, and wet fastness were studied. The results showed that G-POSS was uniformly distributed in the CE matrix and could obviously accelerate the curing reaction of the resin. Large amounts of corrugated and scaled structures were observed on the fractures of G-POSS/CE by the SEM photos. When the G-POSS content increased to 7 phr, the tensile strength (75.45 MPa), elongation at break (3.19%), and impact strength (23.76 kJ m−2) reached maximum values, representing increases of 21.75%, 27.6%, and 157.98% relative to that of pure CE, respectively, which indicated that the addition of G-POSS can significantly improve the toughness of G-POSS/CE composites. When the G-POSS content increased to 4 phr, the dielectric constant decreased from 3.27 to the minimum value of 3.05. The heat resistance and wet fastness of G-POSS/CE hybrid materials decreased with increasing G-POSS content.

Epoxy resin containing trifluoromethyl and pendant polyfluorinated phenyl groups: Synthesis and properties

A novel epoxy resin containing trifluoromethyl and pendant polyfluorinted phenyl groups, 1,1-bis[4-(2,3-epoxypropoxy)phenyl]-1-(3,4,5-trifluorophenyl) -2,2,2-trifluoroethane (6FEP) was synthesized and characterized. The reactivtiy of 6FEP with two aromatic diamines, 4,4′-diaminodiphenyl methane (DDM) and 1,4-bis(4-amino-2-trifluoromethylphenoxy) benzene (6FAPB), and the properties of the cured 6FEP were investigated and compared with those of the commonly used epoxy resin diglycidyl ether of bisphenol A (DGEBA). The experimental results indicated that 6FEP showed lower reactivity than DGEBA. The cured 6FEP exhibited good thermal stabilities with decomposition temperature at 5% weight loss of 374–397°C, high glass transition temperature of 159–177°C and good mechanical properties. The cured 6FEP epoxy resin also showed low dielectric constants at 1 MHz in the range of 3.2–3.4 and dielectric dissipation factors (tan δ) in the range of 2.10–2.48 × 10−3. Moreover, the cured 6FEP epoxy resins exhibited higher surface hydrophobicity and lower moisture absorption compared with DGEBA. The improved dielectric properties and hydrophobic properties of the cured 6FEP epoxy resin could be attributed to the introduction of trifluoromethyl and pendant polyfluorinated phenyl groups into the molecular structure of the epoxy resin.

Curing of DGEBA/ZnO nanocomposite with new fluorinated curing agents

In this study, two new fluorinated curing agents bearing imidazole-bisphenol and imidazole-diamine groups in their structures, namely: 4,4′-(2-(4-(trifluoromethyl)phenyl)-1H-imidazole-4,5-diyl)diphenol (TFIDO) and 4,4′-(4,4′-(2-(4-(trifluoromethyl)phenyl)-1H-imidazole-4,5-diyl)bis(4,1-phenylene)bis(oxy)bis (3-(trifluoromethyl)aniline) (TFIA) were synthesized, fully characterized and used to cure diglycidylether of bisphenol-A (DGEBA)-based epoxy resin and blend of DGEBA with nano ZnO (NZ) particles. Two mechanisms were anticipated to play roles in the curing reactions based on adducts formation and ionic complexes. The DGEBA/TFIDO system was more reactive than the DGEBA/TFIA system, whereas the thermal stability of DGEBA/TFIA was higher than that of DGEBA/TFIDO. These results can be explained by the increase in cross-linking density and more CF3 groups in TFIA. The results indicated that cured materials showed red shift in absorption and fluorescence emission spectra and significant improvements in the water repellency and thermal stability. The NZ particles as catalyst increased the rate of cure reaction by decreasing the activation energy ( Ea) and increasing the rate constant values.