Synthesis of quaternary copolymerized fluorine-containing polyimides with good thermal properties and low dielectric constant

Novel fluorine-containing polyimides were synthesized through copolymerization by using 2,3,3′,4′-biphenyltetracarboxylic dianhydride (α-BPDA) and 4,4′-(4,4′-isopropydenediphenox-y) bis-(phthalic anhydride) (BPADA) as dianhydrides and 4,4′-oxydianiline (ODA) and 2,2 - Bis [4-(4-aminophenoxy)phenyl]-hexafluoropropanane (HFBAPP) as diamines. Noncoplanar structure, flexible ether bond, and trifluoromethyl give the polyimide good thermoplastic, solubility, and heat resistance. The glass transition temperatures of polyimide films are 232.5°C∼262.2°C, the 5% weight loss temperatures are 521.5°C∼531.0°C, and the residual mass is more than 50% as heating to 800°C. With the increase of HFBAPP content in diamine, the dielectric constant of the material decreases from 3.21 to 2.78, and the dielectric loss decreases from 0.00962 to 0.00687 at 1 MHz, which greatly improves the dielectric properties of the material.

One-pot synthesis of dihydroquinolones by sequential reactions of o-aminobenzyl alcohol derivatives with Meldrum's acids

The functionalized 3,4-dihydroquinolin-2-one nucleus has been assembled in good to high yields through the sequential reaction of readily available N-Ts-o-aminobenzyl alcohols with 5-substituted Meldrum's acid derivatives under mild basic conditions. Highly diastereoselective synthesis of 3-substituted-4-phenyl-1-tosyl-3,4-dihydroquinolin-2(1H)-ones was accomplished from N-(2-(hydroxy(phenyl)methyl)phenyl)-4-methylbenzenesulfonamide under the same reaction conditions. Regarding the reaction mechanism, we hypothesized that the formation of dihydroquinolones proceeds through the in situ generation of aza-o-QMs followed by conjugate addition of enolate/cyclization/elimination of acetone and CO₂.

Free volume dependence of dielectric behaviour in sandwich-structured high dielectric performances of poly(vinylidene fluoride) composite films

A dielectric film with a trilayer structure is fabricated to obtain both a high dielectric constant and superior electrical breakdown strength simultaneously. The outer layers of the trilayered composite film are composed of barium titanate (BTO) particles dispersed in poly(vinylidene fluoride) (PVDF) to ensure a relatively high dielectric constant, while the central layer of the composite film consists of exfoliated hexagonal boron nitride nanosheets (BNNS) dispersed in PVDF to provide high electrical breakdown strength. Compared with pristine PVDF, the dielectric constant and breakdown strength are simultaneously enhanced due to the sandwich structure, and the dielectric loss is maintained at a low level. Most important of all, positron annihilation lifetime spectroscopy (PALS) is applied to study the atomic-scale free volume holes of PVDF composite films and the effect of free volume holes on the dielectric constant and breakdown strength. Results show that the size of free volume holes of PVDF increased with the addition of BTO, but it decreased firstly and then increased with the BNNS loading. The correlation between dielectric properties and the size of free volume holes of the PVDF matrix was discussed in each layer. It is illustrated that the experimental dielectric constant of the PVDF/BTO single-layered film is consistent with the theoretical value at a lower BTO loading but smaller than the theoretical value at a higher BTO loading, which is probably ascribed to the increased size of free volume holes. The breakdown strength of the PVDF/BNNS film increased with the introduction of BNNS and the reduced size of free volume holes, which is ascribed to the reduced partial discharge phenomenon. The atomic-scale microstructure analysis based on free volume holes provides valuable ideas and new understanding for the study of the mechanism of the dielectric behaviour of polymer composites.

Self-polymerization of Meldrum's acid-amine compounds: an effective route to polyamides

Meldrum's acid-amine compounds are effective monomers for the synthesis of linear and hyperbranched polyamides in a short reaction time under mild reaction conditions.

Self-crosslinkable polymers from furan-functionalized Meldrum's acid and maleimides as effective precursors of free-standing and flexible crosslinked polymer films showing low dielectric constants

The integration of Michael addition and Diels–Alder reaction in the synthesis of reactive polymers for self-standing and flexible crosslinked polymer films.

Polymerization of Meldrum's Acid and Diisocyanate: An Effective Approach for Preparation of Reactive Polyamides and Polyurethanes

Meldrum's acid (MA) is utilized as a monomer to polymerize with diisocyanates to result in polyamides, containing MA moieties at polymer chains. This reaction is also employed to prepare isocyanate-terminated polyamide segments which are utilized as a precursor for preparation of MA-containing polyurethanes. Based on the thermolysis reaction of MA groups, followed by ketene dimerization reaction, the reactive polyamides and polyurethanes show self-cross-linkable features. The cross-linked polyurethanes exhibit good film formability, thermal stability, and mechanical properties. A new MA-based polymerization method and a novel synthesis route for preparation of reactive polyamides and polyurethanes are demonstrated.

The Michael addition reaction of Meldrum's acid (MA): an effective route for the preparation of reactive precursors for MA-based thermosetting resins

Reactive monomers and polymers possessing Meldrum's acid groups from the Michael addition reaction are demonstrated.

Effective Synthesis Route for Linear and Cross-Linked Biodegradable Polyesters Using Aliphatic Meldrum's Acid Derivatives as Monomers

On the basis of the reaction between ketene and alcohol groups to result in an ester linkage and Meldrum's acid as an effective precursor of ketene group, a bifunctional aliphatic Meldrum's acid compound (BisMA) is synthesized and used as a monomer to react with ethylene glycol and glycerol for the preparation of linear and cross-linked aliphatic polyesters, respectively. A 62 and 35 wt % of biodegradation fraction have been recorded on the linear and cross-linked aliphatic polyesters after an 8 week biodegradation test, respectively, to demonstrate the good biodegradability of the synthesized polyesters. In addition to conventional linear biodegradable polyesters, this synthetic route also provides a new and convenient method for preparation of cross-linked biodegradable polyesters. The types of the required monomers and reaction methods for preparation of the cross-linked biodegradable polyesters are similar to those used for conventional thermosetting resins. An integration of biodegradable polymers and thermosetting resins in polymer chemistry has been demonstrated.

Self-crosslinkable and modifiable polysiloxanes possessing Meldrum's acid groups

Meldrum's acid functionalized poly(dimethylsiloxane)s exhibiting self-crosslinking and post-modifiable features.

A Cocatalytic Effect between Meldrum's Acid and Benzoxazine Compounds in Preparation of High Performance Thermosetting Resins

In this work, a cocatalytic effect between Meldrum's acid (MA) and benzoxazine (Bz) compounds has been explored to build up a self-promoting curing system. Consequently, the MA/Bz reactive blend exhibits a relatively low reaction temperature compared to the required temperatures for the cross-linking reactions of the pure MA and Bz components. This feature is attractive for energy-saving processing issues. Moreover, the thermosetting resins based on the MA/Bz reactive blends have been prepared. The MA component can generate additional free volume in the resulting resins, so as to trap air in the resin matrix and consequently to bring low dielectric constants to the resins. The MA-containing agent is an effective modifier for benzoxazine resins to reduce their dielectric constants.

Crosslinked polyarylene ether nitrile film as flexible dielectric materials with ultrahigh thermal stability

Dielectric film with ultrahigh thermal stability based on crosslinked polyarylene ether nitrile is prepared and characterized. The film is obtained by solution-casting of polyarylene ether nitrile terminated phthalonitrile (PEN-Ph) combined with post self-crosslinking at high temperature. The film shows a 5% decomposition temperature over 520 °C and a glass transition temperature (T_g) around 386 °C. Stable dielectric constant and low dielectric loss are observed for this film in the frequency range of 100–200 kHz and in the temperature range of 25–300 °C. The temperature coefficient of dielectric constant is less than 0.001 °C⁻¹ even at 400 °C. By cycling heating and cooling up to ten times or heating at 300 °C for 12 h, the film shows good reversibility and robustness of the dielectric properties. This crosslinked PEN film will be a potential candidate as high performance film capacitor electronic devices materials used at high temperature.