Ying-Ling Liu

Preparation and thermal properties of epoxy-silica nanocomposites from nanoscale colloidal silica

Epoxy-silica nanocomposites were obtained from directly blending diglycidylether of bisphenol-A and nanoscale colloidal silica and then curing with 4,4-diaminodiphenylmethane. The epoxy-silica nanocompoites showed good transparency and miscibility observed with AFM, SEM, and TEM. The thermal stability of the epoxy resins was improved with the incorporation of the colloidal silica. However, a depression on the glass transition temperature of the resins was observed, owing to the plasticizing effect of the colloidal silica. Moreover, the nanoscale colloidal silica did not show effectively synergistic effect on char formation and flame retardance with phosphorus.

Phosphorus-containing epoxy for flame retardant. III: Using phosphorylated diamines as curing agents

Two phosphorus-containing diamine compounds, bis(4-aminophenoxy)-phenyl phosphine oxide and bis(3-aminophenyl)phenyl phosphine oxide, were synthesized for use as curing agents of epoxy resins. Phosphorylated epoxy resins were obtained by curing Epon 828 and Eponex 1510 with these two diamine agents. For raising the phosphorus contents of the resulting epoxy resins, the phosphorus-containing epoxy, bis(glycidyloxy)phenyl phosphine oxide (BGPPO), was also used. These two diamine agents showed similar reactivity toward epoxies. Their reactivities were higher than DDS and lower than DDM. High char yields in TGA evaluation were found for all the phosphorylated epoxy resins, implying their high flame retardancy. The excellent flame-retardant properties of these phosphorylated epoxy resins were also demonstrated by the high limiting oxygen index (LOI) values of 33 to 51.

Self-healing polymers based on thermally reversible Diels–Alder chemistry

The development of self-healing materials has received much research attention in the last two decades. This review paper gathers recent publications on the self-healing polymeric materials with thermally reversible Diels–Alder (DA) chemistry. The DA reaction is a [4 + 2] cycloaddition involving a diene and a dienophile. The self-healing polymers employing the furan group as a diene and the maleimide group as a dienophile have been widely studied. Multifunctional furan and maleimide compounds construct thermally reversible crosslinked networks showing removability and remendability. Self-healing materials have also been utilized as healing agents for conventional thermosets like epoxy resins. Other diene–dienophile pairs, such as anthracene–maleimide and cyclopentadiene–dicyclopentadiene, have also been utilized for the development of thermally induced self-healing materials. Photo-induced self-healing polymers and some novel applications based on DA reactions have been discussed in this review. Moreover, self-healing polymer systems based on other thermally triggered and assisted reactions are also discussed. The discussed publication has provided promising molecular designs and synthetic strategies for the development of high performance self-healing polymers.

Flame‐retardant epoxy resins: An approach from organic–inorganic hybrid nanocomposites

Phosphorus-containing epoxy-based epoxy–silica hybrid materials with a nanostructure were obtained from bis(3-glycidyloxy)phenylphosphine oxide, diaminodiphenylmethane, and tetraethoxysilane in the presence of the catalyst p-toluenesulfonic acid via an in situ sol–gel process. The silica formed on a nanometer scale in the epoxy resin was characterized with Fourier transform infrared, NMR, and scanning electron microscopy. The glass-transition temperatures of the hybrid epoxy resins increased with the silica content. The nanometer-scale silica showed an enhancement effect of improving the flame-retardant properties of the epoxy resins. The phosphorus–silica synergistic effect on the limited oxygen index (LOI) enhancement was also observed with a high LOI value of 44.5.

Phosphorus-containing epoxy resins for flame retardancy V: synergistic effect of phosphorus-silicon on flame retardancy

Epoxy resins containing phosphorus and/or silicon are prepared from phosphorus/silicon-containing epoxides and diamine curing agents. The flame-retardant properties of the phosphorus/silicon-containing epoxy were studied. Furthermore, the phosphorus–silicon synergistic effect on LOI enhancement and increasing flame retardancy of the epoxy materials were demonstrated. While under flame, phosphorus provides the tendency of char formation, and silicon provides the enhancement on thermal stability of the char, to show their individual benefit on flame retardancy. Introducing both phosphorus and silicon together in the epoxy resin composition brings the success of combining these two factors in a flame retardation mechanism. An LOI enhancement from 26 to 36 is observed for epoxy resins containing both phosphorus and silicon. Moreover, the synergistic effect of phosphorus–silicon on fire resistance can be further leveled up by using siloxane reagents to replace silanes. Epoxy resins with a composition of phosphorus epoxides and siloxane diamines exhibit a high LOI value of 41, to demonstrate the high synergistic efficiency of phosphorus and silicon on flame retardation.

Phosphorus-containing epoxy for flame retardant. I. Synthesis, thermal, and flame-retardant properties

A new phosphorus-containing oxirane, bis-(3-glycidyloxy)phenylphosphine oxide (BGPPO), was synthesized. Further curing BGPPO with diamine curing agents, dicyanodiamide (DICY), 4,4′-diaminodiphenylmethane (DDM), and 4,4′-diaminodiphenylsulfone (DDS), respectively, resulted in several phosphorylated epoxy resins. Compared with Epon 828, Eponex 1015, and DER 732, BGPPO showed relatively high reactivity toward diamine agents via DSC studies. Furthermore, the reactivity of the three curing agents toward BGPPO were found to be in the order of DDM > DICY > DDS. Thermal stability and the weight loss behavior of the cured polymers were studied by TGA. The phosphorylated resins showed lower weight loss temperatures and higher char yields than did the Epon 828-based resins. The high char yields as well as high limited oxygen index (LOI) values of the BGPPO-based resins confirmed the effectiveness of phosphorus-containing epoxy resins as flame retardants.

Synthesis, characterization, thermal, and flame retardant properties of phosphate-based epoxy resins

A new phosphorus-containing oxirane bis-glycidyl phenylphosphate (BGPP), and a diamine, bis(4-aminophenyl)phenylphosphate (BAPP), were synthesized. Both of these two phosphorus-containing compounds lead to phosphate-containing epoxy resin via curing reaction. The kinetics of the curing reaction of BGPP with various curing agents, including BAPP, were studied. The introduction of electron-withdrawing group into the compounds increases the BGPP and decreases the BAPP reactivity in the curing reaction. The thermal and the weight loss behavior of the cured epoxy resins were studied by TGA. High char yields (32–52%) as well as high limiting oxygen index (LOI) values (34–49) of these phosphorylated resins were found, confirming the usefulness of these phosphorus-containing epoxy resins as flame retardants.

Phosphorus-containing epoxy for flame retardance: IV. Kinetics and mechanism of thermal degradation

Abstract The kinetics and mechanisms of thermal degradation of a phosphorus-containing epoxy based on bis-(3-glycidyloxy)phenylphosphine oxide (BGPPO) and 4,4′-diaminodiphenylsulfone (DDS) were studied. Two and four stages were found for BGPPO/DDS degradation in nitrogen and air, respectively. The degradation activation energies calculated from the methods of Kissinger, Friedman and Ozawa were obtained. The first stage of degradation, which results from the decomposition of phosphorous groups, showed lower activation energy than the other stages. Furthermore, via FTIR and TG-FTIR investigations, the degradation of this phosphorus-containing epoxy was determined to begin by the breaking of PPh bonds, followed by dehydration reactions breaking POC bonds, and elimination of propyl groups. Therefore, the degradation of the epoxy resulted in high char yields and residues with high phosphorus contents.

Synthesis and flame-retardant properties of phosphorus-containing polymers based on poly(4-hydroxystyrene)

Phosphorus-containing polystyrene was obtained through incorporating phosphate groups onto poly(4-hydroxystyrene). This was achieved by esterification with diethylchlorophosphate. The phosphorylation was confirmed by IR, 1H-NMR, and 31P-NMR analysis. By varying the feeding ratios of the reactants, the phosphorus content in the polymers could be successfully tailored and gave values of 12.8 to 4.9% by weight. This was further corroborated by elemental analysis. Thermal characteristics and temporal stability of the phosphorylated polymers were evaluated by DSC and TGA. High char yields (64% by weight) and LOI values of 41 were found for these polymers. Such properties make these polymers useful in flame retardants.

A new class of highly-conducting polymer electrolyte membranes: Aromatic ABA triblock copolymers

Highly proton-conducting polymer electrolyte membrane (PEMs) materials are presented as alternatives to state-of-the-art perfluorinated polymers such as Nafion®. To achieve stable PEMs with efficient ionic nanochannels, novel fully aromatic ABA triblock copolymers (SP3O-b-PAES-b-SP3O) based on sulfonated poly(2,6-diphenyl-1,4-phenylene oxide)s (A, SP3O) and poly(arylene ether sulfone)s (B, PAES) were synthesized. This molecular design for a PEM was implemented to promote the nanophase separation between the hydrophobic polymer chain and hydrophilic ionic groups, and thus to form well-connected hydrophilic nanochannels that are responsible for the water uptake and proton conduction. Relative to other hydrocarbon-based PEMs, the triblock copolymer membranes showed a dramatic enhancement in proton conductivity under partially hydrated conditions, and superior thermal, oxidative and hydrolytic stabilities, suggesting that they have the potential to be utilized as alternative materials in applications operating under partly hydrated environments.