Rongqi Zhu

A novel benzoxazine/epoxy blend with multiphase structure

A novel benzoxazine (BOZ)/epoxy resin (ER) blend with multiphase structure was successfully prepared under the catalysis of imidazole (MZ) via reaction-induced phase separation. The toughness and thermal properties of the novel blend were greatly improved compared with the homogeneous PBOZ and PBOZ/ER systems.

A novel benzoxazine/bismaleimide blend resulting in bi-continuous phase separated morphology

A novel modified polybenzoxazine with bi-continuous phase separated morphology was successfully prepared from the blend of bisphenol A-aniline benzoxazine (BA-a), N,N′-(2,2,4-trimethylhexane-1,6-diyl)bismaleimide (TBMI) and catalyst imidazole. The thermal and toughness properties of the phase-separated blend cast were improved compared with polybenzoxazine.

A study on the chain propagation of benzoxazine

The chain propagations of Bisphenol A-aniline benzoxazine (defined as BA-a) polymerized by thermal induction and in the presence of various catalysts or curing agents during the curing process before gelation were investigated in this paper. DSC, gel time test and GPC were used to measure the curing behavior, number-average molecular weight (n), glass transition temperature (Tg), gel time (tgel) and curing conversion (α) of different benzoxazine systems. By comparing the experimental results (n and Tg) with the models of step polymerizations and chain polymerizations proposed by Flory et al., three kinds of chain propagations of benzoxazine were observed and confirmed. The step polymerization occurred in the thermal induction or in the presence of catalyst N,N-dibenzylaniline (tAm), and then the non-living chain polymerization and the living chain polymerization occurred, respectively, when indole (Id) and other additives such as phenol (tBp), acid (HA), imidazole (IMZ) etc. were added to benzoxazine as catalysts or curing agents. Moreover, the relationship between the chain propagation and curing kinetics of benzoxazine was also established. The chain propagation of benzoxazine systems involves step polymerization, non-living chain polymerization andliving chain polymerization, the conversion of the gel point (αgel) is almost equal to, less than and greater than the value of the conversion at which the polymerization rate reaches a maximum (αmax), respectively. The results may contribute to a better understanding of the polymerization mechanism of benzoxazine and provide new approaches to effective control of the polymerization kinetics and growth crosslink structures of benzoxazine.

Study on thermal degradation mechanism of a cured aldehyde-functional benzoxazine

A cured product of aldehyde-functional benzoxazine has good heat-resistant performance. The thermal degradation process of this polybenzoxazine was actively studied by TGA-FTIR and Py-GC/MS. The temperature range of pyrolysis and the major products were determined by TGA-FTIR. A stepwise-temperature testing method based on Py-GC/MS was employed to identify the structures and contents of the pyrolysis products at different temperature stages. Transformation and chemical structures of the polymer bulk during the pyrolysis process were speculated. The results showed that the reactions of the aldehyde groups can form special crosslinking structures which effectively prevent the release of phenols during the pyrolysis process. Additionally, benzophenone compounds and carbon monoxide were detected.

Effect of hydrogen bonds on the polymerization of benzoxazines: influence and control

This work aims to disclose the reason that prohibited the preparation of highly crosslinked polybenzoxazines. Based on experimental study and computer simulations, we found that the dominant –OH⋯N hydrogen bond (Type I –OH⋯N hydrogen bond) of polybenzoxazines blocked high-degree polymerization and resulted in a low crosslink density by decreasing the charge densities of corresponding hydroxyl groups on phenols. As a solution, by introducing additional hydrogen-bond acceptors, the formation of Type I –OH⋯N hydrogen bonds could be suppressed, which enables a high-degree of polymerization of benzoxazines. This novel insight about benzoxazine polymerization is anticipated to help researchers explore more types of polybenzoxazines with enhanced properties.

Preparation and characterization of novel multi-branched polymers in situ cured from benzoxazine/epoxy resin/primary amines blends

High performance polymers with multi-branched structures were prepared in situ from ddm-based benzoxazine (M), cycloaliphatic epoxy resin (T) and diaminodiphenylmethane (ddm) or hexamethylenediamine (6a) via controlling the curing reaction sequence of the system. The curing behavior, cross-linked structures and properties of the system were investigated by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), dynamic mechanical analysis (DMA) and mechanical properties test, respectively. The results suggest that the reaction between T and ddm or 6a was more easily processed than that of M and ddm or 6a, and the multi-branched polymers can be formed in situ in a ternary system based on M, T and ddm or 6a. The heat resistance and mechanical properties of the cured resins with multi-branched structures were greatly improved compared with the polybenzoxazine or poly-benzoxazine/epoxy resin systems. The obtained results provide a new approach to control the chemical cross-linked structures and properties of polybenzoxazines.

Study on the catalytic prepolymerization of an acetylene-functional benzoxazine and the thermal degradation of its cured product

In this paper, the prepolymerization of acetylene-functional benzoxazine was carried out by using nickel acetylacetonate hydrate/triphenyl phosphine as a catalyst at a low temperature. By this method, the reaction heat of acetylene polymerization was partially released and no ring-opening polymerization of benzoxazine occurred. After that, the prepolymer was cured stepwise to obtain the cured product according to a traditional curing process. As a comparison, another cured product was directly obtained from acetylene-functional benzoxazine by the traditional method without prepolymerization. The curing behaviors and the thermal properties of these two polybenzoxazines were investigated and compared by FTIR, DSC, DMA, and TGA. Their thermal decomposition behaviors were further studied by TGA-FTIR, Py-GC/MS, and SEM. The results show that the catalytic prepolymeriztion makes the whole curing process milder and more controllable in a broader processing window. Furthermore, more crosslinked-polyacetylene structures and benzene from the catalytic prepolymerization improve the thermal stability of the polybenzoxazines. Additionally, less amine compounds were detected in the prepolymerization system during the thermal decomposition process and the appearance of the residue was stable and controllable after pyrolysis.

Thermal and dielectric properties of epoxy/DDS/CTBN adhesive modified by cardanol-based benzoxazine

Cardanol-based benzoxazine (Bz-C) was introduced to a ternary resin system to substitute carboxyl-terminated butadiene–acrylonitrile (CTBN) partially and improve the thermal and dielectric properties of the diglycidyl ether of bisphenol-A (epoxy)/4,4′-diaminodiphenylsulfone (DDS)/CTBN adhesive resin system. The effect of Bz-C on the curing behavior of blends was studied, and factors that affect the thermal, mechanical, and dielectric properties were discussed systematically. Results show that reactions between Ep, DDS, and Bz-C decrease the curing temperature of the quaternary blends and increase the cross-linking densities of the network, leading to higher glass-transition temperature and enhanced mechanical properties. The flexibility of the copolymer films was maintained by the introduction of the aliphatic side chain of Bz-C. Substitution of Bz-C for some group of CTBN in the cross-linked network resulted in decreased dielectric constant and dielectric loss in the copolymer films.

Polybenzoxazines: Thermal Responsiveness of Hydrogen Bonds and Application as Latent Curing Agents for Thermosetting Resins

This work aims at exploring the application of polybenzoxazines as thermal latent curing agents for epoxy resins. Thorough studies have shown that hydrogen bonds of polybenzoxazines block the reactivity of phenolic hydroxyl at ambient temperatures and break at elevated temperatures to release the free phenolic hydroxyl. On the basis of these findings, polybenzoxazines are used as thermal latent curing agents. Mixtures of polybenzoxazines and epoxy resins exhibit a long shelf life at room temperature, and the corresponding copolymers possess enhanced properties. This novel insight into using polybenzoxazines as thermal latent curing agents for epoxy resins is anticipated to help researchers explore novel latent curing agents and apply polybenzoxazines more widely.

Effect of phenol on the synthesis of benzoxazine

This work aims to search the key starting materials and the key step of benzoxazine synthesis using primary amine, phenol and formaldehyde as the starting materials. The reaction kinetics were investigated by gas chromatography. The kinetic parameters of benzoxazine formation, such as reaction order, rate constant and activation energy, were found to approximately equal those of phenol consumption, which revealed that phenol was the key starting material and played an important role in the synthesis of benzoxazine. Furthermore, step 2, the reaction between formaldehyde–amine derivatives and phenol for the production of a mannich base was the controlling step. This improved insight into the benzoxazine synthesis is expected to help researchers explore novel benzoxazines and control their synthesis.