Hatsuo Ishida

Physical and mechanical characterization of near‐zero shrinkage polybenzoxazines

A new class of phenolic-like thermosetting resins has been developed that is based on the ring-opening polymerization of a benzoxazine precursor. These new materials were developed to combine the thermal properties and flame retardance of phenolics with the mechanical performance and molecular design flexibility of advanced epoxy systems. The polybenzoxazines overcome many of the traditional shortcomings of conventional novolak and resoletype phenolic resins, while retaining their benefits. The physical and mechanical properties of these new polybenzoxazines are investigated and are shown to compare very favorably with those of conventional phenolic and epoxy resins. The ring-opening polymerization of these new materials occurs with either near-zero shrinkage or even a slight expansion upon cure. Dynamic mechanical analysis reveals that these candidates for composite applications possess high moduli and glass transition temperatures, but low crosslink densities. Long-term immersion studies indicate that these materials have a low rate of water absorption and low saturation content. Impact, tensile, and flexural properties are also studied. Results of the dielectric analysis on these polybenzoxazines demonstrate the suitability of these materials for electrical applications.

General Approach to Nanocomposite Preparation

A novel approach to nanocomposite preparation utilizing a swelling agent, a monomer or polymer known to intercalate/exfoliate smectite clay, has allowed the preparation of several new nanocomposites. Present in small amounts, the swelling agent serves to swell the clay layers, allowing the organic matrix to be virtually any polymer. Twenty-four polymers are used in this study, varying in solubility parameter, molecular weight, and polarity. Many of these polymers do not yield a nanocomposite structure by simple melt mixing of the clay and polymer. Although some polymers are capable of partial intercalation or exfoliation without the addition of a swelling agent, addition of 2 wt % of this additive results in either complete intercalation/exfoliation or an increased percentage of nanocomposite formation, in comparison to the clay-polymer mix. The evidence of a nanocomposite structure is provided by a shift in, or the absence of, clay reflections in X-ray powder diffraction patterns.

The structure of γ-aminopropyltriethoxysilane on glass surfaces

Abstract The structure of γ-aminopropyltriethoxysilane (APS) has been studied in aqueous solution and as a solid using Fourier transform infrared spectroscopy. The monomeric aminosilane forms an internal cyclic chelate structure when hydrolyzed. Two vibrational bands have been found near 1575 and 1600 cm −1 in condensed aminopropylsiloxane polymer. The band at 1575 cm −1 is assigned to the NH 2 deformation mode of the acceptor amine groups involved in strong hydrogen bonding and the band at 1600 cm −1 is assigned to the NH 2 groups. Heat treatment causes the formation of nonring chain-structured aminosilanes. In the study of the structure of APS coupling agent on high-surface-area silica gel (Cab-O-Sil) and E-glass fibers, it was found that the aminosilane adsorbed on silica as essentially a monolayer and the amino group chemically interacted with the glass surface. The adsorbed APS on E-glass fiber exists as a multilayer, and formed a predominately cyclic ring structure in the coupling agent interphase.

Mechanical characterization of copolymers based on benzoxazine and epoxy

A new class of phenolic-like thermosetting resins has been developed that is based on the ring opening polymerization of a benzoxazine precursor. These new materials overcome many of the traditional shortcomings associated with conventional novolac and resole-type phenolic resins, while demonstrating excellent physical and mechanical characteristics. The benzoxazines are copolymerized with an epoxy resin in order to modify their performance. The addition of epoxy to the polybenzoxazine network greatly increases the crosslink density of the thermosetting matrix and strongly influences its mechanical properties. Copolymerization leads to significant increases in the glass transition temperature, flexural stress, and flexural strain at break over those of the polybenzoxazine homopolymer, with only a minimal loss of stiffness. By understanding the structural changes induced by variations of epoxy content and their effect on material properties, the network can be tailored to specific performance requirements.

Curing kinetics of a new benzoxazine-based phenolic resin by differential scanning calorimetry

Abstract The curing reactions of benzoxazine precursors based on bisphenol A and aniline are studied to determine the feasibility of processing them into final phenolic parts. Benzoxazine precursors are able to overcome most of the shortcomings of traditional phenolic resins, and retain the excellent heat resistance and fire and smoke properties of these resins. This new type of phenolic material cures via a ring-opening mechanism that does not produce any condensation or other reaction by-products. Phenol is not used as raw material, which reduces considerably the environmental and health risks. According to differential scanning calorimetry (d.s.c.), the curing of benzoxazine precursors is an autocatalysed reaction until vitrification is reached, and diffusion begins to control the curing process afterwards. Isothermal and non-isothermal d.s.c. tests are performed. Calculations of the activation energy and the overall reaction order are made by various procedures. The vitrification times and the kinetic rate constants are also calculated.

Cationic ring-opening polymerization of benzoxazines

Cationic polymerization of mono and polyfunctional benzoxazine monomers is described. The chemical structure of the polymers from cationic polymerization of benzoxazine monomers has been identified and distinguished from thermally polymerized products from the same monomers. The controllable microstructure of the polymers from benzoxazines prepared by cationic polymerization offers opportunities to prepare and optimize the polymer structure for specific applications.

Development of new class of electronic packaging materials based on ternary systems of benzoxazine, epoxy, and phenolic resins

We have developed new polymeric systems based on the ternary mixture of benzoxazine, epoxy, and phenolic novolac resins. Low melt viscosity resins render void-free specimens with minimal processing steps. The material properties show a wide range of desirable reliability and processability, which are highly dependent on the composition of the monomers in the mixture. A glass transition temperature as high as 170°C and considerable thermal stability at 5% weight loss up to 370°C can be obtained from these systems. Phenolic novolac resin acts mainly as an initiator for these ternary systems while low melt viscosity, flexibility and improved crosslink density of the materials are attributed to the epoxy fraction. Polybenzoxazine imparts thermal curability, mechanical properties as well as low water uptake to the ternary systems. The materials exhibit promising characteristics suitable for application as underfilling encapsulation and other highly filled systems.

Synthesis and thermal characterization of polybenzoxazines based on acetylene-functional monomers

Abstract The high thermal stability of this class of polybenzoxazines is a combined result of polymerization of acetylene terminal functional group and oxazine ring-opening polymerization. The high char yield achieved for this class of materials is in the range of 71–81% by weight at 800°C in a nitrogen atmosphere and 30% by weight at 700°C in air as it is determined by thermogravimetric analysis (TGA). Temperature at 10% weight loss (T10%) is in the range of 520–600°C. The polymerization and post-cure reactions of these benzoxazines are studied by differential scanning calorimetry (DSC). The char formation of the blend of an acetylene-functional benzoxazine with an analogous benzoxazine without acetylene group is also studied by TGA.

Structural effects of phenols on the thermal and thermo-oxidative degradation of polybenzoxazines

The thermal behavior of a series of polybenzoxazines based on aniline and various phenols is examined under both inert and oxidative environments. Under an inert environment, the various phenols substantially affect the char yield of polybenzoxazines without altering the mechanism of Mannich base cleavage. Under an oxidative environment, the various phenols have a significant influence on the degradation behavior of polybenzoxazines below 600°C. The mechanism of the Mannich base cleavage under oxidative degradation has been proposed.

Molecular characterization of the polymerization of acetylene-functional benzoxazine resins

Abstract High char yield polybenzoxazines are obtained from acetylene-functional benzoxazine monomers. Polymerization of acetylene functional group, in addition to oxazine ring opening polymerization, contributes greatly to the exceptional thermal stability. A significant change in char yield is found for these polybenzoxazines by different polymerization environments. The polymerization behaviour of these compounds under air and nitrogen atmosphere has been studied by Fourier transform infra-red spectroscopy, ultra-violet–visible spectroscopy, differential scanning calorimetry and proton nuclear magnetic resonance spectroscopy.