Polybenzoxazines-New high performance thermosetting resins : Synthesis and properties

Advances in addition-cure phenolic resins

Two novel benzoxazine monomers containing allyl groups:  3-allyl-3,4-dihydro-2H-1,3-benzoxazine and bis(3-allyl-3,4-dihydro-2H-1,3-benzoxazinyl)isopropane have been synthesized from phenol and Bisphenol A with allylamine and formaldehyde. Their DSC exhibit two exotherms at ca. 145 °C and at ca. 220 °C which correspond to allyl and oxazine thermal polymerization, respectively. Both monomers undergo thermal cure with the formation of thermosets having excellent thermomechanical properties. These thermosets exhibit higher Tg (ca. 300 °C), maintain their storage moduli at higher temperature, and have better thermal stability than the corresponding polybenzoxazines without allyl groups.

Synthesis and Characterization of Novel Benzoxazine Monomers Containing Allyl Groups and Their High Performance Thermosets

A comparison of the mechanical properties of phenol formaldehyde composites reinforced with banana fibres and glass fibres

Miscibility, morphology, thermal, and mechanical properties of a DGEBA based epoxy resin toughened with a liquid rubber

A novel, addition-curable novolac resin (ABPF) was synthesized by the reaction of diallyl bisphenol A with formaldehyde using p-toluene sulfonic acid as the catalyst. The synthesis conditions were optimized to obtain soluble polymer of desirable molecular weight distribution which was characterized by FT-IR, NMR and SEC. ABPF was reactively blended with bisphenol A bismaleimide (BMIP) and cured through an Alder-ene reaction at high temperatures. The cure characteristics of BMIP–ABPF blend with a maleimide:allyl phenol stoichiometry of 1:1 were studied using FT-IR, DSC and DMA, which evidenced the multi-step cure reactions taking place in the system. Cure optimization was evaluated by DSC, DMA and adhesive property tests. The moderately crosslinked blend was conducive for achieving the optimum adhesive properties on aluminium substrates. Retention of the adhesive properties was greater than 100% at 150 °C.



© 2001 Society of Chemical Industry

Reactive Alder‐ene blend of diallyl bisphenol A novolac and bisphenol A bismaleimide: synthesis, cure and adhesion studies

The adhesive joint strengths at room temperature (25°C) and at 120°C for an epoxy resin cured at room temperature with tris (N,N-dimethylaminomethyl) phenol and containing varying amounts of a carboxyl-terminated polybutadiene-acrylonitrile copolymer (CTBN) were investigated and reported. It was observed that as CTBN content increased, lap shear strength and T-peel strength increased significantly and passed through a maximum at about 10 parts CTBN content per 100 parts epoxy resin and then decreased. To explain the observed results, the effect of CTBN content on the bulk tensile strength, impact energy, glass transition temperature (ETg), and morphology were also evaluated. SEM observations showed microphase separation between CTBN and epoxy matrix for the composition containing 10 parts CTBN per 100 parts epoxy resin, and this composition exhibited maximum bulk tensile strength and impact energy. The enhancement of bulk mechanical properties, hence the adhesive joint strength, was attributed to the higher toughness produced by the dispersed rubber particles. At higher CTBN content, the rubber phase became continuous, and the system exhibited a fall in mechanical properties, hence in adhesive joint strength, which was attributed to the flexibilization effect. The glass transition temperature of the cured epoxy resin was little influenced by CTBN incorporation up to 10 parts per 100 epoxy resin. Higher levels of CTBN content due to the flexibilization effect, decreased the ETg, hence the elevated temperature capability. The results of this study demonstrate that epoxy resins containing low levels of CTBN, cured at room temperature with tris (N,N-dimethylaminomethyl) phenol can be used to formulate structural adhesives for use in elevated temperature environments.

Room temperature curing of CTBN-toughened epoxy adhesive with elevated temperature service capability

An investigation was carried out into the effect of modification of an epoxy resin with carboxyl-terminated poly(propylene glycol) adipate (CTPPGA) liquid rubber, on room temperature and elevated temperature adhesive joint strengths, after curing at room temperature (25°C) with tris-2,4,6-(N,N-dimethyl amino methyl) phenol hardner. CTPPGA prepared by the esterification of poly(propylene glycol) (PPG) and molar excess of adipic acid was incorporated into the epoxy resin by the prereact method. CTPPGA modification showed significant enhancement of adhesive joint strengths over the unmodified epoxy and the joint strengths were found to depend on the molecular weight of CTPPGA and its content in the epoxy resin. The elevated temperature lap shear strength measurement made for the CTPPGA-modified epoxy adhesive showed that the adhesive formulation has a temperature service capability up to 120°C. The results are discussed in terms of the data obtained from the tensile tests, DSC analysis, and SEM observations of the fractured surfaces.

Carboxyl‐terminated poly(propylene glycol) adipate‐modified room temperature curing epoxy adhesive for elevated temperature service environment

Resole phenolic resins containing various p-cresol (PC) to phenol (P) mol ratios were prepared and characterized. These phenolic resins were blended with nitrile rubber (NBR) and the measurements of adhesive joint strength, stress–strain properties, DSC, TGA, DMA, TEM, and SEM were performed using a 50 : 50 NBR/phenolic resin blend. It was observed that the adhesive joint strength and the mechanical properties of the blend enhanced significantly on incorporation of p-cresol into the phenolic resin, and the optimum p-cresol/phenol mol ratio was in the vicinity of 2 : 1. Observation of a more continuous phase and the increase in Tg of the rubber region in the blend indicated increased reactivity and compatibilization of NBR with phenolic resin as p-cresol was incorporated. The effect of silica filler on the properties of the nitrile rubber/phenolic resin blend was also studied without and with p-cresol modification and the results suggest that silica filler take not only the role of a reinforcing filler in the nitrile–phenolic–silica composite, but also a role as surface compatibilizer of the blend components. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1187–1201, 1998

R. Ramaswamy

Papers

Reactive Alder‐ene blend of diallyl bisphenol A novolac and bisphenol A bismaleimide: synthesis, cure and adhesion studies

Room temperature curing of CTBN-toughened epoxy adhesive with elevated temperature service capability

Carboxyl‐terminated poly(propylene glycol) adipate‐modified room temperature curing epoxy adhesive for elevated temperature service environment

Reactive compatibilization of a nitrile rubber/phenolic resin blend: Effect on adhesive and composite properties

Epoxidized hydroxy-terminated polybutadiene — synthesis, characterization and toughening studies