Bismaleimide systems are desirable resins for reinforced composites necessary for high-performance applications, for instance, structural laminates, aerospace, elastomers, and printed circuit boards. The advantages of these systems include high mechanical and thermal stability, constant electrical characteristics over a wide range of temperature, and superior processability.
For commercial applications, bismaleimides are normally cured with petroleum comonomers such as polyimides, polyesters, and epoxies. This polymerization curing process is not 100% complete and the untreated monomers can leach out of the polymers, which has environmental as well as health implications. Moreover, their longer biodegradation times add to the list of disadvantages of bismaleimides.
Luckily, plant oils or fatty acids present a better platform of resins for reinforced composites that are bio-renewable. University of Akron researchers proposed the synthesis of cross-linked thermosets by the reaction of plant oils and fatty acids with bismaleimides through an ene reaction. In their work, they presented the functionalization and characterization of thermosetting resins extracted from plant oils using three bismaleimides. Their work is now published in peer-reviewed journal, Industrial & Engineering Chemistry Research.
In their experiments, soybean and linseed oils were cured in 1,1′-(methylene-di-1,4-phenylene) bismaleimide and oligomeric bismaleimides to yield bio-based thermoset polymers.
The authors found that, one molecule of the soybean oil corresponded to approximately 4.6 carbon-carbon double bonds. In a similar fashion, one molecule of linseed oil corresponded to 6.0 carbon-carbon double bonds. During the heating scan, 1,1′-(methylene-di-1,4-phenylene) bismaleimide melted and was followed by an exothermic curing between the soybean oil and the bismaleimide. The outcomes demonstrated that the curing reaction in bulk was determined by the melting temperature along with fluidity of the bismaleimide.
No transitions were noted in the subsequent heating scan indicating that the ene curing was completed by the end of the first scan. Although linseed oil, soybean oil, and all the three bismaleimides, are soluble in chloroform, dimethyl sulfoxide and methylene chloride, all their cured products are insoluble in these as well as other organic solvents. This shows that the cured products cross-linked.
This study found that plant oils could be cured with bismaleimides by the ene reaction at moderate temperatures without modifying the oils and without using solvents or catalyst. Therefore, this green technology of curing plant oils with bismaleimides by the ene reaction offers an improved approach for manufacturing bio-based thermoset polymers and reinforced composites with superior thermal stability and mechanical properties important for commercialization.
Acknowledgement: This work was initiated through a sub-contract from Premix Inc.’s SBIR Phase II Award 1256123.
Brinda Mehta1, Paula Watt1, Mark D. Soucek2, and Coleen Pugh1. Moderate Temperature Curing of Plant Oils with Bismaleimides via the Ene Reaction. Industrial & Engineering Chemistry Research, volume 55 (2016), pages 11727-11735.Show Affiliations
- Departments of Polymer Science, The University of Akron, Akron, Ohio 44325-3909, United States
- Departments of Polymer Engineering, The University of Akron, Akron, Ohio 44325-3909, United States
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