Thermoset chemistry

Two classes of reactive secondary amines (XX and XXI) were synthesized [90] for the thermoset version of the In Situ Molecular Composite concept. The thermoset chemistry of the bisnadimide (XX) involved that of PMR systems (polymerization of monomeric reactants) [95], The secondary amine (XXI) embodied the more recent ringopening polymerization of benzocyclobutene (BCB) [96]. Polymerization exotherms for both thermoset amines occurred with an onset at 225 °C, maximizing at approximately 260 °C as evidenced by DSC at a heating rate of 10 °C/m. 

Model polyamicdialkylamides were prepared by the reaction of the secondary amines (XX) and (XXI) with the polyisoimide (XVII) in DMAC at room temperature. Unfortunately, the resultant polyamicdialkylamides only exhibited limited softening behavior for processing into bulk specimens. The inability to provide molded specimens prevented the validation of the In Situ Molecular Composite concept. Research is currently being carried out at a number of academic and industrial institutions on new thermoset chemistry, polyamices-ters, and extended chain polyimides. 

Racich, J. L., Koutsky, J. A. Boundary Layers in Thermosets, Chemistry and Properties of Crosslinked Polymers, ed., S. Labana, 303, Academic Press (1977)... 

Lin SC, Pearce EM (1994) High-performance thermosets chemistry, properties, applications. Hanser, Munich... 

Adapted from Table 8.4 in Lin, S.-C. Pearce, E.M. High-performance epoxy resins. Chapter 8. In High-Performance Thermosets, Chemistry, Properties, Applications Hanser New York, 1998, p. 259.)... 

Aqueous Thermosetting Emulsions. The basic concept of a thermosetting emulsion is a logical extension of solvent-based thermosetting chemistry (22. 23). Reaction functionality is copolymerized into the polymer backbone, and after application, the... 

Lin, S.-C., and E. M. Pearce. High-Performance Thermosets Chemistry, Properties. Hanser Publishers, Munich, 1994, chap. 2, pp. 13-63. 

This second edition, built on the success of the first, has become necessary as a result of the continuing development of the world-wide composites industry. This has included, the entry of new companies, new and improved thermoset resin systems and moreover major and important changes in the whole manufacturer/supplier picture, since the first edition was published in 1993. Whilst retaining the comprehensive contact listing of all those companies in an initial directory section together with some basic understanding of thermoset chemistry, a change in the layout of the second part, has not only allowed more resin description and property tabulation within that databook section, but also a much more reader friendly, useful layout. 

In this section we examine some examples of cross-linked step-growth polymers. The systems we shall describe are thermosetting polymers of considerable industrial importance. The chemistry of these polymerization reactions is more complex than the hypothetical AB reactions of our models. We choose to describe these commercial polymers rather than model systems which might conform better to the theoretical developments of the last section both because of the importance of these materials and because the theoretical concepts provide a framework for understanding more complex systems, even if they are not quantitatively successful. 

A number of BMI resias based on this chemistry became commercially available through Rhc ne Poulenc for appHcation ia priated circuit boards and mol ding compounds and Rhc ne Poulenc recognized the potential of bismaleimides as building blocks for temperature-resistant thermoset systems. The basic chemistry, however, was not new, because the Michael addition reaction had been employed by Du Pont to obtain elastomeric reaction products from bismaleimides and Hquid polymeric organic diamines (15). 

R. Siebert, "Rubber-Modified Thermoset Resins," in C. K. Riew and J. K. GiUham, eds., ACS Advances in Chemistry Series 208, American Chemical Society, Washington, D.C., 1983, p. 179 W. D. Bascom and D. L. Hunston, "Rubber Toughened Plastic," Adv. Chem. Ser. No. 222, American Chemical Society, Washington, D.C., 1989. 

The polyimide shown is a tme thermosetting resin, but the general reaction procedure, coupling the dianhydride with the diamine, is extremely important throughout polyimide chemistry. The intermediate polyamic acid polymers form the basis for many of the polyimide resins used in advanced composites. 

This chapter discusses synthetic polymers based primarily on monomers produced from petroleum chemicals. The first section covers the synthesis of thermoplastics and engineering resins. The second part reviews thermosetting plastics and their uses. The third part discusses the chemistry of synthetic rubbers, including a brief review on thermoplastic elastomers, which are generally not used for tire production but to make other rubber products. The last section addresses synthetic fibers. 

Sanding is carried out at this stage and, after clean-up, the final colour or top-coat is applied. There is some variation in the resin chemistry used. Alkyds crosslinked with melamine-formaldehyde are widely used for non-metallic pigmentation. Metallics are usually based on acrylics for better durability. The acrylic may be thermoset with melamine-formaldehyde or a thermoplastic lacquer (plasticised copolymer of methyl methacrylate). A thickness of about 50ftm is applied and stoved for 20 min at 130°C (lacquers receive a bake-sand-bake process for a smoother appearance). 

The chemistry of synthetic polymers is similar to the chemistry of small molecules with the same functional groups, but the physical properties of polymers are greatly affected by size. Polymers can be classified by physical property into four groups thermoplastics, fibers, elastomers, and thermosetting resins. The properties of each group can be accounted for by the structure, the degree of crystallinity, and the amount of cross-Jinking they contain. 

Riew, C.K. and Gillham, J.K. Rubber Modified Thermoset Resins. Advances in Chemistry, 208, American Chemical Society, Washington, DC, 1984. 

The final physical properties of thermoset polymers depend primarily on the network structure that is developed during cure. Development of improved thermosets has been hampered by the lack of quantitative relationships between polymer variables and final physical properties. The development of a mathematical relationship between formulation and final cure properties is a formidable task requiring detailed characterization of the polymer components, an understanding of the cure chemistry and a model of the cure kinetics, determination of cure process variables (air temperature, heat transfer etc.), a relationship between cure chemistry and network structure, and the existence of a network structure parameter that correlates with physical properties. The lack of availability of easy-to-use network structure models which are applicable to the complex crosslinking systems typical of "real-world" thermosets makes it difficult to develop such correlations. 

This chemistry was also performed on one trisphenol, 1,1,1 -tris(4-hydro-xyphenyl)ethane (THPE). The resulting tris(trifluorovinyl ether) monomer forms a thermoset polymer upon curing. 

In the late 1970s, Kirchhoff at Dow Chemical Company developed the use of benzocyclobutenes in polymer synthesis and modification. These efforts culminated in 1985 with the issuance of the first patent describing the use of benzocyclobutene in the synthesis of high-molecular-weight polymer.27 Similar work that involved a thermosetting system based on Diels-Alder cycloaddition between terminal benzocyclobutene and alkyne groups,28,29 was reported separately and independently by Tan and Arnold.28 Since these initial discoveries, the field of benzocyclobutene polymers has expanded rapidly and benzocyclobutene chemistry constitutes the basis of a new and versatile approach to the synthesis of high-performance polymers for applications in the electronics and aerospace industries.30... 

A new method for the syntheses of fluorocarbon polyarylate polymers has been demonstrated. The chemistry utilizes the [2jt+2rr] cyclodimerization of fluorinated olefins and generates polymers of novel composition. The first generation of polymers prepared by this method are polyarylate homopolymers. Theremoplastic polymers of high molecular weight can be achieved via neat or solution polymerization. One example of a thermoset polymer prepared by this method has a high Tg, low dielectric constant and dissipation factor, low moisture... 

---