Thermosetting systems

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). 

Composite Particles, Inc. reported the use of surface-modified rubber particles in formulations of thermoset systems, such as polyurethanes, polysulfides, and epoxies [95], The surface of the mbber was oxidized by a proprietary gas atmosphere, which leads to the formation of polar functional groups like —COOH and —OH, which in turn enhanced the dispersibility and bonding characteristics of mbber particles to other polar polymers. A composite containing 15% treated mbber particles per 85% polyurethane has physical properties similar to those of the pure polyurethane. Inclusion of surface-modified waste mbber in polyurethane matrix increases the coefficient of friction. This finds application in polyurethane tires and shoe soles. The treated mbber particles enhance the flexibility and impact resistance of polyester-based constmction materials [95]. Inclusion of treated waste mbber along with carboxyl terminated nitrile mbber (CTBN) in epoxy formulations increases the fracture toughness of the epoxy resins [96]. 

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... 

J. Gamble, "The Effects on Ridgidity as a Function of Para Ethynylphenoxy Linkages in an Acetylene Terminated Thermosetting System," (M.S. Dissertation), Wright State University, 1981. 

Similarly, other epoxy and polyester thermosetting systems will be invest igated. 

As an aside, we note that the FDEMS sensor input information can also be used to detect the onset of phase separation in toughened thermoset systems and to monitor cure in thin film coatings and adhesive bond lines. It is particularly important that the FDEMS sensor is also very sensitive to changes in the mechanical properties of the resin due to degradation. As such, it can be used for accelerated aging studies and as a dosimeter to monitoring the composite part during use to determine the knockdown in the required performance properties with time. 

The quasielastic method as developed by Schapery [26] is used in the development of the viscoelastic residual stress model. The use of the quasielastic method is motivated by the fact that the relaxation moduli are required in the viscoelastic analysis of residual stresses, whereas the experimental characterization of composite materials is usually in terms of the creep compliances. An excellent account of the development of the quasielastic method is given in [27]. The underlying restriction in the application of the quasielastic method is that the compliance response of the material shows little curvature when plotted versus log time [28]. Harper [27] shows excellent agreement between the quasielastic method and direct inversion for AS4/3510-6 graphite/epoxy composite. For most graphite/thermoset systems, the restrictions imposed by the quasielastic method are satisfied. 

The epoxy resin can be defined as any molecule that contains two or more alpha-epoxy groups which can be reacted to form a thermoset system. An example of a difunctional epoxy resin is diglycidyl ether of Bisphenol-A (DGEBA) which is formed... 

The collection of reviews to be published in ADVANCES IN POLYMER SCIENCE is devoted just to these fundamental problems. The epoxy resin-curing agent formulations are typical thermosetting systems of a rather high degree of complexity. Therefore, some of the formation-structure-properties relationships are still of empirical or semiempirical nature. The main objective of this series of articles is to demonstrate the progress in research towards the understanding of these relationships in terms of current theories of macromolecular systems. 

Mechanism and Kinetics of the Cure Process in Tetraglycidyl-methane Dianiline-Diaminodiphenyl Sulphone Thermoset System... 

This substantial toughening effect of CTBN on the cycloaliphatic epoxide ERL-4221, coupled with significant increase of the strength of the resin without seriously lowering the heat distortion temperature, is quite unusual for thermosetting systems. 

Liquid-crystalline polymers (LCP) can be used in thermoset systems as initially miscible modifiers that phase-separate during cure. 

In the field of high thermomechanical performance polymers, linear and thermosetting systems offer complementary properties. Among the thermosetting materials, BMIs and BNIs have been extensively studied and are now commercially available. In this chapter, firstly the main preparation and characterization methods are reviewed, and then the chemistry of the polymerization processes is discussed for both families. For the BMIs, due to the electrophilic character of their double bond, different polymerization pathways have been published, which is not the case for BNIs. Special attention has been paid to thermal polymerization which has already been used in industrial achievements however, on the other hand, the structure of these materials has been considered for the purpose of establishing relationships between processability, stability and thermomechanical properties. 

In thermosetting systems, the reactive flame retardant can be incorporated either in one or more of the principal chain-forming components, or in the cross-linking agent. Both strategies have been employed with P-containing flame retardants in a variety of thermosets. 

Solid epoxy adhesive formulations can be processed to either a thermoplastic or a thermoset state. Solid epoxy resins of exceptionally high molecular weight (e.g., phenoxy) can be used without any degree of cure as a hot-melt type of adhesive. However, fully crosslinked, thermoset systems are generally employed in structural applications. 

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