Thermoset polymers, development

There are RIM systems based on chemistry unrelated to polyurethanes that are not in significant commercial production compared to the polyurethanes. Development work has taken place with materials such as nylon. The nylon RIM material is based on caprolactam. Nylon RIM polymers offer high toughness and abrasion resistance. Polydicyclo-pentadiene is a proprietary thermoset polymer developed by Hercules. PCPD offers high-impact resistance and stiffness. It is used in the production of snowmobile components. Other polymers are used such as epoxies, polyesters, acrylics, phenolics, and styrenics. 

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. 

If the bismaleimide-amine reaction is carried out with a deficiency of amine the polymer will have terminal double bonds which allows a cure site to give a thermosetting polymer via a double bond polymerisation mechanism. This approach was developed by Ciba-Geigy with their product P13N (Figure 18.42). 

Details are given of the development of energy and material recycling processes for thermosetting polymer composites. Applications in the cement industry and in coal fired fluidised bed combustion plants are discussed. 3 refs. 

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. 

A number of methods have been developed for the determination of the thermal decomposition kinetics of organic and inorganic materials. These include both isothermal and dynamic TGA method28-30 Our studies of the thermal stability of the thermoset polymer utilized isothermal evaluation of zeroth-order decomposition rate kinetics.19... 

Kinloch, A.J. (1986). Rubber toughened thermosetting polymers. In Development in Re.sins and Primers (A.J. Kinloch ed.), Elsevier Appl. Sci. Pub., London. 

The purpose of the second dwell is to allow crosslinking of the matrix to take place. It is during the second dwell when the strength and related mechanical properties of the composite are developed. To characterize the exothermic crosslinking reaction of a thermosetting polymer matrix, a thermal cure monitor technique such as Differential Scanning Calorimetry... 

So many kinds of polymers exist that scientists have developed ways of categorizing them to make it easier to study and describe them. Polymers formed by addition or condensation reactions, for example, are placed in the same category because they are formed by a common chemical reaction and, in many cases, have common physical and chemical properties. Similarly, thermoplastic and thermosetting polymers are grouped together primarily because of their behaviors when exposed to heat, and, hence, applications for which they are likely to he most suitable. 

In recent years a new type of thermosetting polymer based on polydicyclopen-tadiene has been developed and marketed. Usually this is amber in colour and it is made by a reaction injection moulding process employing various catalysts ... 

The field of research on the chemorheology of thermosetting polymers is new and exciting. As our knowledge of the curing processes expands, new materials will come into focus. These too, must be understood. The reader should also look beyond the application of these methodologies to the thermoset materials discussed herein, and use the information to develop further... 

JLnterpenetrating polymer networks (IPNs) are a special class of polymer blends in which the polymers exist in networks that are formed when at least one of the polymers is synthesized or cross-linked in the presence of the other. Classical or true IPNs are based solely on thermosetting polymers that form chemical cross-links. More recently, two classes of thermoplastic IPNs have been developed. Apparent IPNs are based on combinations of physically cross-linked polymers. Semi-IPNs are based on combinations of... 

Glassy polymers, PMMA and PS, are suitable for many applications, but they are brittle when subjected to impact loads. The same things happens with thermoset polymers such as epoxy or phenolic resins. To solve this problem, impact-resistant polymers have been developed that basically consist of a matrix of the brittle polymer in which a second elastomeric... 

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