Introduction

Abstract

There are many applications for which heat-resistant polymers are needed, but there is little doubt that the main impetus for their development has come from the aerospace field. Synthetic activity was at its height during the late fifties and early sixties, but has declined lately for a number of reasons. These include the cutback in aerospace expenditure, the basic difficulties encountered in producing useful materials, and the relatively small markets for and cost of these speciality products. Progress in heat-resistant polymers has been governed by the opposing requirements of thermal stability and processability. The types of chemical structure conveying heat resistance have tended to lead to insolubility and infusibility, and hence structural modifications must often be made so that fabrication is possible. As a consequence, relatively few of the very many polymers that have been synthesized have achieved commercial exploitation. In the past few years no completely new thermally stable organic polymer systems have emerged; effort has been concentrated upon improved methods of synthesis of known structures, or upon modifications to these structures so that easier processing and fabrication are possible without a concomitant loss of stability. There is little evidence at present that any marked increase in thermal stabilities of organic polymers over those currently obtainable will be forthcoming. A survey of those materials available in commercial or development quantities is therefore appropriate, as it is considered probable that such materials are unlikely to be superseded in the near future.