CTPB Rubber
Carboxy-Terminated Polybutadiene.
Early rubber binders for composite rocket propellants were provided by readily available synthetic rubbers. Initially, thiokol polysulphide rubber was employed. This was later replaced with the far more appropriate PBAA rubber. This, in turn, was replaced by PBAN rubber which offered superior physical properties. However, the performance demands of rocket users required the development of more advanced synthetic rubbers.
The first of these custom-made synthetic rubber polymers, pioneered by Phillips
Petroleum Co. and first evaluated in propellant applications by Rocketdyne,
was carboxy-terminated polybutadiene (CTPB). There was an advantage in placing
the carboxyl groups at the end of the polymer chain rather than randomly spacing
them along the chain (as PBAA rubber polymers). This way the rubber polymer
chemist was provided with a uniform structure so he could control his binder
network to give the desired mechanical properties. The reproducibility of a
controlled system was naturally greater than that of a random structure.
However, the demand by the customer (primarily the US Government) for greater
reliability and overall improved performance, combined with lower cost, meant
that CTPB never enjoyed wide spread employment in the rocket industry. Mechanical
failure of the rubber binder was a particular problem, together with a growing
awareness of the environmental problems caused by the combustion of rubber binders.
The search for a successor reulted in HTPB.
