Gradient Polymers.

This paper discusses studies on nonuniform and nonequilibrium penetrant distributions wherein a gradient of the second polymer is frozen in place by the crosslinking reaction. In a general sense, it is expected that ultimately a wide range of physical properties--possibly some quite unique--will arise from controlling not only the choice of the two polymer species but also the composition gradient. The chemical system ultimately selected was a crosslinked polymethylmethacrylate PMMA host that was penetrated by a low-molecular-weight grade of polybutadiene PB, subsequently to be further polymerized and crosslinked in its gradient position. Such a choice necessarily limits the scope of the present study to represent variations of only one class of material the two-component rubber-toughened plastic. However, this is a very important class of structural plastic, and the possible compositional variations are highly diverse in principle. Primary results consist of the measured responses to various types of mechanical deformation, including ultimate limits. These are coupled with information about the chemical composition averages, and gradient character and the microstructure to develop correlations and predictive rules for material performance.