Determination of Crosslinking in High Tg Polymers
Final technical rept. 5 Oct 1977-15 Oct 1979
RESEARCH TRIANGLE INST (RTI) INST RESEARCH TRIANGLE PARK NC
Pagination or Media Count:
Considerable evidence has been accumulated by different investigators which demonstrates that the crosslink density in cured epoxy resins is not uniform. The non-uniformity of the network density can be so pronounced that the system approaches a two-phase system being composed of a large number of densely crosslinked domains of globular shape nodules or network clusters which are imbedded in a common matrix of lower crosslink density. Most of the evidence for nodule formation in cured epoxy resins is derived from electron microscopic investigations of fracture surfaces by replication technique. Generally, the micrographs reveal the presence of globular domains with dimensions in the range of 10-70 nm. So far the existence of nodular structures could not be confirmed by x-ray scattering experiments. In view of the accumulated evidence for the presence of globular network inhomogeneities the lack of x-ray evidence would indicate an extremely small difference between the electron densities of nodules and imbedding matrix material. As a consequence the evaluation of x-ray particle scattering becomes experimentally rather demanding.
- Polymer Chemistry