Structure-property behavior of free radical synthesized polydimethylsiloxane (PDMS) - polystyrene and PDMS-styrene derivative block polymers have been studied. The block polymers were provided by Dr. J. V. Crivello from GE. Two different types of segmented polytetramethyleneoxide (PTMO) based ionene elastomers were also investigated. The PTMO-dihalide ionenes were obtained through the courtesy of Dr. C. M. Leir in 3M, while the PTMO-dipyridinium ionenes were synthesized by Dr. B. Lee in Prof. McGrath’s research group at VPI&SU.

In the free radical synthesized PDMS-PS block polymers, the molecular weight (MW) and the molecular weight distribution (MWD) of the PS blocks varied with the PDMS block length (block MW) comprising the macroinitiators, and the styrene conversion level. As the PDMS block length or the conversion level increased, the average PS block MW increased, and the molecular weight distribution of the PS block became broader. Multi-modal molecular weight distribution of the PS blocks was observed on the high conversion polymers with large PDMS blocks. As the MW and the MWD of the PS blocks changed, the morphology, the degree of phase mixing, and bulk properties of these PDMS-PS block polymers were altered as expected.

At constant conversion level, the morphology of these block polymers changed from spherical PS domains in the PDMS matrix to a lamellar structure as the PDMS block length increased. As expected, their mechanical properties were also changed as morphology varied. At constant PDMS content, the systems with shorter PDMS blocks displayed elastomeric properties, while the polymers having large PDMS blocks behaved like a plastic due to a continuous lamellar morphology. The degree of phase mixing also decreased with an increase of the PS block length because of the increased incompatibility between the two block components. For a constant PDMS block length, the PS block length increased and the MWD of the PS blocks became broader when the styrene conversion level increased. Consequently, the morphology, the degree of phase mixing as well as the bulk properties of the block polymer also varied with conversion level.

Addressing the segmented PTMO based ionene elastomers, these materials displayed excellent elastomeric properties which result from the ion clustering or ionic domain formation in a continuous PTMO matrix. The morphology and bulk properties of these ionene systems were strongly dependent on the strength of ionic association. By varying the ion content, the type of counter ion, or hard segment, the ionic association was changed. Therefore, the morphology and the bulk properties were also altered. Morphological textures of these ionene systems were studied by Transmission Electron Microscopy (TEM) and Small Angle X-ray Scattering (SAXS). Due to the strong ion clustering, an ionene rod-like morphology was observed in the PTMO-dihalide ionene elastomers by both TEM and SAXS at low volume fraction of ionene content (<7 vol%). It is the first time that these two analytical methods have distinctly led to the same end result for any ionomer system! This morphological structure is not predicted by any of existing theories of ion clustering in ionomers nor the classical theories of block/segmented polymers. Finally, the morphology of these ionene systems was altered with ion content. When the ion content was decreased by increasing the PTMO segment length, the long-range ordered structure disappeared as well as the rod-like microphase structure.

A very unique phenomenon, a highly reversible modulus "jump" with increasing temperature, has been observed for these ionene materials which has not been reported before. This "jump" is directly related to the ion content, type of counter ion and the hard segment. Based on experimental evidence, the "jump" is tentatively speculated to be caused by a conformational change in the ionene hard segments. However, further investigations are needed to support or disprove this speculation.