|M.Sc Student||Mahroum-Waked Riham|
|Subject||Synthesis of Porous Simultaneous Interpenetrating Polymer|
Networks through Emulsion Templating
|Department||Department of Materials Science and Engineering||Supervisor||Professor Michael Silverstein|
|Full Thesis text|
PolyHIPEs (PHs) are emulsion-templated polymers synthesized within high internal phase emulsions (HIPEs), emulsion containing over 74% internal phase. PHs are usually synthesized through free radical polymerization (FRP), although biodegradable poly(urethane urea) (PUU) PHs based on polycaprolactone (PCL) oligomers have been successfully synthesized through step-growth polymerization (SGP). Interpenetrating polymer networks (IPNs) are two chemically distinct polymer networks that are physically intertwined at the molecular level, but are not covalently connected. Semi-IPNs consist of one crosslinked polymer while the other is linear. There are two basic methods of synthesizing IPNs, sequential polymerization and simultaneous polymerization. IPN-PHs have not been investigated in depth. There have been some sequential IPN-PHs combining low glass transition temperature (Tg) polymers and high Tg polymers via FRP, but only one article has reported successful synthesis of a simultaneous IPN-PH combining a rigid styrene-based polymer and a soft polyurethane (PUR).
The main objective of this study was to design and synthesize IPN-PHs and semi-IPN-PHs that combine two chemically and functionally distinct soft polymers by employing simultaneous polymerizations. One polymer was a PUU, using various PCLs, that was synthesized using SGP, while the other polymer was a crosslinked polyacrylate, using various acrylates, that was synthesized using FRP.
The composition of ̴ 58% PUU exhibited the lowest density in both the IPN-PHs and the semi-IPN-PHs. The porous structures of the IPN-PHs and semi-IPN-PHs were different from those of the reference PHs containing only one polymer. Unexpectedly, the reference PUU based on a PCL triol (PUU-T) exhibited an unusually low gel content (GC) of 9% similar to that of the reference PUU based on a PCL diol (PUU-D). Adding the FRP initiator potassium peroxodisulfate to the HIPE used to synthesize the PUU-T produced an increase in its GC from 9 to 37%, but did not significantly affect the GC of the PUU-D. All the IPN-PHs and semi-IPN-PHs exhibited a single tan peak, indicating that no macro-phase separation occurred. The tan peak width decreased with increasing PUU-T and PUU-D contents, reflecting mixing of the two polymers at the macromolecular scale with some structural heterogeneity as compared to the PUU reference PHs. The IPN-PHs exhibited one major degradation peak between those of the reference PHs, reflecting the formation of an IPN with molecular-scale mixing. The semi-IPN-PHs exhibited two major degradation peaks, one associated with PUU-D and the other associated with the P(EHA-co-DVB) reference PH (PxA), reflecting a more phase-separated structure. Replacing the PCL diol of 530 g/mol with one of 2000 g/mol resulted in a higher density, a smaller void size, and a higher degree of crystallinity. The use of a longer acrylate side chain reduced the macromolecular mobility within the semi-IPN-PHs. In this work, for the first time, IPN-PHs and semi-IPN-PHs were successfully synthesized, for the first time, through the simultaneous synthesis of soft PUUs using SGP and soft, crosslinked polyacrylates using FRP, with the morphology, thermal properties, and mechanical properties modified through the choice of the components and compositions.