Masters of Engineering (Research)
School of Mechanical, Materials and Mechatronic Engineering
Sadegholvaad, Sasha, Properties of hydrogels prepared with different chain length distribution, Masters of Engineering (Research) thesis, School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, 2013. http://ro.uow.edu.au/theses/4168
Tough (the ability to withstand cracking under an applied stress/load) hydrogels are being developed for many applications because of their significant advantages such as fairly easy synthesis process and useful properties (such as soft and wet character) as well as their capability to bear high mechanical loads . It is always essential and challenging to find a proficient method to synthesise tough hydrogels. A few types of tough hydrogels have been introduced in the last decade, namely topological gels by Okumura and Ito , nanocomposite hydrogels by Haraguchi and Takehisa  and double network hydrogels by Gong et al , which all display advanced mechanical properties for different reasons.
Bimodal elastomers are another example of such tough networks which were the subject of extensive studies in 1980’s . Bimodal networks are in fact interpenetrating networks that share the same composition, but have different network strand lengths. These networks are usually formed by end-linking reactions and show enhanced mechanical properties compared to end-linking samples of the same networks with unimodal distributions of network chain length . Bimodal polymeric networks made of poly(dimethylsiloxane) and also poly(oxyethylene) were introduced by Sun and Mark as unusually tough networks . There is also an example of utilizing this system in order to make tougher hydrogels, recently studied by the same group . Poly(3-hydroxybutyrate-co- 3-hydroxyhexanoate) was used with a number of different nano–fillers (clay, mica, talc and expanded graphite) to synthesise nanocomposites using solution mixing and melt blending methods. Additionally, glycerol-derived alkyd resins also were prepared by melt blending the resin precursors with organoclays. Both of the aforementioned bimodal hydrogels showed highly improved mechanical properties even at very low loadings of filler . However, no study has been conducted on the effect of molecular weight distribution on the mechanical properties of a bimodal hydrogel.
This thesis aims to compare the mechanical properties of the hydrogel networks made of polyetheramine (Jeffamine) and poly(ethylene glycol) diglycidyl ether (PEGDE) with different molecular weights via mechanical testing methods such as tensile and tear testing. The results will provide a better understanding of how molecular weight or strand length distribution affects the mechanical properties of jeffamine-PEGDE hydrogel networks. Hydrogels prepared using free radical reactions of water-soluble vinyl monomers give a random distribution of crosslink lengths and are, therefore, difficult to control the crosslink distribution. End linking pre-polymerisation was chosen as an alternative system to allow better control of the crosslink lengths.