The high strength, resistance and durability of composite materials mean that they are widely used for many different applications; however, it is these same properties which make their disposal challenging. The focus of this talk will be on the development of new materials which, when exposed to a specific external trigger, are able to easily break their covalent crosslinks. Inclusion of reversible crosslinks within a resin or adhesive would allow for the mechanical advantages of a thermoset material to be exploited, while maintaining the beneficial melt properties of a thermoplastic. Initial work has been carried out on the synthesis of polyurethanes (PUs), containing photo-sensitive dimethanol derivatives of nitro-benzene. Photo-degradation of groups within the backbone of the polymer can result in cleavage of covalent bonds and reduction in molecular weight, as demonstrated in figure 1. Each nitro-diol was analysed in comparison to the non-nitro analogue as a control. The polymers were characterised using a range of techniques including UV-vis spectroscopy, 1H-NMR, GPC, TGA and DSC. All analysis was carried out on samples before and after exposure to 142 mWcm-2 UV light. The mechanical properties of the materials were also analysed before and after exposure to UV light by lap shear and T-peel testing and rheological analysis. Analysis shows that chain extended PUs have successfully been synthesised. These displayed a significant reduction in molecular weight and loss of the urethane linkage after UV exposure at 142 mWcm-1. Polymers containing non-nitro analogues did not show any degradation. This implies that photo-degradation of the polymers is initiated from the nitro group.

Synthesis and analysis of photodegradable polyurethanes with poly (propylene glycol) and nitro-benzene derivatives

2019 Fall National Meeting

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