The drive towards producing polymers from renewable sources has become more prevalent in recent years. Currently, petroleum based polymers account for around 99% of the global polymer market. The rapid depletion of fossil fuels and their associated environmental impact requires this figure to be significantly reduced. Terpenes are naturally abundant renewable hydrocarbons sourced from waste streams. The direct polymerisation of terpenes has been widely studied due to the presence of endo and exo cyclic double bonds. Terpenes, however, do not readily undergo free radical polymerisation even in the presence of comonomers. Research carried out in the group has seen the development of new (meth)acrylate based monomers directly derived from terpenes (Fig 1a). Preliminary results showed that these monomers readily polymerise via free radical polymerisation producing polymers with a range of physical properties. Most significantly Tgs as high as 165°C for poly(α-pinene methacrylate) (α-PMA) were observed, rivalling those observed for petroleum based polymers. Due to these observed high Tgs, PαPMA was deemed the most interesting to further investigate, due to the potential for replacing petroleum based monomers in industrial applications. Preliminary experiments of the free radical polymerisation of αPMA, not in the presence of a chain transfer agent, resulted in an insoluble crosslinked polymer. This was surprising due to the absence of any crosslinking agent or crosslinkable double bonds upon the pendant group. We propose the source of this crosslinking is due to hydrogen abstraction upon the pendant group, which in turn could cause the rearrangement of α-pinene to produce a new propagating radical. The source of this crosslinking has been investigated using electron paramagnetic resonance (EPR) and solid-state NMR. PolyHIPEs (high internal phase emulsion) are porous emulsion-templated polymers, which are synthesized within the HIPE. PolyHIPEs are generally synthesized in the presence of a crosslinking agent to increase stability. The exploitation of αPMA’s crosslinking to produce the first renewable methacrylate based PolyHIPE is also described. To the best of our knowledge, this is the first time chain transfer to the pendant group, upon acrylates or methacrylates, has been reported, and self-crosslinking via hydrogen abstraction has been utilized for the formation of polyHIPEs.

Exploiting the hydrogen abstraction driven crosslinking of poly(α-pinene methacrylate) for the production of renewable polyHIPES

2019 Spring National Meeting

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