Researchers from the Massachusetts Institute of Technology (MIT) have experimentally demonstrated that by adding cleavable bonds to the polymer chains (or strands) of covalently crosslinked thermoset plastics can potentially make thermosets recyclable and degradable. Existing strategies to make thermosets with recyclability include dynamic covalent bond exchange, thermomechanical degradation and replacement of the network components with degradable analogues. These methods can degrade the thermoset plastics indiscriminately (or uncontrollably) which can produce products of many types (i.e., broad product distribution) with broad molecular weight distribution.
Model polymer used in the experiments was polydicyclopentadiene (pDCPD). Cleavable groups used were silyl ethers. According to the authors, it is the location of the cleavable bond which controls the degradation process and the product distribution obtained by it. If the cleavable bond is located on the polymer backbone or strand the thermoset degradation can be triggered at mild conditions with low co-monomer (i.e., silyl ether) content. In contrast, if the cleavable group is located within the crosslink of a thermoset the degradation of the plastic is difficult to achieve practically even at very high loading of the co-monomer.
The authors also suggested that low cost of silyl ether co-monomers can also make this strategy economically viable if applied on a large scale e.g., the existing processing units of polydicyclopentadiene can use such comonomers as the additives.
This research has been published in the journal Nature. Click here to go to article.