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Cross-linking a range of alkyl polymers
Some alkyl polymers, such as polyethylene, can be cross-linked by using peroxides or high-energy radiation or through the addition of a radical forming agent. Others, like polypropylene, are likely to undergo chain scission, and this process tends to be uncontrolled in the distribution of the cross-links. Lepage et al. developed a widely applicable approach using bis-diazirine molecules as cross-linking agents (see the Perspective by de Zwart et al.). These molecules can be thermally or photochemically activated to form carbenes that readily insert into the polymer carbon-hydrogen bonds, thus leading to cross-linking. The bis-diazirine is nonexplosive, nonvolatile, and easily activated at relatively mild temperatures and thus could be used to fine-tune the properties of existing polymers through small chemical modifications.
Abstract
Addition of molecular cross-links to polymers increases mechanical strength and improves corrosion resistance. However, it remains challenging to install cross-links in low-functionality macromolecules in a well-controlled manner. Typically, high-energy processes are required to generate highly reactive radicals in situ, allowing only limited control over the degree and type of cross-link. We rationally designed a bis-diazirine molecule whose decomposition into carbenes under mild and controllable conditions enables the cross-linking of essentially any organic polymer through double C–H activation. The utility of this molecule as a cross-linker was demonstrated for several diverse polymer substrates (including polypropylene, a low-functionality polymer of long-standing challenge to the field) and in applications including adhesion of low–surface-energy materials and the strengthening of polyethylene fabric.
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