Polyimides
Second type of endgroup crosslinking has acetylene endgroups and is called Thermid 600
- Crosslinking in Fig 2-7
- First step: joining two polyimid oligomers to form a butadiene linkage which results in chain extension. Each double bond can react with double or triple bonds to form highly crosslinked.
- Addition reaction
- Problems is with too fast a cure and chain extension competing with cross-linking mechanism thus causing MW to build too fast.
- Alleviated with proper solvents.
- Disadvantage is the loss of tackiness in prepregs as the solvent evaporates.