While the crystal thickness and melting point in crystallizable homopolymers are kinetically controlled, an equilibrium degree of chain folding is predicted for crystalline-amorphous block copolymers. We demonstrate this effect in a series of diblock copolymers of hydrogenated polynorbornene and hydrogenated poly(ethylidene norbornene), hPN/hPEN, where the hPN block is induced to fold as many as four times by the attachment of progressively longer amorphous blocks. These diblocks all crystallize from homogeneous melts, permitting the equilibrium solid-state structure to be approached. Increased chain folding produces thinner crystals with lower melting points; these stable melting points can be reproducibly tuned over a 30°C range through the choice of the amorphous block length. Finally, the end group on the hPN chain is shown to influence the melting point as well through its impact on the crystal surface energy.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry