Semi-crystalline PMMA Stereocomplex Fibers*

A mixture of isotactic and syndiotactic PMMA polymers forms a supramolecular helical structure, called ``stereocomplex'' PMMA, which is held together by non-covalent bonding. The helices can pack together, resulting in a semi-crystalline material with a melting point of 172$^{o}$C. Furthermore, the solutions exhibit gelation behavior in appropriate solvents. We have utilized these properties to make oriented stereocomplex PMMA fibers by three different methods -- wet spinning, gel spinning and electrospinning. These fibers are highly oriented and crystalline. They are resistant to high temperatures up to 160$^{\circ}$C. They are also resistant to the PMMA polymerization conditions. We have examined the fibers using X-ray diffraction and Raman spectroscopy. The results agree with the recently proposed triple helical structure where two isotactic PMMA chains wrap around each other in a double helix and then the syndiotactic chain wraps around this double helix. The resulting structure is a triple helix with a 1:2 molar ratio of isotactic : syndiotactic PMMA.