Photopolymerization of reactive mesogens

The photopolymerization of two reactive mesogens with photopolymerizable acrylate endgroups, the methyl substituted 1,4-phenylene-bis{4-[6-(acryloyloxy) hexyloxy]benzoate} 1 and acrylic acid 6-{4-[6-(6-acryloy-loxyhexyloxy) naphthalen-2-yl]-phenoxy}hexyl ester 2 has been investigated using Photo-DSC measurements. Photocrosslinking of 1 in the nematic phase at 100°C leads to a final conversion of 87% of the acrylate groups. It is possible to perform photopolymerization with very small amounts of photoinitiator. Even with 0.001% (10 ppm) of photoinitiator, 47% of the acrylate groups polymerize within 15 min. The polymerization of the reactive mesogen 2 proceeds faster in the smectic A phase at 100°C compared to the isotropic phase at 120°C and leads to a higher conversion of 75%. This can be explained by an increased local concentration of the acrylate groups between the layers of the smectic cores.