Macrocyclic Monomers: Synthesis, Characterization and Ring-opening Polymerization
Interest in macrocyclic monomers can be dated back to the 1960's. The recent surge of research activities in this area is prompted by two facts: the encouraging discovery of high yield synthesis and facile ring-opening polymerization of cyclic polycarbonate; the need for a technique to solve the tough processibility problem of high performance polymers. This work was intended to address the following aspects in the cyclic poly(ether ketone) or sulfone system. The first goal was to understand the structure-property relationship of this type of macrocycles. A large number of macrocycles were synthesized by nucleophilic aromatic substitution cyclization reactions under pseudo-high dilution conditions. Pure individual macrocycles as well as cyclic mixtures were characterized by NMR, HPLC, GPC, FABMS, MALDI-TOF-MS, DSC and TGA. Comparison study suggests that the cyclic distribution is kinetically controlled. Several factors determine the melting points of individual macrocycles. The first factor is the ring size. A series of cyclic monomers for poly(ether ether ketone)s were synthesized and isolated. The melting point decreases as ring size increases. Single crystal X-ray structural results suggest that this phenomenon is related to the increased flexibility of the larger sized macrocycles. The second factor is the functional groups of the macrocycles. X-ray structural and GPC experiments reveal that the sulfone group is more rigid than the ketone group, than ether group. The effect of functional groups on melting point is in the order sulfone>ketone>ether. A third factor is the symmetry of the macrocycles. Breaking the symmetry of macrocycle through comacrocyclization dramatically decreases the melting point of individual macrocycles as well as the cyclic mixture as a whole. Based on these findings, a novel two step method was developed to control the ring size distribution, which effectively reduced the amount of the small sized macrocycle and decreased the melting point. In addition to the nucleophilic aromatic substitution cyclization, it was also demonstrated in this work that macrocycles can be synthesized by Friedel-Crafts acylation cyclization. However, this method is limited by the solubility problem. The ring-opening polymerization of macrocyclic monomers was systematically studied. Several factors were considered in this study: the nature and amount of catalyst, temperature and time. CsF; metallic phenolate and Na2S are good initiators. Conversion to near 100 % is possible under the controlled polymerization conditions. It was found that crosslinking is an inherent phenomenon. The molecular weight of the soluble fraction near complete conversion is almost independent of initiator and polymerization temperature. It is limited by the crosslinking reaction. It is demonstrated for the first time that the macrocyclic monomer techniques can be applied to more valuable semicrystalline systems. Tough polymers such as high performance poly(ether ether ketone)s were produced through ring-opening polymerization. The last chapter is devoted to the challenging synthesis of monodisperse poly(ether ether ketone)s. A convergent strategy was devised. A monofluoroaryl compound was synthesized by Friedel-crafts acylation reaction. The final monodisperse linear oligomers were generated by reacting the monofunctional compound with a bisphenol through a quantitative reaction.
- Doctoral Dissertations