Macrocyclic polymers from cyclic oligomers of poly(butylene terephthalate)

This thesis describes the synthesis, polymerization, and characterization of poly(butylene terephthalate) (PBT) polymers as produced from cyclic oligomers of PBT using a stannoxane cyclic initiator. The properties of the resulting macrocyclic PBT polymer are compared to the properties of four commercial linear PBTs, covering the range of molecular weights for commercial polymers. The macrocyclic polymers are found to have unique properties in both the melt and the solid state. In the melt, the macrocyclic polymers are found to have significantly lower viscosities vs. the linear resins at equivalent molecular weight. The results reported herein show differences in the zero shear viscosity of macrocyclic and linear PBT melts at equivalent molecular weight that are much larger than the differences reported in the literature between macrocyclic and linear polystyrene melts. It is believed that the unique ring expansion polymerization used in this research has resulted in producing simpler cyclic molecules, having no catenation or knotting, than have been reported elsewhere. When crystallized, these cyclic molecules produce a semi-crystalline spherulitic structure. The spherulite formed is unique in that it is highly nucleated, rapidly crystallized, and found to be the same spherulitic form only previously reported as being produced by slow cooling or solvent crystallization processes. The crystalline structure from these macrocyclic molecules is believed to have a lower intercrystalline tie chain density than found in melt cooled linear PBTs. This macrocyclic polymer, produced from cyclic oligomers, is proposed as being capable of being used as a thermoplastic composite resin, with sufficiently low viscosity in the oligomeric state, and sufficiently high polymerization and crystallization rates, that a melt process is feasible. While being very brittle, the fracture toughness of cyclic PBT is found to increase when the macrocyclic structure is degraded, increasing by three times within ten minutes of thermal degradation in the melt. A new initiator is proposed in the thesis, capable of producing linear PBT from cyclic oligomers with the same reaction kinetics as the stannoxane initiator. Such a system is expected to be as tough as high molecular linear PBT, and have the chemical and heat resistant characteristics necessary for a new thermoplastic composite resin