Using branching and endgroups to control the physical properties of macromolecules: Systematic studies of etherimide polymers

In an attempt to relate molecular architecture to physical properties, a series of AB/AB₂ copolymers was prepared from mixtures of AB and AB₂ type monomers ranging in composition from 0 to 1 mole fraction of AB monomer content (x_AB). The preparations resulted in a series of high molecular weight hyperbranched polyetherimides with degrees of branching (DB) between 0 and 0.66. This polymer series was tested for solubility, viscosity, thermal stability, and film formability to establish a correlation with molecular architecture. It was found that the whole series was quite thermally stable with 10% weight loss above 400°C; however, the solubility, viscosity, and film formability changed in a non-linear fashion as x_AB increased in the series. It was postulated that these property changes were a result of the decreasing DB. An attempt to directly measure the DB of this series of polymers was unsuccessful due to aggregation in the 1H NMR which obscured necessary signals. To indirectly measure the DB of the entire series, a reaction scheme was devised using non-polymerizable small molecules that contained A, B, or B₂ functionalities for (A+B)/(A+B₂) reaction. The resulting products of such scheme represented the linear and dendritic connectivities in the AB/AB₂ polymer products. By careful control of stoichiometry and reaction conditions (to mimic polymerization conditions), the model compounds representing polymer units were produced and their ratios monitored by 1H NMR and/or HPLC to indirectly determine DB. In the reactions, the compound with the A unit was consumed in under 2.5 minutes (i.e., p_A = 1 at 2.5 min) and no detectable side products were observed. Excellent agreement in DB was observed for copolymer compositions that could be measured and the corresponding model reactions. This validated the indirect method for measuring DB in this series of AB/AB₂ etherimide copolymers. Subsequent experiments showed that physical properties such as viscosity and film formability did not correlate well with the DB but it was shown that the average linear distance between branch points (L_AB) was a better predictor for these properties.; To survey the effect that end-group composition and constitution have on macromolecular physical properties, end-group modified hyperbranched polyetherimides were prepared by a one-pot, two-step reaction sequence. General synthetic techniques were developed to prepare both mono-functional terminating segments and the corresponding modified polyetherimide hyperbranched polymers. Mono-functional groups were used to terminate an AB₂-type polycondensation reaction, generating capped hyperbranched polymers (HBPs). The composition and constitution of the end groups controlled the solubility and thermal properties of the HBPs. For the same polymer backbone, different end groups were able to shift the glass-transition temperature nearly 100°C. End-group modification also greatly influenced the film-forming ability of the HBPs.