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Modification, characterization and application of hyperbranched polyarylates

Bodan Ma, University of Massachusetts Amherst


Hyperbranched polymers are polymers with highly branched, yet non-crosslinked structures. In this work, the existing laboratory polymerization procedure was scaled up by a suspension method to synthesize hyperbranched poly(5-acetoxy isophthalic acid) of high molecular weight. A method of modifying the residual acyl groups of this polymer with different reagents was also established. Especially, the synthesis of monofunctional etherimide facilitated the compatiblization of the hyperbranched polyarylate with commercial polyetherimide. All modified polymers were characterized by FTIR, $\sp1$H and $\sp{13}$C NMR, elemental analysis and DSC. Through this modification route, hyperbranched polymers with glass transition temperatures ranging from $-$50$\sp\circ$C to 188$\sp\circ$C were prepared. Using fractionation techniques, samples with different molecular weights were obtained. The structural profiles of hyperbranched polyarylate were then investigated. The measurement of the degree of branching indicated that these macromolecules had uniform chemical structures. Solution static light scattering revealed that the hyperbranch polyarylates had very compact structures, the dimension of which remained stable regardless of different polymer-solvent interactions. Light scattering, NMR with LSR (Lanthanide Shift Reagent) as well as molecular simulation showed that molecules such as LSR $\rm(d\sim10$ A) and solvent could penetrate most part of the structure. Thus, these molecules should be treated as hard porous particles with small pore sizes. n$\sp\prime$-Butyl hyperbranched polyarylate and its linear analog poly(1,4-butylene isophthalate) were employed to investigate the effect of hyperbranching topology on blend properties. Under all experimental conditions, including a wide range of annealing temperature, molecular weight and blend composition, the blends were found always immiscible by the observation of glass transitions using DSC. Entropically, the compact nature of the hyperbranched polymer prevented itself from mixing with its linear analog at segmental scale. However, TEM revealed that the domain size of the phase separation was around 400 to 600A, indicating good compatibility. A modified Flory-Huggins theory was introduced to explain the immiscibility. The rheological properties of hyperbranched polymer and its blends presented the most promising aspect for future applications. The relaxation spectrum of hyperbranched polyarylate did not exhibit a plateau zone that is an indication of chain entanglement for linear polymers. This observation was true even for samples with molecular weight over 10$\sp5$. Zero shear viscosity of hyperbranched polyarylate was generally one magnitude lower than that of its linear analog with comparable molecular weight. Furthermore, the viscosities of their blends showed negative deviations from the so-called "log-additivity rule". This finding showed a true opportunity for hyperbranched Folymers to be used as rheology modifiers. Finally, the mechanical property of blends of etherimide modified hyperbranched polyarylate and polyetherimide was investigated. While the tensile modulus of the material was enhanced, the toughness was drastically reduced due to the lack of entanglement between the macromolecules. Possible methods for improving this drawback were proposed.

Subject Area


Recommended Citation

Ma, Bodan, "Modification, characterization and application of hyperbranched polyarylates" (1997). Doctoral Dissertations Available from Proquest. AAI9737555.