Effect of molecular weight and branch structure on the crystallization and rheological properties of poly(butylene adipate)

Abstract

High molecular weight linear and branched poly(butylene adipate)s (PBAs) were prepared, and crystallization behavior and rheological properties were investigated. PBAs showed multiple melting behavior. Increasing molecular weight retarded the crystallization rate and increased the induction time for crystallization. Introducing branches to the polymer led to similar results. The Avrami exponent (n) for the linear and branched PBAs were 3.79-4.39 and 2.09-3.64, respectively. The Mark-Houwink exponent of the PBAs was 0.554. Unlike general-purpose polyesters, high molecular weight PBAs did not exhibit a Newtonian flow region. High molecular weight PBAs exhibited gel-like rheological properties, producing high elasticity. The slopes of a log-log plot of storage modulus (G′) vs. loss modulus (G″) ranged from 1.75 to 1.17, and the slope decreased with increasing molecular weight. For comparable molecular weights, the branched PBAs had higher viscosity and G′ than the linear polymers.