Bone-tissue-engineering material poly(propylene fumarate): Correlation between molecular weight, chain dimension, and physical properties

Poly(propylene fumarate) (PPF) is an important biodegradable and cross-linkable polymer designed for bone-tissue-engineering applications. For the first time we report the extensive characterization of this biomaterial including molecular weight dependences of physical properties such as glass transition temperature T_g, thermal degradation temperature T_d, density ρ, melt viscosity η₀, hydrodynamic radius R_H, and intrinsic viscosity [η]. The temperature dependence of η₀ changes progressively with molecular weight, whereas it can be unified when the temperature is normalized to T_g. The plateau modulus G_N⁰, and entanglement molecular weight M_e, have been obtained from the rheological master curves. A variety of chain microstructure parameters such as the Mark-Houwink-Sakurada constants K and α, characteristic ratio C_∞, unperturbed chain dimension r₀²/M, packing length p, Kuhn length b, and tube diameter a have been deduced. Further correlation between the microstructure and macroscopic physical properties has been discussed in light of recent progress in polymer dynamics to supply a better understanding about this unsaturated polyester to advance its biomedical uses. The molecular weight dependence of T_g for six polymer species including PPF has been summarized to support that M_e, is irrelevant for the finite length effect on the glass transition, whereas surprisingly these polymers can be divided into two groups when their normalized T_g is plotted simply against M_w, to indicate the deciding roles of inherent chain properties such as chain fragility, intermolecular cooperativity, and chain end mobility.