Bone-Tissue-Engineering Material Poly(propylene fumarate):  Correlation between Molecular Weight, Chain Dimensions, 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 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 r 0 2/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.