A Biodegradable and Cross-Linkable Multiblock Copolymer Consisting of Poly(propylene fumarate) and Poly(ε-caprolactone):  Synthesis, Characterization, and Physical Properties

In an effort to develop various controllable biomaterials, a series of novel cross-linkable and biodegradable multiblock poly(propylene fumarate-co-caprolactone) [P(PF-co-CL)] copolymers have been synthesized via a three-step polycondensation of oligomeric polypropylene fumarate (PPF) with polycaprolactone (PCL) diols. The chemical structures of 15 copolymers with various PCL compositions and segment lengths were further characterized by FTIR, 1H NMR, and 13C NMR spectra. Their physical and rheological properties have been determined extensively. The composition dependences of various characteristic temperatures such as glass transition temperature Tg, melting temperature Tm, and thermal degradation temperature Td were demonstrated using a phase diagram. Together with DSC results, polarized optical microscopical graphs of several copolymers with high PCL compositions show spherulite crystalline structure. Particularly a banded spherulite has been found for a copolymer with a PCL composition of 87% when it crystallizes at room temperature. When the PCL composition in these copolymers is lower than 70%, the copolymers are amorphous with a reduced Tg. This is critical for an enhanced rate of biodegradation. Because of the flexibility of PCL segments in the copolymers, P(PF-co-CL) can be either self-cross-linked or photocross-linked without using any cross-linker. The unentangled characteristics have been verified by the melt viscosity's molecular weight dependence and the master curves of storage modulus G? and loss modulus G???. The introduction of PCL into the copolymer chain enhances the solubility in toluene. Dilute solution viscometry shows the effect of microstructure in intrinsic viscosity while this effect is insignificant in melt viscosity. Therefore, the physical properties of such a copolymer can be modulated by the composition and segment length to satisfy the needs in a variety of tissue engineering applications such as bone, cartilage, and nerve tube regenerations. In an effort to develop various controllable biomaterials, a series of novel cross-linkable and biodegradable multiblock poly(propylene fumarate-co-caprolactone) [P(PF-co-CL)] copolymers have been synthesized via a three-step polycondensation of oligomeric polypropylene fumarate (PPF) with polycaprolactone (PCL) diols. The chemical structures of 15 copolymers with various PCL compositions and segment lengths were further characterized by FTIR, 1H NMR, and 13C NMR spectra. Their physical and rheological properties have been determined extensively. The composition dependences of various characteristic temperatures such as glass transition temperature Tg, melting temperature Tm, and thermal degradation temperature Td were demonstrated using a phase diagram. Together with DSC results, polarized optical microscopical graphs of several copolymers with high PCL compositions show spherulite crystalline structure. Particularly a banded spherulite has been found for a copolymer with a PCL composition of 87% when it crystallizes at room temperature. When the PCL composition in these copolymers is lower than 70%, the copolymers are amorphous with a reduced Tg. This is critical for an enhanced rate of biodegradation. Because of the flexibility of PCL segments in the copolymers, P(PF-co-CL) can be either self-cross-linked or photocross-linked without using any cross-linker. The unentangled characteristics have been verified by the melt viscosity's molecular weight dependence and the master curves of storage modulus G? and loss modulus G???. The introduction of PCL into the copolymer chain enhances the solubility in toluene. Dilute solution viscometry shows the effect of microstructure in intrinsic viscosity while this effect is insignificant in melt viscosity. Therefore, the physical properties of such a copolymer can be modulated by the composition and segment length to satisfy the needs in a variety of tissue engineering applications such as bone, cartilage, and nerve tube regenerations.