Abstract
In this paper the preparation and detailed characterization of designed polyurethanes (SPURs) are reported for potential biological, biomedical and/or pharmaceutical applications. Importantly, in order to fulfill these goals all reactants and solvents used were selected according to the proposal of EUR-8 Pharmacopoeia. For the synthesis, a novel strategy was introduced and elaborated. A series of SPUR samples was prepared from poly(ε-caprolactone)-diol, 1,6-hexamethylene diisocyanate and sucrose as a chain extender/crosslinking agent to obtain sucrose containing polyurethanes. In addition, the mol ratios of the sucrose were varied within an order of magnitude. The prepolymers and the products of the syntheses were investigated by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and infrared spectroscopy (IR), respectively. It was found that the reactivity of the eight free hydroxyl groups of sucrose are different, and after curing the SPUR samples at 60 °C no free isocyanate groups can be observed. Furthermore, swelling experiments performed with various solvents of different polarities revealed that the highest degree of swelling took place in dimethyl-sulfoxide. However, low degrees of swelling were recognized in water and hexane. It is important to note that the gel contents were around 90% in all cases, which demonstrate that the crosslinking was almost complete. In addition, the kinetics of swelling were also evaluated and successfully modeled. The crosslink densities were calculated from the data of the swelling experiments by means of the Flory-Rehner equation. Unexpectedly, it was found that the crosslink density decreased with the increasing sucrose content also in line with the results obtained by relaxation modulus experiments and dynamic mechanical analysis (DMA). The Tg and Tm of SPUR samples, determined from DSC and DMA measurements, were around −57 °C and 27 °C, respectively. According to the mechanical tests the SPUR samples showed high elongation at break values, i.e., high flexibilities. Furthermore, the stress-strain curves were also modeled and discussed.
Highlights
The last few decades have witnessed an unprecedented increase in human life expectancy and life quality
We report a one pot synthesis and detailed characterization of biocompatible and completely biodegradable PUR networks synthesized from PCLD/hexamethylene diisocyanate (HDI)/sucrose systems
For the synthesis we worked out a novel synthetic strategy: first, a macro diisocyanates was prepared from PCLD and HDI in melt
Summary
The last few decades have witnessed an unprecedented increase in human life expectancy and life quality. The certain mechanical and structural properties the tissues require for proper functioning are to be provided by biocompatible synthetic polymers, such as poly(ε-caprolactone), polyurethanes and polylactic acid, since through macromolecular engineering their properties can be tailored and fine-tuned more precisely than those of natural polymers [1]. Poly(ε-caprolactones) (PCLs) are useful biomaterials whose utilities span from as materials for biomedical devices to food packaging applications. The Food and Drug Administration (FDA) has approved PCLs for specific human applications. FDA allowed their use in long term implantable devices, absorbable sutures and in certain drug delivery systems. There are some shortcomings with PCLs, such as their low degradation rates and poor mechanical properties, which are not beneficial for their special applications, e.g., for tissue engineering [2,3,4]
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