A structural reconsideration: Linear aliphatic or alicyclic hard segments for biodegradable thermoplastic polyurethanes?

Abstract

Thermoplastic polyurethane elastomers (TPUs) with a biodegradable chain extender and different nonaromatic diisocyanate hard segments were synthesized and tested concerning their thermal, mechanical, and degradation properties and for their processability regarding electrospinning. The design of the TPUs was based on the structural modification of the hard segment using linear aliphatic hexamethylene diisocyanate (HMDI), more rigid alicyclic 4,4′‐methylene bis(cyclohexylisocyanate) (H12MDI), 1,3‐bis(isocyanatomethyl)cyclohexane (BIMC), or isophorone diisocyanate (IPDI). The soft segment consisted of poly(tetrahydrofuran). Bis(2‐hydroxyethyl) terephthalate (BET) was used as chain extender with cleavable ester bonds. Some of the polyurethanes based on alicyclic diisocyanate showed better mechanical performance than the less rigid HMDI‐based TPU. The TPU in vitro degradability was tested for 25 days at elevated temperatures in PBS buffer and indicated a bulk erosion process. Electrospinning experiments were conducted and promising results with respect to further applicability of these materials in vascular tissue engineering were obtained. © 2018 The Authors Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2214–2224

Studying a Flexible Polyurethane Elastomer with Improved Impact-Resistant Performance

“…The structure of the aliphatic, aromatic, and/or ester ring group is in an isocyanate monomer. The hard segments (HS) are composed of isocyanates and chain extenders, which form stiff urethane units, and soft segments (SS) are based on aliphatic polyethers, polyesters, or polydimethylsiloxanes, named as macrodiols [20,21,22,23].…”

State of the Art of Small‐Diameter Vessel‐Polyurethane Substitutes

“…As for the dominant component of PESU hard‐segment domain, isocyanate compounds exert an influence on PESU degradation first through the chemical structure. Generally speaking, PESU synthesized from aliphatic isocyanates (such as HDI) is more resistant than that from aromatic isocyanates (such as MDI) because the aliphatic chain is more flexible and easy to rearrange to form intermolecular hydrogen bonding . The increased density of cross‐linking points due to increasing isocyanate content would also result in the formation of more stable and compact network structure of PESU, which prevents water penetration of the bulk PU substance and blocks the reaction of ester groups with water.…”

Influence of microfibrillated cellulose and soft biocomponent on the morphology and thermal properties of thermoplastic polyurethanes

“…Currently studied biodegradable polymers do not meet all the requirements of biomedical and packaging applications, showing high brittleness or poor thermal and barrier properties 1–5 . Due to their tunable mechanical and degradation properties, thermoplastic polyurethanes (TPUs) are suitable for these applications 6–9 . TPUs with a wide range of physical–chemical and degradation properties may be obtained by varying not only the composition, molecular mass or the ratio between hard and soft segments but also synthesis and processing conditions, chemical structure and intermolecular interactions between segments 8 .…”

“…Aliphatic diisocyanates are preferred as hard segments in TPUs because the degradation of aromatic diisocyanates results in toxic amine‐derived products 8 . It was observed that isophorone diisocyanate (IPDI) and 4,4′‐methylene bis(cyclohexyl isocyanate) led to better mechanical properties of TPUs than hexamethylene diisocyanate (HMDI) 7 . In addition, medical grade polyurethanes were synthesized starting from lysine methyl ester diisocyanate and poly(ethylene oxide) (PEO) 9 …”