Polyurethanes are excellent potential materials for the construction of implantable medical components due to their exceptional mechanical properties and biocompatibility. Currently, soft silicone materials are employed as insulation for implantable cochlear electrode arrays. Siloxane-based thermoplastic polyurethane (TPU) nanocomposites containing synthetic layered silicates are being investigated as new insulation materials with superior tensile and tear strength and reduced surface tack, potentially allowing for thinner insulation and more intricate electrode designs. In this work, ElastEon E5-325 (Aortech Pty Ltd.) TPU nanocomposites reinforced with 2 and 4 wt % low aspect ratio organo-hectorite and high aspect ratio organo-fluoromica (Lucentite SWN, Somasif ME100, both modified with octadecyltrimethylammonium (ODTMA)) were prepared by a solvent casting technique. The mechanical properties of the resulting nanocomposites were measured by tensile, tear, stress relaxation, and creep testing and morphologically were characterized by DSC, DMTA, XRD, TEM, and strained in situ synchrotron SAXS. We found that the hydrophobic low aspect ratio organohectorite acts as a very potent interfacial compatibilizer. At 2 wt % loading, the resulting nanocomposite displays vastly superior mechanical properties to both soft silicone and ElastEon. In addition to providing 30 nm × 1 nm synthetic nanosilicate reinforcing elements which are readily capable of orientation and reinforcement, these nanosilicates also serve to provide more cohesive hard microdomains and thus creep resistance and dimensional stability. Interestingly, at a higher (4 wt %) loading of organohectorite, gross morphological changes in the TPU microdomain texture are observed, adversely effecting the mechanical properties of the TPU.

Poly(alkyl)acrylates are a major class of nonbiodegradable polymers which are difficult to recycle due to an all-carbon backbone. Introducing a certain number of ester bonds in the backbone via radical ring opening copolymerization of acrylates with 2-methylene-1,3 dioxepane (MDO) improves its degradability and may be promising for chemical recycling. The current work examines the influence of monomer addition profiles on the copolymerization of acrylates with MDO. We improved the homogeneity of the MDO insertion through a semibatch approach, which was demonstrated by the molecular weight distribution of fragments after alkali degradation. By detailed NMR analysis, we identified the incorporation of MDO ring retained units, formation of branches on acrylate units, and formation of branches on MDO ring open units as the key side reactions. Theoretical calculations showed that mainly kinetic factors influence the outcome of the polymerization.

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