Phase Separation and Crystallization in High Hard Block Content Polyurethane Thin Films

Abstract

Following studies of bulk behavior, the morphological evolution in thin films of linear TPUs with a high content of hard segment (HS) (from 70 to 100 wt %) on annealing is investigated. In contrast to melt-quenched bulk samples, a mixed phase was obtained for as-spin-cast films, and then, on annealing, a phase-separated mesophase domain, as previously observed by scattering and TEM in bulk samples, was observed by AFM to form directly from the mixed phase. In addition to this overall phase behavior, a crystallization behavior unique to thin films was observed: samples of thickness less than 120 nm and annealed at sufficiently high temperature developed large lamellar crystal blocks. Similar crystal blocks have also been found in thin films of a TPU with a more flexible chain extender, although in this case, with the greater HS/SS compatibility of this material, the phase separation behavior was not observed at all.

Fabrication of Enhanced Mechanical Properties and Intrinsic Flame-Retardant Polyurethane Elastomer Containing 4-(Phenylethynyl) Di(Ethylene Glycol) Phthalate

“…Due to differences in polarity and crystallinity, the “hard segment” and “soft segment” are thermodynamically incompatible and have a tendency to spontaneously separate into two phases. Consequently, TPU can form a microphase separation structure [ 4 , 5 , 6 ]. As result of hydrogen bonds formed by the carbamate group, the “hard segment” is glassy at room temperature and is dispersed in the rubber phase formed by “soft segments”.…”

Soft X-ray Spectromicroscopic Evidence for Site-Specific Nanoscale Phase Segregation of Polyurethane onto a Confined Surface

“…The alternating sequences of chemically distinct species give the freedom to design the higher and lower thermally stable parts in the TPU morphology, which gives rise to the hard and soft segments, respectively . The microphase-separated geometry of a TPU film is comprised of hard segment domains with the matrix as the soft segment, where the interdomain spacing directly varies as a function of film thickness. , The structure–property correlation in the polymeric thin film is critical for determining its suitability in technological applications where the microphase separation structures influence the characteristic features like conduction and optical properties as well as barrier and mechanical properties.…”

Application of Linear Viscoelastic Continuum Damage Theory to the Low and High Strain Rate Response of Thermoplastic Polyurethane

“…for bumpers, seals, moulded gaskets and ducts, often working as impact and vibration mitigators. They benefit from advantageous properties such as flexibility, durability and property recovery after deformation, but simul taneously have dependence on polymer network morphology, temperature, strain rate and loading history [1][2][3][4].…”