Time-Dependent Morphology Development in a Segmented Polyurethane with Monodisperse Hard Segments Based on 1,4-Phenylene Diisocyanate

Abstract

The time-dependent morphology development in a segmented polyurethane, which was prepared by the reaction of equimolar amounts of 1,4-phenylene diisocyanate (pPDI) and poly-(tetramethylene oxide)glycol of 〈Mn〉 of 975 g/mol, was investigated. No chain extender was utilized during the synthesis, and the resultant monodisperse hard segments constituted 14 wt % of the copolymer. Timedependent microphase separation and morphology development was studied at room temperature by using solvent-cast films which were heated above the hard segment melting temperature, 55 °C, to erase the semicrystalline microphase morphology. Atomic force microscopy showed that, following heat treatment, the hard phase first developed into short rods within 30 min, followed by a growth period during which the short rods grew longer and eventually into a well-defined percolated structure. Morphology development was also followed by FTIR spectroscopy. While the intensity of the free CdO peak at 1730 cm -1 decreased, the intensity of the hydrogen-bonded CdO peak at 1695 cm -1 , which was not present in the original annealed sample, increased with time and began to plateau in ∼24 h. A timedependent increase in the storage modulus of the copolymer, following heat treatment, was also noted. This latter change could be described by the Avrami equation, yielding an Avrami exponent of 0.55. Because of the similarity of the copolymer's morphology to that of short fiber reinforced polymer composites, selected models developed for predicting the modulus of such composites could reasonably estimate the initially surprisingly high ambient temperature storage modulus of the copolymer of 0.9 × 10 8 Pa.

Nanocomposites made from cellulose nanocrystals and tailored segmented polyurethanes

“…As previously indicated, in these materials the HS domains act as reinforcement for the soft matrix formed by the SS. 2 Moreover, according to Wegner,20,21 the logarithm of the modulus of a segmented copolymer follows a linear relationship with the volume fraction of HS. The present results plotted in the proposed form confirm this relationship (Fig.…”

“…Usually, there is a long range connectivity of the HS that leads to the percolation of the hard phase through the soft matrix. 2 The SS are polyols typically of molar mass 500-2000 or higher, whereas the HS are built from diisocyanates and chain extenders. 3 Depending on the types and compositions of the soft and HS and the preparation procedures, the structure-property relationships of polyurethanes are extremely diverse and can be tailored for using in different applications, from medical devices to intelligent fabrics or deployable components.…”

Iterative Synthesis of Extenders of Uniform Chain Lengths for Making Thermo-Reversible Polyurethane Supramolecules

“…Harrell 21 synthesized monodispersed hard segments with uniform chain length, but these prepared compounds did not possess any multiple hydrogen-bonding sites. Wilkes 19 and his co-workers reported a morphological study on polyurethanes involving only one hard-segment block in the molecular chains. However, their syntheses do not appear to be flexible enough to prepare extenders with twice or multiple chain lengths due to intrinsic limitations.…”

Thermoplastic Poly(ester urethane)s with Novel Soft Segments

“…The DMA analyses also supported the evidence that these materials are completely amorphous, as semicrystalline polyurethanes display changes in the storage modulus and tan δ at higher temperatures. 45 The DMA data for these poly(ester urethane)s showed no such transitions at higher temperatures.…”

“…42 MarcosFernández et al synthesized several amorphous poly(ester urethane urea)s with poly(caprolactone) as the soft segment and amino acid derivatives as the chain extenders. 43 These materials were durable and elastic, but they were synthesized using heterogeneous chain extensionsan unnecessary synthetic step in preparing useful poly(ester urethane)s. Chain extension, whether heterogeneous or homogeneous, can be avoided altogether in synthesizing durable polyurethane elastomers, as Yilgor et al 44,45 recently proved. Therefore, a more facile, onestep method that excludes the use of chain extenders can be employed to synthesize durable poly(ester urethane)s. Overall, the literature provides several amorphous poly(ester urethane)s that possess some beneficial characteristics for use as biodegradable materials in biomedical applications.…”