Influence of Preparation Conditions on Microdomain Formation in Poly(urethane urea) Block Copolymers

Abstract

Selected poly(urethane urea) block copolymers were prepared under different conditions and their microphase-separated morphologies analyzed primarily with small-angle X-ray scattering (SAXS). Preparation conditions were varied by adjusting the temperature and vacuum pressure during solution casting. Copolymers with relatively high hard segment contents prepared under “low” vacuum conditions, where solvent is removed comparatively slowly and the copolymers spend a longer period of time in the presence of a plasticizer (i.e., solvent), produced films with higher degrees of phase separation. The longer casting times associated with the low vacuum pressure conditions also resulted in larger mean interdomain spacings. We speculate that this may be due to secondary hard domain coalescence. Attenuated total reflectance FT-IR and wide-angle X-ray diffraction experiments were performed, but these were not sensitive to the microdomain organization of these copolymers.

Limitations of predictingin vivobiostability of multiphase polyurethane elastomers using temperature-accelerated degradation testing

“…As shown in Figure 9, all of these studies demonstrated a decrease in the UTS of TPUs aged in aqueous solution at high temperatures. The percent decrease in the UTS of E2A reported in the high temperature aging study is within the range of results reported in other previous studies 18,[37][38][39] These previous high temperature aging results are in contrast with the fact that no significant hydrolytic degradation has been reported at room temperature or body temperature for any of these materials. It is interesting that all of the TPUs show a decrease in UTS independent of the soft block macrodiol used.…”

“…In the previous in vitro high temperature aging study, an assumption of constant water absorption with temperature was made in an attempt to predict changes in M n and tensile properties over long times at 37 C for E2A. 18 The current results show that this assumption is incorrect. Because a second key assumption was not met in the development of the TTS model, this provides yet another clue regarding the failure of the high temperature aging study to accurately predict in vivo results.…”

“…13 Ward et al reported that strained PurSilV R 35 tubing specimens were significantly more biostable than 80A durometer PEUs in a 2-year rabbit study. 18 In addition, PurSilV R 35 was reported to have comparable biostability to 55D durometer PEU in a 5-year canine study. 19 Similar to traditional PEUs, these studies agree that oxidative degradation is the primary degradation mode of interest in PDMS-based polyurethanes, although the extent of oxidative degradation is considerably less in polyurethanes with PDMS soft segments.…”

Comparative dielectric studies of segmental mobility in novel polyurethanes

“…A true understanding of these relationships, also known as structure-property relationships, is essential for optimizing composition and processing to prepare materials with predicted properties [6][7][8]. The importance of MS for controlling PU properties has been a strong motivation for developing methods to calculate the microphase composition and to characterize the DMS.…”

“…PUs are often prepared by a two-step process: formation of prepolymer (PP) with reactive NCO groups by the reaction of a low-molecular-weight polyether or polyester with an aromatic or aliphatic diisocyanate (DIC) at the first stage, which is extended with a low-molecular-weight diol or diamine (chain extender, CE) at the second stage [2,3,8,13]. The ratio PP:CE is very often chosen close to the stoichiometric 1:1, as it has been anticipated that no linear PUs are formed when the mole fraction of CE is significantly reduced [33].…”