Perspectives. Novel crosslinked polyurethanes as shape-memory materials
True, but do we really desire to remember all our memories? I do not think so ☺. But this does not apply here to our research in shape memory polyurethanes.
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Perspectives. Novel crosslinked polyurethanes as shape-memory materials
You never know when you are making a memory. (Rickie Lee Jones)
True, but do we really desire to remember all our memories? I do not think so . But this does not apply here to our research in shape memory polyurethanes. A relatively new and exciting application for polymers is as shape ‘memory’ materials. Therefore, one of the objectives which we will continue to follow in the immediate future will be to focus on novel crosslinked shape-memory polyurethanes. Recently we have done a series of preliminary studies on this topic. Here we report only a few particular aspects of our research. More complete details are given in one of our most recent works (2010) [63]. In the recent study made by us [63], the usual diol chain extender was replaced by a triol (TMP), producing crosslinked PU networks without phase segregation. The aim was to ensure high degrees of strain recoverability, to produce candidate thermally-triggered shape-memory polyurethanes. Again MDI and DBDI were compared as hard segments, but also toluene diisocyanate was used. Numerous polymers have been proposed as shape-memory polymers (SMPs), and many of them are based on polyurethanes. This is because of the intrinsic versatility of segmented copolyurethane systems. By suitable choice of diisocyanate and macrodiol, a wide variation in properties may be obtained, allowing the possibility of tuning the shape-memory response to suit different applications. Usually they are phase-segregated materials. For example, a dispersed rigid phase (usually based on the diisocyanate) provides physical crosslinks, while the macrodiol provides a soft amorphous phase with low glass transition that provides the trigger temperature for shape recovery [63]. An ideal shape-memory polymer for a given application has a small set of parameters that determine the usefulness, or otherwise, for a given application: (1) The fractional recoverable strain: the maximum fraction of the imposed strain that can be recovered when triggered. (2) The temperature of maximum recovery rate T max for a given rate of heating: a measure of the temperature required to trigger
C. Prisacariu, Polyurethane Elastomers, DOI 10.1007/978-3-7091-0514-6 6, c Springer-Verlag/Wien 2011
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6 Perspectives. Novel crosslinked polyurethanes as shape-memory materials
recovery of shape. (3) The width ΔT of the window of temperature within which shape recovery occurs. (4) The tensile modulus ER at the temperature of full recovery: this determines the maximum shape-recovery restoring force if shape recovery is resisted [63]. Since different applications make different demands on SMPs, it is particularly desirable to find polymer systems where parameters T max , ΔT, and ER are variable, so the same basic system can be tuned to suit different applications. Preferably, these will be systems where all the imposed strain is recoverable, that is the fractional recoverable strain is 100% [63]. These attributes are difficult to achieve, all in
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