Title: Shape memory polymer foam.  – and – Shape memory polyurethane elastomer molded article.

 Number/Link: EP0361418 and EP0361419

Applicant/Assignee: Mitsubishi Heavy Industries

Publication date: 27-09-1989

“Gist”: The first shape memory polyurethane foams and elastomers

Why it is interesting: Shape memory polymers are so-called “smart materials” that remain in a deformed shape until a trigger (usually an increase in temperature) makes them return to their original  (“memorized”) shape. In the 1980s these materials were more of a curiosity, only used in some niche applications such as heat shrinkable tubing. Currently however a lot of academic and industrial research is done on these materials, mostly driven by medical applications (e.g. stents, orthopedic casts, self-tightening sutures etc). And not surprisingly a lot of current SMPs are based on polyurethanes (SMPUs).  Interest in shape memory materials was stimulated significantly by the invention of the first SMPUs by Mitsubishi H.I. Ltd. They filed two patents covering both shape memory foams and elastomers. The first SMPUs were based on a di-isocyanate like 4,4′-MDI, a diol like PPG700 and a chain extender like bisphenol-A, and were formulated over a range of Tg’s. The foamed materials were blown with a physical blowing agent (i.e. not water) so that all materials can be considered thermoplastics.

SMP transition from temporary shape (spiral) to permanent shape (rod). (Angew. Chem. Int. Ed. 2002, 41, 2034 ± 2057)