Effect of cationic group content on shape memory effect in segmented polyurethane cationomer

Abstract

To illustrate the importance of cationic groups within hard segments on shape memory effect in segmented polyurethane (PU) cationomers, the shape memory polyurethane (SMPU) cationomers composed of poly(e-caprolactone) (PCL), 4,4 0 -diphenylmethane diisocyanate (MDI), 1,4-butanediol (BDO), and N-methyldiethanolamine (NMDA) or N,N-bis(2-hydroxyethyl)isonicotinamide (BIN) were synthesized. The comparison of shape memory effect between NMDA series and BIN series was made. The relations between the structure and shape memory effect of the two series of cationomers with various ionic group contents were investigated. It is observed that the stress at 100% elongation is reduced for these two series of PU cationomers with increasing ionic group content. Especially for NMDA series, the stress reduction is more significant. The fixity ratio and recovery ratio of the NMDA series can be improved simultaneously by the insertion of cationic groups within hard segments, but not for the BIN series. Characterizations with DSC and DMA suggest that the crystallibility of soft segment in SMPU cationomers was enhanced by incorporation of ionic groups into hard segments, leading to a relative high degree of soft segment crystallization; compared with the corresponding nonionomers, incorporation of charged ionic groups within hard segments can enhance the cohesion force among hard segments particularly at high ionic group content. This methodology offers good control of the shape memory characteristic in thin films and is believed to be beneficial to the shape memory textile industries.

Properties of shape memory polyurethane used as a low-temperature thermoplastic biomedical orthotic material: influence of hard segment content

“…These soft segment and hard segment were used because several reasons: first, generally, the obtain polyurethane possess high mechanical and processing properties [15,28,35]; second, PCL is a type of biomaterial with good biocompatibility, non-toxicity [2,36]; third, more importantly, it has a melting transition at about 50 • C which is in the range of the operating temperature (45-70 • C) [20,21,23,24]. The materials' thermal/mechanical, stress-strain behavior, shape memory effect and softening and hardening process were studied.…”

A review of shape memory polymers bearing reversible binding groups

“…Adding ionic groups as chain extenders alters the phase separated hard segment domains of segmented SMPUs and the thermal characteristics of the soft segment and has been reported for both cation and anion based ionomers. For example, Zhu et al examined the influence of N, N‐bis(2‐hydroxyethyl)isonicotinamide (BINA) concentration on the thermal and thermomechanical behavior of PCL based SMPU cationomers bearing 4,4′‐diphenylmethane diisocyanate (MDI) hard segments. It was observed that the dynamic rubbery modulus and the tensile stress at 100% elongation decreased for up to 8 wt % BINA concentration indicating destabilization of hard segments.…”

“…Incorporating ionic groups into segmented polyurethanes provides an opportunity to alter the thermal stability, glass transition, mechanical behavior, and dilute solution properties . Adding ionic groups as chain extenders alters the phase separated hard segment domains of segmented SMPUs and the thermal characteristics of the soft segment and has been reported for both cation and anion based ionomers. For example, Zhu et al examined the influence of N, N‐bis(2‐hydroxyethyl)isonicotinamide (BINA) concentration on the thermal and thermomechanical behavior of PCL based SMPU cationomers bearing 4,4′‐diphenylmethane diisocyanate (MDI) hard segments.…”

Shape memory ionomers

“…PUIs have been synthesized by a number of methods including polymerization using ionic isocyanates or diols or post‐polymerization modification to introduce ionic functionality . Using semi‐crystalline soft‐segments a number polyurethane ionomers (PUIs) have been prepared using an ion‐containing, or easily modified, diol as a chain extender and their shape memory properties have been investigated …”