Studies on thermally stimulated shape memory effect of segmented polyurethanes

Abstract

ABSTRACT:The shape memory behavior of a series of polycaprolactone/methane diisocyanate/ butanediol ( PCL /MDI /BDO) segmented polyurethanes of different composition was studied. The molecular weight of PCL diols was in the range of 1600 -7000, and the hard segment content varied from 7.8 to 27% by weight. Film specimens for shape memory measurements were prepared by drawing at temperatures above the melting temperature of the soft segment crystals and subsequent quick cooling to room temperature under constrained conditions. The shape memory process was observed and recorded in a heating process. Parameters describing the recovery temperature, ability, and speed were used to study the influence of structure and processing conditions on the shape memory behavior of the sample. It was found that the high crystallinity of the soft segment regions at room temperature and the formation of stable hard segment domains acting as physical crosslinks in the temperature range above the melting temperature of the soft segment crystals are the two necessary conditions for a segmented copolymer with shape memory behavior. The response temperature of shape memory is dependent on the melting temperature of the soft segment crystals. The final recovery rate and the recovery speed are mainly related to the stability of the hard segment domains under stretching and are dependent on the hard segment content of the copolymers.

Effects of Polybenzoxazine on Shape Memory Properties of Polyurethanes with Amorphous and Crystalline Soft Segments

“…Most SMPUs rely on thermal transition of the soft segment phase for shape-memory actuation. The transition temperature can either be a glass transition (T g ) or melting temperature (T m ), respectively, for SMPU with amorphous and crystalline soft segments [21][22][23][24][25][26].…”

Review on the Functional Determinants and Durability of Shape Memory Polymers

“…The list of polymers with SM properties is continuously growing; it includes physically [72][73][74][75][76][77][78] and chemically [79][80][81] cross-linked SMPUs, trans-polyisoprene-based SMPU [82,83], poly(ether ester)s like poly(ethylene oxide)/poly(ethylene terephthalate) copolymers [84][85][86], norbornyl/polyhedral oligomeric silsesquioxane (POSS) copolymers [87,88], poly(methylene-1,3-cyclopentane) and its copolymer with polyethylene [89], styrene/butadiene copolymers [90], thiol-ene/acrylate copolymers [91], polynorbornene [90], polymer networks prepared from poly(ε-caprolactone) (PCL) dimethacrylates [92,93], acrylate-based SMPs [94], (meth)acrylate networks [95,96], cross-linked polyethylene [97], epoxy-based polymers [98][99][100][101] and many others. Moreover, various polymer blends like SMPU/phenoxy resin [102], SMPU/polyvinylchloride (PVC) [103] and several others [104][105][106][107][108][109] have received attention.…”

“…The latter is the reversible phase and accounts for the material's shape recovery behavior due to the reversibility of phase transition [152]. The synthesis route (e.g., the ratio of hard to soft segments) and the polymerization procedure directly impact SM properties and the polymer's crystallinity with respect to domain size distribution, ordering, grain size and symmetry [73,74,153]. Hereafter, some notable developments in the area of SMPUs are reviewed.…”

Segmented shape memory polyurethane and its water vapor transport properties

“…The other interactions are thermally reversible and used for maintaining the transient shapes. Li et al [43,44] stated that high crystallinity of the soft segment regions at room temperature and the formation of stable hard segment domains acting as physical cross-links in the temperature range above the melting temperature of the soft segment crystals are the two necessary conditions for a segmented PU co-polymer with shape memory behavior. The response temperature of shape memory is dependent on the melting temperature of the soft segment crystals.…”

“…A large drop of modulus and an enhanced micro-Brownian motion on heating through glass transition or melting temperature can be used in the molecular design of shape memory behavior [43 -45]. Shape memory characteristics of the segmented PU having a crystallizable soft segment are closely related with the temperature-dependent dynamic mechanical properties of the materials [43,46]. A large glassy-state modulus leads to large shape recovery upon heating and standing at high temperature.…”