Patent Description:
Shape memory polymers (SMPs) constitute a class of mechanically adaptive materials, which allow the fabrication of objects that have a permanent (first) shape, and which can be programmed to adopt a temporary (second) shape when simultaneously subjected to a mechanical force and another appropriate stimulus, such as for example heat, light, an electromagnetic field, or a pH change. <NUM>-<NUM> This process is generally referred to as "fixing" a temporary shape. The original shape can later, when desired, be recovered upon exposure of the object to the same or another suitable stimulus. SMPs require a structure that provides rubber elasticity and a switching phase that is responsive to an external stimulus and which serves as a second type of cross-link that can be switched on or off. Although heat<NUM>,<NUM>-<NUM> remains the most common stimulus to trigger shape memory effects in polymers, the introduction of light-active,<NUM>-<NUM> pH-active,<NUM> or water active<NUM> moieties into elastic polymer networks has permitted the use of other stimuli. A plethora of SMPs has been developed for potential use in advanced technological and biomedical applications. <NUM>-<NUM>,<NUM>-<NUM> Continuous efforts have been dedicated to the overall improvement of the SMPs, certain limitations such as low stiffness,<NUM>-<NUM> low recovery stress,<NUM> long response time,<NUM> limited durability of the SM behavior,<NUM>-<NUM> or complicated synthesis restrict their potential technological use. Other problems include low fixity, poor recovery, or unsuitable requirements for the fixing and release conditions. Of course, the specific property matrix to be attained, depends on the targeted application. While the properties of SMPs can a priori be tailored through the variation of their composition, the mechanical properties of a given material can be further modified by fabricating (nano)composites<NUM>-<NUM> by adding micro or nano sized fillers such as fibers,<NUM>-<NUM> particles,<NUM>-<NUM> or nanocrystals. <NUM>-<NUM> A related design approach to either create new shape memory materials or modifying the properties of existing SMPs is the fabrication of blends. Materials in which the shape memory effect is an emergent property can be accessed by combining an elastic polymer with a second polymer that forms the fixing phase,<NUM>,<NUM> for example a semicrystalline or an amorphous polymer whose mechanical properties can be switched by heating above the melting (Tm) or glass transition (Tg) temperature. <NUM>-<NUM> Shape memory behavior can also be achieved in binary blends of two crystalline polymers, in which one crystal type forms the fixing phase and the other a reversible cross-linking phase. <NUM>-<NUM> It is also possible to tailor the properties of existing SMPs by blending them with another polymer, which may have the same or a different chemical structure as the segments of which the SMP is comprised. <NUM> For instance, shape memory polymer blends of a PU with phenoxy or poly(vinyl chloride) were reported, which exhibited tunable switching transition temperature and improved the mechanical properties, respectively. <NUM>-<NUM>.

For applications in the biomedical field, it is particularly important that the fixation and recovery temperatures can be minutely tailored around the human body temperature. <NUM>-<NUM> It can further be advantageous if the mechanical characteristics of a given materials platform can be modified without changing the SMP's chemical constituents. Most of the prior art materials were tailored to allow objects, products and devices to be applied in a temporary shape with the goal to restore the permanent shape inside or around the body, using either the increase in temperature (provided by the body or external heating) or the physiological fluid (or both) as trigger. Examples include self-tying sutures and self-expanding devices for minimally intrusive surgery, such as the Igaki-Tamai endovascular stent. This self-expanding stent is made of poly(L-lactide), which has a transition temperature around <NUM>, meaning that the expansion of the implant in the veins must be triggered by heating to this relatively high temperature. Examples of shape memory polymer compositions and methods for producing the same are described by J. Karger-Kocsis et. al (<NPL>), by M. Raja et al. (<NPL>) and in <CIT>.

In this specification, all numbers disclosed herein designate a set value, individually, in one embodiment, regardless of whether the word "about" or "approximate" or the like is used in connection therewith. In addition, when the term such as "about" or "approximate" is used in conjunction with a value, the numerical range may also vary, for example by <NUM>%, <NUM>%, or <NUM>%, or more in various other, independent, embodiments. All ranges set forth in the specification and claims not only include the end points of the ranges but also every conceivable number between the end points of the ranges.

The terms "polymer" and "(co)polymer", as used herein, refer to a polymeric compound prepared by polymerizing monomers whether of the same or a different type. As used herein, said terms embrace the terms "homopolymer", "copolymer", "terpolymer" and "interpolymer". The term "interpolymer" as used herein refers to polymers prepared by the polymerization of at least two different types of monomers.

The present invention relates to materials that allow an inversion of this scheme and permit the fabrication of objects and devices that can (i) be provided in their permanent shape, (ii) be heated above a switching temperature above physiological temperature, at which the material becomes deformable or shapeable, (iii) be inserted into the body or placed in contact with the body and be deformed to assume a desired temporary shape, (iv) be fixed in the desired temporary shape by keeping the object/device around body temperature (<NUM>) for a convenient period of time, (v) and largely retain this temporary shape if removed from the body. In preferred embodiments, the objects or devices based on materials according to the present invention (vi) return largely to their original shape when heated again above the switching temperature, and (vii) the shape fixing and releasing cycle can be repeated many times. The shape-memory effect displayed by the polymer ensures that (i) the permanent shape of the device is not irreversibly lost during the procedure, notably heating above the switching temperature and (ii) that the original shape can be recovered when needed, for example when the object or device shall be removed or re-shaped. Applications in which such a material as disclosed herein is desirable include, but are not limited to, hearing aids, such as over-the-counter (OTC) hearing aids, hearables, earbuds, ear-level devices for health monitoring applications, in-ear implants, earpieces of hearing aids, telephones, stethoscope, or other instruments, earphones, in-ear headphones, earplugs, catheter retainers, mouth guards, orthodontic devices, frame temples, surgical staples, materials for surgical reconstruction, pressure garments, toys, automotive parts, ocular prosthesis, manufacturing of shape-memory fibers, shape memory textiles and clothing, gloves, shoe soles and insoles, shape memory foams, adapting grips, sportswear (such as helmets, shin guards), and select portions or components of each. Such and all other objects and devices based on the materials disclosed here are also part of the present invention, as are methods to make and use such materials.

One possible solution to achieve the shape-memory behaviour outlined above is to use a shape memory material with a switching temperature that is above body temperature, but low enough to inflict no or minimal harm when the device is brought in contact with the body at a temperature above this switching temperature, that is, at a temperature at which the material is still shapeable. This solution works for objects and devices with a comparably large mass and/or for which cooling is slow, so that after heating and bringing the device in contact with the body the object's temperature remains above the switching temperature and cools only after shaping. This method is suitable for devices where shape adaptation is simple and fast, and risks associated with "mis-shaping" (i.e., when the device is cooled too fast) or harm to the body are low. Another possibility is to use a shape memory material with a switching temperature above body temperature and "slow" fixation. In other words, when the material and objects or devices fabricated from the material are cooled from above the switching temperature to body temperature, the material remains shapeable for a certain period of time (shaping time) that is sufficiently long to allow the material and objects or devices made from or containing the material to be positioned and shaped as required, before fixation occurs. Materials, objects, and devices with these capabilities constitute the subject of the present invention. This solution is particularly useful for small objects or devices (or parts thereof) that cool faster than the time required for positioning and bringing them into the temporary shape. The shape memory materials according to the present invention have the following attributes:.

A widely investigated, commercially available shape memory poly(ester urethane)<NUM>-<NUM> consisting of crystallizable poly(<NUM>,<NUM>-butylene adipate) (PBA) soft/switching segments and hard segments composed of <NUM>,<NUM>-methylenediphenyl diisocyanate and <NUM>,<NUM>-butanediol (PBA-PU)<NUM>-<NUM> shall serve to illustrate the state of the art and its limitations with respect to the present invention. The first heating cycle of a differential scanning calorimetry measurement of a melt-processed film of the neat PBA-PU, recorded at a rate of <NUM>·min-<NUM> (<FIG>) shows a broad exothermic melting transition with a maximum at a temperature (Tm) of <NUM> and a shoulder around <NUM>, indicative of the presence of melting of PBA segments in a mixture of α and β polymorphs, recrystallization of the β into the α form around <NUM> and melting of the α form above <NUM>. <NUM>-<NUM> The first DSC cooling trace (<FIG>), recorded with a rate of <NUM>·min-<NUM>, reveals a crystallization peak with a maximum temperature Tc of <NUM>. The crystallization temperature Tc shifted to higher temperatures when the cooling rate was decreased to <NUM>·min-<NUM> (<NUM>) and <NUM>·min-<NUM> (<NUM>), but neither a reduction in cooling nor heating rate changed the melting temperature much significantly. Shape memory experiments (see below) show that the temperature at which the PBA segments melt (Tm) serves as switching temperature, and the temperature at which good fixity (><NUM>%) could be rapidly achieved is <NUM>ºC. We recently showed<NUM> that this temperature could be increased to <NUM> by melt-mixing the PBA-PU with <NUM>% w/w dodecanoic acid. The data show that Tc increased to <NUM> (measured at a cooling rate of <NUM>·min-<NUM>), which explains why the switching element can be fixed at a higher temperature than in the neat PBA-PU. Unfortunately, the Tm was slightly reduced in comparison to the neat PBA-PU to <NUM>-<NUM>. Size exclusion chromatography traces revealed a dramatic reduction of the number- and weight-average molecular weights from <NUM>,<NUM> to <NUM>,<NUM> and <NUM>,<NUM> to <NUM>,<NUM> Da, respectively, which suggests that the nucleation process is driven by chain scission and nucleation of the chain ends, as reported previously by others. Furthermore, we screened other potential nucleating agents for PBA-PU, including fatty acids (sodium dodecanoate, sodium palmitate, hexacosanoic acid, sodium octacosanoate) and their salts, benzoic acid derivatives (<NUM>-methoxybenzoic acid, <NUM>-decyloxybenzoic acid), sodium dodecylsulfate and inorganic nucleating agents such as talc, aluminum oxide and potassium carbonate. While the incorporation of <NUM>% w/w of the benzoic acid derivatives, talc and alumina caused no changes of the thermal properties of the PBA-PU, some increase of Tc was observed for all the fatty acids and their salts, sodium dodecyl sulfate, and potassium carbonate with the highest value being recorded for sodium dodecanoate (Tc = <NUM>). However, the reduction in number- and weight-averaged molecular weight caused by the addition of the nucleating agents was even more dramatic than for dodecanoic acid, reaching values as low as <NUM>,<NUM> (Mn) and <NUM>,<NUM> Da (Mw) for sodium dodecanoate. The reduction of the molecular weight was accompanied by a drastic deterioration of the mechanical properties, resulting in the loss of elastomeric properties for the nucleated PBA-PU with the highest Tc. In summary, all these nucleating agents led to a large molecular weight decrease (concomitant with a degradation of the mechanical properties), many reduced the Tm, many had no influence on Tc and none was capable of increasing the temperature at which good fixity (><NUM>%) could be rapidly achieved to above <NUM>.

We now surprisingly found that the fixing temperature can be substantially increased without compromising the mechanical properties or reducing the Tm by melt-mixing PBA-PU with free PBA under conditions disclosed here. Indeed, it was possible to achieve excellent shape fixity (~<NUM> - <NUM>%) at physiological temperature (<NUM>) within <NUM>-<NUM>. Further, on account of a slight increase of Tm, the temperature at which the temporary shape is released was increased vis-à-vis the prior art PBA-PU. An in-depth investigation of the morphology and the thermal and mechanical behavior of these materials reveal the mechanisms at play, which allowed generalization of the invention and adapting the invention to other materials systems.

Thus, in one aspect, the invention relates to a thermoplastic shape memory composition, comprising a thermoplastic shape memory polymer and a modifier polymer; wherein a melting and crystallization of a crystallizable portion of the thermoplastic shape memory composition fixes a temporary shape; wherein a further melting of the crystallized portion of the shape memory composition releases the temporary shape; and wherein a crystallization temperature of said crystallizable portion of said thermoplastic shape memory composition is at least <NUM> higher than that of a crystallizable portion of the thermoplastic shape memory polymer without the modifier polymer.

In a further aspect of the above described shape memory composition the crystallization temperature of said crystallizable portion of said shape memory composition is higher by at least <NUM>, at least <NUM>, at least <NUM>, or at least <NUM> than that of the crystallizable portion of the thermoplastic polymer without the modifier polymer.

In an additional aspect, combinable with any combination of the above aspects, the crystallization temperature and a melting temperature of said crystallizable portion of said shape memory composition differ by at least <NUM>° C, at least <NUM>, or at least about <NUM>° C.

In another aspect, combinable with any combination of the above aspects, the crystallization temperature of the crystallizable portion of said shape memory composition is above about <NUM>, above <NUM>, above <NUM>, above <NUM>, or above <NUM>; wherein the crystallization temperature of the crystallizable portion of said shape memory composition is below <NUM>, below <NUM>, below <NUM>, or below <NUM>; wherein said melting temperature of the crystallizable portion of said shape memory composition is above <NUM> or more, <NUM> or more, <NUM> or more, or <NUM> or above; and wherein in preferred embodiments, the melting temperature of the crystallizable portion of said shape memory composition is less than <NUM>, preferably less than <NUM>, more preferably less than <NUM>, and most preferably less than about <NUM>.

In a further aspect, combinable with any combination of the above aspects, said modifier polymer comprises a polyester, a poly(<NUM>,<NUM>-butylene adipate) or poly(caprolactone); and wherein the amount of modifier polymer is at least <NUM>% by weight, at least <NUM>% by weight, or at least <NUM>% by weight based on <NUM> weight percent of the thermoplastic polymer and the modifier polymer.

In still an additional aspect, combinable with any combination of the above aspects, said modifier polymer is poly(<NUM>,<NUM>-butylene adipate) of a weight-average molecular weight of at least <NUM>·mol-<NUM> or at least <NUM>·mol-<NUM> or poly(caprolactone) of a weight-average molecular weight of at least <NUM>·mol-<NUM>.

In an additional aspect, combinable with any combination of the above aspects, said thermoplastic polymer comprises the reaction product of at least a (A) crystallizable prepolymer, (B) a low-molecular weight chain extender, and a (C) a diisocyanate.

In another aspect, combinable with any combination of the above aspects, said crystallizable prepolymer (A) a polyester or polyamide or polyether and said low-molecular weight chain extender (B) is a diol or diamine, and said diisocyanate (C) is an aromatic diisocyanate, such as toluene diisocyanate and methylene diphenyl diisocyanate or an aliphatic diisocyanate, such as hexamethylene diisocyanate, hydrogenated methylene diphenyl diisocyanate, and isophorone diisocyanate, or a combination thereof.

In a further aspect, combinable with any combination of the above aspects, said thermoplastic polymer and said modifier polymer have at least partially reacted with each other.

In an additional aspect, combinable with any combination of the above aspects, said thermoplastic polymer and said modifier polymer have essentially not reacted with each other.

Thus, disclosed herein is a thermoplastic shape memory composition, comprising: a polymer, wherein melting and crystallization of a crystallizable portion of the shape memory composition fixes a temporary shape; wherein a further melting of the crystallized portion of the shape memory composition releases the temporary shape; and wherein the crystallization temperature of said crystallizable portion of said shape memory composition is above about <NUM>, above <NUM>, above <NUM>, above <NUM>, or above <NUM>; wherein the crystallization temperature of said crystallizable portion of said shape memory composition is below <NUM>, below <NUM>, below <NUM>, or below <NUM>; wherein the melting temperature of said crystallizable portion of said shape memory composition is about <NUM> or more, <NUM> or more, <NUM> or more, or <NUM> or above; wherein the melting temperature of said crystalline portion of said shape memory composition is less than <NUM>, preferably less than <NUM>, more preferably less than <NUM>, and most preferably less than about <NUM>.

In a further aspect of the above described shape memory composition said shape memory polymer composition comprises a polyester, preferably poly(<NUM>,<NUM>-butylene adipate) or poly(caprolactone).

Thus, further disclosed herein is a thermoplastic shape memory composition, comprising: wherein melting and recrystallization of a crystallizable portion of the shape memory composition fixes a temporary shape; wherein a further melting of the recrystallized portion of the shape memory composition releases the temporary shape; wherein a crystallization temperature of said crystallizable portion is above about <NUM>, preferably above <NUM>, above <NUM>, or above <NUM>; and wherein said shape memory polymer comprises poly(<NUM>,<NUM>-butylene adipate).

In an additional aspect, combinable with any combination of the above aspects, a fixity of at least <NUM>%, more than <NUM>%, more than <NUM>%, or more than <NUM>% is achieved when the temporary shape is fixed at <NUM>.

In a further aspect, combinable with any combination of the above aspects, said fixity can be achieved by fixing in <NUM> or less, <NUM> or less, or <NUM> or less.

In one aspect, the invention relates to a method for producing a thermoplastic shape memory composition, comprising the steps of: combining at least a thermoplastic polymer and a modifier polymer and forming a product therefrom, having the characteristics as set forth in any combination of aspects above.

In one further aspect, the invention relates to shape memory object comprising any of the shape memory compositions or polymers according to any of the aspects set forth above.

Thus, in one aspect the invention relates to a shape memory object, wherein the object returns largely to an original shape when heated above the switching temperature, and wherein a shape fixing and releasing cycle can be repeated multiple times.

In a further aspect, the invention relates to the shape memory object according to any of the above aspects, wherein said shape memory object is selected from the list of: hearing aids, such as over-the-counter (OTC) hearing aids, hearables, earbuds, ear-level devices for health monitoring applications, in-ear implants, earpieces of hearing aids, telephones, stethoscope, or other instruments, earphones, in-ear headphones, earplugs, catheter retainers, mouth guards, orthodontic devices, frame temples, surgical staples, objects for surgery and surgical reconstruction, pressure garments, toys, automotive parts, ocular prosthesis, manufacturing of shape-memory fibers, shape memory textiles and clothing, gloves, shoe soles and insoles, shape memory foams, adapting grips, sportswear such as helmets and shin guards, or select portions or components of each.

Thus, in one aspect, the invention relates to a component of a hearing aid device for coupling to an ear of a hearing device user, comprising any of the shape memory compositions or polymers according to any of the above aspects as set forth above.

In a further aspect, the invention relates to a method to program the temporary shape of a shape memory composition or polymer according to any of the above aspects, comprising the steps of: heating the shape memory composition above a melting temperature of the crystallizable portion of the shape memory composition; conforming the thermoplastic shape memory composition to the temporary shape; and cooling the shape memory composition (near above or) below the crystallization temperature of the crystallizable portion of the shape memory composition or polymer while conforming the thermoplastic shape memory composition or polymer to the temporary shape.

The invention will be better understood and other features and advantages will become apparent by reading the detailed description of the invention, taken together with the drawings, wherein:.

The PBA-PU and PTHF-PU based on hard segments composed of <NUM>,<NUM>-methylenebis (phenyl isocyanate) (MDI) and <NUM>,<NUM>-butanediol (BD) as chain extender and soft/switching segments of poly(<NUM>,<NUM>-butylene adipate) (PBA) and poly(tetrahydrofuran) (PTHF) were kindly provided by Covestro Deutschland AG and Bayer MaterialScience (now Covestro) as Desmopan DP <NUM> A and Texin <NUM> respectively. Poly(<NUM> ,<NUM>-butylene adipate) (PBA) (Mw = <NUM>,<NUM>·mol-<NUM>) was purchased from Sigma Aldrich or from Best of Chemicals from BOC Sciences, Shirley, USA and poly(caprolactone) (PCL, Mw = <NUM>,<NUM> ·mol-<NUM>, Mn = <NUM>,<NUM> ·mol-<NUM>) was purchased from Sigma Aldrich. Acetylated PBA (AcPBA) was prepared by reacting PBA with acetyl chloride in tetrahydrofuran/pyridine.

Fabrication of Blends of PBA-PU or PTHF-PU with PBA or AcPBA. The PBA-PU and PTHF-PU were dried at <NUM> for <NUM> in the oven, prior to the fabrication of the blends. PBA-PU was melt-mixed with <NUM> or <NUM> or <NUM>% w/w of PBA or <NUM>% w/w AcPBA and PTHF-PU was melt-mixed with <NUM>, <NUM>, <NUM>, or <NUM>% w/w PBA by combining the respective PU and polyester in a roller blade mixer (RBM, Brabender®GmbH & Co. KG; mixer type 30EHT). The temperature and speed of the mixer were set to <NUM> and <NUM> rpm, respectively. Firstly, the PU (PBA-PU or PTHF-PU) was introduced to the RBM and processed until it formed a homogeneous melt (<NUM>). The PBA was then added to the PU melt and mixing was continued for another <NUM>. The total load of the RBM was kept fixed at <NUM>. For example, the composition of PBA-PU/PBA containing <NUM>% w/w PBA was prepared using <NUM> of PBA-PU and <NUM> of PBA. The compositions were then removed from the mixer and cooled to room temperature. A <NUM>% w/w PBA-PU/AcPBA blend and a <NUM>% w/w PBA-PU/PCL blend were produced using the same protocol, but in the case of the PBA-PU/AcPBA blend, the processing temperature was increased to <NUM>. The different compositions thus made were directly compression-molded to produce films having a thickness of <NUM>-<NUM> using spacers (for uniform thickness) between poly(tetrafluoroethylene) (PTFE) sheets in a Carver® press at <NUM> under a pressure of <NUM> metric tons for <NUM>. The films thus obtained were removed from the hot press and cooled between the PTFE sheets to room temperature. Reference films of the neat PBA-PU and PTHF-PU were also prepared in an analogous manner using an identical protocol of processing the materials in an RBM and subsequent compression molding. All samples were stored under ambient conditions for typically at least <NUM> before analysis. Solution-cast films of the <NUM>% w/w PBA-PU/PBA blend were prepared by dissolving the PBA-PU (<NUM>) and PBA (<NUM>) in warm THF (<NUM>) casting into a poly(tetrafluoroethylene) Petri dish and allowing the solvent to evaporate at room temperature over a period of three days. A portion of the solution-cast material was re-shaped by compressionmolding as described above. Irrespective of the actual structure, the compositions disclosed here are, for convenience, referred to as "compositions", "blends", and "mixtures", and these terms should not be construed to imply any particular molecular structure.

Dynamic Mechanical Analysis (DMA). The dynamic mechanical properties of films of the neat PBA-PU and PTHF-PU as well as their blends with PBA were characterized using a TA Instrument DMA Q800. The experiments were conducted in tensile mode with a strain amplitude of <NUM> and at a frequency of <NUM>. Experiments were carried out in the temperature range of - <NUM> to <NUM>, with a heating rate of <NUM>·min-<NUM>. The samples were analyzed in the shape of strips having a width of <NUM>-<NUM> and a length of <NUM>. The mechanical data shown in Table <NUM> and values quoted for E' in the text represent averages of <NUM>-<NUM> independent measurements ± standard deviation. The stress-strain measurements of the prepared materials were performed using the same DMA instrument with a strain rate of <NUM>%. min-<NUM>, at <NUM>. For these measurements, the films were cut into dog-bone shaped samples. The experiments were performed on <NUM>-<NUM> individual samples and the data is summarized in Table <NUM>.

Thermogravimetric Analysis (TGA). The thermal stability of the neat PBA-PU and PTHF-PU as well as their blends with PBA was probed by thermogravimetric analysis using a Mettler-Toledo STAR thermogravimetric analyzer under N<NUM> atmosphere in the range of <NUM> to <NUM> with a heating rate of <NUM>·min-<NUM> using ~<NUM> of the sample.

Differential Scanning Calorimetry (DSC). DSC measurements were performed on the neat PBA-PU and PTHF-PU as well as their blends with PBA using a Mettler-Toledo STAR system under N<NUM> atmosphere. The experiments were performed on ~<NUM> samples placed in standard DSC pans. Samples were analyzed in the temperature range from <NUM> to <NUM> with heating and cooling rates of <NUM>·min-<NUM>. The maximum of the melting endotherm was established as melting temperature (Tm) while the maximum temperature point of cooling exotherm was established as crystallization temperature (Tc).

Size Exclusion Chromatography. Size exclusion chromatography (SEC) measurements were carried out on an Agilent Technologies <NUM> Infinity system equipped with a refractive index (RI) detector. The column system was composed of one guard column and two mixed bed PSS GRAM analytical linear <NUM> (<NUM> × <NUM>), with a separation range from <NUM> to <NUM> Da, at <NUM>. DMF (LiBr <NUM>) was employed as solvent/eluent and the measurements were carried out at a flow rate of <NUM>/min. Data analyses were carried out on the PSS WinGPC Unchrom software and the mass-average molecular weight (Mw) and Mn values were determined by comparison with poly(styrene) standards.

Optical Microscopy. All optical microscopy images were taken on an Olympus BX51 microscope equipped with a DP72 digital camera and a Linkam LTS350 heating/cooling stage, with a magnification of ten times. Two films of the neat PBA-PB and of the <NUM> % w/w PBA-PU/PBA mixture (thickness ca. <NUM>) were placed on a glass slide. The temperature was increased to <NUM> (hating rate <NUM>/min) and the melting of the crystalline domains was observed between crossed polarizers. The samples were kept at <NUM> for <NUM> and subsequently cooled to <NUM> (cooling rate <NUM>/min). The two samples were monitored during a <NUM> isothermal annealing at <NUM> and the formation of crystallites observed under cross-polarized light. Finally, the thermal stability of the crystallites formed at <NUM> was evaluated by heating the samples to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> and keeping the system at each temperature for <NUM> (<NUM>-<NUM> and <NUM>), <NUM> (<NUM>) and <NUM> (<NUM>).

Wide Angle X-Ray Scattering. Films of the neat PBA, (compression molded at <NUM>, under <NUM> metric tons pressure for <NUM>), PBA-PU, PTHF-PU and their blends with PBA were analyzed by wide angle X-ray scattering (WAXS). WAXS spectra were recorded with a NanoMax-IQ camera (Rigaku Innovative Technologies) equipped with a Cu target sealed tube source (MicroMax-<NUM>, Rigaku) and a Pilatus100 K detector (Dectris). The samples were kept in vacuum at room temperature during the measurements. Raw data were processed according to standard procedures, and the scattering intensity is presented as a function of the momentum transfer q = 4πλ-<NUM> sin(θ/<NUM>). θ is the scattering angle and λ = <NUM> is the photon wavelength. Each spectrum was fitted on the range of <NUM>-<NUM>-<NUM>, against a linear combination of a quadratic function (interpreting the amorphous halo) and Gaussian functions (interpreting the Bragg-reflections from the crystal planes).

Shape Memory Analysis. The shape memory behavior of films of the neat PBA-PU, PTHF-PU and their blends with PBA was analyzed using the same equipment and sample geometry as used for the DMA experiments (see above). Cyclic stress-temperature-strain tests of the samples were conducted in controlled-force mode. The cyclic tests of all the samples started with heating the sample to <NUM> and maintaining it at this temperature for <NUM>. An increasing force of up to <NUM> N (rate of <NUM> N·min-<NUM>) was applied to deform the samples uniaxially with a strain limit of <NUM>% (for neat PBA-PU and its blends with PBA, and the neat PTHF-PU) or <NUM>% (for PTHF-PU blends with <NUM> or <NUM>% w/w PBA). A strain abort step was introduced before applying the force to achieve the targeted strain limit. The samples were maintained stretched at <NUM> for <NUM>, before cooling to <NUM> (PBA-PU, PTHF-PU), <NUM> (PBA-PU, <NUM>% w/w PTHF-PU/PBA), <NUM> (blends of PBA-PU and PTHF-PU with <NUM>% w/w PBA), <NUM> (<NUM> or <NUM>% w/w PBA-PU/PBA ), <NUM> or <NUM> (<NUM>% and <NUM>% w/w PBA-PU/PBA) at a rate of <NUM>·min-<NUM> and maintained at the respective fixing temperature for <NUM> (all samples), <NUM> (samples fixed at <NUM>, <NUM> or <NUM> only), <NUM> (<NUM>% w/w PBA-PU/PBA fixed at <NUM>) or <NUM> (<NUM>% w/w PBA-PU/PBA, <NUM>% w/w PBA-PU/AcPBA and <NUM>% w/w PBA-PU/PCL fixed at <NUM>). After recording the changes in strain, the applied force was unloaded and the sample was maintained in this state for <NUM> to fix the temporary shape. The sample was finally heated to <NUM> at a rate of <NUM>·min-<NUM>, and kept at this temperature for <NUM> to recover the original shape. Three cycles were conducted for each sample and the fixity (%) and recovery (%) for each cycle was calculated according to Eqs. (<NUM>) and (<NUM>): <MAT> <MAT> where, εs is the strain after stretching, εu is the strain after unloading, εr is the recovered strain after heating, and εi is the initial strain.

An alternative shape memory cycle was also used to investigate the behavior when deforming the materials only after first cooling them to the fixing temperature. As for the shape memory test described above, the cyclic tests start with the sample being heated to <NUM> and being kept at this temperature for <NUM>. The samples were then cooled to <NUM> (rate <NUM>/min) to simulate the deployment of an object or a device, and kept at this temperature for <NUM>. The samples were then uniaxially deformed, as described above, and kept under load isothermally for <NUM>. After the removal of the stress, the cycle proceeded as for the conventional cycle.

The polyurethanes used as basis for the development of new SMP polymers and which also serve as reference materials that define the state of the art, PBA-PU and PTHF-PU, are commercially available and feature similar hard phases that are formed by the reaction of <NUM>,<NUM>-butanediol and <NUM>,<NUM>'-methylenebis(phenyl isocyanate). These TPUs contain, however, different soft phases. PBA-PU is based on poly(<NUM>,<NUM>-butylene adipate) as a soft segment, which partially crystallizes upon cooling to sub-ambient temperature and can serve as the switching element for a shape memory effect. The poly(tetrahydrofuran) segments present in PTHF-PU crystallize only poorly,<NUM> and as a result PTHF displays the thermomechanical properties of a typical polyurethane elastomer with poor shape memory characteristics. These PUs were blended with <NUM> - <NUM>% w/w of PBA by melt-mixing the components at <NUM>. The PBA was thought to act as a modifier polymer that, by way of modifying the melting and crystallization behavior of the materials, could be used to modify their shape memory characteristics. The resulting blends were compression-molded at the same temperature into <NUM>-<NUM> thin films, then cooled to room temperature and stored under ambient conditions for at least <NUM> before any characterization was conducted. All films are semitransparent, have a homogeneous appearance, and feature a similar haziness, indicating the absence of any significant macroscopic phase separation.

The thermal behavior of the various compositions was investigated by thermogravimetric analyses (TGA) and differential scanning calorimetry (DSC) experiments. TGA measurements under nitrogen reveal that both polyurethanes and their blends with PBA display only a moderate weight loss (around <NUM>%) upon heating to above <NUM> (<FIG>). The thermal transitions of all materials were analyzed by DSC experiments. Previous studies have established that the neat PBA<NUM> and also the PBA segments included in the PBA-PU<NUM> display a rather complicated crystallization behavior. Crystallization at different temperatures leads to different ratios of two polymorphs, the thermodynamically more stable α form and the kinetically preferred β form, which show slightly different melting temperatures. Recrystallization from the β to the α form is possible and on account of crystal size variations the α form can display two distinct melting transitions. Thus, a broad melting range with more or less well resolved peaks is usually observed. <FIG> and b show the first heating and the first cooling traces of the neat PBA-PU and its blends with PBA; the transition temperatures extracted from these measurements are compiled in Table <NUM>. The first heating trace of the neat PBA-PU shows a broad melting transition with a broad melting peak with a maximum at <NUM> and a shoulder at <NUM>, which indicates the presence of a mixture of α and β polymorphs, recrystallization of the β into the α form around <NUM> and melting of larger α form crystals above <NUM>. <NUM>, <NUM>-<NUM> The first cooling trace of the neat PBA-PU shows a crystallization peak that sets in at around <NUM> and has a maximum at <NUM> (<FIG>). The first DSC heating trace of the neat PBA shows a more narrow melting peak with an onset at <NUM> and a maximum at <NUM> (<FIG>), while the second heating trace shows two transitions at <NUM> and <NUM>, characteristic of a mixture of β and high temperature α form (<FIG>). The first cooling curve of the neat PBA shows an onset of the crystallization at <NUM> and a maximum around <NUM> (<FIG>), while the second cooling curve shows maximum at <NUM> (<FIG>).

The first heating traces of the PBA-PU/PBA blends with <NUM>, <NUM>, or <NUM>% w/w PBA exhibit a broad melting transition with multiple peaks in the <NUM>-<NUM> range and maxima at <NUM>-<NUM>, indicative of a mixture of α and β forms; interestingly, in the case of the <NUM>% and <NUM>% w/w PBA-PU/PBA blend, the DSC trace suggests a majority of (smaller) α crystals (<FIG>, Table <NUM>). Note the absence of the melting peak associated with the neat PBA at a slightly higher temperature. The cooling scans of the PBA-PU/PBA blends each show only one peak, with a maximum at <NUM>, <NUM> or <NUM> for <NUM>, <NUM> and <NUM>% w/w PBA-PU/PBA blends, respectively (<FIG>, Table <NUM>). Taken together, the results suggest that the incorporation of PBA into PBA-PU increases the crystallization temperature substantially. The mechanism may involve "normal nucleation", in that the unbound or free PBA chains added crystallize first and thus nucleate the less mobile PBA segments in the physically cross-linked PBA-PU. It is also possible that (a portion) of the added PBA reacts with the PBA-PU, for example through trans-esterification or an opening of the urea bonds), leading to either longer PBA chains in this polymer or PBA chain ends, both of which also can serve to nucleate the crystallization of the material (vide infra). Observations that the addition of free polymer can impact the crystallization behavior of an SMP were noted in a previous study of PCL-PU/PCL blends, wherein the size of PCL crystals was shown to decrease with increasing PU content. <NUM> However, the prior-art study targeted - and demonstrated - a reduction of the PCL melting temperature, and no changes of the crystallization temperature were mentioned. Further, no indication of the mechanism at play was provided.

The first DSC heating trace of the neat PTHF-PU shows a very weak, broad melting transition in the range of <NUM>-<NUM> (<FIG>), which is related to the melting of a small fraction of crystallized PTHF segments. <NUM> The cooling trace of the neat PTHF-PU does not show any crystallization event (<FIG>), consistent with the sluggish crystallization of this polymer.

The first DSC heating traces of the PTHF-PU/PBA blends show broad melting transitions between <NUM> and <NUM> with maxima at <NUM>-<NUM> (<FIG>, Table <NUM>), indicative of mixtures of PBA α and β crystals. As for the PBA-PU/PBA blends, the melting temperature of the PBA in the PTHF-PU/PBA blends is lower than in the neat PBA. The cooling traces of the PTHF-PU/PBA blends show PBA crystallization peaks between <NUM> (<NUM>% w/w PBA) and <NUM> (<NUM>% w/w PBA) (<FIG>), i.e., at only slightly lower temperatures than in the PBA-PU/PBA blends. Thus, by and large, the thermal transitions of the PBA in the two polyurethanes are very similar, suggesting that the crystallization is primarily driven by the added PBA. Nevertheless, the mobility limiting effect imparted by both polyurethane networks reduces the transition temperatures in comparison to the neat PBA.

Isothermal DSC studies were undertaken to test the possibility to crystallize the PBU-PU/PBA blends above the Tc established by DSC and in particular at body temperature. Although the crystallization onset measured by DSC for all three compositions (<NUM>-<NUM> % w/w of PBA) is below <NUM> (<FIG>), it is known to those skilled in the art that polymers can crystallize when T is Tc ≥ T > Tm and the crystallization rate increases as T approaches Tc. Thus, the samples were heated in the DSC pan to <NUM>, kept at this temperature for <NUM> and then quickly (cooling rate -<NUM>/min) cooled to <NUM>. The heat flow at <NUM> was recorded for <NUM> (<FIG>) and the traces clearly show that, while for the neat PBA-PU no exothermic process takes place within the timeframe of the experiment, for the <NUM>% composition a very broad (i.e. slow) crystallization process is recorded which is further accelerated for the <NUM> and <NUM>% compositions. The traces suggest that the crystallization of the PBA segments is largely complete after <NUM> and <NUM> for the <NUM> and <NUM>% w/w blends, respectively. After the isothermal DSC experiments were completed, the samples were further heated from <NUM> up to <NUM> in order to detect the melting of the crystalline domains formed during annealing at <NUM> (<FIG>). As expected, no endothermal process was observed for the neat PBA-PU, confirming the inability of the neat poly(ester urethane) to crystallize at <NUM> within a desirable timeframe. Conversely, melting peaks are recorded for the PBA-PU/PBA blends with enthalpies increasing with increasing PBA content, clearly confirming that isothermal crystallization at <NUM> is possible in the case of the materials according to the present invention.

The morphology of PBA-PU, PTHF-PU and their blends with PBA was further probed by optical microscopy under dynamic heating and cooling. A comparison between neat PBA-PU and the PBA-PU/PBA <NUM>% mixture was obtained by placing the two films (one <NUM> thick film per composition) side-by-side on a glass slide. The samples were first heated from <NUM> to <NUM> and kept at this temperature for <NUM>. Images taken under cross-polarized light show the loss of birefringence for both samples due to the melting of the crystalline PBA segments (<FIG> a). Next, the samples were cooled to <NUM> and kept at this temperature for <NUM>. Cross-polarized micrographs taken at regular time intervals clearly show the rapid formation (<NUM>-<NUM>) of PBA crystallites in the PBA-PU/PBA <NUM> % w/w sample (<FIG>, left side of every picture), whereas no crystallization is visible for the neat PBA-PU (<FIG>, right side of every picture).

<FIG> shows the wide-angle X-ray scattering (WAXS) patterns of the neat PBA-PU, PBA, and the PBA-PU blends with <NUM> or <NUM>% w/w PBA. The spectrum of the neat PBA shows four characteristic peaks with q-values at <NUM>, <NUM>, <NUM>, and <NUM>-<NUM> (<FIG>), corresponding to a mixture of α and β crystal forms, which is in agreement with a previous report. <NUM> The WAXS spectrum of PBA-PU shows a similar spectrum (<FIG>) and the peak center positions are virtually the same (<FIG>); however, the distribution of the scattering intensities is shifted and suggests a higher fraction of β than α crystals. The scattering pattern of the <NUM>% w/w PBA-PU/PBA blend is nearly the same as that of the neat PBA-PU (<FIG>), whereas the one of the <NUM>% w/w PBA/PBA-PU blend shows a peak pattern that is void of the peaks associated with crystals (<FIG>). The WAXS spectrum confirms the presence of only α peaks (<FIG>). This suggests that in the <NUM>% w/w PBA-PU/PBA blend, the PBA originally present in the PBA-PU and the added PBA may co-crystallize to form thermodynamically stable α crystallites,<NUM> on account of the increased content of PBA and the slower crystal growth rate owing to the mobility limiting effect imparted by the PU network. Thus, quite surprisingly, the incorporation of free PBA into the PBA-PU not only leads to an increase of the crystallization temperature, but can also have a significant influence on the crystal structure.

The WAXS spectrum neat PTHF-PU, shows weak peaks at q-values of <NUM>, <NUM> and <NUM>-<NUM> that are characteristic of the weakly crystalline PTHF phase (<FIG>). The spectra of the <NUM>% and <NUM>% w/w PTHF-PU/PBA blends (<FIG>) are superpositions of this spectrum and the PBA contributions seen in the corresponding PBA-PU/PBA blends, with a mixture of α and β crystals in the <NUM>% blend, and predominantly α crystals in the <NUM>% w/w PTHF-PU/PBA blend (<FIG>-d). Interestingly, this observation suggests that an increased PBA content in the PU blend favors the formation of α crystals, irrespective of the PU matrix employed. It also shows that the presence of PBA in the majority polymer used is not a sine qua non condition.

A comparison of the size exclusion chromatography (SEC) traces of the neat PBA-PU, the neat PBA, and the PBA-PU/PBA blends reveals that the molecular weight of the blends is considerably lower than that of the neat PBA-PU (<FIG>). The SEC trace for the <NUM>% w/w PBA-PU/PBA blend shows a single peak and no other peaks corresponding to either the neat PBA-PU or the free PBA. This is indicative of a largely complete reaction between the PBA-PU and the PBA, either by way of transesterification, or another reaction. The <NUM>% w/w PBA-PU/PBA blend thus is not a physical mixture or blend, but rather a new polymer that is characterized by Mn, Mw and Ð values of <NUM>,<NUM>/mol, <NUM>,<NUM>/mol, and <NUM> respectively. The SEC traces of the <NUM>% and the <NUM>% PBA-PU/PBA blends show a main peak that is similar to that of the <NUM>% w/w PBA-PU/PBA blend, although the retention times are slightly higher (indicating lower molecular weights); in addition, a shoulder at higher retention time us observed, which is more prominent in the <NUM>% w/w PBA-PU/PBA blend and is likely due to the presence of unreacted or "free" PBA. Note that the reduction in molecular weight is not affecting significantly the mechanical properties of the material (vide infra).

These results raise the question whether the desirable thermal properties discovered for the PBA-PU/PBA blends arise from the increase of the PBA content, the presence of free PBA, or if reaction products, which are thought to feature PBA chain ends, could possibly trigger the nucleation. In order to explore this further, we carried out a control experiment on a solution-cast film of a <NUM>% w/w PBA-PU/PBA blend. The sample was prepared by dissolving the two components in tetrahydrofuran, casting into a mould, and drying at moderate temperature. The DSC analysis of the solvent cast film (<FIG> a,b) reveals a thermal behavior that is very similar to the one of the corresponding melt-mixed material, featuring a melting peak at <NUM> upon heating and a crystallization peak at <NUM>, ca. <NUM> degrees lower than the melt mixed <NUM>% w/w PBA-PU/PBA (i.e. <NUM>). When the solvent-cast film was re-molded by compression molding at <NUM> for <NUM>, the Tc of the material increased to <NUM>, suggesting that even a rapid thermal treatment can trigger a reaction between PBA and PBA-PU. Indeed, size exclusion chromatography analyses of the solvent-cast film and the re-molded sample show that, while for the former two distinct peaks corresponding to PBA-PU and PBA are observed, for the latter the thermal treatment causes a shift toward lower molecular weights (<FIG>). We also produced a <NUM>% w/w PBA-PU/AcPBA blend by melt-mixing, assuming that the conversion of the hydroxyl end groups of the PBA into acetates (i.e., in AcPBA), should lead to a reduction or suppression of the reaction with the PBA-PU during melt mixing. Indeed, size exclusion chromatography analyses reveal that the melt-mixed <NUM>% w/w PBA-PU/AcPBA blend shows two discrete peaks that overlap with those of the neat PBA-PU (which, for purpose of comparison was also processed in the melt-mixer under identical conditions) and the neat PBA, indicating the absence of any significant reaction between PBA-PU and AcPBA (<FIG> a). The DSC traces reveal a thermal behavior that is indeed very similar to the one of the corresponding solution cast or melt-mixed materials, featuring a melting peak at <NUM>-<NUM> upon heating and a crystallization peak at <NUM> (<FIG> b). The isothermal DSC experiment at <NUM> is identical to that of the solution-cast film, whereas the crystallization is slightly slower than in the case of the melt-processed <NUM>% w/w PBA-PU/PBA blend (<FIG> c). The <NUM>% w/w PBA-PU/AcPBA blend displayed excellent fixity (<NUM>%) in the <NUM>st and <NUM>nd cycle when programmed at <NUM> with fixation time of <NUM>. Thus based on the findings that (a) the <NUM>% w/w melt-processed PBA-PU/PBA blend, which appears to be void of free PBA but has a reduced molecular weight relative to the neat PBA-PU, (b) the <NUM>% w/w melt-processed PBA-PU/PBA blend, which appears to contain residual free PBA, (c) the solution-cast <NUM>% w/w PBA-PU/PBA and the melt-processed <NUM>% w/w PBA-PU/AcPBA blends, which featured free PBA or AcPBA and shows no significant molecular weight reduction relative to the PBA-PU, all show an increase of Tc, which seems to scale with the PBA content, we conclude that it is primarily the increase of the PBA content that drives the crystallization behavior, although it is also well possible that the effect is connected to an increased mobility of the PBA in the "blends" vis a vis the original PBA-PU, either because the PBA added remains free, is (through reaction) placed at chain ends, or has a higher molecular weight than the PBA originally present in the PBA-PU. It is further demonstrated that both melt mixing and solvent-based methods as well as combinations thereof can be employed to prepare shape memory materials according to the present invention and that the molecular weight can be retained or reduced at will.

The mechanical properties of the films of the neat PUs and their blends with <NUM> or <NUM>% w/w PBA were investigated by dynamic mechanical analyses (DMA) in a temperature range of - <NUM> to <NUM>. The DMA trace of the neat PBA-PU reveals a gradual reduction of the storage modulus (E') upon heating from -<NUM>, a sharp, step-like modulus drop around <NUM>-<NUM>, which is related to the melting of crystalline PBA domains, a rubbery plateau that extends from about <NUM> to <NUM>, and another sharp modulus reduction above this temperature, which is related to the dissociation of the PU's hard segments (<FIG>). At <NUM>, the binary blends of PBA-PU with PBA (<FIG>) display an increased storage modulus vis à vis the neat PBA-PU (<NUM> MPa); the <NUM>% w/w PBA blend exhibits an E' of <NUM> MPa, whereas a further increase of the PBA content to <NUM>% w/w did not change E' much more (<NUM> MPa) (Table <NUM>). The shape of the DMA trace remained largely unaffected, although the transition associated with the PBA melting seems to become sharper upon introduction of the PBA and the temperature at which the hard phase dissociates decreases with increasing PBA content from ca. <NUM> to ca. Interestingly, in the rubbery plateau (that is above the Tm of the PBA) the E' values of the blends are lower than those of the neat polymers, which can be advantageous as the materials are softer and shaping of a temporary shape is easier.

The DMA trace of the neat PTHF-PU (<FIG>) reveals a Tg at~ -<NUM>, a hint of a Tm associated with melting of a minor fraction of a crystallized soft phase at ~<NUM>,<NUM> a continuous modulus drop up to ~<NUM>, and a sharp modulus reduction above this temperature, which is related to the melting of the hard segment phase. Blends of PTHF-PU with PBA also show an increase of E' of up to <NUM> MPa (<NUM> and <NUM>% w/w PBA), and a pronounced step-wise reduction of E' due to melting of the PBA crystals appears between <NUM> and <NUM> (Table <NUM>, <FIG>). As for the PBA-PU blends, a reduction, albeit less pronounced, of the hard phase's melting temperature from <NUM> to ~<NUM> was observed (<FIG>).

<FIG> shows the stress-strain curves of PBA-PU and its blends with PBA acquired at <NUM>. The trace of the neat PBA-PU reveals an elastic regime with a Young's modulus of <NUM> MPa before yielding at a stress and strain of ca. <NUM> MPa and <NUM>%, respectively. The plastic regime shows significant strain hardening and the samples fail at a maximum stress of <NUM> MPa and an elongation of <NUM>% (Table <NUM>). This mechanical behavior is consistent with the morphology of the neat PBA-PU and reflects a rearrangement of the crystallized PBA segments beyond the yield point. Blending the PBA-PU with <NUM>% w/w PBA led to a significant increase of the Young's modulus (<NUM> MPa) and yield stress (<NUM> MPa), while the elongation at break increased moderately to <NUM>-<NUM>% (Table <NUM>); interestingly the strain hardening was completely suppressed, perhaps because of the more localized deformations and reduced chain entanglements on account of the increased crystalline content in the blends. <NUM> Increasing the concentration of PBA to <NUM>% and <NUM>% did not lead to significant changes of the tensile behavior vis à vis the <NUM>% blend.

The stress-strain curves of PTHF-PU and its blends with PBA are shown in <FIG>. The trace of neat PTHF-PU shows an elastic regime up to <NUM>% with a Young's modulus of <NUM> MPa and yield stress of c. <NUM> MPa and elongation strain at break of <NUM>%. The neat PTHF-PU also shows strain hardening with maximum stress of <NUM> MPa. A significant increase of the Young's modulus (<NUM> MPa) and yield stress (<NUM> MPa) with reduced strain hardening was observed for the <NUM>% w/w PTHF-PU/ PBA blend. However, a further increase of the PBA content (<NUM>% w/w) in the PTHF-PU blends did not change the Young's modulus significantly but reduced the elongation at break drastically (<NUM>%). This could be the result of increased extent of micro-phase separation stemming from the increased PBA content, which leads to inhomogeneous and dislocated deformations and thus the failure in the plastic regime.

The shape memory behavior of PBA-PU, PTHF-PU and their respective blends with PBA was investigated on thin films, using a DMA in controlled force mode according to a reported protocol. <NUM>,<NUM> In one set of experiments, the temporary shape was programmed by heating the samples to <NUM>, deforming them to either ca. <NUM>% (PBA-PU blends and neat PTHF-PU) or ca. <NUM>% (<NUM>% w/w PTHF-PU/PBA blend) strain (based on the mechanical characteristics established by tensile testing), and subsequent cooling under applied stress to a given fixing temperature, which was varied. After maintaining the samples under load at the fixing temperature for typically <NUM>, and in some cases <NUM> or <NUM>, the stress was removed, and the temperature was increased again to <NUM>, to release the temporary and (partially) recover the original shape. The cycle was repeated several times. Representative shape memory cycles are shown in <FIG>, <FIG>, <FIG>, while the values for % fixity and % recovery were extracted from <NUM>st or <NUM>nd and <NUM>rd cycles, using Eqs. <NUM>-<NUM> (see Experimental Section), are reported in Tables <NUM> and <NUM>. Thermoplastic PUs are known to display an incomplete recovery when they are first deformed (notably at elevated temperatures) due to irreversible hard-segment rearrangements, and therefore cyclic shape memory experiments display a large "hysteresis" between the first and subsequent cycles. To take this into account, the first cycle is usually omitted for the analysis.

The neat PBA-PU, outside of the invention, shows an excellent fixity of <NUM>% when programmed for <NUM> at a fixation temperature of <NUM> (<FIG>, Table <NUM>) indicating efficient PBA crystallization at this temperature as suggested by the Tc established by DSC analysis (<NUM>). A similar fixity was observed if the fixation was carried out at <NUM> with an extended fixation time of <NUM> (<FIG>, Table <NUM>), but if the time was reduced to <NUM>, the fixity dropped to <NUM> ± <NUM>. However, when the fixing temperature was increased to <NUM> the fixity was reduced to <NUM>-<NUM>%, even at a fixing time of <NUM>, whereas the recovery rate was only <NUM>-<NUM>% (<FIG>, Table <NUM>). The <NUM>% w/w PBA-PU/PBA blend displays a higher crystallization temperature (~<NUM>, Table <NUM>), which permitted fixation at <NUM> and <NUM> (extended fixation time) with superior fixity value (<FIG>, Table <NUM>). Increasing the PBA content (<NUM>% w/w) further raises the crystallization temperature (DSC shows an onset at ~ <NUM> and a maximum at <NUM>, Table <NUM>) and the <NUM>% w/w PBA-PU/PBA blend showed a fixity of <NUM>% at a fixing temperature of <NUM> (<FIG>). Further elevating the fixation temperature to <NUM> yielded an excellent fixity of <NUM>% at a fixation time of <NUM> (<FIG>). With possible biomedical applications in mind, the fixation temperature was increased to <NUM>, and fixity values of <NUM> and <NUM>% were achieved at fixing times of <NUM> and <NUM>, respectively (<FIG>-d, Table <NUM>). On account of its higher Tc (<NUM>), the <NUM>% w/w PBA-PU/PBA blend was able to achieve a good fixity of <NUM>% at <NUM> even with short fixation time of <NUM> while the fixity increases further to <NUM>% when the fixation time is extended to <NUM> (<FIG>-f, Table <NUM>). The data in Table <NUM> show further that the fixity achieved in the first programming cycle is in all cases comparable to that of subsequent cycles, and that the recovery rate is typically <NUM>% or higher, except for the first cycle data, which the lower recovery rate reflects the intrinsic hysteresis associated with the deformation of pristine PUs. The data also show that the time/temperature required for fixing the temporary shape can be conveniently controlled via the composition of the blend.

Thus, blending PBA-PU with PBA indeed affords shape memory materials in which a temporary shape can be programmed at a substantially higher temperature than in the case of the neat PBA; notably, excellent shape fixity can be achieved at physiological temperature. Eliminating the hysteresis effect<NUM>-<NUM> in the first shape memory cycles, recovery ratios extracted from <NUM>nd and <NUM>rd cycles were excellent (<NUM>-<NUM>%) for the neat PBA-PU and its blends with PBA (Table <NUM>).

The neat PTHF-PU was deformed up to <NUM>% strain and cooled to <NUM> for temporary shape fixation (as no crystallization peak could be discerned in DSC), PTHF-PU shows good fixity of <NUM>% at this temperature (<FIG>, Table <NUM>). The <NUM>% w/w of PTHF-PU/PBA blend was deformed up to <NUM>% strain and the deformed shape was fixed either at <NUM> (crystallization temperature) or <NUM> (ambient temperature). The blend displayed good fixity of <NUM>% in the first and the consecutive cycles at <NUM> (<FIG>, Table <NUM>), however at <NUM> better fixity (<NUM>%) in the first cycle and a lower fixity (<NUM>%) was observed in the consecutive cycles, which can be explained by the lower content and the crystallization temperature of the PBA (<FIG>, Table <NUM>).

An alternative shape memory cycle was also used to investigate the behavior when deforming the materials only after first cooling them to the fixing temperature. This protocol is perhaps better suited to characterize the behavior under practically useful conditions where an object or device containing the shape-memory material is (i) heated above the transition temperature (Tm) to soften the material, (ii) is cooled to a temperature low enough as to cause no harm or discomfort when inserted in or around the body, and (iii) is positioned in the deployment position where the material adapts its shape to the surrounding environment (i.e. stress is applied) at the body temperature (i.e. <NUM>). As for the shape memory test described above, the cyclic tests start with the sample being heated to <NUM> and being kept at this temperature for <NUM>. The samples were then cooled to <NUM> (rate <NUM>/min) to simulate the deployment of an object or a device, and kept at this temperature for <NUM>. The samples were then uniaxially deformed, as described above, and kept under load isothermally for <NUM>. After the removal of the stress, the cycle proceeded as for the conventional cycle. Gratifyingly, the revised shape-memory cycle recorded for the <NUM>% w/w PBA-PU/PBA blend (<FIG>) allows to achieve excellent fixity and recovery of <NUM> and <NUM> %, respectively. Moreover, due to the deformation occurring at lower temperature, the alternative shape memory cycle does not suffer from the pronounced hysteresis observed during the first cycle on the standard shape-memory tests.

To demonstrate broader applicability of the invention, we also created melt-mixed blends or PBA-PU and PCL of Mw/Mn of <NUM>,<NUM>/<NUM>,<NUM>·mol-<NUM>. For example, the <NUM>% w/w PBA-PU/PCL mixture shows a Tm of <NUM> and <NUM> in the first and second DSC heating cycle and a Tc of <NUM> in the first and second cooling cycle, with a small shoulder around <NUM> (<FIG>). While the latter is indicative of free PCL, the crystallization peak centered around <NUM> reveals that the crystallization temperature of the PBA segments in the PBA-PU can also be increased by using PCL as a modifier polymer. The <NUM>% w/w PBA-PU/PCL mixture shows an excellent fixity of <NUM>% (<NUM>st cycle) and <NUM>% (<NUM>nd cycle) when programmed for <NUM> at a fixation temperature of <NUM> (<FIG>) indicating efficient PBA crystallization at this temperature.

To demonstrate the technical applicability of the invention in an example, an earpiece, that is the in-ear-part of a hearing aid device, was produced by injection-molding the <NUM>% w/w PBA-PU/PBA blend using a suitable mould. Reference earpieces were also made from the neat PBA-PU. The coupling of hearing devices and especially the earpiece component thereof to the ear is of great importance for the acoustic performance of the hearing device and also the wearing comfort. The anatomy of the ear canal varies between individuals and customizing earpieces so that they fit to the geometry of the user's ear canal is considered of great importance. This could readily be achieved by using the PU-PBA/PBA blend according to the present invention. The earpiece was heated to <NUM> in an oven, removed, and within <NUM> inserted into an individual's ear. After <NUM>, the earpiece was removed from the ear end clearly remained in the shape that was programmed by the process. By contrast, a reference experiment with the neat PU-PBA under the same conditions showed that shape fixation at body temperature is not possible with the prior-art material.

In summary, we have shown that the thermal, mechanical and shape memory properties of a commercially available shape memory poly(ester urethane) with crystallizable switching segments (PBA-PU) can be modified by formulating this material with a commercially accessible, crystalline modifier. Most interestingly, incorporating free PBA into PBA-PU increased the shape fixing temperature from <NUM> to <NUM>, which is very beneficial for the utilization of such material in biomedical applications. This effect is general and could be used to increase the fixing temperature of PTHF-PU blends with PBA. Simple melt-mixing process was utilized to formulate the blends, which affords an easy route for the property modification of existing SMPs and upscaling of such materials for the technological applications.

Claim 1:
A thermoplastic shape memory composition, comprising: a thermoplastic shape memory polymer and a modifier polymer;
wherein a melting and crystallization of a crystallizable portion of the thermoplastic shape memory composition fixes a temporary shape;
wherein a further melting of the crystallized portion of the thermoplastic shape memory composition releases the temporary shape;
and wherein a crystallization temperature of said crystallizable portion of said thermoplastic shape memory composition is at least <NUM> higher than that of a crystallizable portion of the thermoplastic shape memory polymer without the modifier polymer.