Untitled record

ES 2 359 631 T3

DESCRIPTION

Shape memory polymers based on semi-crystalline thermoplastic polyurethanes containing nanostructured hard segments

Related requests reference

This application claims priority over Provisional Application Nos. Serial 60 / 418,023 filed October 11, 2002, 60 / 466,401 filed April 29, 2003; 60 / 419,506 filed Oct. 18, 2002; 60 / 488,590 filed July 18, 2003 and 60 / 488,323 filed July 18, 2003.

Technical field

The present invention relates to shape memory polymers and more specifically to thermoplastic polyurethanes with an alternating sequence of hard and soft segments wherein a nanostructured polyhedral oligomeric silsesquioxane diol is used as a chain extender to form a crystalline hard segment, and it also refers to methods for the preparation of these thermoplastic polyurethanes and their applications.

Background of the invention

Shape memory materials are characterized by the ability to transform from a frozen temporary shape to a permanent shape when there is a triggering environmental stimulus, such as heat, light, or steam. Used creatively, this phenomenon can be harnessed for a wide range of applications. Although shape memory alloys (SMA) and shape memory polymers (SPM) exhibit similar shape memory properties by thermal stimulation, their mechanisms of action are quite different. Advantages of SMAs include rapid strain recovery (within 1 second), potential bimodal reversible memory training, and apparent superelasticity due within the austenite phase at low temperatures. Instead, polymers inherently exhibit shape memory effects derived from their considerably coiled constituent chains that are collectively extensible through mechanical work and this energy can be stored indefinitely, known as shape fixation, by cooling below Tg or Tm. . Polymeric samples can later perform mechanical work and return to a stress-free state when heated above the critical temperature, mobilizing frozen chains to regain entropy from their coiled state. Compared to SMAs, thermally stimulated SMPs have the following advantages: (i) large recoverable strains in excess of several hundred percent strain; (ii) easy adjustment of transition temperature through variation of polymer chemistry; and (iii) ease of processing at low cost.

Thermally stimulated SMPs with different thermomechanical properties have been previously synthesized and characterized to function in various applications, for example as medical devices and mechanical actuators. Materials span a wide range of room temperature moduli, from rigid glassy materials with storage moduli of various GPa to compatible rubbers with modulus as low as tens of MPa. On the other hand, the shrinkage moduli (elastic) have been adjusted in the range 0.5 <E <10 MPa, as prescribed by the end application. An example of this is chemically cross-linked polycyclooctene (PCO), a rigid semi-crystalline rubber that is elastically deformed above Tm to a temporary shape that is fixed by crystallization. Quick and complete recovery from severe deformations is achieved by immersion in hot water. These SMPs have been described in US Provisional Patent Application Serial No. 60 / 419,506 filed October 18, 2002 entitled Chemically Crosslinked Polycyclooctene, the priority of which is claimed. In WO 03/093341, entitled Castable Shape Memory Polymers, stiffer SMPs that offer adjustable critical temperatures and elastic modulus are described using a thermosetting random copolymer made of two vinyl monomers that provide controlled Tg and cast type processing. These copolymers were crosslinked with a difunctional vinyl monomer (crosslinking agent), so that the crosslinking agent concentration controlled the elastic modulus and thus the working potential during recovery. In addition to their shape memory effects, these materials are also pourable, allowing more complex shapes to be poured. Furthermore, they are optically transparent, which makes them useful for additional applications.

The use of chemical crosslinking in both cases limits the types of processing possible and forever establishes the equilibrium shape at the point of network formation. Therefore, combinations of a semi-crystalline polymer with amorphous polymers have also been intensively investigated due to their attractive crystalline and mechanical properties. For blends that are miscible at the molecular level, a single glass transition occurs, without spreading, an important aspect for shape memory. Additionally, in such miscible blends the equilibrium crystallinity (which controls the modulus of the plateau between Tg and Tm when shape fixing is performed) also changes dramatically and systematically with the composition of the blends. This provides a simple route to alternative shape memory plastics; ie SMP with relatively high modulus in the fixed state at room temperature, which have a sharp, adjustable transition, and

ES 2 359 631 T3 the permanent shape can be repeatedly reshaped above certain softening temperatures. These SMP combinations have been described in US Provisional Patent Application Serial No. 60 / 466,401 filed April 29, 2003 and entitled Blends of Amorphous and Semicrystalline Polymers with Shape Memory Properties of which priority is claimed.

Microphase separated semi-crystalline thermoplastic polymers exhibiting two sharp softening transitions Tm2> Tm1> room temperature, where the difference of the two softening points is at least 20 ° C, are also good candidates for shape memory, offering the advantage of to be processed in the molten state above Tm2, ​​and to repeatedly regain the equilibrium shape by relaxing the stress in the fluid state. Representative old examples of these polymers in this class of SMP are conventional polyurethanes whose soft domains are vitreous or semi-crystalline with a low softening point (but above the Tcrit) and whose hard domains have a higher softening point, only exceeded during the prosecution.

Another microphase-separated system is one described by Fu et al, in Polymer, vol. 42 (2001), pages 599-611. However, the incorporation of a polyhedral oligomeric silsesquioxane (POSS) in only one of the two phases in this system will not have altered the thermal activation temperature of the composite in general, which will have remained essentially the same as that of the phase without POSS.

Objects of the invention

An object of the present invention is to provide shape memory polymers comprising hybrid polyurethanes.

It is another object of the invention to provide shape memory polymers having a medium and adjustable modulus in the fixed state at room temperature, with an adjustable and sharp transition, the permanent shape of which can be repeatedly remodeled above a certain temperature of softening.

It is another object of the invention to provide polyurethane hybrid SMPs that demonstrate steep and adjustable transition temperatures, adjustable stiffness above their transition temperatures, and thermal processability above the softening point of POSS domains.

It is another object of the invention to provide polyurethane hybrid SMPs which possess excellent reshaping effect at the recovery temperature and wherein the retraction force is adjustable according to the composition of the POSS.

Still another object of the invention is to provide hybrid polyurethanes that are biocompatible and can be used as medical devices and implants.

Another object of the invention is a method for the synthesis of such hybrid polyurethanes.

Compendium

In general terms the invention provides a method for producing hybrid polyurethane SMPs by reaction of (A) a polyol, (b) a chain extender which is a dihydroxyl terminated POSS and (C) a diisocyanate, where POSs represents a polyhedral silsesquioxane diol and where the shape memory polymer has a thermal activation of 30 to 60 ° C. The polyol (A) can be polyethylene glycol (PEG), polycaprolactone (PCL), polycyclooctene (PCO), trans-1,4-butadiene, trans-isoprene, polynorbornene diol and polymethacrylate copolymer, the chain extender (B) can be TMP cyclopentyldiol-POSS, TMP cyclohexyldiol-POSS, TMP isobutyldiol-POSS, trans-cyclohexanediolcyclohexane POSS, or trans-cyclohexanediolisobutyl POSS, and the diisocyanate (C) can be selected from a large number of diisocyanates and is preferably 4,4'-diphenylmethane diisocyanate (MDI). Other diisocyanates (C) that are suitable for use in the synthesis of SMP based on hybrid polyurethanes include: 2,4-toluene diisocyanate (TDI), 2,6-toluene diisocyanate, 1,6-hexamethylene diisocyanate (HDI ), isophorone diisocyanate (IPDI), and hydrogenated 4,4'-diphenylmethane diisocyanate (H12MDI).

The polyol can be semi-crystalline and is preferably selected from polyethylene glycol (PEG), polycaprolactone (PCL), polycyclooctene (PCO), trans-1,4-butadiene, trans-isoprene or it can be amorphous, for example with a Tg in the range of 20 ° C-80 ° C, in which case it can be a polynorbornene diol and / or polymethacrylate copolymer.

The method for producing hybrid polyurethane SMPs and the new hybrid polyurethanes thus prepared are illustrated by the following non-limiting reaction schemes.

ES 2 359 631 T3

<img file="ES2359631T3_D0001.tif" />

This scheme shows an example of TPU synthesis using polyethylene glycol as polyol, trans-cyclohexanediol isobutyl POSS as chain extender to react with 4,4'-diphenyl methylene diisocyanate in toluene.

<img file="ES2359631T3_D0002.tif" />

This scheme shows an example of TPU synthesis using polycaprolactone diol as polyol, TMP IsobutyldiolPOSS as chain extender to react with 4,4'-diphenyl methylene diisocyanate.

<img file="ES2359631T3_D0003.tif" />

This scheme shows an example of TPU synthesis using polycyclooctene diol as polyol, TMP IsobutyldiolPOSS as chain extender to react with 4,4'-diphenyl methylene diisocyanate.

The following is a general formula for POSS-based TPUs incorporating PEG diol, prepared analogously to Scheme 1 but using a different Isobutyldiol-POSS. Polymers allow a systematic variation in the X / Y ratio (1 to 20), the polyol degree of polymerization (1 &lt;n &lt;1000), and the total degree of polymerization, 2 &lt;m &lt;100.

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<img file="ES2359631T3_D0004.tif" />

The hybrid polyurethanes of the invention demonstrate steep and tunable transition temperatures, tunable stiffness above their transition temperatures, and thermal processability above the softening point of the POSS domains. Hybrid polyurethanes also exhibit excellent shape recovery effect at recovery temperature and a shrinkage force that is adjustable according to POSS composition. They also possess a unique property that is different from other shape memory polymers and that is that it has now been found (in the PEG embodiment) that recovery can be activated with moisture (liquid or vapor) as well as heat. For the thermal activation mechanism, the range of 30 ° C to 60 ° C is important depending on the proportion of the components used and (very important) of the heat treatment to produce crystallinity in the steady state (equilibrium). Recovery can be completed in seconds when heated to 20 ° C above the transition temperature. Additional advantages of the materials include that the materials are rigid at room temperature, the polymers are generally biocompatible and in some cases biodegradable, and can be used as medical devices and implants. Products can also be tinted to any color or made radiopaque to d-ray radiographs depending on application requirements.

Any of the hybrid polyurethane polymers mentioned above can be loaded, for example with boron nitride nanoparticles, silica, titanium dioxide, montmorillonite clay, Kevlar, staple fibers, aluminum nitride, barium subcarbonate and bismuth subcarbonate. For example, clay and silica can be used to increase the modulus of the plastic. For example, dispersing agents and / or compatibilizing agents can be used to improve the mixing between polymers and the mixing of polymers with fillers. Dispersing and / or compatibilizing agents include, for example, ACRAWAX® (ethylene bis-stearamide), polyurethanes and ELVALOY® (acrylic functional polyethylene). Polymers can be cross-linked by application of radiation such as e, UV, gamma rays, x-rays or by heat activated chemical crosslinking techniques. Radiation techniques have the advantage that the polymer does not normally have to be overheated to cause crosslinking. If e-rays are used, an exposure of about 200-300, for example 250 kGy, usually provides sufficient crosslinking.

Brief description of the drawings

FIGURE 1 graphically illustrates the DMA curve for TMP BOSS-based thermoplastic polyurethane (TPU) with PEG: POSS molar ratio of 1: 6, 1: 4 respectively;

FIGURE 2 graphically illustrates DSC results for TMP POSS-based TPU with different PEG: POSS molar ratios;

FIGURE 3 illustrates equipment used to measure stress-strain; and FIGURE 4 graphically illustrates the stress-strain curve of TPU based on TMP POSS (PEG: POSS = 1.6).

Detailed description

Thermoplastic polyurethanes of different compositions were synthesized by the one-stage condensation polymerization technique, using the scheme indicated above. Toluene was used as solvent and Dilaurate

ES 2 359 631 T3 dibutyl tin as a catalyst. The reaction was kept at 90 ° C under nitrogen for 2 hours and then cooled to room temperature and precipitated in hexane. The product was thoroughly dried and dissolved in toluene to make a 10% by weight solution. The molecular weights and molecular weight distributions of this series of samples obtained by size exclusion chromatography are summarized in Table 1.

Table 1. Molecular weights and molecular weight distributions of POS-based polyurethanes having polyol blocks (PEG) with a length of 10,000 g / mol

<td>Sample</td><td>Mn (g / mol)</td><td>Mw / Mn</td>

<td>PEG: POSS = 1: 3</td><td> 47.400</td><td> 1,42</td>

<td>PEG: POSS = 1: 4</td><td> 48.800</td><td> 1,44</td>

<td>PEG: POSS = 1: 6</td><td> 54.000</td><td> 1,54</td>

<td>PEG: POSS = 1: 8</td><td> 49.200</td><td> 1,30</td>

Polyurethane samples with different compositions were characterized by differential scanning calorimetry (TA Instruments DSC2920). All samples were characterized under the same conditions: Two sweeps were made for each sample with heating and cooling rates of 10 ° C / min (Figure 2). This series of polyurethanes was observed to have two softening points, one in the range 45 &lt;Tm1 &lt;50 ° C which corresponds to a softening temperature of the soft PEG block. The other softening transition appears in the interval 110 &lt;T_m2 &lt;130 ° C, which corresponds to the softening of a POSS-reinforced hard segment phase. It is observed that the softening temperature of the soft segment shifts to lower values ​​with a broadening of the softening peak while the softening temperature of the hard segment shifts to higher values ​​with a sharpening of the softening peak when the mole ratio polyol / chain extender decreases. This result can be explained because as the PEG: POSS ratio decreases, the resulting block copolymer will have less PEG content as a whole, which will directly affect the size and perfection of the crystallization of the PEG blocks. Therefore, the softening temperature moves towards lower values ​​and the peak widens. In contrast, POSS content will increase in block copolymers, providing clearer aggregation of hard segments to form larger, more perfect crystals. Therefore, the softening temperature of the hard segment shifts towards higher values ​​as the peak sharpens (Figure 2).

The dried films of the polyurethanes formed were cut into thin strips for the tests of provisional fixation and subsequent recovery, or shape memory. For example, a sample was first heated in the hot phase to 65 ° C, which is well above the first transition temperature but is a low enough temperature to avoid softening of the elastic network of the POSS-rich phase. It was then stretched to a certain degree of elongation and cooled to room temperature. The deformed shape was fixed at room temperature. Finally, the deformed shape was heated again on a hot plate to 65 ° C and it was observed that the sample recovered its original length completely and in a few seconds. A similar phenomenon was observed when water was used as the stimulus for reshaping, except that the sample underwent secondary swelling to form a strong hydrogel.

The hybrid polyurethanes of the invention can be used for the following applications.

to. Stents, patches and other implants for human health care.

b. Surgical instruments that require adjustable shapes but high rigidity.

c. Structural instruments of arbitrarily adjustable shape, including personal care items (dishes, brushes, etc.) and tool handles.

d. Self-healing plastics.

and. Medical devices (a serrated panel is repaired by heating or plasticizing with solvent).

F. Matrices for drug administration.

g. High strength thermoplastic (non-crosslinked) superabsorbent hydrogels.

h. Aqueous rheological modifiers for paints, detergents and personal care products.

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i. Impression material for molding, duplicating, rapid prototyping, dentistry and figure printing.

j. Toys.

k. Reversible enhancements to store information.

l. Temperature and humidity sensors.

m. Safety valves.

n. Heat shrinkable tapes or seals.

or. Heat controlled couplings and fasteners.

p. Large force actuators, large deformation.

q. Coatings, adhesives.

r. Textiles, clothing.

The shape memory polymers of the invention are particularly suitable as biomaterials due to their low thrombogenicity, high biocompatibility, as well as unique mechanical properties. According to the invention, shape memory polyurethanes were formulated so that the softening temperature of a segment decreased within a useful temperature range for biomedical applications: 37 ° C-50 ° C.

The present invention provides an advantageous shape memory polymer including thermoplastic polyurethane-based shape memory polymers formed by reacting, in one step, a polyol, a POSS chain extender and a diisocyanate, having a medium and adjustable modulus. in the fixed state at room temperature, it has an adjustable sharp transition, the permanent shape of which can be repeatedly reshaped above a certain softening point.

Although the polymers and processing methodologies of the present invention have been described with reference to specific illustrative embodiments thereof, the present invention is not limited to such illustrative embodiments. Rather, as will be apparent to those skilled in the art, the descriptions in the present disclosure are susceptible to many embodiments and / or applications, without departing from the scope of the present invention. Indeed, modifications and / or changes in the selection of specific polymers, polymer ratios, processing conditions, and end-use applications are contemplated, and such modifications and / or changes are included within the scope of the present invention set forth in the following claims.