THERMOPLASTIC SHAPE MEMORY MATERIAL

Abstract

The present invention relates to a process for producing a shaped body (SB) comprising the preparation of a thermoplastic polyurethane, the production of a shaped body (SB*) from the thermoplastic polyurethane, the heating of the shaped body (SB*) to a temperature below the temperature of permanent deformability of the shaped body (SB*) and above the switching temperature of the thermoplastic polyurethane, the expanding of the heated shaped body (SB*) to obtain a shaped body (SB), and the cooling of the shaped body (SB) to a temperature below the switching temperature of the thermoplastic polyurethane, and to the shaped bodies obtained or obtainable by such a process. The present invention further relates to the use of a thermoplastic polyurethane for production of a shaped body having shape memory effect within a temperature range from 20 C. to 120 C.

Claims

1. A process for producing a shaped body (SB), the process comprising: (a) preparing a thermoplastic polyurethane by conversion of (i) at least one polyisocyanate composition, (ii) at least one chain extender, and (iii) at least one polyol composition, wherein the polyol composition comprises at least one bisphenol derivative selected from the group consisting of bisphenol A derivatives having a molecular weight Mw>315 g/mol and bisphenol S derivatives having a molecular weight Mw>315 g/mol, wherein at least one of the OH groups of the bisphenol derivative has been alkoxylated, and wherein the polyol composition comprises at least one further polyol and the at least one further polyol is selected from the group consisting of polyetherols, polyesterols, polycarbonate alcohols and hybrid polyols; (b) producing a shaped body (SB*) from the thermoplastic polyurethane; (c) heating the shaped body (SB*) to a temperature below the temperature of permanent deformability of the shaped body (SB*) and above the switching temperature of the thermoplastic polyurethane; (d) expanding the heated shaped body (SB*) to obtain a shaped body (SB); and (e) cooling the shaped body (SB) to a temperature below the switching temperature of the thermoplastic polyurethane.

2. The process according to claim 1, wherein the thermoplastic polyurethane is a compact thermoplastic polyurethane.

3. The process according to claim 1, wherein a commencement of permanent deformability corresponds to a commencement of melting of the hard phase of the thermoplastic polyurethane, and a switching temperature corresponds to a commencement of the highest phase transition in terms of temperature before the melting range.

4. The process according to claim 1, wherein the switching temperature of the thermoplastic polyurethane (T.sub.switch) is in the range from 20 to 120 C.

5. The process according to claim 1, wherein an extent of the shaped body (SB) obtained in the expanding (d) in at least one dimension is at least 150% of an extent of the shaped body (SB*).

6. The process according to claim 1, wherein the shaped body (SB*) is produced in the producing (b) by extrusion, injection molding or sintering methods.

7. The process according to claim 1, wherein the chain extender used in (i) is a diol having a molecular weight Mw<220 g/mol.

8. The process according to claim 1, wherein the chain extender and the bisphenol derivative present in the polyol composition are used in a molar ratio of 40:1 to 1:10.

9. The process according to claim 1, wherein the at least one bisphenol derivative has the following general formula (I): ##STR00007## wherein R1 is in each case independently a methyl group or H, R2 and R3 are a methyl group or R2-CR3 together are OSO, X is a C(R1).sub.2-, C(R1).sub.2-C(R1).sub.2- or C(R1).sub.2-C(R1).sub.2-C(R1).sub.2- group, p and q are independently an integer from 1 to 4, and n and m are independently an integer >0.

10. The process according to claim 1, wherein the at least one bisphenol derivative has only primary OH groups.

11. (canceled)

12. The process according to claim 1, wherein the polyisocyanate is an aromatic diisocyanate.

13. The process according to claim 1, wherein the polyisocyanate is an aliphatic diisocyanate.

14. The process according to claim 1, wherein the shaped body (SB) undergoes recovery as a result of heating to a temperature above the switching temperature.

15. A shaped body obtainable or obtained by a process according to claim 1.

16. The shaped body according to claim 15, wherein the shaped body is a tube or a film.

17. The shaped body according to claim 15, wherein the shaped body has a shape memory effect within a temperature range from 20 C. to 120 C.

18. The shaped body according to claim 17, wherein the shaped body is a shrink tube or a shrink film.

Description

EXAMPLES

1 The Following Feedstocks were Used

[0171] Polyol 1: polyether polyol having an OH number of 113.3 and exclusively primary OH groups (based on tetramethylene oxide, functionality: 2) [0172] Polyol 2: bisphenol A-started polyether polyol having an OH number of 313 and exclusively primary OH groups, functionality: 2 [0173] Polyol 3: bisphenol A-started polyether polyol having an OH number of 236 and exclusively primary OH groups, functionality: 2 [0174] Polyol 4: polyester polyol based on adipic acid MEG with MW 470 g/mol and an OH number of 240, functionality: 2 [0175] Polyol 5: polyester polyol based on phthalic anhydride and DEG with MW 356 g/mol and an OH number of 315 [0176] Polyol 6: aromatic polyester polyol with MW 468 g/mol and an OH number of 240 [0177] Isocyanate 1: aliphatic isocyanate (4,4 methylene dicyclohexyl diisocyanate) [0178] Isocyanate 2: aromatic isocyanate (4,4 methylene diphenyl diisocyanate) [0179] CE: butane-1,4-diol [0180] Catalyst 1: tin(II) isooctoate (50% in dioctyl adipate) [0181] Stabilizer 1: sterically hindered phenol [0182] Additive 1: ester wax

2. General Preparation Example

[0183] The polyols were initially charged at 80 C. in a vessel and mixed with the components according to table 1 and table 2 with vigorous stirring. The reaction mixture was heated to more than 110 C. and was then poured out onto a heated, Teflon-coated table. The cast slabs obtained were heat-treated at 80 C. for 15 hours, then pelletized and processed by injection molding.

TABLE-US-00001 TABLE 1 Compounds used Number Comparative 1 Example 1 Example 2 Example 3 Example 4 Example 5 Polyol 1 [g] 700 490 280 0 0 420 Polyol 2 [g] 180 Polyol 3 [g] 0 210 420 600 600 Isocyanate 1 [g] 588.00 675.3 763.39 752.81 752.81 624.83 CE [g] 183.33 147.72 151.91 147.83 145.22 130.68 Catalyst 1 571 L 609 L 646 L 600 L 599 L 813 L Stabilizer 1 [g] 7.18 7.67 7.56 7.54 Additive 1 [g] 2.87 3.07 3.02 3.02 Index 1000 1000 1020 990 1000 1000 Hard segment 37.90% 37.90% 36.78% 38.52% 37.91% 37.70% content Initiation 80 C. 80 C. 80 C. 80 C. 80 C. 80 C. temperature Casting 110 C. 110 C. 110 C. 110 C. 110 C. 110 C. temperature

TABLE-US-00002 TABLE 2 Compounds used Number Comparison 2 Example 6 Example 7 Polyol 1 [g] 800 320 623.08 Polyol 2 [g] 0 480 Polyol 3 [g] 126.92 Isocyanate 2 [g] 400.00 561.31 690 CE [g] 71.32 80.91 157.40 Stabilizer 1 [g] 12.84 14.57 16.14 Index 1000 1000 Hard segment 21.20% 21.20% 37.87% content Initiation 80 C. 80 C. temperature Casting temperature 110 C. 110 C.

3. Mechanical Properties

[0184] The measurements compiled in table 3 were established using injection-molded sheets or extrusion products from example 7.

TABLE-US-00003 TABLE 3 Mechanical properties for example 7 Shore D 62.sup. Tensile strength 51 MPa Elongation at break 390% Tear propagation resistance 120 kN/m Compression set (72 h/23 C./30 min) 26% Compression set (24 h/70 C./30 min) 35% Compression set (24 h/100 C./30 min) 49% Abrasion 38 mm.sup.3 Burst pressure of heat-treated 5.8 * 8.2 mm hoses at 23 C. 41.5 bar Burst pressure of heat-treated 5.8 * 8.2 mm hoses at 70 C. 20 bar Switching temperature 92 C. [0185] The following properties of the polyurethanes obtained were determined by the processes mentioned: [0186] Hardness: DIN ISO 7619-1 [0187] Tensile strength and elongation at break: DIN 53504 [0188] Tear propagation resistance: DIN ISO 34-1, B (b) [0189] Abrasion measurement: DIN ISO 4649 [0190] 4. Determination of shrinkage characteristics: [0191] Strips of about 1.5 cm in width and 9.3 cm in length (SB*) were cut out of injection-molded sheets and heated in water at 98 C. Subsequently, the strips are stretched with two pairs of pliers and held in such an elongated state while being cooled down to 30 C., and the shaped body SB is obtained. Thereafter, the shaped body SB is placed back into water at 98 C. and the reset characteristics are observed. [0192] For various samples, the shrinkage characteristics were determined by the general method of determination. The results are compiled in table 4.

TABLE-US-00004 TABLE 4 Shrinkage characteristics of various TPUs Observation in hot Length after Stretches water after Shrinks Sample pulling (SB) to shrinkage by Compar- 9.3 cm (does not 100% no shrinkage 0% ison 1 soften) Example 1 17 cm 183% shrinks to 10 cm 41% Example 2 22 cm 237% shrinks to 11.3 cm 49% Example 4 25 cm 269% shrinks to 11 cm 56% Example 5 20 cm 215% shrinks to 10 cm 45% Compar- 9.3 cm (does not 100% no shrinkage 0% ison 2 soften) Example 6 24 cm 258% shrinks to 10.5 cm 56%