WO2008068072A1

WO2008068072A1 - Method for the production of an alternating multi-block copolymer with shape memory

Info

Publication number: WO2008068072A1
Application number: PCT/EP2007/059583
Authority: WO
Inventors: Andreas Lendlein; Günter Malsch; Hans-Jürgen KOSMELLA; Helmut Kamusewitz; Steffen Kelch; Nico Scharnagl
Original assignee: Gkss-Forschungszentrum Geesthacht Gmbh
Priority date: 2006-12-08
Filing date: 2007-09-12
Publication date: 2008-06-12
Also published as: DE102006058755A1

Abstract

The invention relates to a method for the production of an alternating multi-block copolymer with shape memory whose structure is composed of the macromonomers A and B alternating in succession, using the steps of (a) provision of the macromonomer A having bilateral functionalization using a nucleophilic end group and provision of the macromonomer B having bilateral functionalization using an electrophilic end group and (b) reaction of the nucelophilically end-group-functionalized macromonomer A with the electrophilically end-group-functionalized macromonomer B in solution, where a stoichiometric ratio of the nucleophilic end group with respect to the electrophilic end group is established, in such a way that any molar deviation from the stoichiometric ratio is at most ± 8 mol%. The invention further encompasses an alternating multi-block copolymer which can be prepared by the method claimed.

Description

Process for the preparation of an alternating multiblock copolymer with shape memory

The invention relates to a method for producing a shape memory polymer, which - in addition to a permanent mold - can store at least one temporary shape. The polymer is an alternating multiblock copolymer having a structure consisting of the alternating successive macromonomers A and B.

In the prior art so-called shape memory polymers or SMPs (shape memory polymers) are known which, when induced by a suitable stimulus, show a shape transition from a temporary shape to a permanent shape according to a prior programming. Most often, this shape memory effect is thermally stimulated, that is, when the programmed polymer material is heated above the defined transition temperature, the return driven by entropy elasticity takes place. Shape memory polymers are typically polymer networks in which chemical (covalent) or physical (noncovalent) crosslinks determine the permanent shape. The programming is carried out by deforming the polymer material above the transition temperature of a switching segment and then cooling it down while maintaining the deformation forces under this temperature in order to fix the temporary shape. Reheating above the transition temperature results in a phase transition of the switching segment defining phase and restoration of the original permanent shape.

Shape memory polymers are usually random multiblock copolymers, which are mostly composed of two thermodynamically incompatible segments (macromonomers A and B). The blocks A and B must each have a minimum molecular weight and a minimum proportion, so that a phase separation of the blocks in the polymer is ensured. Statistical multiblock copolymers form physical crosslinks. The responsible phase is called hard segment and has the highest thermal transition temperature T _tran s _A in the system. The phase with the next lower thermal transition temperature T _tra ns B is that which determines the switching segment. de phase and is for switching the thermally induced shape memory effect with the switching temperature T _SC hait

B) responsible.

Statistical multiblock copolymers are prepared by polyaddition or polycondensation of the macromonomers A and B. The chemical structure of these multiblock copolymers is generally characterized by a statistical sequence of the macromonomers A and B. This results in a different number of repeat units A and B within the multiblocks and thus a heterogeneous distribution of each coupled blocks of the same type (-AA- or -BB-) or other type (-AB-) (eg AABABBBAB). On the other hand, a distinction is made between (strictly) alternating multiblock copolymers, which are characterized by an alternating sequence of blocks A and B and accordingly have the structure - (AB) _n -. Alternating multiblock copolymers with shape memory have not been realized so far.

No. 6,388,043 B1 (EP 1 062 278 A) and US Pat. No. 6,160,084 B (EP 156 487 A) describe block copolymers which are composed of at least two different segments (blocks) and can store at least two temporary forms in their "shape memory" , In the specific embodiment, PDS macromonomers (copolymer of p-dioxan-2-one and ethylene glycol monomers) and poly (ε-caprolactone) macromonomers (PCL) are linked together. The Kijpplungsreaktion for the preparation of the multiblock copolymers is carried out by reaction of the macrodiols with a low molecular weight diisocyanate, that is on Diurethanbrücken, creating random multiblock copolymers.

Other random multiblock copolymers and their methods of preparation are described, for example, by Lendlein & Langer (Science 296 (2002), 1673-1676), Lendlein & Kelch (Angew. Chem. 1 14 (2002), 2138-2162) and Cho et al. (J. Appl. Polym., 93 (2004), 2410-2415).

Teng et al. (J. Polymer Sci. 42, 2004, 5045-53) discloses a multiblock copolymer composed of poly (ε-caprolactone) and poly (L-lactide) blocks. The polymer is prepared from the PCL diisocyanate (α, ω-macrodiisocyanate) and the PLLA diol (α, ω-macrodiol). The coupling reaction of the end group-functionalized macromonomers takes place from the melt at variable mass ratios of the segments, so that statistical multiblock copolymers are to be expected. It will be the influence of Composition and molecular weight on the thermal behavior and the crystalline properties studied, while the mechanical properties and shape memory behavior is not reported.

The known processes for the preparation of multiblock copolymers have the disadvantage that the incorporation of the macromonomers A and B into the polymer chain always takes place statistically, that is to say result in statistical multiblock copolymers. In the case of a synthesis from the solution, it can not be ruled out that due to a different solubility of the macromonomers used in the solvent used or due to reactivity differences, the rate of incorporation thereof into the multiblock copolymer varies. The reason for this is presumably a more or less good steric accessibility or differences in the activation of the competing reactive end groups of the two macromonomers A and B, as a result of different widening of the wedge. Thus, the dipole component with increased solubility and reactivity, in particular at low conversions, is intensified incorporated the multiblock copolymer. The resulting non-uniformity of the chemical composition contributes to irregularities of the microstructure. In the case of carrying out the coupling reaction in the melt, however, no homogeneous mixing of the two macromonomers A and B can be ensured, so that there are different concentration ratios of the components in the different partial volumes of the melt.

Another disadvantage of the known production methods leading to random multiblock copolymers is their lack of reproducibility. Thus, randomly the statistical sequence of the macromonomers A and B in the product may differ even with identical reaction mixtures, with the result that the resulting thermomechanical properties of the polymer also vary widely and the shape memory effect due to the not regularly formed microstructure can not be programmed and triggered. Further, it has been observed that good mechanical properties and shape memory performance are achieved only when the multiblock copolymer has comparatively high molecular weights. Typically, number-average molecular weights M _n of at least 30,000 g / mol and weight-average molecular weights M _w of at least 100,000 g / mol are required in this connection. These required lent molecular weights can be realized so far only with considerable procedural effort.

The invention is therefore based on the object to provide a method for producing a multi-block copolymer with shape memory, which leads with high reliability to an alternating sequence of blocks A and B or to a homogeneous distribution of sequence / nit narrow length distribution and thus produces polymer products which have an improved performance profile in terms of SM effect and mechanical properties. In this case, it is also important in particular that the resulting multiblock copolymers - as well as their statistical comparison samples - achieve a minimum molecular weight required for the formation of the SM effect.

This object is achieved by a process for producing an alternating multiblock copolymer with shape memory properties which has a structure consisting of the alternately successive macromonomers A and B, with the following steps:

(A) providing the macromonomer A with a two-sided functionalization with a nucleophilic end group and providing the macromonomer B with a bilateral functionalization with an electrophilic end group and

(b) Reaction of the nucleophile end-group-functionalized macromonomer A with the electrophile-endgroup-functionalized macromonomer B in solution, adjusting a stoichiometric ratio of the nucleophilic end group to the electrophilic end group such that a molar deviation from the stoichiometric ratio is minimized, in particular at most ± 8 mol%.

In the first process stage, therefore, end functionalization creates electrophilic and nucleophilic reaction centers so that an alternating "crossover coupling" is achieved by their reaction in the second process stage. Targeted selection of the two end groups and the preparation of the correspondingly functionalized macromonomers A and B in step (a) can minimize reactivity differences of the macromonomers and preclude interfering influences on the homogeneity of the coupling steps in step (b). The multiblock copolymer resulting from the process has a largely regular AB block structure in which the macromonomers A and B follow one another alternately according to the structure (AB) _n . To achieve this, on the one hand, it has proved essential to have the strictest possible stoichiometry

- A - to maintain the nucleophilic end group of the macromonomer A and the electrophilic end group of the macromonomer B in step (b), that is to set a molar ratio of the nucleophilic end group to the electrophilic end group of 1, with a maximum molar deviation of ± 8 mol% still tolerable has been found. The reliability of the process can be further increased if the molar deviation from the stoichiometric ratio is at most ± 5 mol%, in particular at most ± 3 mol%. Furthermore, it is important to carry out the coupling reaction in step (b) in solution. Together with the strict stoichiometry, this measure ensures - unlike the implementation in melt - a homogeneous mixing of the reactants, so that ideally in each subvolume of the reaction mixture corresponding concentrations of the macromonomers A and B are present.

According to a particularly advantageous embodiment of the method according to the invention, the number-average molecular weights M _{n of} the end group-functionalized macromonomers A and B are matched as far as possible for their reaction in step (b). In this case, a difference between the degrees of polymerization of the macromonomers A and B is set, which is at most 15%, in particular at most 10%, preferably at most 5%, based on the number-average degree of polymerization P _{n of} the heavier macromonomer. This measure requires two advantageous effects. First, by aligning the molecular weights, it is achieved that both end group functions have similar steric accessibility during the reaction in solution in step (b) and the segment lengths in the product are broadly consistent. This results in consistent rates of incorporation of the macromonomers A and B into the chain of the resulting multiblock copolymer and thus further support for the alternate construction. Second, the approach results in approximately consistent chain segment lengths of blocks A and B in the product, which in turn favors the formation of a homogeneous, phase-segregated morphology in the polymer product that forms the basis for particularly advantageous SM thermomechanical properties.

The resulting multiblock copolymer has thermally inducible shape memory properties, that is, it is capable of assuming at least a temporary shape as well as a permanent form depending on the temperature. Is one of the blocks A or B of the switching segment determining block with defined thermal transition temperature and the other block of the hard segment determining block, can store a shape in the "shape memory". Alternatively, however, both blocks A and B can contribute to the construction of switching segment-forming phases that form mutually different transition temperatures, so that two temporary shapes are programmable in addition to the permanent shape. The term switching segment is understood to mean a phase in the solid polymer whose structure is defined by the macromonomers A and B used in the synthesis. The formation of a separate phase by phase separation in the solid is thus the basis for the formation of the typical material properties of the corresponding compound. In this way it is achieved that the polymer system as a whole has material properties that can be assigned to the respective blocks. The switching temperatures for the thermally induced effect may in particular be glass transition or melting temperatures.

In the context of the present invention, it has been found that, due to the homogeneous sequence of the components A and B, materials are obtained which, owing to their homogeneous microstructure, have very good mechanical properties and particularly good shape memory properties (shape memory properties). Particularly surprising was the finding that, compared with the corresponding statistical counterparts, relatively low molecular weights are already sufficient to realize superior mechanical properties and defined shape transitions. Accordingly, an advantageous embodiment of the invention provides that the number average molecular weight M _{n of} the alternating multiblock copolymer in the range of 10,000 to 50,000 g / mol, in particular in the range of 20,000 to 40,000 g / mol, while the preferred weight average molecular weight M _{w of} the alternating Multiblockcopolymers in the range of 40,000 to 80,000 g / mol, in particular in the range of 50,000 to 70,000 g / mol. In contrast, in the multiblock copolymers described in the prior art, higher molecular weights are necessary for achieving good mechanical properties and a highly reproducible SM effect. Here, the number average molecular weight M _{n is} defined by Equation 1 and the weight average molecular weight M _w by Equation 2, where M, the molecular weight of the polymer type i means n, the number of all produced polymers with the molecular weight M, and n the total number of polymers.

As further advantageous, it has been found that the switching temperatures of the alternating multiblock copolymers, that is, the transition temperatures of the phase transition, lie in a narrower temperature range than the statistical counterparts. This means a sharper and well-defined transition. Also, the polymers of the invention have an increased modulus of elasticity (modulus of elasticity) over the random polymers. In particular, on average, an E-modulus is achieved which is larger by one order of magnitude than in the case of the corresponding random multiblock copolymers at comparable elongation at break (ε _max ~ 1000%).

According to a further preferred embodiment of the invention, a hydroxyl group is used in step 1 of the method as the nucleophilic end group, that is, the nucleophile endgruppenfunktionalisierte macromonomer A is an α, ω-diol. This has the advantage that many macromonomers that can potentially be used as blocks in multiblock copolymers with shape memory are commercially available as α, ω-diol.

As the electrophilic end group can advantageously be used isocyanate group. In this case, the electrophilic end group-functionalized macromonomer B is an α, ω-diisocyanate. On the one hand, isocyanates readily react with hydroxyl groups and on the other hand can be prepared in good yield from the commercially available .alpha.,. Omega.-diols. In addition, isocyanates have comparable reactivities to hydroxyl groups, which, as already explained above, favors the construction of an alternating and homogeneous product structure. The α, ω-diisocyanate of the macromonomer B is particularly preferably provided in step 1 by reacting the corresponding α, ω-diol of the macromonomer B with an isocyanate alkane. In particular, the reaction can be carried out with a Diisocyanatalkan, for example, with 1, 6-diisocyanato-2,2,4-trimethylhexane or 1,6-diisocyanato-2,4,4-trimethylhexane (TMDI), a mixture of isomers of these or 1,6 - Diisocyanatohexane (HDI). In order to achieve the most quantitative possible reaction of the hydroxyl groups with the isocyanate, an excess of isocyanate groups with respect to hydroxyl groups is advantageously presented. In particular, a molar ratio of isocyanate groups to hydroxyl groups of at least 20: 1, preferably at least 50: 1 is set. A specific embodiment of the invention provides that one of the macromonomers A or B is a polyester of the general formula I where n = 1 ... 14 or a co-polyester with different n or a derivative of these. In the context of the present invention include derivatives of the polyester of Formula I structures in which one or more of the hydrogen radicals of the methylene units (-CH ₂ -) are replaced by straight or branched, saturated or unsaturated C1 to C14 radicals. Crucial in the selection of the substituents in the specified framework is that the formation of a separate phase of the switching segments is not prevented by crystallization. Particular preference is given to using a poly (ε-caprolactone) (PCL), ie a polyester of the general formula I where n = 5, or a poly (pentadecactone), ie a polyester of the general formula I where n = 14.

In a further advantageous embodiment of the invention, one of the macromers A or B is a polyether of the formula II (poly (p-dioxanone), PPDO), the formula III (poly (ethylene oxide), PEO), the formula III (poly (tetrahydrofuran), PTHF), the formula V (poly (propylene oxide))) or a derivative of these, in which one or more of the hydrogen radicals of the methylene units (-CH ₂ -) are replaced by unbranched or branched, saturated or unsaturated C 1 to C 6 radicals , However, preference is given to using an unsubstituted polymer of the formula II, that is to say poly (p-dioxanone) (PPDO). The abovementioned macromers according to the formulas II to V generally function as switching segments ("soft segments") in the corresponding multiblock copolymers.

According to a particularly advantageous embodiment, a polyester of the formula I, in particular PCL, is used as a first macromonomer, and a polyether of the formula II, in particular PPDO, as a second macromonomer. In this case, the PCL with the electrophilic end group can be functionalized on both sides, in particular with isocyanate groups (α, ω-PCL diisocyanate), and the PPDO with the nucleophilic end group, in particular with hydroxyl groups (α, ω-PPDO-diol). Likewise, however, in the second process step α, ω-PPD0 diisocyanate can be reacted with α, ω-PCL diol.

According to an alternative embodiment, a macromonomer of the formula I with n <5 and a macromonomer of the formula I with n> 10 are converted to an alternating multiblock copolymer after the functionalization has taken place. In this case, the macromonomer of the formula I with n <5 is preferably provided with an electrophilic end group (in particular diisocyanate) and macromonomer of the formula I where n> 10, preferably with a nucleophilic end group (in particular diol).

A further aspect of the present invention relates to a multiblock copolymer which can be prepared by the process according to the invention and which has the described advantageous material properties.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

The invention will be explained below in embodiments with reference to the accompanying drawings. Show it:

1 shows the chemical process steps for producing an alternating multiblock copolymer according to a first embodiment of the invention, in which the α, ω-macrodiisocyanate of PCL is reacted with the α, ω-macrodiol of PPDO; Figure 2 shows the chemical process steps for producing an alternating

A multiblock copolymer according to a second aspect of the invention, wherein the α, ω-macrodiisocyanate of PPDO is reacted with the α, ω-macrodiol of PCL;

FIG. 3 shows FTIR spectra of PCL after different reaction times of the diisocyanation;

Figure 4 FTIR reference spectra of α, ω-diisocyanate functionalized PCL;

Figure 5 ¹ H-NMR spectra of PCL after different reaction times of

Diisocyanatisierung;

FIG. 6: ¹ H-NMR spectrum of the alternating multiblock copolymer PCL-10K-bl

PPDO-1.5K;

FIG. 7 ¹ H-NMR spectrum of the alternating multiblock copolymer PCL-2K-bl

PPDO-1.5K;

FIG. 8 shows a stress-strain diagram of an alternating poly- (PCL-old)

PPDO) -Multiblockcopolymers;

Figure 9 shows time courses of the temperature and the elongation of an alternating

Poly (PCL-old PPDO) multiblock copolymer in a cyclic, thermomechanical experiment.

The principle of the process according to the invention for the production of alternating multiblock copolymers with shape memory will be explained below using the example of a polyetherester multiblock copolymer from the macromonomers poly (ε-caprolactone) (PCL) and poly (p-dioxanone) (PPDO). In this selection, PCL blocks determine the switching segment that thermally induces a phase transition (melt transition), and PPDO blocks due to physical crosslinking determine the hard segment that has the highest thermal transition temperature in the polymer product. According to the invention, the synthesis takes place in two steps, the diisocyanation of one of the two macromonomer diols taking place in the first step, and the reaction of the α, ω macrodiisocyanate thus produced with the α, ω macrodiol of the other macromonomer by crossover Clutch. The α, ω-macrodiisocyanate of PCL can be reacted with the α, ω-macrodiol of PPDO (Example 1) or the α, ω-macro-diisocyanate of PPDO with the α, ω-macrodiol of PCL (Example 2).

In general, in the first stage of the process for end-group functionalization of the α, ω-macrodiols, an α, ω-diisocyanate alkane, preferably 1,6-diisocyanato-2,4,4-trimethylhexane (TMDI), is used. To minimize side reactions and to achieve the highest possible conversion and high degrees of functionalization with Diisocyanatendgruppen be high molar [NCO] / [OH] ratios of 50 mol / mol (50-fold molar excess of NCO based on OH) for to be carried out in solution Submitted reaction and metered in a solution of the macrodiol with stirring. Thus, a stable high excess of NCO groups is ensured. The reaction can advantageously be supported catalytically by a suitable catalyst. The diisocyanatizations of the .alpha.,. Omega.-macrodiols of PCL and PPDO necessitate an adaptation of the reaction instructions in order to obtain the desired reaction products because of the distinctly different solubility.

The crossover coupling in the second process stage of α, ω-PCL diisocyanate and α, ω-PPDO-diol (Example 1) or α, ω-PPDO diisocyanate and α, ω-PCL diol (Example 2) is under a stoichiometric (molar) ratio of the NCO and OH groups of the macromonomers used. The concentrations of the end groups are calculated assuming the fullest possible α, ω-end functionalization of the macro-diisocyanates to be coupled from the number average molecular weight M _n . Thereafter, an equimolar incorporation rate of the macromonomers is given in the multiblock copolymer. In contrast, with widely differing molecular weights M _{n of} the coupling macromonomers, incorporation rates differ significantly, with the lower molecular weight macromonomer achieving a lower incorporation rate, with the result that the higher molecular weight macromonomer appears partially cumulated in the product polymer. This leads to a multiblock copolymer with a statistical structure. In contrast, according to the invention to achieve an alternating structure with of a 1: 1 stoichiometry in the product, the number average molecular weights M _{n of} the macromonomers match as closely as possible. The coupling reaction can be catalyzed by a suitable catalyst.

Example 1: Preparation of a PCL-PPDO multiblock copolymer from the α, ω-macro-diisocyanate of PCL and the α, ω-macrodiol of PPDO

Process stage 1:

The functionalization of PCL-macrodiol with isocyanate end groups is carried out according to the reaction shown in Figure 1 (1st step). For this purpose, a solution of 1, 6-diisocyanato-2,4,4-trimethylhexane (TMDI) (Sigma Aldrich) in anhydrous tetrahydrofuran (THF) is placed under an argon atmosphere. A solution of the PCL macrodiol (PCL 3.3 K: prepared from ε-caprolactone from Sigma Aldrich, PCL 2K and PCL 1 OK from Sigma Aldrich) in anhydrous THF is added dropwise to this template while stirring. During the addition of the reaction mixture and the polymer solution is kept at about 0 ⁰ C. The concentration of TMDI in the template is adjusted so that there is a 50-fold molar excess of TMDI with respect to the PCL macrodiol with respect to the completed reaction mixture. After complete addition of the solution of PCL-macrodiol, the reaction mixture is heated to about 60 ⁰ C and stirred under argon atmosphere at this temperature over a period of 24-72 h. This is facilitated by the good solution behavior of PCL in THF - a temperature control, under which during the addition at low temperature, the reaction is suppressed and after increasing the temperature, a uniform reaction start. Subsequently, the PCL diisocyanate is precipitated from the solution, washed extensively, dried under vacuum to constant weight and stored cooled.

The reaction described above was carried out in three different batches using PCL macrodiols with molecular weights of 2,000 g / mol (PCL 2K), 3,300 g / mol (PCL 3.3K) and 10,000 g / mol (PCL 10K). The products were subjected to comprehensive analysis of FTIR spectroscopy, ¹ H NMR spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC).

The FTIR spectra recorded as a function of the reaction time are shown in FIG. 3, while FIG. 4 shows as reference the FTIR spectra of PCL macrodiol (PCL 1 R), and PCL macro diisocyanate (PCL 1 R-NCO) and TMDI. The recorded with FTIR Intensities of the NCO stretching vibration at 2270 cm ^-1 (FIG. 3) shows that the final conversion is reached after approx. 48 h.

In order to determine the degree of functionalization with isocyanate groups, the ratio of the CH ₃ signal of terminal TMDI units at chemical shifts of approximately 0.9 ppm and the characteristic CH ₂ signals of the functionalized PCL was characterized by ¹ H NMR spectroscopy. Blocks determined at about 2.3 ppm (Figure 5). In this determination, isocyanate end group functionalization levels of 70 to 90% were determined. By combined application of GPC and ¹ H NMR spectroscopy, as a side reaction coupling rates could be determined within a narrow range of 1, 5 to 3 coupling steps, based on coupling of already formed NCO macromer with unreacted macrodiol despite the high [NCO ] / [OH] ratio can be attributed. The consideration of the number of coupling steps on the evaluation of the signal intensity ratios in the ¹ H-NMR spectrum in the end group analysis leads to a nearly complete Diisocyanatisierungsrate.

Process level 2:

The "crossover coupling" of the two macromers occurs under strict equimolarity of the end group concentration of the two reactants. Therefore, unlike the random multiblock copolymers, the alternating composition of the multiblock copolymer as defined by the number average molecular weight M _n inevitably results. For the targeted adjustment of the molar composition of PCL and PPDO macromonomer units, therefore, an adaptation of the molecular weights M _{n of} the PPDO macrodiols to the molecular weights M _{n of} the PCL macro diisocyanates used (here: 10 K, 3.3 K and 2 K) according to table 1, where present limits are set by the commercial availability of macromonomers. Since the monomer units have different molar masses ([-PPDO-]: 102 g / mol; [-PCL-]: 14 g / mol), the molecular weights M _n of PPDO listed in the table are with a factor of 1.12 to 1 To multiply 14 to arrive at the corresponding molecular weights M _n of PCL.

Table 1

Mole fraction adjustment M _n , PPDO

XPCL XPPDO M _n , PCL = 1 0 KM _n, P _C L = 3.3 KM _n , PCL - 2 K

0.9 0.1 1050 380 250

In the second reaction step of the crossover coupling of the .alpha.,. Omega.-PCL diisocyanate with the .alpha.,. Omega.-PPDO diol shown in FIG. 1 (2nd step) is catalyzed with a suitable catalyst. For this purpose, the α, ω-PCL diisocyanate dissolved in dichloroethane (DCE) is heated to 70 ^° C. under argon atmosphere and with stirring. This is followed by the dropwise addition of dissolved in DCE α, ω-PPDO-diol. As a rule, 20% by weight PCL and 10% by weight PPDO solutions are used for this reaction. The reaction is carried out at 70 ⁰ C over a period of 24 h. The product is then precipitated and dried to constant weight.

The reaction products were characterized chemically by ¹ H-NMR spectroscopic analysis (Figures 6 and 7), thermally by DSC (Table 2) and mechanically by tensile strain measurement and shape memory properties by cyclic thermodynamic studies (Figures 8 and 9). The results are discussed below together with the results of Example 2.

Example 2 Preparation of a PCL-PPDO Multiblock Copolymer from the α, ω-macro-diisocyanate of PPDO and the α, ω-macrodiol of PCL

Process stage 1:

The functionalization of PPDO-macrodiol with isocyanate end groups is carried out according to the reaction shown in Figure 2 (1st step). Compared with the functionalization of PCL (Example 1), the homogeneous reaction of the PPDO macrodiols is considerably more difficult due to their low solubility and limited to the use of DCE as a solvent under elevated temperatures. A solution of TMDI in anhydrous DCE is placed under an argon atmosphere. A solution of the PPDO macrodiol (prepared from p-dioxanone from Boehringer-Ingelheim) in anhydrous form is added to this initial charge with stirring DCE added dropwise. During the addition of the reaction mixture and the polymer solution is maintained at about 70 ⁰ C to keep the PPDO-diol in solution. The concentration of TMDI in the template is adjusted so that there is a 50-fold molar excess of TMDI over the PPDO macrodiol with respect to the completed reaction mixture. After complete addition of the solution of PPDO macrodiol, the reaction mixture is stirred at about 70 ⁰ C under an argon atmosphere over a period of 48 h. The self-adjusting turbidity of the solution persists throughout the reaction time. Subsequently, the PPDO diisocyanate is precipitated from the solution, washed extensively, dried under vacuum to constant weight and stored refrigerated. The products were subjected to comprehensive analysis of FTIR spectroscopy, ¹ H NMR spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC).

The determination of the degree of functionalization with isocyanate end groups was carried out analogously to Example 1. Coupling rates within a narrow range of 1.5 to 3 coupling steps could be determined by combined application of GPC and ¹ H NMR spectroscopy. The consideration of the number of coupling steps leads to an almost complete end-group functionalization. However, such a coupling occurring in the first reaction stage can also be used selectively, especially in the case of PPDO diols with generally low molecular weights of M _n <3,000 g / mol, in order to realize higher proportions of this component in the alternating multiblock copolymer.

Process level 2:

As in Example 1, the "crossover coupling" of the two macromers is carried out under strict equimolarity of the end group concentration of the two reactants and the molecular weights M _{n of} the PCL macrodiisocyanates used are adjusted.

The second reaction step of the crossover coupling of the α, ω-PPDO diisocyanate with the α, ω-PCL diol shown in FIG. 2 (2nd step) is catalyzed with a suitable catalyst. For this purpose, the dissolved in DCE α, ω-PPDO diisocyanate is heated to 70 ° C under argon atmosphere and stirring. This is followed by the dropwise addition of dissolved in DCE α, ω-PCL diol. As a rule, 20% by weight PCL and 10% by weight PPDO solutions are used for this reaction. The reaction takes place at 70 ⁰ C over a period of from 24 h. The product with anhydrous and cooled to -30 ⁰ C di- ethyl ether is precipitated and dried to constant weight.

The reaction products were characterized chemically by means of ¹ H-NMR spectroscopic analysis (FIGS. 6 and 7), thermally by means of DSC (Table 2), mechanically by means of tensile strain measurements and the shape memory properties by means of cyclic, thermo-mechanical investigations (FIGS. 8 and 9). characterized.

¹ H-NMR spectroscopic characterization of the alternating multiblock copolymers The ¹ H-NMR spectrum of a multiblock copolymer PCL-10K-bl-PPDO-1.5K prepared according to Example 1 is shown in FIG. 6, while FIG. 7 shows the ¹ H-NMR spectrum of a also prepared according to Example 1 Multiblockcopolymers PCL-2K-bl-PPDO-1.5K. The molar fraction of PCL in the multiblock copolymers was determined to be about 4.05 ppm and PPDO (PPDO, dd) at about 3.8 or 4.35 ppm according to the integral intensities of the characteristic doublet doublet signals of PCL (PCL, dd) according to the equation

PCL (mol%) = PCL, dd / (PCL, dd + PPDO, dd). For PCL-1 OK-bl-PPDO-1.5K (FIG. 6), a PCL fraction of 84.5 mol% and for PCL-2K-bl-PPDO-1.5K (FIG. 7) of 53.5 mol% % determined.

Thermomechanical Characterization of Alternate Multiblock Copolymers Table 2 shows the enthalpies ΔH determined in DSC measurements on selected poly (PCL-old-PPDO) multiblock copolymers according to the present invention of different composition. It can be stated that there is a significant dependence of the enthalpy of fusion on the crystalline parts of the PCL as well as the PPDO block segment. In particular, an approach of the enthalpies of fusion of the PCL segment to the enthalpy of fusion of the pure PCL-10K macrodiol as a reference sample can be observed with increasing PCL content. Analogously, this applies to the enthalpies of fusion of the PPDO-1, 5K segment.

Table 2

The stress-strain curve of an unannealed sample of a poly (PCL-old-PPDO) multiblock copolymer (M _n = 23,600 g / mol; M _w = 52,400 g / mol; C _PCL = 68.0 wt%) shown in Figure 8 with curve 1 and characterized by three areas. The elastically beginning, visco-elastic stretching region A shows a significant increase in stress at low elongation of up to 10%. In the following area B, which extends to an elongation of about 200%, occurs purely plastic strain (so-called "necking behavior"), wherein the material "flows" without voltage increase. The subsequent third region C, which extends to an elongation of about 1000%, is characterized by the proportionality between stress and strain. In contrast, the sample annealed at 55 ° C. for 48 h (curve 2) exhibits viscoelastic deformation in the initial range up to about 200% elongation, while in the further course up to 1000% elongation an analogous behavior to that of the untempered sample is observed.

The values for the maximum tensile strength σ _max , the maximum elongation ε _max and the E modulus E were determined for the inventive alternating poly (PCL-old-PPDO) multiblock copolymers from stress-strain studies according to FIG. 8 and comparatively used mechanical properties Properties of the corresponding random poly (PCL-old PPDO) multiblock copolymers (from: Lendlein & Kelch: Clin Hemorheol, Microcirc., 32 (2005), 105-116). The mechanical properties are summarized in dependence on the temperature (T = 20 ⁰ C, 37 ° C and 50 ⁰ C) in Table 2 below. It can be seen that for the alternating as well as for the statistical multiblock copolymers the maximum tensile strength σ _max , the maximum elongation ε _max and the modulus of elasticity decrease with increasing temperature. The comparison of the thermomechanical characteristics of the alternating poly (PCL-old-PPDO) multiblock copolymers prepared according to the invention with the statistical variants of comparable composition also shows that the former have comparable values for σ _max and ε _max at lower molecular weights. However, the alternating multiblock copolymers have distinctly higher moduli of elasticity than their statistical reference patterns, which indicates an influence on the materials produced according to the invention by the formation of a molecular superstructure.

Cyclic thermomechanical investigations on a tempered sample of poly (PCL-old-PPDO) multiblock copolymers (M _n = 23,600 g / mol; M _w = 52,400 g / mol; C _PCL = 68) were used to characterize the shape memory properties (SM behavior). 0% by weight). FIG. 9 shows the time profiles of the elongation (curve 1) and the temperature (curve 2) during the first three cycles. For this purpose, the sample was stretched within a cycle at T _n = 52 ° C to ε _max = 100% and then cooled to T ₁ = -5 ° C. The graph shows an increase in elongation to 110% during this cooling. After retraction of the outer tensile force used to stretch to zero force, at T ₁ = -5 ° C, when fixing the sample, the sample is easily relaxed to 105%. This state, referred to as a temporary shape, can be maintained over a longer period even at room temperature without spontaneous change in shape. Subsequent heating of the sample to a temperature of T _n = 52 ° C initiates the thermally-stimulated recovery of the sample - the so-called switching - indicated by the recovery of elongation to less than 20% in the first cycle. On this basis, the sample is stretched again in the second cycle to the sample length already set in the first cycle. The second and third cycles confirm the SM behavior, which is evidenced by the recovery of the strain from about 105% to about 20% in all three cycles. From these three cycles, the quantities for quantifying the SM behavior can be determined. Thus, the elongation fixing ratio R _{f is determined} from the ratio of the elongation of the fixed sample and the real maximum elongation ε _m applied for fixing. The average of the cycles in Figure 9 is R _f (1-3) 96%. Furthermore, the strain recovery ratio R _{r of} the Nth cycle can be calculated from ε _m and the strain after recovery in the previous (N-1) th cycle. Thereafter, the Rr values for the three described cycles R _r (1) are 84%, R _r (2) 98% and R _r (3) 99%. Table 3:

Polymeric mechanical properties

CpCL molecular weights

T Omax £ max modulus

(Wt%) (kg / mol) ( ⁰ C) (MPa) 10 /. (MPa) M _n M _w old stat old stat old stat old stat old stat old stat

87.3 90.0 36.4 75.6 73.1 158.7 20 20 ± 3 16 ± 1 700 ± 50 1037 ± 100 275 ± 30 34 ± 8

20 22 ± 5 21 ± 1 805 ± 50 1100 ± 100 410 ± 50 39 ± 5 37 15 ± 3 11 ± 2 695 ± 105 1200 ± 70 77 ± 33 10 ± 3

68.4 70.0 18.7 62.8 64.6 134.4 50 3 ± 0.3 0.6 ± 0.1 340 ± 40 740 ± 60 4 ± 1 0.9 ± 0.1

20 32 ± 0.7 13 ± 2 815 ± 2 700 ± 50 214 ± 1 34 ± 5 37 28 ± 0.2 10 ± 2 835 ± 25 800 ± 50 121 ± 29 15 ± 3

53.4 60.0 20.2 31.5 117 76.5 50 18 ± 3 4 ± 0.6 735 ± 120 560 ± 60 94 ± 19 2 ± 0.6

13.0 10.2 17.8 38.0 45.4 65.4 20 20 ± 5 25 ± 4 400 ± 50 730 ± 50 680 ± 65 90 ± 30

Claims

A process for the preparation of an alternating multi-block copolymer with shape memory which has a structure consisting of the alternately successive macromonomers A and B, comprising the steps

(a) providing the macromonomer A with bilateral functionalization with a nucleophilic end group and providing the macromonomer B with bilateral functionalization with an electrophilic end group and

(b) Reaction of the nucleophile end-group-functionalized macromonomer A with the electrophile-endgroup-functionalized macromonomer B in solution, setting a stoichiometric ratio of the nucleophilic end group to the electrophilic end group such that a molar deviation from the stoichiometric ratio is at most ± 8 mol%.

2. The method according to claim 1, characterized in that the molar deviation of the stoichiometric ratio of the nucleophilic end group to the electrophilic end group in step (b) is at most ± 5 mol%, preferably ± 3 mol%.

3. The method according to any one of the preceding claims, characterized in that the number average molecular weights M _{n of} the end-group functionalized macromonomers A and B for their implementation in step (b) are aligned with each other such that a difference between the degrees of polymerization of the macromonomers at most 15%, in particular at most 10%, preferably at most 5%, based on the number-average degree of polymerization P _{n of} the heavier macromonomer.

4. The method according to any one of the preceding claims, characterized in that the number average molecular weight M _{n of} the alternating multiblock copolymer in the range of 10,000 to 50,000 g / mol, in particular in the range of 20,000 to 40,000 g / mol.

5. The method according to any one of the preceding claims, characterized in that the weight-average molecular weight M _{w of} the alternating multiblock copolymer in the range of 40,000 to 80,000 g / mol, in particular in the range of 50,000 to 70,000 g / mol.

6. The method according to any one of the preceding claims, characterized in that the nucleophilic end group is a hydroxyl group and the nucleophile endgruppenfunktionalisierte macromonomer A is an α, ω-diol.

7. The method according to any one of the preceding claims, characterized in that the electrophilic end group is an isocyanate group and the electrophilic endgruppenfunktionalisierte macromonomer B is an α, ω-diisocyanate.

8. The method according to claim 7, characterized in that the provision of the α, ω-diisocyanate by reacting an α, ω-diol of the macromonomer B with an isocyanate, in particular a Diisocyanatalkan, preferably with 1, 6- diisocyanato-2.2 , 4-trimethylhexane or 1,6-diisocyanato-2,4,4-trimethylhexane (TMDI) or 1,6-diisocyanatohexane.

9. The method according to claim 8, characterized in that in the reaction of the α, ω-diol of the macromonomer B with the isocyanato an excess of isocyanate natgruppen is presented to hydroxyl groups, in particular a molar ratio of isocyanate groups to hydroxyl groups of at least 20: 1 , preferably of at least 50: 1.

10. The method according to any one of the preceding claims, characterized in that one of the macromonomers A or B is a polyester of general formula I with n = 1 ... 14 or a co-polyester with different n or a derivative thereof, in particular poly (ε-caprolactone) with n = 5 or poly (pentadekalactone) with n = 14

1 1. The method according to any one of the preceding claims, characterized in that one of the macromers A or B is a polyether according to one of the formulas II to V or a derivative thereof

12. Alternating multiblock copolymer, which can be prepared by the process according to one of claims 1 to 11.

13. Use of an alternating multiblock copolymer according to claim 12 for biomedical applications.