THERMOSET SHAPE MEMORY POLY(UREA-URETHANE) WITH TUNABLE RESHAPING TEMPERATURE AND ITS APPLICATIONS

Abstract

The disclosure provides a system of thermoset shape memory poly(urea-urethane) with permanent reshaping property and its application. The breakthrough of the present invention is that the reshaping temperature can be tuned in a wide range by incorporation of urea bonds into the polymer network. The permanent shape for shape memory poly(urea-urethane) can be repeatedly and cumulatively reshaped at certain temperature, largely facilitating the fabrication of complex structures.

Claims

1. An application method of the shape memory poly(urea-urethane) possessing permanent reshaping property, the method comprising the steps of: a) transforming synthesized crosslinked poly(urea-urethane) into an arbitrary desired shape above a reshaping temperature with an external force applied; b) undertaking bond exchange within the material under the temperature and force; c) permanently fixing a new shape under cooling and now defined as a new original shape; d) altering processed polymer to a temporary shape above a phase transition temperature under an external force; e) fixing the temporary shape under cooling; f) recovering the polymer to the permanent shape obtained on reheating lastly; wherein the steps a)-c) are reshaping processes, and can be implemented cumulatively at arbitrary lifetime of polymer in usage; wherein the steps d)-f) are the shape memory process; and wherein the crosslinked poly(urea-urethane) contains carbamate bonds and urea bonds in the network with bond exchange catalyst present.

2. The method of claim 1, wherein in the step a) of the reshaping process, the original shape of the crosslinked poly(urea-urethane) is transformed into a new original shape through manipulation such as stretch, compression, and twist; or hot pressed in a new mold after ground into particles or powders.

3. The method of claim 1, wherein the carbamate bonds are obtained by the reaction of polyols and isocyanate, and the urea bonds are obtained by the reaction of polyamines and isocyanate.

4. The method of claim 1, wherein the bond exchange catalyst includes 1,5,7-triazabicyclo[4.4.0]dec-5-ene, benzyldimethylamide, and salts of tin, zinc, magnesium, cobalt, calcium, titanium and zirconium.

5. The method of claim 1, wherein the amount of the bond exchange catalyst ranges from 0.05-5% by weight.

6. The method of claim 1, wherein the phase transition temperature should be glass transition temperature or melting temperature, ranging from 15-150 C.

7. The method of claim 1, wherein the permanent reshaping temperature should be at least 5 C. higher than the phase transition temperature.

8. The method of claim 1, wherein the reshaping temperature is higher than 45 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The following drawings are provided to form the specification and are included to further demonstrate certain embodiments or various aspects of the disclosure. The description and the accompanying drawings are used for a certain specific example.

[0036] FIG. 1. The Dynamic Mechanical Analysis (DMA) showing shape memory cycles and plasticity cycles of Example 1.

[0037] FIG. 2. The Dynamic Mechanical Analysis (DMA) showing shape memory cycles and plasticity cycles of Example 2.

[0038] FIG. 3. The shape memory cycles and plasticity cycles of Example 3.

[0039] FIG. 4. Demonstration of complex shape manipulation of Example 1.

[0040] FIG. 5. Demonstration of reprocessing and the shape memory properties of Example 2 and Example 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The following examples presented herein are intended to illustrate the disclosure. However, the scope is not limited to the following embodiment of the disclosure and it should be recognized that numerous variations and modifications may be made while remaining within the scope of the disclosure.

(a) Materials and Synthesis.

Example 1. Shape Memory Polyurethane

[0042] Materials:

[0043] Poly(ethylene glycol) diol (PEG) (M.sub.n=8,000 g mol.sup.1) was obtained from Sigma-Aldrich with Formula (1a):

##STR00001##

[0044] Hexamethylene diisocyanate (HDI) was purchased from Aladdin with Formula (1b):

##STR00002##

[0045] Glycerin was obtained from Aladdin with Formula (1c):

##STR00003##

[0046] Ditin butyl dilaurate (DBTDL, as the catalyst) was purchased from Aladdin with Formula (1d):

##STR00004##

[0047] Polymer network synthesis: PEG was dehydrated in a vacuum drying oven for 4 hours at 100 C. prior to use. In a typical experiment, 0.75 mmol of PEG was weighted into a glass bottle and dissolved in butyl acetate at 60 C. Afterwards, 0.6 mmol of glycerin, 1.65 mmol of HDI, and the catalyst DBTDL (1 wt %) were added into the bottle and stirred for several minutes. After mixing homogenously, the mixture was poured into an aluminum pan and curing was conducted thermally at 60 C. for 4 hours. Finally, the cured sample was vacuum-dried at 100 C. overnight and demolded.

Example 2. Shape Memory Poly(Urea-Urethane)

[0048] Material:

[0049] Poly(ethylene glycol) diol (PEG) (M.sub.n=3,350 g mol.sup.1) was obtained from Sigma-Aldrich.

[0050] Hexamethylene diisocyanate (HDI) was purchased from Aladdin.

[0051] Glycerin was obtained from Aladdin.

[0052] Ditin butyl dilaurate (DBTDL, as the catalyst) was purchased from Aladdin.

[0053] N,N-Di-tert-butylethylenediamine (TBEA) was purchased from TCI with Formula (2a):

##STR00005##

[0054] Polymer network synthesis: PEG was dehydrated in a vacuum drying oven for 4 hours at 100 C. prior to use. In a typical experiment, 0.35 mmol of PEG was weighted into a glass bottle and dissolved in butyl acetate at 60 C. Afterwards, 0.2 mmol of glycerin, 1.15 mmol of HDI, 0.5 mmol of TBEA, and the catalyst DBTDL (1 wt %) were added into the bottle and stirred for several minutes. After mixing homogenously, the mixture was poured into an aluminum pan and curing was conducted thermally at 60 C. for 4 hours. Finally, the cured sample was vacuum-dried at 100 C. overnight and demolded.

Example 3. Shape Memory Poly(Urea-Urethane)

[0055] Material:

[0056] Poly(ethylene glycol) diol (PEG) (M.sub.n=2,000 g mol.sup.1) was obtained from Sigma-Aldrich.

[0057] Hexamethylene diisocyanate (HDI) was purchased from Aladdin.

[0058] Glycerin was obtained from Aladdin.

[0059] Ditin butyl dilaurate (DBTDL, as the catalyst) was purchased from Aladdin.

[0060] N,N-Di-tert-butylethylenediamine (TBEA) was purchased from TCI with Formula (2a):

##STR00006##

[0061] Polymer network synthesis: PEG was dehydrated in a vacuum drying oven for 4 hours at 100 C. prior to use. In a typical experiment, 0.35 mmol of PEG was weighted into a glass bottle and dissolved in butyl acetate at 60 C. Afterwards, 0.2 mmol of glycerin, 1.63 mmol of HDI, 0.98 mmol of TBEA, and the catalyst DBTDL (1 wt %) were added into the bottle and stirred for several minutes. After mixing homogenously, the mixture was poured into an aluminum pan and curing was conducted thermally at 60 C. for 4 hours. Finally, the cured sample was vacuum-dried at 100 C. overnight and demolded.

(b) Characterization Methods.

[0062] Dynamic mechanical analysis (DMA) and differential scanning calorimetry analysis (DSC) experiments were performed to test the mechanical and thermal property, respectively. The choices of different molecular of PEG chain will tune the phase transition temperature in a wide range from room temperature to around 50 C. The phase transition temperature of the Example 1 is around 50 C. The phase transition temperature of the Example 2 is around 45 C. The phase transition temperature of the Example 3 is around 37 C.

[0063] In order to evaluate its shape memory and reshaping properties, samples were cut into rectangle shapes and the shape memory cycles and the stress relaxation cycles were performed by DMA experiments.

[0064] To test the reshaping property of the network, the samples were conducted in an iso-strain stress relaxation experiment, in which a sample was stretched to a 50% strain and the stress was monitored. Bond exchange reaction occurring during the reshaping process will result in the strain relaxation. The higher degree of strain relaxation, the better reshaping effect.

[0065] With carbamate bonds only, the samples (Example 1) need to be heated into 130 C. to ensure the full relaxation in a reasonable time. With low concentration of the hindered urea bond included (Example 2), the stress relaxation is accelerated. Only heated into 90 C., the similar full relaxation is achievable. Increasing the hindered urea bond (Example 3), the similar stress relaxation curves can be obtained only at around 45 C. Therefore, we can achieve a set of poly(urea-urethane) networks with tunable reshaping temperature by tuning the ratio of two kinds of dynamic reversible bonds, the urea bond and the carbamate bond.

Example 1. Shape Memory Polyurethane

[0066] Shape memory cycles: The sample was heated to 80 C. and the shape was changed with an external force. The sample was then cooled down to 0 C. under load. After the load removal, the temporary shape was fixed. When the sample was reheated to 80 C., the temporary shape was recovered to its original shape.

[0067] Stress relaxation cycles: The sample was heated to 130 C. and the shape was changed with an external force. At this state, the bond exchange reaction was activated. Keeping temperature and force constant, the network topographic changed and the deformed shape was nonrecoverable without any internal force.

Example 2. Shape Memory Poly(Urea-Urethane)

[0068] Shape memory cycles: The sample was heated to 50 C. and the shape was changed with an external force. The sample was then cooled down to 0 C. under load. After the load removal, the temporary shape was fixed. When the sample was reheated to 50 C., the temporary shape was recovered to its original shape.

[0069] Stress relaxation cycles: The sample was heated to 90 C. and the shape was changed with an external force. At this state, the bond exchange reaction was activated. Keeping temperature and force constant, the network topographic changed and the deformed shape was nonrecoverable without any internal force.

Example 3. Shape Memory Poly(Urea-Urethane)

[0070] Shape memory cycles: The sample was heated to 38 C. and the shape was changed with an external force. The sample was then cooled down to 0 C. under load. After the load removal, the temporary shape was fixed. When the sample was reheated to 38 C., the temporary shape was recovered to its original shape.

[0071] Stress relaxation cycles: The sample was heated to 45 C. and the shape was changed with an external force. At this state, the bond exchange reaction was activated. Keeping temperature and force constant, the network topographic changed and the deformed shape was nonrecoverable without any internal force.

(c) Manipulation.

[0072] As FIG. 4 showed, the original shape is a square film with through-line patterns. The line patterns allow for shape manipulation using the Jianzhi technique. As such, the Example 1 can be deformed into a permanently elongated three-dimensional shape by simply applying a stretching force followed by annealing at 130 C. (higher than reshaping temperature). This permanent shape can be fixed into various temporary shapes at 0 C., including a pyramid, a twisted pyramid, and a flat film. All of these temporary shapes can fully recover to its permanent shape by reheating to 80 C. Importantly, this permanent shape can be further deformed back into the original flat square, which can also be fixed into temporary shapes.

[0073] As FIG. 5 showed, the original shape of Example 2 and Example 3 are circular and triangle sheet, respectively. They are cut into particles with similar sizes and charged into the same rectangle mold at 1:1 weight ratio. The temperature is 100 C., which is higher than both the reshaping temperature of the poly(urea-urethane) of Examples 2 and 3. The obtained rectangle sheet possesses one homogeneous network because of the bond exchange between the two poly(urea-urethane) network. The phase transition temperature and the reshaping temperature of the obtained network fall between those of example 2 and 3. So, this is an effective method to tune the reshaping temperature and the phase transition temperature by combination of two poly(urea-urethane) network.

[0074] It is to be appreciated that the foregoing description of the invention has been presented for purpose of illustrations and explanation and is not intended to limit the invention to the precise form of practice herein. It is to be appreciated therefore, that changes may be made by those who are skilled in the art without departing from the spirit of the present invention.