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Water‐Responsive Shape MemoryPolyurethane Block Copolymer Modified withPolyhedral Oligomeric SilsesquioxaneYong Chae Jung a , Hyang Hwa So a & Jae Whan Cho aa Department of Textile Engineering , Konkuk University , Seoul , KoreaPublished online: 16 Aug 2006.

To cite this article: Yong Chae Jung , Hyang Hwa So & Jae Whan Cho (2006) Water‐Responsive Shape MemoryPolyurethane Block Copolymer Modified with Polyhedral Oligomeric Silsesquioxane, Journal of MacromolecularScience, Part B: Physics, 45:4, 453-461, DOI: 10.1080/00222340600767513

To link to this article: http://dx.doi.org/10.1080/00222340600767513

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Water-Responsive Shape Memory PolyurethaneBlock Copolymer Modified with Polyhedral

Oligomeric Silsesquioxane

YONG CHAE JUNG, HYANG HWA SO, AND JAE WHAN CHO

Department of Textile Engineering, Konkuk University, Seoul, Korea

Nanostructured polyurethane block copolymers with shape memory were synthesizedby using polyhedral oligomeric silsesquioxane (POSS) molecules and poly(ethyleneglycol) (PEG), which acted as the hydrophobic and hydrophilic groups, respectively.The hard segment domains appeared to be dominantly governed by POSS moleculesaccording to X-ray diffraction and Fourier transform-infrared (FT-IR) measurements.As the POSS content increased, the phase separation between hard and soft segmentsgradually developed, followed by the crystallization of POSS molecules, and the meltingtemperature and heat of fusion for POSS crystals increased. The water-responsive shapememory behavior which resulted from the dissolution of soft segments was demonstratedat 308C. More than 70% shape recovery was achieved in the water-responsive shaperecovery test, which depended on the POSS content.

Keywords POSS, shape memory, water-responsive, polyurethane, block copolymer

1 Introduction

Shape memory materials have been utilized in many applications, such as actuator,

biomedical robot, medical, and industrial applications. Up to now, shape memory

alloys, like Nitinol, have been primarily used; however, shape memory polymer has

recently received increasing attention as a substitute or competing material for shape

memory alloys. Shape memory polymer has many advantages compared with shape

memory alloys, for example, lightness, flexibility, easy processing, high shape recovery,

and low cost.

The shape memory effect of polymers was achieved by thermal stimulation due to

heating above a transition temperature such as the glass transition temperature or

melting temperature. Polyurethane block copolymer (PU) is a typical example of such

shape memory polymers.[1,2] However, some other stimulating sources, such as pH,

electric field, and chemicals, may also be useful for actuating shape memory

polymers.[3,4] Recently, electroactive shape memory has been reported in polyurethane

block copolymer composites containing carbon nanotubes.[3,5]

An interesting water-responsive shape memory polymer may be created by introdu-

cing hydrophilic and hydrophobic groups in the soft and hard segments, respectively.

Received 2 January 2006; Accepted 8 January 2006.Address correspondence to Jae Whan Cho, Department of Textile Engineering, Konkuk

University, Seoul 143-701, Korea. E-mail: jwcho@konkuk.ac.kr

Journal of Macromolecular Sciencew, Part B: Physics, 45:453–461, 2006

Copyright # Taylor & Francis Group, LLC

ISSN 0022-2348 print/1525-609X online

DOI: 10.1080/00222340600767513

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Polyhedral oligomeric silsesquioxane (POSS) is one of potential candidates as the hydro-

phobic group. It is composed of a polyhedral silicon oxygen nanostructured skeleton with

intermittent siloxane chains, and has novel mechanical properties due to its cage-like

molecule.[6 – 8] Polyurethane containing POSS molecules in the polymer chain has a

strongly enhanced tensile modulus and strength due to the presence of POSS molecules

as nanoscale reinforcement agents as well as formation of well phase-separated hard

segment domains from soft segments.[9 – 13] Block copolymers containing poly(ethylene

oxide) (PEO) as the hydrophilic block, like Pluronic polymers, have high solubility in

water due to their excellent hydrophilicity.[14,15] Recently some interesting research on

PEO-containing amphiphilic block copolymers was also reported in applications of

water-swellable elastomers. Some PEO-POSS amphiphilic triblock copolymers show

significantly improved properties compared with other triblock copolymers.

In this study, polyurethane block copolymer modified with POSS were synthesized,

and their structural characteristics and water-responsive shape memory were investigated.

2 Experimental

2.1 Synthesis of POSS-PU and Film Preparation

Poly(ethylene glycols) (PEG) with molecular weights of 10,000 g/mol (Aldrich Co.) were

purified by the process of precipitation by n-hexane from tetrahydrofuran solution,

followed by drying in a vacuum oven. 1-[2-Ethyl-2-[(3-dimethylsiloxy) propoxymethyl]-

1,3-propanediol]-3,5,7,9,11,13,15-isobutylpenta cyclo-[9.5.1.1.1]-octasiloxane (POSS,

95%, Hybrid Plastics) and 1,4-phenyldiisocyanate (PDI, 98%, Mw ¼ 160.13 g/mol,

Aldrich Co.) were used as received.

The PU used in this study was synthesized in a one-step polymerization method.

Determined amounts of PEG and POSS were dissolved in toluene. Various mole ratios

of PDI were added to the reactor, which was heated at 508C. After the reaction mixture

was heated to 908C, dibutyltin dilaurate (95%, Aldrich Co.) was added through a

syringe. The reaction was kept at 908C for 2 h under nitrogen atmosphere before com-

pletion. Then the reacted solution was precipitated into an excess amount of n-hexane,

filtered, and dried. The final film was obtained by casting a solution of 10 wt% in

toluene. A schematic description of the polymerization procedure is shown in Fig. 1.

Molecular weight of the polymers was measured, it was dependent on the mole ratio of

POSS:PEG as represented in Table 1. It was measured by using a gel permeation

chromatograph (Waters 2414) equipped with Styragel HR2, HR4, and HR5 columns.

2.2 Characterization of Samples

The Fourier transform-infrared (FT-IR) spectra using film were obtained with a Jasco

FT-IR 300E spectrometer equipped with attenuated total reflectance. X-ray diffractograms

were obtained with a Rigaku Rint 2100 series X-ray diffractometer, using CuKa radiation

at a scan rate of 58/min. Differential scanning calorimetric (DSC) measurements were

carried out with a TA instrument (DSC 2010). Samples were heated from room tempera-

ture to the melt at a rate of 108C/min in a nitrogen atmosphere. The surface topology of the

spin-coated samples was obtained using a Seico SPI-300HV SPM in the contact mode with

a Pt coated tip.

The water-triggered shape recovery was measured by immersing the sample in ring

form in the water at 308C. Shape-fixing was made by bending a rectangular strip with

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2 mm width and 20 mm length in a ring form at 608C, followed by quenching into a dry-ice

bath. Then, images of shape recovery were recorded by using a video camera, and change

in curvature was measured to calculate shape recovery (SR) using Eq. (1).

SR ð%Þ ¼ ðð90� uÞ=90Þ � 100 ð1Þ

Hence, u (degree) indicated an angle between a tangential line at a midpoint of the sample

and a line connecting the midpoint and end of the curved sample.

3 Results and Discussion

Polyurethanes having POSS and PEG groups as the hard and soft segments, respectively,

were synthesized in a one-step polymerization as shown in Fig. 1. From the FT-IR

measurements, formation of the urethane linkages due to reaction between the hydroxyl

Figure 1. Polymerization procedure of the POSS-PU block copolymer.

Table 1Specification of POSS-PU samples synthesized in this study

Samples code

Feed mole ratioMW

(g/mol) Mw/Mn

HS content

(wt%) DPS (%)PEG POSS PDI

10K-P-134 1 3 4 34,189 6.26 28 49.42

10K-P-145 1 4 5 25,696 6.95 33 49.81

10K-P-156 1 5 6 22,438 8.91 38 49.61

10K-P-167 1 6 7 30,223 9.36 43 49.77

10K-P-178 1 7 8 17,945 7.69 49 49.53

HS: hard segment, DPS: degree of phase separation.

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groups of PEG and diisocyanates of PDI and the hydroxyl groups of POSS diol and

diisocyanates could be seen.

Figure 2 shows FT-IR spectra of the PUs at different POSS:PEG mole ratios. Two

characteristic peaks near 1703 cm21 and 1727 cm21 are ascribed to the stretching

vibration of carbonyl (–C55O) groups in the hard segments.[16 – 18] The former peak is

due to the presence of hydrogen-bonded carbonyl groups formed by phase separation

and intermolecular interaction with 22NH in hard segments, whereas the latter peak

is due to the presence of nonhydrogen-bonded carbonyl groups due to their dissolution

in the matrix of soft segments. These absorption peaks near 1703 cm21 and 1727 cm21

are useful to evaluate the phase separation of PU. That is, the degree of phase

separation (DPS) based on the carbonyl groups can be calculated by the following

equation.

DPS ¼ R=ð1þ RÞ ð2Þ

Where R indicates a ratio of A1727 to A1703, and A1703 and A1727 are the absorbance values

at 1703 cm21 and 1727 cm21, respectively.

The calculated DPS values are presented in Table 1, and essentially do not change

with the mole ratio of POSS:PEG or hard segment content. The phase separation

increases with increasing hard segment content in most cases of polyurethane. Our

results indicate that the phase separation for our PU samples may be not completely

governed by the carbonyl groups, recalling that the DPS value is calculated from the

phase separation based on the hydrogen and nonhydrogen bonds due to the carbonyl

group in hard segments. In other words, it may be explained by the fact that the hard

segment content is primarily governed by POSS molecules in spite of the significant

contribution of carbonyl groups in the hard segments.

The X-ray diffraction profiles of POSS:PEG are shown in Fig. 3. The pure PEG shows

reflections at 2u ¼ 21.48 (4.10 A), 24.28 (3.68 A), and 36.58 (2.46 A), corresponding to the

(110), (200), and (020) reflections of the usual orthorhombic PEG crystal structure.[19] The

PUs in this study show additional peaks at 2u ¼ 8.28 (11.04 A) and 10.78 (8.23 A) besides

Figure 2. FT-IR spectra of PU samples with different POSS:PEG mole ratio.

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diffraction peaks at 2u ¼ 21.48, 24.28, and 36.58 due to PEG crystals. These clearly

correspond to the reflections of POSS crystals.[6,9,13] This indicates that the POSS

molecules in this study are not individually dispersed at a molecular level, but form the

crystals in the polyurethane copolymer. As the POSS content increases, the relative

intensity corresponding to each reflection of the POSS and PEG crystals changes

gradually. That is, the PUs has two separate crystalline components, of POSS and PEG.

This indicates that the POSS molecules play an important role in formation of the hard

segments in PU. As a result, the crystallization in the hard segment domain is primarily

governed by aggregation of POSS molecules.

Figure 4 shows DSC thermograms of PU samples, which were obtained during

heating at a rate of 108C/min. All the samples exhibit two endothermic peaks near

458C and 1158C.[20,21] The peaks at lower and higher temperatures are due to the

melting temperatures of PEG soft segment crystals and POSS hard segment crystals,

respectively. It can also be seen that the PEG endothermic area is relatively larger than

the POSS endothermic area. This is because of the low crystallinity due to crystallization

or aggregation of POSS molecules. According to Waddon et al.[6] it is impossible for the

POSS molecules in polyethylene-POSS copolymer to crystallize in three-dimensions of

crystals due to considerable spatial constraints imposed on the crystal shape, and they

develop in two-dimensional crystals. On the other hand, the melting temperature and

heat of fusion of the hard segment domain increase, whereas those of the soft segment

domain decrease with an increase in POSS content as shown in Figs. 5 and 6. This

reflects the dependence of phase separation on the mole ratio of POSS:PEG.

Figure 3. X-ray reflections of samples with different mole ratio of POSS:PEG.

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The scanning probe microscopy (SPM) topographical images of thin films prepared by

spin-coating are shown in Fig. 7. The bright areas correspond to POSS absorption, and thus

the phase separated morphology differs with POSS content. As the POSS content increases,

the POSS molecules are dispersed in smaller domains, indicating that a more developed

phase separation of hard and soft segments appears with the increased POSS content. The

most developed phase-separation is seen for the 7:1 POSS:PEG sample, and it is apparent

that the POSS has a dominant effect on the phase separation.

Figure 8 shows the water-responsive shape recovery behavior of a rectangular PU strip

when it is immersed into water at 308C. The initial straight shape of the sample was fixed in a

Figure 4. DSC thermograms of samples with different mole ratio of POSS:PEG obtained on heating.

Figure 5. Melting temperatures of samples vs. mole ratio of POSS:PEG.

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ring form by deforming at 608C and cooling to room temperature. The original shape of the

sample is nearly recovered in 300 seconds when the ring sample is immersed into water at

308C. It was also found that water-responsive shape recovery is dependent on the tempera-

ture of water used. That is, as temperature of water is increased, more rapid recovery

Figure 6. The heat of fusion of samples vs. mole ratio of POSS:PEG.

Figure 7. SPM images of samples with a different mole ratio of POSS : PEG: (a) 3:1, (b) 4:1, (c) 5:1,

(d) 6:1, (e) 7:1.

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appears, for example, the shape recovery in water at 608C was 10 seconds; above the melting

temperature of PEO crystals, very rapid shape recovery occurs due to combined effects of

water absorption and thermal heating. Shape recovery greater than 70% is observed in

the water-responsive shape recovery test, as shown in Fig. 9. The best shape recovery of

85% is observed in the sample at a mole ratio of 5:1 POSS:PEG.

4 Conclusion

From investigation of structure and properties of polyurethane block copolymers modified with

POSS, the following conclusions were derived. The hard segment domain was governed by

crystallization of POSS molecules due to the phase separation. As the POSS content

increased, higher melting temperature and crystallinity due to POSS crystals were obtained,

whereas the melting temperature and crystallinity due to PEG soft segments were lowered.

Water-responsive shape recovery at 308C of more than 70% was achieved for all samples. Con-

sequently, POSS-PU may be useful for the water-responsive shape memory materials.

Acknowledgments

This work was supported by the Korea Research Foundation Grant (KRF-2004-041-

D00827).

Figure 8. Typical example of water-sensitive shape recovery behavior of POSS-PU sample at 358C.

Figure 9. Water-sensitive shape recovery of samples vs. mole ratio of POSS:PEG.

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References

1. Lendlein, A.; Kelch, S. Shape-memory polymers. Angew. Chem. Int. Ed. 2002, 41, 2034.

2. Lee, B.S.; Chun, B.C.; Chung, Y.C.; Sul, K.I.; Cho, J.W. Structure and thermomechanical

properties of polyurethane block copolymers with shape memory effect. Macromolecules

2001, 34, 6431.

3. Cho, J.W.; Kim, J.W.; Jung, Y.C.; Goo, N.S. Electroactive shape-memory polyurethane compo-

sites incorporating carbon nanotubes. Macromol. Rapid Commun. 2005, 26, 412.

4. Lendlein, A.; Jiang, H.; Junger, O.; Langer, R. Light-induced shape-memory polymers. Nature

2005, 434, 879.

5. Watanabe, M.; Wakimoto, N.; Hirai, T.; Yokoyama, M. Thermal switching of the actuation

ability of an electroactive polymer actuator. J. Appl. Polym. Sci. 2005, 95, 1566.

6. Zheng, L.; Waddon, A.J.; Farris, R.J.; Coughlin, E.B. X-ray characterizations of polyethylene

polyhedral oligomeric silsesquioxane copolymers. Macromolecules 2002, 35, 2375.

7. Schwab, J.J.; Lichtenhan, J.D. Polyhedral oligomeric silsesquioxane (POSS)-based polymers.

Appl. Organomet. Chem. 1998, 12, 707.

8. Bharadwaj, R.K.; Berry, R.J.; Farmer, B.L. Molecular dynamics simulation study of norbonone-

POSS polymers. Polymer 2000, 41, 7209.

9. Phillips, S.H.; Haddad, T.S.; Tomczak, S.J. Developments in nanoscience: polyhedral

oligomeric silsesquioxane-polymers. Curr. Opin. Solid St. M. 2004, 8, 21.

10. Pyun, J.; Mtyjaszewski, K.; Wu, J.; Kim, G.-M.; Chun, S.B.; Mather, P.T. ABA triblock copo-

lymers containing polyhedral oligomeric silesquioxane pendant groups: synthesis and unique

properties. Polymer 2003, 44, 2739.

11. Fu, B.X.; Lee, A.; Haddad, T.S. Styrene-butadiende-styrene triblock copolymers modified with

polyhedral oligomeric silsesquioxanes. Macromolecules 2004, 37, 5211.

12. Zheng, L.; Farris, R.J.; Coughlin, E.B. Novel polyolefin nanocomposites: synthesis and

characterizations of metallocene-catalyzed polyolefin polyhedral oligomeric silsesquioxane

copolymers. Macromolecules 2001, 34, 8034.

13. Fu, B.X.; Lee, A.; Haddad, T.S. Styrene-butadiende-styrene triblock copolymers modified with

polyhedral oligomeric silsesquioxanes. Macromolecules 2004, 37, 5211.

14. Li, G.; Cai, Q.; Bei, J.; Wang, S. Relationship between morphology structure and composition of

polycaprolactone/poly(ethylene oxide)/polylactides copolymeric microspheres. Polym. Advan.

Technol. 2002, 13, 636.

15. Su, Y.-I.; Wang, J.; Liu, H.-Z. Melt, hydration, and micellization of the PEO-PPO-PEO block

copolymer studied by FTIR spectroscopy. J. Colloid Interf. Sci. 2002, 251, 417.

16. Wang, F.C.; Feve, M.; Lam, T.M.; Pascault, J.P. FTIR analysis of hydrogen bonding in

amorphous linear aromatic polyurethanes. I. influence of temperature. J. Polym. Sci. Polym.

Phys. 1994, 32, 1305.

17. Wang, F.C.; Feve, M.; Lam, T.M.; Pascault, J.P. FTIR analysis of hydrogen bonding in

amorphous linear aromatic polyurethanes. II. influence of styrene solvent. J. Polym. Sci.

Polym. Phys. 1994, 32, 1315.

18. Garrett, J.T.; Xu, R.; Cho, J.; Runt, J. Phase separation of diamine chain-extended

poly(urethane) copolymers: FTIR spectroscopy and phase separation. Polymer 2003, 44, 2711.

19. Schmalz, H.; Knoll, A.; Muller, A.J.; Abetz, V. Synthesis and characterization of ABC triblock

copolymers with two different crystalline end blocks: influence of confinement on crystalliza-

tion behavior and morphology. Macromolecules 2002, 35, 10004.

20. Saiani, A.; Daunch, W.A.; Verbeke, H.; Leenslag, J.-W.; Higgins, J.S. Origin of multiple

melting endotherms in a high hard block content polyurethane. 1. thermodynamic investigation.

Macromolecules 2001, 34, 9059.

21. Saiani, A.; Rochas, C.; Eckhaut, G.; Daunch, W.A.; Leenslag, J.S.; Higgins, J.S. Origin of

multiple melting endotherms in a high block content polyurethane. 2. structural investigation.

Macromolecules 2004, 37, 1411.

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