DESIGN OF MULTI-STIMULI RESPONSIVE SHAPE-MEMORY POLYMER MATERIALS BY REACTIVE EXTRUSION

Shape-memory polymers (SMPs) are a new class of stimuli-responsive materials that attract a tremendous attention in various applications, especially in the medical field. They

are able to “memorize” a temporary shape and recover back to a permanent shape when an appropriate external stimulus is applied[1]. While most SMPs are thermally-actuatedrelated with a change of thermal transition (e.g. melting temperature), SMPs that could be actuated upon exposition of light or application of magnetic field, are being emerged.Recently, there has been a new interest into multiple stimuli-responsive SMPs in order to span the range of applications for these smart materials[2].

Florence Pilate1, Rosica Mincheva1, Jean-Marie Raquez1, Linbo Wu2, Philippe Dubois1

1Laboratory of Polymeric and Composite Materials (LPCM)Center of Innovation and Research in Materials & Polymers (CIRMAP), University of Mons (UMONS), 23 Place du Parc, B-7000 Mons, Belgium

2Department of Chemical & Biological Engineering, State Key Laboratory of Chemical Engineering, Zhejiang University, Hangzhou 310027, P. R. China

References1. Lendlein, A.; Kelch, S. Angew. Chem. Int. Ed. 2002, 41, 2034-2057.2. Schattling, P.; Jochum, F. D.; Theato, P. Polym. Chem. 2014, 5, 25-36.3. Raquez, J-.M.; Degee, P.; Dubois, P. Polym. Eng. Sci. 2005, 45, 622-629.

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AcknowledgmentsLPCM thanks the Belgian Federal Government Office of Science Policy (SSTC- PAI 6/27) forgeneral support and is much indebted to both “Région Wallonne” and the EuropeanCommission “FSE and FEDER” for financial support in the frame of Phasing-out Hainaut. F.Pilate is a FRS-FNRS PhD student and J.-M. Raquez is a FRS-FNRS research associate.

• Synthesis of poly(e-caprolactone-co-para-dioxanone) copolymers

• Synthesis of PURs by chain-extension and determination of SMP properties

In this work, we propose the synthesis of poly(ester-urethane)s (PURs) made of a thermally-actuated poly(e-caprolactone) (PCL) segments of various degrees of crystallinity andlight-actuated N,N-bis(2-hydroxyethyl) cinnamide (BHECA) monomer by reactive extrusion technology in order to design double light- and temperature-responsive SMPs (Fig.1).

Entry CL molar content ĐXb Yieldc Tm

d

(°C)DHm

d

(J/g)

(Th.) (Exp.)a (Th.) (Exp.)a

1 100 100 4200 4400 1.6 91 53 74

2 90 93 4100 5300 1.7 80 44 70

3 80 83 3300 3700 1.7 69 30 53

4 70 78 3900 5100 1.7 94 26 45

In order to tune the SMP properties (temperature or light), the crystallinity of PCL segmentwas finely adjusted by copolymerization of e-caprolactone with para-dioxanone in bulk at160°C for 3 hours using tin(II) octoate and initiated by 1,8-octanediol as reported elsewhere [3].

Table 1. Molecular and thermal parameters of copolyesters

The resulting polyester segments were afterwards coupled with BHECA using n-octyl diisocyanate at 130°C into a 15cm³ twin-screw DSM microcompounder at 130°C and 75 rpm.The molar ratio between both sensitive segments was fixed at 80 mol% BHECA, representing 15.5 wt%.

aAs determined by proton 1H NMR technique recorded in CDCl3; bAs determined by SEC (THF + 2%NEt3) upon PS calibration; cAsdetermined by gravimetry; dAs determined by DSC analyses (from -80°C– to 100°C at a heating rate of 10°C/min – 2nd scan).

PURs with double-SMEs were successfully obtained by chain-extension between a,w-diol PCL-based oligomers of various degree of crystallinity, BHECA monomer asphotoreversible monomer and 1,8-octanediisocyanate as coupling agent by reactive extrusion processing. In order to tune the temperature- and light-SMEs, the crystallinity ofPCL segment was finely adjusted by copolymerization of e-caprolactone with para-dioxanone in bulk at 160°C using tin(II) octoate, and the resulting polyester segments wereafterwards coupled with BHECA using n-octyl diisocyanate at 130°C. The SMP properties of resulting PURs were correlated with DSC and DMTA measurements. Further additionof di- and tetracinnamate PCL segments incorporated in these SMPs was also studied in order to enhance the light-SMEs of resulting PURs.

Thermal shape-memory effectFirst, the SMP film was exposed to UV light (l> 260 nm) for 2 hours to fix the system(Fig. 3).Then the thermal shape-memory effect of the samples was characterized usingDMA in tensile mode test with the following program (Fig. 4):

Thermal SME Light SME

Entry CL mol% DHm (J/g)a Rf (%) Rr (%) Rf (%) Rr (%)

PUR (1) 100 53.5 ~100 ~100 98 18

PUR (2) 93 45.0 ~100 ~100 78 15

PUR(3) 83 1.3 92 97 45 55

PUR (4) 78 0.7 ND ND 43 27

The light effect was obtained by extension of the sample to 200% and exposition towavelengths > 260nm for 2h (Fig. 5). The same sample was then exposed towavelengths < 260nm (Fig. 6).

1)Deformation: constant loading at 65°C 2)Fixing: cooling at 0°C3)Unloading at 0°C 4)Recovery :heating to 65°C

Light shape-memory effect

The shape memory effect of the systems can be quantified by :

Fixity ratio (Rf) (in %) = ability to store the temporary shape after unloading

Recovery ratio (Rr)(in %) = ability to recover the permanent shape

l> 260nm

Table 2. Light and thermal-actuated shape-memory properties of PURs

Figure 5. Extension and exposition to l> 260nm Figure 6. exposition to l < 260nm

Figure 3. Exposition of a thinfilm of SMP to l>260nm.

Figure 4. Cyclic thermomechanical process (DMTA) of PUR containing a PCL/BHECA molar ratio of 20/80

Figure 1.Synthesis of the PUR networks.

Figure 2.Synthesis of the copolyesters

Introduction

Original approach

Synthesis and Results

aAs determined by DSC analyses (from -80°C– to 100°C at a heating rate of 10°C/min – 2nd scan).

Conclusions

l> 260nm l <260 nm