Synthesis of Biodegradable Thermoplastic Elastomers from e-Caprolactone and Lactide Yuushou Nakayama, 1 Kazuki Aihara, 1 Hitomi Yamanishi, 1 Hiroshi Fukuoka, 1 Ryo Tanaka, 1 Zhengguo Cai, 2 * Takeshi Shiono 1 1 Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan 2 State Key Lab of Chemical Fibers and Polymer Materials, College of Material Science and Engineering, Donghua University, Shanghai 201620, China Correspondence to: Y. Nakayama (E - mail: yuushou@hiroshima-u.ac.jp) Received 23 July 2014; accepted 1 November 2014; published online 00 Month 2014 DOI: 10.1002/pola.27463 ABSTRACT: This article reports the synthesis and the properties of novel thermoplastic elastomers of A-B-A type triblock copoly- mer structure, where the hard segment A is poly(L-lactide) (PLLA) and the soft segment B is poly(e-caprolactone-stat-D,L-lac- tide) (P(CL-stat-DLLA)). The P(CL-stat-DLLA) block with DLLA content of 30 mol % was applied because of its amorphous nature and low glass transition temperature (T g 5 approximately 240  C). Successive polymerization of L-lactide afforded PLLA- block-P(CL-stat-DLLA)-block-PLLAs, which exhibited melting tem- perature (T m 5 approximately 150  C) for the crystalline PLLA segments and still low T g (approximately 230  C) of the soft segments. The triblock copolymers showed very high elonga- tion at break up to approximately 2800% and elastic properties. The corresponding D-triblock copolymers, PDLA-block-P(CL-stat- DLLA)-block-PDLAs (PDLA 5 poly(D-lactide)) were also prepared with the same procedure using D-lactide in place of L-lactide. When the PLLA-block-P(CL-stat-DLLA)-block-PLLA was blended with PDLA-block-P(CL-stat-DLLA)-block-PDLA, stereocomplex crystals were formed to enhance their T m as well as tensile properties. V C 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 00, 000–000 KEYWORDS: biodegradable; block copolymers; elastomers; lactide; steteocomplex; e-caprolactone INTRODUCTION Poly(L-lactide) (PLLA) is one of the most promising biomass-based polymers and has been attracting great interests. 1–7 PLLA also has characteristic features, such as biodegradability and biocompatibility. PLLA possesses melting temperature (T m ) up to 180  C and glass-transition temperature (T g ) at approximately 60  C, and is a rigid poly- mer. However, its brittle nature is limiting its application. In order to overcome the brittle nature of PLLA, the introduc- tion of some soft component has been studied. 8–10 On the other hand, triblock or multiblock copolymers with soft and hard segments have been known as thermoplastic elastomers (TPE), which have advantages of easier molding and better recycling ability in comparison with vulcanized rubbers. 11 When polylactide (PLA) was applied to the hard segment of TPE, the material would possess partial biode- gradability. Several PLA-block-S-block-PLA (S 5 soft segment) triblock copolymers have been reported, where the soft seg- ment S are aliphatic polyester, 12–17 polycarbonate, 16,18 poly- ether, 12,19,20 polyisoprene, 21,22 and so on. 23,24 The triblock copolymers with an aliphatic polyester as a soft segment should be completely biodegradable. Hillmyer and co- workers reported PLA-block-PM-block-PLA (PM 5 polymen- thide), which should be derived from biomass-based men- thone. 13,14 The PLA-block-PM-block-PLA was found to exhibit high elongation at break (960%). The same group also reported PLA-block-PMCL-block-PLA (PMCL 5 poly(6-methyl- e-caprolactone)), which showed higher elongation at break (1880%). 15 Mehrkhodavandi and co-workers synthesized PLLA-block-P(rac-b-BL)-block-PLLA (P(rac-b-BL) 5 poly(rac- b-butyrolactone)) and PLLA-block-P(rac-b-BL)-block-PDLA (PDLA 5 poly(D-lactide)) by a dinuclear indium complex bearing N–N–O tridentate ancillary ligand. 25 Ling and co- workers adopted poly(e-decalactone) (PDL), which was derived from caster oil, and pentablock copolymers, PLLA- block-PDL-block-PEG-block-PDL-block-PLLAs (PEG 5 poly(- ethylene glycol)), were prepared. 17 The pentablock copoly- mers were chain-extended by diisocyanate to produce poly(ester-urethane), showing high elongation at break (723%). In this study, we adopted poly(e-caprolactone-stat-D,L-lactide) (P(CL-stat-DLLA)) as a soft segment for PLLA-containing tri- block copolymers, which were prepared from common and V C 2014 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 00, 000–000 1 JOURNAL OF POLYMER SCIENCE WWW.POLYMERCHEMISTRY.ORG ARTICLE