Synthesis and characterization of well-defined random and block copolymers of e-caprolactone with L-lactide as an additive for toughening polylactide: Influence of the molecular architecture Megha D. Deokar, Susheela B. Idage, Bhaskar B. Idage, Swaminathan Sivaram Polymer Science and Engineering Division, Council of Scientific and Industrial Research–National Chemical Laboratory, Pune 411 008, India Correspondence to: S. Sivaram (E - mail: s.sivaram@ncl.res.in) ABSTRACT: Well-defined multiarmed star random and block copolymers of e-caprolactone with L-lactide with controlled molecular weights, low polydispersities, and precise numbers of arms were synthesized by the ring-opening polymerization of respective cyclic ester monomers. The polymers were characterized by 1 H-NMR and 13 C-NMR to determine their chemical composition, molecular structure, degree of randomness, and proof of block copolymer formation. Gel permeation chromatography was used to establish the degree of branching. Star-branched random copolymers exhibited lower glass-transition temperatures (T g ’s) compared to a linear ran- dom copolymer. When the star random copolymers were melt-blended with poly(L-lactic acid) (PLA), we observed that the elonga- tion of the blend increased with the number of arms of the copolymer. Six-armed block copolymers, which exhibited higher T g ’s, caused the maximum improvement in elongation. In all cases, improvements in the elongation were achieved with no loss of stiffness in the PLA blends. V C 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43267. KEYWORDS: biodegradable; copolymers; differential scanning calorimetry; mechanical properties; ring-opening polymerization Received 11 September 2015; accepted 23 November 2015 DOI: 10.1002/app.43267 INTRODUCTION Poly(L-lactic acid) (PLA) is the quintessential bioderived, biore- newable, biodegradable, and biocompatible polymer with a unique set of properties unmatched by any other polymer in its class. It is, therefore, not surprising that it has elicited wide- spread attention from researchers in academia and industry. 1,2 Derived from the simplest of self-polymerizable AB monomers, PLA possesses attractive physical properties, including a high melting temperature (T m ), high strength, high modulus, and good optical clarity. However, the polymer is also beset by sev- eral drawbacks, namely, poor impact properties, a low elonga- tion at break, a poor melt viscosity, a low heat deflection temperature, and slow rates of crystallization. These drawbacks limit the range of applications accessible to PLA. Consequently, substantial research efforts have been made to devise methods to improve these properties. Several methods for toughening PLAs have been reported recently in the literature. 3,4 The toughening of glassy and semi- crystalline polymers by melt blending with elastomers has been the most frequently used method for improving the impact properties of brittle polymers. Elastomeric ethylene–butyl acry- late–glycidyl methacrylate terpolymers, 5 poly(n-butyl acrylate)- g-PLA, 6 core–shell nanoparticles consisting of Polyhedral oligo- meric silsesquioxane–PLA-b-Poly(D-lactide), 7 and PLA-grafted elastomer 8 have been reported to improve the toughness of PLA. The majority of these efforts have been made toward the melt blending of PLA with low-glass-transition-temperature (T g ) polymers or copolymers derived from monomers such as e-caprolactone (e-CL), trimethylene carbonate, and d- valerolactone or polymers such as poly(butylene succinate), pol- yhydroxybutyrate, and linear low-density polyethylene. Although some of these polymers caused improvements in elongation, invariably, this was accompanied by a loss of the modulus of rigidity. 4 More recently, Odent and coworkers 9,10 examined the toughen- ing ability of random copolymers of e-CL with d-valerolactone and with lactic acid. Both these polymers are also biodegradable. A random copolymer of e-CL (45 mol %) with d-valerolactone [55 mol %; number-average molecular weight (M n ) 5 60,000 g/ mol] was melt-blended with PLA (M n 5 95,000 g/mol, 10 wt %). The resulting blend showed a 300% improvement in the impact strength. The random copolymer was an amorphous rubbery Additional Supporting Information may be found in the online version of this article. V C 2015 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2016, DOI: 10.1002/APP.43267 43267 (1 of 12)