Abstract
Polylactide (PLA) stereocomplexes (SCs) containing amorphous block copolymers have gained enormous interest due to their unique properties and wide range of potential applications. In this work, we report the synthesis and properties of non-covalent triblock terpolymers: polystyrene–SCPLA–polyisoprene (PS–SC–PI) via the stereocomplexation of PS-b-PDLA with PI-b-PLLA diblock copolymers through the solution-precipitation method. The diblock copolymers were prepared by combining the anionic polymerization high-vacuum technique with ring-opening polymerization (ROP). First, several well-defined ω-hydroxyl polystyrenes and polyisoprenes (PS-OH and PI-OH) with varied molecular weights were synthesized by anionic polymerization using sec-BuLi as the initiator. PS-OH and PI-OH were used as the macroinitiators for the ROP of DLA and LLA catalyzed by tin(II) 2-ethyl hexanoate to afford PS-b-PDLA and PI-b-PLLA. PS–SC–PIs were prepared by mixing PS-b-PDLA and PI-b-PLLA solutions (in dichloromethane) and precipitated into methanol. The molecular characteristics of the block copolymers were determined by 1H NMR spectroscopy and size exclusion chromatography. The formation of PS–SC–PIs was evidenced by differential scanning calorimetry, X-ray diffraction, and Fourier-transform infrared, and circular dichroism spectroscopies. A preliminary study by atomic force microscopy reveals the thin-film phase behavior and the supramolecular organization of the PS–SC–PI.
Highlights
Polylactides (PLAs) have attracted significant attention in the past few decades due to their outstanding thermal and mechanical properties, biodegradability, and biocompatibility.[1−4] PLAs have been widely used as biodegradable plastics, as nanocarriers in drug delivery, in tissue engineering, and in 3D printing, among other applications.[5−8]PLAs can be prepared by ring-opening polymerization (ROP) of lactide (LA).[9]
The end-capping of the living chain end with ethylene oxide (EO) followed by the addition of methanol results in OH-functionalized polymers with a high degree of functionalization (>99%).[55,56]
It was expected that anionic polymerization of isoprene using sec-BuLi as the initiator and benzene as the solvent would lead to the formation of PI having a high content of cis-1,4 microstructure, which will be discussed later in the nuclear magnetic resonance (NMR) section.[57]
Summary
Polylactides (PLAs) have attracted significant attention in the past few decades due to their outstanding thermal and mechanical properties, biodegradability, and biocompatibility.[1−4] PLAs have been widely used as biodegradable plastics, as nanocarriers in drug delivery, in tissue engineering, and in 3D printing, among other applications.[5−8]PLAs can be prepared by ring-opening polymerization (ROP) of lactide (LA).[9]. Sn(Oct)[2] is widely used as the catalyst for ROP of LAs and lactones because it is cheap, commercially available, has good solubility in organic solvents, is stable at high temperature, and promotes a well-controlled ROP with a high degree of stereoregularity.[10]. LAs possess two stereocenters and provide three stereoisomeric forms: (R,R)L-lactide (LLA), (S,S)D-lactide (DLA), and (R,S)meso-lactide (mLA).[11] The polymerization of LLA or DLA with Sn(Oct)[2] leads to the formation of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) with a high degree of isotacticity. Isotactic PLLA and PDLA undergo a stereoselective association to form a PLA stereocomplex (SC) in melt or solution.[11,12] Stereocomplexation of PLAs has gained significant interest in material science because the resulting SC has improved mechanical and thermal properties compared with the corresponding homopolymers.[13]
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