Precise Synthesis of ABA Triblock Copolymers Comprised of Poly(ethylene oxide) and Poly(β-benzyl-l-aspartate):  A Hierarchical Structure Inducing Excellent Elasticity

Abstract

ABA triblock copolymers comprised of poly(β-benzyl-l-aspartate) (PBLA) as an A segment and poly(ethylene oxide) (PEO) as the B segment were precisely synthesized by a ring-opening polymerization of the N-carboxyanhydride of BLA initiated from amines at both terminals of the PEO chain. The copolymers have a number-average molecular weight (M n) of 1.5 × 104−3.6 × 104 and a monodisperse molecular weight distribution in the range 1.04−1.07. The copolymer films casted from a dichloromethane solution were flexible and elastic despite their low M n. The film formed a hierarchical structure, i.e., the chains adopted an α-helix−72 helix−α-helix conformation and was highly crystallized, forming a long-range ordering structure which resulted in a rodlike construct arranged like ripples, as confirmed by Fourier transformed infrared spectroscopy, X-ray diffraction, and atomic force microscopy. Differential scanning calorimetry confirmed that the film showed a melting endotherm of the PEO segment at 313−326 K depending on the PBLA content. The film became very soft and behaved like rubber above the melting temperature. When the film was successively cooled, the crystalline diffraction became less intense, especially in terms of the PBLA segments whose conformation partially transformed from α-helices to β-sheets, and the film showed enhanced strength and drastically increased deformation, with a strain of more than 500% accompanied by a necking phenomenon. The relationship between the mechanical properties and the structure is also discussed.

Mass Ratio of CdS/Poly(ethylene oxide) Controlled Photoluminescence of One‐Dimensional Hybrid Fibers by Electrospinning

“…In addition, a striking feature observed on all samples is that the fibers are not continuous and there are some fragments on them. As we known, PEO is a semicrystalline polymer, the use of high voltage in the electrospinning process possibly led to the crystalline and orientation of PEO 19. As a result, the fibers become crisp, which could be responsible for the fragments.…”

Conformational Transition of Poly(γ-benzyl-L-glutamate)-Poly(ethylene glycol) Block Copolymers in Bulk

“…30 The WAXD patterns at 19 o and 23 o are characteristics of PEO crystals where the PEO chains form a 2/7 helix structure. 17 This means all GE series keep the α-helical conformation, and the contents of β-conformation increased PBLG parts are reduced because of repulsion between PEG and PBLG. The β-sheet conformation is also indicated by small shoulder peak in FT-IR spectra Liquid Crystalline Image.…”

“…16 But they are so brittle that it is difficult to apply them to living organs without combing them with other techniques. 17 PEO, that is one of the best-studied in a wide range of chemical and biomedical field, is quite safe in living body. So many research groups with PBLG-PEO copolymer have been investigated to find good mechanical properties or to control with nanometer length scale.…”

Melting Behaviour for Gels Formed from the Solution of Chloroform and ABA Triblock Copolymer comprised of Poly (L-leucine) and Poly(ethylene glycol)

“…For block copolymers, including telechelic hydrophobically modified hydrophilic polymer, physical properties are currently researched with wide range attentions; those are rich morphological textures in solid, macromolecular assembly to generate polymeric micelles and ordered structure in selective solvents, potential applications as compartibilisers in polymer blends and as biomedical materials. [8][9][10][11][12][13][14][15][16] In particular, ABA triblock copolymer is the one of the key technologies to realise self-assembly both in solid and in solution, because it has well-defined structures on the nanometer scale and the capacity for the control of self-organisation in such systems by the combination of opposite interactions that can result in processing order over multiple length scales.…”