Stereocomplexes of A−B−A Triblock Copolymers Based on Poly(l-Lactide) and Poly(d-Lactide) A Blocks

Abstract

A series of A−B−A triblock copolymers was prepared by a Sn(II) 2-ethylhexanoate catalyzed chain extension of various telechelic soft segments, with l,l-lactide (LLA). Poly(ε-caprolactone)s, PεCL, poly(ethylene glycol)s, PEG, and a poly(dimethyl siloxane), PDMS, served as soft segments. The lengths of both soft and hard segments (poly-LLA, PLLA, or poly-d,d-lactide, PDLA) were varied. For the lactide blocks, average lengths of 25, 50, and 100 lactic acid units were selected. An analogous series of A−B−A triblock copolymers was prepared with DLA. Compositions and block lengths of these triblock copolymers were characterized by 1H NMR spectroscopy. Furthermore, stereocomplexes (racemates) of PLLA- and PDLA-based triblock copolymers were prepared to find out if the attractive forces between PLLA and PDLA blocks or the repulsive forces between incompatible soft segments dominate the morphology. Both neat triblock copolymers and stereocomplexes were characterized by differential scanning calorimtery measurements by wide-angle X-ray diffraction. The influence of block lengths on glass transition (T g) and melting temperatures (T m) of soft and hard segments was studied in detail. Stereocomplexes of all triblock combinations were obtained, even when the soft segments were incompatible.

Investigation of poly(lactide) stereocomplexation between linear poly(L‐lactide) and PDLA‐PEG‐PDLA tri‐block copolymer

“…This showed that the PEG segments could improve the crystallization capacity of PLA, due to the flexibility of the PEG segments . Analogous studies have been reported by Zeng et al and Kricheldorf et al This is because PEG segments could assist the mobility and rearrangement of polymer segments in the crystallization process, especially for melting crystallization . Figure (c) displays the DSC second heating curves of the blend.…”

Phase Transitions and Honeycomb Morphology in an Incompatible Blend of Enantiomeric Polylactide Block Copolymers

“…Kricheldorf et al studied the stereocomplex formation and morphology in PLLA-and PDLA-containing A-B-A triblock copolymers with A being the PLA blocks. 18 By variation of the chemical structures of the B blocks using incompatible polymers, it was found that the attractive interactions between the PLLA and PDLA blocks, rather than the repulsive interactions between incompatible soft B blocks, dominated the stereocomplex formation and the final morphology.…”

Synthesis of hyperbranched poly(ether nitrile)s by one‐step polycondensation of an AB2 monomer

“…Kricheldorf reported that 2,4-difluorobenzonitrile favors the formation of cyclic compounds. 18 In this study, the prolonged reaction caused the dominant formation of cyclic oligomers. The formation of cyclic oligomers causes the consumption of terminal units and the formation of unexpected linear units.…”

“…17 Kricheldorf reported the formation tendency of multicycles of difluorobenzonitriles. 18 The MALDI-TOF MS spectroscopic measurement of the acetylated polymers was carried out to discuss the possibility of the cyclic formation, as shown in Figure 7. For the polymer prepared for 1 h, two sets of double peaks were observed in the measured mass range.…”