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A series of poly(l-lactide) stereocopolymers with various optical purities (100%–88%) were synthesized by ring-opening copolymerization of the enantiomeric feedstock mixtures of l-lactide and D-lactide at 140 °C for 16 h under reduced pressure. The obtained relationship between microstructure and optical composition of poly(l-lactide) (PLLA) copolymers confirmed that the stannous octoate-catalyzed...
A series of ABA type triblock copolymers based on biodegradable poly(butylene carbonate) (PBC) and poly(l-lactide) (PLLA) were synthesized with PBC as the core and varying the PLLA chain length. A significant reduction in the crystallinity of the PBC component is observed in the block copolymers as evidenced by DSC and wide angle X-ray diffraction. A systematic increase in the crystallinity of the...
Novel and well defined macrophotoinitiators with two-arm poly(ε−caprolactone) (PCL) and poly(l-lactide) (PLLA) chains bearing two benzoin photofunctionalities (BPI) at the connection point of the polymer chains have been synthesized by combination of ring opening polymerization (ROP) and click chemistry. Initially, dibromo end-functionalized two-arm PCL, (PCL)2-(Br)2, and PLLA, (PLLA)2-(Br)2, were...
Among the various crystalline phases of polylactides, an elusive orthorhombic gamma phase (γPLLA) had been obtained so far only by epitaxial crystallization on hexamethylbenzene. A recent work by J. Shao et al. (Macromolecules, 2013, 46, 6933) reports on two “novel modified crystallites” of PLLA obtained “under the confinement of stereocomplex PLLA/PDLA crystallites” produced on cooling blends of...
A unique oscillation shear injection molding was utilized to investigate the crystallization of poly (l-lactide) (PLLA) under the coexistence of an intense shear flow and nucleating agents. The crystalline morphology and its distribution of injection-molded PLLA were probed by wide-angle X-ray diffraction, showing that an intense shear flow promotes the crystallization significantly, whereas the nucleation...
Semicrystalline polymers have to be described by a three phase model consisting of a mobile amorphous (MAF), a crystalline (CF), and a rigid amorphous fraction (RAF). For nanocomposites based on a semicrystalline polymer the RAF is due to both the crystallites (RAFcrystal) and the filler (RAFfiller). Polymer nanocomposite based on poly(l-lactide) and MgAl layered double hydroxide nanofiller were prepared...
Selective localization of nanoparticles at the interface of immiscible polymer blends has been witnessed as an efficient method to improve blend properties and even provide some added functionalities. Nevertheless, it is still a great challenge to achieve thermodynamically stable interface-localization of the nanoparticles mainly due to their low interfacial stabilities as well as high transfer speeds...
Two triblock ABA copolymers poly(l-lactide-b-dimethylsiloxane-b-l-lactide) (PLLA-b-PDMS-b-PLLA) and poly(l-lactide-b-ethylene glycol-b-l-lactide) (PLLA-b-PEG-b-PLLA) containing poly(l-lactide) were synthesized by ring opening polymerization of l-lactide using bis(hydroxyalkyl) terminated PDMS and hydroxyl end-capped polyethylene glycol as macroinitiators, respectively. Both the triblock copolymers...
Ring-banded spherulites have never been formed directly from the glassy state of poly(l-lactide) (PLLA), particularly in case of its copolymers containing some stereodefective D-lactic units, which kinetically hinder the crystallization. By utilizing compressed CO2, banded spherulites have been directly obtained by treating the glassy PLLA containing 4–6% d-isomer. Specifically, ring-banded spherulites...
The reactions of methylenediphenyl 4,4’-diisocyanate (MDI) with hydroxy-terminated 4-armed star-shaped l-lactide oligomer (H4LAOn) and 4-armed star-shaped ε-caprolactone oligomer (H4CLOn) with the degree of polymerization per one arm, n = 3, 5 or 10 produced conetworks [MH4(LA/CL)Ons] with the feed H4LAOn/H4CLOn weight ratios of 75/25, 50/50 and 25/75. The formation of conetwork structures with different...
This work examined the effect of nucleating agents on the strain-induced crystallization of poly(l-lactide) (PLLA). Talc and poly(d-lactide) (PDLA) were used as the nucleating agents of PLLA. Wide angle X-ray scattering (WAXS) revealed that the original injection molded specimens of nucleated PLLA blends were free of PLLA α crystal. The structural evolution during uniaxial stretching of neat and nucleated...
PEG/PLLA block copolymers bearing various number of arms were synthesized. The molecular weights of PLLA in the block polymers were determined by 1 H NMR and GPC. For 1-arm, 2-arm, 4-arm PEG/PLLA block copolymers, DSC and WAXD results indicated that the different architectures and compositions of the block copolymers didn't alter the structures of PEG and PLLA crystallites, but markedly affected...
Semi-interpenetrating polymer networks (semi-IPNs) were prepared by reactions of methylenediphenyl 4,4’-diisocyanate (MDI) and hydroxy-terminated 4-arm star-shaped ε-caprolactone oligomers (H4CLOn's) with the degrees of polymerization per one arm, n = 3, 5 and 10 in the presence of poly(l-lactide) (PLA). Morphologies, thermal and mechanical properties of the MDI-bridged H4CLOn (MH4CLOn)/PLA semi-IPNs...
Enhancing matrix crystallization has been demonstrated to be an effective method to simultaneously improve the impact toughness and heat resistance of poly(l-lactide) (PLLA) modified with flexible polymers, such as poly(ε-caprolactone) (PCL). Unfortunately, increasing PLLA matrix crystallinity alone cannot guarantee the enhancement of impact toughness in most cases, so other structural parameters...
It is well known that the environmental conditions e.g. humidity can alter the shape-memory properties of polymers. In this work we applied an atomistic molecular dynamics simulation approach to model the influence of the addition of 1 wt% and 2 wt% water on the simulated shape-memory behavior of the amorphous switching domains of poly(l-lactide) (PLLA) with a molecular weight of Mn = 52,000 g mol...
The morphology of solution grown single crystals of a series of double crystalline diblock copolymers derived from l-lactide and ɛ-caprolactone has been investigated by means of transmission electron microscopy. The copolymers had a variable composition with a poly(l-lactide) weight percentage that ranged between 81 and 10%. All samples had a low polydispersity index (1.4–1.1) and a similar number...
A wood hydrolysate derived hemicellulose-rich fraction was functionalized with L-lactide oligomers through a ring opening polymerization mediated grafting-from reaction. The graft copolymer was designed to act as a compatibilizer in hydrolysate/poly(L-lactide) (PLLA) blend films. The PLLA addition improved the tensile behavior of the hydrolysate matrix and this effect was enhanced further by the addition...
The synthesis, morphological characterization and cyclic deformation behaviour of a double crystalline triblock copolymer containing crystalline poly(l-lactide) (PLLA) or random copolymer of poly(l-lactide) and polycaprolactone (PCL) hard segment and a random copolymer of polycaprolactone and poly(trimethylene carbonate) (PTMC) soft segment are presented. The hard segment content was varied via the...
Shear effect on crystal structure, morphology and melting behavior of poly(l-lactide) (PLLA) were investigated by wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and in-situ polarized optical microscope (POM). Influences of steady shear on PLLA melt was investigated during annealing. The impacts of crystallization temperature (T c ) and shear rate (SR) on crystal...
This investigation characterizes the molten morphologies following isothermal crystallization of poly(l-lactide-block-dimethyl siloxane-block-l-lactide) triblock copolymers, which were synthesized by ring-opening polymerization of l-lactide using hydroxyl-telechelic PDMS as macroinitiators, via small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The break-out and preservation...
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