Structure,electrical and optical properties of (PVA/LiAsF6) polymer composite electrolyte films

In this work, Li⁺ ion conducting polymer composite electrolyte films (PECs) were prepared based on poly (vinyl alcohol) (PVA), lithium hexafluoro arsenate (LiAsF₆), and ceramic filler TiO₂ using solution cast technique. The XRD and FTIR spectra were used to determine the complexation of the PVA polymer with LiAsF₆ salt. The ionic conductivities of the (PVA + LiAsF₆) and (PVA + LiAsF₆ + TiO₂) films have been determined by the A.C. impedance measurements in the temperature range 320–440 K. The maximum conductivity was found to be 5.10 × 10^?4 S cm^?1 for PVA:LiAsF₆ (75:25) + 5 wt% TiO₂ polymer composite film at 320 K. The calculation of Li⁺ ion transference number was carried out by the combination of A.C. impedance and D.C. polarization methods and is found to be 0.52 for PVA:LiAsF₆ (75:25) + 5 wt% TiO₂ film. Optical properties such as direct energy gap, indirect energy gap, and optical absorption edge values were investigated in pure PVA and salt complexed PVA films from their optical absorption spectra in the wavelength range of 200–600 nm. The absorption edge was found at 5.76 eV for undoped film, while it is observed at 4.87 and 4.70 eV for 20 and 25 wt% LiAsF₆ doped films, respectively. The direct band gaps for these undoped and salt doped PVA films were found to be 5.40, 5.12, and 4.87 eV, respectively, whereas the indirect band gaps were determined as 4.75, 4.45, and 4.30 eV. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Investigation of N<Subscript>2</Subscript>-fixation on polyaniline electrodes in methanol by electrochemical impedance spectroscopy

The ac response of polyaniline thin films on platinum electrodes was measured at different dc potentials during the N₂-fixation in methanol + LiClO₄ electrolyte with 0.03 mol L⁻¹ H₂SO₄ for the first time. The optimum film thickness was found to be 1.5 μm, N₂-pressure 50 bar and an optimum electrolysis potential of −0.12 V (NHE). The diffusion coefficients for N₂ into the polymer film was found to be (5 ± 2)×10⁻⁹ cm² s⁻¹.     

Preparation and electrochemical properties of spherical LiFePO<Subscript>4</Subscript> and LiFe<Subscript>0.9</Subscript>Mg<Subscript>0.1</Subscript>PO<Subscript>4</Subscript> cathode materials for lithium rechargeable batteries

The spherical LiFePO₄/C and LiFe_0.9Mg_0.1PO₄/C powders were successfully prepared from spherical FePO₄ via a simple uniform-phase precipitation method at normal pressure, using FeCl₃ and H₃PO₄ as the reactants. The FePO₄, LiFePO₄/C, and LiFe_0.9Mg_0.1PO₄/C powders were characterized by scanning electron microscopies (SEM), powder X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), and tap-density testing. The uniform spherical particles produced are amorphous, but they were crystallized to FePO₄ after calcining above 400 °C. Due to the homogeneity of the basic FePO₄, the final products, LiFePO₄/C and LiFe_0.9Mg_0.1PO₄/C, are also significantly uniform and the particle size is of about 1 μm in diameter. The tap-density of the spherical LiFePO₄/C and LiFe_0.9Mg_0.1PO₄/C are 1.75 and 1.77 g cm⁻³, respectively, which are remarkably higher than the non-spherical LiFePO₄ powders (the tap-density is 1.0–1.3 g cm⁻³). The excellent specific capacities of 148 and 157 mAh g⁻¹ with a rate of 0.1 C are achieved for the LiFePO₄/C and LiFe_0.9Mg_0.1PO₄/C, respectively. Comparison of the cyclic voltammograms of LiFePO₄/C and LiFe_0.9Mg_0.1PO₄/C shows enhanced redox current and reversibility for the sample substituting Mg on the Fe site. LiFe_0.9Mg_0.1PO₄/C exhibits better high-rate and cycle performances than the un-substituted LiFePO₄/C.     

Nanocomposite hybrid membranes containing polyvinyl alcohol or poly(tetramethylene oxide) for fuel cell applications

New hybrid membranes containing polyvinyl alcohol (PVA) and poly(tetramethylene oxide) (PTMO) with heteropolyacid (HPA) as a hydrophilic inorganic modifier in an organic/inorganic matrix were developed for low-temperature proton exchange membrane fuel cells (PEMFCs). A maximum conductivity of 4.8 × 10⁻³ S cm⁻¹ was obtained at 80 °C and 75% RH for PVA/PWA/PTMO/H₃PO₄ (10/15/70/5 wt%), whereas the PVA/SiWA/MPTS/H₃PO₄ (50/10/10/30 wt%) membrane demonstrated a maximum conductivity of 8.5 × 10⁻³ S cm⁻¹ under identical conditions. These hybrid composite membranes were subsequently tested in a fuel cell. A maximum current density of 240 mA cm⁻² was produced at 70 °C for the PVA/PWA/PTMO/H₃PO₄ membrane, and the corresponding value for the PVA/SiWA/MPTS/H₃PO₄ membrane under identical conditions was 230 mA cm⁻². The small deviations in cell performance can be explained in terms of the variations in thickness of the membranes as well as differences in their conductivities. The fuel cell performances of these membranes decreased drastically when the temperature was increased to 100 °C.     

LiFePO4 cathode in N-methyl-N-propylpiperidinium and N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide

Ternary [Li⁺][MePrPip⁺][NTf₂⁻] and [Li⁺][MePrPyrr⁺][NTf₂⁻] room temperature ionic liquids (ILs) were obtained by dissolution of solid lithium bis(trifluoromethanesulfonyl)imide (LiNTf₂) in liquid N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide and N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, respectively, and studied as electrolytes for the use in Li/LiFePO₄ or C(Li)/LiFePO₄ batteries. The cell worked properly in the presence of 10 wt% of vinylene carbonate (VC). Impedance-spectroscopy studies showed that the additive (VC) forms a protective coating on the anode. The LiFePO₄ cathode shows good efficiency (135 mAh g⁻¹) working together with [Li⁺][MePrPip⁺][NTf₂⁻] + VC and [Li⁺][MePrPyrr⁺][NTf₂⁻] + VC ionic liquid electrolytes. The flash point of ionic liquid electrolytes containing 10 wt% of VC is above 300 °C, which makes them practically non-flammable.     

A Simple and Facile Preparation of LiFePO<Subscript>4</Subscript> by a One-step Microwave Hydrothermal Method

A novel method was used to synthesize LiFePO₄, using inorganic salts as raw materials, and PEG-4000 as the surfactant. The results show that LiFePO₄ powders with various morphologies were prepared by microwave hydrothermal method, and it is very important to synthesize the LiFePO₄ powders with well-defined shape and size controlling experimental conditions, such as the solution pH and surfactant. The modified preparation of LiFePO₄ was built. The coating carbon on LiFePO₄ powders as a core–shell structure was carried out by annealing in 3%H₂/97%N₂ at 700 °C for 2 h. As a result, the diffusion coefficient of lithium ions can be increased, and the reversibility of lithium intercalation and deintercalation can be improved markedly. In addition, LiMn_0.08Fe_0.92PO₄ powders were synthesized, which were observed in an ordered olivine structure, but great changes occurred in morphology. Doping Mn²⁺ does not destroy the lattice structure and enlarges the lattice volume. Consequently, the conductivity can be enhanced, and the lithium ion diffusion coefficient can be boosted. Initial discharge capacity is improved obviously, and increases to 99.6 mA h g⁻¹ and 93.8 mA h g⁻¹ respectively. The microwave assisted hydrothermal approach presented here opens a potential avenue to explore the synthesis of LiFePO₄ powders.     

Determination of cadmium (II) using H<Subscript>2</Subscript>O<Subscript>2</Subscript>-oxidized activated carbon modified electrode

Pristine activated carbon (AcC) was oxidized by H₂O₂ under ultrasonic conditions. Compared with pristine AcC, the H₂O₂-oxidized AC possesses higher accumulation ability to trace levels of Cd²⁺. Based on this, a highly sensitive, simple and rapid electrochemical method was developed for the determination of Cd²⁺. In 0.01 mol L⁻¹ HClO₄ solution, Cd²⁺ was effectively accumulated at the surface of H₂O₂-oxidized AcC modified paste electrode, and then reduced to Cd under −1.10 V. During the following potential sweep from −1.10 to −0.50 V, reduced Cd was oxidized and a sensitive stripping peak appears at −0.77 V. The stripping peak current of Cd²⁺ changes linearly with concentration over the range 5.0 × 10⁻⁸ to 5.0 × 10⁻⁶ mol L⁻¹. The limit of detection was found to be 3.0 × 10⁻⁸ mol L⁻¹ for 2-min accumulation. Finally, this new sensing method was successfully used to detect Cd²⁺ in waste water samples.     

Characterization of (PVDF + LiFePO<Subscript>4</Subscript>) solid polymer electrolyte

LiFePO₄ nanopowders (50 nm) were prepared through a simple hydrothermal process. Poly vinylidene fluoride (PVDF): LiFePO₄ complex membranes as solid polymer electrolytes were characterized. X-ray diffraction (XRD) and differential scanning calorimetric (DSC) studies show a decrease in crystalline size and crystallinity of the polymer PVDF with increasing LiFePO₄ concentration. Scanning electron micrographs show smaller spherical domains in the dry film with increased LiFePO₄ nanopowder content. Impedance measurements suggest that the ionic conductivity of (PVDF + LiFePO₄) increases with increased temperature and lithium powder concentration.     

Synthesis of semiconducting polyphenylacetylene catalyzed by Ni(MeCN)6(BF4)2/AlEt2Cl

Summary Phenylacetylene (PhA) is polymerized by the dicationic nickel complex Ni(MeCN)₆(BF₄)₂ associated with AlEt₂Cl as co-catalyst. The production of 200g of polymer per gram of nickel per hour represents a typical activity of this system. Under our experimental conditions, the polymer displays an exclusive trans structure. The molecular weight distribution of the polymer is polymodal (5000 g.mol⁻¹ and 200 g.mol⁻¹). The highest average molecular weight fraction (5000 g. mol⁻¹) represents the highest published value for polyphenylacetylene (PPA) where a nickel catalyst is employed. The electrical conductivities vary between 10⁻⁷ and 10⁻¹⁶ S.cm⁻¹, and are characteristic of a semi-conductor polymer. Equivalent values are cited in the literature only in the case of doped PPA. Experimental observations enabled us to propose a mechanism for the formation of the active species through the reaction of Ni(MeCN)₆(BF₄)₂ with AlEt₂Cl. Received: 13 September 2001/Revised version: 10 January 2002/ Accepted: 11 January 2002     

Fumigant and Contact Toxicities of Monoterpenes to <Emphasis Type="Italic">Sitophilus oryzae</Emphasis> (L.) and <Emphasis Type="Italic">Tribolium castaneum</Emphasis> (Herbst) and their Inhibitory Effects on Acetylcholinesterase Activity

A comparative study was conducted to assess the contact and fumigant toxicities of eleven monoterpenes on two important stored products insects—, Sitophilus oryzae, the rice weevil, and Tribolium castaneum, the rust red flour beetle. The monoterpenes included: camphene, (+)-camphor, (−)-carvone, 1-8-cineole, cuminaldehyde, (l)-fenchone, geraniol, (−)-limonene, (−)-linalool, (−)-menthol, and myrcene. The inhibitory effect of these compounds on acetylcholinesterase (AChE) activity also was examined to explore their possible mode(s) of toxic action. Although most of the compounds were toxic to S. oryzae and T. castaneum, their toxicity varied with insect species and with the bioassay test. In contact toxicity assays, (−)-carvone, geraniol, and cuminaldehyde showed the highest toxicity against S. oryzae with LC₅₀ values of 28.17, 28.76, and 42.08 μg/cm², respectively. (−)-Carvone (LC₅₀ = 19.80 μg/cm²) was the most effective compound against T. castaneum, followed by cuminaldehyde (LC₅₀ = 32.59 μg/cm²). In contrast, camphene, (+)-camphor, 1-8-cineole, and myrcene had weak activity against both insects (i.e., LC₅₀ values above 500 μg/cm²). In fumigant toxicity assays, 1-8-cineole was the most effective against S. oryzae and T. castaneum (LC₅₀ = 14.19 and 17.16 mg/l, respectively). Structure-toxicity investigations revealed that (−)-carvone—, a ketone—, had the highest contact toxicity against the both insects. 1-8-Cineole—, an ether—, was the most potent fumigant against both insects. In vitro inhibition studies of AChE from adults of S. oryzae showed that cuminaldehyde most effectively inhibited enzyme activity at the two tested concentrations (0.01 and 0.05 M) followed by 1-8-cineole, (−)-limonene, and (l)-fenchone. 1-8-Cineole was the most potent inhibitor of AChE activity from T. castaneum larvae followed by (−)-carvone and (−)-limonene. The results of the present study indicate that (−)-carvone, 1,8-cineole, cuminaldehyde, (l)-fenchone, and (−)-limonene could be effective biocontrol agents against S. oryzae and T. castaneum.     

Preparation of a PVA/HAP composite polymer membrane for a direct ethanol fuel cell (DEFC)

A novel PVA/Hydroxyapatite (HAP) composite polymer membrane was prepared by the direct blend process and solution casting method. The characteristic properties of the PVA/HAP composite polymer membranes were investigated using thermal gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), micro-Raman spectroscopy and the AC impedance method. An alkaline direct ethanol fuel cell, consisting of an air cathode with MnO₂ carbon inks based on Ni-foam, an anode with PtRu black on Ni-foam, and the PVA/HAP composite polymer membrane, was assembled and investigated. It was found that the alkaline direct ethanol fuel cell comprising of a novel cheap PVA/HAP composite polymer membrane showed an improved electrochemical performance in ambient temperature and air. As a result, the maximum power density of the alkaline DEFC, using a PtRu anode based on Ni-foam (10.74 mW cm⁻²), is higher than that of DEFC using an E-TEK PtRu anode based on carbon (7.56 mW cm⁻²) in an 8M KOH + 2M C₂H₅OH solution at ambient temperature and air. These PVA/HAP composite polymer membranes are a potential candidate for alkaline DEFC applications.     

Effects of phenyl-based pendent groups on helical conformation of poly(<Emphasis Type="Italic">N</Emphasis>-propargylamides)

Five achiral N-propargylamide monomers with various phenyl-based substitutents, [HC ≡ CCH₂NHCOR, R for M1: C₆H₄CH₃; M2: C₆H₄CH₂CH₃; M3: C₆H₄(CH₂)₂CH₃; M4: C₆H₄(CH₂)₃CH₃; M5: C₆H₄C(CH₃)₃], were synthesized and polymerized with a rhodium catalyst, (nbd)Rh⁺B^-(C₆H₅)₄ (nbd = 2,5-norbornadiene). The corresponding five homopolymers were obtained in high yields of 90–95% and with moderate molecular weights (M _n ≥ 10 000). All the polymers possessed high cis contents (≥95%). Poly(1)–poly(3) exhibited UV-vis absorption peaks at approx. 350 nm, which indicates that the three polymers formed helical conformations, while no UV-vis absorption peaks could be observed in poly(4) and poly(5) in the wavelength range of 320–500 nm, demonstrating that these two polymers could not adopt helical structures under the examined conditions. To confirm the helical structures formed in poly(1)–poly(3), a chiral monomer, M6, was utilized to copolymerize with M2, which was used as the representative for M1−M3. M6 was utilized since its polymer could form stable helices under suited conditions. The resulting copolymers exhibited remarkable CD effects, however, the maximum wavelength in the copolymers varied remarkably, mainly depending on the composition of the copolymers. It is concluded that in the formation of ordered helical conformations, the substitutents of varied bulk led to different steric repulsion and varied synergic effects among the neighboring pendent groups.     

Voltammetric behavior and the determination of quercetin at a flowerlike Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles modified glassy carbon electrode

Flowerlike Co₃O₄ nanoparticles were used as a modifier on the glassy carbon electrode to fabricate a quercetin (Qu) sensor. The morphology and crystallinity of the prepared Co₃O₄ material were investigated by scanning electron microscopy and X-ray diffraction. Electrochemical behavior of Qu at the sensor was studied by cyclic voltammetry and semi-derivative voltammetry. Results suggested that the modified electrode exhibited a strong electrocatalytic activity toward the redox of Qu. The electron transfer coefficient (α), the number of electron transfer (n), and the diffusion coefficient (D) of Qu at the sensor were calculated. Under the optimum conditions, the catalytic peak currents of Qu were linearly dependent on the concentrations of Qu in the range from 5.0 × 10⁻⁷ to 3.3 × 10⁻⁴ M, with a detection limit of 1.0 × 10⁻⁷ M. This proposed method was successfully applied to determine the quercetin concentration in Ginkgo leaf tablet and human urine samples.     

Electropolymerization of benzotriazole in room temperature ionic liquid [bmim]PF<Subscript>6</Subscript>

The electropolymerization of benzotriazole on an Au electrode was investigated via cyclic voltammetry and chronoamperometry in a room temperature ionic liquid medium, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF₆) containing glacial acetic acid. The chronoamperometric investigation revealed that the instantaneous nucleation predominated the potentiostatic electropolymerization of benzotriazole at the oxidation peak potential. Scanning electron microscopy indicated that the polymer film was compact and relatively smooth and infrared spectroscopy suggested the polymer chains were formed mainly via coupling of the unsaturated nitrogen atoms. The polymer was found to be highly electroactive, showing a quasi-reversible and stable pair of redox peaks centering at 0.9 V versus Ag/AgCl in 0.1 mol L⁻¹ H₂SO₄.     

Synthesis,characterization and acidochromism of Poly (2-<Emphasis Type="Italic">N,N</Emphasis>–dimethylamino-4,6-Bis (2-thienyl)-pyrimidine)

A new monomer (2-N,N-dimethylamino-4,6-Bis (2-thienyl)–pyrimidine) was synthesized and its homopolymer was successfully prepared by using Ferric trichloride (FeCl₃) as an oxidant. The structure of the polymer and monomer was fully characterized by ¹H–NMR, FTIR, UV-vis, Fluorescent spectroscopy and X-ray diffraction pattern. The polymer gives rise to a band at λ _max = 391 nm. The polymer showed the PL spectrum, gave a peak at 507 nm.We have observed that the polymer was sensitive to inorganic acids and the acidochromism behavior was investigated applying organic acid such as CF₃COOH. The corresponding UV-Vis peaks were observed at 464 nm and 357 nm respectively. X-ray diffraction data shows that polymer has a certain crystallinity. The polymer exhibited an [η] value of 0.26 dLg⁻¹ at 25 °C in H₂SO₄ (w = 98%).     

Chemical and electrochemical characterization of TiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> atomic layer depositions on AZ-31 magnesium alloy

In this study, innovative TiO₂/Al₂O₃ mono/multilayers were applied by atomic layer depositions (ALD) on ASTM-AZ-31 magnesium/aluminum alloy to enhance its well-known scarce corrosion resistance. Four different configurations of ALD layers were tested: single TiO₂ layer, single Al₂O₃ layer, Al₂O₃/TiO₂ bilayer and Al₂O₃/TiO₂/Al₂O₃/TiO₂ multilayer deposited using Al[(CH₃)]₃ (trimethylaluminum, TMA), and TiCl₄ and H₂O precursors. All depositions were performed at 120°C to obtain an amorphous-like structure of both oxide layers. The four coatings were then investigated using different techniques, such as scanning electron microscope (SEM), stylus profilometer, glow discharge optical emission spectrometry (GDOES) and polarization curves in 0.05-M NaCl solution. The thickness of all the coatings was around 100 nm. The layers compositions were successfully investigated by the GDOES technique, although obtained data seem to be affected by substrate roughness and differences in sputtering rates between ceramic oxides and metallic magnesium alloy. Corrosion resistance showed to be strongly enhanced by the nanometric coatings, giving lower corrosion current densities in 0.05-M NaCl media with respect to the uncoated substrate (from 10⁻⁴ to 10⁻⁶ A/cm² for the single layers and from 10⁻⁴ to 10⁻⁸ A/cm² for the bi- and multilayers). All polarization curves on coated samples also showed a passive region, wider for the bi-layer (from −0.58 to −0.43 V with respect to Ag/AgCl) and multilayer (from −0.53 to −0.38 V with respect to Ag/AgCl) structures.     

Polymeric ionic liquid membranes as electrolytes for lithium battery applications

A new kind of polymeric ionic liquid (PIL) membrane based on guanidinium ionic liquid (IL) with ester and alkyl groups was synthesized. On addition of guanidinium IL, lithium salt, and nano silica in the PIL, a gel PIL electrolyte was prepared. The chemical structure of the PIL and the properties of gel electrolytes were characterized. The ionic conductivity of the gel electrolyte was 5.07 × 10⁻⁶ and 1.92 × 10⁻⁴ S cm⁻¹ at 30 and 80 °C, respectively. The gel electrolyte had a low glass transition temperature (T _g ) under −60 °C and a high decomposition temperature of 310 °C. When the gel polymer electrolyte was used in the Li/LiFePO₄ cell, the cell delivered 142 mAh g⁻¹ after 40 cycles at the current rates of 0.1 C and 80 °C.     

Electrochemical oxidation of an acid dye by active chlorine generated using Ti/Sn<Subscript>(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript>Ir<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> electrodes

The generation of active chlorine on Ti/Sn_(1−x)Ir _x O₂ anodes, with different compositions of Ir (x = 0.01, 0.05, 0.10 and 0.30 ), was investigated by controlled current density electrolysis. Using a low concentration of chloride ions (0.05 mol L⁻¹) and a low current density (5 mA cm⁻²) it was possible to produce up to 60 mg L⁻¹ of active chlorine on a Ti/Sn_0.99Ir_0.01O₂ anode. The feasibility of the discoloration of a textile acid azo dye, acid red 29 dye (C.I. 16570), was also investigated with in situ electrogenerated active chlorine on Ti/Sn_(1−x)Ir _x O₂ anodes. The best conditions for 100% discoloration and maximum degradation (70% TOC reduction) were found to be: NaCl pH 4, 25 mA cm⁻² and 6 h of electrolysis. It is suggested that active chlorine generation and/or powerful oxidants such as chlorine radicals and hydroxyl radicals are responsible for promoting faster dye degradation. Rate constants calculated from color decay versus time reveal a zero order reaction at dye concentrations up to 1.0 × 10⁻⁴ mol L⁻¹. Effects of other electrolytes, dye concentration and applied density currents also have been investigated and are discussed.     

Thermoelectric Properties of <Emphasis Type="Italic">x</Emphasis>PbTe/Yb<Subscript>0.2</Subscript>Co<Subscript>4</Subscript>Sb<Subscript>12</Subscript> Hot-Pressed Samples

The xPbTe/Yb_0.2Co₄Sb₁₂ compounds were prepared by the ball-milling and hot-pressed process. Electrical conductivity of the composite samples are reduced with a increase in PbTe content; and, their temperature dependence coefficients show the positive values. The maximum electrical conductivity of composite materials is ~80000 Sm⁻¹ at 800 K. The Seebeck coefficient (absolute value) of the composite material is obviously improved with an increase in the dispersed phase (PbTe) content; the Seebeck coefficient (absolute value) of the 10PbTe sample is ~260 μVK⁻¹ at 700 K, which increases by 13.6% relative to that of the Yb_0.2Co₄Sb₁₂ sample. The thermal conductivity of the composite samples is improved due to introduction of PbTe, and the thermal conductivity of the 10PbTe sample is ~3 Wm⁻¹ K⁻¹ at 550 K. The maximum value of ZT is 0.78 at 700 K for the 2.5PbTe sample.     

Exploring the effect of alkyl end group on poly(L-lactide) oligo-esters. Synthesis and characterization

Poly(L-lactide) (PLLA) oligo-esters with α-hydroxyl-ω-alkyl (alkyl = −CH₂−[CH₂−CH₂]_m−CH₃, where m = 1, 2, 4, 5, 6, 7, 8, 9, and 10) end groups were synthesized by ring-opening polymerization of L-lactide (L-LA) catalyzed by tin(II) 2-ethylhexanoate Sn(Oct)₂ in the presence of aliphatic alcohols as initiators (HO−CH₂−[CH₂−CH₂]_m−CH₃, where m = 1, 2, 4, 5, 6, 7, 8, 9, and 10). High yields (~ 62 to 71%) and M _n(NMR) in the range of 2120–2450 Da (PLLA) were obtained. Effects of alkyl end groups on thermal properties of the oligo-esters were analyzed by DSC, TGA and SAXS. Glass transition temperature (T _g) gradually decreases with increase in the percent of−CH₂−[CH₂−CH₂]_m−CH₃ end group, as results alkyl end group provides most flexibility to PLLA. An important effect of alkyl end group on a double cold crystallization (T _c1 and T _c2) was observed, and is directly related with the segregation phase between alkyl end group and PLLA. TGA analysis revealed that PLLA oligo-esters are more thermally stable with docosyl (−C₂₂H₄₅) respect to the butyl (−C₄H₉) end group, probably is due to steric hindrance of the end group (docosyl respect to butyl) toward intermolecular and intramolecular transesterification. SAXS analysis showed that alkyl end group as docosyl restricted the growth of lamellae thickness (D) due to steric hindrance. Characterization of hydroxyl and alkyl end groups in the PLLA oligo-esters was determined by MALDI-TOF, GPC, FT-IR and ¹ H and ¹³ C NMR.