PEG Block Length Research Articles

Preparation of peptide-loaded polymer microparticles using supercritical carbon dioxide

In this study, peptide-loaded microparticles were prepared using an aerosol solvent extraction system (ASES) by employing supercritical carbon dioxide as an antisolvent. The effects of the molecular weight of poly(Llactide) (PLLA), poly(ethylene glycol) (PEG), the block length of methoxy poly(ethylene glycol)-b-poly(L-lactide) (mPEG-PLLA), the blending of PLLA and PEG, and the drug-to-polymer feed ratio on the formation of leuprolide acetate (LA)-loaded microparticles and their release characteristics were investigated. Scanning electron microscope observations showed that the LA-loaded polymer particles had a spherical morphology with a smooth surface. The entrapment efficiency of LA in the ASES-processed microparticles was found to be extremely high (about 99%), whereas the initial release rate of the LA-loaded microparticles was very low for PLLA. The release rate of LA was observed to increase as the PEG block length of mPEG-PLLA and/or the drug content in the microparticles increased. When PLLA was blended with PEG, the release rate of LA from the PLLA/PEG microparticles was significantly faster compared with the corresponding mPEG-PLLA copolymer.

W/O/W 다중유화법을 이용한 젬시타빈 함유 Methoxy Poly(ethylene glycol)-b-Poly(L-lactide) 미립자 제조

In this study, gemcitabine-loaded methoxy poly(ethylene glycol)-b-poly(L-lactide) (MPEG-PLLA) microparticles with different PEG block lengths were prepared by a W/O/W double emulsion technique. The present study focuses on the investigation of the influence of various preparative parameters such as the ratio of internal water phase and oil phase, polymer concentration, solvent composition of organic phase and salt concentration of external water phase on the morphology and encapsulation efficiency of the microparticles. The microparticles fabricated at high volume ratios of internal water phase to oil phase and at high polymer concentrations showed a relatively high encapsulation efficiency and low porosity. When a dichloromethane/ethyl acetate mixture was used as solvent, both the encapsulation efficiency and drug loading of the microparticles decreased as the level of ethyl acetate increased. The addition of a salt (NaCl) to the external water phase significantly improved the encapsulation efficiency up to 40%, and the microparticles became more spherical with their size and porosity decreased.

A2BA2 Block Copolymers of Poly(N-isopropylacrylamide) (A) and Poly(ethylene glycol) (B): Synthesis and Thermal Gelation Properties of Aqueous Solutions

A2BA2 block copolymers of poly(N-isopropylacrylamide) (A, PNIPAM) and poly(ethylene glycol) (B, PEG) were synthesized by SET-LRP for the first time. The 1H-NMR and GPC analyses showed that the block copolymers prepared had in average 3.5–3.8 PNIPAM arms/macromolecule and low polydispersities (Mw/Mn=1.25–1.35). The thermogelation behavior of their 20 wt% aqueous solutions was investigated by DSC, dynamic rheometry and the tube inversion method as a function of the molecular weight of both PEG block and PNIPAM arms. The results showed that both phase transition temperature, as determined by DSC, and gelation temperature, determined by the tube inversion method, increased with the PEG block length and decreased with the MW of the PNIPAM arms, while the forming gels were more stable for longer PEG chains. By comparing the thermoresponsive properties of the H-shaped block copolymers synthesized with those of some linear PNIPAM-PEG-PNIPAM triblock copolymers of similar molecular weights of both PNIPAM side blocks and PEG middle chain, almost identical results were obtained, indicating practically no influence of the shape of the PNIPAM blocks from this point of view.

Macromolecular Diffusion in Self-Assembling Biodegradable Thermosensitive Hydrogels.

Hydrogel formation triggered by a change in temperature is an attractive mechanism for in situ gelling biomaterials for pharmaceutical applications such as the delivery of therapeutic proteins. In this study, hydrogels were prepared from ABA triblock polymers having thermosensitive poly(N-(2-hydroxypropyl) methacrylamide lactate) flanking A-blocks and hydrophilic poly(ethylene glycol) B-blocks. Polymers with fixed length A blocks (~22 kDA) but differing PEG-midblock lengths (2, 4 and 10 kDa) were synthesized and dissolved in water with dilute fluorescein isothiocyanate (FITC)-labeled dextrans (70 and 500 kDA). Hydrogels encapsulating the dextrans were formed by raising the temperature. Fluorescence recovery after photobleaching (FRAP) studies showed that diffusion coefficients and mobile fractions of the dextran dyes decreased upon elevating temperatures above 25 °C. Confocal laser scanning microscopy and cryo-SEM demonstrated that hydrogel structure depended on PEG block length. Phase separation into polymer-rich and water-rich domains occurred to a larger extent for polymers with small PEG blocks compared to polymers with a larger PEG block. By changing the PEG block length and thereby the hydrogel structure, mobility of FITC-dextran could be tailored. At physiological pH the hydrogels degraded over time by ester hydrolysis, resulting in increased mobility of the encapsulated dye. Since diffusion can be controlled according to polymer design and concentration, plus temperature, these biocompatible hydrogels are attractive as potential in situ gelling biodegradable materials for macromolecular drug delivery.

Vesicle Formation of PLAx−PEG44Diblock Copolymers

Three PLAx−PEG44 diblock copolymers with fixed hydrophilic PEG block and various lengths of hydrophobic PLA block were synthesized via ring-opening polymerization. The micelle formation and micelle morphologies of the PLAx−PEG44 copolymers in selective solvents were investigated by using cryogenic transmission electron microscopy (cryo-TEM) and light scattering techniques. PLAx−PEG44 diblock copolymers in aqueous solution form various micelle structures when increasing x from 56 to 212 in order to minimize the overall free energy of the systems. The micelles transform from wormlike micelles for PLA56−PEG44 into vesicles for PLA212−PEG44. Interestingly, vesicular structures with various morphologies, such as large polydisperse vesicles, entrapped vesicles, hollow concentric vesicles, ellipsoidal vesicles, open bending lamellae, vesicles with irregular shapes, etc., were found to be coexisting in PLA212−PEG44 THF/H2O and PLA212−PEG44 dioxane/H2O mixtures with 30 and 40 wt % water contents. Toroid micelles w...

Investigations on the morphology and melt crystallization of poly(L‐lactide)‐poly(ethylene glycol) diblock copolymers

AbstractRing opening polymerization of L‐lactide was realized in the presence of monomethoxy poly(ethylene glycol), using zinc lactate as catalyst. The resulting PLLA‐PEG diblock copolymers were characterized by using 1H‐NMR, SEC, WAXD, and DSC. All the copolymers were semicrystalline, one or two melting peaks being detected depending on the composition. Equilibrium melting temperature (Tm0) of PLLA blocks was determined for three copolymers with different EO/LA molar ratios. Tm0 decreased with decreasing PLLA block length. A copolymer with equivalent PLLA and PEG block lengths was selected for melt crystallization studies and the resulting data were analyzed with Avrami equation. The obtained Avrami exponent is equal to 2.6 ± 0.2 in the crystallization temperature range from 80 to 100°C. In addition, the spherulite growth rate of PLLA‐PEG was analyzed by using Lauritzen‐Hoffmann theory in comparison with PLLA homopolymers. The nucleation constant was found to be 2.39 × 105 K2 and the free energy of folding equal to 53.8 erg/cm2 in the range of 70–94°C, both higher than those of PLLA homopolymers, while the spherulite growth rate of the diblock copolymer was lower. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers

Surface Characterization of Poly(l-lactic acid)−Methoxy Poly(ethylene glycol) Diblock Copolymers by Static and Dynamic Contact Angle Measurements, FTIR, and ATR-FTIR

The surface composition and surface free energy properties of two types of amphiphilic and semicrystalline diblock copolymers consisting of poly(L-lactic acid) coupled to (methoxy poly(ethylene glycol) (PLLA-MePEG) having differing block lengths of PEG were investigated by using static and dynamic contact angle measurements, transmission Fourier infrared spectroscopy (FTIR), and attenuated total reflection spectroscopy (ATR-FTIR) and compared with results obtained from PLLA and MePEG homopolymers. The contact angle results were evaluated by using the van Oss-Good method (acid-base method), and it was determined that the Lewis base surface tension coefficient (gamma-) of the copolymers increased with an increase of the PEG molar content at the copolymer surface. This result is in good agreement with the transmission FTIR and ATR-FTIR results but not proportional to them, indicating that the surfaces of the copolymers are highly mobile and that the molecular rearrangement takes place upon contact with a polar liquid drop. The dynamic contact angle measurements showed that the strong acid-base interaction between the oxygen atoms in the copolymer backbone of the relatively more hydrophilic PEG segments with the Lewis acidic groups of the polar and hydrogen-bonding water molecules enabled the surface molecules to restructure (conformational change) at the contact area, so that the PEG segments moved upward, whereas the apolar methyl pendant groups of PLLA segments buried downward.

In vivo fate of unimers and micelles of a poly(ethylene glycol)-block-poly(caprolactone) copolymer in mice following intravenous administration

Methoxy poly(ethylene glycol)- b-poly(caprolactone) (MePEG- b-PCL) copolymers with varying PEG block lengths and a constant PCL block length were synthesized by cationic ring-opening polymerization and used to form nano-sized micelles. Due to their small size and superior in vitro stability, the MePEG 5000- b-PCL 5000 micelles were selected for further in vitro characterization and an in vivo evaluation of their fate and stability following intravenous (i.v.) administration. Specifically, 3H-labelled MePEG 5000- b-PCL 5000 micelles were i.v. administered to Balb/C mice at copolymer doses of 250, 2 and 0.2 mg/kg in order to examine the distribution kinetics of (1) copolymer assembled as thermodynamically stable micelles, (2) copolymer assembled as thermodynamically unstable micelles and (3) copolymer unimers, respectively. Overall, it was found that when the copolymer is assembled as thermodynamically stable micelles the material is effectively restricted to the plasma compartment. Interestingly, the copolymer was found to have a relatively long circulation half-life even when administered at a dose that would likely fall to concentrations below the CMC following distribution. Analysis of plasma samples from this group revealed that even 24 h post-administration a significant portion of the copolymer remained assembled as intact micelles. In this way, this study demonstrates that the hydrophobic and semi-crystalline nature of the PCL core imparts a high degree of kinetic stability to this micelle system.

Structural characterization and mass transfer properties of segmented polyurethane: influence of block length of hydrophilic segments

AbstractAn attempt has been made to investigate the effect of the block length of hydrophilic segments on the structure and mass transfer properties of segmented polyurethane (HSPU). Three different block lengths of hydrophilic poly(ethylene glycol) (PEG) segments were used, namely PEG‐200, PEG‐2000 and PEG‐3400, where the numbers indicate the molecular weight of the PEG in g mol−1. The HSPU were characterized using Fourier‐transform infrared (FTIR) spectroscopy, wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and tensile testing. Mass transfer properties were measured by sorption and water vapour flux (WVF) measurements. The control sample polyurethanes without PEG and a sample with PEG‐200 showed amorphous structure and an unclear phase separation as detected by WAXD, DSC and DMTA. There is evidence that the introduction of PEG blocks into the polyurethane matrix aids soft‐segment crystallization. The percentage crystallinity of soft segments was the highest with PEG‐2000 and an increase of PEG block length to 3400 g mol−1 resulted in a decrease in crystallinity. Mechanically, polyurethane without PEG is tough while percentage strain at maximum load increased with increasing block length of PEG. In addition, sorption and WVF increased linearly with increasing PEG block length and with temperature. The permeability of such HSPUs is a function of temperature and showed a good fit to an Arrhenius form. Copyright © 2005 Society of Chemical Industry

Probing the micellization of diblock and triblock copolymers of poly(l-lactide) and poly(ethylene glycol) in aqueous and NaCl salt solutions

The micelle formation of a series of amphiphilic block copolymers in aqueous and NaCl solutions was studied by a fluorescent probe technique using pyrene as a "model drug". These copolymers were synthesized from poly (ethylene glycol) (PEG) and l-lactide by a new calcium ammoniate catalyst. They had fixed PEG block lengths (44, 104 or 113 ethylene oxide units) and various poly(l-lactide) (PLLA) block lengths (15–280 lactide units). The critical micelle concentration (cmc) was found to decrease with increasing PLLA content. The distinct dissimilarity of the cmc values of diblock and triblock copolymers based on the same block length of PEG provided evidence for the different configurations of their micelles. It was also observed that the introduction of NaCl salt significantly contributed to a decrease in the cmcs of the copolymers with short PEG and PLLA blocks, while it had less influence on the cmcs of copolymers with long PEG or PLLA blocks. The dependence of partition coefficients ranging from 0.2×105 to 1.9×105 on the PLLA content in the copolymer and on the micelle configuration was also discussed. The contribution of NaCl salt to increasing the partition of pyrene into a micellar phase was observed.

Quantification of ligand surface concentration of bulk-modified biomimetic hydrogels

This study describes a method for the quantification of active ligand surface concentration for bulk-modified hydrogels. Two poly(propylene fumarate-co-ethylene glycol) (P(PF-co-EG)) block copolymers were synthesized with terminal poly(ethylene glycol) (PEG) chains of number average molecular weight 1960 and 5190 g/mol. Hydrogels were synthesized with bulk-modified biotin as a model ligand, making use of a PEG spacer arm with a molecular weight of 3400 g/mol. Bulk concentration of biotin was calculated from the initial concentration of biotin, sol fraction, equilibrium water content, and relative incorporation of the polymers to the hydrogel. Surface concentration of biotin bulk-modified hydrogels was quantified with an enzyme linked immunosorbent assay using mouse monoclonal anti-biotin antibody (IgG), horseradish peroxidase-conjugated anti-mouse IgG, and a chemiluminescent substrate. The larger size of the IgG relative to the mesh size of the hydrogels allowed for the quantification of the active biotin at the surface of the hydrogels. Luminescent imaging was used to qualitatively show the isolation of the horseradish peroxidase-conjugated antibodies to the surface of the bulk-modified hydrogel. The active biotin ligands at the surface of hydrogels synthesized with terminal PEG chains of 1960 g/mol were at the top 7.2 nm while for those synthesized with terminal PEG chains of 5190 g/mol were at the top 4.4 nm of the bulk-modified hydrogel. The relationship between bulk ligand concentration and the active ligand concentration at the surface was dependent on the hydrogel composition. The relative magnitude of the PEG spacer arm of the ligand compared to the PEG block length of the copolymer affected the surface availability of the ligand. The results suggest that steric hindrances caused by mobile PEG chains of the copolymer of molecular weight greater than that of the PEG spacer arm contributed to the decreased surface concentration of ligand. This work relates the bulk concentration of a ligand to its surface concentration, an important parameter for the adhesion, migration, and function of anchorage dependent cells.

In vivo bone and soft tissue response to injectable, biodegradable oligo(poly(ethylene glycol) fumarate) hydrogels

This study was designed to assess in vivo bone and soft tissue behavior of novel oligo(poly(ethylene glycol) fumarate) (OPF) hydrogels using a rabbit model. In vitro degradation of the OPF hydrogels was also investigated in order to compare with in vivo characteristics. Four groups of OPF hydrogel implants were synthesized by alternation of crosslinking density, poly(ethylene glycol) (PEG) block length of OPF, and cell-binding peptide content. The in vitro degradation rate of OPF hydrogels increased with decreasing crosslinking density of hydrogels, which was characterized by measuring weight loss and swelling ratio of hydrogels and medium pH change. Examination of histological sections of the subcutaneous and cranial implants showed that an uniform thin circumferential fibrous capsule was formed around the OPF hydrogel implants. Quantitative evaluation of the tissue response revealed that no statistical difference existed in capsule quality or thickness between implant groups, implantation sites or implantation times. At 4 weeks, there was a very limited number of inflammatory and multinuclear cells at the implant–fibrous capsule interface for all implants. However, at 12 weeks, OPF hydrogels with PEG block length of number average molecular weight 6090±90 showed extensive surface erosion and superficial fragmentation that was surrounded by a number of inflammatory cells, while OPF hydrogels with PEG block length of number average molecular weight 930±10 elicited minimal degradation. Constant fibrous capsule layers and number of inflammatory cells were observed regardless of the incorporation of cell-binding peptide and crosslinking density of OPF hydrogels with PEG block length of number average molecular weight 930±90. These results confirm that the degradation of implants can be controlled by tailoring the macromolecular structure of OPF hydrogels. Additionally, histological evaluation of implants proved that the OPF hydrogel is a promising material for biodegradable scaffolds in tissue engineering.

Synthesis of controlled-structure sulfate-based copolymers via atom transfer radical polymerisation and their use as crystal habit modifiers for BaSO4

Atom Transfer Radical Polymerisation (ATRP) has been used to polymerise ammonium 2-sulfatoethyl methacrylate (SEM) in aqueous media using various poly(ethylene glycol) (PEG) macro-initiators to give a range of controlled-structure, sulfate-based block copolymers. Such PEG–SEM diblock copolymers are effective crystal habit modifiers for the in situ precipitation of BaSO4 in dilute aqueous solution. In the presence of the PEG–SEM copolymer, near-monodisperse, lozenge-shaped BaSO4 particles were obtained, depending on the relative block lengths. X-Ray diffraction and thermogravimetric analysis of these particles demonstrated that they are polycrystalline in nature and contain around 8% copolymer by mass. This compares with the characteristic polydisperse rectangular platelets of single crystal BaSO4 obtained in the absence of the copolymer. Control experiments suggest that, while only the SEM block interacts directly with the particle surface, the PEG block also plays an important role in controlling the crystal growth. Independent variation of the PEG and SEM block lengths therefore provides a subtle mechanism for controlling the morphology, size distribution and crystalline structure of the inorganic phase.

Preparation and characterization of new immunoprotecting membrane coated with amphiphilic multiblock copolymer

New immunoprotecting membranes were prepared by spin coating the amphiphilic random multiblock copolymers of poly(ethylene glycol) (PEG) and poly(tetramethylene ether glycol) (PTMEG) or poly(dimethyl siloxane) (PDMS) on porous Durapore® membrane. The copolymer coating was intended to make a biocompatible, immunoprotecting diffusional barrier and the supporting porous substrate was for mechanical stability and processability. By filling Durapore® membrane pores with water, the penetration of coating solution into the pores was minimized during the spin coating process. A single coating process produced a completely covered thin surface layer (∼1 μm in thickness) on the porous substrate membrane. The permselectivity of the coated layer was influenced by PEG block length, polymer composition, and thickness of the coating layer. A composite membrane with the coating layer prepared with PEG 2 K/PTMEG 2 K block copolymer showed that its molecular weight cut-off at day 40 based on dextran was close to the molecular size of IgG (Mw = 150 kDa). However, IgG permeation was detected from protein permeation test, while glucose oxidase (Mw = 186 kDa) was not permeable through the coated membrane.

Thermoreversible gelation of biodegradable poly(ε-caprolactone) and poly(ethylene glycol) multiblock copolymers in aqueous solutions

The multiblock copolymers composed of poly(ethylene glycol)s (PEGs) and biodegradable poly(ε-caprolactone)s (PCLs) were synthesized through one-step condensation copolymerization with hexamethylene diisocyanate (HDI) as a coupling agent. The typical phase diagram of these multiblock copolymers in aqueous solution displayed a critical gel concentration (CGC) and an upper phase-transition temperature, which were mainly determined by the PEG/PCL block ratio, the PEG or PCL block lengths and the molecular weight. With decreasing PEG/PCL block ratio, the CGC decreased with an elevated sol–gel transition temperature on account of the enhanced hydrophobicity. The HDI/Diols ratio was used to control the molecular weight. At high molecular weights, the CGC decreased, related to the enhanced aggregation of PCL blocks and physical crosslinkage between PCL block domains due to the increased number of PCL blocks in each molecule. For the sample containing the long PCL 2000 block ( M n, 2000), the CGC dropped dramatically due to the high hydrophobicity and the poor compatibility between PCL and PEG. The dynamic phase transition process was observed by combining optical microscopy (OM) and differential scanning calorimetry (DSC) in a certain heating/cooling rate. Finally, a possible phase separation-induced gelation mechanism is suggested.

Effects of Block Lengths and Initial Water Content on the Swelling and Degradative Characteristics of an Injectable Poly(propylene Fumarate-Co-Ethylene Glycol) Block Copolymer Hydrogel

AbstractThe overall goal of this project is to develop an in-situ polymerizable, biodegradable material for use in cardiovascular applications that minimizes non-specific cell adhesion and contains functional moieties for the attachment of peptides to induce specific cell attachment. A novel block copolymer has been developed incorporating poly(propylene fumarate) (PPF) and poly(ethylene glycol) which satisfies these criteria. PPF is a new biodegradable polymer currently being investigated for orthopedic and cardiovascular applications while PEG is a hydrophilic polymer that has been extensively studied for biomedical applications. The copolymer is chemically crosslinked with PEG diacrylate using an ammonium persulfate-ascorbic acid redox initiator system to form the hydrogel. The PEG and PPF block lengths can be varied to modulate the properties of the hydrogel formed. In this study, the following three parameters were studied, (1) PPF block length, (2) PEG block length, and (3) initial water content, were varied to examine their effects on swelling, degradation and elastic modulus. A factorial experimental design was implemented to assess which of these three parameters had the greatest impact on swelling, degradation and elastic modulus. Swelling was found to be most affected by the initial water content followed by PEG block length and PPF block length. The swelling of the hydrogels ranged from 48% water uptake with low initial water content to up to 77% water uptake with the high initial water content. After three weeks, degradation of the hydrogels ranged from 4-13% mass fraction lost. Elastic modulus was determined by tensile testing of the various hydrogel formulations and ranged from 0.4 to 7.7 MPa.

A controlled release system for proteins based on poly(ether ester) block-copolymers: polymer network characterization

The properties of a series of multiblock copolymers, based on hydrophilic poly(ethylene glycol) (PEG) and hydrophobic poly(butylene terephthalate) (PBT) blocks were investigated with respect to their application as a matrix for controlled release of proteins. The degree of swelling, Q, of the copolymers increased with increasing PEG content and with increasing molecular weight of the PEG segment. Within the composition range tested, Q varied from 1.26 for polymers with PEG segments of 600 g/mol and a PBT content of 60 weight.% up to 3.64 for polymers with PEG segments of 4000 g/mol and a PEG/PBT weight ratio of 80:20. Equilibrium stress (compression)–strain measurements were performed in order to estimate mesh sizes. The mesh size of the copolymers ranged from 38 to 93 Å, which was experimentally confirmed by diffusion of vitamin B12 (hydrodynamic diameter dh=16.6 Å), lysozyme (dh=41 Å) and bovine serum albumin (dh=72 Å). The in vitro degradation of PEG/PBT copolymers with a PEG block length of 1000 g/mol and PEG/PBT weight ratios of 70:30, 60:40 and 40:60 was studied. Matrices with increasing PEG contents exhibited a faster weight loss in phosphate-buffered saline (pH 7.4) at 37°C. Over a degradation period of 54 days, Mn decreased by about 35–45%, while the composition of the matrices, determined by NMR, remained almost constant.

Synthesis and characterization of poly(ethylene glycol)/poly( l-lactic acid) alternating multiblock copolymers

Thermoplastic hydrogels of alternating multiblock copolymers, consisting of poly(ethylene glycol) (PEG) and poly( l-lactic acid) (PLLA), were synthesized. Dicarboxylated oligomeric PLLAs were synthesized by the condensation reaction of l-lactic acid in the presence of succinic acid. Changing the feed ratio of l-lactic acid to succinic acid controlled PLLA molecular weights. Alternating multiblock copolymers with different block lengths of PEG and PLLA were obtained from the polycondensation reaction between PEG and dicarboxylated-PLLA in the presence of dicyclohexyl carbodiimide and N-dimethyl aminopyridine as catalysts. The chemical compositions of dicarboxylated PLLAs and multiblock copolymers were verified by 1H-NMR and FT-IR, and the molecular weight and distribution were measured by gel permeation chromatography. DSC thermograms showed that there existed a high degree of phase mixing, as well as microphase separation in the multiblock copolymer, demonstrated by a large T g peak from the amorphous phase-mixing domain and a small T m peak from crystalline microdomains of the PLLA component. The block copolymers with low molecular weights were water-soluble and clouded at a temperature which is associated with a lower critical solution temperature (LCST) phenomonon. However, the high molecular weight polymers could swell in water and their optical transparency was influenced by temperature. This observation can be attributed to an enhanced hydrophobic interaction between hydrophobic moieties in the polymer chains, caused by an increase in temperature. The weight swelling ratio (absorbed water/polymer) of the polymers was controlled by polymer composition and molecular weight. These block copolymers may offer potential for applications in drug delivery and various other biomedical projects.

The effect of hydrophile–lipophile balance of water-soluble poly(ethylene glycol)–poly(lactic acid) diblock copolymers on the stability of microscopic emulsion films and nanoemulsions

The effect of the PEG and PLA block length of amphiphilic water-soluble poly(ethylene glycol)-poly(lactic acid) diblock copolymers on the stability to rupture of microscopic liquid films and nanoemulsions is investigated.