Effect of Composition and Molecular Structure of Poly(l-lactic acid)/Poly(ethylene oxide) Block Copolymers on Micellar Morphology in Aqueous Solution

Abstract

The effect of the hydrophobic block length in diblock (PLLA x -b-PEO113, x = 64, 166, 418) and triblock (PLLA y -b-PEO91-b-PLLA y , y = 30, 52, 120) copolymers of l-lactic acid and ethylene oxide on the structure of micelles prepared by dialysis was studied by wide- and small-angle X-ray scattering in dilute aqueous solution, dynamic light scattering, transmission electron microscopy, atomic force microscopy, and force spectroscopy. It was found that the size of the crystalline PLLA core is weakly dependent on the PLLA block length. In addition to individual micelles, a number of their micellar clusters were detected with characteristic distance between adjacent micelle cores decreasing with an increase in PLLA block length. This effect was explained by the change in the conformation of PEO chains forming the micellar corona because of their overcrowding. Force spectroscopy experiments also reveal a more stretched conformation of the PEO chains for the block copolymers with a shorter PLLA block. A model describing the structure of the individual micelles and their clusters was proposed.

Single crystals and two‐dimensional crystalline assemblies of block copolymers

“…The parameter of reduced tethering density for BCPSCs can also be applied to 2D crystalline assemblies of BCPs. Lamellar crystalline micelles tend to be formed when is located in the weak interaction regime, whereas BCPs incline to form rod‐like or spherical self‐assemblies when is quite high 102,110 . From the viewpoint of , a higher fraction of crystalline block is favorable to formation of 2D structure 102,111,112 …”

Nanoformulations of Drugs Based on Biodegradable Lactide Copolymers with Various Molecular Structures and Architectures

“…In [88], using the method of small angle neutron scattering, it was found that an increase in the length of the P(L)LA block from 58 to 88 units in the series of triblock P(L)LA y -b-PEG 202 -b-P(L)LA y copolymers leads to a slight increase in the diameter of the semi-crystalline core of the particles from 22 to 30 nm. In [89], when studying aqueous suspensions of PEG 113 -b-P(L)LA x and P(L)LA y -b-PEG 91 -b-P(L)LA y nanoparticles, it was found that a significant increase in the length of the P(L)LA block x from 64 to 418 and y from 30 to 120 monomer units in the series of diblock and triblock copolymers, respectively, practically does not affect the size of the formed particles. The hydrodynamic radius R h of PEG 113 -b-P(L)LA x and P(L)LA yb-PEG 91 -b-P(L)LA y nanoparticles, regardless the length of the P(L)LA block, was ~20 and 30 nm, respectively.…”

“…It was found by SAXS that the radius R of the semi-crystalline P(L)LA core for all samples, except for PEG 113 -b-P(L)LA 418 , was 11 nm. At the given polymerization degrees of the P(L)LA block and under the given conditions of their preparation (con-centration, temperature, and rate of solvent displacement), the size of PEG-b-P(L)LA particles is determined not only by the hydrophilic-hydrophobic balance in the copolymer, but also by the conditions of P(L)LA block crystallization [89]. We note that in [88], particles were formulated by the method of heating block copolymer solutions in D 2 O to 80°C and their subsequent cooling, while in [89], dialysis was used to prepare the particles.…”

“…At the given polymerization degrees of the P(L)LA block and under the given conditions of their preparation (con-centration, temperature, and rate of solvent displacement), the size of PEG-b-P(L)LA particles is determined not only by the hydrophilic-hydrophobic balance in the copolymer, but also by the conditions of P(L)LA block crystallization [89]. We note that in [88], particles were formulated by the method of heating block copolymer solutions in D 2 O to 80°C and their subsequent cooling, while in [89], dialysis was used to prepare the particles. Thus, various patterns in the change in the PEG-b-P(L)LA particle size with increasing length of the P(L)LA block may be associated with the parameters of the particle preparation process, which are usually far from thermodynamically equilibrium conditions.…”

The Role of Integrated Approach in the Determination of Nanoparticle Sizes in Dispersions

“…Secondly, polymeric NPs of the "core-corona" and "Janus" types can be studied by TEM only with the use of the selective contrasting procedure [15]. For example, to employ TEM for studying polymeric "core-corona" NPs, which are formed from amphiphilic block copolymers, such as poly(lactide)-block-poly(ethylene oxide) (PLA-b-PEO) [16,17], as well as hydrophobic PLGA copolymers in the presence of PVA as a hydrophilic stabilizer [18,19], toxic uranyl acetate is commonly used as a negative contrasting agent. In addition, when samples are dried at the stage of sample preparation, the stabilizing corona of particles collapses, and the D value determined for NPs by the TEM method turns out to be significantly lower than the value of their D h .…”