ABA Poly Research Articles

“Uncontrolled” Preparation of Disperse Poly(lactide)-block-poly(styrene)-block-poly(lactide) for Nanopatterning Applications

We report the facile synthesis of well-defined ABA poly(lactide)-block-poly(styrene)-block-poly(lactide) (LSL) triblock copolymers having a disperse poly(styrene) midblock (Đ = 1.27–2.24). The direct synthesis of telechelic α,ω-hydroxypoly(styrene) (HO-PS-OH) midblocks was achieved using a commercially available difunctional free radical diazo initiator 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide]. Poly(lactide) (PLA) end blocks were subsequently grown from HO-PS-OH macroinitiators via ring-opening transesterification polymerization of (±)-lactide using the most common and prevalent catalyst system available, tin(II) 2-ethylhexanoate. Fourteen LSL triblock copolymers with total molar masses Mn,total = 24–181 kg/mol and PLA volume fractions fPLA = 0.15–0.68 were synthesized and thoroughly characterized. The self-assembly of symmetric triblocks was analyzed in the bulk using small-angle X-ray scattering and in thin films using grazing incidence small-angle X-ray scattering and atomic force microscop...

Drug-induced morphology switch in drug delivery systems based on poly(2-oxazoline)s.

Defined aggregates of polymers such as polymeric micelles are of great importance in the development of pharmaceutical formulations. The amount of drug that can be formulated by a drug delivery system is an important issue, and most drug delivery systems suffer from their relatively low drug-loading capacity. However, as the loading capacities increase, i.e., promoted by good drug–polymer interactions, the drug may affect the morphology and stability of the micellar system. We investigated this effect in a prominent system with very high capacity for hydrophobic drugs and found extraordinary stability as well as a profound morphology change upon incorporation of paclitaxel into micelles of amphiphilic ABA poly(2-oxazoline) triblock copolymers. The hydrophilic blocks A comprised poly(2-methyl-2-oxazoline), while the middle blocks B were either just barely hydrophobic poly(2-n-butyl-2-oxazoline) or highly hydrophobic poly(2-n-nonyl-2-oxazoline). The aggregation behavior of both polymers and their formulations with varying paclitaxel contents were investigated by means of dynamic light scattering, atomic force microscopy, (cryogenic) transmission electron microscopy, and small-angle neutron scattering. While without drug, wormlike micelles were present, after incorporation of small amounts of drugs only spherical morphologies remained. Furthermore, the much more hydrophobic poly(2-n-nonyl-2-oxazoline)-containing triblock copolymer exhibited only half the capacity for paclitaxel than the poly(2-n-butyl-2-oxazoline)-containing copolymer along with a lower stability. In the latter, contents of paclitaxel of 8 wt % or higher resulted in a raspberry-like micellar core.

In-Depth LCCC-(GELC)-SEC Characterization of ABA Block Copolymers Generated by a Mechanistic Switch from RAFT to ROP

A recently introduced procedure involving a mechanistic switch from reversible addition–fragmentation chain transfer (RAFT) polymerization to ring-opening polymerization (ROP) to form diblock copolymers is applied to synthesize ABA (star) block copolymers. The synthetic steps include the polymerization of styrene with R-group designed RAFT agents, the transformation of the thiocarbonyl thio end groups into OH functionalities, and their subsequent chain extension by ROP. The obtained linear ABA poly(ε-caprolactone)-block-poly(styrene)-block-poly(ε-caprolactone) (pCL-b-pS-b-pCL) (12 500 g mol–1 ≤ Mn ≤ 33 000 g mol–1) and the star-shaped poly(styrene)-block-poly(ε-caprolactone) (Mn = 36 000 g mol–1) copolymers were analyzed by size exclusion chromatography (SEC), nuclear magnetic resonance (NMR), infrared (IR) spectroscopy, and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The focus of the current study is on the detailed characterization of the ABA (star) block polymers via multidimensional chromatographic techniques specifically high performance liquid chromatography coupled to size exclusion chromatography (HPLC-SEC). In particular, we demonstrate the first time separation of poly(ε-caprolactone) (pCL) homopolymer and additionally poly(styrene) (pS) from the ABA poly(ε-caprolactone)-b-poly(styrene)-b-poly(ε-caprolactone) and star-shaped poly(styrene)-b-poly(ε-caprolactone) block copolymer utilizing critical conditions (CC) for pCL with concomitant gradient elution liquid chromatography (GELC).

Science and technology of perfluorocyclobutyl aryl ether polymers

The authors for this article have notified us about an error in Highlight article “POLA22390”, Figure 4, in Volume 45, Issue 24, pages 5705–5721. The revised Figure 4 is shown below. We apologize for any inconvenience this may have caused. Poly(methylphenyl-phosphazine) with PFCB aryl ether chain extensions (25) and ABA poly(styrene)-PFCB aryl ether triblock copolymers (26).

Comparison of oil-in-water emulsion films produced using ABA or AB n copolymers

Film thickness and disjoining pressure in emulsion films formed between two oil droplets in aqueous solutions of two ABA poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymers of the Pluronic series, F108 and P104, were investigated at different NaCl concentrations. The microinterferometric thin film pressure balance experimental technique was used. The results obtained were compared with those previously reported for an AB n graft copolymer of hydrophobically modified inulin, namely INUTEC SP1. It was noted that there are marked differences in the behavior of the emulsion films stabilized with Pluronics ABA copolymers and those based on the AB n graft copolymer INUTEC SP1. This difference in behavior was used to throw some light on the difference in stability of practical emulsions when using these two types of polymeric surfactants. It is concluded that emulsions using INUTEC SP1 should be more stable than those using Pluronics ABA copolymers in particular at high electrolyte concentrations.

Synthesis and Characterization of Narrow Molecular Weight Distribution AB and ABA Poly(vinylpyridine)−Poly(dimethylsiloxane) Block Copolymers via Anionic Polymerization

The synthesis is described of AB and ABA narrow molecular weight distribution poly(2-vinylpyridine)−poly(dimethylsiloxane) (P2VP−PDMS) and poly(4-vinylpyridine)−poly(dimethylsiloxane) block copolymers. Three synthesis methods were explored. The first and most general procedure (method 1) involves the anionic polymerization of 2VP or 4VP initiated by an acetal-functionalized alkyllithium. Acid hydrolysis of the acetal and titration of the resulting hydroxyl group with triphenyllithium gave a lithium alkoxide end group. This functionality was used to initiate hexamethylcyclotrisiloxane (D3), giving the living P2(4)VP-b-PDMSLi block copolymers that were terminated or coupled with trimethylchlorosilane and dimethyldichlorosilane, respectively, to give the AB and ABA block copolymers. An alternative synthesis (method 2) applicable only to the synthesis of P2VP-b-PDMS or P2VP-b-PDMS-b-P2VP involved alkylation of the lithium P2VP anion with a bromo-functionalized acetal. Acetal hydrolysis and titration with triphenylmethyllithium gave the lithium alkoxide end-functionalized P2VP that was used to initiate D3 followed by termination or coupling with trimethylchlorosilane and dimethyldichlorosilane, respectively. P2VP−PDMS block copolymers could also be synthesized (method 3) by end-capping of living P2VPLi with 2-isopropenylpyridine followed by addition of 1 equiv of ethylene oxide. Addition of D3 to the resulting lithium alkoxide and coupling with trimethylchlorosilane or dimethyldichlorosilane gave the desired AB and ABA block copolymers.

Determination of the surface tension of block copolymer micelles by phagocytosis.

This work was carried out to determine the surface tension of block copolymer micelles of 14C labelled ABA poly (oxyethylene-bi-isoprene-b-oxyethylene) which have a long circulating half life in animals. The method used was that of phagocytosis. The percentage of micelles phagocytosed by human mononuclear cells was determined in solutions of different surface tension. The values obtained were 72 mN/m which may be predicted for a particle with a long circulating half life in animals. The method also gave an estimate of the surface tension for the mononuclear cells. This technique has the advantage of determining the surface tension of highly hydrated small particles including stable micelles in an environment similar to that in which they normally exist.

New macromolecular carriers for drugs. I. Preparation and characterization of poly(oxyethylene‐b‐isoprene‐b‐oxyethylene) block copolymer aggregates

AbstractThis work describes the formation of discrete micelles (⋍ 0.1 μm) from ABA poly(oxyethylene‐b‐isoprene‐b‐oxyethylene) block copolymers in water. An efficient labeling of the micelles by polymerization of [14C]‐styrene within the hydrophobic core is also described. These micellar nanoparticles are being considered as promising materials for controlled release and/or site‐specific drug delivery systems. In experimental animals the micelles remained in circulation with a half‐life in excess of 50 h. Our results demonstrate the advantages of using block copolymers for the preparation of “perfect” biocompatible surfaces such as are required for well‐tolerated, long‐circulating particulate drug carriers.

Penetration of poly(oxyethylene)—poly (oxypropylene) block copolymer surfactant into soya phospholipid monolayers

The surface tension of aqueous solutions of ABA poly (oxyethylene)-poly (oxypropylene) block copolymer nonionic surfactant, has been measured as a function of time. The kinetics and final equilibrium values were surfactant concentration dependent. From these values, using the simple form of the Gibbs equation, the area per molecule has been calculated. The small molecular area (40.7 Å 2) suggests that surfactant molecules form close-packed coil monolayers with hydrophilic poly (oxyethylene) groups immersed in the aqueous phase. The penetration of the surfactant into monolayers of soya phosphatidylcholine spread at the air-water interface was followed by the variation of the surface pressure (△π) at constant area. As revealed by the results at low surfactant concentrations, the adsorption of surfactant is enhanced by the presence of the phospholipid film. Analysis of equilibrium penetration values, obtained by the use of different thermodynamic approaches, shows that the equations of Pethica and Alexander-Barnes are better adapted for calculation of surfactant penetration into the monolayers only in their condensed state (102–122 Å 2/molecule). Conversely, the equation of Motomura et al. enabled the calculation of the adsorbed surfactant quantities, for the expanded state of phospholipid monolayers (140–230 Å 2/molecule).

A Thermo-Sensitive Hydrogel: Poly(ethylene oxide-dimethyl siloxane-ethylene oxide)/Poly(N-isopropyl acrylamide) Interpenetrating Polymer Networks II. On-Off Regulation of Solute Release from Thermo-Sensitive Hydrogel

Interpenetrating polymer networks (IPNs) of poly(ethylene oxide-dimethyl siloxane-ethylene oxide) (PEO-PDMS-PEO) ABA triblock copolymer and poly(N-isopropyl acrylamide) (PIPAAm) has been synthesized as thermosensitive gels. Indomethacin and ketoprofen were selected as model drugs and incorporated into thermosensitive gel. Pulsatile drug release produced from these thermosensitive gels was strongly influenced by the swelling-deswelling kinetic properties of thermosensitive gels solubility dependence of drug as a function of temperature, and the temperature applied. However, the release behavior of indomethacin and ketoprofen at several fixed temperatures from the thermosensitive gel showed similar patterns. The exact initiation temperatures for drug release of both drugs were similar and slightly below the swelling transition temperature of an unloaded gel.

A New Thermo-Sensitive Hydrogel: Poly(ethylene oxide-dimethyl siloxane-ethylene oxide)/Poly(N-isopropyl acrylamide) Interpenetrating Polymer Networks I. Synthesis and Characterization

Interpenetrating polymer networks (IPNs) composed of poly(ethylene oxide-dimethyl siloxane-ethylene oxide) (PEO-PDMS-PEO) ABA triblock copolymer and poly(N-isopropyl acrylamide) (PIPAAm) were synthesized. Transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) studies of bulk IPNS revealed micro phase separation with partial phase mixing between two chemically independent networks. Aqueous equilibrium swelling curves were examined as a function of temperature. DSC thermograms of the swollen IPNS exhibited the same swelling transition temperature as that of PIPAAm, although the degree of swelling of IPNS was affected by polymer composition. These observations indicate that each network in the swollen IPNs exists independently and many have different morphology than the dried bulk state. The aqueous swelling-deswelling kinetics by temperature modulation of IPNs could be controlled by gel composition nd temperatures applied.

The micellar properties of the poly(oxyethylene) - poly(oxypropylene) copolymer Pluronic F127 in water and electrolyte solution

The micellar properties of the ABA poly(oxyethylene)-poly(oxypropylene) block copolymer Pluronic F127 have been examined in water and electrolyte solution by photon correlation spectroscopy, total intensity light scattering and viscometric techniques. The hydrodynamic micellar radius in water, as calculated from diffusion data at the critical micelle concentration, remained constant at 10.2 ± 0.1 nm, over the temperature range 35–45 °C. Viscometric studies, however, showed a progressive dehydration of the micelles with temperature increase and it is clear from total intensity light scattering that this dehydration is accompanied by a concomitant increase in anhydrous volume such that the overall hydrated volume is unaffected by temperature change. Increase of solution concentration above about 10 g · dl −1 over this temperature range caused a marked increase of mean micellar size and of the polydispersity of micellar sizes, indicative of the onset of gelation. The influence of temperature on micellar size and hydration was less pronounced in the presence of 0.5 mol-dm −3 sodium chloride and gelation commenced at higher solution concentrations. The relevance of these studies to the thermal gelation of this poloxamer is discussed.

A new asymmetric membrane having blood compatibility

A new asymmetric membrane has been synthesized from an ABA poly(styrene-bisoprene) (SIS) block copolymer ( M n = 89,000; 30 mol% polyisoprene with 68% 1,4 links and 32% 3,4 links). The asymmetric structure of the membrane obtained by casting the collodium (block copolymer in THF/DMF mixture) has been evidenced by scanning electron microscopy. A chemical modification of the membrane by reaction with gaseous chlorosulfonylisocyanate leads to a heparin-like compound with enhanced blood compatibility properties. Elemental analysis and infrared measurements show the presence of sulfamate and carboxylate groups on the modified block copolymer. These functional groups increase the hydrophilicity of the membrane and therefore enhance its water permeability.

Preparation, fractionation, and dilute‐solution behavior of ABA poly(methyl methacrylate‐b‐α‐methylstyrene) block copolymers

AbstractThe preparation by anionic polymerization of six ABA poly(methyl methacrylate‐b‐α‐methylstyrene) block copolymers and of sixteen poly(α‐methylstyrene)s is described. The block copolymers, of similar molecular weight but with different chemical compositions, were fractionated by preparative gel permeation chromatography and their behavior in dilute solution was investigated using viscometry. The results obtained indicate that the intramolecular phase separation does not occur under the conditions utilized, the block copolymers assuming randomcoil configurations in all of the copolymer/solvent systems studied. Consequently the block copolymer molecules are more expanded than homopolymers of the same molecular weight. The series of poly(α‐methylstyrene)s covered the molecular weight range 2.7 × 103–1.3 × 106 and enabled the determination of Mark–Houwink–Sakurada constants for poly(α‐methylstyrene) in the solvents chosen for the block copolymer studies.

Adhesion of block copolymers to glass: Lap shear strengths as a function of bonding conditions

AbstractABA poly(styrene‐b‐isoprene) block copolymers with various molecular weights and composition were used as heat activated films in simple overlap glass joints. The influence of bonding temperature on their shear strength at break was investigated. On increase of temperature, the joint resistance for most of the copolymers passed through a maximum, which temperature was dependent on the molecular characteristics of the copolymers. The decrease in melt viscosity or chemical degradation could not explain the data. A morphological interpretation which fits well the present and previous observations is proposed and verified for one copolymer used in this work.

Concentrated solution rheology of an ABA poly(styrene- b-butadiene) copolymer in various solvents

The critical concentrations of an SBS copolymer in cyclohexane, carbon tetrachloride, toluene, tetralin and cyclohexanone were determined. Using an equation proposed by Cornet, it was shown that at the critical concentrations the unperturbed root mean square end to end distances were, within experimental error, the same as that found for dilute solutions, indicating that the interpenetrating conformation of the blocks established for dilute solutions was maintained up to at least the critical concentrations.

Glass transition temperatures of ABA poly(styrene‐b‐isoprene) block copolymers by differential scanning calorimetry

AbstractThe glass transition behavior of two sets of ABA poly(styrene‐b‐isoprene) block copolymers was examined by differential scanning calorimetry. In one series, the triblock copolymers had different total molecular weights and the same (30 wt %) polyisoprene content, in the other, the molecular weight was constant (30,000 g/mol) and the elastomer content was the variable. For all triblock copolymers studied, the data show an inward shift for the glass transition temperatures Tg of the corresponding homopolymers. This shift increases for the rigid‐phase Tg as the polystyrene block length decreases. Depending on their molecular characteristics, two, three, or only one Tg were found. The third Tg was interpreted in terms of the existence of an interphase. Some of these conclusions could be confirmed by transmission electron microscopy.

Molecular-weight dependence of the glass transition temperatures of rigid SIS triblock copolymers studied by DSC

Differential scanning calorimetry (DSC) measurements have been carried out on a series of ABA poly(styrene-b-isoprene) triblock copolymers with 30% polyisoprene content and various molecular weights. The DSC data show an inward shift for the glass transition temperatures (T g) of the blocks compared to the corresponding homopolymers. As a function of the molecular weight, one to three transitions were found. The additional thirdT g gives some further evidence of the existence of an interphase between the microdomains.

Tensile strength of joints bonded with ABA poly(styrene-b-isoprene) films

Tensile strength of joints bonded with ABA poly(styrene-b-isoprene) films

Stress-strain behavior of thin ABA poly(styrene-b-isoprene) films

Stress-strain behavior of thin ABA poly(styrene-b-isoprene) films