Jinchuan Yang

Characterization of Poly(ε-Caprolactone) via Size Exclusion Chromatography with Online Right-Angle Laser-Light Scattering and Viscometric Detectors

Poly( l -caprolactone) was characterized by size exclusion chromatography on-line with a right-angle laser-light scattering photometer and a four-capillary bridge design differential viscometer (SEC/RI/RALLS/DV) in tetrahydrofuran (THF) at 25°C. The dependence of intrinsic viscosity and radius of gyration of poly( l -caprolactone) on molecular weight was established, and Florys characteristic ratio C X was calculated for this polymer from these data. The results show that THF is a good solvent for poly( l -caprolactone). Poly( l -caprolactone) exhibits a random-coil conformation in THF, and SEC with online RALLS and DV detectors offer an easy way to obtain information on chain flexibility. The C X results are in good accord with previously reported values for this polymer.

Capillary electrophoresis of associative diblock copolymers

Water soluble diblock copolymers composed of a long poly(styrene sulfonate) chain (between 200 and 400 monomers) and a short poly(ethylene propylene) or poly(tert.-butylstyrene) hydrophobic end (20-50 monomers) are highly associative and form micelles in aqueous solution. The micelles are composed of a small hydrophobic core and a polyelectrolyte corona, the dimensions of which can be estimated by neutron and light scattering. These physical techniques are, however, not amenable to discriminate easily between the free copolymer and the copolymer micelle. Capillary electrophoresis was implemented in this work as a new and effective tool to investigate the behaviour of such associative copolymer systems. Since the rate of exchange between the micellised and free states is very slow in comparison with the time scale of the electrophoretic process, the electropherograms of the diblock copolymers obtained in plain aqueous borate buffers exhibit two peaks assigned to the two states mentioned above. The identification of the two peaks was first made on the basis of the retention orders of the two peaks equally obtained in similar conditions by size-exclusion chromatography. The copolymer micelles appeared to have a smaller electrophoretic mobility than the free copolymers. This peak assignment is also consistent with the observed ratio of the time-corrected peak areas and peak dispersions. The effects of the copolymer concentration, electric field, temperature and hydroorganic composition of the medium was also studied. Such systems do not exhibit a defined concentration threshold equivalent to a classical critical micelle concentration. Adding methanol to the electrolyte resulted in the progressive loss of baseline return between the two peaks, which might be attributed to a slight increase in the rate of exchange between the two states. Finally, adding a neutral surfactant to the electrolyte at a concentration in excess of its critical micelle concentration resulted in a decrease in the electrophoretic mobility of the peak attributed to the free copoplymer, while the electrophoretic mobility of the copolymer micelle remained unperturbed.

MALDI/TOF/MS as a Method for Characterizing Micelle-Forming Polymers: A MALDI/TOF/MS Study of Amphiphilic Diblock Copolymers Based on Sulfonated Polystyrene

Abstract Matrix-assisted laser desorption/ionization time-of-flight mass spectra (MALDI/TOF/MS) of sodium poly(styrenesulfonate)-block-poly (tert-butylstyrene) (NaPSS-b-PtBS) and polystyrene-block-poly (tert-butylstyrene) (PS-b-PtBS) diblock copolymers were obtained. MALDI/TOF/MS of NaPSS-b-PtBS directly yields molecular weights and polydispersities of these micelle-forming amphiphilic block copolymers. MALDI/TOF/MS allows direct determination of molecular weights and molecular weight distributions of NaPP-b-PtBS. Classical molecular weight methods, such as light scattering and osmometry, are not suitable for molecular weight determinations of these polymers due to their extremely low critical micelle concentrations. By comparing the molecular weights of NaPSS-b-PtBS and their precursors, PS-b-PtBS, extents of sulfonation were also obtained.

Oil-in-water microemulsions stabilized by charged diblock copolymers

We present here oil-in-water microemulsions stabilized by charged diblock copolymers alone, along with their structural characterization by small-angle neutron scattering measurements. They consist of swollen spherical micelles containing small amounts of oil in their core, which is surrounded by a corona of stretched polyelectrolyte chains. Structural changes, including core size variations, are evidenced when using a cosurfactant, or upon addition of salt, through a contraction of the charged corona. Attempts to relate the micellar structure to the individual copolymer characteristics are also presented, and show that the size of the hydrophobic block mainly determines that of the micelles.

Structure and buckling of charged diblock copolymer films at liquid interfaces

Abstract Adsorbed and spread charged diblock copolymer layers are studied at flexible interfaces. In both cases, equilibrium situations can be reached and the structure and fluctuations in height of the interface are examined by different experimental means. In particular, buckled deformations of the air–water interface are evidenced by optical and X-ray scattering techniques. Preliminary results at the oil–water interface with similar copolymers are discussed.