Structure of PEP-PEO block copolymer micelles: Exploiting the complementarity of small-angle X-ray scattering and static light scattering

The structure of large block copolymer micelles is traditionally determined by small-angle neutron scattering (SANS), covering a large range of scattering vectors and employing contrast variation to determine the overall micelle morphology as well as the internal structure on shorter length scales. The present work shows that the same information can be obtained by combining static light scattering (SLS) and small-angle X-ray scattering (SAXS), which provide information on, respectively, large and short length scales. Micelles of a series of block copolymers of poly(ethylene propylene)-b-poly(ethylene oxide) (PEP–PEO) in a 70% ethanol solution are investigated. The polymers have identical PEP blocks of 5.0 kDa and varying PEO blocks of 2.8–49 kDa. The SLS contrasts of PEP and PEO are similar, providing a homogeneous contrast, making SLS ideal for determining the overall micelle morphology. The SAXS contrasts of the two components are very different, allowing for resolution of the internal micelle structure. A core–shell model with a PEP core and PEO corona is fitted simultaneously to the SAXS and SLS data using the different contrasts of the two blocks for each technique. With increasing PEO molecular weight, a transition from cylindrical to spherical micelles is observed. This transition cannot be identified from the SAXS data alone, but only from the SLS data.</jats:p

Solution Properties of Water-Soluble “Smart” Poly(N-acryloyl-N′-ethyl piperazine-co-methyl methacrylate)

Water-soluble copolymers of N-acryloyl-N′-ethylpiperazine (AcrNEP) with methyl methacrylate (MMA) were synthesized to high conversion by free-radical solution polymerization. The composition of the copolymers was determined using Fourier Transform Infra-red Spectroscopy (FTIR). Copolymers containing AcrNEP content above 44 mol% were readily soluble in water and exhibited the critical solution temperature behavior. The copolymers were strongly responsive to changes in pH of the external medium due to the presence of tertiary amine functions that could be protonated at low pH. The influence of various factors such as copolymer composition, pH, temperature, salt and surfactant concentration on the LCST of the copolymers were systematically studied. The intrinsic viscosity of the copolymers in dimethyl formamide decreased with increase in temperature due to a decrease in thermodynamic affinity between polymer chains and solvent molecules. The viscosity behavior of the copolymers in sodium chloride solution was similar to that of classical polyelectrolytes and hydrophobically modified polyacrylate systems

Studies of some novel piperazine derived amphiphiles and polymeric materials

This thesis describes the study of some novel piperazine derived amphiphiles and polymeric materials.Master of Scienc

Stimuli-Responsive Cationic Hydrogels in Drug Delivery Applications

Stimuli-responsive, smart, intelligent, or environmentally sensitive polymers respond to changes in external stimuli such as pH, temperature, ionic strength, surfactants, pressure, light, biomolecules, and magnetic field. These materials are developed in various network architectures such as block copolymers, crosslinked hydrogels, nanogels, inter-penetrating networks, and dendrimers. Stimuli-responsive cationic polymers and hydrogels are an interesting class of “smart” materials that respond reversibly to changes in external pH. These materials have the ability to swell extensively in solutions of acidic pH and de-swell or shrink in solutions of alkaline pH. This reversible swelling-shrinking property brought about by changes in external pH conditions makes these materials useful in a wide range of applications such as drug delivery systems and chemical sensors. This article focuses mainly on the properties of these interesting materials and their applications in drug delivery systems