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This work investigated polyacrylonitrile copolymers synthesized using methyl acrylate (MA) and dimethyl itaconate (DMI) as second monomers by bulk polymerization in the presence of magnesium chloride as a reagent to control the tacticity of polyacrylonitrile copolymers. The copolymers synthesized by solution polymerization were used as a control group to study the tacticity effect. The C-NMR results confirm that the isotacticity by bulk polymerization is increased approximately double for either P(AN- co-MA) or P(AN- co-DMI). The X-ray diffraction (XRD) and the isothermal DSC results show that the P(AN- co-MA) produced by bulk process, as compared to that by solution polymerization, has higher domain size ( L ) and crystallinity (CI); moreover, its cyclization period is decreased significantly. It indicates that the increase of isotacticity for P(AN- co-MA) makes the crystalline domain larger and the cyclization takes place more easily. However, such positive correlations do not hold good for the P(AN- co-DMI) system. It is due to the high steric-hindrance effect for the DMI monomer, which has long reactive branches on both sides of the vinyl DMI monomer, complicating the mechanisms of crystallization and cyclization and resulting in diminishing the contribution of high isotacticity to lower the barrier of cyclization reaction. [ABSTRACT FROM AUTHOR]

A hyperbranched copolymer, hyperbranched-g-( N-isopropylacrylamide-co-itaconamic acid) ('hyperbranch-g-(NIPAAm-co-IAM)'), serving as a pH- and thermo-responsive material, was synthesized via atomic transfer radical polymerization (ATRP) and characterized in this study. A macroinitiator was prepared from a commercially available hyperbranched polymer, 'hyperbranched bis-(methylol)propionic acid (bis-MPA) polyester-16-hydroxyl, generation 2' (hyperbranch-OH) and used as a core structure of the hyperbranched copolymer. The hyperbranch-OH has 16 hydroxyl groups; among them, 12 arms were derived from substitution of the hydroxyl groups with poly(NIPAAm-co-IAM) by ATRP. The polydispersity index (PDI) of the newly synthesized hyperbranched copolymer can be controlled to be less than 1.4. The hyperbranched copolymer shows more significant size change as the environmental pH value changes, compared to the linear random poly(NIPAAm-co-IAM). The particle size decreases with temperature but increases with the pH value. As the molar fraction of IAM in the hyperbranched copolymer increases, the lower critical solution temperature (LCST) increases. Hyperbranch-g-(NIPAAm-co-IAM) with a molar ratio of NIPAAm/IAM equaling to 3:1 shows a LCST of the aqueous solution close to the body temperature, indicating potential use in biomedical applications such as drug release. [ABSTRACT FROM AUTHOR]

A star-shaped copolymer, poly( N-isopropylacrylamide-co-itaconamic acid (poly(NIPAAm-co-IAM)), being pH- and thermo-dual-responsive, was synthesized by atomic transfer radical polymerization (ATRP) and characterized in this work. The lower critical solution temperature (LCST) of the star copolymer increases with the molar fraction of IAM. The particle size decreases as the temperature increases but increases as the pH value increases. Transmission electron microscopy (TEM) reveals that the star-shaped copolymer has a near-spherical core-shell structure that favors drug delivery. The star copolymer can be used in drug encapsulation as well as drug release. The star copolymer has different drug release rates in environments of different pH, and thus it can carry drugs in an acidic (gastric) environment and release the drugs in a neutral or less acidic (intestinal) environment. [ABSTRACT FROM AUTHOR]