Papers by Keyword: Star Polymer

Abstract: This research studied ways to increase the stability of a polymer thin film with a thickness of approximately 10 nm. Our system consisted of a polystyrene (PS) thin film filled with three arm polystyrene (TAP) as additives. Formation of dewetting was investigated by atomic force microscopy and optical microscopy which showed that complete dewetting of the pure PS film occurs after being annealed at 120 oC for 5 h. The dewetting dynamics were dramatically suppressed when a small amount of TAP polymer was added into the PS thin film. We hypothesize that the nitrogen atom in the TAP polymer provides dipolarity between the polymeric thin films and the substrate followed by an increase in the interfacial interaction of the TAP/PS thin films, which in turn leads to increased film stability. However, if the concentration of TAP is too high, this leads to phase separation of the thin films. We also observed that the amount of TAP within the PS thin film largely affected the efficiency of inhibiting dewetting. This method could be utilized for the study of the mechanism in a blended polymer film.

Abstract: Covalently tethered well-defined new three-arm star hydrophilic poly(ethylene glycol) monomethacrylate (PEGMA) brushed nanoparticles on silicon surface have been successfully prepared by (i) synthesis a novel type of three-arm star-shaped preceding initiator, trifunctional hydroxy-based N-allyl-3,4,5-trihydroxybenzamide (NATHB), (ii) UV-induced hydrosilylation of NATHB with the hydrogen-termined Si(100) (Si-NATHB surface), (iii) coupling of 2-bromo isobutyrl bromide with the hydroxyl of NATHB by the esterification to provide the initiators (Si–NATHB–R3Br) for the subsequent ATRP, (iv) surface-initiated ATRP of PEGMA and 2-hydroxyethl methacrylate monomethacrylate (HEMA) to give the linear Si–NATHB–g–P(PEGMA) brushes and the Si–NATHB–g–P(HEMA) surface, (v) further coupling of 2-bromo isobutyrl bromide with the hydroxyl of P(HEMA) by the esterification to produce the macroinitiators (Si–NATHB–g–P(HEMA)-R3Br) and (vi) surface-initiated ATRP of PEGMA to give the comb-shaped Si–NATHB–g–P(HEMA)–g–P(PEGMA) brushes surface. Kinetics study indicated that the chain growth of P(PEGMA) and P(HEMA) from the functionalized silicon surfaces was consistent with a “controlled” or “living” process. The chemical composition and functionality of the silicon surface were tailored by the well-defined star linear and comb-shaped P(PEGMA) brushes, which provide with this type of surface structures formed in three brushes under conditions of spatial constraints imposed by their chemical connection to a single grafting site. XPS spectra testify that the linear and comb-shaped P(PEGMA) have been grafted on the Si-NATHB surface. AFM imaging of the hydrophilic polymer brushed nanoparticles imaged distinctive morphology when they were prepared into linear and comb-shaped brushes structure.

Abstract: A series of novel miktoarm star polymers were synthesized by combination of at-om transfer radical polymerization(ATRP), chemical modification and ring-opening polymeri-zation(ROP). These miktoarm star polymers carring one poly[6-(4-methoxy-4’-oxy-azobenzene) hexylmethacrylate] azobenzene (PMMAZO) side-chain liquid crystalline(LC) arm and two polycaprolactone(PCL) arms. These precursors and miktoarm star polymers were characterized by proton nuclear resonance (1H-NMR), and gel permeation chramatograph(GPC). The information of PMMAZO(OH)2 and PMMAZO-(PCL)2 miktoarm star polymer confirmed the expected structure.

Abstract: 6-arm star-shaped Poly (ε-caprolactone)-dextran (sPCL-dextran) was synthesized and characterized. The core of the star polymer is dipentaerythritol, the inner block in the arm is hydrophobic poly (ε-caprolactone) (PCL), and the outer block in the arm is hydrophilic dextran. The synthesis involves three steps: (1) The ring-opening polymerization of ε-caprolactone (CL) initiated by dipentaerythritol produces 6-arm star-shaped PCL (sPCL-OH). (2) The sPCL-OH reacts with acryloyl chloride to get star-shaped PCL with acrylate end group (sPCL-CH=CH₂). (3) The amino ended dextran (dextran-NH₂) is then attached to sPCL-CH=CH₂ terminus by Micheal addition to form star-shaped sPCL-dextran. The architecture of products was characterized with ¹H NMR, GPC and element analysis. Micellization of sPCL-dextran in aqueous solutions was investigated by DLS. The results showed that the micelle size (R_h) and size distribution are related to the concentration of the sPCL-dextran. Salt, pH value and temperature have no obvious influence on the R_h.

Abstract: The electrophoretic deposition of polystyrene/divinylbenzene (PS/DVB) star polymer-europium sulphide (EuS) nanocomposite films from a colloidal suspension is reported. Liquid suspension, containing both the PS/DVB star polymer and EuS nanocrystals were prepared by separately injecting dichloromethane (DCM) based solutions of EuS nanocrystals and of the star polymers, respectively, into a stratified liquid combination of hexane and DCM. Scanning electron microscopy illustrates images of the dependence of surface morphology on nanocrystal concentration of the PS/DVB-EuS star polymer film. These polymer-encased nanocrystal films may be a more practical option for the fabrication of magneto-optical thin film devices, such as optical switches, optical isolators, and optical memories.