Search

No abstract

End-linked, degradable, amphiphilic polymer conetworks (APCNs) of various compositions and architectures were synthesized by sequential atom transfer radical terpolymerization of monomers and cross-linker using a cleavable, bifunctional initiator, bearing two acid-labile hemiacetal ester groups. The incorporation of the initiator residue into the conetworks rendered them cleavable in the middle of their elastic polymer chains. The temporal evolution of the swollen mass of the conetworks in acidified THF-water mixtures was studied and it was determined that the APCN hydrolysis rates were dependent on both conetwork composition and architecture. Regarding the former, hydrophobic APCNs degraded slowly or they even did not dissolve at all. Regarding the latter, conetworks with hydrophobic monomer and hydrophobic cross-linker units distributed around the initiator fragment also dissolved more slowly or they did not degrade at all. Finally, characterization of the star copolymers, produced from conetwork hydrolysis, allowed the determination of the APCN core functionality to be around 30. 3 1 105 116 Cited By :25

Conetworks based on end-linked homopolymers and amphophilic gradient copolymers were synthesized by the atom transfer radical polymerization (ATRP) of 2-(dimethylamino)ethyl methaerylate (DMAEMA, hydrophilic monomer), methyl methaerylate (MMA, hydrophobic monomer), and ethylene glycol dimethacrylate (EGDMA, hydrophobic cross-linker). Sequential, rather than step-wise polymerizations, were performed to enhance the livingness of the polymerization, particularly for the end-linking step, and to ultimately obtain conetworks based on gradient rather than pure block copolymers. Amphiphilic conetworks based on end-linked MMA-DMAEMA-MMA gradient copolymers of different compositions were successfully synthesized as confirmed by the narrow molecular weight distributions of the linear precursors, the rigidity of the amphiphilic conetwork products and the low sol-fraction extracted from the conetworks. Similarly successful was the ATRP synthesis of an end-linked conetwork based on a DMAEMA-MMA statistical copolymer and of a randomly cross-linked conetwork that resulted from the simultaneous terpolymerization of DMAEMA, MMA and EGDMA. An amphiphilic conetwork based on an end-linked DMAEMA-MMA-DMAEMA gradient copolymer presented a less rigid, mucous-like, texture. The degrees of swelling (DS) in tetrahydrofuran of all the conetworks were higher than those measured in pure water, whereas the aqueous DS values increased by lowering the pH and increasing the DMAEMA content of the conetworks. © 2010 Wiley Periodicals, Inc. 48 9 1878 1886 Cited By :20

The document first gives definitions of basic terms related to liquid-crystalline and mesomorphic states of matter and then terms specific to the classification of liquid-crystal polymers. The terms have been restricted to those most commonly encountered in the structural description of the latter class of materials. The terms have been selected from the recently published comprehensive document "Definitions of basic terms relating to low-molar-mass and polymer liquid crystals" [Pure and Applied Chemistry 73 (5), 845-895 (2001)] and are intended to form a readily usable guide for the reader interested in the structural description of polymer liquid crystals. The more comprehensive document should be used for terminology associated with types of mesophases and the optical and physical characteristics of liquid-crystalline materials. The advice given by representatives of the International Liquid Crystal Society for the preparation of this document is gratefully acknowledged. Fil:Barón, M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

International audience; Metal complexes stabilized by appropriate ligands, particularly CuI/L systems, have proven powerful for the controlled polymerization of acrylates and other monomers by atom transfer radical polymerization (ATRP). The polymerization of acrylates by CuI/L systems, however, is haunted by interference of catalyzed radical termination (CRT), which reduces the chain-end fidelity. Other monomers do not appear to be affected by this phenomenon to any significant extent. The phenomenon appears to involve the formation of an organometallic intermediate by reversible radical trapping, as in organometallic mediated radical polymerization (OMRP). We summarize here the current knowledge and the efforts made to elucidate the CRT pathway and products.

WOS:000456766500005; International audience; The work reported herein details the synthesis, as well as the photophysical and photochemical investigation, of novel benzophenone-based photosensitive alkoxyamines for potential application in nitroxide-mediated photopolymerization. As benzophenone has found widespread application in photosensitive alkoxyamines, serving as an intramolecular photosensitizer, the deleterious effects of competitive excited state hydrogen atom abstraction processes are examined. In order to reduce the efficiency of excited state hydrogen atom abstraction processes, electron donating methoxy and pyrrolidine substituents were incorporated para to benzophenone's carbonyl moiety to modulate the excited state character of the substituted benzophenone motifs. Whilst the incorporation of electron donating substituents reduced the efficiency of excited state hydrogen atom abstraction processes, this did not translate into increased photo-dissociation efficiencies. Greater photo-dissocia tion efficiencies were obtained for benzophenone-based alkoxyamines lacking the electron donating functionalities. The excited state character of the benzophenone moiety is therefore a key parameter governing both the hydrogen atom abstraction and photo-dissociation efficiencies of benzophenone-based photosensitive alkoxyamines.

International audience; Block copolymer synthesis often results in a complex polymer mixture containing not only the desired block copolymer macromolecules but also one or both parent homopolymers. Such complex polymer mixtures resulting from Atom Transfer Radical Polymerization (ATRP) and Nitroxide Mediated Polymerization (NMP) syntheses of PS-b-PEO-b-PS were characterized using Liquid Chromatography under Limiting Conditions of Desorption (LC LCD). The presence of PS homopolymer depends only on experimental synthesis conditions, such as the dilution of the reaction medium, the styrene/PEO molar equivalent ratio and the reaction time. Presence of residual PEO homopolymer is not only influenced by experimental synthesis conditions but also by the presence of unfunctionalized PEO in the corresponding PEO macro-initiator samples.