ABSTRACT
This report describes two different methodologies for the synthesis of aryl end-functionalized poly(lactide)s (PLAs) catalyzed by indium complexes. In the first method, a series of para-functionalized phenoxy-bridged dinuclear indium complexes [(NNO)InCl]2(µ-Cl)(µ-OPhR) (R = OMe (1), Me (2), H (3), Br (4), NO2 (5)) were synthesized and fully characterized. The solution and solid state structures of these complexes reflect the electronic differences between these initiators. The polymerization rates correlate with the electron donating ability of the phenoxy initiators: the para-nitro substituted complex 5 is essentially inactive. However, the para-methoxy variant, while less active than the ethoxy-bridged complex [(NNO)InCl]2(µ-Cl)(µ-OEt) (A), shows sufficient activity. Alternatively, aryl-capped PLAs were synthesized via immortal polymerization of PLA with A in the presence of a range of arylated chain transfer agents. Certain aromatic diols shut down polymerization by chelating one indium centre to form a stable metal complex. Immortal ROP was successful when using phenol, and 1,5-naphthalenediol. These polymers were analysed and chain end fidelity was confirmed using 1H NMR spectroscopy, MALDI-TOF mass spectrometry, and UV-Vis spectroscopy. This study shed light on possible speciation when attempting to generate PLA-lignin copolymers.
Subject(s)
Coordination Complexes/chemical synthesis , Dioxanes/chemistry , Phenols/chemistry , Polymerization , Polymers/chemical synthesis , Catalysis , Coordination Complexes/chemistry , Electrons , Indium/chemistry , Lignin/chemistry , Magnetic Resonance Spectroscopy , Molecular Structure , Naphthalenes/chemistry , Polymers/chemistryABSTRACT
The first example of a one-component precursor to star-shaped polyesters, and its utilization in the synthesis of previously unknown star-shaped poly(hydroxybutyrate)-poly(lactic acid) block copolymers, is reported. A series of such mono- and bis-benzyl alkoxy-bridged complexes were synthesized, fully characterized, and their solvent dependent solution structures and reactivity were examined. These complexes were highly active catalysts for the controlled polymerization of ß-butyrolactone to form poly(hydroxybutyrate) at room temperature. Solution studies indicate that a mononuclear propagating species formed in THF and that the dimer-monomer equilibrium affects the rates of BBL polymerization. In the presence of linear and branched alcohols, these complexes catalyze well-controlled immortal polymerization and copolymerization of ß-butyrolactone and lactide.
Subject(s)
Hydroxybutyrates/chemistry , Indium/chemistry , Lactic Acid/chemistry , Polymers/chemistry , Catalysis , Crystallography, X-Ray , Polyesters , PolymerizationABSTRACT
OBJECTIVE: Low-intensity laser therapy (LILT) is defined to supply direct biostimulative light energy to the cells. While several studies have demonstrated that LILT has stimulating effects on bone cells and can accelerate the repair process of the bone, others reported delayed fracture healing or no effects after LILT. The aim of this article was to review the studies evaluating the biomodulation effects of LILT on bone-derived stem cells. MATERIALS AND METHODS: To access relevant articles, searching in three electronic databases including PubMed, Google Scholar and Science Direct was conducted until April 2012. The key words used were low-level laser, low-intensity laser, low-power laser therapy, stem cell, bone marrow stem cell, bone and osteoblast. The articles that met the eligibility criteria were included in this review of literature. RESULTS: Twenty-five relevant articles (13 in vitro and 12 animal studies) were included. Eleven in vitro studies showed positive results with regard to acceleration of cell proliferation and differentiation. All animal studies showed improved bone healing in sites irradiated with low-intensity laser. CONCLUSION: Based on the results of the reviewed articles, low intensity laser therapy can accelerate bone healing in extraction sites, bone fracture defects and distraction osteogenesis, provided proper parameters were applied.
ABSTRACT
This paper gives an overview of a number of advanced techniques for image compression, which are under investigation in the Signal Processing Laboratory at the Swiss Federal Institute of Technology of Lausanne. Various applications ranging from High definition television (HDTV) to multimedia will be discussed. In particular, systems based on subband decomposition, edge based representation, as well as symmetries will be presented.
