Poly(para‐phenylene vinylene) (PPV) and its derivatives are important semiconducting polymers for organic electronics. Herein, an alkene metathesis approach to obtain PPVs is reported. Tri(iso propyl)silyl‐substituted norbornadienes are employed as solubilizing agents. As PPV precursors divinylbenzene is used for acyclic diene metathesis and paracyclophane diene for a ring‐opening metathesis polymerization‐type approach. The resulting polymers are analyzed by gel permeation chromatography (GPC), UV‐vis, fluorescence, and nuclear magnetic resonance (NMR) spectroscopy. All of the polymers show good solubility in common solvents.
Three‐ and four‐arm star shaped polymers, as well as diblock copolymers, are synthesized via acyclic diene metathesis (ADMET) polymerization. This is accomplished by using an asymmetric α,ω‐diene containing a terminal double bond and an acrylate, which is polymerized in the presence of multifunctional acrylates as selective and irreversible chain transfer agents using Hoveyda‐Grubbs second generation catalyst. High cross‐metathesis selectivities are achieved at low temperatures enabling good control over molecular weights. Furthermore, additional polyethyleneglycol (PEG) blocks are attached to these polymers via Heck coupling of the acrylate end‐groups of these polymers with aryl iodide functionalized PEG, obtaining three‐ and four‐arm star shaped di‐ and triblock copolymers with molecular weights up to 31 kDa.
Degradable polymers are a currently growing field of research for biomedical and materials science applications. The majority of such compounds are based on polyesters and polyamides. In contrast, their phosphorus‐containing counterparts are much less studied, in spite of their potential precise degradation profile and biocompatibility. Herein, the first library of poly(phosphorodiamidate)s (PPDAs) with two P?N bonds forming the polymer backbone and a pendant P?OR group is prepared through acyclic diene metathesis polymerization. They are designed to vary in their hydrophilicity and are compared with the structural analogues poly(phosphoester)s (PPEs) with respect to their thermal properties and degradation profiles. The degradation of PPDAs can be controlled precisely by the pH: under acidic conditions the P?N linkages in the polymer backbone are cleaved, whereas under basic conditions the pendant ester is cleaved selectively and almost no backbone degradation occurs. The PPDAs exhibit distinctively higher thermal stability (from thermogravimetric analysis (TGA)) and higher glass transition and/or melting temperatures (from differential scanning calorimetry (DSC)) compared with analogous PPEs. This renders this exotic class of phosphorus‐containing polymers as highly promising for the development of future drug carriers or tissue engineering scaffolds. 相似文献
The reaction of [(Cp*Mo)2(μ‐Cl)2B2H6] ( 1 ) with CO at room temperature led to the formation of the highly fluxional species [{Cp*Mo(CO)2}2{μ‐η2:η2‐B2H4}] ( 2 ). Compound 2, to the best of our knowledge, is the first example of a bimetallic diborane(4) conforming to a singly bridged Cs structure. Theoretical studies show that 2 mimics the Cotton dimolybdenum–alkyne complex [{CpMo(CO)2}2C2H2]. In an attempt to replace two hydrogen atoms of diborane(4) in 2 with a 2e [W(CO)4] fragment, [{Cp*Mo(CO)2}2 B2H2W(CO)4] ( 3 ) was isolated upon treatment with [W(CO)5⋅thf]. Compound 3 shows the intriguing presence of [B2H2] with a short B−B length of 1.624(4) Å. We isolated the tungsten analogues of 3 , [{Cp*W(CO)2}2B2H2W(CO)4] ( 4 ) and [{Cp*W(CO)2}2B2H2Mo(CO)4] ( 5 ), which provided direct proof of the existence of the tungsten analogue of 2 . 相似文献
A main‐chain liquid crystalline polymer has been obtained by applying a Hoveyda–Grubbs 2nd generation catalyst in acyclic diene metathesis polymerization (ADMET) of a monomer containing on one end a terminal dimethylvinylsilyl group and at the other end a terminal C C double bond. This material showed an interesting Iso‐de Vries SmA* – SmC* – Glass phase transition with a very small layer shrinkage on progressing from the SmA* phase into the SmC* phase. Will this material present a helical structure along the fiber axis in the SmC* temperature range? Several physical characterization methods including XRD, optical observation, and microtome technique have been used to investigate the internal structural organization in this liquid crystalline fiber.
Poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA)‐based brush poly(phosphoamidate)s are successfully synthesized by a combination of ring‐opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP) following either a commutative two‐step procedure or a straightforward one‐pot process using Grubbs ruthenium‐based catalysts for tandem catalysis. Compared with the traditional polymerization method, combining ROMP and ATRP in a one‐pot process allows the preparation of brush copolymers characterized by a relatively moderate molecular weight distribution and quantitative conversion of monomer. Moreover, the surface morphologies and aggregation behaviors of these polymers are studied by AFM and TEM measurements.
