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Controlled Molecular Weights (controlled + molecular_weight)

Distribution by Scientific Domains

Polymers and Materials Science	100%

Selected Abstracts

Preparation of polyacrylonitrile with improved isotacticity and low polydispersity

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010
Jianguo Jiang
Abstract The preparation of a polymer with both low polydispersity and high tacticity is one current challenge we face and warrants thorough investigation from both the theoretical and experimental standpoints. In this study, we synthesized polyacrylonitrile (PAN) with simultaneously controlled molecular weight and tacticity on the basis of the strategy of the atom transfer radical polymerization (ATRP) of acrylonitrile (AN) in the presence of Lewis acids. A new combined initiation system of 3-bromopropionitrile (3-BPN)/Cu2O/N,N,N,,N,-tetramethylethylenediamine (TMEDA) was used for the ATRP of AN for the first time. When the polymerization was performed with the ratio [AN]0/[Initiator]0/[Cu2O]0/[TMEDA]0 = 190/1/0.5/1.5 (where the subscript 0 indicates the initial conditions) in ethylene carbonate at 60°C for 48 h, the polydispersity of the obtained PAN was 1.13, and the molecular weight was up to 13,710. The polymerization kinetics results show that the polymerizations proceeded with a living/controlled nature except that an induction period existed during the polymerization process because of the lower initiating activity of 3-BPN. Also, two kinds of Lewis acid, AlCl3 and yttrium trifluororomethanesulflnate, were used in the ATRP system of AN for the tacticity control. The addition of 0.01 equiv (relative to AN) of the Lewis acid AlCl3 in the polymerization afforded PAN with an improved isotacticity [meso/meso triad (mm) = 0.32] and a very narrow polydispersity (1.06). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

A Novel Strategy to Synthesize Double Comb-Shaped Water Soluble Copolymer by RAFT Polymerization

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 9 2006
De-Hui Han
Abstract Summary: A double comb-shaped water soluble copolymer, poly[poly(ethylene oxide) methyl ether methacrylate]- block -poly(N -isopropylacrylamide)- block -poly[poly (ethylene oxide) methyl ether methacrylate], abbreviated as [P(MA-MPEO)- block -PNIPAM- block -P(MA-MPEO)], with a controlled molecular weight and narrow polydispersity was successively synthesized using a macromonomer technique. The 60Co , irradiation polymerization of MA-MPEO in the presence of dibenzyl trithiocarbonate (DBTTC) at room temperature afforded a polymer, P(MA-MPEO)-SC(S)S-P(MA-MPEO), which was subsequently used as a macro RAFT agent in the RAFT polymerization of N -isopropylacrylamide, and water soluble double comb-shaped copolymers, P(MA-MPEO)- block -PNIPAM- block -P(MA-MPEO), were successfully obtained. Structure of the double comb-shaped copolymer. [source]

Macromolecular brushes synthesized by "grafting from" approach based on "click chemistry" and RAFT polymerization

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2010
Dongxia Wu
Abstract Well-defined macromolecular brushes with poly(N -isopropyl acrylamide) (PNIPAM) side chains on random copolymer backbones were synthesized by "grafting from" approach based on click chemistry and reversible addition-fragmentation chain transfer (RAFT) polymerization. To prepare macromolecular brushes, two linear random copolymers of 2-(trimethylsilyloxy)ethyl methacrylate (HEMA-TMS) and methyl methacrylate (MMA) (poly(MMA- co -HEMA-TMS)) were synthesized by atom transfer radical polymerization and were subsequently derivated to azide-containing polymers. Novel alkyne-terminated RAFT chain transfer agent (CTA) was grafted to polymer backbones by copper-catalyzed 1,3-dipolar cycloaddition (azide-alkyne click chemistry), and macro-RAFT CTAs were obtained. PNIPAM side chains were prepared by RAFT polymerization. The macromolecular brushes have well-defined structures, controlled molecular weights, and molecular weight distributions (Mw/Mn , 1.23). The RAFT polymerization of NIPAM exhibited pseudo-first-order kinetics and a linear molecular weight dependence on monomer conversion, and no detectable termination was observed in the polymerization. The macromolecular brushes can self-assemble into micelles in aqueous solution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 443,453, 2010 [source]

Synthesis of comb-like polystyrene with poly(N -phenyl maleimide- alt-p -chloromethyl styrene) as macroinitiator

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2006
Yan Shi
Abstract The copolymerization of N -phenyl maleimide and p -chloromethyl styrene via reversible addition,fragmentation chain transfer (RAFT) process with AIBN as initiator and 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate as RAFT agent produced copolymers with alternating structure, controlled molecular weights, and narrow molecular weight distributions. Using poly(N -phenyl maleimide- alt - p -chloromethyl styrene) as the macroinitiator for atom transfer radical polymerization of styrene in the presence of CuCl/2,2,-bipyridine, well-defined comb-like polymers with one graft chain for every two monomer units of backbone polymer were obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2069,2075, 2006 [source]

Synthesis and properties of biomimetic poly(L -glutamate)- b -poly(2-acryloyloxyethyllactoside)- b -poly(L -glutamate) triblock copolymers

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2004
Chang-Ming Dong
Abstract A novel class of biomimetic glycopolymer,polypeptide triblock copolymers [poly(L -glutamate),poly(2-acryloyloxyethyllactoside),poly(L -glutamate)] was synthesized by the sequential atom transfer radical polymerization of a protected lactose-based glycomonomer and the ring-opening polymerization of ,-benzyl- L -glutamate N -carboxyanhydride. Gel permeation chromatography and nuclear magnetic resonance analyses demonstrated that triblock copolymers with defined architectures, controlled molecular weights, and low polydispersities were successfully obtained. Fourier transform infrared spectroscopy of the triblock copolymers revealed that the ,-helix/,-sheet ratio increased with the poly(benzyl- L -glutamate) block length. Furthermore, the water-soluble triblock copolymers self-assembled into lactose-installed polymeric aggregates; this was investigated with the hydrophobic dye solubilization method and ultraviolet,visible analysis. Notably, this kind of aggregate may be useful as an artificial polyvalent ligand in the investigation of carbohydrate,protein recognition and for the design of site-specific drug-delivery systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5754,5765, 2004 [source]