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Two-step Polymerization (two-step + polymerization)
Selected AbstractsHTPB-based polyurethaneurea membranes for recovery of aroma compounds from aqueous solution by pervaporationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Yunxiang Bai Abstract Hydroxyterminated polybutadiene (HTPB)-based polyurethaneurea (PU), HTPB-PU, was synthesized by two-step polymerization and was firstly used as membrane materials to recover aroma, ethyl acetate (EA), from aqueous solution by pervaporation (PV). The effects of the number,average molecular weight (Mn) of HTPB, EA in feed, operating temperature, and membrane thickness on the PV performance of HTPB-PU membranes were investigated. The membranes demonstrated high EA permselectivity as well as high EA flux. The DSC result showed two transition temperatures in the HTPB-PU membrane and contact angle measurements revealed the difference of hydrophobicity of the membrane at both sides, which were induced by glass plate and air, respectively, due to movement of the soft hydrophobic polybutadiene (PB) segments in HTPB-PU chains. Furthermore, the PV performance of the HTPB-PU membrane with the hydrophobic surface facing the feed was much better than that with the hydrophilic surface. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 552,559, 2007 [source] Synthesis and properties of thermoplastic polyimides with ether and ketone moietiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2010Xiaohui Yu Abstract A series of polyimides containing ether and ketone moieties were synthesized from 1,3-bis(4-fluorobenzoyl) benzene and several commercially available dianhydrides via a conventional two-step polymerization. The inherent viscosities of Polyamide acids ranged from 0.46 to 0.73 dL/g. Thermal properties, mechanical properties, and thermalplasticity of the obtained polimide films were investigated by focusing on the chemical structures of their repeat units. These films were amorphous, flexible, and transparent. All films displayed low Tgs (184,225 °C) but also excellent thermal stability, the 5% weight loss temperature was up to 542 °C under nitrogen. The films showed outstanding mechanical properties with the modulus up to 3.0 GPa and the elongation at break in the range of 8,160%. The uniaxial stretching of PI-a at high temperature was studied owing to its excellent flexibility. The PI-a had an elongation at break up to 1600% at 245 °C and the uniaxially stretched film exhibited a much higher modulus (3.9 GPa) and strength (240 MPa) than undrawn film. The results indicated that PI-a can potentially be used to prepare materials such as fiber, ultra-thin film or ultra-high modulus film. All the obtained films also demonstrated excellent thermoplasticity (drop of E, at Tg > 103) which made the polyimides more suitable for melt processing. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2878,2884, 2010 [source] Synthesis and characterization of thermally stable, high-modulus polyimides containing benzimidazole moietiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2009Shuang Wang Abstract A series of novel benzimidazole-containing aromatic polyimides were prepared from synthesized 5,4,-diamino-2-phenyl benzimidazole (DAPBI), and commercial dianhydrides by the conventional two-step polymerization. The obtained films were amorphous and could afford flexible, transparent, and tough films with excellent thermal and mechanical properties. They showed high levels of tension strength of up to 234 MPa, modulus of up to 5.6 GPa without any stretching. According to thermal stability measurements, the glass-transition temperatures of the polymers were observed between 329 and 425 °C. The 5% weight-loss temperatures of most polyimides were above 600 °C in nitrogen. Excellent properties of these polyimides were proved to be attributed to the rigid-rod structure and hydrogen bond of intermacromolecular. SAXS and SEM results showed self-molecular orientation caused the formation of rod-like extended conformations. It was demonstrated that high degree of supramolecular order led to the increase of thermal stability and mechanical properties of the polyimide films. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2024,2031, 2009 [source] Thermosensitive Poly[(2-(diethylamino)ethyl methacrylate)- co -(N,N -dimethylacrylamide)] Cryogels Prepared by a Two-Step Polymerization MethodMACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2006Tuncer Caykara Abstract Summary: Temperature-sensitive P(DEAEMA- co -DMAAm) cryogels with five different DMAAm contents were synthesized via a two-step polymerization method, the initial polymerization being conducted for various times at 22,°C, followed by polymerization at ,26,°C for 24 h. The influence of the first-step time and the content of DMAAm on the swelling ratio and network parameters such as the polymer/solvent interaction parameter, the average molecular mass between crosslinks, and the mesh size of the cryogels were reported and discussed. The swelling studies indicated that the swelling increased in the following order: 22C45,>,22C30,>,22C15,>,22C0. The cryogels exhibited swelling/deswelling transitions (reentrant phenomena) in water depending on temperature. These properties were attributed to the macroporous and regularly arranged network of the cryogels. Scanning electron microscope graphs reveal that the macroporous network structure of the cryogels can be adjusted by applying a two-step polymerization. Chemical structure of the P(DEAEMA- co -DMAAm) cryogels. [source] Synthesis of Multiblock Polymer Containing Narrow Polydispersity BlocksMACROMOLECULAR RAPID COMMUNICATIONS, Issue 1 2006Jian Hong Abstract Summary: We have developed a new strategy to prepare multiblock polymers and copolymers via one- or two-step polymerization using a polymerizable cyclic trithiocarbonate (CTTC), 4,7-diphenyl-[1,3]dithiepane-2-thione. CTTC undergoes ring-opening process to incorporate a trithiocarbonate moiety. The trithiocarbonate moiety in turn, functions as a reversible addition fragmentation chain transfer (RAFT) agent. Through this mechanism, multiblock polystyrenes and polystyrene- block - poly(butyl acrylate) copolymers containing various narrow polydispersity blocks can be prepared. Integrated process of ring-opening and RAFT polymerizations involving cyclic trithiocarbonates. [source] | ||||||||||