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Step-growth Polymerization (step-growth + polymerization)
Selected AbstractsCyclic Polymers by Kinetically Controlled Step-Growth PolymerizationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 5-6 2003Hans R. Kricheldorf Abstract The theory of step-growth polymerizations including the cascade theory is discussed in the light of new results focussing on the role of cyclization reactions. The identification of cyclic oligomers and polymers in reaction products of step-growth polymerizations has been eased considerably by means of MALDI-TOF mass spectrometry. Experimental examples concern syntheses of polyesters, polycarbonates, polyamides, polyimides, poly(ether sulfone)s, poly(ether ketone)s and polyurethanes. It was found in all cases that the percentage and molecular weight of the cycles increases when the reaction conditions favor high molecular weights. In the absence of side reactions all reaction products will be cycles when conversion approaches 100%. Cyclization may even take place in the nematic phase but even-numbered cycles are favored over odd-numbered ones due to electronic interactions between mesogens aligned in parallel. In contrast to Flory's cascade theory, cyclization also plays a decisive role in polycondensations of abn -type monomers, and at 100% conversion all hyperbranched polymers have a cyclic core. Furthermore, it is demonstrated that in a2+b3 polycondensations intensive cyclization in the early stages of the process has the consequence that either no gelation occurs or the resulting networks consist of cyclic and bicyclic oligomers as building blocks. Finally, a comparison between cyclization of synthetic polymers and biopolymers is discussed. Schematic representation of a network structure mainly consisting of cyclic oligomers and multicyclic building blocks as derived from "a2" + "b3" polycondensation. [source] Protonatable Ionenes for Nucleic Acid ComplexationMACROMOLECULAR BIOSCIENCE, Issue 11 2009Sean M. Ramirez Abstract Novel tboc-protected ionenes with exceeding 30 kDa were prepared from the step-growth polymerization of tert- butyl bis[3-(dimethylamino)propyl]carbamate and 1,12-dibromododecane. The protected ionenes yielded pH-sensitive, protonatable ionenes with pKa,,,6.6 for the conjugate acid of the protonated secondary amine. Polyplexes of the protected and deprotected ionenes, whose cytotoxicity for endothelial cells was analyzed using the MTT assay, efficiently complex plasmid DNA. Polyplexes destabilized cellular membranes as revealed using the lactate dehydrogenase assay at high concentrations. The polyplexes were successfully transfected into HBMECs at mass ratios 2, 4, 8, 12, and 16 (polymer/DNA) at polyplex concentrations less than 10,µg,·,mL,1. [source] Polymeric Photoinitiator Containing In-Chain Thioxanthone and Coinitiator AminesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 6 2004Xuesong Jiang Abstract Summary: A polymeric photoinitiator (PTXP) containing in-chain thioxanthone (TX) and coinitiator amines was synthesized by step-growth polymerization, as well as low-molecular-weight model compounds. Photopolymerizations of methyl methacrylate (MMA) initiated by these photoinitiator systems were studied. Compared with corresponding low-molecular-weight model compounds, PTXP has a similar UV-vis spectrum with a red-shifted maximum absorption, and weaker fluorescence emission, and can photoinitiate the polymerization of MMA more effectively. The structure of PTXP, the photoinitiator synthesized here. [source] Kinetic Modeling of Thiol-Ene Reactions with Both Step and Chain Growth AspectsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 4 2005Oguz Okay Abstract Summary: A kinetic model is presented for thiol-ene cross-linking photopolymerizations including the allowance for chain growth reaction of the ene, i.e., homopolymerization. The kinetic model is based on a description of the average chain lengths derived from differential equations of the type of Smoluchowski coagulation equations. The method of moments was applied to obtain average properties of thiol-ene reaction systems. The model predicts the molecular weight distribution of active and inactive species in the pre-gel regime of thiol-enes, as well as the gel points depending on the synthesis parameters. It is shown that, when no homopolymerization is allowed, the average molecular weights and the gel point conversion are given by the typical equations valid for the step-growth polymerization. Increasing the extent of homopolymerization also increases the average molecular weights and shifts the gel point toward lower conversions and shorter reaction times. It is also shown that the ratio of thiyl radical propagation to the chain transfer kinetic parameter (kp1/ktr) affects the gelation time, tcr. Gelation occurs earlier as the kp1/ktr ratio is increased due to the predominant attack of thiyl radicals on the vinyl groups and formation of more stable carbon radicals. The gel point in thiol-ene reactions is also found to be very sensitive to the extent of cyclization, particularly, if the monomer functionalities are low. Number-average chain length of carbon radicals (solid curves) and thiyl radicals (dashed curves) plotted against the vinyl group conversion, xM, during thiol-ene polymerization. Calculations were for six different kp/ktr ratios. [source] Preparation and characterization of bis- ortho -diynylarene (BODA)-derived submicrogratingsPOLYMER ENGINEERING & SCIENCE, Issue 12 2007Huseyin Zengin The objective of this study was to illustrate how submicrogratings can be prepared from bis- ortho -diynylarene (BODA)-derived polymers. BODA monomers undergo thermal step-growth polymerization and careful control of this conversion, with respect to molecular weight and viscosity, can be used to produce reactive, processable branched polyarlyene intermediates. "Soft-lithography" techniques were used to prepare submicrogratings from these intermediates, which were subsequently stabilized by further polymerization. The surface morphology and dimensions of the submicrogratings were examined using scanning electron microscopy techniques and crystallinity was studied. Reflectivity data was also obtained from linear submicrogratings. These BODA-derived microstructures can be carbonized at 1000°C, or above, to obtain carbonized microstructures with potential for application in optical and electronic microdevices. POLYM. ENG. SCI., 47:2095,2099, 2007. © 2007 Society of Plastics Engineers [source] Cyclic Polymers by Kinetically Controlled Step-Growth PolymerizationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 5-6 2003Hans R. Kricheldorf Abstract The theory of step-growth polymerizations including the cascade theory is discussed in the light of new results focussing on the role of cyclization reactions. The identification of cyclic oligomers and polymers in reaction products of step-growth polymerizations has been eased considerably by means of MALDI-TOF mass spectrometry. Experimental examples concern syntheses of polyesters, polycarbonates, polyamides, polyimides, poly(ether sulfone)s, poly(ether ketone)s and polyurethanes. It was found in all cases that the percentage and molecular weight of the cycles increases when the reaction conditions favor high molecular weights. In the absence of side reactions all reaction products will be cycles when conversion approaches 100%. Cyclization may even take place in the nematic phase but even-numbered cycles are favored over odd-numbered ones due to electronic interactions between mesogens aligned in parallel. In contrast to Flory's cascade theory, cyclization also plays a decisive role in polycondensations of abn -type monomers, and at 100% conversion all hyperbranched polymers have a cyclic core. Furthermore, it is demonstrated that in a2+b3 polycondensations intensive cyclization in the early stages of the process has the consequence that either no gelation occurs or the resulting networks consist of cyclic and bicyclic oligomers as building blocks. Finally, a comparison between cyclization of synthetic polymers and biopolymers is discussed. Schematic representation of a network structure mainly consisting of cyclic oligomers and multicyclic building blocks as derived from "a2" + "b3" polycondensation. [source] What does polycondensation mean?MACROMOLECULAR SYMPOSIA, Issue 1 2003Hans R. Kricheldorf Abstract This contribution has the function of an introduction to the entire volume. It deals with several fundamental definitions and classifications related to the chemistry of polycondensation processes, and it includes modifications of the classical theory of step-growth polymerizations. [source] | ||||||||||