0000001279 00000 n Whether it occurs through an anionic, cationic, or radical mechanism, polymerization of alkenes involves a chain reaction. endstream endobj 406 0 obj<>/Outlines 13 0 R/Metadata 27 0 R/PieceInfo<>>>/Pages 26 0 R/PageLayout/OneColumn/StructTreeRoot 29 0 R/Type/Catalog/Lang(EN)/LastModified(D:20070607142447)/PageLabels 24 0 R>> endobj 407 0 obj<>/Font<>/ProcSet[/PDF/Text]/Properties<>/ExtGState<>>>/Type/Page>> endobj 408 0 obj<> endobj 409 0 obj<> endobj 410 0 obj<> endobj 411 0 obj<> endobj 412 0 obj<> endobj 413 0 obj[/ICCBased 428 0 R] endobj 414 0 obj<> endobj 415 0 obj<> endobj 416 0 obj<> endobj 417 0 obj<> endobj 418 0 obj<>stream Polymeri­ zations were in the first place classified into several classes according to the relative magni­ tude of the rates of the elementary steps. ��s;��``�~� �@,����H�00�z�}(���r�f"� �:B_ The structures and photophysical properties of the separated GNRs were confirmed by … Just by looking at the equation of reaction, we expect that every time a polymer molecule is made, a monomer molecule is used up. 1937, 59, 466-470). This form of the rate law is called the differential rate law, because it is expressed in terms of the rate of change of one thing with the rate of change of the other. startxref 1.Step polymerization 2.Chain polymerization (Faster) • Free radical polymerization Initiation Propagation Termination • Anionic polymerization • Cationic polymerization 4. SO the rate of consumption of reactant functional groups equals the rate of appearance of product functional groups. Thus, we are discussing the degree of polymerization \( \overline{DP} \) and the polymerization rate of step polymerization using these two polymers as examples. It has been shown that the usually assumed maximum value of 2 for PDI can lead to erroneous molecular weight. This set of Polymer Engineering Multiple Choice Questions & Answers (MCQs) focusses on “Kinetics of Step-Growth Polymerization”. For example, polyester formation often involves the substitution of an alcohol functional group at a carboxylic acid, making an ester. Because of a very specific feature of condensation polymerizations, it isn't really the concentration of ethylene glycol or oxalic acid. Step-growth polymerization follows a step-by-step formation of elementary reactions between reactive sites, which are generally functional groups, such as alcohol, acid, and isocyanate. Kinetics of Chain Polymerization The polymerization of alkenes occurs in a very different way than monomers that undergo condensation reactions. Polymer synthesis 3 • Polymers may be formed by two major kinetic schemes. We report on the marked similarity between the self-assembly of metal nanoparticles and reaction-controlled step-growth polymerization. 0000004783 00000 n It was supposed to be linear. This is exponential growth. In contrat to chain-growth, all monomers are reactive. First, dimers, trimmers, and tetramers are formed. Soc. Of course, some chains may be much shorter (Flory actually shows, based on probability, that there will be a number of monomers left over) and as such they contribute less to the overall sample. The Kinetics of Step - Growth Polymerization Flory investigated polyesterifications of the type If youve already forgot that we use As and Bs to represent the monomers reactive functional groups, refresh your memory with the following example So here A-A is a diacid and B-B is a dialcohol 0000005184 00000 n What is the fraction of chains of length x? If we do a little algebra, we get a variation on that piece of information. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Comparing to cyclization of small molecular monomers controlled by both thermodynamics and kinetics, the distance of coupling groups in an individual macromonomer is always more than 20 chemical bonds. Note that, based on the stoichiometry (the ratio of monomers in the equation of reaction), we would probably run this polymerization with equal amounts of diol and dicarboxylic acid. We can take Flory's data again and give it this new treatment. They want to know how the gowth of the polymer chain is progressing. Flory assumed that all steps, that is, the formation of dimers, trimers and so forth, have equal rate constants. 405 31 Flory also established a statistical basis for predicting molecular weights and molecular weight distributions in polymers. This information can tell us how long it will take for a polymer to reach an optimum length. −− −⎡⎤ ⎡⎤ ⎡⎤⎣⎦ ⎣⎦ ⎣⎦ == = =⎡⎣ ⎤⎡ ⎤⎦⎣ ⎦ Assume r =1, where r is the stoichiometric ratio. The rates of step-growth polymerization can be described with Flory 's equal reactivity principle its key characteristics = ⎤⎡... 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