Polymers Large molecules stereoregular

The most common states of a pure substance are solid, liquid, or gas (vapor), state property See state function. state symbol A symbol (abbreviation) denoting the state of a species. Examples s (solid) I (liquid) g (gas) aq (aqueous solution), statistical entropy The entropy calculated from statistical thermodynamics S = k In W. statistical thermodynamics The interpretation of the laws of thermodynamics in terms of the behavior of large numbers of atoms and molecules, steady-state approximation The assumption that the net rate of formation of reaction intermediates is 0. Stefan-Boltzmann law The total intensity of radiation emitted by a heated black body is proportional to the fourth power of the absolute temperature, stereoisomers Isomers in which atoms have the same partners arranged differently in space, stereoregular polymer A polymer in which each unit or pair of repeating units has the same relative orientation, steric factor (P) An empirical factor that takes into account the steric requirement of a reaction, steric requirement A constraint on an elementary reaction in which the successful collision of two molecules depends on their relative orientation. 

A considerable number of papers describe the resulting molecules from the pyrolysis of polystyrene [2-26], etc. These studies include pyrolysis in inert conditions, in the presence of various catalysts [4], in the presence of carbon black [27], pyrolysis of H-T and H-H polymers, pyrolysis of polymers with different average molecular weights, pyrolysis of stereoregular polystyrene [28], pyrolysis of polystyrene obtained by controlled radical polymerization in the presence of 2,2,6,6-tetramethylpiperidine-N-oxyl (stable nitroxide) [29], pyrolysis in the presence of water in subcritical conditions [30], pyrolytic studies for the understanding of large scale processes [31-36], etc. 

Due to the large size of the calixarene molecules, they were also used for the synthesis of stereoregular polymers. Thus, neodymium complex containing the calixarene 32 was active in the formation of isotactic polypropylene oxide (Scheme 4.20) [80]. 

In the last two decades, the rare earth compounds have importantly contributed to the development of polymerization catalysis [6]. Rare earth derivatives are very versatile catalysts that are able to polymerize with high efficiency a large variety of monomers, from olefinic ones to acrylates, and cyclic polar molecules. Controlled polymerization leading to stereoregular polymers and living processes with polymers yielding well-defined macromolecular characteristics giving rise to the preparation of sequenced copolymers are now quite commonly reachable. 

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