Polymerization head-to-tail

Terpenoid (Chapter 6 Focus On. Section 27.5) A lipid that is formally derived by head-to-tail polymerization of iso-prene units. 

The results presented above indicate that the previously unknown head-to-tail polymerization is the major reaction product of the iminium methide species. To investigate the generality of this reaction, we next studied a neutral ene-imine species shown in Scheme 7.9.48 As illustrated in this scheme, the generation of this reactive species requires quinone reduction followed by elimination of acetic acid. The ene-imine is structurally related to the methyleneindolenine reactive species that is a metabolic oxidation product of 3-methylindole (Scheme 7.9).57 59... 

Head-to-tail polymerization of propylene produces a polymer in which every other atom is a stereocenter. 

Before the mechanism of vinyl polymerization was understood, the question of the structure of vinyl polymers was of considerable interest. Staudinger had written these polymers as having a head-to-tail arrangement of recurring units, but he had not really furnished evidence of the structure. As Carothers once said, Staudinger had assigned the structure by pronouncement. He was as usual correct, and chemical evidence was developed to establish such structures. For example, when monovinyl methyl ketone polymerized, it could produce by head-to-head, tail-to-tail reaction a 1,4-diketone. By head-to-tail polymerization it would give a 1,5-diketone. These two types have different reactions. The study of the polymer proper showed that the polymer was a 1,5-diketone. In the case of polyvinyl chloride, a head-to-head, tail-to-tail polymerization would lead to a 1,2-dihalide compound, and a head-to-tail polymerization would lead to a 1,3-dihalide. 

HEAD-TO-TAIL POLYMERIZATION ACTIN ASSEMBLY KINETICS MICROTUBULE ASSEMBLY KINETICS Heat and matter transfer,... 

Wegner, A. 1976. Head to tail polymerization of actin. J Mol Biol. 108 139—50. 

IQ. Unusual Head-to-Tail Polymerizations 1. Cationic Intra-Intermolecular Polymerizations... 

The reagent will always react with the end carbon atom because then the conjugation of the n electrons of the phenyl or carbonyl group with the free electron, the sextet or the free pair on the a-carbon atom, remains intact. The predominant head to tail polymerization is therefore produced. 

In radical polymerization, the more substituted radical always adds to the less substituted end of the monomer, a process called head-to-tail polymerization. 

A similar study was carried out by the same group [17] on propene oxide (PO) polymerization. In this case unsaturation was developed in the polymer due to a transfer reaction, but for the most part a standard head to tail polymerization occurred. At 80°C using NaOMe initiator and essentially bulk monomer, the second order rate coefficient reported was approximately 2.6 x 10" Imole" sec". The activation energy in this case was 17.4 kcal mole". ... 

These (+)-catechin polymers arise from repeated condensation reactions between the A ring of one unit and the B ring of another, through a mechanism which is known as head to tail polymerization (Scheme XXI). 

Dehydrodicatechin B4 (XLIII), a dimer resulting from (+)-catechin head to tail polymerization (Scheme XXI, continuation), is the precursor of dehydrodicatechin A (XLIV), which is derived from the former through a single step involving enzymatic oxidation followed by an internal stabilization via two intramolecular nucleophilic additions (Scheme XXII). 

Stereoisomerism refers to molecular species that have the same composition and bond sequence but a different arrangement in space of their atoms. Stereoisomers that are characterized by different interatomic distances between certain atoms that are not bound directly are called diastereoisomers. Examples of diastereoisomers are cis-trans isomers of compounds containing C = C bonds and syn-anti isomers of compounds containing C = N bonds. Other diastereoisomers are not based on the presence of a double bond. For example, a molecule with more than one tetrahedral carbon that has different substituents may form diastereoisomers. For example, for a head-to-tail polymerized monosubstituted vinyl monomer, there are three possible structures indicated as isotactic, syndiotactic and atactic, which are schematically shown below ... 

Solubilities, Processabilities, and Head-to-Tail Polymerization of Liquid-Crystalline Polymers, Including First Super-Strong Polymers... 

The theories in this paper are first-principles statistical mechanics theories used to calculate static thermodynamic and molecular ordering properties (including solubilities of LCPs in various kinds of solvents) and dynamic properties (diffusion from Brownian motion). The diffusion of the LCP molecules constitutes a lower limit for the speed of processing of the LCPs. The static theory is used to calculate the packing of the bulky relatively rigid side chains of SS LCPs these calculations indicate that head-to-tail polymerization of the monomers of these SS LCPs will be very strongly favored. The intermolecular energies and forces calculated from the static theory are used in the dynamic theory. 

For some of the first theoretically designed candidate SS LCPs, new results are now presented for (1) enhanced solubilities of the molecules (compared with backbone LCPs) in nonpolymeric LC solvents calculated using the static theory, (2) diffusion (i.e., lower limit of processability) of the molecules calculated using the dynamic theory, and (3) head-to-tail polymerization of the monomers predicted from the packing of the bulky relatively rigid side chains of the molecules as calculated using the static theory. Melt processability of some SS LCPs is also discussed. 

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