Polymers monomeric structures

T], rj ). A molecular weight determination for the complex supports a monomeric structure in solution. Reaction of ZnMe2 with (H0)2Si(0 Bu)2 leads to the formation of polymeric species, [Zn0Si(0 Bu)20] , that are soluble in organic solvents [107]. For comparison, the zinc sUoxane polymer [Zn0SiPh20] reported by Hornbraker and Conrad is an insoluble material contaminated with ZnO [108]. 

In addition to alternating polymers, other structures are known in which the monomeric units appear in an ordered sequence. Examples are ... 

No rational monomeric structure can be devised to fit these data. Actually, SbF6 is a very viscous liquid and it must be significantly associated. Cyclic or linear polymers could be formed by association through trans fluorine bridge bonds. However, this type of polymer would have as the recurring unit... 

This suggestion was supported by experiments. First, the polymerization catalyzed by the hexamethylphosphoramide complex, which has a monomeric structure, gave a high yield of isotactic polymer even... 

The amino alcohol-catalyzed enantioselective addition of dialkylzincs to aldehydes, detailed in Chapter 5 (27), is accomplished with polymer catalysts containing DAIB, a camphor-derived auxiliary, and other chiral amino alcohols (28). Reactions that involve matrix isolation of the catalyst not only result in operational simplicity but also greatly facilitate understanding of the reaction mechanism. In solution, the catalytic chiral alkylzinc alkoxide derived from a dialkylzinc and DAIB exists primarily as dimer (27) however, when immobilized, its monomeric structure can be maintained. 

The behaviour in solution of dimethyltin(IV) complexes containing different aminopoly-carboxylic acids were also investigated293,294. The X-ray crystal structure analyses of the tin complexes with IV-methyliminodiacetate (mida), pyridine-2,6-dicarboxylate (pdc) and ethylenediamine-iV.iV -di acetate (edda) revealed dimeric structures for the first two compounds and a monomeric structure for the complex dimethyltin (edda). In contrast, the dimethyltin(IV) complex (137) with ethylcncdiarninc-/V,/V,iV, /V -tetraacetate (edta) and water is a polymer in which each tin atom adopts a distorted pentagonal-bipyramidal configuration with the two methyl groups in axial positions. 

The second method separates the functional groups into two monomers, which facilitates synthetic work and offers greater choices to monomeric structure. In the first step, A2 and B3 monomers couple together to form an AB2-type dimer that continues to react to form the hyperbranched architecture (Scheme 6). This is the case, only if the molar ratio of A2 to B3 is 1 1 and the initiation is considerably faster than the propagation [29]. It becomes immediately clear that the resultant structure is highly dependant on the type of monomers and the polymerization conditions. For the latter, it has been found that the mode of monomer addition plays a crucial role. Whereas the addition of a B3 monomer into a solution of A2 yields insoluble polymer gel, the opposite addition mode furnishes hyperbranched polymers with excellent solubility [30]. 

For n = 6, known compounds are confined to methylamine and ethylamine these are probably [MnA6]X2 species. Tetrakis species are better defined here than for NH3 and probably have [MnX2A4] monomeric structures but the most common stoichiometry is MnX2A2. These latter species probably have the linear polymer structure of (8). 

Co-units constituted by a Mannich ba.se may also be present to a limited extent, as modifiers or residual initiators- (390 and 392), in the macromolecular chain originated by other different monomeric species (Z). In addition, when the polymerizable moieties arc located in both the R and R residues of the Mannich base, polymers of structure 393 are formed, along with branched as well as crosslinked derivatives. 

Bamberger was able to isolate a low molecular weight polymer having a composition corresponding to a quinonoid monomeric structure 62 from -tolyl azide. 

The considerable importance of copolymers for practical purposes generated a considerable number of studies dedicated to thermal stability and pyrolysis of copolymers (see e.g. [10-15]). The presence of two or more monomeric structures in a macromolecule can influence significantly the thermal behavior and the composition of its pyrolysate. Depending on the ratio of the comonomers, as well as on the structure of the polymer (random, alt, block, graft, etc ), the pyrolysis output can be very different. Based on this, pyrolysis results are frequently used for the analysis of copolymer structures. 

Case 1. Both Monomeric Structural Unit and Polymer Display an Enantlotroplc Mesophase... 

Case 2. The Monomeric Structural Unit Displays a Virtual or a Monotropic Mesophase The Polymer Displays a Monotropic or an Enan-tlotropic Mesophase... 

The Commission on Macromolecular Nomenclature defined 52 terms related to polymer structure, including polymer, constitutional units, monomer, polymerization, regular polymer, tactic polymer, block polymer, graft polymer, monomeric unit, degree of polymerization, addition polymerization, condensation polymerization, homopolymer. 

Synthesis of highly crowded graft copolymers with graft frequencies of up to 50% of the total monomeric units in approximately alternate positions on the polymer backbone (structure 24). 

Light-emitting polymers generally share a conjugated structure along the polymer backbone. The 7t-electrons are delocalized, which is the precondition for the conductivity of the polymer. The structure of conjugated polymer is easily tuned by different methods. Modification of monomeric units can improve the solubility of the polymer and regulate the... 

The fluorescence spectra were recorded as powder coatings on paper. Neither the monomeric structures 5, 6 and 7, nor the polymers 8 and 9, show any noticeable PL. Just polymer 10 exhibits a broad, but very weak, PL centered around 420 nm. The fact that S, 6 and 7 do not exhibit any PL confirms our previous results in attributing the fluorescence of our materials to both (1) their polymeric structure and (2) the presence of silicon rings. The absence of PL for the polymers 8 and 9 very likely showing linear structures (compare Scheme 5) leads us to consider both of the above conditions (1) and (2) as necessary but not sufficient. Additionally, the existence of a higherdimensional network as present in polymer 10 seems to be necessary to bring about fluorescence in the type of compounds investigated in this study. 

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