Branching structure

Figure 6.25 shows the 3q band of FICN in which V3 is the C—FI stretching vibration. The transition is of the type showing clear P- and i -branch structure like a diatomic... 

Branching can to some extent reduce the ability to crystallise. The frequent, but irregular, presence of side groups will interfere with the ability to pack. Branched polyethylenes, such as are made by high-pressure processes, are less crystalline and of lower density than less branched structures prepared using metal oxide catalysts. In extreme cases crystallisation could be almost completely inhibited. (Crystallisation in high-pressure polyethylenes is restricted more by the frequent short branches rather than by the occasional long branch.)... 

Use of trifunctional acids or amines to give branched structures. 

Although the structure of [SsN] has not been established by X-ray crystallography, the vibrational spectra of 30% N-enriched [SsN] suggest an unbranched [SNSS] (5.22) arrangement of atoms in contrast to the branched structure (Dsh) of the isoelectronic [CSs] and the isovalent [NOs] ion (Section 1.2). Mass spectrometric experiments also support the SNSS connectivity in the gas phase.Many metal complexes are known in which the [SsN] ion is chelated to the metal by two sulfur atoms (Section 7.3.3). Indeed the first such complex, Ni(S3N)2, was reported more than twenty years before the discovery of the anion. It was isolated as a very minor product from the reaction of NiCl2 and S4N4 in methanol. However, some of these complexes, e.g., Cu and Ag complexes, may be obtained by metathetical reactions between the [S3N] ion and metal halides. 

FIGURE 7.21 Amylose and amylopectin are the two forms of starch. Note that the linear linkages are o (1 4), but the branches in amylopectin are o (1 6). Branches in polysaccharides can involve any of the hydroxyl groups on the monosaccharide components. Amylopectin is a highly branched structure, with branches occurring every 12 to 30 residues. 

To get an insight into the branched structure of PEs it is important to analyze them for their content and distribution in the macromolecules. The branching analysis of PEs have been reviewed by many workers [13,20,21]. 

Rigo e.t al,6j were the first to propose that head addition does occur but is immediately followed by a 1,2-chlorine atom shift. The viability of 1,2-chlorine atom shifts is well established in model studies and theoretical calculations.64 Experimental support for this occurring during VC polymerization has been provided by NMR studies on reduced PVC /lfl Starnes et a/.61 proposed that head addition is followed by one or two 1,2-chlorine atom shifts to give chloromethyl or dichloroethyl branch structures respectively (Scheme 4.8). There also is kinetic data to support this hypothesis. 

The presence of 1,2-dichloroethyl end groups and branch structures is likely to confuse attempts to determine head-to-head linkages by chemical methods (e.g. iodometric titration68). 

Due to dieir compact, branched structure and to die resulting lack of chain entanglement, dendritic polymers exhibit much lower melt and solution viscosity dian their lineal" counterparts. Low a-values in die Mark-Houwink-Sakurada intrinsic viscosity-molar mass equation have been reported for hyperbranched polyesters.198 199 Dendrimers do not obey diis equation, a maximum being observed in die corresponding log-log viscosity-molar mass curves.200 The lack of chain entanglements, which are responsible for most of the polymer mechanical properties, also explains why hyperbranched polymers cannot be used as diermoplastics for structural applications. Aldiough some crystalline or liquid... 

This has been found to be a general reaction for many types of olefins. It has also been applied to highly branched structures, such as 2,4,4-trimethyl-2-pen-tane and propylene trimers and tetramers [177], to unbranched olefins with internal double bonds, such as methyl oleate [178] and tricosane, and to a-ole-fins [179], In all cases the data indicate that the reaction occurs at the double... 

A branched hydrocarbon C4H10 reacts with chlorine in the presence of light to give two branched structural isomers with the formula C4H9C1. Write the structural formulas of (a) the hydrocarbon (b) the isomeric products. 

FIGURE 19.25 The amylopectin molecule is another component of starch. It has a more highly branched structure than amylose, as emphasized in the inset. 

Ramsey and Dunnill (9) reported the formation of highly branched structures in nylon 6,6 by reacting under anhydrous conditions. According to them this could be prevented by reacting under a blanket of super-heated steam. 

The unique properties of SDIBS are due to the branched structure of the DIB core, and consequently the double-network stmcture in which a covalent network is embedded into a self-assembling thermolabile network, as shown in Figure 7.9. 

The opto-electronic properties of branched structures have been an area of some interest for a number of years, especially as NLO and light-emitting materials [82]. In particular, the use of u-conjugated dendrimers (mono-disperse macromolecules [83]) has flourished for a number of reasons ... 

In sodium bis(2-ethylhexyl) phosphate microemulsions, which are composed of cylindrical micelles in the dilute region, it has been observed that the formation of micellar clusters is characterized by a branched structure as the volume fraction (<1>) of the aggregates increases. At d> > 0.2, these clusters mutually overlap, forming a network expanded overall [283]. 

Experimental data on the solution properties and melt rheology of highly branched structures are scarcely found in the literature. This might be because of the structural nonuniformity of hyperbranched polymers, which makes it difficult to obtain reliable data. Because of the purely statistical nature of the poly-... 

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