Polymer chain intermolecular structure

The cause of noninterpenetration in Vollmert s experiments was left up in the air because of the possibility of thermodynamic (and even steric) incompatibility. Braun (1976) endeavoured to circumvent this ambiguity by carrying out crosslinking reactions on identical polymer molecules. This was based upon the observation that 1,1-diphenylethylene in the presence of sodium metal forms radical anions that rapidly dimerize in quantitative yield. This reaction was applied to poly(l-phenyl-l-(4-vinylphenyl) ethylene-costyrene), which can in principle undergo both intramolecular and intermolecular reactions. Intramolecular reactions cause coil contraction, which is manifest by a decrease in the intrinsic viscosity of the polymer solutions. Intermolecular reactions stiffen the polymer chains, their structure... 

The process proceeds through the reaction of pairs of functional groups which combine to yield the urethane interunit linkage. From the standpoint of both the mechanism and the structure type produced, inclusion of this example with the condensation class clearly is desirable. Later in this chapter other examples will be cited of polymers formed by processes which must be regarded as addition polymerizations, but which possess within the polymer chain recurrent functional groups susceptible to hydrolysis. This situation arises most frequently where a cyclic compound consisting of one or more structural units may be converted to a polymer which is nominally identical with one obtained by intermolecular condensation of a bifunctional monomer e.g., lactide may be converted to a linear polymer... 

The properties of the polycarbonate of bisphenol A are directly related to the structure of the polymer. The molecular stiffness associated with this polycarbonate arises from the presence of the rigid phenyl groups on the molecular chain or backbone of the polymer and the additional presence of two methyl side groups. The transparency of the material arises from the amorphous (noncrystalline) nature of the polymer. A significant crystalline structure is not observed in the polycarbonate of bisphenol A because intermolecular attractions between phenyl groups of neighboring polymer chains in the melt lead to a lack of flexibility of the chains that deters the development of a crystalline structure. 

On the basis of the X-ray structural data as well as the mode of polymerization, Yasuda et al. [3a] proposed a coordination anionic mechanism involving an eight membered transition state for the organolanthanide-initiated polymerization of MM A (Fig. 6). The steric control of the polymerization reaction may be ascribed to the intermolecular repulsion between C(7) and C(9) (or the polymer chain), since completely atactic polymerization occurred when the monomer was methyl or ethyl acrylate. 

Complex formation is important in photophysics. Two terms need to be described here first, an exciplex, which is an excited state complex formed between two different kinds of molecules, one that is excited and the other that is in its grown state second, an excimer, which is similar to exciplex except that the complex is formed between like molecules. Here, we will focus on excimer complexes that form between two like polymer chains or within the same polymer chain. Such complexes are often formed between two aromatic structures. Resonance interactions between aromatic structures, such as two phenyl rings in PS, give a weak intermolecular force formed from attractions between the pi-electrons of the two aromatic entities. Excimers involving such aromatic structures give strong fluorescence. 

The Tg increases as the intermolecular forces in the polymer and the regularity or crystallinity of the polymer chain structure increase. Thus polyvinyl chloride (PVC) has a higher Tg than linear polyethylene (hdpe) because of the presence of dipole-dipole interactions between the chains in PVC. 

It has been suggested that the copper acetylides are coordination polymers, with intermolecular interaction between the C C bonds of the acetylides and copper atoms as shown in (XL) (13). The chains may be broken with tertiary phosphines (PR s) to give complexes of the type [CuC -CR(PR 3)]4. The X-ray structure of the complex [CuC CPh(PMe3)]4 has some very interesting and unexpected features (46a)-, see structure (XL). 

Intermolecular Forces. It is the principal function of the plasticizer to interpose itself between the polymer chains. The main obstacles to this endeavor are the attractive forces between the polymer molecules, which depend on the chemical and physical structure of the polymer. 

Sometimes the estimation of the electronic structures of polymer chains necessitates the inclusion of long-range interactions and intermolecular interactions in the chemical shift calculations. To do so, it is necessary to use a sophisticated theoretical method which can take account of the characteristics of polymers. In this context, the tight-binding molecular orbital(TB MO) theory from the field of solid state physics is used, in the same sense in which it is employed in the LCAO approximation in molecular quantum chemistry to describe the electronic structures of infinite polymers with a periodical structure -11,36). In a polymer chain with linearly bonded monomer units, the potential energy if an electron varies periodically along the chain. In such a system, the wave function vj/ (k) for electrons at a position r can be obtained from Bloch s theorem as follows(36,37) ... 

The occurrence of this chain transfer reaction results in a cis-trans isomerisation of double bonds in the polymer chains however the cis or trans structure of these double bonds has no essential influence on their susceptibility to a backbiting reaction. An important implication of the intermolecular secondary metathesis reaction is, instead, the tendency of the molecular weight distribution in the resulting polymer to attain the equilibrium condition Mw/Mn = 2 [122]. 

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