Polymers, intramolecular attractions

Excimer emission from polymers continues to attract widespread interest particularly with regard to segmental motion in polymers. Intramolecular excimer formation of me30-2,4-di( N-carbazoyl)pentane dissolved in poly(propylene oxide) is shown to be controlled by... 

The intra- and intermolecular interaction between cationic center and tt-electron system have attracted many chemists and much knowledge on the interaction has been accumulated (1). In 1975, we intended to apply such a kind of interaction to cyclopolymerization. Thus, it is expected that the transition state leading to a strained cyclic unit in the polymerization could be stabilized by the intramolecular attractive interaction between cationic growing-end and ir-system There had been few examples of cyclopolymerizations giving strained units. A paracyclophane unit was employed as a strained cyclic unit in the polymer main chain. In Table I are summarized some cyclophanes with their strain energies. 

In the temperature region near to or less than the 0 temperature, it is no longer valid to use a pseudo-potential, and the detailed structure of the segmental interaction matters. For example, polymers in dilute solutions collapse well below the temperature due to the intramolecular attractive force. The radius of gyration of a fully collapsed polymer depends on the hard core radius bf, of the segment, and will be written as... 

Unmodified ( native ), polymeric membranes often show strong plasticization effects when exposed to high partial pressures of C02, hydrocarbons, or ethylene oxide. Plasticization increases the inter-molecular distance and molecular motion of the polymer chains due to a decrease in inter- and/or intramolecular attractive forces. Consequently, the permeability for all feed components increases, whereas the selectivity decreases. Strong plasticization can even lead to a partial dissolution of the membrane. Hydrocarbons present in natural gas can reduce the selectivity by 30-50% due to plasticization. Plasticization can be limited by cross-linking the polymer chains through either covalent or ionic bonds (Figure 2) but will not be detailed here further (see Ref. 36 instead). - ... 

The question whether the intramolecularly crosslinked microparticles of non-aqueous polymer dispersions are really microgels is also justified, considering non-aqueous dispersions prepared from acrylic copolymers and melamine/formaldehyde crosslinker with particle sizes of about 300 nm. [45, 343]. In any case, these crosslinked polymeric microparticles are useful constituents of high-solids coatings, imparting a yield stress to those solutions which probably involves attractive forces between the microparticles. 

Polysilanes are cr-conjugated polymers composed of Si-Si skeletons and organic pendant groups. They are insulators with filled intramolecular valence bands and empty intramolecular conduction bands. However, because of strong cr conjugation, they have rather narrow band gaps of less than 4 eV [24,25] and are converted to conductors by photoexcitation or by doping electron donors or acceptors. Recently they have attracted much attention because of their potential utility as one-dimensional conductors, nonlinear optical materials, and electroluminescent materials [26-28]. 

Macrosyneresis, in which the network polymer is contained only in one phase is not the only possibility for phase equilibria in networks. Under favorable conditions two polymer phases can coexist in a network with a diluent phase (50). The two polymer phases in equilibrium differ in the conformations of the network chains. The transition resembles the condensation of a real gas or, in macromolecules, an intramolecular transition due to long-range net attraction between segments in a poor solvent (coil-globule type transition [139)). 

The collapse produced in both of these simulations arises from the intramolecular short-range attractive two-body interactions experienced by a polymer in a poor solvent. Another interesting type of collapse was recently proposed/45 then identified in a simulation on a diamond lattice/46 and subsequently verified by experiment with copolymers of acrylamide and V-isopropylacrylamide. 47 This collapse mechanism operates in grafted layers of chains when the short-range binary interactions are repulsive, but higher order interactions in W-clusters are attractive. The value of N is found experimentally to be three for copolymers of acrylamide and /V-isopropylacrylamide, 46 as was assumed in the simulation. 47 ... 

Since the strength of an article made of discrete polymer molecules depends on the sum of intermolecular attractions, it is obvious that any process that increases the extent to which such macromoiccules overlap with each other will result in a stronger product. If the article is oriented, polymer molecules tend to become stretched out and mutually aligned. The number of intermolecular contacts is increased at the expense of intramolecular contacts of segments buried in the normal ball-like conformation of macromolecules. The article will be much stronger in the orienlalion direction. Examples are given below in Section 1.8. 

Both intermolecular and intramolecular additions of carbon radicals to alkenes and alkynes continue to be a widely investigated method for carbon-carbon bond formation and has been the subject of a number of review articles. In particular, the inter- and intra-molecular additions of vinyl, heteroatomic and metal-centred radicals to alkynes have been reported and also the factors which influence the addition reactions of carbon radicals to unsaturated carbon-carbon bonds. The stereochemical outcome of such additions continues to attract interest. The generation and use of alkoxy radicals in both asymmetric cyclizations and skeletal rearrangements has been reviewed and the use of fi ee radical reactions in the stereoselective synthesis of a-amino acid derivatives has appeared in two reports." The stereochemical features and synthetic potential of the [1,2]-Wittig rearrangement has also been reviewed. In addition, a review of some recent applications of free radical chain reactions in organic and polymer synthesis has appeared. The effect of solvent upon the reactions of neutral fi ee radicals has also recently been reviewed. ... 

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