Poly motivation

A number of examples have been studied in recent years, including liquid sulfur [1-3,8] and selenium [4], poly(o -methylstyrene) [5-7], polymer-like micelles [9,11], and protein filaments [12]. Besides their importance for applications, EP pose a number of basic questions concerning phase transformations, conformational and relaxational properties, dynamics, etc. which distinguish them from conventional dead polymers in which the reaction of polymerization has been terminated. EP motivate intensive research activity in this field at present. 

In Figure 8-1 we show the chemical structure of m-LPPP. The increase in conjugation and the reduction of geometrical defects was the main motivation to incorporate a poly(/ -phenylene)(PPP) backbone into a ladder polymer structure [21]. Due to the side groups attached to the PPP main chain excellent solubility in nonpolar solvents is achieved. This is the prerequisite for producing polymer films of high optical quality. A detailed presentation of the synthesis, sample preparation,... 

The development of a bioerodible implant capable of releasing controlled amounts of a contraceptive steriod from a subcutaneous implant for periods of time ranging from three months to about a year has been in progress for many years. The three principal bioerodible polymers currently in use are copolymers of lactic and glycolic acid (25), poly(e-caprolactone) (26), and poly (ortho esters) (14). The desire to develop such a contraceptive system was the principal motivation for the initial development of the poly(ortho ester) polymer system. 

In this section, we will investigate the surface structure of the electrode in the potential range before a surface or bulk oxide starts forming, and will restrict ourselves to the adsorption of atomic oxygen only (not OH ) [Jacob and Scheffler, 2007]. Furthermore, in our simulations, we assume a single-crystal Pt(lll) electrode, which will be compared with the experimental CV curve (Fig. 5.9) for poly crystalline Pt. This simplification is motivated by the fact that our interest here is to describe the general behavior of the system only. 

Attempts to dope organic semiconductors have been made very early in the field, motivated by the prospect of possibly reaching metallic conductivities [108, 109]. These synthetic metals, however, have not been realized. While p-type doping could be obtained, for example, with iodine gases for poly-p-phenylene vinylene (PPV) derivatives, and n-type doping was demonstrated with sodium for a cyano-derivative of PPV, the doping levels obtained were not stable with time. The dopant molecules readily diffused into the organic semiconductor, yet also out of it. Due to the lack of stability, these approaches were not suitable for commercial applications. 

In 1958, Natta and co-workers polymerized acetylene for the first time by using a Ti-based catalyst. This polymerization proceeds by the insertion mechanism like the polymerization of olefins. Because of the lack of processability and stability, early studies on polyacetylenes were motivated by only theoretical and spectroscopic interests. Thereafter, the discovery of the metallic conductivity of doped polyacetylene in 1977 stimulated research into the chemistry of polyacetylene, and now poly acetylene is recognized as one of the most important conjugated polymers. Many publications are now available about the chemistry and physics of polyacetylene itself. 

Substituted polyacetylenes has been most intensively examined as gas-permeable materials aiming at practical application. These studies are motivated by the extremely high gas permeability of poly(TMSP), ... 

Branching in PVAc, and its influence on various properties of the polymer, have since been extensively studied, notably by Graessley and his co-workers 44,89, 95,177-180), but also by a number of others including Berry and his coworkers 43,59,181,182). There has also been a considerable amount of work in Japan, no doubt motivated by the strong industrial interest in PVAc and poly(vinyl alcohol) in that country Nozakura s paper 183) gives references to previous Japanese work. 

Despite different sequences and repetitive motives, all gliadins have the same secondary structure of loose spirals which are a balanced compromise between the p-spiral and poly-L-proline structure (polyproline helix II) (Parrot et al., 2002), the balance is dependent on temperature, type of solvent, and hydration level (Miles et al., 1991). Similar sequences can be found in other proteins, mainly animal proteins such as elastin and collagen, and they are responsible for particular biomechanical properties connected to reverse P-spirals or p-sheet structures (Tatham and Shewry, 2000). 

The synthesis and characterization of the hydrogenation product of polystyrene (PS), poly(cyclohexylethylene) (PCHE), have been the subject of persistent research efforts. The earliest published report on this material dates to 1929, with new work appearing steadily up to the present. The primary motivation for saturating the phenyl rings in polystyrene is the potential to improve the stability of polystyrene with respect to oxidative and radiation-induced degradation. It has now also been established that the hydrogenation of polystyrene leads to a substantial increase in the glass transition temperature (Tg). 

Retention of Rohrschneider-McReynolds standards of selected chiral alcohols and ketones was measured to determine the thermodynamic selectivity parameters of stationary phases containing (- -)-61 (M = Pr, Eu, Dy, Er, Yb, n = 3, R = Mef) dissolved in poly(dimethylsiloxane) . Separation of selected racemic alcohols and ketones was achieved and the determined values of thermodynamic enantioselectivity were correlated with the molecular structure of the solutes studied. The decrease of the ionic radius of lanthanides induces greater increase of complexation efficiency for the alcohols than for the ketone coordination complexes. The selectivity of the studied stationary phases follows a common trend which is rationalized in terms of opposing electronic and steric effects of the Lewis acid-base interactions between the selected alcohols, ketones and lanthanide chelates. The retention of over fifty solutes on five stationary phases containing 61 (M = Pr, Eu, Dy, Er, Yb, n = 3, R = Mef) dissolved in polydimethylsiloxane were later measured ". The initial motivation for this work was to explore the utility of a solvation parameter model proposed and developed by Abraham and coworkers for complexing stationary phases containing metal coordination centers. Linear solvation... 

Another motivation for measurement of the microhardness of materials is the correlation of microhardness with other mechanical properties. For example, the microhardness value for a pyramid indenter producing plastic flow is approximately three times the yield stress, i.e. // 3T (Tabor, 1951). This is the basic relation between indentation microhardness and bulk properties. It is, however, only applicable to an ideally plastic solid showing no elastic strains. The correlation between H and Y is given in Fig. 1.1 for linear polyethylene (PE) and poly(ethylene terephthalate) (PET) samples with different morphologies. The lower hardness values of 30-45 MPa obtained for melt-crystallized PE materials fall below the /// T cu 3 value, which may be related to a lower stiff-compliant ratio for these lamellar structures (BaM Calleja, 1985b). PE annealed at ca 130 °C... 

In another approach, supramolecular polymers can be formed by planar structures that have the possibility to assemble on both sides of the plane. Here, one structural element is responsible for the formation of the polymer, and chain stoppers are difficult to design. Hence, the DP is completely governed by the association constant and the concentration. As a result of the structural motive, these supramolecular polymers are rather stiff and resemble rodlike poly-... 

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