Poly concentrated solution

Formaldehyde is produced and sold as water solutions containing variable amounts of methanol. These solutions are complex equiUbrium mixtures of methylene glycol, CH2(OH)2, poly(oxymethylene glycols), and hemiformals of these glycols. Ultraviolet spectroscopic studies (13—15) iadicate that even ia highly concentrated solutions the content of unhydrated HCHO is <0.04 wt%. 

Analysis for Poly(Ethylene Oxide). Another special analytical method takes advantage of the fact that poly(ethylene oxide) forms a water-insoluble association compound with poly(acryhc acid). This reaction can be used in the analysis of the concentration of poly(ethylene oxide) in a dilute aqueous solution. Ereshly prepared poly(acryhc acid) is added to a solution of unknown poly(ethylene oxide) concentration. A precipitate forms, and its concentration can be measured turbidimetricaHy. Using appropriate caUbration standards, the precipitate concentration can then be converted to concentration of poly(ethylene oxide). The optimum resin concentration in the unknown sample is 0.2—0.4 ppm. Therefore, it is necessary to dilute more concentrated solutions to this range before analysis (97). Low concentrations of poly(ethylene oxide) in water may also be determined by viscometry (98) or by complexation with KI and then titration with Na2S202 (99). 

Licjuid Crystals. Ferroelectric Hquid crystals have been appHed to LCD (Uquid crystal display) because of their quick response (239). Ferroelectric Hquid crystals have chiral components in their molecules, some of which are derived from amino acids (240). Concentrated solutions (10—30%) of a-helix poly(amino acid)s show a lyotropic cholesteric Hquid crystalline phase, and poly(glutamic acid ester) films display a thermotropic phase (241). Their practical appHcations have not been deterrnined. 

Choline is a strong base (pif = 5.06for0.0065-0.0403 Afsolutions ) (3). It crystallizes with difficulty and is usually known as a colorless deHquescent sympy hquid, which absorbs carbon dioxide from the atmosphere. Choline is very soluble in water and in absolute alcohol but insoluble in ether (4). It is stable in dilute solutions but in concentrated solutions tends to decompose at 100°C, giving ethylene glycol, poly(ethylene glycol), and trimetbylamine (5). 

For poly electrolyte solutions with added salt, prior experimental studies found that the intrinsic viscosity decreases with increasing salt concentration. This can be explained by the tertiary electroviscous effect. As more salts are added, the intrachain electrostatic repulsion is weakened by the stronger screening effect of small ions. As a result, the polyelectrolytes are more compact and flexible, leading to a smaller resistance to fluid flow and thus a lower viscosity. For a wormlike-chain model by incorporating the tertiary effect on the chain... 

In their original form these cements came as a zinc oxide powder and a concentrated solution of poly(acrylic acid) (Wilson, 1975b). Since then they have been subject to a number of chemical modifications. 

Ellis and Wilson studied cements formed from concentrated solutions of poly(vinylphosphonic acid) (PVPA) and oxides and silicate glasses, which they termed metal oxide and glass polyphosphonate cements (Wilson ... 

An unusual synthetic approach to PF copolymers was demonstrated by Bunz and coworkers [370], who prepared poly(fluorene ethynylene) 281a-e by metathesis polymerization reaction (Scheme 2.44) [370], The aggregation of polymers 281 in concentrated solutions and in solid state is manifested in slight (up to 10-20 nm) red shift of the absorbance and emission peaks, although solutions and films emit pure blue light. 

As discussed extensively in this chapter, most of the surprising properties of polyelectrolyte dynamics are due to the coupling of counterion dynamics with polymer dynamics. But, there is no adequate understanding of how much of the counterions are mobile and how much are effectively condensed on polymer chain backbone. Theoretical attempts [77, 78] on counterion condensation need to be extended to concentrated poly electrolyte solutions. 

Functionalized organozinc halides are best prepared by direct insertion of zinc dust into alkyl iodides. The insertion reaction is usually performed by addition of a concentrated solution (approx. 3 M) of the alkyl iodide in THF to a suspension of zinc dust activated with a few mol% of 1,2-dibromoethane and MeaSiCl [7]. Primary alkyl iodides react at 40 °C under these conditions, whereas secondary alkyl iodides undergo the zinc insertion process even at room temperature, while allylic bromides and benzylic bromides react under still milder conditions (0 °C to 10 °C). The amount of Wurtz homocoupling products is usually limited, but increases with increased electron density in benzylic or allylic moieties [45]. A range of poly-functional organozinc compounds, such as 69-72, can be prepared under these conditions (Scheme 2.23) [41]. 

Concentration of the polymeric adhesive. In general, the more concentrated the poly-merie adhesive, the lower its bioadhesive strength. The coiled molecules become solvent poor in a concentrated solution which, in turn, reduces the available chain length for interpenetration into the mueus layer. Therefore, a critical concentration of the polymeric adhesive is required for optimum bioadhesion [37]. 

Flory, in 1956, predicted that solutions of rodlike polymers could also exhibit LC behavior. The initial synthetic polymers found to exhibit LC behavior were concentrated solutions of poly(gamma-benzyl glutamate) and poly(gamma-methyl glutamate). These polymers exist in a helical form that can be oriented in one direction into ordered groupings, giving materials with anisotropic properties. 

Indeed, at very high polymer concentrations enhancement of these effects occurs. Recent studies by Franks et al. 23) on the rheological behaviour and freeze fracture electron microscopical analysis of several synthetic linear flexible polymers, including poly(vinylpyrrolidone) and polyethylene glycol) in concentrated solutions, suggest that these molecules do not form a network mesh but rather exhibit aggregation. Anionic polysaccharides, on the other hand, are known to form an anisotropic packing array in condensed films. These films may be stretched to enhance orientation and be used for X-ray diffraction studies... 

The zero-shear viscosity r 0 has been measured for isotropic solutions of various liquid-crystalline polymers over wide ranges of polymer concentration and molecular weight [70,128,132-139]. This quantity is convenient for studying the stiff-chain dynamics in concentrated solution, because its measurement is relatively easy and it is less sensitive to the molecular weight distribution (see below). Here we deal with four stiff-chain polymers well characterized molecu-larly schizophyllan (a triple-helical polysaccharide), xanthan (double-helical ionic polysaccharide), PBLG, and poly (p-phenylene terephthalamide) (PPTA Kevlar). The wormlike chain parameters of these polymers are listed in Tables... 

It is well established that poly(styryl)lithium is predominantly associated into dimers in hydrocarbon solutions (14,15), while it is monomeric in tetrahydrofuran (j ). Furthermore, concentrated solution viscosity measurements have shown that the equilibrium constant (K ) for the process shown in eq l [PSLi = poly(styryl)lithium] ha i value... 

The state of association of poly(dienyl)lithium compounds in hydrocarbon solutions is a matter of current controversy (15-18). Aggregation states of two (.16 and four (.15) have been reported based on light-scattering and concentrated solution viscosity measurements. The most recent concentrated solution viscosity studies ( 1 6 J 7.) > which include results of various endcapping and linking techniques, provide convincing evidence for predominantly dimeric association of poly(isoprenyl)lithium in hydrocarbon solution. The effect of tetrahydrofuran on the degree of association of poly(isoprenyl)lithium has also been examined by concentrated solution viscosity measurements (13). These results indicate that the equilibrium constant for the process shown in eq 3 [PILi = poly(isoprenyl)lithium] exhibits an equilibrium... 

Studies of the triplet-triplet absorption spectrum of P1VN 59) and P2VN 60-61> in degassed fluid solution have shown that triplet annihilation is still important at room temperature. The triplet absorbance of dilute poly(vinylnaphthalene) solutions is only 0.05-0.2 times as large as that of the corresponding ethylnaphthalene solution having the same concentration of naphthyl groups. While quantitative data on kMXX at room temperature are unavailable, the ordinary triplet decay rate kx has been extensively studied for monochromophoric compounds. 

Masuda,T., Toda,N., Aoto,Y, Onogi,S. Viscoelastic properties of concentrated solutions of poly(methyl methacrylate) in diethyl phthalate. Polymer J. (Japan) 3, 315-321... 

Nemoto.N., Ogawa.T., Odani,H., Kurata,M. Shear creep studies of narrow-distribution poly(cis-isoprene). III. Concentrated solutions. Macromolecules 5, 641-644 (1972). 

Stress-strain properties and structure of poly (dimethylsiloxane) networks. Microsymposium on macromolecules Polymer gels and concentrated solutions. Inst, of Macromolecular Chemistry, Prague 1967, E6. 

Preliminary polarizing microscope studies on poly(/ -phenylethyl isocyanide) show the spontaneous reversible formation of a highly birefringent mesophase in concentrated solutions. These observations suggest that small differences in conformations due to concentration changes give rise to the occurrence of a phase separation and molecular ordering. 

Fig. 5. Viscosity of poly-/>-benzamide solutions in dimethyl acetamide/lithium chloride as a function of concentration and intrinsic viscosity 29). Values of intrinsic viscosity are (1) 0.47, (2) 1.12, (3) 1.68, (4) 2.96...

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