Linear polymers polarity

Melt viscosity is lower dian the one of corresponding linear polymers, but polar endgroups can increase die viscosity by several orders of magnitude. 

The presence of a large number of chain-ends in the fully synthesized dendrimer molecules makes them highly soluble and also readily miscible, for example with other dendrimer solutions. The solubility is controlled by the nature of the end-groups, so that dendrimers with hydrophilic groups, such as hydroxyl or carboxylic acid, at the ends of the branches are soluble in polar solvents, whereas dendrimers with hydrophobic end-groups are soluble in non-polar solvents. The density of the end-groups at the surface of the dendrimer molecule means that they have proportionately more influence on the solubility than in linear polymers. Hence a dendritic polyester has been shown to be more soluble in tetrahydrofuran than an equivalent linear polyester. 

Linear polymers, polystyrene and cellulose triacetate exhibit differences in hydrodynamic behavior in solution. Cellulose and its derivatives are known to have highly extended and stiff chain molecules below a Dp of about 300, but as the Dp Increases above 300 the chain tends to assume the character of a random coll (27,28). The assumption that hydrodynamic volume control fractionation in GPC may not be true for polystyrene and cellulose triacetate, though it has been found satisfactory for non-polar polymers in good solvents (29). 

The density of the hydroxyfunctional hyperbranched polyesters is 1.295 g cm" and pressure-volume-temperature (PVT) measurements show that the thermal expansion and compressibility are slightly lower compared to polar linear polymers, such as PVC, poly(e-caprolactone), and poly(epichlorohydrine). ... 

As mentioned before, problems with monomers with functionalities with acid hydrogen have been encountered with some types of catalysts. Now, the direct incorporation of polar functional groups along the backbone of linear polymers made via ROMP is possible due to the development of functional group-tolerant late transition metal olefin metathesis catalysts (10). 

Chitosan is a cationic polysaccharide produced from the deacetylation of chitin, a component of crab and shrimp shells [7,57,58], Chitin is composed of units of 2-deoxy-2-(acetylamino) glucose joined by glycosidic bonds that form a linear polymer. Ilium et al. [7,57,58] demonstrated the ability of chitosan to increase the bioavailability of insulin and other small peptides and polar macromolecules in different animal models. In both the sheep and rat models, the addition of chitosan at concentrations of 0.2%-0.5% to nasal formulations of insulin resulted in significant increases in plasma insulin and reductions in blood glucose. Reversibility studies indicated that the effect of chitosan on the nasal absorption of insulin... 

Linear polarization, and NLO properties, 12, 102 Linear polymers, siloxanes, synthesis, 3, 660 Linkage isomerism, for photochromic behavior, 1, 245 Linked cages, metallacarboranes, 3, 245 Linkers, traceless, chromium carbonyls as, 5, 251 Lipids, in bioorganometallic chemistry, 1, 904 Liquefied noble gases, in low-temperature infrared studies, 1, 264... 

Tubulin is a 110-kDa heterodimeric protein composed of two subunits a- and P- (-450 amino acids each) and it is the basic subunit of MT. MT are hollow cylindrical protein fibers formed by the lateral association of protofilaments, where each protofilament is a linear polymer of tubulin heterodimers that are bound head to tail. The parallel arrangement of protofilament forms the cylindrical MT wall. Typically, MT contain 13 protofilaments in cross-section aligned with the same polarity. The two ends of a MT are not identical. The minus end is crowned by a-tubulin subunits and serves as the site of nucleation at the centrosome, while the plus end is crowned by P-tubulin subunits and faces outward from the nucleus to the plasma membrane. The repeating subunits are held together in the polymers by non-covalent interactions [4-6],... 

The type of cleavage of the alkyl titanium bond is certainly dependent upon the titanium valence state. Tetravalent compounds will tend to cleave homolytically, but heterolytic cleavage will become more favorable at the lower valence states because of higher bond polarity (290). Ethylene polymerization takes place more readily on alkyl vanadium compounds than on alkyl titanium compounds and yields higher molecular weight linear polymer (340). This is attributable to the fact that... 

For polymer chemists it is interesting to know how well-known linear polymers can be linked with dendritic architectures and what the supramolecular consequences of this approach might be. Combination of dendrimers with linear polymers in hybrid linear-dendritic block copolymers has been employed to achieve particular self-assembly effects. Block copolymers with a linear polyethylene oxide block and dendritic polybenzylether block form large micellar structures in solution that depend on the size (i.e., the generation) of the dendritic block [10]. Amphiphilic block copolymers have been prepared by the combination of a linear, apolar polystyrene chain with a polar, hydrophilic poly(propylene imine) dendrimer [11] as well as PEO with Boc-substituted poly-a, -L-lysine dendrimers, respectively [12]. Such block copolymers form large spherical and cylindrical micelles in solution and have been described as superamphi-philes and hydra-amphiphiles , respectively. 

A similar technique is used in the industrial preparation of polarizing films. Amon and Kane21) impregnated an organic plastic film successively with solutions of rubean-ate and copper salts to synthesize linear polymers in this film. These polymers become oriented to give the polarizing film when the latter is stretched in one direction. 

Historically, high-pressure free radical copolymerization has been used to produce highly branched, ill-defined copolymers of ethylene and various polar monomers. Although these materials are in production and extensively used throughout the world, the controlled incorporation of polar functionality coupled with linear polymer structure is still desired to improve material properties. Recent focus in this area has led to the development of new transition metal catalysts for ethylene copolymerization however, due to the electro-philicity of the metal centers in these catalysts, polar functional groups often coordinate with the metal center, effectively poisoning the catalyst. There has b een some success, but comonomer incorporation is hard to control, leading to end-functionalized, branched polyethylenes [44, 46]. These results are undesirable due to low incorporation of polar monomer into the polymer as well... 

Typical polymer hosts have Lewis-base sites and include the simple linear polymers PEO, PPO, and poly(ethyleneimine), and a munber of comb polymers, in which oligoether side chains are built on a flexible backbone. A tremendous variety of polymer electrolytes can be prepared. Not only can the anion and cation of the salt be varied, but a wide range of polar polymers that might be suitable hosts for salts can be envisioned. 

Non-linear Electric Polarization. Consider a polymer or colloidal solution so dilute that interaction between the macromolecules or particles can be omitted. Also, assume the solvent not to afiect their properties. On these assumptions, the electric polarization of the system is given by (251), with the total dipole moment of the macromolecule />( <,) given in a linear approximation by (248). Of particular rdevance is the polarization component in the field direction ... 

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