Solubility polymerisation degree

Changes of average polymerisation degree D P and solubility degree Sa vs time of biotransformation process (for cellulase from Aspergillus niger). 

The biotransformation of pulp causes, in comparison to the initial pulp, several changes as follows decrease in the average polymerisation degree and crystalline degree, reduction of hydrogen bonds, increase in intrinsic surface and increase in the solubility in aqueous sodium hydroxide. 

Lignin is water-insoluble and it contains only a few hydrophilic functionalities (primarily the phenolic groups). In order to increase its solubility, aqueous pulping processes therefore seek either to introduce water solubilising groups, or to reduce the degree of polymerisation or both. 

The binders vary quite widely—the most common being starch, soy protein and latexes in conjunction with other soluble polymers. Styrene-butadiene latexes have been the most popular but ethylene-vinyl acetate binders are also used. The method of polymer synthesis provides a way of modifying the properties of the latex. For example, adjustment of the ratio of styrene butadiene in the co-polymer gives rise to different degrees of softness or hardness. This property has a profound influence on the quality of the coating. It is also possible to co-polymerise monomers so as to introduce, for example, carboxy groups on to the surface of the latex particle which in turn assist in... 

Due to the neighbourhood of secondary alcohol groups and remaining hydro-phobic acetyl groups in a not fully hydrolysed polymer, a balanced situation results that dictates the overall water solubility. Temperature plays an important role in that interplay between the intermolecular attracting forces and the polymer water interaction. An optimum in cold water solubility can be observed with a DH of 87-89 mol% for molecular weights between 25,000 and 100,000 Da (degree of polymerisation, DP, 600-2,400). 

Water-in-oil concentrated emulsions have also been utilised in the preparation of polymer latexes, from hydrophilic, water-soluble monomers. Kim and Ruckenstein [178] reported the preparation of polyacrylamide particles from a HIPE of aqueous acrylamide solution in a non-polar organic solvent, such as decane, stabilised by sorbitan monooleate (Span 80). The stability of the emulsion decreased when the weight fraction of acrylamide in the aqueous phase exceeded 0.2, since acrylamide is more hydrophobic than water. Another point of note is that the molecular weights obtained were lower compared to solution polymerisation of acrylamide. This was probably due to a degree of termination by chain transfer from the tertiary hydroxyl groups on the surfactant head group. 

There is an ill-defined boundary between molecular and polymeric covalent substances. It is often possible to recognise discrete molecules in a solid-state structure, but closer scrutiny may reveal intermolecular attractions which are rather stronger than would be consistent with Van der Waals interactions. For example, in crystalline iodine each I atom has as its nearest neighbour another I atom at a distance of 272 pm, a little longer than the I-I distance in the gas-phase molecule (267 pm). However, each I atom has two next-nearest neighbours at 350 and 397 pm. The Van der Waals radius of the I atom is about 215 pm at 430 pm, the optimum balance is struck between the London attraction between two I atoms and their mutual repulsion, in the absence of any other source of bonding. There is therefore some reason to believe that the intermolecular interaction amounts to a degree of polymerisation, and the structure can be viewed as a two-dimensional layer lattice. The shortest I-I distance between layers is 427 pm, consistent with the Van der Waals radius. Elemental iodine behaves in most respects - in its volatility and solubility, for example - as a molecular solid, but it does exhibit incipient metallic properties. 

If the monomers are bifunctional, as in the above example, then a linear polymer is formed. Terminating monofunctional groups will reduce the average degree of polymerisation. Polyfunctional monomers, such as glycerol and phthalic acid, are able to form branching points, which readily leads to irreversible network formation (see Chapter 9). Bakelite, a condensation product of phenol and formaldehyde, is an example of such a space-network polymer. Linear polymers are usually soluble in suitable solvents and are thermoplastic - i.e. they can be softened by heat without decomposition. In contrast, highly condensed network polymers are usually hard, are almost completely insoluble and thermoset - i.e. they cannot be softened by heat without decomposition. 

Crystal appearance and growth are slower in red wines than in white wines and also differ within red wines. Arabinogalactan-proteins and mannoproteins were the major polysaccharides in the precipitates while rhamnogalaturonan II could not be detected. The average degree of polymerisation of proanthocyanidins in the deposit was higher that that of wine proanthocyanidins, indicating that polymers were selectively associated with the tartrate crystals. A preferential association of apolar fiavonols was similarly observed, presumably as their lower solubility favours adsorption on surfaces. 

Due to the limited solubilising power of the substituents, only oligomers (n = 2-6) of the ferf-butylphenyl polymer 96 (Scheme 42) were obtained. The octylphenyl groups in 97 provided much better solubility, so that this polymer was obtained with Mn = 66 400 g/mol, Mw/Mn = 3.86 (measured against a polyphenylene standard), corresponding to a degree of polymerisation of about n = 66 (ca. 200 phenylene rings). 

PTFE has a remarkable range of properties. It possesses the simple monomer unit, -(CFj-CE )-, with a molecular weight of 100, an SG of 2.1-2.3 and a degree of polymerisation of 10 000. PTFE is extremely stable and inert, is not soluble in any known liquid solvent and is unaffected by concentrated acids and alkalis. It will not bum in air, is flexible down to -80 °C and dimensionally stable up to 4-250 °C. It has a low coefficient of friction, good abrasion resistance and has excellent liquid repellency properties. It is predominantly available as a thin membrane that is laminated to one or more textile fabrics. PTFE is thus well suited for use against chemicals and liquids in harsh environments. One of the special uses of the membrane is in a shock-expanded microporous form, which confers high liquid barrier properties with high water vapour permeability. In this form laminates are... 

Diequatorially linked polypyranose structures form fibres when the polysaccharides are undecorated - indeed, oligosaccharides beyond a degree of polymerisation of 6 become almost water insoluble. When, however, the backbone chain is substituted ( decorated ), as it is in the plant hemicelluloses, the decoration interferes with the parallel packing of the chains and much more soluble polymers result. 

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