Inter-polymer hydrogen bonds

A new convenient polymer modification for synthesis of silanol-containing polymer was developed by the selective oxidation of the Si—H bond with a dimethyldioxirane solution in acetone. The oxyfunctionalization of the silane precursor polymers can be utilized to synthesize a wide variety of silanol-containing polymers. Control over the properties of these silanol polymers, such as stability and self-association of silanols, was realized through the placement of different substitute groups bonded directly to the silicon atom. The miscibility in either polymer blends or polymeric hybrids was achieved by the formation of strong inter-polymer hydrogen bonds between the... 

The basic requirement for cellulose dissolution is that the solvent is capable of interacting with the hydroxyl groups of the AGU, so as to eliminate, at least partially, the strong inter-molecular hydrogen-bonding between the polymer chains. There are two basic schemes for cellulose dissolution (i) Where it results from physical interactions between cellulose and the solvent (ii) where it is achieved via a chemical reaction, leading to covalent bond formation derivatizing solvents . Both routes are addressed in details below. 

Fig. 6.3 shows the empirical Yg values of the different series of condensation polymers characterised by their functional groups as a function of the number of the CH2 groups in the structural unit (Nch2)- It is evident that for all series, except the polyamides, polyurethanes and polyurea s, the slope of the lines is constant, viz. 2.7, the increment of the CH2 group (Fig. 6.3a). Only for the polymers mentioned - all containing hydrogen bonding groups - the slope is 4.3. Networks of inter-molecular hydrogen bonds obviously cause an apparent increase of the CH2 increment from 2.7 to 4.3 (Fig. 6.3b).

Both thiourea (tu) and thiosemicarbazide (tsc) are bifunctional ligands, containing a DD face in addition to one or two co-ordination sites. The reaction of [Zn(tu)4]2+ with a dicarboxylate normally occurs with displacement of thiourea to give coordination polymers of the type [Zn(tu)2(p-dicarboxylate)] in which the chains are cross-linked by DD-AA interactions [157]. The fumarate derivative contains identical inter-plane hydrogen bonding to that observed in (NEt4)2 [fumarate] 2tu [158], in which the zinc atom has formally been replaced by two tetraethylammonium cations. 

The natural crystal is made up from meta-stable Cellulose I with all the cellulose strands parallel and no inter-sheet hydrogen bonding. The reason for this meta-stable crystalline form is that the conversion of glucose into cellulose takes place on the surface of an enzyme having about 30 active sites. As a consequence polymer molecules grow together in the same direction, producing a parallel faces crystal. 

The higher temperature endothermic transitions is related to the break-up of the inter-urethane hydrogen bonds [198]. This series of transitions is representative of the two phases that are present in the polymer and reflect the relative amounts of the HS and SS present. As the percentage of the HS is increased, the peak endothermic temperatures increase. The Tq of the SS increases as the HS content increases. 

Cellulose is a linear chain of ringed glucose molecitles and has a flat ribbon-like conformation. The intra- and inter-chain hydrogen bonding network makes cellulose a relatively stable polymer. These cellulose fibrils contain both crystalhne and amorphous phases, (Fig. l.la-c). 

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