Poly ureas, structures

Stefanescu, E. A. Stefanescu, C. Huvard, G. S. McHugh, M. A. Influence of co-monomers architecture on the structure of poly urea microcapsules. Polymer Preprints (American Chemical Society, Division of Polymer Chemistry) (2009), 50(2), 506-507. 

The majority of the structures is prepared from AB2 monomers by polycondensation, to result in hb polyesters, polyamides, polyethers, poly(ester amide)s, polysulfones, poly(ether ketone)s, polyphenylenes (among others), and increasingly also by polyaddition leading to, for example, poly(carbosilane)s, poly(urea urethane)s, polyarylenes, poly(ether amide)s or polythioethers, and many others [6-11, 13, 17, 21]. In particular, cycloaddition reactions offer the advantage of an often very selective and clean, high-yield reaction that is not influenced by special functionalities [33]. The relatively easy synthesis of the hb polyphenylenes described by Mullen et al. [34]. is an excellent example of this. In addition, certain cycloaddition reactions form as Hnear units nonstable intermediates, which allows the preparation of hb polymers without any linear units, which therefore exhibit formally a DB of 100% [35]. 

The synthesis of model compounds mimicking the structural characteristics of the possible subunits, and the comparison of their spectra with that of the hb polymer, represents a common method for assigning signals to subunits. This procedure, for the assignment of urea and urethane carbonyl carbon signals of a hb poly(urea urethane) synthesized from an AA (2,4-toluylene diisocyanate) and B2 B (diethanol amine) monomer [94], is shown in Figure 24.3. 

An example of this is shown in Figure 24.8, where the broadly distributed hb poly(ether amide) [134] was fractionated into molar masses of between 60000 and 700 000 g mol . The differences between the polydispersity of the hb sample directly after the one-pot synthesis, and of the individual samples obtained after its fractionation, were clearly distinguished (Figure 24.8). In aU fractionations performed on the hb polymers, independent of their chemical origin - whether polyesters, poly(ether amide)s, or poly(urea urethane)s - it was observed that the solubility had been governed by the molar mass. The question of whether this influence of molar mass is exclusive, or not, should be resolved by an analysis of the DB and the chemical structure of the single fractions. 

Fig. 6 (a) Poly(urea) oligraners structure 2) are conformatiraially more stable than poly(aryla-mides) structure 1) [80]. (b) Structure of poly(phenylene ethynylene) polymers and oligomers [5]. (c) Conformation of poly(phenylene ethynyloie) polymers at the oil-water interface [5]... 

The effect of structural variations in siloxane oligomers in the synthesis and properties of the resulting siloxane-urea copolymers have also been investigated 161). In these studies aminopropyl-terminated poly(dimethyl-diphenyl)siloxane and poly-... 

Urethane hydrolyzes into an amine, an alcohol, and carbon dioxide. So the possible degradation products of a poly(phosphoester-urethane) are diamines, diols, phosphates, carbon dioxide, and even ureas. Urea is possible because the isocyanate is extremely sensitive to moisture, which would convert the isocyanate to an amino group. One is therefore bound to have traces of diamine in the polymerization that leads to a urea bond in the backbone. We think the cytotoxicity seen in the macrophage functional assay comes from the TDI structure. 

First step (a) represents the initial system - solution of the poly(acrylic acid) (urea and formaldehyde are not shown). Then, growing macromolecules of urea-formaldehyde polymer recognize matrix molecules and associate with them forming polycomplex. This process leads to physical network formation and gelation of the system (step b). Further process is accompanied by polycomplex formation to the total saturation of the template molecules by the urea-formaldehyde polymer (step c). Chemical crosslinking makes the polycomplex insoluble and non-separable into the components. In the final step (c), fibrilar structure can be formed by further polycondensation of excess of urea and formaldehyde. 

Properties of composites obtained by template poly condensation of urea and formaldehyde in the presence of poly(acrylic acid) were described by Papisov et al. Products of template polycondensation obtained for 1 1 ratio of template to monomers are typical glasses, but elastic deformation up to 50% at 90°C is quite remarkable. This behavior is quite different from composites polyacrylic acid-urea-formaldehyde polymer obtained by conventional methods. Introduction of polyacrylic acid to the reacting system of urea-formaldehyde, even in a very small quantity (2-5%) leads to fibrilization of the product structure. Materials obtained have a high compressive strength (30-100 kg/cm ). Further polycondensation of the excess of urea and formaldehyde results in fibrillar structure composites. Structure and properties of such composites can be widely varied by changes in initial composition and reaction conditions. 

Chenite, A., and Brisse, F. (1992) Poly(tetrahydrofuran)-urea adduct a structural investigation, Macromolecules, 25, 776-782. 

Yoon [83] studied by X-ray photoelectron spectroscopy the surface structure of segmented poly(ether urethane)s and poly(ether urethane urea)s with various perfluorinated chain extenders and noticed that the surface topography of such polymers depended strongly on the extent of phase separation. 

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