Polyaddition, polyurethane

The third approaeh to synthetic polymers is of somewhat less commereial importance. There is in fact no universally accepted deseription for the route but the terms rearrangement polymerisation and polyaddition are commonly used. In many respects this process is intermediate between addition and condensation polymerisations. As with the former teehnique there is no moleeule split out but the kinetics are akin to the latter. A typical example is the preparation of polyurethanes by interaction of diols (di-alcohols, glycols) with di-isocyanates Figure 2.7). 

Adhesive-Coated Material. The addition of an adhesive-coated material [335] to proppants decreases the flowback of the particulates. Such adhesive-coated materials can be inorganic or organic fibers, flakes, and the like. The adhesive-coated material interacts mechanically with the proppant particles to prevent the flowback of particulates to the wellbore. The consolidation of a proppant also may occur via a polyurethane coating, which will slowly polymerize after the fracturing treatment because of a polyaddition process [1856]. 

Equations of an analogous type can be used for other polyurethane-forming systems, although the numerical values of the constants may be different, because Eq. (2.29) must be treated primarily as empirical. It is reasonable to expect that an adequate approximation for other systems would be n equal to 2 (which is typical for polyaddition reactions) and m also equals to 2. Such values of the constants m and n are valid, for example, for RIM-2200 (produced by Union Carbide ), which consists basically of polyester and 4.4-diphenylmethane diisocyanate.4... 

Figure 7.6 Schematic representation of hard clusters in (a) a polyurethane network composed of a long diol, a triol, and a diisocyanate (polyaddition reactions, Chapter 2). (b) a hybrid inorganic-organic network composed of a silane end-capped long diol (polycondensation reactions, Chapter 2).

F. Bachmann, J. Reimer, M. Ruppenstein, and J. Thiem, Synthesis of novel polyurethanes and polyureas by polyaddition reactions of dianhydrohexitol configurated diisocyanates, Macromol. Chem. Phys., 202 (2001) 3410-3419. 

Just as alcohols add to isocyanates, diols add to diisocyanates. In a polyaddition reaction polyurethanes are then produced, like the one shown here ... 

This plastic includes a large group of polyaddition polymers which are formed through the reaction of bifunctional or trifunctional alcohols with di- or polyisocyanates. By varying the starting materials, linear as well as crosslinked macromolecules with correspondingly different properties are formed. Alcohols with three functional groups and/or triisocyanate are used to make crosslinked polyurethane elastomers (PUR). 

In contrast to the process of creating a secondary dispersion as was used for the preparation of, e.g., polyurethanes and epoxide resins, it was shown that the miniemulsion polymerization process allows one to mix monomeric components together, and polyaddition and polycondensation reactions can be performed after miniemulsification in the miniemulsified state [125]. 

Fig. 21. a Typical latex obtained in a polyaddition process in miniemulsion (Epikote E828 (bisphenol-A-diglycidylether) and 4,4 -diaminobibenzyl) b TEM micrograph of a polyurethane latex obtained by isophorone diisocyanate and 1,12 dodecanediol... 

Otto Bayer discovers the polyaddition synthesis of polyurethanes and proves that some form of cross linking is necessary for reversible elasticity... 

High-brisance crystalline explosives, such as RDX or octogen, can be embedded in curable or polyadditive plastics such as polysulfides, polybutadiene, acrylic acid, polyurethane, etc. The mixture is then cured into the desired shape. Other components such as aluminum powder can also be incorporated. The products obtained can be of any desired size, and specified mechanical properties can be imparted to them, including rubber-like elasticity (-> LX and -> PBX). They can also be shaped into foils. 

As a third possibility, nanocapsules in a miniemulsion system could be achieved using different interfacial reactions in inverse miniemulsions. The formation of polyurea, polythiourea, and polyurethane nanocapsules synthesized through the polyaddition reaction has been described in detail [110-112], The size of the nanocapsules could be controlled by the amount of surfactant used and the addition time of the diisocyanate. The wall thickness was adjusted by the amount of employed monomers. dsDNA molecules were successfully encapsulated into poly-butylcyanoacrylate (PBCA) nanocapsules by anionic polymerization, which took place at the interface between the miniemulsion droplets and the continuous phase [113]. 

For the polyureas prepared by the polyaddition reaction of uracil and adenine with hexamethylene diisocyanate, and the polyurethanes containing pendant nucleic acid bases, base-base interactions were studied spectroscopically. The polymers were tested further for their anticlotting property84. ... 

As a process characterizing name, the term step polyaddition is preserved for cases where a monomer with multiple bonds is copolymerizing with saturated monomers. The formation of polyurethanes is an example of such a process... 

Although a low molecular weight by-product such as water or alcohol is usually generated by each propagation reaction, polyadditions may also proceed by a step mechanism. For example, no by-product is generated by the reaction of diols and diisocyanates to form polyurethane. Because the product always contains reactive end groups, unless one of the reac-... 

Barrere and Landfester [184] prepared a hybrid miniemulsion in which isophorone diisocyanate was condensation polymerized with dodecanediol to form polyurethane at the same time that the polystyrene or polyBA was free radical polymerized. Unlike previous work, the polyurethane was not prepared in organic solvent in advance. Therefore, in this one-pot synthesis, polyaddition and free radical polymerization both take place in the same particle. HD was used as the costabihzer. After miniemulsification, the polycondensation was allowed to take place, and then a free radical initiator was added to polymerize the styrenic or acrylic monomer. Molecular weight distributions were bimodal the PU had a substantially lower molecular weight than the polyacrylate. Neither intra- nor interparticle phase separation could be detected by TEM the particles appeared to be homogeneous. No measurements of grafting were made, but since there was no unsaturation in the PU, none was expected. 

Polyurethane [117] and polyester [118] particles have also been prepared by the dispersion polyaddition of ethylene glycol (EG) and toluene diisocyanate (TDI) in paraffin, and the polycondensation of acid and ester at a high polymerization temperature, respectively. Table 3 provides an overview of microspheres of monomers other than vinyl monomers obtained by dispersion polymerization. 

Before going into the methods for radical reactions it most be said tlmt polycondensation or polyaddition have led to more industrial preparation. In this connection epoxy resins, the polyurethanes obtained from prepolymers and, more recently, more specialized polymers such as the PEB AC (ATOCHEM), amid-ether or polyimids (KHERIMIDE from RHONE POULENC must be mentioned). Moreover, it is interesting to note that the ionic methods (cationic or anionic ones) have not produced industrial products (except dihydroxy poly (dimethyl siloxanes), poly (tetrahydro-furanes)) but they have facilitated theoretical studies both on the analytical aspects and the materials we can obtain. 

A highly ordered polyurethane with high head-to-tail regularity was prepared by polyaddition reaction of l-isocyanato-2-[(4-isocyanatophenyl)methyl]-benzene with 1,2-ethylene glycol using 1,3-... 

Urethane-forming reaction between isocyanate and hydroxyl group was utilized by Osakada et al. to prepare polyurethane-cyclodextrin pseudoro-taxanes (Scheme 15) [86]. Polyaddition of a diol and MDI in the presence of permethylated a-cyclodextrin or permethylated (5-cyclo dextrin was carried out in DMF for 20 h at 120 °C to yield the pseudopolyrotaxane. The molar... 

Polyurethanes are formed by polyaddition of diisocyanates and dihydroxy components. When, instead of diols, polyhydric alcohols are used, more rigid cross linked polyurethanes are formed. The more OH-functionalities present in the hydroxyl... 

Regarding their curing reaction these adhesive systems differ considerably from the described epoxy and polyurethane adhesives that are characterized by the principle of polyaddition. 

The diisocyanates are used mainly in the manufacture of polyurethanes (PUR). These are produced by polyaddition of diisocyanates and dihydric alcohols, in particular the polyether alcohols (i.e., polyethylene glycols, polypropylene glycols, and the reaction products of propylene oxide with polyhydric alcohols). In addition, oligomeric esters from dicarboxylic acids and diols (polyester alcohols) are also used [91] ... 

Polyurethanes with a few chromophoric hard segment units which do not show phase separation can be obtained by a polyaddition reaction of only a macrodiol and a diisocyanate in nearly stochiometric amount (slight excess of diisocyanate) together with a small amount of a difunctional chromophore (DAAB), counterbalancing the diisocyanate excess. The structure of such polyurethanes investigated here are given in Fig. 13. 

Polyurethanes are macromolecules resulting from the polyaddition of diols and diisocyanates ... 

As mentioned previously, the synthesis of polyurethanes, by the reaction of a diisocyanate (or polyisocyanate) with oligo-diols (or oligo-polyols), is a polyaddition reaction (or step-addition polymerisation), a particular type of polycondensation reaction. There is a great difference between the polycondensation and the polyaddition reactions and the classical radical polymerisation or ionic (living) polymerisation reactions. In radical polymerisations (typical chain reactions), the high MW polymer is formed at the beginning of polymerisation. The reaction system is constituted from monomer and high... 

As in all polycondensation reactions, in polyaddition reactions (for example in polyurethane synthesis), the molar ratio between the reactive group (in our case between [-NCO]/ [hydroxyl groups]), has a very strong influence on the MW of the resulting polyurethane polymer. The maximum MW is obtained at an equimolecular ratio [-NCO]/[OH] = 1 [29]. A small excess of one reactant (isocyanate or hydroxyl groups), drastically reduces the MW of the resulting polyurethane (Figure 2.7). 

---