Cyclic polyaddition

Very often graft copolymers have been synthesized by the polyaddition of cyclic monomers, such as ethylene oxide, ethylene imine or caprolactam, to cellulose, proteins, polyamides, polyvinyl alcohol, etc. 

Dendrimers (Newkome et al., 1996) and hyperbranched polymers, HBP, look like functional microgels in their compactness but they differ in two aspects they do not contain cyclic structures and, more importantly, they are much smaller, in the range of a few nanometers in size. They are prepared stepwise in successive generations (dendrimers) or they are obtained by the polyaddition/polycondensation of ABf monomers, where only the A + B reaction is possible (HBP Voit, 2000). Both molecules have tree-like structures, but a large distribution of molar masses exists in the case of HBP. 

The ROP of lactones, cyclic diesters (lactides and glycolides), and cyclic ket-ene acetals is an alternative method, which has been successfully employed to yield high molecular mass polymers under relatively mild conditions. This polyaddition reaction can be carried out with no or very limited side-reactions, and this makes it possible to control properties like molecular weight and molecular weight distribution (MWD). Both polycondensation and ROP have been reported in the literature for the synthesis of polyesters. 

Ring-opening polymerization is different from the addition and condensation polymerizations described so far. It does not produce byproducts (e.g., water) as polycondensation does, and there is no unsaturated double bond in the monomers to lead to additional polymerization. However, some similarities do exist. Ringopening polymerization is initiated by the opening of a cyclic structure in the monomers and followed by polyaddition. As a result, a linear polymer with a chemical composition identical to that of the monomer is obtained. 

Data on MMD (Table 14) indicate that cyclolinear polymers with the most homogeneous structure and composition are formed on the reduced catalyst. The more so, every particular case displays its own optimal type of the reduced form, i.e. catalytic system for synthesizing cyclolinear polymers should be selected with regard to activity of dihydrorganocyclosiloxane in polyaddition reaction. It should be noted that as yellow colloid is applied as the catalyst, the reaction temperature has no ef-fect on the shape of MMD curves for ethyl-substituted polymers with tetra- and hexasiloxane cyclic fragments. 

Reviewed in this paper is synthesis of cyclolinear copolymers with regular disposition of mono-cyclic fragments in dimethylsiloxane backbone using HFC and hydride polyaddition reaction as the methods for synthesis of polymers. 

Besides HFC reaction of preliminarily prepared cyclic organosiloxanes with functional groups and difunctional organosilicon compounds, which give an opportunity to preserve cyclic groups in the polymeric backbone, hydride polyaddition is also widely used, which proceeds under soft conditions and does not involve cyclic structures, introduced into the backbone. 

Thus, synthesis of cyclolinear organosiloxane and carbosiloxane copolymers with monocyclic frag-ments in the backbone, obtained in HFC, hydride polyaddition and polymerization reactions, are considered in this review. The above-shown data on high-molecular polymers with regular dispo-sition of cyclic fragment in the backbone are mainly synthesized by HFC and hydride polyaddition reactions. As for polymerization of bicyclosiloxanes, they are almost useless for high polymer syn-thesis. 

Epoxy resins may be cured in the manner of polyadditions, i. e., homogeneously catalyzed by multifunctional amines and isocyanates, or cyclic anhydride, dicyan-diamide, or biguanide derivatives. On the other hand epoxy resins are also subject to homopolymerization. The catalysts represent Lewis bases, preferably tertiary amines, imidazoles, or ureas (the latter exclusively for the dicyandiamide curing)... 

It is often difficult to make a comparison between the various results obtained for the same polyenes as different reaction conditions (ratio of reactants, temperature, time) were used in each case. The addition of dichlorocarbene (chloroform/base/phase-transfer catalysis) to straight chain and cyclic unconjugated di- and trienes, carried out under identical conditions but varying the catalysts, showed the peculiar properties of tetramethylammonium chloride. Under precisely tailored conditions, either highly selective mono- or polyaddition of dichlorocarbene to the polyenes is possible tetramethylammonium chloride was the most efficient catalyst for monocyclopropanation. (For the unusual properties of tetramethylammonium salts on the phase-transfer catalyzed reaction of chloroform with electrophilic alkenes see Section 1.2.1.4.2.1.8.2. and likewise for the reaction of bromoform with allylic halides, see Section 1.2.1.4.3.1.5.1.). For example, cyclopropanation of 2 with various phase-transfer catalysts to give mixtures of 3, 4, and 5, ° of 6 to give 7 and 8, ° and of 9 to give 10 and 11. °... 

Perhaps the most widely exploited cyclic monomer in reactive processing of composite materials via a stepwise reaction is the oxirane or epoxy group (Hodd, 1989). Epoxy resins are principally used to form three-dimensional networks, but linear polymerization is possible. The main linear polyaddition reactions involve catalysed ring-opening in an ionic chain reaction. However, it is appropriate to consider the chemistry of the oxirane group in its reaction with nucleophilic reagents, principally amines, at this point so that the range of possible reactions may be introduced. 

Tomita, H., Sanda, F., and Endo, T. Structural Analysis of Polyhydroxyurethane Obtained by polyaddition of Bifunctional Five-Membered Cyclic Carbonate and Diamine Based on the Model Reaction, Journal Polymer Sci. A 39 (2001) 851 -859. 

These dimethylsiloxane-bridged ot,(i>dienes can be converted to the previously described reactive silicones by reaction with cyclic dimethylsiloxanes (e.g. D4) as shown in Scheme 4. Since this reaction is possible without cleavage of auxiliary groups these a,o)-dienes are of great interest. Reactive terminal C=C double bonds are generally required to get fast reactions with hydrosiloxanes. For example, it is possible to build up a polymer network from Si-H-functionalized siloxanes via noble-metal-catalyzed polyaddition reactions. Another specific feature of these compounds containing vinylcyclopentane moieties is the low tendency of the terminal double bonds... 

Poly(dimethylsiloxane) and the hydrosilylation polyaddition product were placed in a three-neck flask. After they has been heated to 60 °C 200 ppm of (PNChli was added and the mixture was heated to 100 °C. At a temperature of 80-100 °C poly(dimethylsiloxane-co-methylhydrosiloxane) was mixed with the other components. The equilibration process is accompanied by a visible homogenization and decrease in viscosity of the reaction mixture. The viscosity should reach a value below 180 mm Vs. The equilibration was complete after approximately 2 h and was stopped by neutralization with 1 % (w/w) MgO. After filtration and the removal of low molecular weight cyclic siloxanes in vacuum a fluid transparent oil was obtained and the SiH content was calculated by Si NMR spectroscopy. 

Intramolecular hydrosilylation, leading to cyclic product, competes with polyaddition according to the general scheme (Scheme 34). 

Due to the equilibrium situation of the polyaddition reaction, the conversion of the caprolactam to PA 6 is 89 - 90 %, the rest being monomer and cyclic oligomers. These oligomers must be removed by hot water extraction, in other words washing the chips in a countercurrent demineralised water flow. 

Polymerization by a ring-opening reaction is confined to cyclic monomers which contain at least one heteroatom. The mechanism is very often a polyaddition-type with a product which has a polycondensation-type character. For example, ethylene oxide and other cychc esters can be polymerized into linear chains by this type of reaction. An even more compficated example of this type of polymerization reaction is the polymerization of e-caprolactam into Nylon 6 (PA 6). 

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