Reactions polyaddition

The polyaddition reaction is influenced by the stmcture and functionaHty of the monomers, including the location of substituents in proximity to the reactive isocyanate group (steric hindrance) and the nature of the hydroxyl group (primary or secondary). Impurities also influence the reactivity of the system for example, acid impurities in PMDI require partial neutralization or larger amounts of the basic catalysts. The acidity in PMDI can be reduced by heat or epoxy treatment, which is best conducted in the plant. Addition of small amounts of carboxyHc acid chlorides lowers the reactivity of PMDI or stabilizes isocyanate terrninated prepolymers. 

In the manufacture of highly resident flexible foams and thermoset RIM elastomers, graft or polymer polyols are used. Graft polyols are dispersions of free-radical-polymerized mixtures of acrylonitrile and styrene partially grafted to a polyol. Polymer polyols are available from BASF, Dow, and Union Carbide. In situ polyaddition reaction of isocyanates with amines in a polyol substrate produces PHD (polyhamstoff dispersion) polyols, which are marketed by Bayer (21). In addition, blending of polyether polyols with diethanolamine, followed by reaction with TDI, also affords a urethane/urea dispersion. The polymer or PHD-type polyols increase the load bearing properties and stiffness of flexible foams. Interreactive dispersion polyols are also used in RIM appHcations where elastomers of high modulus, low thermal coefficient of expansion, and improved paintabiUty are needed. 

Polyaddition reactions based on isocyanate-terminated poly(ethylene glycol)s and subsequent block copolymerization with styrene monomer were utilized for the impregnation of wood [54]. Hazer [55] prepared block copolymers containing poly(ethylene adipate) and po-ly(peroxy carbamate) by an addition of the respective isocyanate-terminated prepolymers to polyazoesters. By both bulk and solution polymerization and subsequent thermal polymerization in the presence of a vinyl monomer, multiblock copolymers could be formed. 

Moreover, polyaddition reactions of two low-molecular weight compounds can yield MAIs. Ueda et al. 

Analysis of data pertaining to the modulus of PEO gels obtained by the polyaddition reaction [90] shows that even in this simplified case the network structure substantially deviates from the ideal one. For all samples studied, the molecular weight between crosslinks (M p) exceeds the molecular weight of the precursor (MJ. With decreasing precursor concentration the M xp/Mn ratio increases. Thus, at Mn = 5650 a decrease in precursor concentration from 50 to 20% increases the ratio from 2.3 to 12 most probably due to intramolecular cycle formation. 

The polyaddition reaction in stoichiometric mixtures of glycidyl ethers and bisphenol A resulted in macromolecular chains. Although these chains lack any fixed order in space, their composition is remarkably regular since each epoxy group reacts with one phenol and each phenol group reacts with just one epoxy group (Fig. 2.1) Side reactions are much less favoured. The reaction is essentially complete. 

Provided that they are carried out at temperatures below 100- 120°C, polyaddition reactions between epoxides and carboxylic acids or anhydrides lead to linear... 

Polar protic solvents, 91 Polar substituents, 277 Polk, Malcolm B., 529 Polyaddition reactions, 84-85 Poly(alkylene adipate)s, melting points of, 34... 

Block copolymers containing polysiloxane segments are of great interest as polymeric surfactants and elastomers. Polycondensation and polyaddition reactions of functionally ended prepolymers are usually employed to prepare well-defined block copolymers. The living polystyrene anion reacts with a,co-dichloropoly(dimethyl-siloxane) to form multiblock copolymers398. ... 

Stage 1 Difunctional monomers A, with functional groups called c, react by an alternating polyaddition reaction with an excess mixture of difunctional D and trifunctional T monomers, which all have the same functional groups, called h (and thus are equally reactive), to (mainly) h-terminated prepolymer PI. In some calculations tetra-functional Q monomers with equally reactive h functional groups were present as well. 

More recently, Mullen et al., have worked out very efficient methods for generating highly arylated, branched oligophenylene- and related oligoarylene derivatives, following different synthetic procedures based on polyaddition reactions in the key step. 

The method of migration polymerization (polyaddition reaction) finds extensive application in the production of silicon-, germanium- and tin-containing hetero-organic polymers 97). 

CH2-CH2- amounts to more than 100 1. Isomerization of the allyloxy group is not observed and can be limited to a maximum of 1 mole percent based on spectral data [12], Chain extention by polyaddition reaction can therefore be neglected. 

These are produced by polycondensation of pyromellitic anhydride and p,p -diamino diphenyl ether. The reaction, is carried out in stages. To start with, the reaction is carried out in suitable solvents, like DMF, at around 50°C, when a polyaddition reaction occurs with the formation of polyamic acid as under ... 

For commercial preparation of these polymers polyaddition reaction between a diisocyanate with a diol or triol is very frequently used ... 

The kinetics of polyhydrosailylation reactions has been studied. Quantum-chemical calculations of the model system and data of NMR 1H spectra of the real products of the polyaddition reaction have confirmed probability of passing polyhydrosilylation reaction according to the aforementioned two concurrent directions obtaining both a and (5 adducts. For the evaluation of relative activity for selected monomers the algebraic-chemical approach has been used. 

Andrianov K.A., Gavrikova L.A., Rodionova E.F. Investigation of the polyaddition reaction of oc,ra-divinylalkyl(aryl)siloxane oligomers with a,ra-dihydroalkyl(aryl)-siloxane oligomers. Visokomolekuliarnie soedinenya. (Polymer science) XIII(A), 4 937-939 (1971) (Rus.). 

Random hyperbranched polymers are generally produced by the one-pot polymerization of ABX monomers or macromonomers involving polycondensation, ring opening or polyaddition reactions hence the products usually consist of broad statistical molecular weight distributions. 

Some of the transformations of F into furanic monomers are shown in Scheme 1. In recent years renewed interest in these syntheses has produced much progress in terms of yields, simplicity and economy. Thus, for example, very convenient routes leading to 2-vinylfuran (9) and 2-mryl oxirane (10) have been reported. The structures of the monomers in Scheme 1 simulate those of aliphatic and aromatic counterparts which are the basis of most polyaddition reactions and which are prepared in typical petrochemical operations. The only (but major) difference stems from the presence of the furan ring in each of the structures. 

Isomerization polymerizations are polyaddition reactions where the propagating species rearranges to energetically preferred structures prior to subsequent chain growth. 

Copolyurethanes based on L-arabinitol and 2,2 -dithiodiethanol have been obtained by polyaddition reaction of mixtures of 2,2 -dithiodiethanol (DiT) and 2,3,4-tri-O-methyl-L-arabinitol (9) or 2,3,4-tri-O-benzyl-L-arabinitol (11) to 1,6 hexamethylene diisocyanate (HDI) [118]. 

Galbis and co-workers [113] also obtained a polyurea 100 by polyaddition reaction of the diaminopentitol 39 with 1,6 hexamethylene diisocyanate (HDI). This polymer was a semicrystalline material that showed high melting temperature and thermal stability up to 250°C. 

HA copolymers were prepared by radical copolymerization of HEMA with polyamine macromonomer which had been synthesized by a self-polyaddition reaction of N, N -diethyl-AT-(vinylphenethyI)ethyIenediamine (EDAS) in the presence of lithium diisopropylamide [98-100]... 

The polyaddition reaction is influenced by the structure and functionality of the monomers, including the location of substituents in proximity to the reactive isocyanate group (steric hindrance) and the nature of the hydroxy] group (primary or secondary). Impurities also influence the reactivity of tlie system. 

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... 

Many reactions familiar to organic chemists may be utilized to carry out step polymerizations. Some examples are given in Table 2.2 for polycondensation and in Table 2.3 for polyaddition reactions. These reactions can proceed reversibly or irreversibly. Those involving carbonyls are the most commonly employed for the synthesis of a large number of commercial linear polymers. Chemistries used for polymer network synthesis will be presented in a different way, based on the type of polymer formed (Tables 2.2 and 2.3). Several different conditions may be chosen for the polymerization in solution, in a dispersed phase, or in bulk. For thermosetting polymers the last is generally preferred. 

The polyaddition reaction involves epoxy groups reacting with primary and secondary amines. Amines are the most commonly used curing agents/hard-eners for epoxides. One epoxy ring reacts with each aminoproton ... 

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. 

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. 

The use of alkali-metal amides instead of the amine itself has the advantages of avoiding polyaddition reactions and the need of using an excess of amines (see above). This process has been applied to the synthesis of SMA. A chloromethylsilane was condensed with an amide preformed from an acidic amine function. In general, good yields were obtained.17 81 88 91... 

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

---