Polyaddition

We shall first consider polyaddition, such as occurs in the polymerization of ethylene and other vinyl compounds. We can recognize three essential processes initiation, propagation and termination. A fourth process, chain transfer, takes place as a rule, but it is not always important. 

In all polymerizations, a cat yst or initiator starts the reaction. In the initiation an active molecule (e.g., a free radical, or an ion) is formed  

When ionic polymerizations are carried out in apolar media, the positive and negative ions stay together as pairs. 

In some polymerizations the catalyst is an active complex (usually a metal-organic complex), that is added as such, or that is formed in the reactor from two catalyst components. We shall indicate radicals, ions (positive or negative) and active complexes with an asterisk X. In most polymerizations, the monomer contains a double bond, that is attacked by the active group X, that adds to it, resulting in another active group. The addition of the first monomer molecule M is then c ed the initiation  

The process goes on as a chain reaction. This is called the propagation M M 

In contrast to the process of creating a secondary dispersion (as for the preparation of polyurethanes and epoxide resins), it was shown that the miniemulsion polymerization process would allow monomeric components to be mixed together, and that the polyaddition and polycondensation reactions could be performed after miniemulsification in the miniemulsified state [24]. 

The principle of miniemulsion polymerization to polyadditions of epoxy-resins was successfully transferred to mixtures of different epoxides with varying diamines, dithiols, or diols heated to 60 °C to form the respective polymers [24]. One requirement to formulate miniemulsions is that both components of the polyaddition reaction have a relatively low water solubility (at least one with solubihty 10-5 g L-i)  

It has been shown that the use of hydrophobic organo-tin catalysts, a solvent of the polyaddition medium or an off-stoichiometric ratio of the isocyanate and the diol component allows a considerable increase in the molecular weight of the polymer. It was also shown that hybrid polymer nanoparticles based on polystyrene/ polyurethane (PS/PU) or poly(butyl acrylate)/polyurethane (PBA/PU) can be synthesized using a one-pot procedure [26]. 

Polyaddition was also performed using chitosan as a stabilizer (for further details, see Section 2.5) [27]. 

If A is an oxygen atom, polyepoxides are obtained if the ring reacts with another bifunctional group like diols, diamines or carbonic acid anhydrides, epoxy resins are formed. 

The characteristic of these processes closely follows those of polycondensation reactions thus, a stepwise growth with all the limitations as described in Section 2.3.2 can be observed. An advantage - also from an environmental point of view - is that there are no low molecular weight products formed. 

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The second category of polymerization reactions does not involve a chain reaction and is divided into two groups poly addition and poly condensation [4]. In botli reactions, tire growth of a polymer chains proceeds by reactions between molecules of all degrees of polymerization. In polycondensations a low-molecular-weight product L is eliminated, while polyadditions occur witliout elimination ... 

The addition polymerization of diisocyanates with macroglycols to produce urethane polymers was pioneered in 1937 (1). The rapid formation of high molecular weight urethane polymers from Hquid monomers, which occurs even at ambient temperature, is a unique feature of the polyaddition process, yielding products that range from cross-linked networks to linear fibers and elastomers. The enormous versatility of the polyaddition process allowed the manufacture of a myriad of products for a wide variety of appHcations. 

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. 

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). 

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. 

Realizing a wide range of selection of composing members including vinyl polymers, polycondensation polymers, and polyaddition polymers, which opens a variety of application areas in the polymer manufacturing and processing industries. 

Among other approaches to the synthesis of SAH are also reactions in the polymer chains and polyaddition. 

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 field has been subdivided according to the classical polycondensation-polyaddition structure. Polyaddition products have in turn been classified in two broad categories,... 

In conclusion, furan and 2-alkylfurans can be polymerized only by acidic initiators or by y-radiation because the other standard methods of polyaddition fail to induce a chain-propagation reaction. 

While the products of 2-furaldehyde polymerization by heat are branched polycondensates with highly conjugated structures (see Section Il-C), the photopolymerization of this furan derivative gives a linear polyaddition product 24>7S). 

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... 

Another family of polyols is the filled polyols.llb There are several types, but die polymer polyols are die most common. These are standard polyether polyols in which have been polymerized styrene, acrylonitrile, or a copolymer thereof. The resultant colloidal dispersions of micrometer-size particles are phase stable and usually contain 20-50% solids by weight. The primary application for these polyols is in dexible foams where the polymer filler serves to increase foam hardness and load-bearing capacity. Other filled polyol types diat have been developed and used commercially (mainly to compete with die preeminent polymer polyols) include the polyurea-based PEID (polyhamstoff dispersion) polyols and the urethane-based PIPA (poly isocyanate polyaddition) polyols. 

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. 

Diamine 108 led to 95% ee for the alkylation of l,3-diphenyl-2-propenyl acetate with 90% yield. By polycondensation with a diacid chloride or polyaddition with a diisocyanate, this ligand led, respectively, to an insoluble poly(amide) 109 or poly(urea) 110 with excellent yields. Poly(amide) 109 gave a better ee (80%) than poly(urea) 110 (38%), albeit with a lower conversion (respectively, 38 and 72%), when they were used as palladium hgands... 

Beside the polymerization routes of 1,3-cyclohexadiene derivatives repetitive Diels-Alder polyadditions were widely used to prepare arylated PPPs. Stille et al. developed a set of suitable monomers (1,4-diethynylbenzene and 1,4-phenyl-ene-bis(triphenylcyclopentadienone) derivatives) to generate phenylated PPPs (e.g. 17) with molecular weights of 20,000-100,000 [31]. Unfortunately, the repetitive polyadditon does not proceed regioselectively polymers containing para-as well as mefa-phenylene units within the main chain skeleton are formed. 

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. 

Polycondensation pol5mers, like polyesters or polyamides, are obtained by condensation reactions of monomers, which entail elimination of small molecules (e.g. water or a hydrogen halide), usually under acid/ base catalysis conditions. Polyolefins and polyacrylates are typical polyaddition products, which can be obtained by radical, ionic and transition metal catalyzed polymerization. The process usually requires an initiator (a radical precursor, a salt, electromagnetic radiation) or a catalyst (a transition metal). Cross-linked polyaddition pol5mers have been almost exclusively used so far as catalytic supports, in academic research, with few exceptions (for examples of metal catalysts on polyamides see Ref. [95-98]). 

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