Poly addition

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 difficulties encountered in the early studies of anionic polymerization of methyl methacrylate arose from the unfortunate choice of experimental conditions the use of hydrocarbon solvents and of lithium alkyl initiators. The latter are strong bases. Even at —60 °C they not only initiate the conventional vinyl poly-addition, but attack also the ester group of the monomer yielding a vinyl ketone1, a very reactive monomer, and alkoxide 23). Such a process is described by the scheme. 

The early work of Wessely suggested the occurrence of some side reactions which led to the formation of diketopiperazines (77) or hydan-toins (27). These reactions may put an upper limit to the degree of polymerisation which may be obtained in poly-additions of NCA s but it is more probable that these products arise from an unsuccessful initiation (see p. 40) rather than from a termination. Their participation in the process decreases the yield of C02 evolved in the polymerisation. 

The discovery of high molecular-weight synthetic polypeptides came as a result of systematic studies by Blout and his co-workers of the conditions which limit the degree of polymerisation of products formed by polymerisation of NCA. Contrary to previous beliefs, it was found that the polymerisation initiated by n-hexyl amine in dry dioxane yields polypeptides of higher molecular weights than expected from the monomer-to-initiator ratio, provided M/I < 100. It should be stressed again that this observation demonstrates that some additional modes of propagation contribute to the reaction, i. e. the "simple poly-addition mechanism cannot account in toto even for the polymerisation initiated by primary amines in dioxane. 

Quantitative conversion is one of the essential preconditions to achieve a significant molecular weight in stepwise polymerization process. Consequently, an iron-catalyzed Michael reaction would be a suitable elementary step for a polyaddition. Bis-donor 24c and bis-acceptor 41b, readily accessible from common starting materials [69], were converted with FeCl3-6H20 to yield a poly-addition product... 

Poly addition of dicyanates with various bifunctional monomers leads to linear, branched or crosslinked polymer [3],... 

Dicyanates react with diisocyanates. The poly addition results in the formation of crosslinked polymers with cyanurate and isocyanurate rings [32]. The polymers have high deformation and decomposition temperature in the case of a crosslinked copolymer from 9,9-bis(4-cyanatophenyl)fluorene the corresponding values are 480 °C and 440 °C (in air), respectively. 

Figure 1. Time dependence of changes in active =Si-H% groups during poly addition of a, CD-dihydridedimethylsiloxane (n = 6) with l,5-divinyl-l,5-dimethylhexaphenylcyclo-pentasiloxane 1 - at 85°C 2 - at 80°C and 3 - at 75°C.

H NMR spectra of copolymers indicate that catalytic hydride poly addition mainly proceeds by the Farmer rule with formation of dimethylenic bridges. In these spectra a reflex of —CH2-CH2- group with... 

Figure 2. Decrease of=Si-H bond concentration during hydride poly addition of a,...

Polyetheriflcation means formation of an ether bond or sequence of ether bonds by (poly)addition of epoxy groups which is released by proton donors (like the OH group formed in the amine-epoxy addition), ionic catalysts or other initiators... 

When poly(ethylene glycol) of molecular weight 1000 was used as the starting material for this poly addition reaction, polymers of molecular weight more than 20000 were obtained. As the functional groups are located in equidistant order, neighbouring effects can be excluded in this copolymer. 

The over-all rate of lactam consumption in the initiation (115) and poly addition (117) reactions is then given by... 

A lthough the diisocyanate poly addition process was discovered by O. 

In our particular type of step-addition polymerisation, monomers, dimers, trimers, oligomers and polymers are the reactive species which participate in the chain growth. Initially, the monomers react with monomers and give dimers, dimers react with monomers and dimers and give trimers and tetramers, respectively. The high MW polymer is formed only in the last stages of the poly addition reaction, at high conversion rates. Chain transfer and termination reactions are absent. 

Because hydrazine hydrate contains water, after the poly addition reaction 6.21 it is necessary to eliminate water by vacuum distillation. The reaction between hydrazine and TDI is very exothermic and the temperature increases rapidly in a short time, for example from room temperature to 50 °C to the reflux temperature ( 100 °C or more) [7, 8, 67-73]. 

In Chapter 3, the chemistry and technology of the most important oligo-polyols used for elastic polyurethanes fabrication, in fact high MW oligomers (2000-12000 daltons) with terminal hydroxyl groups and low functionality (2-4 hydroxyl groups/mol) were discussed. Polyalkylene oxide polyols (homopolymers of PO or copolymers PO - EO, random or block copolymers), polytetrahydrofuran polyols, filled polyols (graft poly ether polyols, poly Harnstoff dispersion - polyurea dispersions (PHD) and polyisocyanate poly addition (PIPA) polyols), polybutadiene polyols and polysiloxane polyols were all discussed. The elastic polyurethanes represent around 72% of the total polyurethanes produced worldwide. 

Many important polyols used as starters for synthesis of rigid polyether polyols are solid in the conditions used for PO (or/and EO) poly addition, having a melting point higher than 130 °C. Such polyols are sucrose (mp = 179-180 °C), pentaerythritol (mp = 253 °C), dipentaerythritol (mp = 222 °C), a-methyl glucoside (mp = 164-165 °C) and other polyols. As mentioned previously, the main technical problem is to react a solid polyol with a gaseous monomer. This problem was solved by several practical solutions ... 

Further developments in the field of chain polymerization were centered on radical poly-addition. Its mechanism was firmly established in the 1930 s and attracted much attention. The interest in anionic polymerization was marginal and the activities in this field were centered at that time around Ziegler in Germany and Lebedev in Russia. Both groups were interested in polymerization of styrene and dienes initiated by sodium metal and their work led to industrial production of synthetic rubber marketed by I. G. Far-benindustrie as Buna . 

Similar ring-opening poly-addition of the bis-sultam monomer 147 occurs with aliphatic diamines (equation 241). Polysulphonamides have also been obtained from the corresponding bis-2,2 -disubstituted keto sultams (equation 242)295. 

Allgemeine Methoden der makromolekularen Chemie - Synthese von makromolekularen Stoffen durch Polymerisation - Synthese von makromolekularen Stoffen durdi Polykondensation und Poly addition - Reaktionen makromolekularer Stoffe... 

In step growth reactions, no specific activated centers are present to force the connection of the monomers. Instead, the monomers are tied together in discreet, independent steps via conventional organic reactions such as ester, ether, amide, or urethane formation. Depending on whether small molecules are set free in the connection step, one distinguishes between polycondensations and poly additions. 

Poly addition growth of polymer chains proceeds by addition reactions between molecules of all degrees of polymerization. 

The synthesis of monomers derived from fatty acids incorporating end-functions susceptible to classical poly addition reactions has been revived recently and yielded interesting results. Vinyl oleate (VO) and vinyl linoleate (VL) were synthesised by a transvinylation reaction of the corresponding fatty acids with an excess of vinyl acetate (VAc) in bulk using a safe iridium-based catalyst instead of previously used mercury-based counterparts (which are not acceptable today because of safety concerns) [91]. Scheme 4.21 summarises this synthesis in the case of OA. 

As a result of the poly addition of the DBDI based materials by the one shot synthesis in melt, it obtained opaque solid elastomer blends consisting of two copolymers, one of which was soluble in DMF (87%), while the other was insoluble in DMF (13%), (PUioo — Table 3.11). 

So-called anaerobic polyurethane adhesives also belong to this category. This system combines urethane poly-addition chemistry with free-radical initiated addition polymerization. A polymerizable alcohol such as j -hydroxyethyl methacrylate is reacted with an equivalent amount of a diisocyanate such as TDI or with an isocyanate-terminated urethane prepolymer. An organic hydroperoxide is then added to such intermediates... 

Recently, two reports highlighted the use of MS/ MS to investigate fragmentation pathways of 4-alkyl-substituted PSs [90] and poly (alpha methylstyrene) [91]. The authors noted that the molar mass of the repeat unit is 118 g/mol for both polymers. This is an exceptional case. As a matter of fact, some common polymers obtained by poly addition are PS, PMMA, poly (butadiene), and poly(isoprene), and the LIr values do not superpose (they are 104,100,54, and 68 Da, respectively). 

Step-growth polymerizations in extruders, both polycondensations and polyadditions, are far less investigated than chain growth reactions. Because the polymer has to remain thermoplastic, only bifunctional monomers should be used, and the molecular weight can be controlled by the addition of a small amount of monofunctional monomers. For both polycondensation and poly-addition reactions the feeding should be very accurate and stochiometrically correct, because otherwise the conversion and therefore pressure built up will be seriously restricted. 

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