Poly additions, monomers

Reaction with additional monomers leads to the formation of larger rings (3, 4) and eventually to high molecular weight polymers, namely poly-... 

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. 

Photostabilizers, regardless of their mechanism of action, have been added as low molecular weight materials at some point in processing. Subsequently, these stabilizers are often lost in further processing due to their volatility or else later migrate to the surface and evaporate. One method which avoids this modifies the polymer to include the quencher as an additional monomer in the polymerization. This paper will describe some recent efforts in our laboratory to pursue this latter approach in the stabilization of poly(ethylene terephthalate). 

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. 

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

Because the heat of polymerization Is high. Hall was able to use a calorimetric method (10,11) to determine polymerization rates. The process can be described by Initiator I attacking the B-lactone M to give the B substltuted carboxylate IM, which attacks additional monomer molecules to give the poly-B-lactone IM2 In those cases when kp Is only slightly less than kj, the... 

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. 

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 ... 

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. 

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. 

To produce polymer wood, wood is degassed and then loaded according to wood type with 35%-95% monomer. The monomer is then converted by polycondensation or addition polymerization to polymer. For polycondensation, monomers that do not eliminate volatile components during polyreaction are, of course, preferred. Ring-shaped monomers as well as monomers with carbon-carbon double bonds can be polymerized. In the latter case, polymerization can be induced by 7-rays, peroxides, redox systems, etc. Not all monomers, however, are suitable for the preparation of polymer wood. For example, acrylonitrile is not soluble in its own monomer. In wood, therefore, the precipitation polymerization leads to powdery deposits and not to a continuous phase. The same problem occurs with vinyl chloride, and in this case, the boiling point of the monomer is too low. Poly (vinyl acetate) has a glass transition temperature which is too low. In addition, monomers with G values (see Chapter 12) which are too low require high 7-ray doses to induce polymerization. Copolymers of styrene and acrylonitrile, poly (methyl methacrylate), and unsaturated polyesters are used commercially. 

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. 

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. 

Step polymerizations in which the monomers react together without the elimination of other molecules are termed poly additions. The preparation of polyurethanes by the RA2 + RB2 reaction of diisocyanates with diols is one of relatively few important examples of linear polyaddition... 

Recently, we succeeded on the synthesis of ordered(-abcd-) poly(amide-thioether) by poly(addition-direct condensation) of a pair of two nonsynunetric monomers, 4-(actyloxy)benzoic acid (XabX) and 4-aminobenzenethiol (YcdY), where a polyaddtion was combined with a polycondensation to prepare the ordered polymer (4). Because, the selective amidation of carboxylic acids would be difficult using condensing agents due to the small difference of pKa values between carboxylic acids. An active ester is also useful as a substitute for a carboxylic acid component. 

We considered three kinds of nucleophiles and electrophiles for the preparation of ordered polymer from three nonsymmetric monomers by poly(addition-direct condensation). Then, we thought to combine the two concenpts in our papers (ref. 4 and 5) for the selection of these components, and decided to use acylhydrazide, aromatic amine, and thiol as nucleophiles, and carboxylic acid, active ester and vinyl ester as electrophiles, respectively. 

Several studies have demonstrated the successful incoriDoration of [60]fullerene into polymeric stmctures by following two general concepts (i) in-chain addition, so called pearl necklace type polymers or (ii) on-chain addition pendant polymers. Pendant copolymers emerge predominantly from the controlled mono- and multiple functionalization of the fullerene core with different amine-, azide-, ethylene propylene terjDolymer, polystyrene, poly(oxyethylene) and poly(oxypropylene) precursors [63,64,65,66,62 and 66]. On the other hand, (-CggPd-) polymers of the pearl necklace type were fonned via the periodic linkage of [60]fullerene and Pd monomer units after their initial reaction with thep-xy y ene diradical [69,70 and 71]. 

If a polymer is formed from a single monomer, as in addition and ringopening polymerizations, it is named by attaching the prefix poly to the name... 

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