Polar substituents, polymerization

Dow Chemicals group and coworkers [276,350] synthesized similar triarylamine-fluorene copolymers 251 and 252, possessing carboxylic acid substituents, via hydrolysis of the corresponding ethyl ester polymers, prepared by Suzuki polymerization. Due to the very polar substituents, the copolymers 251 and 252 are only soluble in polar solvents such as DMF but not in aromatic hydrocarbons as toluene or xylene, which allowed simple fabrication of multilayer PLEDs by solution processes (Chart 2.65). 

Reversed-phase liquid chromatography shape-recognition processes are distinctly limited to describe the enhanced separation of geometric isomers or structurally related compounds that result primarily from the differences between molecular shapes rather than from additional interactions within the stationary-phase and/or silica support. For example, residual silanol activity of the base silica on nonend-capped polymeric Cis phases was found to enhance the separation of the polar carotenoids lutein and zeaxanthin [29]. In contrast, the separations of both the nonpolar carotenoid probes (a- and P-carotene and lycopene) and the SRM 869 column test mixture on endcapped and nonendcapped polymeric Cig phases exhibited no appreciable difference in retention. The nonpolar probes are subject to shape-selective interactions with the alkyl component of the stationary-phase (irrespective of endcapping), whereas the polar carotenoids containing hydroxyl moieties are subject to an additional level of retentive interactions via H-bonding with the surface silanols. Therefore, a direct comparison between the retention behavior of nonpolar and polar carotenoid solutes of similar shape and size that vary by the addition of polar substituents (e.g., dl-trans P-carotene vs. dll-trans P-cryptoxanthin) may not always be appropriate in the context of shape selectivity. 

Polar monomers, such as methyl (meth)acrylate, methyl vinyl ketone, and acrylonitrile, are more reactive than styrene and 1,3-dienes because the polar substituent stabilizes the carba-nion propagating center by resonance interaction to form the enolate anion. However, the polymerizations are more complicated than those of the nonpolar monomers because the polar... 

Since only Ta and Nb catalysts, which are not tolerant to polar groups, are available for the polymerization of disubstituted acetylenes, it is generally difficult to synthesize disubstituted acetylene polymers having such a highly polar substituent as a hydroxy group. Recently, synthesis of poly[l-phenyl-2-( -hydroxyphenyl)acetylene] has been achieved by the polymerization of 1-phenyl-2-(p-siloxyphenyl)acetylene and the subsequent acid-catalyzed deprotection reaction. 

The centres of coordination polymerizations should be able to form only a weak and reversible coordination bond with the monomer. Compounds irreversibly solvating the coordination centres (under the given conditions) act as catalytic poisons. Thus monomers with unscreened polar substituents and most heterocycles cannot be polymerized on Ziegler-Natta coordination centres (see Chap. 3 Sect. 4.1). 

We possess more information on systems containing polar monomers. Organolithium and organomagnesium compounds initiate the polymerization of a number of monomers with an electron-withdrawing substituent. These polymerizations are rarely of the living type. The initiator usually reacts not only with the double bond of the monomer, but also with the polar substituent (both on the monomer and the polymer) yielding inactive products. 

Monomer molecules with strongly polar substituents mutually associate and form complexes with the solvent and with their own polymer. All kinds of association cause changes in polymerization kinetics and sometimes even in the properties of the generated polymer. 

The scope of the living cationic polymerizations and synthetic applications of these functionalized monomers will be treated in the next chapter on polymer synthesis (see Chapter 5, Section III.B). One should note that the feasibility of living processes for these polar monomers further attests to the formation of controlled and stabilized growing species. Conventional nonliving polymerizations, esters, ethers, and other nucleophiles are known to function as chain transfer agents and sometimes as terminators. In addition, the absence of other acid-catalyzed side reactions of the polar substituents, often sensitive to hydrolysis, acidolysis, etc., demonstrates that these polymerization systems are free from free protons that could arise either from incomplete initiation (via addition of protonic acids to monomer) or from chain transfer reactions (/3-proton elimination from the growing end). 

A great variety of substances is capable of acting as activators. The first group comprises iV-substituted lactams with polar substituents at the nitrogen. These iV-substituted lactams must be able to acylate lactam anions with opening of the lactam ring of the activator at a rate comparable to the rate of polymerization. The main representatives of this group are acyllactams [84, 89, 107—110] (V), iV-substituted [111] (VI) or iV,Af-disubstituted [112] carbamoyllactams (VII), JV-carboxylic acid esters of lactams [112] (VIII) and salts of lactam-N-carboxylie acids [107] (IX), viz. 

The ylide nickel-catalyzed oligo-/polymerization of ethylene in the presence of styrene or substituted styrenes with unpolar or polar substituents results predominantly in styrene-terminated ohgo-/polyethylenes. Usually, no styrene homopolymerization takes place. The ethylene pressure has to be adjusted relative to the styrene concentration to reduce the competing formation of simple a-olefms. High styrene concentration and low ethylene pressure favor homologous series of the composition aryl-C ,H2, . While the aryl group is frequently located at one... 

Problem 8.4 Lower molecular weights and polymerization rates observed in anionic polymerizations of polar monomers are attributed to the reactivity of the polar substituents toward nucleophiles, leading to termination and side reactions that are competitive with both initiation and propagation. Explain this behavior considering the case of methyl methacrylate monomer. 

Compatible Polyblends. When the polymeric materials are compatible in all ratios, and/or all are soluble in each other, they are generally termed polyalloys. Very few pairs of polymers are completely compatible. The best known example is the polyblend of polyCphenylene oxide) (poly-2,6-dimethyl-l,4-phenylene oxide) with high-impact polystyrene (41). which is sold under the trade name of Noryl. It is believed that the two polymers have essentially identical solubility parameters. Other examples include blends of amorphous polycaprolactone with poly(vinyl chloride) (PVC) and butadiene/acrylonitrile rubber with PVC the compatibility is a result of the "acid-base" interaction between the polar substituents (1 ). These compatible blends exhibit physical properties that are intermediate to those of the components. 

Having forsworn polar substituents, the prescient polymer chemist would quickly see that by elimination, the logical composition would be a polymeric hydrocarbon. The chains would then have to be very smooth and well-fitting to achieve crystallization, because the forces of attraction between chains would be quite weak. The smoothest chain would be one of methylene groups. On consulting the literature, the chemist would be encouraged by the fact that the... 

W. A. Waters (Oxford University) Investigations of the extent to which complexes such as (CuCl)+ and undissociated CuCL affect the chain length in the polymerization associated with the Sandmeyer reaction are in progress at Oxford. It is well known that ions that complex well with cupric, e.g., (CN) , can be introduced into aryl nuclei by the Sandmeyer procedure in preference to chloride even when diazonium chlorides have initially been taken. The system, however, is complicated by the fact that the complexing of cuprous and cupric salts alters the redox potential, and this affects the facility of both stages 1 and 3 of the reaction sequence. The effects of introducing polar substituents into the aryl nuclei (Table I) indicates the importance of such effects. 

Cossee type. The mechanism comprised of olefin metathesis type elementary processes involving a metal carhene complex and a metallacyclobutane was established only recently after the development of the chemistry of metal-carbene complexes [129], Understanding of the novel kind of reaction mechanism opened a new horizon in polymerization. Various new types of polymerization of cyclic monomers have been realized by ROMP. An advantage of the process is that the processes are tolerant to polar reactants and solvents enabling ready incorporation of polar substituents into polymers. Another advantage is that the ROMP is living in nature and polymers of narrow molecular weight distributions are available by the method. 

Ta- and Nb-based catalysts are good for the polymerization of disubstituted acetylenes but they are not tolerant of polar groups. It is generally difficult to synthesize disubstituted acetylene polymers having protic and/or highly polar substituents such as hydroxy, carboxy, and sulfonic acid groups. Therefore, polymer reactions have been employed to introduce polar groups, and examples of such polymer reactions are illustrated in Scheme 15.3. 

New Polymers by Ring-Opening Polymerization of Norbornene Derivatives with Polar Substituents... 

In the course of the studies on the behavior of unsaturated compounds containing polar groups toward the metathesis catalyst(16), we have found that this type of catalyst can Induce efficiently the ring-opening polymerization of norbornene derivatives with various polar substituents, including nitrile group. The polymerization of ester, nitrile, pyridyl and acid... 

As in the polymerization of monomers without polar substituent, the catalytic activity was markedly enhanced by the addition of a third component (C component) such as alcohols, peroxides, hydroperoxides and epoxides. We have found that ketones, aldehydes and polymerization product of aldehydes are particularly effective as the C component for this type of catalyst. 

Although Z.N. catalysts are very sensitive to polar substituents which tend to clock active sites, coordination polymerization by modified complexes is of course not limited to unsaturated hydrocarbons. A few examples are discussed hereafter which have put in evidence interesting new concepts. 

Similar micro structures are obtained when norbornene is replaced by norbomadiene. 5-and 6-substituted norbornene derivatives when polymerized by ROMP give more complex micro structures (Figure 11). By ROMP it is possible, more easily than by Ziegler-Natta catalysts, to polymerize norbor-nenes with polar substituents such as carbomethoxy, carboethoxy, or trifluoromethyl groups. " ... 

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