Chloral polymerization

The polymerization of aldehydes is initiated by ionic initiators and the polymerization proceeds by ionic propagation. No radical polymerization of aldehydes has been documented yet. In the case of anionic polymerizations the growing ion is an alkoxide ion. The cationic polymerization has as the propagating species an oxonium ion. Most recent experimental results have shown that haloaldehydes, such as chloral polymerize exclusively by an anionic mechanism. 

The best studied haloaldehyde polymerization is that of chloral. No accurate kinetic study of chloral polymerization has been undertaken because chloral polymer is insoluble. When polymerization was initiated, the initiator solution reacted instantaneously with the monomer to form insoluble polymer which prevented thorough mixing of the initiator with the monomer solutions prior to polymerization. 

Fig. 26. Rate of chloral polymerization (NMR). Initiator concentration, 0.2 mole % (O) PhaP (x), LiOCiCHala ( ), collidine. No solvent. Mixing temp., 60°C cooling bath temp., 0°C.

Alkali metal salts with nucleophilic anions are notably good initiators for chloral anionic polymerization (Fig. 26). The most studied initiator is lithium ferf-butoxide. When 0.2 mole % of lithium ferf-butoxide (based on chloral) was added to neat chloral monomer at 60°C the alkoxide (CH3)3C0CH(CCl3)0 Li was formed instantaneously, but no further addition of chloral occurred. This reaction was observed by an NMR study of the system and confirmed by the chemical reactions of the product alkoxide, which acted as the initiator. Tertiary amines such as pyridine and NR3 where R is an alkyl group have been found to be good initiators for chloral polymerization. They are slower initiators than lithium... 

Chloride initiation of chloral polymerization could be readily achieved with tetraalkyl ammonium chlorides, such as tetrabutyl ammonium chloride, or with trialkyl sulphonium chlorides as initiators. Chloral polymerization initiated with R4NCI behaved very similarly to that with tertiary amine initiation. It is likely that the actual initiator of chloral polymerization with tertiary amines was chloride ion, which was presumably formed by chloride abstraction from chloral by the amine. The ease of chloride exchange in chloral reactions was demonstrated by initiation studies with Cl as initiator. 

Extensive studies of chloral polymerization were carried out with tertiary phosphines and with phosphonium chlorides as initiators. Tertiary phosphines, for example triphenyl phosphine, reacted instantaneously and quantitatively with one mole of chloral to form PH3p —OCH=CCl2CP. The phosphonium chloride had the same ability to initiate chloral polymerization as triphenylphosphine. 

The rate of chloral polymerization was studied by estimating the monomer disappearance by NMR. Figure 26 shows a comparison of the rate of polymerization of chloral initiated by lithium tert-butoxide, a quaternary ammonium chloride and triphenyl phosphine. The rate of chloral polymerization initiated with lithium lert-butoxide was much faster than the chloride initiated polymerization. This may be explained by the much more efficient and essentially quantitative initiation with the butoxide and consequently the greater number of growing polychloral chains. 

Chloral polymerization to give uniform samples of polychloral cannot be carried out by an isothermal polymerization because the polymer is not soluble in the monomer. All previous work on rates and conversions of chloral polymerization is very questionable. The present author s data [62] are good for conversions the rates are semiquantitative but internally self-consistent. The cooling bath temperature was accurately controlled, but the rate of heat generation caused by the polymerization, the heat dissipation and consequently the internal temperature of the polymerization mixture varied as the polymerization progressed, but was between 48° and 50°C during most of the polymerization. The polymerization was carried out under quiescent conditions. After about 2% conversion a self-supporting gel was formed, but the polymerization was then allowed to go to completion. 

Kambe et al. [63] studied quite recently equilibria in chloral polymerization unfortunately with only one initiator, sodium naphthalene. Unlike the chloral polymerization without solvent where the polymerization temperature is 58°C [62], in the case of one molar monomer concentration it was 12°C [63], the ceiling temperature of chloral polymerization. In Kambe s work the initiator was always added below the polymerization... 

We consider these results very important as it is known that copper(II) acetylacetonate complexes act as catalysts in chloral polymerization(20) and polyurethane formation(21) (in presence of... 

In order to compare the rates of polymerization of perhaloacetaldehyde polymerization with different initiators, the polymerization of DCBA was studied at -10 C. and at initiator concentrations of 2 mole perr cent. The rate of polymerization of DCBA with pyridine is very fast. The rate of DCBA polymerization with sulfuric acid is much slower but is faster than that of chloral polymerization which is shown in curve A. 

Chlorinated by-products of ethylene oxychlorination typically include 1,1,2-trichloroethane chloral [75-87-6] (trichloroacetaldehyde) trichloroethylene [7901-6]-, 1,1-dichloroethane cis- and /n j -l,2-dichloroethylenes [156-59-2 and 156-60-5]-, 1,1-dichloroethylene [75-35-4] (vinyhdene chloride) 2-chloroethanol [107-07-3]-, ethyl chloride vinyl chloride mono-, di-, tri-, and tetrachloromethanes (methyl chloride [74-87-3], methylene chloride [75-09-2], chloroform, and carbon tetrachloride [56-23-5])-, and higher boiling compounds. The production of these compounds should be minimized to lower raw material costs, lessen the task of EDC purification, prevent fouling in the pyrolysis reactor, and minimize by-product handling and disposal. Of particular concern is chloral, because it polymerizes in the presence of strong acids. Chloral must be removed to prevent the formation of soflds which can foul and clog operating lines and controls (78). 

Most of the compounds in this class have been prepared from preexisting crown ether units. By far, the most common approach is to use a benzo-substituted crown and an electrophilic condensation polymerization. A patent issued to Takekoshi, Scotia and Webb (General Electric) in 1974 which covered the formation of glyoxal and chloral type copolymers with dibenzo-18-crown-6. The latter were prepared by stirring the crown with an equivalent of chloral in chloroform solution. Boron trifluoride was catalyst in this reaction. The polymer which resulted was obtained in about 95% yield. The reaction is illustrated in Eq. (6.22). 

Polymerization of the bulky monomer chloral yields an optically active product when one uses a chiral initiator, e.g., lithium salts of methyl (+)- or (—)-mandelate or (R)- or (S)-octanoate [Corley et al., 1988 Jaycox and Vogl, 1990 Qin et al., 1995 Vogl, 2000], The chiral initiator forces propagation to proceed to form an excess of one of the two enantiomeric helices. The same driving force has been observed in the polymerization of triphenyl-methyl methacrylate at —78°C in toluene by initiating polymerization with a chiral complex formed from an achiral initiator such as n-butyllithium and an optically active amine such as (+)-l-(2-pyrrolidinylmethyl)pyrrolidine [Isobe et al., 2001b Nakano and Okamoto, 2000 Nakano et al., 2001]. Such polymerizations that proceed in an unsymmetrical manner to form an excess of one enantiomer are referred to as asymmetric polymerizations [Hatada et al., 2002]. Asymmetric polymerization has also been observed in the radical... 

Antimony trichloride is used as a catalyst for polymerization, hydrocracking and chlorination reactions as a mordant and in the production of other antimony salts. Its solution is used as an analytical reagent for chloral, aromatics and vitamin A. 

The variety of ways in which chloral and trinitrotoluene (TNT) derivatives can be used to prepare novel polyimides and polymeric materials is very promising. The use of chloral and TNT derivatives allows for the synthesis of a large number of monomers which, in turn, can impart a variety of useful properties to their respective polymers. The possibility of preparing, from available raw materials, high-molecular-weight compounds with increased heat and thermal resistance in combination with improved solubility and, consequently, easiness of processing is especially attractive and may provide impetus for further work in this field. 

Aldehyde Polymers Asymmetric anionic polymerization can lead trichloroacetalde-hyde (chloral) to a one-handed helical, isotactic polymer having a 4/1-helical conformation with... 

As mentioned, the spectrum and amount of impurities formed during oxychlorination is much larger compared with direct chlorination. Some key impurities are listed below 1,1,2-trichloroethane (TCE), chloral (CCl3-CHO), trichloroethylene (TRI), 1,1- and 1,2-dichloroethylenes, ethyl chloride, chloro-methanes (methyl-chloride, methylen-chloride, chloroform), as well as polychlorinated high-boiling components. In particular, chloral needs to be removed immediately after reaction by washing because of its tendency to polymerization. 

The formation of addition products with chloral is much easier than with acet-aldehyde itself, due to the influence of the three negative chlorine atoms in the alkyl radical. Chloral undergoes polymerization, as does acet-aldehyde, the product being meta-chloral (CCl3CHO)3. 

Polymerizations of halo aldehydes are often discussed separately from those of the aliphatic higher polyaldehydes [61]. Chloral and fluoral have... 

We found recently [62] that chloral can be polymerized readily and reproducibly in a two step process. Monomer and initiator are first mixed above the polymerization temperature to form a homogenous solution. The initiated monomer polymerized rapidly and in the case of neat monomer the reaction was complete in a few minutes. In dilute solution the polymerization temperature was lower. 

Fig. 27. Residual monomer concentration in the polymerization of chloral versus catalyst—monomer ratio. - -), direct polymerization (—o—), repolymerization ...

In addition to chloral the polymerization of other chlorinated aldehydes was studied by Kambe et al., for example that of oi-chloro iso-butyraldehyde. It was also found in this case that the initiation was almost instantaneous and the growing polymer ends could be acetylated when acetylation was carried out immediately at the low polymerization... 

Asymmetric anionic polymerization can convert trichloroacetaldehyde (chloral) to a one-handed helical, isotactic polymer (44) having a 4/1-helical conformation with high optical activity ([oi]d +4000° in film).28114-118 Anionic initiators such as 45,115 46,115 and 47117 and Li salts of optically active carboxylic acids or alcohols are used for the polymerization. Although the polymers are insoluble in solvents and their conformation in solution cannot be directly... 

The polymerization of bulky aldehydes such as chloral using enantiopure lithium alkoxides (7,8) gives insoluble, isotactic polymers that exhibit optical activity in the sohd state (Scheme 6) [8,50,51]. The solution and solid-state hel-... 

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