Alcohol initiators polymerizations

Schindler, A., Hibionada, Y. M., and Pitt, C. G., Aliphatic polyesters III. Molecular weight and molecular weight distribution in alcohol-initiated polymerization of e-caprolactone, J. Polym. Sci., Part A Polym. Chem., 20. 319-326, 1982. 

Schindler, A., Hibionada, V.M. and Pitt, C.G. (1982) Aliphatic polyesters 111. Molecular weight and molecular weight distributions in alcohol-initiated polymerizations of -c2ipxo 2LCV>n>t. Journal of Polymer Science, Poly mer Chemisiry Edition. 20, 319-826. 

Finally, cyclic anhydrosulfites of a-hydroxycarboxylic acids (l,3-dioxa-2-tho-lane-4-one-2-oxides, see Formula 16.5g) need to mentioned. First syntheses and polymerization experiments were reported by Blaise et al. [75] as early as 1922. Systematic smdies of this highly reactive class of monomers began about 40 years later [76-88]. Tighe et al. concentrated their kinetic studies on thermal and alcohol-initiated polymerizations. They found that increasing size and number of substituents do not stabilize these heterocycles [83]. They concluded that the first step of a thermal polymerization is a decomposition into SO2 and an a -lactone (compare OCAs in Formula 16.5). Another interpretation of thermal and pyridine-catalyzed polymerizations is presented in Chap. 15. 

Calculated from Michaelis-Menten constants using lipase catalyst. Polymerization with zinc octanoate/butyl alcohol initiator system in bulk. 

These initiators may be used in the presence of protic sources such as MeOH.780 The rapid and reversible exchange of propagating alkoxides with alcohol leads to a narrow molecular weight distribution (for example, Mw/Mn<1.15 for oligomeric PCL), with the number of polymer molecules closely approaching the sum of the number of molecules of initiator and alcohol. In the absence of alcohol, the polymerization of CL is less well behaved with Mw/Mn= 1.5, presumably a consequence of unfavorable initiation and propagation rates. 

Organic-inorganic redox pairs initiate polymerization, usually but not always by oxidation of the organic component, for example, the oxidation of an alcohol by Ce4+,... 

Tertiary amines with an a-hydrogen are among the most effective electron donors other electron donors include alcohols, amides, amino acids, and ethers. A third process, direct hydrogen atom transfer from RH to the ketone, is not common hut does occur with some photoinitiators. The overall result is the same as the electron-transfer process. Although two radicals are produced by photolysis of the photoinitiator, only one of the radicals is typically active in initiation—the aroyl and amine radicals in Eqs. 3-48 and 3-49, respectively. The other radical may or may not initiate polymerization, hut is active in termination. The decrease in photoinitiator concentration during polymerization is referred to as photo-bleaching. 

Tin(II) 2-ethylhexanoate is an important industrial initiator for cyclic ester polymerization [Duda and Penczek, 2001 Kricheldorf et al., 2001 Storey and Sherman, 2002]. Metal car-boxylates are useful initiators only in the presence of alcohols. The polymerization rate is very slow in the absence of alcohol, less than 1% of the rate in the presence of alcohol. The actual initiator is the metal alkoxide formed by the reaction between metal carboxylate and alcohol. 

Redox initiation is often an efficient method for graft polymerization. Hydroxyl-containing polymers such as cellulose and poly(vinyl alcohol) undergo redox reaction with ceric ion or other oxidizing agents to form polymer radicals capable of initiating polymerization... 

Suspension Polymerization. The suspension or pearl polymerization process has been used to prepare polymers for adhesive and coaling applications and for conversion to poly(vinyl alcohol). Suspension polymerization are carried out with monomer-soiubie initiators predominantly, with low levels of stabilizers Continuous tubular polymerization of vinyl acetate in suspension yields stable dispersions of beads with narrow particle size distributions at high yields. 

The polymerization of an NCA may be initiated by any moderately strong base or by nucleophiles. Weak nucleophiles, such as water, alcohols, or primary amines, generally initiate polymerization by the normal (nucleophilic) mechanism or by the carbamate mechanism. Tertiary amines and strong bases, such as methoxide, initiate polymerization by the active monomer mechanism. Secondary or primary amines may initiate polymerization by any one or all of these mechanisms. More than one mechanism may be active at any one time and frequently a polymerization may begin by the active monomer mechanism and then, at a later stage, propagate by the normal mechanism. 16 ... 

Alkylation of aluminum with ethylene yields products that find application as initiators and starter compounds in the production of a-olefins and linear primary alcohols, as polymerization catalysts, and in the synthesis of some monomers like 1,4-hexadiene. Triethyl aluminum [97-93-8], A1(C2H5)3, is the most important of the ethylene-derived aluminum alkyls. 

Latexes initiated with persulfate normally have terminal sulfate groups, but these can be hydrolyzed to alcohols and then oxidized to carboxyl groups. Terminal alcohol groups also result from hydrogen peroxide or hydroperoxide initiated polymerization. Ottewill and Shaw (22) first showed by electrophoresis that latexes stripped of salts and emulsifiers by dialysis have both strong and weak acid sites. Van den Hul and Vanderhoff (23) then found that conductometric titrations were most effective for... 

Fig. 6.21. Electrochromatographic separation of benzene derivatives on monolithic capillary column prepared by UV initiated polymerization. Conditions capillary column, 100 pm i.d. x 25 cm active length stationary phase poly(butyl methacrylate-co-ethylene dimethaciylate) with 0.3 wt. % 2-acrylamido-2-methyl-l-propanesulfonic acid pore size, 296 nm mobile phase, 75 25 vol./vol mixture of acetonitrile and 5 mmol/L phosphate buffer pH 7 UV detection at 215 nm 25 kV pressure in vials, 0.2 MPa injection, 5 kV for 3 s. Peaks thiourea (1), benzyl alcohol (2), benzaldehyde (3), benzene (4), toluene (5), ethylbenzene (6), propylbenzene (7), butylbenzene (8), and amylbenzene (9).

The first step is the formation of an alkoxide anion by the initiating alcohol (allyl alcohol is the initiator most commonly used, although other initiators have been suggested). The appropriate oxide(s) is (are) then added to the alcohol initiator. This causes the opening of the oxirane ring in the oxide and propagates the chain growth of the alkylene oxide on the initiator. The last step is the neutralization of the alkoxide anion to terminate the polymerization. 

Some interesting solvent effects observed in the TBHP-SOi-initiated polymerization of MMA have been mentioned before. It has been further observed that when polymerization of MMA and AN is carried out in the presence of alcohols, the rate of polymerization is in the order methanol > ethanol > isopropyl alcohol > tert-butyl alcohol, cyclohexanol. This suggests that the over-all polymerization mechanism (or the initiation mechanism itself) depends on the polar contribution of the alcohol. A similar observation was made by Imoto et al. with a benzoic anhydride— dimethylaniline N-oxide system as the initiator (20). 

Russian workers have proposed that the increased activity of allyl acetate and allyl alcohol in free radical or gamma ray initiated polymerization in the presence of zinc chloride may be connected with the decreased degradative chain transfer with complexed monomer or the activation of the stabilized allyl radical in the complexed monomer—i.e., the conversion of degradative chain transfer to effective transfer (55, 87). However, these explanations have been partially rejected as inadequate. 

Boron trichloride and tribromide successfully polymerize styrenes and isobutene. These Lewis acids are typically used in combination with water or alkyl chlorides, acetates, ethers, and alcohols [105,153]. In contrast to earlier reports, BC13 can self-initiate polymerization of styrene and isobutene [137] by haloboration, and subsequent activation of the resulting alkyl chlorides by excess Lewis acid. Direct initiation was confirmed by the formation of lower molecular weight polymers than pre-... 

Tube-type carbons are obtained when organic compounds are carbonized in a thin-film state on the template pore walls [6], The tube-type carbon can be obtained even after the entire volume of pores is filled with carbon source, if the excess carbon source is removed before the carbonization is completed. For example, cylindrical pores are generated along the center of the carbon frameworks due to the systematic volume decrease when furfiiryl alcohol is pyrolyzed under vacuum after the initial polymerization. Alternatively, the tube-type carbons can be synthesized as follows carbonization can be controlled to occur partially by catalyst at the pore walls at moderate temperatures. The remaining carbon source is removed by evacuation, and the carbonization is completed by pyrolysis at high temperature. Chemical vapor deposition on the pore walls can also be used to produce the tube-type carbon [11] as well as the aforementioned rod-type carbons [12]. The structure of the resultant carbon depends on the thickness of the carbon deposition. 

The presence of a substituent in the 3-position of the NCA precludes equilibrium (6) and hence prevents the occurrence of reaction (18). It follows that, on the basis of the mechanisms described above, such NCA s should not polymerize unless a protic base (for example a primary or secondary amine) or other source of protons (for example, 3-methyl hydantoin) is present. If it could be established that polymerization does proceed with an aprotic base in aprotic media then some other mechanism of polymerization must be operative. This matter has been of central importance in discussions of various mechanisms of polymerization which have been advanced (Section 3). Experimentelly, it is not easy to obtain definitive evidence because of the high sensitivity of NCA s to protonic impurities (such as water and alcohols) in the presence of bases. It has been shown [18, 19, 38a] that proline NCA (X) and sarcosine NCA (I Ri = R2 = H, R3 = CH3) do not polymerize in the presence of tertiary bases under strictly aprotic conditions. With alkoxides, realization of such conditions is difficult, but it would appear that, at least with proline NCA, such strong bases can bring about ionization of the methine hydrogen and hence initiate polymerization as shown in (26). Evidence for this mechanism is provided by the observation that while sodium methoxide enriched... 

The results of experiments run with both styrene and toluene in a 1 1 SLS/lauryl alcohol solution showed that identical "tails" formed on the styrene and toluene droplets, indicating that this phenomenon was not the result of thermally initiated polymerization of the styrene. Also, no "tails were observed on air drops in the same mixed emulsifier solution or on styrene droplets in an aqueous solution of SLS alone. 

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