Amines, tertiary polymerization

The mechanism of the polymerization of NCA with tertiary amine is still controversial. Mori and Iwatsuki claim that the true initiator is the primary amino group formed by hydrolysis of the NCA with contaminated water and that tertiary amine forms a complex with the NCA and accelerates the addition reaction37 . Harwood et al. confirmed the propagating carbamate by NMR in polymerization initiated with a strong base37 . The successive addition of NCA to the polymer end catalyzed with a strong base affords an alternative procedure for the synthesis of block copolypeptides. Block copolypeptides of poly(oxyethylene) were prepared by triethyl amine catalyzed polymerization of NCA in the presence of poly(oxyethylene)bis-eMoroformate38 . 

Primary amine-containing polymeric particles are available from a number of manufacturers and have either aliphatic or aryl amine groups on their surface. Occasionally, a particle type may have secondary or tertiary amines present, but these should be avoided for covalent coupling, as primary amines typically give better reaction yields than secondary amines and tertiary amines are unreactive. 

Tertiary amines initiate polymerization by zwitter-ion formation [13.14]. 

The hydroxymethyl compounds do not initiate polymerization. Only when there is a significant amount of tertiary amine can polymerization begin. Tertiary amine is formed more rapidly from secondary amines, because there is only one hydrogen atom to be replaced. Branching on the a-carbon of primary amines makes the formation of triazine sterically impossible. 

The photoreduction of aromatic ketones by tertiary amines is reported [38] to proceed at rates which are substantially faster than those observed for the corresponding photoinduced hydrogen abstraction from, e.g. alcohols. A limit case is given by fluorenone, the photoreduction of which does not occur in alcohol, ether or alkane solution, but readily takes place in the presence of amines, tertiary amines being the most effective [39,40]. Xanthone has also been reported to be easily photoreduced by iV,A-dimethylaniline [41], but not by 2-propanol [42]. However, the oxidation of tertiary amines photosensitized by fluorenone and xanthone is much less efficient than when sensitized by benzophenone, apparently because of lower rates of hydrogen abstraction [43]. Fluorenone/tertiary amine systems have been used successfully to photoinitiate the polymerization of MMA, St, MA and AN [30,38,44] and rather similar results have been obtained in the photoinitiated polymerization of MA by the benzophenone/EtsN system [45]. Thus, the great variety of substrates participating in exciplex formation has been readily extended to polymer-based systems. 

This type of photoinitiating system has been studied carefully using a series of 6-alkoxy-2,4-diiodo-3-fluorones and 2-acyl- or 7-alkyl-2,4,5-triiodo-3-fluorones [117-120] as the primary light absorbers. The systems have been further evaluated as initiators for photopolymerization in the presence of a tertiary aromatic amine. Photoinitiated polymerization was triggered with an argon-ion (514.5 nm line) or He-Ne (632 nm line) laser. 

The polymerization of fluoral [61] has been studied in detail by Busfield [64]. It was found that fluoral polymerized very slowly in the presence of 2 mole % of formic acid but extremely quickly in the presence of as little as 0.2 mole % of a tertiary amine such as pyridine or trimethyl amine. Gasphase polymerization of fluoral was studied with trimethyl amine and it was found that the ceiling temperature was 73°C. The half life (50% conversion to polymer) of fluoral polymerization with formic acid was 12 h but for pyridine or trimethyl amine it was about 30 sec. 

Protonic acids are efficient initiators for the polymerization of both sulfides and amines. The polymerization of thiiranes initiated with perchloric acid proceeds without induction periods. Induction periods are present, however, with methyl fluorosulfonate initiator 11). Secondary sulfonium salts are more reactive than tertiary ones (the opposite is true with oxonium ions)12) and induce rapid polymerization ... 

Anionic Anionic polymerization is widely used. Initiators alkali metal oxides, tertiary amines, tertiary phosphines, organometaUic compounds, etc. Chloral is mixed with an anionic initiator above the threshold temperature, for bulk polymerization, and the mixture is then cooled (usually to 0°C under quiescent conditions). Thus, jxjlychloral pieces of desired shape can be prepared. (2-4)... 

The propagation reactions in tertiary amine initiated polymerizations can be pictured as follows [339] ... 

The tertiary-amine-initiated polymerization proceeds by another mechanism. 

Amines. Tertiary amines R3N are catalysts that open the epoxy ring and thus catalyze the polymerization reaction. They may be used with hydroxyl-containing molecules to catalyze homopolymeiization (Fig. 3.26), but more often they are used to catalyze copolymerization of epoxy resins with amine or acid curing agents. Several more specialized amines are also mentioned as catalysts (Fig. 3.27). 

Reactions take place in organic solvents (typically in dimethyl sulfoxide, DMSO) and are catalyzed with standard catalysts used for the synthesis of polyurethanes metal salts and tertiary amines [26]. Polymerization mechanisms differ as a function of the catalyst and are briefly discussed below. 

Introduction of the NH group ortho to the sulfone bridge of the poly(ethersulfone) was performed via a method developed by Guiver et al. [73,74]. The poly(ether sulfone amine) was then stepwise alkylated to the secondary and the tertiary polymeric amine by sequential addition of n-BuLi and CH3I [43]. 

Polymerized by a chain process using a Lewis acid (cationic polymerization) or a tertiary amine (anionic polymerization) as activator (see Chapter 8) in this case, the bifunctional diepoxide behaves as a tetravalent monomer ... 

Secondary amines also yield linear polypeptides, when their nucleophilicity is not reduced by steric hindrance (e.g., dimethylamine or piperidine). Imidazole is an exception mainly yielding cyclic polypeptides. Cyclic polypeptides are also formed by sterically hindered secondary amines and by tertiary amines. Thermal polymerizations also yield cyclic polypeptides. Mechanisms and preparative aspects of aU these polymerizations are discussed in Chap. 15. 

Many perfluoroaUphatic ethers and tertiary amines have been prepared by electrochemical fluorination (1 6), direct fluorination using elemental fluorine (7—9), or, in a few cases, by fluorination using cobalt trifluoride (10). Examples of lower molecular weight materials are shown in Table 1. In addition to these, there are three commercial classes of perfluoropolyethers prepared by anionic polymerization of hexafluoropropene oxide [428-59-1] (11,12), photooxidation of hexafluoropropene [116-15-4] or tetrafluoroethene [116-14-3] (13,14), or by anionic ring-opening polymeriza tion of tetrafluorooxetane [765-63-9] followed by direct fluorination (15). 

Beryllium Hydride. BeryUium hydride [13597-97-2] is an amorphous, colorless, highly toxic polymeric soHd (H = 18.3%) that is stable to water but hydroly2ed by acid (8). It is insoluble in organic solvents but reacts with tertiary amines at 160°C to form stable adducts, eg, (R3N-BeH2 )2 (9). It is prepared by continuous thermal decomposition of a di-/-butylberylhum-ethyl ether complex in a boiling hydrocarbon (10). 

Commercially, polymeric MDI is trimerized duting the manufacture of rigid foam to provide improved thermal stabiUty and flammabiUty performance. Numerous catalysts are known to promote the reaction. Tertiary amines and alkaU salts of carboxyUc acids are among the most effective. The common step ia all catalyzed trimerizations is the activatioa of the C=N double boad of the isocyanate group. The example (18) highlights the alkoxide assisted formation of the cycHc dimer and the importance of the subsequent iatermediates. Similar oligomerization steps have beea described previously for other catalysts (61). 

Other Rea.ctions, The photolysis of ketenes results in carbenes. The polymeriza tion of ketenes has been reviewed (49). It can lead to polyesters and polyketones (50). The polymerization of higher ketenes results in polyacetals depending on catalysts and conditions. Catalysts such as sodium alkoxides (polyesters), aluminum tribromide (polyketones), and tertiary amines (polyacetals) are used. Polymers from R2C—C—O may be represented as foUows. 

Monofunctional, cyclohexylamine is used as a polyamide polymerization chain terminator to control polymer molecular weight. 3,3,5-Trimethylcyclohexylamines ate usehil fuel additives, corrosion inhibitors, and biocides (50). Dicyclohexylamine has direct uses as a solvent for cephalosporin antibiotic production, as a corrosion inhibitor, and as a fuel oil additive, in addition to serving as an organic intermediate. Cycloahphatic tertiary amines are used as urethane catalysts (72). Dimethylcyclohexylarnine (DMCHA) is marketed by Air Products as POLYCAT 8 for pour-in-place rigid insulating foam. Methyldicyclohexylamine is POLYCAT 12 used for flexible slabstock and molded foam. DM CHA is also sold as a fuel oil additive, which acts as an antioxidant. StericaHy hindered secondary cycloahphatic amines, specifically dicyclohexylamine, effectively catalyze polycarbonate polymerization (73). 

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