Branched-chain poly amines

It is also possible to prepare them from amino acids by the self-condensation reaction (3.12). The PAs (AABB) can be prepared from diamines and diacids by hydrolytic polymerization [see (3.12)]. The polyamides can also be prepared from other starting materials, such as esters, acid chlorides, isocyanates, silylated amines, and nitrils. The reactive acid chlorides are employed in the synthesis of wholly aromatic polyamides, such as poly(p-phenyleneterephthalamide) in (3.4). The molecular weight distribution (Mw/Mn) of these polymers follows the classical theory of molecular weight distribution and is nearly always in the region of 2. In some cases, such as PA-6,6, chain branching can take place and then the Mw/Mn ratio is higher. 

Aziridines Ethylenimine is the simplest aziridine and its CROP is already known since 1941 [126]. Currently, poly(ethyleneimine) is still produced on an industrial scale via CROP. However, the CROP of ethylenimine, that is, unsubstituted aziridine, produces a highly branched poly(ethylenimine) because of the occurrence of proton transfer reactions, chain transfer reactions as well as various termination reactions resulting in a polymer that contains a mixture of primary, secondary, and tertiary amine groups. This extensive occurrence of transfer reactions is caused by the high nucleophilicity of the secondary amine groups in the polymer that strongly compete with the monomer. The CROP of 2-methylaziridine and 2-phenylaziridine have also been reported, but are even... 

S.3.2.2 Azetidines The CROP of azetidines without the N-substituent is very similar to the CROP of ethylenimine as discussed in the previous section. As such, the CROP of azetidine is accompanied by a large number of hydrogen transfer, chain transfer, and termination reactions resulting in the formation of branched poly(propylenimine) comprising a mixture of primary, secondary, and tertiary amines [141]. 

A further technically important polymer produced via cationic polymerization is poly (ethylene imine) (PEI). PEI is polymerized from aziridine via protons (Fig. 3.15). It is a highly branched product due to chain growth also through the secondary amines, and it is used, for example, for paper treatment and coatings. More recently, it has also drawn interest for biomedical applications despite its relatively high cytotoxicity [9]. 

Poly(ethylene imine). Poly(ethylene amine) (PEI) is the simplest polybase. It can be prepared directly via the acid-catalyzed polymerization of ethyleneimine (aziridine, 24C) (Fig. 40). 24C may be prepared via a number of routes with ethanolamine being a convenient precursor (223). The cationic polymerization of 24C is very rapid due to the release of the ring strain associated with the monomer. However, the synthesis of PEI under these conditions leads to highly branched structnres dne to chain transfer reactions involving the —NH— species in the polymer backbone. Cyclic products can also be prodnced nnder these conditions. Copol5nnerization with an appropriate comonomer can rednce the degree of chain branching (224). 

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