Monomer stabilization aromatic amines

The high efficiency of aromatic amines in rubbers, and R /ROO scavenging capacities due to some amine transformation products, encouraged an extended use of amines in stabilization of PO [47,88] and, moreover, in stabilization of vinylic monomers [89]. For example, combinations of PD with the respective BQDI, i.e. the ROO /R scavenging system, are effective stabilizers against premature polymerization [90]. A similar activity is performed by 11 in vinylic... 

Stability and performance of AEM prepared using poly(4-vinyl pyridine-costyrene), quaternized with 1-bromooctane, and deposited on fibrous woven paper was unsatisfactory [189]. Sanchez and coauthors [190] discussed problems related to the use of certain AEMs. They pointed out that the so-called Hoffman degradation that involves attack of a hydroxyl on a-hydrogen in p-position to a quaternary ammonium attached to an aliphatic chain may cause its removal, followed by release of a tertiary amine and formation of a double bond at the end of a broken chain. Attachment of DABCO on short leash prevented chain break due to Hoffman degradation, but release of DABCO and generation of a double bond attached to the chain could take place. Perhaps thermal cross-linking by DABCO of poly(vinyl benzyl chloride) may solve this problem. Sulfonated polymers prepared by polymerization or copolymerization of phosphazene, siloxans, styrene, vinylidene fluoride, and various monomers with aromatic backbones, and possibly with aliphatic spacers, have been used. Various imides as well as PPS, PEK, PEEK, PSU, PEEKK, and PPSU can also be used [190,191]. 

An AB2-type monomer (1-13, Scheme 8), was synthesized by Yamanaka et al. [133] starting from 3,5-dimethoxyphenol via a polyamic acid methyl ester precursor. The aromatic hb-PIs were prepared by chemical imidization in the presence of acetic anhydride and pyridine. The synthesized polyimides were soluble in polar aprotic solvents and showed thermal stability, with a Tajo% of 470°C in nitrogen and a Tg of 193°C. In another work by Yamanaka et al. [134], the same AB2 monomer containing free amine end groups of the precursor was end-capped with acetyl, n-heptanoyl chloride, and 4-methylphthalic anhydride. By chemical imidization of these precursors in the presence of acetic anhydride and pyridine, hb-PIs were prepared. The DB of the hb-PIs was 50% as expected. The hb-PIs showed a above 395°C, and Tg values of 189, 138, and 186°C for the end groups of acetoamide, -heptanoamide, and 4-methylphthalimide, respectively. 

Olefins react directly at the electron-rich and rather electron-deficient oxygens. If the dimer is much more reactive toward olefins than the monomer, only a small fraction of the alkaloid-Os04 complex need be present as a dimer (94a). Houk developed a symmetrical five-membered transition-structure model on the basis of X-ray crystal structures of Os04-amine complexes and osmate ester products and ab initio transition structures of analogous reactions (Scheme 40). The MM2 calculations based on this [3 + 2] reaction model reproduce the stereoselectivities of the stoichiometric reactions observed with several chiral diamines (94b). The transition state may be stabilized by tt-tt interaction of the alkene substrate and the ligand aromatic ring (95). 

Aromatic tri-functional acid and amine monomers are used to obtain reticulated polyamides, which have better mechanical and chemical stability and, for that reason, they are preferred for nanofiltration and reverse osmosis membrane materials. In these membranes, a thin polyamide layer (less than l jm thickness) is fabricated by interfacial polymerization on the top of a porous support (normally an ultrafiltration polysulfone membrane), which usually presents a non-woven reinforcement for mechanical stability as can be seen in Figure 8. Despite its small thickness, the polyamide dense layer is the main regulator of the rejection/transport of water and ions across the membrane. 

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