Phenoxy end-capping

Brominated C rbon te Oligomers. There are two commercial brominated carbonate oligomer (BrCO) products. Both are prepared from tetrabromobisphenol A and phosgene. One has phenoxy end caps [28906-13-0] and the other trihromophenoxy [71342-77-3] end caps. These are used primarily in PBT and polycarbonate/acrylonittile—butadiene—styrene (PC/ABS) blends. 

Kinetic study of this reaction usually requires sampling the polymerizing mixture and analyzing for the concentrations of the various reaction species at different polymerization times. Vofsi and Tobolsky in 1965 reported the use of radioactively tagged initiator (10), while Saegusa amd coworkers in 1968 developed a "phenoxy end-capping" method in which the oxonium ion is trapped with sodium phenoxide and the derived phenyl ether at the polymer chain end quantitatively determined by UV spectrophotometry (11). 

Direct initiation with metal (and metalloid) halides, described in Sect. 3.2.9 for THF-PFs system, has recently been studied by Vladimirova a.o. for a-epichloro-hydrin and SnCl4. Th ori nal proposal of Eastham who advanced the dizwitter-ionic growth for oxirane and SnCl4, has been confirmed by using the new analytical methods tracer and phenoxy end-capping. 

To improve the processability of PPQ, appropriate phenylquinox-aline oligomers were end-capped with acetylenic groups using 3-(3,4-diaminophenoxy)phenylacetylene (43) or 4-(3- and 4-ethynyl-phenoxy)benzil (44, 45) (Eq. 10). The processability was improved but at the sacrifice of the thermooxidative stability. In general, cured acetylene-terminated heterocyclic polymers are less stable in a thermooxidative environment than the parent linear polymer. 

In cationic polymerization end-capping was first applied by Saegusa in the polymerization of THF and then of other cyclic ethers sodium phenoxide was used as the end-capping reagent and the phenoxy end groups were determined by UV. End-capping is sufficiently fast and the phenolate is exclusively formed in reaction with the growing species ... 

Along these lines of thinking block copolymers of styrene and 6-[4-(4-methoxyphenyl)phenoxy]hexylmethacrylate (MPPHM) were synthesized by anionic polymerization. Styrene was polymerized first in benzene using 5-BuLi as the initiator. After completion of polymerization the living PSIi chains were end-capped with diphenylethylene and the solvent was changed to THE Anhydrous liCl was introduced to the reactor, and the temperature was lowered to - 40 °C. At that temperature a solution of purified MPPHM in THE was introduced slowly. After complete reaction of the liquid crystalline monomer, polymerization was terminated with methanol . The procedure is outlined schematically in Scheme 9. 

Wang et al. [135] prepared a novel ABB monomer (1-14, Scheme 8), namely 4-[4-(2,4-diaminophenoxy)phenoxy] phfhalic acid 2-methyl ester, which was polymerized to form the precursor polyamic acid monomethyl ester. The direct polycondensation of the ABB monomer was carried out to form polyamic acid monomethyl ester as a precursor and had a M of 12,000 Da. Chemical imidization in the presence of acetic anhydride and pyridine gave hb-PIs with low DB. The DB of the precursor, as determined by the H NMR spectra, was only 7%. They ascribed the low DB to the differences in the reactivities of the amino groups. End modification reactiOTis were accomplished with acetyl chloride, benzoyl chloride, and phthalic anhydride to form end-capped polyimides. The end-group-modified polyimides were soluble in polar aprotic solvents such as DMSO, DMF, and NMP. TGA measurements showed Ta,s% in the range of 400-520°C, and Tg of 200-258°C. The hb-PIs showed film-forming ability, but they were more brittle than analogous linear polymers. 

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