Oligomers bischloroformate

Phosgene addition is continued until all the phenoHc groups are converted to carbonate functionahties. Some hydrolysis of phosgene to sodium carbonate occurs incidentally. When the reaction is complete, the methylene chloride solution of polymer is washed first with acid to remove residual base and amine, then with water. To complete the process, the aqueous sodium chloride stream can be reclaimed in a chlor-alkah plant, ultimately regenerating phosgene. Many variations of this polycarbonate process have been patented, including use of many different types of catalysts, continuous or semicontinuous processes, methods which rely on formation of bischloroformate oligomers followed by polycondensation, etc. 

The degree of polymerization of bischloroformate oligomers prepared in the pyridine system is controlled primarily by the molar ratio of phosgene to bisphenol-A, as long as the ratio is greater than 1. Increas-... 

A newer process for preparation of mixtures of cycHc oligomers has been discovered (15,35). This process utilizes a triethylamine-catalyzed hydrolysis condensation of BPA bischloroformate in a pseudo-dilution reaction. This efficientiy provides 85—90% yield of a mixture of cycHc oligomers having a degree of polymeriza tion of 2 to about 12 (eq. 12). 

Bisphenol-A is present as the disodium salt in the aqueous phase of the two-phase mixture. Phosgene enters the system and dissolves in the organic phase. It is believed that the reaction between phosgene and bisphenol-A occurs at the organic-aqueous interface to form the monochloroformate—Reaction 1—or bischloroformate—Reaction 2— ester of bisphenol-A. The chloroformate esters that form grow to oligomers by reaction with additional bisphenol-A or by self-condensation —Reactions 3 and 4, respectively. 

Figure 2. GPC curves for bisphenol-A oligomer bischloroformates prepared by the interfacial technique at the reaction temperatures and stirrer speeds shown...

Analysis of Bisphenol-A Carbonate Oligomers for Chloroformate Chlorine. Chloroformate chlorine end groups were determined by a modified Volhard procedure in which the bischloroformate first reacts with aqueous pyridine to convert chloroformate to chloride ion. The chloride ion is extracted into water and titrated by the Volhard procedure. 

The various peaks in Figure 2 occur often in GPC analysis of bis-phenol-A oligomer bischloroformates. The peaks that elute at 30.9 and 29.6 counts, respectively, were identified as monomer and dimer bisphenol-A bischloroformate. Trimer bisphenol-A bischloroformate elutes at 28.8 counts, but it is not resolved in Figure 2. The broad portion of the elution curve that peaks around 27 counts consists of all oligomers that are three and higher in degree of polymerization. 

Figure 4. GPC curves of the products separated by the boiling-hexane extraction of bisphenol-A oligomer bischloroformates prepared by the aqueous alkaline technique at mole ratio (NaOH ...

Figure 5. GPC curves of bisphenol-A oligomer bischloroformates prepared in benzene and THF using the same phosgene excess...

Figure 6. GPC curves of bisphenol-A oligomer bischloroformates prepared in benzene and THF. When the phosgene excess is increased from 11 to 50% with benzene as cosolvent, the molecular-weight distribution is relatively unchanged, compared with Figure 5. However, with THF as cosolvent, a change in phosgene excess from 12.5 to 25% causes a marked change in molecular-weight...

Figure 7. GPC curves for the benzene-soluble and insoluble bisphenol-A oligomer bischloroformates prepared using benzene as...

Narrow-distribution bisphenol-A oligomer bischloroformates can be isolated by fractional precipitation of pyridine-prepared oligomers. Oligomer XII was separated into three fractions by adding hexane to a... 

Figure 8. GPC curves of the bisphenol-A oligomer bischloroformates prepared using a 25% excess of phosgene in THF as cosolvent, and fractionated by precipitating from methylene chloride solution by addition of n-hexane. The volume ratios of solvent and nonsolvent are noted...

Other cyclic monomers have been prepared and polymerized through fast ROP. The main focus has been first on bisphenol A carbonate oligocyclic monomers (Brunelle et al., 1994). The oligocyclic monomers were prepared using an amine-catalyzed reaction of bisphenol A bischloroformate, via an interfacial hydrolysis/condensation reaction that also produces linear oligomers and polymers, depending on the structure and concentration of the tertiary amine (Aquino et al., 1994, Table 2.28). 

Recently, a,co-bis-hydroxy-terminated poly(l,3-propylene succinate) has been chain-extended to yield high molecular weight poly(ester-carbonates) [44] using a bischloroformate route. Thus, using a molar ratio of 1,3-propanediol to succinic acid of 1.02, an oligomer having Mn of 2,200 and Mw of 3,000 was ob-... 

Currently it is possible to obtain low-molecular-weight cyclic oligomers completely selectively with respect to linear oligomers by applying pseudo-high-dilution conditions to a hydrolysis/condensation reaction of BPA bischloroformate, catalyzed by EtsN in biphasic dichloromethane/NaOHaq. (Scheme 14). 

---