Polycarbonate cyclic

In addition to copolymers, various blends containing polyalkylstyrenes are used in practice. One such polymer is poly(4-methoxystyrene) 1/1 w/w blend bisphenol A polycarbonate. The thermal decomposition of this polymer when heated from ambient to 500° C generates CO2, 4-methoxystyrene, a-methyl-4-methoxystyrene, p-cresol and small amounts of other phenols, poly (4-methoxystyrene), dimer and trimer with vinylidene and saturated ends, polycarbonate cyclic dimer and chain fragments, bisphenol A, etc. [94]. 

Approximately, 110 million metric tons of carbon dioxide per year (30 million metric tons carbon equivalent) are used as a raw material for the production of urea, methanol, polycarbonates, cyclic carbonates, and specialty chemicals. The largest use is for urea production, which reached about 90 million metric tons per year in 1997. ... 

MECHANISM FOR THE AMINE-CATALYZED FORMATION OF POLYCARBONATE CYCLICS... 

Mechanism for the Amine-Catalyzed Formation of Polycarbonate Cyclics. 21... 

The polycarbonate cyclic oligomers exhibit a melt viscosity of approximately 10 poise at 250 C versus the melt viscosity of the corresponding high molecular weight polymer of 50,000 to 100,000 poise at 250°C. 

Polycarbonates were first prepared by Einhom in 1898 by reacting the dihydroxybenzenes, hydroquinone and resorcinol, separately with phosgene in solution in pyridine. The hydroquinone polycarbonate was an infusible and insoluble crystalline power whereas the resorcinol polymer was an amorphous material melting at about 200°C. The third dihydroxybenzene, catechol, yields a cyclic carbonate only, which is not surprising bearing in mind the proximity of... 

The occurrence of thermal failures in a plastic depends not only on the cyclic frequency and applied stress level but also on the thermal and damping characteristics of the material. For example, polycarbonate has very little... 

The polymerization of cyclic low-molar-mass polycarbonates, polyarylates, and PBT to high-molar-mass thermoplastics has been extensively studied by the General Electric Company during the last decade.57,58 Due to very low viscosity, cyclic oligoesters can be processed like thermosetting resins but retain thermoplastic properties in the final state, after polymerization in the presence of suitable... 

Oxidoreductases Transferases Hydrolases Lyases Isomerases Ligases Phenolic polymers, polyanilines, vinyl polymers Polysaccharides, cyclic oligosaccharides, polyesters Polysaccharides, polyesters, polycarbonates, poly(amino acid)s, polyphosphates... 

Lipase CA catalyzed the polymerization of cyclic dicarbonates, cyclobis (hexamethylene carbonate) and cyclobis(diethylene glycol carbonate) to give the corresponding polycarbonates [105]. The enzymatic copolymerization of cyclobis(diethylene glycol carbonate) with DDL produced a random ester-carbonate copolymer. As to enzymatic synthesis of polycarbonates, reported were polycondensations of 1,3-propanediol divinyl dicarbonate with 1,3-propanediol [110], and of diphenyl carbonate with bisphenol-A [111]. 

More active zinc phenoxide initiators of the type [Zn(0Ar)2(Et20)2]956 were found to catalyze both the copolymerization of CHO with C02 and the terpolymerization of CHO, PO, and C02 attempts to copolymerize PO and C02 yielded predominantly cyclic carbonates. For example, (332) copolymerizes CHO and C02 at 80 °C and 800 psi to give a copolymer containing 91% syndiotactic polycarbonate linkages (and 9% polyether junctions due to the non-insertion of C02) with good activity (>350g polymer/g [Zn] in 69 h).957 However, the polymerization is not well-controlled (Mw/Mn>2.5). Variation of the phenoxide ligands revealed that (333) is 4 times... 

Aromatic polycarbonates are currently manufactured either by the interfacial polycondensation of the sodium salt of diphenols such as bisphenol A with phosgene (Reaction 1, Scheme 22) or by transesterification of diphenyl carbonate (DPC) with diphenols in the presence of homogeneous catalysts (Reaction 2, Scheme 22). DPC is made by the oxidative carbonylation of dimethyl carbonate. If DPC can be made from cyclic carbonates by transesterification with solid catalysts, then an environmentally friendlier route to polycarbonates using C02 (instead of COCl2/CO) can be established. Transesterifications are catalyzed by a variety of materials K2C03, KOH, Mg-containing smectites, and oxides supported on silica (250). Recently, Ma et al. (251) reported the transesterification of dimethyl oxalate with phenol catalyzed by Sn-TS-1 samples calcined at various temperatures. The activity was related to the weak Lewis acidity of Sn-TS-1 (251). 

Cyclic oligomers of condensation polymers such as polycarbonates and polyesters have been known for quite some time. Early work by Carothers in the 1930s showed that preparation of aliphatic cyclic oligomers was possible via distillative depolymerization [1, 2], However, little interest in the all-aliphatics was generated, due to the low glass transition temperatures of these materials. Other small-ring, all-aliphatic cyclic ester systems, such as caprolactone, lactide... 

Aluminum porphyrins with alkoxide, carboxylate, or enolate can also activate CO2, some catalytically. For example, Al(TPP)OMe (prepared from Al(TPP)Et with methanol) can bring about the catalytic formation of cyclic carbonate or polycarbonate from CO2 and epoxide [Eq. (6)], ° - and Al(TPP)OAc catalyzes the formation of carbamic esters from CO2, dialkylamines, and epoxide. Neither of the reactions requires activation by visible light, in contrast to the reactions involving the alkylaluminum precursors. Another key difference is that the ethyl group in Al(TPP)Et remains in the propionate product after CO2 insertion, whereas the methoxide or acetate precursors in the other reactions do not, indicating that quite different mechanisms are possibly operating in these processes. Most of this chemistry has been followed via spectroscopic (IR and H NMR) observation of the aluminum porphyrin species, and by organic product analysis, and relatively little is known about the details of the CO2 activation steps. 

Carbon dioxide is one of the most abundant carbon resources on earth. It reacts with an epoxide to give either a cyclic carbonate or a polycarbonate depending on the substrates and reaction conditions. Kinetic resolution of racemic propylene oxide is reported in the formation of both cyclic carbonate and polycarbonate. The fe ei value defined as ln[l-(conversion)(l+%ee)]/ln[l-(conversion)(l% ee)] reached 6.4 or 5.6 by using a Co(OTs)-salen complex with tetrabutylammonium chloride under neat propylene oxide or using a combination of a Co-salen complex and a chiral DMAP derivative in dichloromethane, respectively. 

Co(OAr)-salen complex [Ar = 2,4-(N02)2CeH3] with tetrabutylammonium chloride under neat propylene oxide, quite similar to the conditions for the cyclic carbonate synthesis, give polycarbonate with fe ei of 3.5. ° Without any additives, the use of Co(OAc)-salen provides the polycaronate with fe ei of 2.8. ... 

Salen Metal Complexes as Catalysts for the Synthesis of Polycarbonates from Cyclic Ethers and Carbon Dioxide... 

Abstract This chapter focuses on well-defined metal complexes that serve as homogeneous catalysts for the production of polycarbonates from epoxides or oxetanes and carbon dioxide. Emphasis is placed on the use of salen metal complexes, mainly derived from the transition metals chromium and cobalt, in the presence of onium salts as catalysts for the coupling of carbon dioxide with these cyclic ethers. Special considerations are given to the mechanistic pathways involved in these processes for the production of these important polymeric materials. 

Polymerization of a cyclic carbonate ester yields a linear polycarbonate [Kuhling et al., 1989 Rokicki, 2000], For example, the cyclic oligomer (m — 2-20 in Eq. 7-85) of the... 

Isosorbide and equimolar amounts of various diols were polycondensed with diphosgene in p3ridine. Different bisphenols, l,3-bis(4-hydroxybenzyloxy)pro-pane, and 1,4-cyclohexane diol were used as comonomers [59]. In some cases, large amounts of cyclic oligo- and polycarbonates were formed. 

Cyclic carbonates are not commercially available and have to be synthesized prior to use. As a result, commercially available carbonates such as diethyl carbonate [55-57] or diphenyl carbonate [93] were evaluated in polycondensation reactions with diols to prepare polycarbonates since they allow a broader spectrum of polymers to be accessed. Unfortunately, polymerizations employing diethyl carbonate require the use of an excess diethyl carbonate [55]. Nevertheless, polymers with molecular weight of 40kDa were achieved within 16 h. Also, the polymerization of diphenyl carbonate with butane-1,4-diol or hexane-1,6-diol via the formation of a cyclic dimer produced polymers with molecular weights ranging from 119 to 339kDa [93]. 

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