Alternating copolymerization of propylene oxide and carbon dioxide with an alumina supported diethylzinc catalyst

Current research efforts in the field of poly(propylene carbonate) prepared from carbon dioxide and propylene oxide are reviewed. Interest in the polymer has been revived in light of the current discussion on sustainability and biodegradability. The progress in understanding and increasing the activity of heterogeneous zinc catalysts is steadily increasing, but without a quantum leap. The microstructure, the properties of the melt, and the solid material are given. The material property profile can be expanded through the synthesis of terpolymers based on propylene oxide, carbon dioxide and other epoxides, lactones or anhydrides etc. with the same catalyst; or the preparation of poly(propylene carbonate) blends with biodegradable or biocompatible components like calcium carbonate, wood flour, fibers, or other biodegradable polymers.

Copolymerization of carbon dioxide and propylene oxide with highly effective zinc hexacyanocobaltate(III)-based coordination catalyst

The homopolymerization of propylene oxide was first conducted at 80°C in the absence of any solvent by using various metal salts of acetic acid and it was found that Mg(OAc)2, Cr(OAc)3, Mn(OAc)2, Co(OAc)2, Ni(OAc)2, Zn(OAc)2, and Sn(OAc)2 were effective for the polymerization. The copolymerization of propylene oxide and carbon dioxide was next examined by using these effective metal salts of acetic acid as catalysts. Most of these were effective also for the copolymerization. The nature of the polymer obtained was strongly dependent on the catalyst used. Co(OAc)2 and Zn(OAc)2 gave an alternate copolymer of propylene oxide and carbon dioxide, Mg(OAc)2, Cr(OAc)3, and Ni(OAc)2 gave a random copolymer, while Sn(OAc)2 gave a homopolymer of propylene oxide. Then the copolymerization of propylene oxide and carbon dioxide was kinetically investigated in some detail by using Co(OAc)2 as a catalyst. On the basis of the results obtained, a plausible mechanism was proposed for both the homopolymerization of propylene oxide and copolymerization of propylene oxide and carbon dioxide.

Diethylzinc was allowed to react with various metal oxides in n‐heptane at 60°C, and the copolymerization of propylene oxide and carbon dioxide was investigated at 60°C in solution in dioxane with reaction products as catalysts. An alternate copolymer was obtained with every catalyst, but the yield of copolymer and the number‐average molecular weight depended significantly on the supporting materials. In a kinetic study of the copolymerization we found that the catalytic efficiency (number of propagating species per number of zinc supported) was only a few percent with every catalyst. The copolymerization was also examined by using several kinds of silica, whose pore diameters are markedly different, as supports. The results obtained strongly suggested that only the active species existing in large pores act as the propagating species.

Copolymerization of CO2 and propylene oxide using ZnGA/DMC composite catalyst for high molecular weight poly(propylene carbonate)

Cobalt porphyrin complex (TPPCoIIIX) (TPP = 5, 10, 15, 20‐Tetraphenyl‐ porphyrin; X = halide) in combination with ionic organic ammonium salt was used for the regio‐specific copolymerization of propylene oxide and carbon dioxide. A turnover frequency of 188 h−1 was achieved after 5 h, and the byproduct propylene carbonate was successfully controlled to below 1%, where the obtained poly(propylene carbonate) (PPC) showed number average molecular weight (Mn) of 48 kg/mol, head‐to‐tail content of 93%, and carbonate linkage of over 99%. When the polymerization time was prolonged to 24 h, PPC with Mn over 115 kg/mol and head‐to‐tail linkage maintaining 90% was prepared, whose glass transition temperature reached 44.5 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5959–5967, 2008

The reactions between (TPP)AlX, where TPP = tetraphenylporphyrin and X = Cl, O(CH(2))(9)CH(3), and O(2)C(CH(2))(6)CH(3), and propylene oxide, PO, have been studied in CDCl(3) and have been shown to give (TPP)AlOCHMeCH(2)X and (TPP)AlOCH(2)CHMeX compounds. The relative rates of ring opening of PO follow the order Cl > OR > O(2)CR, but in the presence of added 4-(dimethylamino)pyridine, DMAP (1 equiv), the order is changed to O(2)CR > OR. From studies of kinetics, the ring opening of PO is shown to be first order in [Al]. Carbon dioxide inserts reversibly into the Al-OR bond to give the compound (TPP)AlO(2)COR, and this reaction is promoted by the addition of DMAP. The coordination of DMAP to (TPP)AlX is favored in the order O(2)C(CH(2))(6)CH(3) > O(2)CO(CH(2))(9)CH(3) >> O(CH(2))(9)CH(3). The microstructure of the poly(propylene carbonate), PPC, formed in the reactions between (TPP)AlCl/DMAP and (R,R-salen)CrCl and rac-PO/S-PO/R-PO and CO(2), has been investigated by (13)C [(1)H] NMR spectroscopy. The ring opening of PO is shown to proceed via competitive attack on the methine and methylene carbon atoms, and furthermore attack at the methine carbon occurs with both retention and inversion of stereochemistry. On the basis of these results, the reaction pathway leading to ring opening of PO can be traced to an interchange associative mechanism, wherein coordination of PO to the electrophilic aluminum atom occurs within the vicinity of the Al-X bond (X = Cl, OR, O(2)CR, or O(2)COR). The role of DMAP is two-fold: (i) to labilize the trans Al-X bond toward heterolytic behavior, and (ii) to promote the insertion of CO(2) into the Al-OR bond.

Propylene oxide was homopolymerized and copolymerized with carbon dioxide in the presence of catalysts based on ethylzinc phenoxide or ethylzinc 1-phenoxy-2-propoxide and/or diethylzinc and γ-alumina as a support. The propylene oxide homopolymerization yielded poly(propylene oxide) with an average molecular weight of about 20 × 103, and consisting of the prevailing amorphous fraction and the crystalline fraction. The copolymerization of propylene oxide and carbon dioxide produced poly(propylene carbonate) with an average molecular weight of about 30 × 103 and was accompanied by the formation of propylene carbonate. The polymeric products obtained were characterized by means of elemental analysis, IR, UV, 1H-NMR and 13C-NMR spectroscopy, and molecular weight determinations. On the basis of these studies, especially those concerning the polymer end-groups and the chain microstructure, a possible structure of the active sites in γ-alumina-supported zinc coordination catalysts and a possible mechanis...

To improve the thermal and mechanical properties of poly(propylene carbonate) (PPC), the copolymerization of CO2 with PO was successfully carried out in the presence of a third monomer, 4,4′-diphenylmethane diisocyanate (MDI) using supported multi-component zinc dicarboxylate as catalyst. Chemical structure, the molecular weight, as well as thermal and mechanical properties of the resulting new copolymers were fully investigated. The experimental results show that the yield increases with increasing MDI feed content from 0 to 2 wt.%. The introduction of MDI leads to an increase in the molecular weight of PPC with light crosslinking. When the MDI feed content is lower than 3 wt.%, the PPC copolymers have number average molecular weight (Mn) ranging from 153 K to 424 K g/mol and molecular weight distribution (MWD) values ranging from 1.71 to 2.79. The resulting PPC copolymers show higher glass transition temperature (Tg) and decomposition temperature compared with poly(propylene carbonate) (PPC) without MDI. Considering the gel content of the resulting copolymers, the optimized MDI feed content should be smaller than 1.5 wt.% based on PO content. The introduction of small amount of MDI provides a very effective way to improve the mechanical properties and thermal stabilities of PPC due to the increase in its molecular weight.

A series of cobalt(III) complexes LCoX, where L = 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TFPP), and 2,3,7,8,12,13,17,18-octaethylporphyirn (OEP) and X = Cl or acetate, has been investigated for homopolymerization of propylene oxide (PO) and copolymerization of PO and CO2 to yield polypropylene oxide (PPO) and polypropylene carbonate (PPC) or propylene carbonate (PC), respectively. These reactions were carried out both with and without the presence of a cocatalyst, namely, 4-dimethylaminopyridine (DMAP) or PPN(+)Cl(-) (bis(triphenylphosphine)iminium chloride). The PO/CO2 copolymerization process is notably faster than PO homopolymerization. With ionic PPN(+)Cl(-) cocatalyst the TPPCoOAc catalyst system grows two chains per Co center and the presence of excess [Cl(-)] facilitates formation of PC by two different backbiting mechanisms during copolymerization. Formation of PPC is dependent on both [Cl(-)] and the CO2 pressure employed (1-50 bar). TPPCoCl and PO react to form TPPCo(II) and ClCH2CH(Me)OH, while with DMAP, TPPCoCl yields TPPCo(DMAP)2(+)Cl(-). The reactions and their polymers and other products have been monitored by various methods including react-IR, FT-IR, GPC, ESI, MALDI TOF, EXAFS, and NMR ((1)H, (13)C{(1)H}) spectroscopy. Notable differences are seen in these reactions with previous studies of (porphyrin)M(III) complexes (M = Al, Cr) and of the (salen)M(III) complexes where M = Cr, Co.

Propylene oxide, PO, reacts when heated to 60 °C over a zinc glutarate catalyst to form poly(propylene oxide), PPO, which is regioregular, HTHTHT, and favors isotactic triads ii. Under 50 bar of CO2, poly(propylene carbonate), PPC, is formed with less than 5% polyether linkages and with an even smaller component of propylene carbonate, PC. These reactions have been studied as a function of time, and the products have been analyzed by GPC, MALDI−TOF/MS, and 13C {1H} NMR spectroscopy. Polymerization of PO yields PPO with −OH and −H end groups, and in the copolymerization of PO and CO2 the low molecular weight chains are readily identified as an alternating copolymer represented as (PO)n-alt-(CO2)m, where m = n − 1, n − 2, n − 3, n − 4, n − 5, with terminal −OH and −H groups. These results, combined with NMR data, implicate Zn−OH groups as the active initiating species, and furthermore from the molecular weight of the polymer produced at short reaction times, we can infer that some Zn−OH sites are highly act...

SummaryA nanoscopic heterogeneous catalyst system based on zinc glutarate is used to prepare poly(propylene carbonate) (PPC) from CO2 and propylene oxide (PO). The catalyst was exposed to a defined humid atmosphere. The water uptake resulted in a deactivation to a minimum of 25% of the original activity, depending on time of exposure and water concentration. In addition, the progress of the copolymerization at constant pressure was monitored by measuring the CO2 uptake. It is shown that the rate is linear with time after an initial phase and that this rate is in linear correlation with the amount of catalyst. The copolymerization was also performed in several modes of discontinuous addition of PO. The productivity of the catalyst was in the range of 1.6–2.0 kg PPC/g Zn, the highest productivity reported for the zinc carboxylate catalyst system so far. High molecular weights of around 220 kg/mol (Mw) and low polydispersities of 2.2–2.5 were achieved in all experiments.

The reactivities of chromium(III) complexes LCrX, where L = 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TFPP), and 2,3,7,8,12,13,17,18-octaethylporphyrin (OEP) and X = Cl or OH, have been studied with respect to their ability to homopolymerize propylene oxide (PO) and copolymerize PO and CO(2) to yield polypropylene oxide (PPO) and polypropylene carbonate (PPC) or propylene carbonate (PC), respectively, with and without the presence of a cocatalyst, namely, 4-dimethylaminopyridine (DMAP) or PPN(+)Cl(-) (bis(triphenylphosphine)iminium chloride). The homopolymerization is notably faster (TOF ≈ 2000 h(-1) at room temperature) than copolymerization, which commonly leads to ether-rich polymers. Studies of kinetics reveal that for TPPCr(OH) with DMAP (1 equiv) the propagation reaction rate is first order in [Cr] with excess PO. With PPN(+)Cl(-) as a cocatalyst the reaction order in [Cr] and [Cl(-)] is complicated by the presence of two growing chains, and the presence of excess [Cl(-)] facilitates the formation of PC by two different backbiting mechanisms. The fixation of CO(2) is promoted by [Cl(-)] but is not greatly influenced by CO(2) pressure (1-50 bar). The reactions and polymers have been monitored by UV-visible spectroscopy, react-IR, GPC, ESI, and MALDI TOF, and NMR ((1)H, (13)C{(1)H}) spectroscopy. Notable differences are seen in these reactions when compared with earlier studies by Darensbourg et al. with salen chromium(III) systems and related aluminum(III) porphyrins.

Synthetic routes to a series of new (salen)CoX (salen = N,N′‐bis(salicylidene)‐1,2‐diaminoalkane; X = Br or pentafluorobenzoate (OBzF5)) species are described. Several of these complexes are active for the copolymerization of propylene oxide (PO) and CO2, yielding regioregular poly(propylene carbonate) (PPC) without the generation of propylene carbonate byproduct. Variation of the salen ligand, as well as the inclusion of organic‐based ionic or Lewis basic cocatalysts, has dramatic effects on the resultant (salen) CoX catalytic activity. Highly active (R,R)‐(salen‐1)CoOBzF5 (salen‐1 = N,N′‐bis(3,5‐ di‐tert‐butylsalicylidene)‐1,2‐diaminocyclohexane) catalysts with [Ph4P]Cl or [PPN]Y ([PPN] = bis(triphenylphosphine)iminium; Y = Cl or OBzF5) cocatalysts exhibited turnover frequencies up to 720 h−1 for rac‐PO/CO2 copolymerization, yielding PPC with greater than 90% head‐to‐tail connectivity. Additionally, the (R,R)‐(salen‐1)CoOBzF5/[PPN]Cl catalyst system demonstrated a krel of 9.7 for the enchainment of (S)‐ over (R)‐PO when the copolymerization was carried out at low temperatures. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5182–5191, 2006

In this investigation, nanoSchiff bases Cobaltic complex was synthesized and used as the initiator in the copolymerization of carbon oxide and propylene oxide (PO). The nanoCobaltic complex was characterized by infrared spectroscopy (IR), and nuclear magnetic resonance spectroscopy (NMR). The influences of different factors, including reaction time, reaction temperature, and pressure of CO2 on the synthesis of polycarbonate were described. The results show that nanoCobaltic complex could be successfully applied in the copolymerization of CO2 and PO. The optimum conditions of the polymerization, which include CO2 pressure of 30 bar, reaction temperature of 80 °C, and reaction time of 3 hours.