Poly(alkylene carbonate) polyahls are randomized, polymers containing alkylene carbonate moieties and optionally ether moieties such as di- and higher polyalkylenoxy units. Poly(alkylene carbonate) polyahls are useful in preparing polyurethanes, and as adhesives and surfactants.
Polyether polyols and polyester polyols are well-known polymers which can be further polymerized with organic polyisocyanates to prepare polyurethanes. Polyether polyols are prepared by the reaction of hydroxy-containing hydrocarbons, such as an aromatic or aliphatic diol, and epoxides, for instance ethylene oxide and propylene oxide. Polyester polyols are prepared by the reaction of polyacids, such as adipic or terephthalic acid, or esters of polyacids, such as dimethyl adipate or dimethyl terephthalate with dihydroxy-containing hydrocarbons, such as aromatic and aliphatic diols. Some poly(alkylene carbonate) polyol properties resemble polyester polyol properties, while other properties resemble polyether polyols.
It is known to prepare polycarbonates from aliphatic dihydroxyl compounds either by a process of phosgenation in which hydrogen chloride is liberated or bound by bases, such as pyridine or quinoline, or by a process of transesterification with carbonic acid esters of alcohols or phenols, preferably diphenylcarbonate, optionally with the aid of transesterification catalysts. In either case, it is essential to use phosgene or a mixture of carbon monoxide and chlorine as source of carbonic acid. Commercial processes which involve the preparation and handling of phosgene are difficult and costly because of the considerable safety risks involved and the high cost of materials due to corrosion. To this are added ecological problems, since either the spent air is contaminated with hydrogen chloride or the effluent water with sodium chloride.
Polycarbonates produced by these methods, using dihydrocarbyl compounds, may have a functionality of less than two due to inadequate or incomplete esterification or transesterification, which often prevents the products from forming high molecular weight polymers in subsequent reactions.
Stevens (in U.S. Pat. Nos. 3,248,414; 3,248,415; and 3,248,416) discloses the preparation of poly(alkylene carbonate) polyols from (1) carbon dioxide and 1,2-epoxides; (2) cyclic carbonates such as ethylene carbonate; or (3) cyclic carbonates and a 1,2-epoxide. A minor amount of a polyol is employed as an initiator. The reaction is usually conducted in the presence of a metal carbonate, metal hydroxide, trisodium phosphate, or tertiary amine.
Poly(alkylene carbonate) polyols have also been prepared by polymerization of ethylene carbonates using basic catalysts and a minor amount of glycol as initiator, Buysch et al. (U.S. Pat No. 4,105,641). These products are low in carbonate and high in ether groups concentration due to decomposition of the ethylene carbonate. In Stevens' patents discussed hereinbefore, the patentees exposed a poly(alkylene carbonate) polyol derived from ethylene carbonate and monoethylene glycol to temperatures of 160.degree. C. at 2 mm Hg pressure to remove unreacted ethylene carbonate. Hostetler (U.S. Pat. No. 3,379,693) removed unreacted ethylene carbonate from products similar to poly(alkylene carbonate) polyols by heating them to about 130.degree. C. under 1-5 mm Hg. Maximovich (U.S. Pat. No. 3,896,090) reacted ethylene carbonate with diethylene glycol and treated the reaction product under reduced pressure to remove the unreacted ethylene carbonate and diethylene glycol.
Several workers have prepared poly(alkylene carbonate) polyols and related materials by controlling an equilibrium between the reaction materials of a diol and alkylene carbonate and the products of a poly(alkylene carbonate) polyol and monoethylene glycol. The reaction is controlled by the removal of monoethylene glycol.
Malkemus (U.S. Pat. No. 3,133,113) reacted ethylene carbonate and diethylene glycol at 125.degree. C. to 130.degree. C. under reduced pressure of 10 mm Hg with concurrent removal of monoethylene glycol as distillate. This was followed by removal of starting material. This process requires large excesses of ethylene carbonate. This procedure is plagued by the presence of volatile ethylene carbonate, which condenses as a solid through the system, causing severe plugging and reducing ethylene carbonate conversion while monoethylene glycol is being removed.
Springmann et al. (U.S. Pat. No. 3,313,782) further studied this process under reduced pressure in the presence of catalysts and set limits on the reaction conditions; the reaction temperatures must be lower than the boiling point of the alkylene carbonate, but high enough to distill off the monoethylene glycol formed.
Lai et al. (U.S. Pat. No. 4,131,731) used staged reductions in pressure during the reaction of alkylene carbonate with a diol, wherein the final stage was to remove monoethylene glycol. The patentees characterized their reaction conditions by stating that the alkylene carbonate must have a boiling point 4.9.degree. C. greater than monoethylene glycol. The chemistry based on the above equilibrium was improved by Buysch et al. (U.S. Pat. No. 4,105,641) by carrying out the reactions in a solvent (e.g., cumene) capable of removing monoethylene glycol as an azeotrope with the solvent.
Until recently, the molecular weights of poly(alkylene carbonate) polyols from alkylene carbonates have been controlled by either the stoichiometry of the reactants (that is, higher alkylene carbonate to initiator ratios for higher molecular weights) or the removal of monoethylene glycol from the reaction mixture wherein an ethylene carbonate to initiator equivalent ratio of about 1 is used. Catalysts are used in most cases, as reaction rates are very slow in the absence of a catalyst. When high alkylene carbonate to initiator ratios are used to make higher molecular weight poly(alkylene carbonate) polyols, reaction rates drop severely as higher conversions are approached: long reaction times are required and the products are contaminated by unreacted alkylene carbonate. If temperatures are increased to increase the rate, product decomposition occurs with CO.sub.2 loss. However, in the process of co-pending application Ser. No. 750,362, filed July 1, 1985 and incorporated herein by reference, rates of molecular weight build up are rapid without CO.sub.2 loss. Prior to copending application Ser. No. 750,362, the choice of the ratio of starting reactants and catalysts resulted in an upper limit on the molecular weight of the poly(alkylene carbonate) polyol which could be prepared. Furthermore, the products of such processes are of relatively low molecular weight and have a broad molecular weight range; that is, they have a high poly-dispersity index and are often contaminated with unreacted starting materials and relatively low molecular weight reaction intermediates. Furthermore, the particular reactant ratio and catalyst used have a significant effect on the amount of alkylene carbonate moieties in the backbone of the chain.
A process for preparing higher molecular weight poly(alkylene carbonate) polyols beyond the limitations imposed by the stoichiometry and catalyst used at reasonable reaction rates and free of low molecular weight contaminants is disclosed in copending application Ser. No. 750,362, filed July 1, 1985. What is needed is a process for preparing higher molecular weight poly(alkylene carbonate) polyahls which are modified by the incorporation of other materials chemically bound into the polymer backbone. The introduction of a modifier allows adjustment of the physical and chemical properties of the poly(alkylene carbonate) polyahl prepared by the present process to maximize its effectiveness in specific applications. Modifiers can be materials such as polyahls which can react with the carbonate moieties of poly(alkylene carbonate) polyahls or they can be materials such as poly acids, polyesters or cyclic anhydrides which can react with the active hydrogen moieties (ahl) of poly(alkylene carbonate) polyahls. Some modifiers could be reactive toward both moieties.
As defined, for example, in U.S. Pat. No. 4,431,754 a polyahl is any polyfunctional compound having more than 1 active hydrogen moiety.