Patent GB-588834-A (GB)
Title: Stabilisation of polyesters
IPC: C08G63/692
Filed: 1944-08-21
Abstract: High molecular weight polyesters from one or more dibasic carboxylic acids and one or more saturated aliphatic dihydrin alcohols, the recurring units of which have a chain length of at least seven carbon atoms are stabilized by condensing the ingredients to a molecular weight which is 65-90 per cent of that desired in the final polymer, adding at that stage .0015-.075 gram mols. per kilogram of polyester of a trivalent phosphorus compound selected from the group, phosphorous acid, organic esters thereof, and organic esters of thiophosphorous acid, and heating the resulting mixture.  The stabilized polyester may be heated in air at 125 DEG  C. for sixteen hours without substantial degradation or continued polymerization, and may be applied from hot melts. The final heating is preferably performed under an inert gas and/or under reduced pressure.  Suitable dihydrin alcohols are ethylene glycol, trimethylene glycol, propylene, butylene, hexylene, octylene, dodecylene, diethylene, triethylene and tetraethylene glycol or b -thiodiglycol.  Suitable dibasic acids are succinic, glutaric, a -methyl glutaric, a -ethyl glutaric, adipic, b -methyl adipic, pimelic, suberic, azelaic, sebacic, bassilic, tetradecanedioic, paraphenylene diacetic, 2 - 2 - di - carboxymethoxyphenylpropane, phthalic, terephthalic, hexahydroterephthalic, isophthalic, diglycollic, thiodibutyric, or diphenic.  Mixtures of acids may include unsaturated acids, e.g. maleic, fumaric, or dihydrosuccinic.  Anhydrides, acids, chlorides or esters may be used or salts of the acids with the halides corresponding with the glycols.  The reaction may be conducted under reduced pressure, and volatile products may be removed by passage of a gas, e.g. hydrogen or nitrogen.  Suitable catalysts are acidic, e.g. toluene sulphonic and zinc chlorides. Suitable stabilizing agents are phosphorous acid, phosphite esters, e.g. tricresyl, triphenyl, dibutylphenyl, phenyl ethyl, trimethyl, triethyl, trioctyl, diamyl, monoamyl, diphenoxyethyl, or dicyclohexyl phosphites and the corresponding thiophosphites. In the examples: (1) sebacic acid and excess glycol were refluxed with a condenser maintained at 100 DEG  C. to permit removal of water. The temperature was then increased, the condenser removed and vacuum applied.  When the polymer reached an intrinsic viscosity of 0.8, triphenyl phosphite (.00658 gm. mol/kgm. of polyester) was added and reaction continued until the intrinsic viscosity reached 0.9.  A stabilized product suitable for extrusion coating of wire was obtained.  Example 2 is similar with zinc chloride as a catalyst and earlier addition of the stabilizing agent and a product with intrinsic viscosity of 0.944.  Example 3 uses tricapryl phosphite.  Example 4 uses tri-diisobutylphenyl phosphite.  Example 5 uses triphenylethyl phosphite, example 6 tri-(diiso-butylphenoxyethyl) phosphite, example 7 phosphorous acid.  The products are stabilized against degradation by heat, light and hydrolysis.  Example 9, a stabilized polyester was prepared from sebacic acid, propylene chloride and zinc chloride with addition of tricresyl phosphite when the intrinsic viscosity reached 0.7, the reaction being then continued in nitrogen until a viscosity of 0.768 was reached.  The product was compounded with butadieneacrylonitrile synthetic rubber.  Example 10 uses ethylene glycol and succinic acid catalysed by zinc chloride with triphenyl phosphite as stabilizer.  Example 11 uses a mixture of ethylene and propylene glycols with a mixture of sebacic acid and maleic anhydride with triphenyl phosphite as stabiliser.  If desired other antioxidants may be added to the polymeric compositions in addition to the phosphites.  Specifications 510,899 and 588,833 are referred to.  The Specification as open to inspection under Sect. 91 includes the use as stabilising reagent of any ester-forming compound having an ester-forming functionality greater than two and gives a long list of substances falling within this definition.  It also mentions specifically as suitable dihydric alcohols, -cyclohexanediols, 1,2 - di - b  - hydroxyethylbenzene, di - b  - hydroxyethoxybenzene, 2.2,-(di - b  - hydroxyethoxyphenyl) propane and xylylene glycols. It contains an example in which phosphorous trichloride is used as the stabiliser, and others which employ pentaerythritol, tricarballylic acid, phosphoric acid and triphenyl phosphate.  It also has an example of a polyester from azelaic acid and dimethyl trimethylene glycol stabilised with tricresyl phosphate.  This subject-matter does not appear in the Specification as accepted.