0001 The present invention discloses a process for the preparation of a stabilized polyester that is low in the generation of aldehydes which comprises reacting one or more diacids with one or more diols in an esterification process, and/or one or more diesters with one or more diols in a transesterification process in the presence of an effective amount of a stabilizer selected from the group consisting of (a) a polyhydric alcohol; (b) a phosphinic acid; (c) a sterically hindered amine; or (d) a polyacrylamide. Such polyesters, for example PET, when extrusion compounded exhibit a lower residual acetaldehyde content than does PET alone when similarly treated. The invention pertains to any polyester used in the manufacture of bottles or containers which in turn are used to store consumer materials, especially food, pharmaceuticals, beverages and most especially water. 0002 A low amount of contaminants (e.g. aldehydes) in polyester water bottles is beneficial for improved taste or flavor in bottled water or other bottled beverages in said containers. The reduction in the amount of acetaldehyde in polyethylene terephthalate (PET) is highly beneficial in this respect. Acetaldehyde is known as a decomposition product of polyesters such as PET. The acetaldehyde imparts an undesirable taste or flavor to bottled water stored in polyethylene terephthalate bottles. It has been a long sought objective of the industry to reduce the level of acetaldehyde which migrates out of the PET bottle walls into the water or other beverage stored therein. A number of engineering or design changes to extruders, injection molding machines for preforms and bottle making machinery have been made to minimize formation of acetaldehyde when PET is processed. Modification to the PET composition itself have been made to lower its melting point or its melt viscosity in order to allow less severe thermal or mechanical damage when PET is processed into preforms or bottles. 0003 U.S. Pat. No. 5,235,027 teaches the preparation of a modified copolyethylene terephthalate for processing by extrusion blow molding with a low acetaldehyde content in the presence of a tri- or tetrahydroxyalkane. 0004 WO-A-00/73379 discloses a process for preparing a stabilized polyester that is low in the generation of aldehydes by reacting one or more diacids with one or more diols in an esterification process, and/or one or more diesters with one or more diols in a transesterification process, and adding a phosphorus-containing stabilizer to a polyester between the end of the melt phase and prior to subsequent secondary melting of the polyester in processing to the final article such as a bottle, characterized in that the stabilizer comprises one or more tri(phenyl) phosphites, wherein each phenyl group independently contains at least one substituted ortho position and, optionally mixed with one or more phenolic antioxidants. 0005 These known processes for preparing polyesters do not satisfy in every respect the high requirements which a polyester is required to meet, especially with regard to aldehyde content of the polyester after extrusion to an end-use article like a bottle for mineral water, color properties and transparency. As a result there continues to be a need for an improved process for the preparation of polyesters. 0006 The instant invention pertains therefore to a a process for the preparation of a stabilized polyester that is low in the generation of aldehydes which comprises reacting one or more diacids with one or more diols in an esterification process, and/or one or more diesters with one or more diols in a transesterification process in the presence of an effective amount of a stabilizer selected from the group consisting of 0007 a) a polyhydric alcohol of the formula I

E(OH)n(I)

0008 wherein n is 3 to 4000, and 0009 E is an aliphatic, cycloaliphatic, aromatic or a mono-, di- or poly-sucrose moiety; with the proviso that, if n is 3 or 4 and E is an aliphatic moiety, then additionally at least one sterically hindered hydroxyphenylalkylphosphonic ester or monoester is present; 0010 b) a compound of the formula II 2

0011 wherein 0012 R1 is hydrogen, C1-C20alkyl, phenyl or C1-C4alkyl substituted phenyl; biphenyl, naphthyl, CH2OC1-C20alkyl or CH2SC1-C20alkyl, 0013 R2 is C1-C20alkyl, phenyl or C1-C4alkyl substituted phenyl; biphenyl, naphthyl, CH2OC1-C20alkyl or CH2SC1-C20alkyl, or R1 and R2 together are a radical of the formula III 3

0014 wherein 0015 R3, R4 and R5 independently of each other are C1-C20alkyl, phenyl or C1-C4alkyl substituted phenyl, 0016 c) a sterically hindered amine which comprises at least a radical of the formula IV or V 4

0017 wherein 0018 G is hydrogen or methyl, and 0019 G1 and G2 are hydrogen, methyl or together are oxygen, 0020 d) a polyacrylamide of the formula VI 5

0021 wherein 0022 R1, and R2 are independently of each other hydrogen, C1-C20alkyl, phenyl or C1-C4-alkyl substituted phenyl; biphenyl, naphthyl, CH2OC1-C20alkyl or CH2SC1-C20alkyl; or R1 and R2 together are a radical of the formula III 6

0023 R1 and R2 together with the nitrogen atom to which they are attached form an unsubstituted or C1-C4alkyl substituted imidazolyl, pyrrolyl, pyrrolidonyl, piperidinyl or piperazinyl ring; and 0024 q is 5 to 300000; or 0025 a polyacrylamide copolymer wherein the comonomer is an acrylic acid, an acrylic acid salt or an acrylic ester; or 0026 e) hydroxylamines and/or nitrones. 0027 Of interest is a process comprising components (a), (b), (c) or (d) with the proviso that the comonomer in component (d) is acrylic acid or an acrylic ester. 0028 Also of interest is a process comprising in addition to components (a), (b), (c), (d) or (e) at least one sterically hindered hydroxyphenylalkylphosphonic ester or monoester component (f). 0029 Of special interest is a process comprising all components (a), (b), (c), (d), (e) and (f) in any combination, for example (a) (b); (a) (c); (a) (d); (a) (e); (a) (f); (b) (c); (b) (d); (b) (e); (b) (f); (c) (d); (c) (e); (c) (f); (d) (e); (d) (f); (a) (b) (c); (a) (b) (d); (a) (b) (e); (a) (b) (f); (b) (c) (d); (b) (c) (e); (b) (c) (f); (c) (d) (e); (c) (d) (f); (a) (d) (e); (b) (d) (e); (c) (d) (e); (a) (c) (d); (a) (c) (e); (a) (b) (c) (d); (a) (b) (c) (e); (b) (c) (d) (e); (a) (c) (d) (e) or (a) (b) (c) (d) (e). 0030 Components (a), (b), (c), (d) or (e) and optionally the sterericlly hindered hydroxyphenylalkylphosphonic ester or monoester are used for example in an amount of 0.005 to 1% by total weight of the reactants, preferably in an amount of 0.01 to 0.30% by total weight of the reactants. 0031 A preferred sterically hindered hydroxyphenylalkylphosphonic ester or monoester is a compound of the formula VII 7

0032 wherein 0033 R6 is isopropyl, tert-butyl, cyclohexyl or cyclohexyl which is substituted by 1-3 C1-C4alkyl groups, 0034 R7 is hydrogen, C1-C4alkyl, cyclohexyl or cyclohexyl which is substituted by 1-3 C1-C4alkyl groups, 0035 R8 is C1-C20alkyl, unsubstituted or C1-C4alkyl-substituted phenyl or naphthyl, 0036 R9 is hydrogen, C1-C20alkyl, unsubstituted or C1-C4alkyl-substituted phenyl or naphthyl; or is 1

\frac{M^{r +}}{r};

0037 Mr is an r-valent metal cation, 0038 p is 1, 2, 3, 4, 5 or 6, and 0039 r is 1, 2 or 3. 0040 C1-C20alkyl substituents are radicals such as methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, stearyl or corresponding branched isomers; C2-C4alkyl radicals are preferred. 0041 C1-C4alkyl substituted phenyl or naphthyl, which preferably contains 1 to 3, in particular 1 or 2, alkyl groups, is, for example, o-, m- or p-methylphenyl, 2,3-dimethylphenyl, 2,4-dimethylphenyl, 2,5-dimethylphenyl, 2,6-dimethylphenyl, 3,4-dimethylphenyl, 3,5-dimethylphenyl, 2-methyl-6-ethylphenyl, 4-tert-butylphenyl, 2-ethylphenyl, 2,6-diethylphenyl, 1-methylnaphthyl, 2-methylnaphthyl, 4-methylnaphthyl, 1,6-dimethylnaphthyl or 4-tert-butylnaphthyl. 0042 C1-C4alkyl substituted cyclohexyl, which preferably contains 1 to 3, in particular 1 or 2, branched or unbranched alkyl radicals, is, for example, methylcyclohexyl, dimethylcyclohexyl, trimethylcyclohexyl or tert-butylcyclohexyl. 0043 A monovalent, divalent or trivalent metal cation is preferably an alkali metal cation, alkaline earth metal cation, heavy metal cation or aluminium cation, for example Na, K, Mg, Ca, Ba, Zn or Al. Particular preference is given to Ca. 0044 Preferred compounds of the formula VII are those which contain at least one tert-butyl group as R6 or R7. Very particular preference is given to compounds of the formula VII in which R6 and R7 are simultaneously tert-butyl. 0045 p is preferably 1 or 2, very particularly preferably 1. 0046 Very particularly preferred sterically hindered hydroxyphenylalkylphosphonic ester or monoester are the compounds of the formula P1 and P2. 8

0047 The compound of the formula P1 is commercially available as Irganox 1425 (RTM) and that of the formula P2 is commercially available as Irganox 1222 (RTM) both from Ciba Specialty Chemicals Inc.. 0048 Preferred diacids are selected from the group consisting of aromatic dicarboxylic acids having 8 to 14 carbon atoms, aliphatic dicarboxylic acids having 4 to 12 carbon atoms, cycloaliphatic dicarboxylic acids having 8 to 12 carbon atoms, and mixtures thereof. 0049 Preferably such diacids are terephthalic acid, isophthalic acid, o-phthalic acid, naphthalene dicarboxylic acid, cyclohexane dicarboxylic acid, cyclohexanediacetic acid, diphenyl-4,4-dicarboxylic acid, succinic acid, glutaric acid, adipic acid, sebacic acid and mixtures thereof. 0050 Especially preferred are terephthalic acid and 2,6-naphthalene dicarboxylic acid. 0051 Preferred diols are compounds of the formula VIII

HOROH(VIII)

0052 wherein R is an aliphatic, cycloaliphatic or aromatic moiety of 2 to 18 carbon atoms. 0053 Preferably such diols are for example ethylene glycol, diethylene glycol, triethylene glycol, propane-1,3-diol, propane-1,2-diol, butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol, 1,4-cyclohexanedimethanol, 3-methylpentane-2,4-diol, 2-methylpentane-1,4-diol, 2,2-diethylpropane-1,3-diol, 1,4-di-(hydroxyethoxy)benzene, 2,2-bis(4-hydroxycyclohexyl)-propane, 2,4-dihydroxy-1,1,3,3-tetramethylcyclobutane, 2,2-bis-(3-hydroxyethoxyphenyl)propane, 2,2-bis-(4-hydroxypropoxyphenyl)ethane and mixtures thereof. 0054 Most preferably, the diol is ethylene glycol or 1,4-cyclohexanedimethanol. 0055 Instead of, or in addition to the diacids mentioned above, various diesters may be used. For example, diesters that correspond in respect of their acid moiety to the aforementioned diacids may be used. Suitable diesters therefore also include the aliphatic and the aromatic kind. Very suitable diesters are for example the C1-C4alkyl esters of terephthalic acid, isophthalic acid, o-phthalic acid or naphthalene dicarboxylic acid. 0056 Preferably, the esterification and transesterification processes are carried out in the presence of a catalyst. 0057 Catalysts of interest for the esterification process are for example antimony or germanium compounds, e.g. antimony(III)oxide (Sb2O3) or germanium dioxide (GeO2). Of interest are also titanium catalysts as disclosed for example in DE-A-19 513 056 or titanium based catalysts in combination with cobalt and phosphorous based compounds as disclosed for example in DE-A-19 518 943. 0058 Catalysts of interest for the transesterification process are for example titanium compounds, e.g. titanium(IV)butoxide. 0059 The catalysts are preferably used in the preparation of polyesters in an amount of 0.005 to 0.035% by weight of the total amount of reactants. 0060 Polyesters may be produced in a conventional batch process, wherein the product of the transesterification or sterification is formed in one vessel and then transferred to a second vessel for polymerization. The second vessel is agitated and the polymerization reaction is continued until the power used by the agitator reaches a level indicating that the polyester melt has achieved the desired intrinsic viscosity and therefore, the desired molecular weight. For example, in the preparation of polyethylene terephthalate (PET), the esterification or transesterification is typically conducted at an elevated temperature between for example 200 to 350 C. to produce a polyester having an intrinsic viscosity of 0.3 to 0.8 dl/g, commonly about 0.6 to 0.75 dl/g (determined by ASTM D-4603-86 at 30 C. in a mixture of 60% by weight of phenol and 40% by weight of tetrachloroethane). 0061 Alternatively, these steps may also be carried out in a continuous process. For example, the continuous process disclosed in WO-A-97/44376 is conducted by combining the diol with the diacid or diester at a temperature of about 240 to 290 C. and at a pressure of from about 30 to 600 kPa for about 1 to 5 hours to yield low molecular weight oligomers and water. In general, a continuous feed of reactants is used employing a molar ratio of diol to diacid or diester of from about 1.0 to 1.6. The water or alcohol so produced is removed as the reaction proceeds. 0062 In the second stage of the continuous process, which is a polycondensation stage generally conducted in a series of 2 or more vessels, the oligomers are agitated at a temperature of about 240 to 305 C. for about 1 to 4 hours in the presence of a polymerization catalyst to form the polyester melt. 0063 Typically, the polycondensation reaction begins in a first vessel operated at a pressure range of from about 0 to 10 kPa. Diol produced in the polycondensation is removed from the polyester melt using an applied vacuum. The polyester melt is typically agitated to allow the diol to escape from the polyester melt. 0064 As the polyester melt is fed into successive vessels, the molecular weight and thus the intrinsic viscosity of the polyester melt increases. The temperature of each vessel is generally increased and the pressure decreased to allow greater polymerization in each successive vessel. The final vessel is generally operated at a pressure of from about 0 to 5.5 kPa. Each of the polymerization vessels communicates with a flash vessel. The retention time in the polymerization vessels and the feed ratio of the reactants into the continuous process are determined in part based on the target molecular weight of the poly st r. 0065 The polymerization catalyst employed in the continuous process is generally added prior to, at the start of, or during the polymerization stage. 0066 When the polymerization process is completed, the resulting polyester, which is still in the form of a melt, is generally filtered and the typically extruded and pelletized before being worked up into specific polyester articles or injection molded in a preform or coating into an item such as a bottle. Such steps are also typically labeled as polyester processing but refer of course to later working of the finished polyester rather than to the chemical processing steps used to form the polyester in the first place. 0067 For example, polyester melt may be extruded into polyester sheets, filaments, pellets, chips or similar particles (so-called primary extrusion step). Preferably, the polyester melt is extruded shortly or immediately after exiting the polycondensation stage, whereupon it is quenched, for example in a water trough or alternative cooling unit. The formation of pellets or chips is particularly convenient for storage, transport and handling purposes. 0068 The pellets of chips may be subjected to solid state polymerization (SSP), for example, to raise the intrinsic viscosity to 0.7 to 1.2 dl/g, preferably to about 0.83 dl/g. 0069 In order to produce the final polyester articles, in the form of bottles, filaments, sheets, molded articles and the like, the pellets or chips are re-melted and re-extruded or injection molded. The extrusion and injection molding conditions are conventional. For example, the polyester may be extruded at a temperature in the range of 240 to 315 C. 0070 A preferred polyhydric alcohol of the formula I is, for example starch, cellulose, a sugar or a sugar alcohol, especially cellulose or starch. 0071 An especially preferred polyhydric alcohol of the formula I is poly(ethylene-co-vinyl alcohol), poly(styrene-co-allyl alcohol), sorbitol, isomalt, xylitol, sucrose, mucic acid dibutylester, mucic acid di(phenyl-1-ethyl)ester, pentaerythritol, maltose, maltitol, maltopentaose hydrate, maltoheptaose, maltot traose, maltulose monohydrate, D,L-glucose, dextrose, D-mannitol, trimethylol propane, triethylol propane or glycerol. 0072 Preferred compounds of the formula II are those in which 0073 R1 is hydrogen, C1-C12alkyl, phenyl, biphenyl, naphthyl, CH2OC1-C12alkyl or CH2SC1-C12alkyl, and 0074 R2 is C1-C12alkyl, phenyl, biphenyl, naphthyl, CH2OC1-C12alkyl or CH2SC1-C12alkyl. 0075 Of special interest are compounds of the formula II wherein R1 and R2 are C4-C12alkyl. 0076 The preferred radicals R1 and R2 are identical to the preferred radicals R1 and R2. 0077 An especially preferred component (c) is for example a compound of the formula H1, H2, H3, H4, H5, H6, H7, H8, H9, H10, H11, H12, H13, H14or H15 9

0078 in which 0079 m is a number from the range from 2 to 200, 11

0080 Preferred hydroxylamines of component (e) are compounds of th formula IX 12

0081 wherein 0082 T1 is straight or branched chain alkyl of 1 to 36 carbon atoms, cycloalkyl of 5 to 12 carbon atoms, aralkyl of 7 to 9 carbon atoms, or said aralkyl substituted by one or two alkyl of 1 to 12 carbon atoms or by one or two halogen atoms; and 0083 T2 is hydrogen, or independently has the same meaning as T1. 0084 In the present invention the compounds of component (e) are, for example, N,N-dihydrocarbylhydroxylamines of the formula IX wherein T1 and T2 are independently benzyl, methyl, ethyl, octyl, lauryl, dodecyl, tetradecyl, hexadecyl, heptadecyl or octadecyl, or wherein T1 and T2 are each the alkyl mixture found in hydrogenated tallow amine. 0085 The compounds of component (e) in the present compositions and methods are, e.g. N,N-dihydrocarbylhydroxylamines selected from the group consisting of N,N-dibenzylhydroxylamine, N,N-diethylhydroxylamine, N,N-dioctylhydroxylamine, N,N-dilaurylhydroxylamine, N,N-didodecylhydroxylamine, N,N-ditetradecylhydroxylamine, N,N-dihexadecylhydroxylamine, N,N-dioctadecylhydroxylamine, N-hexadecyl-N-tetradecylhydroxylamine, N-hexadecyl-N-heptadecylhydroxylamine, N-hexadecyl-N-octadecylhydroxylamine, N-heptadecyl-N-octadecylhydroxylamine, N-methyl-N-octadecylhydroxylamine and N,N-di(hydrogenated tallow)hydroxylamine. 0086 Component (e) in the present invention may be for example the N,N-di(alkyl)hydroxylamine produced by the direct oxidation of N,N-di(hydrogenated tallow)amine Irgastab FS-042 (RTM), Ciba Specialty Chemicals Corp.. 0087 The hydroxylamines are for example those disclosed in U.S. Pat. No. 4,590,231 or U.S. Pat. No. 4,612,393. 0088 Preferred nitrones of component (e) are compounds of the formula X 13

0089 wherein 0090 L1 is straight or branched chain alkyl of 1 to 36 carbon atoms, cycloalkyl of 5 to 12 carbon atoms, aralkyl of 7 to 9 carbon atoms, or said aralkyl substituted by one or two alkyl of 1 to 12 carbon atoms or by one or two halogen atoms; and 0091 L2 and L3 are independently hydrogen, straight or branched chain alkyl of 1 to 36 carbon atoms, cycloalkyl of 5 to 12 carbon atoms, aralkyl of 7 to 9 carbon atoms, or said aralkyl substituted by one or two alkyl of 1 to 12 carbon atoms or by one or two halogen atoms; or L1 and L2 together form a five- or six-membered ring including the nitrogen atom. 0092 The nitrones of component (e) may be the corresponding oxidation products of the hydroxylamines. That is to say, the nitrones of component (e) may be nitrone analogues of the hydroxylamines. The nitrones may be for example, N-benzyl--phenylnitrone, N-ethyl--methylnitrone, N-octyl--heptylnitrone, N-lauryl--undecylnitrone, N-tetradecyl--tridcylnitrone, N-hexadecyl--pentadecylnitrone, N-octadecyl--heptadecylnitrone, N-hexadecyl--heptadecylnitrone, N-ocatadecyl--pentadecylnitrone, N-heptadecyl--heptadecylnitrone, N-octadecyl--hexadecylnitrone, N-methyl--heptadecylnitrone the nitrone derived from N,N-di(hydrogenated tallow)hydroxylamine or the compound of the formula N1 14

0093 The nitrones of component (e) may be for example as described in U.S. Pat. No. 4,898,901. 0094 Of special interest is a process for the preparation of a stabilized polyester that is low in the generation of aid hydes wherein the diacid is terephthalic acid or isophthalic acid; the diester is a C1-C4alkyl ester of terephthalic acid or isophthalic acid; the diol is ethylene glycol; component (a) is poly(ethylene-co-vinyl alcohol), poly(styrene-co-allyl alcohol), maltitol, isomalt, sorbitol, xylitol, sucrose, mucic acid dibutylester, mucic acid di(phenyl-1-ethyl)ester, pentaerythritol or dipentaerythritol; component (b) is di-iso-octyl-phosphinic acid; component (c) is a compound of the formula H1, H2, H3, H4, H5, H 6, H7, H8, H9, H10, H11, H12, H13, H14 or H15 according to claim 13; component (d) is polyacrylanilide, an anionic acrylic polymer or a cationic acrylamide copolymer; and component (e) is N,N-dioctadecylhydroxylamine or a compound of the formula N1 15

0095 A preferred embodiment of the present invention is the use of a stabilizer selected from the group consisting of components (a), (b), (c), (d) or (e) for the preparation of polyesters that are low in the generation of aldehydes during melt processing of the polyesters. 0096 Likewise, the instant invention pertains to a polyester obtainable by the process of the instant invention; and to mineral water bottles, films, trays, containers, baby toys and automobile wind shields prepared from a polyester obtained by the process of the instant invention. 0097 The instant invention also pertains to a process for forming a bottle preform or a PET bottle or container suitable for storing water (mineral, natural, ozonated) or other foodstuffs, which allows the desirable taste of the water or foodstuff after packaging to remain unaltered after being placed in said bottle or container prepared from the polyester of the instant invention. 0098 The following examples are for illustrative purposes only and are not to be construed to limit the scope of the instant invention in any manner whatsoever. 0099 Analytical Procedures: 0100 Intrinsic Viscosity (I.V.): 1 g of polymer is dissolved in 100 g of a 1:1 mixture of phenol and dichlorobenzene. The viscosity of this solution is measured at 30 C. in an Ubelode-Viscosimeter and recalculated to the instrinsic viscosity. 0101 Acetaldehyde Analysis: The concentration of acetaldehyde in PET is quantitatively determined using a thermal desorption GC-MS method adapted from B. Nijassen et al., Packaging Technology and Science, 9, 175 (1996); S. Yong Lee, SPE ANTEC 1997, pp 857-861; and M. Dong et al., J. Chromatographic Science, 18, 242 (1980). A general example follows below: 0102 The PET samples are analyzed, in duplicate, by weighing 250 mg of powdered PET pellets (cryogenically pulverized) in a 5 ml crimp sealed headspace vial. The sample vial is heated at 120 C. for one hour in a Tekmar model 5000 static headspace analyzer. The headspace gas (5 cc) is then transferred via a heated transfer line to a Fisons MD-800 GC-MS system for SIR detection of the acetaldehyde. The acetaldehyde is detected by monitoring its fragment ions of 29 and 44 m/e. The Total Ion Current (TIC) of the GC-MS is also monitored in the retention time region of 4-8 minutes. The presence of acetaldehyde in the samples is confirmed by three different detectors. By using a known acetaldehyde value for PET, the ration of peak areas for the known PET resin and for the experimental PET resins are compared and the amount of acetaldehyde in the experimental PET can be obtained. Alternatively a commercially available standard of acetaldehyde in water (approx. 1 ppm) may be used to establish calibration of the GC-MS.

EXAMPLE 1

Preparation of Polyethylene Terephthalate 0103 1621.3 g of ethylene glycol, 3338.5 g of terephthalic acid, 66.8 g of isophthalic acid, 1.36 g of antimony trioxide are mixed within a metal container with a stabilizer in an amount as indicated in Table 1. The mixture is transferred into a 10 liter reactor (stainless steel) fitted with stirrer, refluxing unit and an outlet-die at the bottom of the reactor. The reactor is pressurized with nitrogen up to 6 bars. The monomer mixture is heated from room temperature to 250 C. within 30 minutes. A water/ethylene glycol mixture is distilled off for 3.5 hours. The temperature is increased consecutively to 280 C. Within the next 5 hours the pressure is continuously reduced to further distill off water and ethylene glycol. Then polyester product is extruded through the bottom die, cooled to room temperature in a water bath and pelletized to yield clear polyethylene terephthalate (PET) granules. From these granules the acetaldehyde content in ppm Total Ion Current method (TIC) and the Intrinsic Viscosity (I.V.) in dl/g was measured. The results are summarized in Table 1. 1TABLE 1AcetaldehydeAcetalde-content in ppmhyde contentExam-Stabilizerafter polycon-I.V.in ppm afterpleweight %densationdl/gextrusion1aa)none1700.755.01bb)0.20% compound 101c)400.501.61cb)0.09% compound 101c)760.681db)0.05% compound 101c)620.652.81eb)0.10% compound 102d)720.731fb)0.10% compound 103e)490.701gb)0.10% compound 104f)580.571hb)0.10% compound 105g)820.701ib)0.10% compound 106h)940.681jb)0.10% compound 107i)780.641kb)0.10% compound 108j)620.721lb)0.10% compound 109k)780.643.91mb)0.10% compound 110l)970.690.25% compound 111m)1nb)0.10% compound 112n)990.701ob)0.05% compound 113o)580.682.31pb)0.05% compound 114p)570.691qb)0.10% compound 115q)520.713.81rb)0.10% compound 116r)560.301sb)0.05% compound 117s)530.671tb)0.05% compound 118t)780.701ub)0.10% compound 119u)410.591vb)0.10% compound 120v)290.481wb)0.10% compound 121w)460.621xb)0.10% compound 122x)370.651yb)0.10% compound 123y)540.621zb)0.10% compound 124z)710.651aab)0.10% compound 125aa)340.521abb)0.10% compound 126ab)720.691acb)0.10% compound 127ac)520.581adb)0.10% compound 128ad)360.611aeb)0.10% compound 129ae)770.711afb)0.05% compound 130af)680.73a)Example for comparison. b)Example according to the invention. c)Compound 101 is poly(ethylene-co-vinyl alcohol) 63 mole % vinyl alcohol, 27 mole % ethylene, melt flow rate (210 C./2.16 kg) of 3.9 g/10 minutes. d)Compound 102 is poly(styrene-co-allyl alcohol) 60 mole % styren, 40 mole % allyl alcohol, molecular weigth 2000 g/mole. e)Compound 103 is maltitol. f)Compound 104 is isomalt a mixture of 43% O--D-glucopyranosyl-D-sorbitol (GPS) and 57% O--D-glucopyranosyl-D-mannitol-dihydrate (GPM). g)Compound 105 is sorbitol. h)Compound 106 is xylitol. i)Compound 107 is sucrose. j)Compound 108 is mucic acid dibutylester. k)Compound 109 is mucic acid di(phenyl-1-ethyl)ester. l)Compound 110 is pentaerythritol. m)Compound 111 is calcium bis(ethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate) of the formula P-1

0104

0105 n) Compound 112 is di-iso-octyl-phosphinic acid. 0106 o) Compound 113 is Tinuvin 123 (RTM) (Ciba Specialty Chemicals Inc.) of the formula H1 17

0107 p) Compound 114 is Tinuvin 622 (RTM) (Ciba Specialty Chemicals Inc.) of the formula H2 18

0108 in which m is a number from the range from 2 to 200. 0109 q) Compound 115 is polyacrylanilide with a number average molecular weight Mn: 10600 g/mol; weight average molecular weight Mw: 45000 g/mol measured by GPC, eluent and solvent is tetrahydrofurane; internal standard is cyclohexane. 0110 r) Compound 116 is dipentaerythritol. 0111 s) Compound 117 is Tinuvin 765 (RTM) (Ciba Specialty Chemicals Inc.) of the formula H4 19

0112 t) Compound 118 is Tinuvin 770 (RTM) (Ciba Specialty Chemicals Inc.) of the formula H8 20

0113 u) Compound 119 is a compound of the formula H9 21

0114 v) Compound 120 is a compound of the formula H10 22

0115 w) Compound 121 is a compound of the formula H11 23

0116 x) Compound 122 is a compound of the formula H12 24

0117 y) Compound 122 is a compound of the formula H13 25

0118 z) Compound 124 is a compound of the formula H14 26

0119 aa) Compound 125 is a compound of the formula H15 27

0120 ab) Compound 126 is Magnafloc 611 (RTM) (Ciba Specialty Chemicals Inc.), an anionic acrylic polymer, sold as flocculant. 0121 ac) Compound 127 is Zetag 7633 (RTM) (Ciba Specialty Chemicals Inc.), a cationic acrylamide copolymer, sold as sewage and industrial sludge flocculant. 0122 ad) Compound 128 is Magnafloc 139 (RTM) (Ciba Specialty Chemicals Inc.), a weak anionic acrylic polymer with low molecular weight, sold as flocculant. 0123 ae) Compound 129 is a compound of the formula N1 (nitrone) 28

0124 af) Compound 130 is N,N-dioctadecylhydroxylamine. 0125 The polycondensation in the melt as described above is followed by a solid state polycondensation (SSP) for further increasing the molecular weight by monitoring the instrinsic viscosity. Furthermore, this process decreases the content of acetaldehyde. 0126 The following description illustrates the general technical procedure: 2.5 kg of polyethylene terephthalate according to Examples la is placed at room temperature into a vacuum tumbling dryer. During continuous tumbling of the polyethylene terephthalate under a vacuum of 0.06 mbar the following temperature protocol is followed: a) 1 hour at 120 C., b) 1 hour at 160 C., c) 1 hour at 190 C., and d) 5 hours at 220 C. The obtained product revealed an intrinsic viscosity value of 0.82 dl/g and a content of acetaldehyde of 0.85 ppm. Additionally all polyethylene terephthalate samples according to Examples 1b-1q were treated similar under solid state polycondensation condition. The target intrinsic viscosity value of 0.800.02 is achieved by adjusting the solid state polycondensation processing conditions like for example time and temperature. The content of acetaldehyde after solid state polycondensation of Examples 1b-1q is proven to be below 1 ppm in all samples. 0127 Examples 1a, 1b, 1d, 1l, 1o and 1q which were treated under solid state polycondensation condition were additionally melt extruded in a Leistritz 18 mm co-rotating, intermeshing twin screw extruder at a temperature range of 280-284 C. From these extruded polyethylene terephthalate samples the content of acetaldehyde is measured. The results which are summarized in the last column of Table 1 clearly reveal that a significant reduction of the rebuilding of acetaldehyde during extrusion is observed in Examples 1b, 1d, 1l, 1o and 1q according to the invention which contain a stabilizer in comparison to Example 1a which does not contain a stabilizer.