CA1084649A - Thermoplastic copolyesters - Google Patents

Abstract

Thermoplastic copolyesters Abstract of the Disclosure Copolyesters which are based on poly-1,4-butylene terephthalate and contain 2.5-15 mol%, relative to the poly-ester, of branched aliphatic dicarboxylic acids with 7-30 C
atoms are outstandingly suitable for the manufacture of moul-dings having improved toughness properties.

Description

;49 The present invention relates to copolyesters which are based on poly-1,4-butylene terephthalate and contain co-condensed branched aiiphatic dicarboxylic acids.
Recently, reinforced and unreinforced poly-1,4-butylene terephthalate has gained importance as a high-grade material. This thermoplastic moulding composition is one of the so-called engineering pla~tics, that is to say those materials from which mouldings with high mechanical strength properties can be manufactured by means of suitable moulding processes~ for example injection moulding or extrusion. These moulding compositions are also distingui-shed by advantageous processing properties.
In spite o~ this advantageous spectrum of properties, this material cannot satis~y the demands made in all the fields of application. Thus, it has not been possible hitherto to replace other materials, such as, ~or example, the polyamides, which are known for the same intended application but possess certain disadvantages. Inter alia, the absorption of moisture, and the dependence, associated therewith, of mechanical properties on the environmental conditions, is a disadvantage when using polyamides. It is thus desirable to modify poly-1,4-butylene terephthalate in such a way that it can fulfil the demands made in various fields of application where, for example, a higher flexib ility and a higher toughness of the material is required.
In addition to pure poly-1,4-butylene tereph-thalate, copolyesters with other diols and dicarboxylic acids have also been disclosed. In German Offenlegung~schrift

2,051,232 , poly-1,4-butylene terephthalates of higher molecular weight and copolyesters thereof with aliphatic dicarbo~ylic acids are proposed ~or the manufacture of moulded articles. The only branched dicarboxylic acid "' ' :
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4~3 mentioned here is dimethylmalonic,;acid. German Offenlegungs-schrift 2,049,538 describes cry$~alline sheets of poly-1,4-butylene terephthalate and copolyesters thereof with aliphatic dicarboxylic acids, such as adipic acid, azelaic acid and dimethylmalonic acid. A process ~or the manufacture of copo]yesters of polyalkylene terephthalates is described in German Of~enlegungsschrift 2,336,026 ,the co-components mentioned being some linear aliphatic dicarboxylic acids, such as, or example, glutarlc acid and sebacic acid.
Finally, German Offenlegungsschrift 2,340,959 discloses adhesive compositions from a vinyl-aromatic polymer and a copolyester of poly-1,4-butylene terephthalate and dimer acid (dicarboxylic acids obtained by dimerisation of unsaturated fatty acids). These copolyesters can also contain other aliphatic dicarboxylic acids, such as, for example, maleic acid, dimethylmalonic acid, adipic acid or 2-methyladipic acid.
It is the object of the present invention to provide copolyesters based on poly-1,4~butylene terephthalate (PBT) which, compared with pure PBT, has increased flexibility and notched impact strength, without the advantageou-~processing properties being unduly impaired thereby.
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The present invention relates to linear thermoplas-tic copolyesters from terephthalic acid, 1,4-butanediol and a saturated aliphatic dicarboxylic acid, which have a relative viscosity of at least 1.6, measured at 30 in a 1% strength solutlon of equal parts of phenol and symmetrical tetrachloroethane, wherein, as the aliphatic dicarboxylic acid, 2.5-15 mol ~, relative to the polyester, of one or more branched dicarboxylic acids with 7 to 30 carbon atoms per molecule are co-condensed in the polyester in statistical distribution.

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Preferably, 3 to 10, especially 4 to 7.5, mol ~ of dicarboxylic acid are co-condensed, the relative viscosity is preferably 1.6 to 3.5, the branched dicarboxylic acid preferably contains 8 to 22 carb'on;atoms and the branched dicarboxylic acid preferably contains branched alkylene groups.
The branched dicarboxylic acid can have one or several branches and the alkyl of the side chain can preferably contain 1 to 18 carbon atoms. Both long-chain dicarboxylic acids with short side chains, for example methyl, and short-chain dicarboxylic acids with longer side chains, for example ethyl to eicosyl, are suitable. The short-chain dicarboxylic acids preferably contain 1 to 4 carbon atoms in the alkylene and 4 to 18 carbon atoms in the alkyl. The shorter the alkylene, the longer preferably is the alkyl.
Examples o suitable dicarboxylic acids are:
n-butylmalonic acid, decylmalonic acid, n-propylglutaric acid, 2,3-diethylglutaric acid, 2-methyladipic acid, 2,2,4-trimethyladipic acid, octadecylglutaric acid, 1,3-dodecanedicarboxylic acid, 1,6-tetradecanedicarboxylic acid, 1,8- or l,9-heptadecanedicarboxylic acid, 1,12-penta-decanedicarboxylic acid, 1,17-octadecanedicarboxylic acid and 1,12-eicosanedicar~oxylic acid.
The copolyesters according,to the invention are manufactured, by means of known processes, by a polycon- , densation reaction of terephthalic acid, an aliphatic branched dicarboxylic acid with 7 to 30 carbon atoms or , , polyester-forming derivatives thereof, with 1,4-butanediol.

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Examples of the known processes for the manufacture of the new polyesters are solution condensation, azeotropic condensation, interface condensation, melt condensation or solid phase condensation and also combinations of these methods, depending on which polyester-forming derivatives and which reaction catalysts are used. The polyester--forming derivatives of terephthalic acid and of the aliphatic branched dicarboxylic acids are in the main the low-molecular dialkyl estexs ~ith 1 to 4 carbon atom$ in the molecule, preferably dimethyl esters or diphenyl esters.
Moreover, the acid dihalides, in particular the acid dichlorides, and the anhydrides are also suitable.
The new polyesters can be manufactured by ester-ifying, or transesterifying, terephthalic acid and branched aliphatic dicarboxylic acids, or low-molecular dialkyl esters thereof, with 1,4-butanediol in an inert atmosphere, for example a nitrogen atmosphere, in the presence of catalysts and with simultaneous removal of the resulting water or alkanol respectively, at 150-250UC and subse~uent~
ly carrying out the polycondensation at 200 to 270C and under reduced pressure in the presence of certain catalysts, until the polycondensed products have the desiredviscosity.
Amines, inorganic or organic acids, for example hydrochloric acid or p-toluenesulphonic acid, or metals or metal compounds, which are also suitable as the trans-esterification catalyst, can be used in a known manneer as the esterification catalysts.
Since some catalysts preferentially accelerate the transesterification and other catalysts preferentially accelerate the polycondensation, it i8 advantageous to use a combination of several catalysts. Examples of suitable ., ': . ' ' ' " ' ' ' ' ' '.

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transesterlfication catalysts are the oxides, salts or organic compounds of the metals calcium, magnesium, zinc, cadmium, manganese, titanium and cobalt. The metals as such can also be used as catalysts. For example, the polycon-densation is catalysed by metals such as lead, titanium, germanium, tin and, in particular, antimony, or bycompounds thereof. These catalysts can be added to the reaction mixture together or separately. Thése catalysts are employed in amounts of about 0.001 to 1.0 per cent by weight, relative to the acid component.
In the manufacture of the new polyesters, catalysts which are used with particular advantage are those which accelerate both the transesterification and the polycon-densation. Possible catalysts of this type are above all mixtures of different metals or metal compounds and also corresponding metal alloys.
The polycondensation reaction is continued until the polyesters have a relative ~iscosity of at least 1.6, preferably 1.6 to 3.5. Depending on the type of catalyst used and on the size of the batch, the reaction times amount to about 30 minutes up to several hours. After the resulting polyester melt has been removed from the reaction vessel and cooled, it is granulated, or cut into chips, in the customary manner.
In another process for the manufacture of the new polyesters, dicarboxylic acid dihalides, preferably the acid dichlorides, are subjected to a polycondensation with 1,4-butanediol in the presence of a basic catalyst in the temperature range from 0 to 100C, hydrogen halide being eliminated. The basic catalysts used are preferably amines or quaternary ammonium salts. The proportion of basic ': ' ' '' ., ' ' , 6g~9 ': ' ' catalyst can be from 0.1 to 100 mol %, relative to the acid halides. It is also possible to carry out this process without a solvent or in the present of a solvent.
The polycondensation can also be carried out in such a way that the starting compounds are first subjected to a condensation in the melt up to a certain viscosity, the pre-condensate prepared in this way i9 then granulated, ~or example with the aid of an underwater granulator, and the granules are drled and then subjected to a solid phase condensation, a vacuum being applied and a temperature below the melting point of the granules being employed.
Higher viscosities can be achieved in this way.
Inert additives of any type, such as, for example, reinforcing fillers, especially 5 to 50% by weight of sized glass fibres, inorganic or organic pigments, optical brighteners, delustering agents, agents which promote crystallisation, mould release agents or flame-retardant agents, can be added to the reaction composition when the polyester melt is being worked up or even before the poly-condensation reaction, or after the reaction in the molten phase has ended.
If the polycondensation reaction is carried out dis-continuously, the inert additives can be added already during the lask stages of the condensation, for example in the solid phase condensation or at the end of the melt condensation.
The copolyesters according to the invention are crystalline and, surprisingly, crystallise somewhat more readily than, for example, copolyesters with linear dicar-boxylic acids, such as, for example, adipic acid. This " ' ~ ': . ,,.
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behaviour is unexpected since it has been assumed hitherto that the introduction of branched radicals into the poly-ester chain more extensively disturbs the symmetry and hence impairs the crystallisability to a greater extent.
The somewhat improved crystallisabilitymanifests itself in shorter cycle times, for example particularly in mass production.
Furthermore, the copolyesters according to the in-vention have a higher flexibility than pure linear PBT, the flexibility being approximately similar to that of polyamide 11 or polyamide 12, and also have better tough-ness properties, better arc resistance and a lower after-shrinkage. It has been found here, surprisingly, that the notched impact strength is increased by aliphatic branched dicarboxylic acids having a minimum carbon number of about 7, starting from a minimum addition of about 2.5 mol ~.
The copolyesters are valuable thermoplasticmaterials from which mouldings of various types can be manufactured by the customary moulding processes, such as casting, in]ection moulding or extrusion. Examples of these moul-dings are fuel lines or compressed air lines, conductor sheathing, components of technical apparatus, profiles or electrical insulations. They can also be used as a sintered powder for surface-coatings and for the manufacture of films, sheets and fibres.
Those copolyesters according to the invention which contain 3 to 10, in partlcular 4-7.5l mol % of branched dicarboxylic acids are preferentially employed for processing by injection moulding and extrusion. Copoly-esters which contain more than 7.5 up to 15 mol ~ are also suitable for use as hot-melt adhesives or as bonding . . .
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fibres or fusible fibres for the manufacture of spunbonded nonwovens.
The polyesters prepared in accordance with theexamples which follow are characterised in more detail by the following characteristic data. The polyesters are charac-terised by those morphological changes which are measured, by means of differential thermal analysis, on a sample which has been heattreated fox 3 minutes at a temperature 30C above the melting point or softening point and then rapidly chilled. The chilled sample is heated, at a heating rate of 16C/minute, by means of the "DSC-lB" Differential Scanning Calorimeter from Messrs. Perkin-Elmer. The ther-mogram of the sample shows the glass transition temperature ITg) and the melting point (Tm). The point of in~lection at the discontinuous increase of the speci~lc heat in the thermogram is quoted as the ~lass transition temperature and the tip of the endothermic peak is quoted as the mel-ting point. The relative viscosity of the polycondensed products is measured, at 30C, on solutlons of l g of polyester in lO0 ml of a mixture consisting o~ equal parts of phenol and symmetrical tetrachloroethane.
The crystallisation temperature (Tc) is determined, after the sample has been heated up, by allowing the sample to cool at the same rate. The tip of the e~othermic peak in the thermogram, which is obtained in accordance with the differential thermal analysis indicated above, is desig-nated as the crystallisation temperature. In contrast to customary methods, the Tc is here determined ~rom above since it is not possible, because of the ready crystal-lisation of the polyesters, to prepare supercooled m01ts, that is to say amorphous products. The methods of deter-mining the mechanicalpropertiesareindicatedin the examples.

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, 6~9 Example_l: 3,492 g (45 mol %) of dimethyl terephthalate (DMT), 3,605 g of butane-1,4-diol (50 mol %), 376 g (5 mol %) of dimethyl 2,2,4-trimethyladipate and 2,29 g of isopropyl titanate are filled into a 10 litre reactor equipped with a stirrer, nitrogen inlet, condenser and temperature measurement. Whilst stirring and passing nitrogen through the reactor, 97% of the amount of methanol which is theoretically to be expected are distilled off in the course of 1 hour and 35 minutes, the temperature of the reaction mixture rising to 214C. After the reaction mixture has been heated to 240C, a vacuum of 60 mm Hg is applied in the course of half an hour by means of a water pump and, at the same time, the reaction temperature is raised to 250C. The vacuum is increased to 0.90 mm Hg in the course of 50 minutes by means of a vacuum pump, the ~ -reaction temperature remaining the same, and the mixture is left under this vacuum for;210 minutes. The melt is then discharged and granulated.
The characteristic date of the polyester are in-dicated in Table 1. The polyester is injection-moulded to give standard small bars and the mechanical properties indicated in Table 1 are determined on these bars.

Examples 2-7: The procedure followed is as ln Example 1. ~fter the reaction temperature has been reached, the vacuum is increased to 0.45 mm Hg in the course of 40 minutes and the mixture is left under this vacuum for 125 minutes. The co-components and the characteristic data of the polyesters obtained are indicated in Table 1.
For comparison, the properties of P~T are also indicated in Table 1.

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lL~)1!3916~53 PBT has a Tc of 177C and a copolyester with 5 mol~
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Claims (8)

WHAT IS CLAIMED IS:

1. Linear thermoplastic copolyester from terephthalic acid, 1,4-butanediol and a saturated aliphatic dicarboxylic acid, having a relative viscosity of at least 1.6, measured at 30°C on a 1% strength solution in equal parts of phenol and symmetrical tetrachloroethane, wherein, as the aliphatic dicarboxylic acid, 2.5-15 mol %, relative to the polyester, of one or more branched dicarboxylic acids with 7 to 30 carbon atoms per molecule are co-condensed in the polyester in statistical distribution.

2. Copolyester according to claim 1, wherein 3-10 mol % of dicarboxylic acid are co-condensed.

3. Copolyester according to claim 1, wherein the branched dicarboxylic acid contains 8 to 22 carbon atoms.

4. Copolyester according to claim 1, wherein the side chains of the co-codensed branched dicarboxylic acids contain alkyl groups with 1 to 18 carbon atoms.

5. Copolyester according to claim 1, wherein the co-condensed dicarboxylic acid has several branches.

6. Copolyester according to claim 1, wherein 2,2,4-tri-methyladipic acid, octadecylsuccinic acid, t-butyladipic acid or a mixture of the 1,8- and 1,9-isomers of heptadecane-dicarboxylic acid is co-condensed.

7. Copolyester according to claim 1, which contains 3-5 mol % of heptadecanedicarboxylic acid or 5-8 mol % of 2,2,4-trimethyladipic acid.

8. An injection or extrusion moulded article formed of a copolyester as defined in claim 1, 2 or 3.