Polyesters showing a high crystallization rate and procedure for their preparation

Polyesters with a high crystallization rate synthesized by the polycondensation of terephthalic acid with at least one C.sub.2 -C.sub.4 alkylenic glycol in the presence of 0.1-1.5 mol % of a copolymerizable reagent having the general formula: EQU ROOC--Ar--OOC--Ar'--COO--Ar--COOR where Ar and Ar'represent aromatic radicals and R represent a halogen, a hydrogen atom or a C.sub.1- C.sub.4 alkyl radical.

The present invention relates to polyesters with a high crystallization 
rate and the procedure for their preparation. 
More specifically, the present invention relates to polyesters with a high 
crystallization rate, the procedure for their preparation and their use in 
the preparation of moulded shaped articles obtained by means of normal 
transformation techniques of thermoplastic polymers. 
It is well-known that polyester resins, such as polyethyleneterephthalate 
(PET), have good physical and chemical characteristics which make them 
particularly suitable for the preparation of fibres, films, cable holders, 
moulded products, etc. 
It is also known that their behaviour on crystallization influences many of 
the above applications and presents obvious defects. It is sufficient to 
remember, for example, that when PET is injected, long moulding cycles are 
required due to the slow crystallization rate. 
Numerous methods are cited in the art for increasing the crystallization 
rate of polyester resins. One of these, described in European Patent 
Application publication 258.636 or in U.S. Pat. No. 4.486.561, discloses 
the use of the salts of weak acids, such as carboxylic acids, and the 
salts of phenols, as additives. This kind of modification is usually 
defined as chemical nucleation and its operating mechanism is described in 
an article by J. P. Mercier in Polymer Engineering and Science, Vol. 30, 
1990, pages 270-278. 
Another method referred to in literature for improving the crystallization 
kinetics of polyester resins is mixing with other polymers, for example 
HDPE (European Patent Application publication 104.131), polyamides 
(European Patent Application publication 303.234), polyesteramides (Patent 
Application publication 143.953) or crystalline liquid polyesters 
(Japanese Patent Application publication 89/170.-646). Another method 
consists of mixing with organic compounds such as phthalimides (U.S. Pat. 
No. 4.639.480), acetals, amides, nitriles, sulphones and sulpohoxides 
(German Patent Application publication 3.532.033). 
All these methods however require mixing with additives which means that 
the polymer resulting from the synthesis should undergo a thermal cycle, 
with the consequent effects of degradation. 
This problem is particularly evident in the chemical nucleation of 
polyethyleneterephthalate with the salts of weak acids and of phenols 
which cause considerable degradation of PET. In this case it is necessary 
to use reactive compounds towards the terminal groups, such as epoxy 
resins, to limit the reduction in the molecular weight of the polymer. 
It has now been found by the Applicant that the drawbacks in the known art, 
relating to the crystallization kinetics of polyester resins, can be 
overcome by using small molar quantities of a specific reagent in the 
polymerization mixture which allows the polymer to crystallize very 
rapidly (intrinsic crystallization) without the use of particular 
additives. 
The present invention consequently relates to polyesters with a high 
crystallization rate obtained by the polycondensation of at least one 
C.sub.2 -C.sub.4 alkylenic glycol with a mixture composed of terephthalic 
acid, possibly substituted with halogens, such as chlorine, or with 
C.sub.1 -C.sub.4 alkyl radicals, or one of its derivatives, and of 
0.1-1.5% in moles of the total of a copolymerizable reagent having the 
general formula: 
EQU ROOC--Ar--OOC--Ar'--COO--Ar--COOR (I) 
where Ar and Ar', either the same or different, represent aromatic radicals 
containing from 6 to 20 carbon atoms whereas R represents a halogen such 
as chlorine, a hydrogen atom, or a C.sub.1 -C.sub.4 alkyl radical. 
Preferred polyesters in accordance with the present invention are those 
obtained in the presence of 0.5-1% in moles of the reagent having general 
formula (I). 
Preferred reagents having general formula (I) are those wherein R 
represents a hydrogen atom or a methyl or ethyl radical and wherein Ar and 
Ar' are selected from or naphthalene rings, in particular naphthalene 
rings having reactive functions in positions (1,2), (1,3), (1,6), (2,3), 
(2,6), (2,7). 
Examples of alkylenic glycols particularly suitable for the present 
invention are ethylene glycol and butylene glycol. 
The compounds corresponding to general formula (I) are well-known products 
whose preparation is described in Chemical Abstracts, vol. 99, no. 218533, 
1983 and Chemical Abstracts, vol. 97, no. 72969, 1982. 
Polyesters with a high crystallization rate subject of the present 
invention have an inherent viscosity, measured in phenol/tetrachloroethane 
(60/40 by weight) at 30.degree. C. with concentrations of 0.25 g/dl, 
higher than 0.5 dl/g, generally between 0.6 and 1.5 dl/g, a 
crystallization temperature which is higher than 170.degree. C., generally 
between 175.degree. and 200.degree. C., and a glass transition temperature 
(Tg) higher than 75.degree. C. 
In particular, the polyesters basically obtained from terephthalic acid, 
ethylene glycol and the reagent having formula (I) wherein Ar and Ar' are 
aromatic radicals having a strongly non-linear symmetry or are sterically 
hindered radicals (benzene rings with functional groups in position 1,2 
and 1,3 or naphthene radicals with functional groups in position 2,3) have 
a Tg of 80.degree. C., about 5.degree. C. higher than that of traditional 
PET. This is a surprising result in that it is well-known that the 
introduction into PET of increasing amounts of asymmetrical units, such as 
those deriving from isophthalic acid, causes a decrease in both the Tg and 
crystallization temperature. 
The polymers of the present invention are suitable for use in the 
production of moulded bodies which can be prepared with the conventional 
transformation technologies of thermoplastic polymers such as, for 
example, injection moulding or extrusion, they can be processed in the 
form of either film or fibre, they can be used as matrixes for composite 
materials based on fibres or inorganic charges and they can be used in the 
preparation of mixtures with other polymers. 
One procedure for the preparation of polyesters with a high crystallization 
rate, subject of the present invention, is to react at least one C.sub.2 
-C.sub.4 alkylenic glycol with a mixture composed of terephthalic acid, 
possibly substituted, or one of its derivatives, and of 0.1-1.5% in moles 
of the total of a copolymerizable reagent having the general formula: 
EQU ROOC--Ar--OOC--Ar'--COO--Ar--COOR 
where Ar, Ar' and R have the meaning specified above. 
More specifically, the procedure of the present invention can be carried 
out as described in "Comprehensive Polymer Science", G. C. Eastmond, A. 
Ledwith, S. Russo, P. Singwalt Eds. Pergamon Press, Oxford 1989, vol. 5, 
page 275. 
In a typical synthesis procedure starting from diester of bicarboxylic 
acid, the reaction mixture is degassed, put in an inert atmosphere 
(nitrogen) and heated to 180.degree. C., the distillation temperature of 
the alcohol released in the alcoholysis reaction. The temperature is then 
gradually increased to 280.degree.-290.degree. C. and the pressure reduced 
to 0.1-0.2 Torr. to favour polycondensation. 
The reactions which occur during the above syntheses are catalyzed by 
compounds of an acid nature, for example protic acids such as H.sub.2 
SO.sub.4 or Lewis acids such as manganese acetate, zinc acetate, etc. In 
the polycondensation phase it is convenient to use acid oxides such as 
those of antimony and germanium or the alcoholates of transition metals 
such as titanium tetraisopropoxide. In the present procedure it is 
preferable to use tetrahydrated manganese acetate and antimony oxide, as 
this catalytic system is less active in the decomposition catalysis of the 
polymer at high temperatures. 
The importance of the present invention is therefore evident to experts in 
the art. The possibility of producing an intrinsic increase in the 
crystallization kinetics avoids the necessity of resorting to nucleants, 
especially the salts of weak acids, which cause considerable degradation, 
which are extended in each recycling operation of the material and produce 
additional costs. Moreover, an increase in the glass transition 
temperatures, for example in the case of PET, can provide greater 
compatability of the polymer with typical tecnologies of the packaging 
industry, such as heat filling.

The examples which follow provide an illustration of the present invention 
but do not limit it in any way. 
EXAMPLE 1 
This example describes the preparation of a polyester from dimethyl 
terephthalate, dimethyl 4,4'-(terephthaloyldioxy) dibenzoate and ethylene 
glycol. 
153.6 g of dimethyl, terephthalate, 3.47 g of dimethyl 
4,4'-(terephthaloyldioxy)dibenzoate, 110.1 g of ethylene glycol and 150 mg 
of manganese acetate tetrahydrate were charged into a 500 ml glass flask 
under an inert atmosphere. The reaction mixture was brought to 180.degree. 
C. and kept at this temperature for 90 minutes to distill the methanol. 
The temperature was then brought to 210.degree. C. and 70 mg of antimony 
trioxide and 450 mg of 2,6-di-tert-butyl-4-methylphenol were added. After 
increasing the temperature to 240.degree. C., the pressure was slowly 
reduced to 0.1 Torr and the temperature raised to 290.degree. C., these 
conditions being maintained for 30 minutes; during this period, the excess 
ethylene glycol was removed. After bringing the apparatus back to room 
temperature and atmospheric pressure with N.sub.2, the polymer obtained 
had an inherent viscosity, measured in phenol/tetrachlorethane (60/40 by 
weight) of 0.73 dl/g. 
Its glass transition temperature, obtained by using a thermal scanning 
calorimeter (DSC), is shown in Table 1 where it is compared to that of a 
PET having a viscosity of 0.64 produced by the company Montefibre of 
Milan. 
Table 2 indicates the temperature corresponding to the minimum hexothermal 
crystallization peak, hereafter referred to as Tc. This temperature was 
obtained by means of DSC, by bringing the sample to above melting point 
and subsequently carrying out a temperature scanning towards the lower 
temperatures. It will be evident to experts in the art that the higher the 
above temperature, the more rapid will be the appearance of crystals and 
consequently the crystallization of the polyester. Also in this case, a 
PET with a viscosity of 0.64 produced by Montefibre in Milan was used as a 
comparison. 
EXAMPLE 2 
The procedure described in Example 1 was repeated using, however, dimethyl 
4,4'-(isophthaloyldioxy)dibenzoate. 
153.6 g of dimethyl terephthalate, 3.47 g of dimethyl 
4,4'-(isophthaloyldioxy)dibenzoate, 110.0 g of ethylene glycol, 150 mg of 
manganese acetate tetrahydrate and 20 mg of cobalt acetate tetrahydrate 
were polymerized. 70 mg of antimony trioxide and 450 mg of 
2,6-di-tert-butyl-4-methylphenol were added at a temperature of 
230.degree. C. 
The resulting polymer had an inherent viscosity of 0.66 dl/g. The Tg and Tc 
data are shown in Tables 1 and 2. It can be noted that, in spite of the 
addition of a non-symmetrical comonomer, there is a considerable increase 
in the Tg and Tc also with respect to the data relating to Example 1. 
EXAMPLE 3 
The procedure described in Example 2 was repeated, using a lower molar 
percentage of dimethyl 4,4'-(isophthaloyldioxy) dibenzoate. 
96.5 g of dimethyl terephthalate, 1.08 g of dimethyl 
4,4'-(isophthaloyldioxy)dibenzoate, 68.2 g of ethylene glycol and 100 mg 
of manganese acetate tetrahydrate were reacted. 45 mg of antimony trioxide 
and 300 mg of 2,6-di-tert-butyl-4-methoxyphenol added at a temperature of 
200.degree. C. 
The resulting polymer had an inherent viscosity of 0.76 dl/g. The Tg and Tc 
data are shown in Tables 1 and 2. It can be noted that, in spite of the 
addition of asymmetrical monomers, there is a considerable increase in the 
Tg and Tc, also with respect to the data relating to Example 1. 
EXAMPLE 4 
The procedure described in Example 2 was repeated using a higher molar 
percentage of dimethyl 4,4'-(isophthaloyldioxy) dibenzoate. 
95.1 g of dimethyl terephthalate, 4.34 g of dimethyl 
4,4'-(isophthaloyldioxy)dibenzoate, 68.2 g of ethylene glycol and 100 mg 
of manganese acetate tetrahydrate were reacted. 45 mg of antimony trioxide 
and 250 mg of 2,6-di-tert-butyl-4-methoxyphenol were added at a 
temperature of 200.degree. C. 
The resulting polymer had an inherent viscosity of 0.75 dl/g. The Tg and Tc 
data are shown in Tables 1 and 2. It can be noted that, even though 
monomers with a non-linear symmetrical substitution have been introduced, 
there is a considerable increase in the Tg and Tc, also with respect to 
the data relating to Example 1. 
EXAMPLE 5 
The procedure described in Example 1 was repeated, using dimethyl 
3,3'-(terephthaloyldioxy)di-2,2'-naphthoate. 
119.1 g of dimethyl terephthalate, 3.31 g of dimethyl 
3,3'-(terephthaloyldioxy)di-2,2-naphthoate, 84.7 g of ethylene glycol and 
124 mg of manganese acetate tetrahydrate were polymerized. 56 mg of 
antimony trioxide and 370 mg of 2,6-di-tert-butyl-4-methylphenol were 
added at a temperature of 200.degree. C. 
The resulting polymer had an inherent viscosity of 0.72 dl/g. The Tg and Tc 
data are shown in Tables 1 and 2. It can be noted that even though 
monomers with strongly hindered esther groups were introduced, there is a 
considerable increase in the Tg and Tc, also with respect to the data 
relating to Example 1. 
EXAMPLE 6 
Crystallization kinetics were obtained on the comparison PET and on one of 
the polyesters of the present invention, i.e. that referred to in Example 
2. These were derived from DSC measurements, with the following procedure: 
the sample was heated to 280.degree. C. and kept at melting temperature for 
2 minutes, in order to destroy all crystalline centres; 
the temperature was rapidly decreased (150.degree. C./minute) to the 
required value; 
keeping the temperature constant, the values of the thermal exchange with 
relation to the time were registered; 
the semicrystallization time was considered as that corresponding to an 
area equal to half of the hexothermal crystallization peak. 
FIG. 1 shows the semicrystallization times with relation to the temperature 
of the PET used as a reference and the polyester whose synthesis is 
described in Example 2. In this latter case, there is a drastic reduction 
in the semicrystallization times, corresponding to a considerable increase 
in the crystallization rate. There is also a wider temperature range at 
which rapid crystallization occurs, with corresponding advantages during 
the moulding. 
TABLE 1 
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Sample Tg (.degree.C.) 
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PET (comparison) 75 
Example 1 80 
Example 2 81 
Example 3 78 
Example 4 78 
Example 5 81 
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TABLE 2 
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Sample Tg (.degree.C.) 
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PET (comparison) 177 
Example 1 188 
Example 2 195 
Example 3 182 
Example 4 179 
Example 5 196 
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