IE902414A1

IE902414A1 - Cryoextensible thermoplastic elastomer, process for its¹preparation

Info

Publication number: IE902414A1
Application number: IE241490A
Authority: IE
Original assignee: Atochem
Priority date: 1989-07-04
Filing date: 1990-07-03
Publication date: 1991-06-19
Also published as: FI903353A0; JPH0747635B2; FR2649402A1; AU5861990A; NO902965D0; JPH0350231A; KR910002958A; PT94577A; NO902965L; AU629003B2; DD300107A5; CA2020290A1; KR940002186B1; FR2649402B1; EP0409678A1

Abstract

Cryoextensible thermoplastic elastomers. They are obtained by drawing, especially at room temperature. After relaxation and cooling to low temperature they exhibit a reversible elongation in the drawing direction.

Description

The present invention relates to thermoplastic elastomers which are cryoextensible, that is to say which exhibit a macroscopic dilation on cooling after drawing.

Low-temperature dilation phenomena have been observed in the case of drawn rubbers (W.H. Smith, C.P. Saylor, Bur. Stand. J. Research, 21. 257 (1938)), and in the case of crosslinked and drawn polyethylene (M.J. Machin, A. Keller, J. Macromol. Sci., (Phys.) Bl(l), 41 (1967).

The invention provides thermoplastic elastomers whose characteristic is that of being cryoextensible, more particularly cryoextensible thermoplastic elastomers consisting of block or multi15 sequence copolymers which comprise crystallizable flexible sequences.

Crystallizable flexible sequences, as used herein, are sequences or blocks which are not crystal-line at room temperature or whose degree of crystallinity is lower than or equal to approximately 0.5 times that of the homopolymers of the same chemical nature and of the same molecular mass as the said sequences, cooled under the same conditions from the molten state to room temperature at a rate of approximately 10°C/min.

These flexible sequences can be crystallized by drawing and/or at low temperature.

As used herein, room temperature corresponds - 3 to a temperature of 15° to 40°C, and, in general, close to °C.

'•Drawing” means a uniaxial or tensile stress applied to a sample, which produces an elongation of the latter in the drawing direction.

The expression cooling to low temperature means that the sample is taken to a temperature below room temperature, generally from 20° to -100°C and preferably from 20° to -40°C.

The crystallizable flexible sequences of the thermoplastic elastomers according to the invention generally consist essentially of polyether and/or polyester units, preferably of high molecular weight (Mn > 1000 and preferably Mn > 2000).

In addition to the crystallizable flexible sequences, these thermoplastic elastomers contain rigid sequences or blocks of a thermoplastic nature alternating with flexible sequences which form the nodes of thermally reversible physical crosslinking.

The rigid sequences of the cryoextensible thermoplastic elastomers may be based on polyurethane, polyester and/or polyamide, for example.

It is important that the segregation between the flexible sequences and the rigid sequences should be sufficient to prevent the crystallization of the flexible sequences, in other words that the structural defects linked with the copolymerization of the various sequences should - 4 not prevent the crystallization of the crystallizable flexible sequences.

In the case of a thermoplastic elastomer whose rigid sequences are crystalline, such as polyamide or polyester sequences, it is desirable that the difference between the melting temperature of rigid sequences within the copolymer and the melting temperature of these same sequences before copolymerization is not greater than 10°C and preferably not greater than 5°C.

The low-temperature elongation or cryoextensibility of the thermoplastic elastomers in accordance with the invention and drawn uniaxially can be up to 20 % of the dimension along the drawing axis after drawing and relaxation.

The cryoextensibility is reversible, that is to say that when the thermoplastic elastomer is brought back to room temperature it regains its permanent dimensions, that is to say those which it had after drawing and relaxation (and/or annealing) and before cooling.

This reversibility is reproducible: each time the thermoplastic elastomer is cooled it will elongate and, when returned to room temperature, it will regain its permanent dimensions.

As examples of thermoplastic elastomers there may be mentioned: - polyurethane-based block copolymers which may be obtained by reaction of a diol of high molecular mass - 5 which constitutes the crystallizable flexible sequence of the elastomer, with a diisocyanate and a diol of low molecular mass, which give rise to the rigid sequence, - polyester-based block copolymers such as 5 those obtained by copolymerization of a polybutylene (PBT) or of a polyethylene terephthalate (PET) which constitutes the rigid and crystalline sequences and of a glycol of low molecular weight (e.g. butanediol, diethylene glycol) which, in combination with a polyalkylene ether glycol forms the crystallizable flexible sequence, - the polyamide-based block copolymers whose rigid sequences consist of polyamide and the crystallizable flexible sequences of polyether, also called polyetheramides .

These block polyether amides can result especi-ally from the copolycondensation of polyamide sequences containing reactive ends with polyether sequences con-taining reactive ends, such as: a) polyamide sequences containing diamine chain ends with polyoxyalkylene sequences containing dicarboxylic chain ends; b) polyamide sequences containing dicarboxylic chain ends with polyoxyalkylene sequences containing diamine chain ends, obtained by cyanoethylation and hydrogenation of aliphatic alpha,omega-dihydroxylated polyoxyalkylene sequences, called polyetherdiols; c) polyamide sequences containing dicarboxylic chain ends with polyetherdiols, the polyetheramides obtained being, in this particular case, polyetheresteramides, which are particularly preferred.

The composition and the manufacture of such polyetheresteramides have been described in French Specifications No. 74/18913 and 77/26678; the content thereof is hereby incorporated by reference.

The number-average molecular mass of these polyamide sequences is typically from 500 to 10,000, more particularly from 600 to 5,000. The polyamide sequences of the polyetheresteramides are preferably made up of polyamide 6, 66, 612, 11 or 12 and/or of amorphous polyamide or of copolyamide resulting from the polycondensation of the monomers of such polymers.

The number-average molecular mass of the polyethers is generally from 1,000 to 10,000 and preferably greater than 2,000.

The polyether sequences preferably consist essentially of polytetramethylene glycol (PTMG). In addition to PTMG, they may, for example, contain polyethylene glycol (PEG) and/or polypropylene glycol (PPG).

The inherent viscosity of the polyetheresteramides is advantageously from 0.8 to 2.05, measured in metacresol at 2 0°C with an initial concentration of 0.5 g of polymer per 100 g of metacresol.

The polyetheresteramides are typically made up of 10 to 85 % by weight of polyether, and of 90 to 15 % by - Ί weight of polyamide, and preferably of 30 to 80 % by weight of polyether and of 70 to 20 % by weight of polyamide.

The polyetheresteramides which are preferred are those in which the polyamide sequences are derived from polyamide 12 and in which the polyether sequences are derived from PTMG.

The invention also provides a process for the preparation of such cryoextensible thermoplastic elastomers.

According to this process, the sample of 10 thermoplastic elastomer is subjected to a uniaxial tension resulting in a deformation which is lower than that leading to the failure of the sample for example with the aid of a tensometer.

The operation is generally carried out at a 15 temperature of 20° to 120°C and preferably 20° to 70°C.

The drawing speed is generally from 1 to 500 mm/min.

The initial drawing E of the sample is equal to the ratio: length of the sample after drawing - initial length E = - x 100 initial length these two lengths being measured in the drawing direction.

It can go up to, say, 1,000 %, but is preferably from 100 to 400 %.

When the sample is highly drawn (drawing > - 8 400 %), the flexible sequences are crystallized during the drawing, and this can have the effect of significantly decreasing the degree of cryoextensibility.

However, the crystallization under drawing can 5 also be avoided by drawing at elevated temperature (> 70°C) and/or by performing an annealing of the sample during the relaxation at a temperature above the melting temperature of the crystallizable flexible sequences.

By way of example, in the case of the 10 polyether sequences based on PTMG, the annealing is carried out at approximately 60°C.

Once the sample is drawn, it is relaxed for, say, at least 1 min and preferably at least 5 min at a temperature which is generally from 20° to 120°C, and preferably at room temperature.

The permanent elongation Ep is equal to the ratio: (Length of the sample after - (initial length) drawing and relaxation) Ep = - x 10 initial length these two lengths being measured in the drawing direction.

The permanent elongation is generally smaller than the initial drawing, and this is so whatever the value 25 of this initial drawing. It increases with the intensity of the initial drawing and also when the proportion of the - 9 rigid sequences within the thermoplastic elastomer increases.

The sample is then cooled to low temperature. The operation can be carried out gradually or very rapidly by performing a kind of quenching.

No elongation of the sample is then found, except in the drawing direction.

The order of magnitude of this cryoelongation can be up to, say, 20 % of its permanent dimension.

The thermoplastic elastomers in accordance with the invention may be employed in many applications, especially in the form of objects or films, moulded, extruded and/or injection-moulded in temperature ranges where the cryoextensibility is produced.

For example the polymers can be employed as seals at low temperature: these are moulded, drawn, relaxed and installed at room temperature.

By choosing the initial drawing judiciously it is possible to obtain a cryoelongation of the said seal ensuring a perfect leaktightness of the connection.

The following Examples further illustrate the present invention.

EXAMPLE 1 Dumbbell-shaped test pieces in accordance with ASTM standard D638 type 4 are cut from plaques of various samples of polyetheresteramide in which the crystallizable flexible sequences consist of PTMG and the rigid sequences - 10 of polyamide 12.

Table I below shows the number-average molecular masses of the flexible and rigid sequences of the samples studied and the weight quantity of PA-12 in the sample.

TABLE I Sample No. PTMG Mn PA-12 Mn Weight % of PA-12 in the copolymer A 2,000 600 23 B 2,000 850 29.8 C 2,900 850 22.7 D 2,900 1,200 29.3 The test pieces from samples A to D are then drawn uniaxially in accordance with standard D638 at room temperature.

The samples are subjected to an initial 20 drawing E of between 100 and 500 % and the permanent elongation Er is measured after relaxation at room temperature for 5 min.

The results of the measurements are combined in Table II. - 11 TABLE II Initial drawing E (%) Permanent elongation Er (%) of sample No. A B C D 100 300 500 7 90 221 13 132 265 11 107 250 20 147 300 The drawn test pieces are cooled and then relaxed from room temperature to -40°C, the rate of cooling being 10°C/min.

The change in length δ(L) in the drawing direction is measured as a function of the temperature and for various values of the preliminary drawing (of between 0 and 700 %). δ(L) is equal to the difference between the length of the sample at the cooling temperature T and the length of the sample at room temperature after drawing and relaxation.

Figure 1 expresses the degree of change in length 6(L) for a given initial drawing.

It can be seen that in the case of an initial drawing lower than 100 % there is a contraction of the sample (i(L) > 0).

It will also be noted that, whatever the initial drawing applied (> 100 %), the maximum increase in length 6(L) is - 12 produced at a temperature of approximately -10°C. The maximum increase in length S(L) corresponds to an initial drawing of the order of 350 %.

Also determined for each drawn sample is the 5 cryoelongation X between 20°C and -40°C and along the drawing axis: length at -40°C - length at 20°C χ = length at 2 0°C X 100 , the length at 20°C corresponding to the length after drawing and relaxation at room temperature.

It is observed that in the case of the polyetheresteramide of sample A there is no cryoelongation in the case of an initial drawing lower than 100 %.

The results are expressed in Table III below.

TABLE III E (%) X (%) 0 -2.12 100 -2.56 200 1.67 350 5.82 500 3.9 700 2.22 - 13 EXAMPLE 2 The samples B, C, and D are taken again and are drawn and relaxed as indicated in Example 1.

Each drawn sample is then cooled from 20°C to 5 -40°C, under the same conditions as those described in Example 1. i(L) is measured and X, as defined in Example 1, determined as a function of the initial drawing E.

The curves of X as a function of the initial 10 drawing E are plotted in Figure 2.

Claims

1. A thermoplastic elastomer which is cryoextensible in a reversible and reproducible manner.

2. A thermoplastic elastomer according to Claim 1, which is multisequenced and comprises rigid seguences and crystallizable flexible sequences.

3. A thermoplastic elastomer according to Claim 1 or 2 in which the number-average molecular mass of crystallizable flexible sequences is at least 1,000 .

4. A thermoplastic elastomer according to claim 3 in which said molecular mass is at least 2,000.

5. A thermoplastic elastomer according to any one of Claims 2 to 4, in which the crystallizable flexible sequences are polyether and/or polyester sequences and preferably based on polytetramethylene.

6. A thermoplastic elastomer according to claim 5 in which the crystallizable flexible sequences are polytetramethylene sequences.

7. A thermoplastic elastomer according to any one of Claims 2 to 6 in which the rigid sequences are polyurethane, polyester and/or polyamide sequences.

8. A thermoplastic elastomer according to any one of Claims 2 to 7 which is a polyetheresteramide.

9. A thermoplastic elastomer in which the rigid sequences are based on a (co)polyamide or on a mixture of aliphatic polyamide(s), and the crystallizable flexible sequences are based on polytetramethylene glycol. - 15

10. A thermoplastic elastomer according to claim 1 substantially as described in Example 1 or 2.

11. Process for the manufacture of a thermoplastic elastomer which comprises: a) drawing the elastomer uniaxially at room temperature (as hereinbefore defined); b) relaxing it either at room temperature or by carrying out an annealing; and c) cooling the thermoplastic elastomer to low temperature (as hereinbefore defined).

12. Process according to Claim 11 in which the drawing is at most 1,000 %.

13. Process according to claim 12 in which the drawing is 100 to 400%.

14. Process according to claim 11 substantially as described in Example l or 2.

15. A thermoplastic elastomer whenever manufactured by a process as claimed in any one of claims 11 to 14 .

16. Use of a thermoplastic elastomer as claimed in any one of Claims 1 to 10 and 15 for the production of a moulded, extruded and/or injection-moulded object or film.