IE50927B1 - Polymers containing pyrrolidine-ring-containing compounds as stabilizers against uv-radiation;and method of stabilizing polymers - Google Patents

Description

This invention relates to polymers containing pyrrolidine-ring-containing compounds as stabilizing agents against the action of UV-radiation; the polymers may be polyolefins, more particularly polyethylene and polypropylene; the present invention also relates to a method of stabilizing polymers.

It is well known that polyolefins, such as polypropylene and polyethylene, exhibit a tendency towards decay under the action of radiation, especially UV-radiation, and of weathering agents in general.

Such a degradation proceeds with the loss of certain physical properties of the polymers, such as a decrease of the tensile strength and a loss of pliability.

The decay of the properties indicated above can quantitatively be assessed by determining the viscosity index of the polymers in the molten state, that is the Melt Flow Index, MFI.

An exceedingly high increase of the MFI indicates a considerable degradation of the polymer concerned. - 2 SOS27 In order that such a degradation may be prevented, it has been common practice to add to the polymers small amounts of stabilizing compounds, care being taken that the compounds in question were not such as to alter the other, desirable, properties of the polymers so treated.

According to the present invention there is provided a polymer of an olefin, in which is incorporated, as a stabilizer against ultraviolet radiation, a straight chain fatty acid ester of an N-(beta-hydroxyethyl)-2,2,3,4,5,5hexamethylpyrrolidine.

The present invention also provides a method of stabilizing a polymer of an olefin against the effect of ultraviolet radiation, which comprises incorporating into the polymer, as the stabilizer, a straight chain fatty acid ester of an N-(beta-hydroxyethyl)-2,2,3,4,5,5-hexamethylpyrrolidine.

The esterifying fatty acids of the esters are, for example, butyric, palmitic, lauric and stearic acids. The esters are claimed in our Patent Specification No. 322/81. The esters, which are sterically hindered at the N-atom, have excellent stabilizing properties against the action of UVradiation in polyolefins such as polyethylene and polypropylene.

The production of such novel esters can be carried out with conventional procedures, such as, for example, the methods of Hennion and Di Giovanna, as reported in the Journal of Organic Chemistry, August 1965, pages 2645 and seq.

The stabilizer may be present in an amount of from 0.9 to 1% by weight.

In order that the present invention may be better understood, a few examples will be set forth hereinafter, which in addition to being illustrative of the syntheses of the lauric acid and palmitic acid esters of the N-(beta-hydroxyethyl)-2,2,3,4,5,5-hexamethylpyrrolidine, are illustrative of their practical use as anti-UV stabilizers for polypropylene. - 3 50027 EXAMPLE 1.

Preparation of the 2,2,3,4,5,5-hexamethylpyrrolidine.

Grams of di-tert. propargylamine were dissolved in 300 ml of acetic acid and introduced into an autoclave together with 50 g of a Pd-based catalyst supported on activated charcoal, the Pd content being 5% by weight.

The reaction mixture was maintained under a hydrogen atmosphere at room temperature and subsequently the temperature was raised to 140°C until no further absorption of hydrogen was observed.

Eventually, the reaction mixture was brought back to room temperature and filtered, to remove the catalyst therefrom.

The filtrate was made alkaline with a 30½ aqueous solution of NaOH and twice extracted with diethyl ether.

The ethereal extracts were combined and dried over NaOH and evaporated to dryness.

The expected product was obtained as a mixture of stereo-isomerides and had a boiling point (b.p.) of 65°C - 70°C under an absolute pressure of 15 mmHg (millimetres of mercury). (The literature shows a b.p. of 70°C-74eC under 20 mmHg). The product was obtained at a yield of 50½ relative to the starting material.

The product was identified by mass-spectroscopy and NMR analysis.

EXAMPLE 2.

Preparation of the N-(beta-hydroxyethyl)-2,2,3,4,5,5-hexamethylpyrrolidine.

The compound obtained in Example 1 hereof was N-substituted (hydroxyethylated) with a conventional method by charging an autoclave with 15 g of hexamethyl4 30827 pyrrolidine, 20 ml water and ethylene oxide in an amount which slightly exceeded the stoichiometric quantity.

After a four-hour reaction at 120°C, the organic layer was separated and distillation was carried out.

The expected N-(beta-hydroxyethy1)-2,2,3,4,5,5-hexamethylpyrrolidine was obtained in a yield of over 90%, in the form of a colourless viscous liquid having a b.p. of 80°C-83°C under an abs. pressure of 3 mmHg.

EXAMPLE 3.

Preparation of the 2,2,3,4,5,5-hexamethylpyrrolidine-N-ethyl-2-lauric acid ester. 50 Grams of N-(beta-hydroxyethyl)-pyrrolidine (a mixture of the stereo-isomerides), prepared as described hereinabove in Example 3, were introduced into a flask together with 300 ml of benzene and 35 ml of triethylamine.

Grams of lauroyl chloride were introduced into the flask through a dropping funnel and the temperature was raised to 80°C-90°C.

The reaction mixture was allowed to react at the temperature specified above until such time as all the N-(beta-hydroxyethyl)-pyrrolidine had reacted, which required 5 hours approximately.

The reaction mixture was subsequently filtered to remove the solids, and eventually distilled.

The expected product was obtained in a yield of over 90%. It was a transparent viscous liquid, having a light straw-yellow colour and a b.p. of _2 187°C-19O°C under a pressure of 5.10 mmHg.

The thus obtained esterified products were exploited for the stabilization of polypropylene and the protective activity has been assessed in comparison with - 5 50327 customary stabilizers in current conmercial use, such as benz-triazole (Tinuvin P. Trade Mark) and benzophenone (Tinuvin 531, Trade Mark), according to the testing procedure specified hereinafter.

Five different portions of general purpose polypropylene, already compounded with conventional stabilizers and processing aids, were supplemented with a respective anti-UV stabilizer: the anti-UV stabilizers tested were: hexamethylpyrrolidine ethyl laurate (1) in an amount of 0.9% by weight, hexamethyl pyrrolidine ethyl palmitate (2) in an amount of 1% by weight, benztriazole (Tinuvin P, Trade Mark) in amounts of 0.5% and 0.9% by weight, and benzophenone (Tinuvin 531, Trade Mark) also in the amount of 0.5% by weight.

The two commercial anti-UV stabilizers were added in the amount of 0.5% by wt., because this is the value which is currently suggested by manufacturers. One of the two conmercial anti-UV stabilizers was also added in an amount of 0.9%, to correspond to the amount of ethyl palmitate stabilizer used.

The blending of the anti-UV .stabilizing agents was carried out according to the procedures which are conventionally used for incorporating stabilizers in polyolefins, that is, in a roll mill at 180°C for 5 minutes.

Platelets, 0.5 mm thick, were then prepared in a compression press at 180°C with the following cyclical sequence: 5-minute preheating - 5-minute pressing. The thus prepared platelets were exposed in an Atlas (Trade Mark) Heatherometer o having two arc lamps with emission peaks at 3,600 - 3,850 and 4,200 Angstrom units, and with a rain cycle (102 minutes light, 18 minutes rain).

The resistance of polypropylene to exposure to UV-radiation was assessed by viscosity measurements (Melt Flow Index, MFI) according to the texting prescriptions of Specification ASTM D-1238 after several exposure times. - 6 50S27 In the following Table, the MFI trends of the several polypropylene samples with increasing exposure times are tabulated.

The improved constancy of MFI values for the polymers supplemented with the stabilizers of the present invention, as compared with the commercial stabilizers, can readily be appreciated.

With the comnercial stabilizers, the viscosity index trend is irregular and shows an abrupt increase in correspondence with prolonged UV-exposure.

Tests performed with higher amounts of bentriazole (0.9 or 1% by wt.) showed that this commercial product has a destabilizing action if such a higher concentration level is adopted.

These facts are nothing but a confirmation of the improved stabilizing effect afforded by the anti-UV stabilizers according to this invention whenever comparatively long exposure times to weathering agents are experienced.

Melt Flow Index Trend General purpose polypropylene with various anti-UV stabilizers Exposure time, hours 0 Start 500 750 1,000 1,250 1,800 POLYPROPYLENE, as such 3.8 4.8 5.7 7 9 50 do.+0.9% hmp ethyl laurate (1) 3.8 - 5.5 8 8.5 8.5 do.+ 1% hmp ethyl palmitate (2) 3.7 4.5 5.8 7.5 8 8.4 do.+0.5% benz-triazole (Tinuvin P) 3.6 5.1 5.2 6 6.5 23 do.+0.5% benzophenone (Tinuvin 531) 4.5 5.2 5.6 8 6 50 do.+0.9% benz-triazole derivative (Tinuvin P) 4.3 - 14 47 bmp = hexamethylpyrrolidine

Claims (9)

1. A polymer of an olefin, in which is incorporated, as a stabilizer against ultraviolet radiation, a straight chain fatty acid ester of an N-(beta-hydroxyethyl)-2 > 2,3,4,5,5-hexamethylpyrrolidine.

2. A stabilized polymer according to Claim 1, wherein the straight-chain fatty acid moiety of the ester is lauric acid.

3. A stabilized polymer according to Claim 1, wherein the straight-chain fatty acid moiety of the ester is palmitic acid.

4. A stabilized polymer according to any preceding claim, wherein the stabilizer is present in an amount of from 0.9 to 1% by weight.

5. A stabilized polymer according to any preceding claim, wherein the olefin is ethylene or propylene.

6. A method of stabilizing a polymer of an olefin against the effect of ultraviolet radiation, which comprises incorporating in the polymer, as the stabilizer, an ester as specified in Claim 1, 2 or 3.

7. A method according to Claim 6, wherein the stabilizer is incorporated in an amount of from 0.9 to 1% by weight.

8. A stabilized polymer according to Claim 1, substantially as described in the foregoing Example 3.

9. A method according to Claim 6, substantially as described in the foregoing Example 3. Dated this 14th day of January 1986. (Signed) BY: