US2925400A - Poly-alpha-olefins stabilized with long chain alkyl gallates - Google Patents

Description

- Uni ed .i e k s Peefltq; 1

"PO Ya-Q EE STAB LI D 40 5 97 i CHAIN AEKi9aLFeT.E.- t V .t Clarence E. Tholstrup and Alan Bell, Kingsport, Tenn., assignors to EastmanKodak; Company, Rochester, wflfuwme a n q Ne J rs No Drawing. Application October 18,.1957 I -'SerialN0."690,'890

Claims. (Cl. 260-4535) ll his invention relates tot-he stabilization of-organic .s po dswh szh are subiecttoflogtid d radatigni through the inclusion of certa" 0f ganic 391d MQilliQii flcarbon atoms, in organic plasticcornpos polymerized toirfrlqli'dolffiiisi ilf -oxidants with fats, oils, a r d-..;fat ff U hen used alone orin synergistic ca ac .able preference has been'shownyhow Another'object of the present invention is to provide such compositions of matter comprising 'poly-u-mono- P idi kifiiiFffl}? olefins in combination yvith certain long chain alkyl esters- $3, 3 i P? h i i qii of gallic acid wherein the -a1k'y1 group contains 12-18 would not enhance the antioxidant ch as carbon atoms 'galli c riioiety due to "stericefiects'f""M'orepv v -tEtiiti'oxidaiit potency' per ufiitfof iiioleculafvve ght'vvo ldie b expected for the highei alky'l g'a'natesfi Alsa, 15 or 'alkyl" gallates such as'etliyl ofpropy V used to stabilize polyrn'eri'c' coin 'jositions s'ulzhas ethylene. It would be an obvious ixpectatio" when tested on an'equal Weight basis, the pjoren I gallate compounds would tend to decrease asithe ester group incr eas es'to fairly larg e sizeand vveight. Thus, it would be" supposedfthat 'as the 'alkyl moiety beco'r'ne's larger; the active antioxidant gallic 'inoiety vvould beconie smaller in pr0'portion, resulting 'in'a cominensur e decrease in the relative antioxidantfcapabilitygot thecompound. For example, in the"propylfgallate molecule, the "active 'gallic moiet conipris'es' aboutj'8 0 %"of fthe'figvei ght of the, molecule; whereasgin dodecyhg 'allate thefjacfiye gallic'irioiety.comprisefonly aboutl'%fof t hernol' L 10mg" chain 'a lkyl' gallate's, such ;as la'uryl g allat been jsuggest'ed 'as antioiidants for foodsfco 'con'su'tuentsj whereby there isacli' a compatibility even though the-presenc V V I s'ixnilar' large allcyl radical obviously dir'nini 1 es the p 'o- 'port ion of 'the active gallic rnoityin inversekelajtion to the size of such alkyl radicals. As 'to thef "compatibility {of propyl gallatein organic plastics siich"as polyethylene,

aforementioned compositions wherein the gallic ester stabilizers possess the properties of unusually low volatility,

9 d uhereinth t Still another object of this invention is to provide the hese ompost.

itiiszpointed out in prior art such as BritishPat'entNo. ;O53:* "'S v19,57 nqwmatentor --618,839'that a Wide range of proportions" can be 'enflployed such as 0.05% to'5% by weighttl'thusjenhanced icornpatibility over pr opyl g'allate isobviously iiot'l't edlii'red. =Moreover,-buty1 gallateand it s'branchedchain on efrs normally have substantially no 'be'tter laiitioitidant prop- -erties thanthe adjacent -propyl fho r'nolofgj iltfl't herefore appears that'there'wo'uld be nothing to' gain an rnuch I to be lost in trying higher alkylihornolo gs. fl 'uitherinp fi the parent compound, gallic aciditselfi ha's shown highly satisfactory results in the other direction,li.e., tw the 5 -"an'tioiiitlantcapability of propyl gallate.

8;' Y Bl el -e des ribe d tai his testingjP M e a i I t 1 S abilitw h n p y i y testedat C; ratherrthan erat k for polyethylene. EXia'eri- V akesv itclear that polyethylene isiibt a I a en of polymerized homolqgs7such'jas:pr3- ene to. since poiyethylenehasamuchhiglier rent stability. ".More over theothe'r poly-ia-morioole- Withyvh i iithislinvention isparticularlyconcernedare or 'sydiotactic polymers.

' te that a particularly outstanding With these considerationsin mind, it is apparent that it eefinii tigiin nes in the unexpectedly'achieved to those skilled in the" an i the present invention qu te :i'i' envious. 'Thus, it has no'w been found th v along =chain alkyl esters of gallic aeid, jn'ore arly ithe "alkyl esterswherein the ""ilk yl g roufi contains' 1'2"-1'8" greater thermal; electrical,and pxidative stabilityxiffhus,

1i s l m ts re is adamage fromwhaas h rtigs, ygother especially rivaluabie itstabilized polymers relates to their exceptional resistance to degradation during extrusion or while otherwise shaping polymers at high temperatures.

Moreover, this invention provides stabilized compositions in which inclusion of the stabilizer doesmot impart a stain or discoloration to the product. I This advantage is especially worthwhile when it is desired to ncorporate a pigment. Moreover, inasmuch as the stabilizers as advantageously employed according to this inventlon do not cause discoloring of the product, the stabilized synthetic resin may be-colored in more delicate shades than'when a stabilizer causing discoloration is used in amounts required for effective stabilization. Thus, the product is better adaptable for use in the manufacture of containers and wrappers for food and the like. Along with improved non-staining characteristics, the specified longchain alkyl esters of gallic acid are highly compatible with poly-a-olefins, making them easily introduced into an organic plastic composition. Moreover, the esters of our invention display excellent low volatility which is animportant advantage, especially in products which are subjected to elevated temperatures or other conditions where the stabilizer may be partially lost. The poly-a-monoolefins referred .to'in thi invention include polyethylene, polypropylene, polybutene-l, and their copolymers as well as other polymerized u-monoolefins such as 2,2-dimethylbutene-1.

The high molecular weight esters of gallic acid within the purview of the invention are represented by the following general structure:

O HO lib-O-R any desired modifiers or pigments, on heated rolls inaccordance with conventional practice. The composition can be removed from the rolls thereafter. If desired, 'it can be comminuted by means of a cutter such as a Roll and Jewel cutter. Other means of preparing the stabilized compositions can also be employed, such as mixing in a Banbury mixer or other standard mixing equipment. If desired, the ester can be incorporated --with the poly-u olefin in a solvent which can be removed by subsequent working and seasoning.

The compositions of this invention can include modifiers, plasticizers, lubricants, coloring matter, fillers, or other synthetic or natural resins, in addition to combinations of other stabilizers, antioxidants, and metal deactivators known for retarding the catalytic eliect of iron, copper or the like in promoting oxidation. Either colored or colorless products may be produced employing a suitable choice of such materials.

The compositions of this invention can be extruded or molded according to conventional techniques to furnish finished articles in the form of sheets, rods, tubes, films, filaments, nuggets, or any other physical shapes commonly assumed by polyolefinic compositions. An efiicacious antloxidant is particularly important during the extrusion of poly-a-monoolefins, such as during film manufacture, for without one, small portions of the polyolefin which remain at the head of the extruder for lengthy periods of time at elevated temperatures decompose mto solid obstructions thereby requiring frequent shutdowns to permit cleaning of the. ext uder.

Taea'saoo p r The invention and its unobviousnessis further illustrated but not restricted by the following tables wherein examples show poly-a-monoolefins stabilized with gallic acid and gallic acid esters, These tables clearly show the remarkable results obtained when the alkyl esters have 12-l8 carbon atoms in the alkyl radical. The aforementioned thermal stability test was used to .obtain the results shown; the percentages of the stabilizer compounds are based on the total weight.

' TABLE I Oven life of polyethylene +0.10% stabilizer measured at C. by described thermal stability test Stability As Hours of Oven Life Stabilizer 1. None (Control) 2. Short Chain Alkyl Gallates:

(b) propyl ester (c) butyl ester (d) isobutyl From Table I it is apparent that the miscellaneous esters (alkyl and aryl) encompassed within items 2 and 3 are no better than gallic acid. Moreover, there is not any significant variation of properties among the various alkyl gallates which would indicate that propyl gallate (which has proven commercial adequacy) could be greatly improved upon. Thus, it would appear from items 2, 3 and 4 of this table that in general all esters of gallic acid are substantially equivalent in degree of efficacy. It was therefore quite surprising to find, as clearly demonstrated by item 5 of Table I, that a limited number of long chain alkyl esters possess an entirely different order of stabilizing potency. This represents a remarkable difierencein kind in the results achieved.

The results shown in item 5 of Table I are representative of similar results which can be achieved using the '13, 14, 15, 16 and 17 carbon atom homologs as well as the isomers of the 12 and 18 carbon atom alkyl gallates shown in item 5.' Such homologs and isomers include tridecyl gallate, tetradecyl gallate, 2-ethy1tetradecyl gallate, pentadecyl gallate, hexadecyl gallate, S-methyl-hexadecyl gallate, heptadecyl gallate, etc.

When. the testprocedures employed in gathering the results for Table I were repeated using 10 times as much of some of the stabilizers, it was found that the ratios of oven lives for stabilized polyethylene to the control sample were no more than about doubled for propyl gallate, cyclohexyl gallate and gallic acid (none others except dodecyl gallate were tested). In contrast, when 10 times as much dodecyl gallate was used, the achieved oven life ratio remained substantially the same. This demonstrates another unexpected feature of this invention in that the long chain alkyl gallates of the invention can achieve their excellent results at unusually low concentrations whereas a previously known gallate such as propyl gallate even at 1.0% concentration is but little more effective than at 0.1% concentration.

Table II shows the stabilization of isotactic polymers or a-monoolefins which is similar to the results achieved in regard to stabilizing polyethylene as shown in Table 1. Similar results can be achieved as regards other isotactic and .syndiotactic polymers such as can be derived from 3'm6thylbi1 t1 1?1 pentene-l, 3,3-dimethylbutene-1, "4

methylpentene-l, 4,4-dimethylpentene-1 and other amonoolefins containing from 3 to 8 carbon atoms such as styrene and includes the various copolymers.

TABLE II Oven life of polypropylene +05% stabilizer measured at 140 C. by described thermal stability test Stability Stabilizer As Hours of Oven Life 1. None (Control) 0.5 2. Pro yl Gallat 7.0 3. Do ecyl (innate 70.0

of a-monoolefins containing from 3 to 8 carbon atoms 3. Substantially isotactic polypropylene in, an essen- 'tially solid. state stabilized with an alkyl ester of gallic acid wherein the alkyl group contains 12--.18 carbon.

atoms. l

4. Polyethylene in an essentially solid state stabilized withabout 0.10% by weight, based on totalweight of In addition to the compositions of matter covered by 7 this invention, it also covers the related processes such as a process for stabilizing a solid colorless polyu-monoolefin against oxidative degradation whereby about 0.001% to 3% by weight of an alkyl ester of gaIlic acid wherein the alkyl group contains 12-18. carbon atoms is combined at above 140 C. with said poly-asmonoolefin without appreciable staining of said composition, whereby a stabilized solid poly-a-monoolefin is formed characterized by being substantially colorless, retaining its electrical ro erties durin ex osure to elevated temperatures v l r p p g with about 0.05% to 3.0% by we ght of the dodecyl ester p of gallic acid.

for extended periods of time, and being 'free from loss due to volatilization or separation ofsaid stabilizer at elevated temperatures.

This invention produces especially efficacious. and un I obvious results at stabilizer concentrations of from 0.01% to 0.05% by weight in polyethylene and from 0.05% to 3% by weight in the other poly-u-monoolefins such as polypropylene, etc. Of course, higher quantities can be used in both cases, but generally there is relatively little additional advantage to be'gained thereby. A very valuable attribute, of the stabilizers of this invention in polyethylene is that they serve quite effectively at concentrations such as 0.05% by weight; whereas, even 1.0% of propyl gallate only improves the AOM stability by a factor on the order of 2m 4 times and concentrations as low as 0.05% are practically ineffective. In contrast, the small amount of 0.1% of dodecyl gallate results in an improvement factor on the order of more than 30 times (see Table I) and less than half this concentration (lower than 0.05%) is still highly effective. In fact, it is generally quite feasible to employ 0.05% by weight of the stabilizers of this invention as an effective concentration in polyethylene of standard commercial quality.

Although the invention hasbeen described in consid-' erable detail with reference to certain preferred embodimodifications can be effected without departing from the r spirit and scope of the invention as described hereinabove compositiomof an alkyl ester of gallic acid wherein the alkyl group contains 12-l8 ,carbon atoms.

, '5. Polypropylene in an essentially-solid state stabilized 7 withabout 0.5% by weight, based on total wcightgof composition, of-analkyl ester of gallic acid wherein the alkyl group contains l 2-18 carbon-atoms.

6. Polyethylene in an essentially solid state stabilized with about 0.001% to 0.05 by weight of the octadecyl ester of gallic acid. I l

7. Polyethylene in an essentially solid state stabilized ester of gallic acid.

8. Polypropylene in an essentially solid state stabilized with about 0.001% to 0.05% weight of the dodecyl 9 Polypropylene in an essentially solid statestabilized "with about.0.05% to 3.0% by weight of the octadecyl ester of gallic acid.

10. A process for stabilizing a solid colorless poly-amonoolefin against oxidative degradation whereby about 0.001% to 3% by. weight, of an alkyl ester of gallic acid wherein the alkyl group contains 12-18 carbon atoms is combined at above C. with said poly-u-monoolefin without appreciable staining of said composition, whereby a stabilized solid poly-a-monoolefin is formed characterized by being substantially colorless, retaining its elec- References Cited in thefile of this patent UNITED STATES PATENTS 2,448,799 Happoldt Sept. 7, 1948 I FOREIGN PATENTS a V 618,839 Great Britain Feb. 28, 1949 Bergelz' Chemistry and Industry, Apr. 1, 1944. pages 1 127-128. (Copy in Scientific Library.)

Claims (1)

1. A SOLID POLYMER OF AN A-MONOOLEFIN SELECTED FROM THE GROUP CONSISTING OF POLYETHYLENE, SUBSTANTIALLY ISOTACTIC POLYMERS OF A-MONOOLEFINS CONTAINING FROM 3 TO 8 CARBON ATOMS AND SUBSTANTIALLY SYNDIOTACTIC POLYMERS OF A-MONOOLEFINS CONTAINING FROM 3 TO 8 CARBON ATOMS STABILIZED WITH ABOUT 0.001% TO 3% BY WEIGHT, BASED ON TOTAL WEIGHT OF COMPOSITION, OF AN ALKYL ESTER OF GALLIC ACD WHEREIN THE ALKYL GROUP CONTAINS 12-18 CARBON ATOMS.