Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F210/00—Copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F210/00—Copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
  • C08F210/04—Monomers containing three or four carbon atoms
  • C08F210/06—Propene

Definitions

• the invention relates to a process for the preparation of a stable ⁇ -olefin copolymer, wherein ⁇ -olefin is caused to react with a comonomer which stabilizes the copolymer.
• the invention also relates to an ⁇ -olefin copolymer which comprises, as the monomer units, repeating units (mers) of the ⁇ -olefin and repeating units (mers) of a comonomer stabilizing the copoly ⁇ mer.
• the invention relates to a process for the preparation of a copolymer-stabilizing comonomer of the above type and to the use of a phenol resembling the said copolymer- stabilizing comonomer as an activator in the polymerization of ⁇ -olefins.
• a Ziegler-Natta catalyst system which consists of a so-called procat ⁇ alyst and a cocatalyst.
• the procatalyst is based on a compound of a transition metal belonging to any of groups 4-8 of the Periodic Table of the Elements (IUPAC)
• the cocatalyst is based on a compound of a metal belonging to any of groups 1(A)- 8(A) of the Periodic Table of the Elements (IUPAC).
• a separate group among the procatalysts is formed by metallocene-type transition-metal compounds, i.e. compounds in which one un- saturated ring or several, such as a cyclopentadienyl ring, is bonded to the transition metal with a u-bond.
• US patent publication 3 242 099 discloses a catalyst system intended for the polymerization of ⁇ -olefins, in which system bis-cyclopentadienyl titanium dichloride is combined with an oligomeric alumoxane compound.
• US patent publication 4 404 344 discloses a process for the preparation of homopolymers and copolymers of ethylene and propylene by the polymerization of one or several monomers by means of a catalyst system formed by bis-cyclopentadienyl zir- conium dimethyl and a lower alkyl alumoxane.
• the publication states that ethylene can be copolymerized with propylene, 1- butene, 1-hexene or ⁇ , ⁇ -dienes.
• EP-69 952 and US-4 542 199 describe the polymerization of C_- C 10 olefins in the presence of a catalyst system which is made up of bis-cyclopentadienyl zirconium dichloride or bis- cyclopentadienyl zirconium mon ⁇ methylmonochloride and linear o cyclic methylalumoxane.
• stabilizers and other additives may migrate to the surface of products, whereby their stabilizing effect is re ⁇ substituted.
• Additive losses may be caused by evaporation during melt processing, loss during the washing step, the migration of polar additive components, and uneven distribution of stabil ⁇ izer additives in the polymer matrix.
• the last-mentioned is often caused by the incompatibility of stabilizers, due to high polarity, with paraffin-type hydrocarbon-based polymers.
• amine stabilizers such as paraphenyldiamine deriv ⁇ atives, tend to separate from the polyolefin matrix.
• the stabilizer amount which can be added to polyolefins is limited, since the additive tends to crystallize.
• DE publication 1 947 590 discloses a method for the preparation of copolymers, wherein ⁇ -olefin is caused to react ethylenically with an unsaturated metal phenoxide in the presence of a catalyst made up of a titanium or vanadium halo ⁇ gen compound and an organoaluminum or organozinc compound.
• the organometal compounds may be omitted if the metal phenoxide has a metal-carbon bond.
• DE publication 1 570 541 discloses the copolymerization of propylene with 4-( ⁇ -alken ⁇ l)-N,N-dimeth ⁇ l- aniline by using as the catalyst a heterogenous Ziegler-Natta catalyst which is sensitive to polar stabilizer comonomers.
• polymerization activity has been so low that the processes have remained laboratory curiosities.
• the polymerizations have name ⁇ ly been performed by means of an old-fashioned catalyst which is based on titanium trichloride or titanium tetrachloride and alkyl and aluminum compounds.
• the olefin polymerization technology has developed to the present level, in which one gram of catalyst is capable of polymerizing up to 30 kg of ⁇ -olefin.
• the copolymerization of polar components with these high-yield catalysts has not been known on an industrial scale owing to the tendency of these components to form, with the active centers of the cat ⁇ alyst, compounds which inhibit polymerization.
• polar components such as alcohols, water and acetone have indeed been used for discontinuing polymerization when the desired molar mass has been reached.
• Another obstacle is evidently that in polymerization a sterically large-sized stabilizer monomer is not capable of approaching the active centers on the surface of a carrier.
• An object of the present invention is to provide a process for the preparation of a stable ⁇ -olefin copolymer with a maximal yield.
• a more detailed object is the copolymerization of ⁇ - olefin with a monomer-type stabilizer by using a high-yield catalyst system of a new type. The plan is in this case to prepare, directly in the polymerization step, stabilized poly ⁇ mer particles of a suitable size.
• a key object is also to pro ⁇ vide a usable copolymer the stabilizer component of which will remain evenly distributed in the polymer product without becom ⁇ ing separated as a separate phase. It is also an aim of the invention to provide a compound or comonomer which stabilizes the copolymer and at the same time has an activating effect on the polymerization.
• ⁇ -olefin is caused to react with a comonomer which stabilizes the copolymer, in which case the ⁇ -olefin used is an olefin according to Formula (I)
• R and R' are, independently of each other, hydrogen or a c l ⁇ c 10 - ⁇ l ⁇ yl' - n & e copolymer-stabilizing comonomer used is a compound according to Formula (II)
• X is a carbon-carbon bond between vinyl carbon and ben ⁇ zene carbon or a hydrocarbon bridge
• R- j _, R R3 and R 4 are hydrogen sub stituents and/or C-L-C20 hydrocarbon substituents in the be: :ene ring
• the catalyst is a n-cyclopentadienyl transition m tal compound and an alumoxane compound.
• the ⁇ -olefin usable in the process according to the invention can be any ⁇ -olefin copolymerizable with a Ziegler-Natta sys ⁇ tem.
• Typical ⁇ -olefins of this type are ethylene, propylene, 1- butene, isobutylene and 4-methyl-1-pentene.
• the ⁇ -olefin ac ⁇ cording Formula (I) used in the process according to the inven ⁇ tion may also be a mixture which contains polymerizable ⁇ -ole ⁇ fins of various types.
• monomers other than mono ⁇ mers according to Formulae (I) and (II) may also participate in the polymerization of the process according to the invention. Since polypropylene is, with respect to its commercial impor ⁇ tance, relatively unstable and easily oxidizable, the invention is especially usable if the ⁇ -olefin according to Formula (I) is propylene.
• an ⁇ -olefin accord ⁇ ing to Formula (I) is thus caused to react with a copolymer- stabilizing comonomer according to Formula (II).
• a copolymer- stabilizing comonomer according to Formula (II) it is a prerequisite for the functioning of a Ziegler- Natta system, which the n-cyclopentadienyl transition metal compound/alumoxane compound used in the present invention is also deemed to be, that the copolymer-stabilizing comonomer must not, with its reactive hetero group, poison the catalyst.
• substituents in the benzene ring of the comonomer according to Formula (II) may be quite freely distributed, it is, however, preferable if in the comonomer at least one, and preferably two, of the group which includes the bridge X and substituents R ⁇ , R 2 , R 3 anc * R4, is a secondary, most preferably tertiary, alkyl which is in the ortho-position relative to the hydroxyl group.
• the bridge X which is a C 1 -C 2Q hydrocarbon bridge, is attached in the ortho- or para-position of the benzene ring, in which case R ⁇ is preferably a branched C -Cg alkyl and is at- tached in the ortho-position of the benzene ring, and at least two of groups R 2 , R 3 and R 4 are hydrogen.
• the hy- droxyl of the benzene ring is flanked by at least one, and preferably two, alkyl substituents, and preferably a branched alkyl substituent.
• the copolymer-stabilizing comonomer according to Formula (II) is 6- tert.-butyl-(2-(1,l-dimethylhept-6-enyl) )-4-methylphenol.
• an ⁇ -olefin is copoly- merized with a copolymer-stabilizing comonomer in the presence of a catalyst which is based on a n-cyclopentadienyl transition metal compound and an alumoxane compound.
• n-cyclopentadienyl transition metal compound in this context a catalytically active transition metal compound in which the transition metal has at least one cyclopentadienyl ligand bonded with a n bond.
• a ligand is very stable, and it can be deemed to form a six-electron aromatic anion CgHg " . Owing to its aromatic stability it may also be substituted, especially in such a manner that it is fused with another ring.
• These compounds are also called metallocenes.
• the n-cyclopentadienyl transition metal compound has the following general formula (III)
• Cp is an unsubstituted, substituted or fused n-cyclo- ⁇ pentadienyl
• R is an organic group
• Y is a halogen
• m is an integer 1-3
• n is an integer 0-3, and o is an integer 0-3.
• the n-cyclopentadienyl transition metal compound is a compound or derivative of two n-cyclopentadienyl ligands and a group 4 transition metal, such as bis-n-cyclo ⁇ pentadienyl titanium(IV) derivative, bis-n-cyclopentadienyl zirconium(IV) derivative, or bis-n-cyclopentadienyl hafnium(IV) derivative, preferably a bridged bis-indenyl zirconium(IV) derivative or a bridged bis-indenyl hafnium(IV) derivative.
• a group 4 transition metal such as bis-n-cyclo ⁇ pentadienyl titanium(IV) derivative, bis-n-cyclopentadienyl zirconium(IV) derivative, or bis-n-cyclopentadienyl hafnium(IV) derivative, preferably a bridged bis-indenyl zirconium(IV) derivative or a bridged bis-indeny
• bridged is meant that both of the indenyl ligands are bound to each other by a chemical group such as ethylene or silylene, in which case the ethylene or silylene bridge is attached to the six-carbon-atom ring of the indenyl group.
• indenyl derivative is also meant that the indenyl may be fully aromatic or the six-carbon-atom fusion ring may be aliphatic, i.e. it may contain four hydrogen atoms (IndH 4 ).
• the n-cyclopentadienyl transi ⁇ tion metal compound used in the process and serving as a cata ⁇ lyst is (CH3) 2 Si(IndH 4 ) 2 rCl2 or (C 2 H 4 ) (IndH 4 ) 2 ZrCl 2 , preferab ⁇ ly racemic rac. (CH ⁇ SidndH ⁇ ZrC ⁇ , where IndH 4 stands for a tetrahydroindenyl group, see above.
• These preferred n-cyclo ⁇ pentadienyl transition metal compounds have been discussed in, for example, EP patent application 344 887 A3, which is incor ⁇ porated herein by reference.
• n-cyclopentadienyl transition metal compounds which we deem to be the most preferable have been stated above, it is also possible to use other analogous compounds. Such compounds have been listed, for example, in EP application 303 519 from page 3, line 59 to page 4, line 31 and in EP application 260 999 on page 4, lines 14-30. Both publications are hereby incorporated in the present application by ref ⁇ erence.
• the other catalyst component in the polymerization process according to the invention is an alumoxane compound. It prefer ⁇ ably has the following general formula (IV)
• Formula (IVa) applies when the alumoxane compound is ring-like by structure and Formula (IVb) applies when the structure of the alumoxane compound is linear.
• Group R in the alumoxane compound according to Formula (IV) is preferably a lower alkyl group having 1-5 carbon atoms, and most preferably methyl, p in the formula is preferably such that alumoxane is at least an oligomer, and it is preferably an integer 4-20.
• the alumoxane used in the invention can be prepared in many ways, for example by contacting water with trialkylaluminum or by contacting trialkylaluminum with hydrogenated salt, such as hydrogenated copper sulfate or iron sulfate.
• the alumoxane is pref ⁇ erably prepared with the aid of hydrogenated iron(IV) sulfate or hydrogenated copper sulfate.
• the dilute solu ⁇ tion of trialkylaluminum in toluene, benzene or xylene is treated with FeS0 4 »7H 2 0 or CuS0 4 *5H 2 0.
• the molar ratio of hy ⁇ drogenated sulfate to trialkyl aluminum is in general 1:5 - 1:10, and the reaction temperature is within the range -40°C - +60°C, in which case methane gas is released in the reaction.
• the product obtained consists of both linear and ring ⁇ like alumoxane having an oligomerization degree of 6 or higher when the reaction is a success.
• the molar ratio between the metals of the alumoxane compound and the n-cyclopentadienyl transition metal compound used as a catalyst in the polymerization process according to the inven ⁇ tion may vary widely.
• the general rule is that aluminum is used in a considerably larger amount than is the transition metal compound.
• the said molar ratio between the metals is within the range 100,000:1 - 10:1, pref ⁇ erably 10,000:1 - 1000:1, and most preferably approx. 5000:1 - 1000 : 1.
• the catalyst system used in the process according to the inven ⁇ tion may be either homogenous or heterogenous.
• a carrier can be used both for the n-cyclopenta ⁇ dienyl transition metal compound and for the alumoxane com ⁇ pound, or a n-cyclopentadienyl transition metal compound and a carrier treated, for example impregnated, with an alumoxane compound can be added to the polymerization mixture.
• Suitable carriers include silica, alumina, magnesia, zirconia, magnesium silicate, alkylated silicates, and certain polymers, such as granular polyethylene.
• a carrier-free catalyst system of a n-cyclo ⁇ pentadienyl transition metal compound and an alumoxane com ⁇ pound the polymerization and catalysis being preferably car ⁇ ried out in a hydrocarbon solvent, such as toluene.
• the catalyst system used in the process according to the invention is based on a n-cyclopentadienyl transition metal compound and an alumoxane compound, it may also contain other catalytic components and catalyst auxiliaries. These include other transition-metal compounds and aluminum compounds and possibly electron donors.
• the polymerization is typically carried out by feeding into an inert polymerization reactor a copolymer-stabilizing comonomer, a n-cyclopentadienyl transition metal compound, an alumoxane, a solvent, and a gaseous ⁇ -olefin to start polymerization.
• a copolymer-stabilizing comonomer e.g., ethylene glycol dimethacrylate
• a n-cyclopentadienyl transition metal compound e.g., a n-cyclopentadienyl transition metal compound
• an alumoxane e.g., alumoxane
• solvent eous ⁇ -olefin
• an autoclave flushed with dry and oxygen-free nitro ⁇ gen, is filled with a solvent, such as toluene, whereafter the first portion of the solution of alumoxane in the solvent is added.
• a solvent such as toluene
• the n-cyclopentadienyl transition metal compound is added to the second portion of the alumoxane solu ⁇ tion, whereafter this second portion is also fed into the reactor.
• ⁇ -olefin may be fed into the reactor, possibly by using pressure, to initiate the polymerization wit only ⁇ -olefin, i.e. to achieve so-called prepoly erization.
• a copolymer-stabilizing co ⁇ monomer may be added, which has been suitably dissolved in the solvent used in the polymerization.
• the feeding in of the sta ⁇ bilizer comonomer may be done, for example, by means of pres ⁇ surized ⁇ -olefin, such as propylene.
• the rate of ⁇ -olefin is maintained constant, for ex ⁇ ample by adjusting the reaction pressure.
• polymerization is discontinued by removing, when neces ⁇ sary, any unreacted ⁇ -olefin and by adding a catalyst poison, such as alcohol. Finally the obtained stable ⁇ -olefin copolymer is separated, washed and dried.
• the ⁇ -olefin is caused to react with the copolymer-stabilizing monomer at a temperature of 5-50 °C, preferably 10-30 °C, and most preferab ⁇ ly 15-25 °C.
• a suitable reaction time is approx. 10-120 min, preferably approx. 20-80 min.
• the molar ratio Al/comonomer preferably Al/6-tert.- butyl(2-(l,l-dimethylhept-6-enyl) )-4-meth ⁇ lphenol is adjusted to a value of 3-10, preferably to a value of 4-8.
• the ⁇ -olefin being gaseous at NTP and being preferably propylene, to adjust the partial pressure of ⁇ -olefin in the reaction to 1-5 bar.
• the invention has focussed on the copolymerization of only one ⁇ -olefin and one copolymer-stabilizing comonomer, it is evident from the viewpoint of the idea of the invention that it is also possible to use a plurality of copolymer-stabilizin comonomers.
• the invention also relates to a stable ⁇ -olefin copolymer which comprises, as monomer units, repeating units (mers) of an ⁇ -olefin and repeating units (mers) of a copolymer-stabilizing comonomer.
• the ⁇ -olefin copo ⁇ lymer according to the invention is mainly characterized in what is stated in the characterizing clause of Claim 16. It has thus been realized that an ⁇ -olefin copolymer is easy to pre ⁇ pare and that it is stable if it is made up of ⁇ -olefin units, which are in accordance with the following formula (V)
• R and R' are, independently of each other, hydrogen or a l" c 10 al ⁇ Yl' an ⁇ that the repeating unit of the copolymer- stabilizing comonomer is in accordance with Formula (VI)
• X is a carbon-carbon bond between vinylene carbon and benzene carbon or a C 1 -C 20 hydrocarbon bridge, preferably a Cg- c 12 hydrocarbon bridge
• R ⁇ , R 2 , R3 and R are hydrogen substituents and/or C-,-C2 Q hydrocarbon substituents in the benzene ring.
• An ⁇ -olefin copolymer according to the invention may contain ⁇ - olefin units of one or more types, such as a unit of ethylene, propylene, 1-butene, isobutylene or 4-methyl-l-pentene. It is especially preferable if, in the ⁇ -olefin repeating unit ac ⁇ cording to Formula (V), R is methyl, i.e. the repeating unit is a propylene unit.
• the ⁇ -olefin copolymer may also contain a plurality of repeating units according to Formula (V) and addi- tionally other comonomer units.
• At least one, and preferably two, of bridges X and substituents R lf R 2 , R3, and R 4 is a secondary, preferably tertiary, alkyl- ene or alkyl, which is in the ortho-position with respect to the hydroxyl group.
• the bridge X is attached in the ortho- or para-position of the benzene ring
• R ⁇ is a branched C 3 -Cg alkyl and attached in the ortho-position in the benzene ring
• at least two of the groups R2, R3 and R are hydrogen.
• the repeating unit, in accordance with Formula (VI), of the copolymer-stabilizing comonomer is a 6-tert.- butyl-(2-(l,l-dimethylhept-6-enylen ⁇ l) )-4-methylphenol unit.
• the molar mass distribution was considerably narrow, which suggests that the catalyst has ac ⁇ tive centers of only one type.
• the molar mass distribution measured as a ratio of polydispersity, i.e. weight-average molar mass, to the number-average molar mass, M w /M n is prefer ⁇ ably below 4, and most preferably approx. 1.5-2.5.
• the stable ⁇ -olefin copolymer according to the invention and the process for the preparation thereof are also closely as ⁇ sociated with a process for the preparation of a comonomer which stabilizes the copolymer and crucially activates the polymerization.
• the invention thus also relates to a process for the preparation of the most preferred copolymer-stabilizing comonomer, i.e. 6-tert.-but ⁇ l-(2-(l,l-dimeth ⁇ lhept-6-en ⁇ l) )-4- methylphenol.
• This compound has the formula (VII)
• Process a) is typically carried out by mixing the components and heating them to, for example, 50-100 °C, and by thereafter adding to the mixture an acid catalyst, such as sulfuric acid. Thereafter the mixture is allowed to react for 24 hours, where ⁇ after neutralization and extraction by means of a suitable solvent, such as hexane, are carried out. Finally separation, for example by distillation, is performed.
• an acid catalyst such as sulfuric acid.
• process b) the components are mixed together, heated, and treated with an acid catalyst in quite the same manner as in process a). After an approximately equally long reaction time, neutralization, extraction, and separation, for example by distillation, are carried out.
• R lf R 2 , R 3 , R 4 , and R 5 are hydrogen or a C 1 -C 0 hydrocar ⁇ bon, in which case at least two of the R-groups are C ⁇ -C 2Q hydrocarbons, as an activator in ⁇ -olefin polymerization where ⁇ in the catalyst used consists of a n-cyclopentadienyl transi ⁇ tion metal compound and an alumoxane.
• the preferred embodiments are in the main the same parameters as were stated above in connection with the polymerization process according to the invention.
• the 6-tert.-butyl- (2-(l,l-dimethylhept-6-enyl) )-4-methylphenol was prepared sub ⁇ stantially by an acid-catalyzed reaction between 2-tert.-butyl- 4-methylphenol and 7-methyl-l,7-octadiene, which will be de ⁇ scribed below.
• the sample-taking from the n-cyclopentadienyl transition metal compound and alumoxane and from the phenolic monomer took place in a nitrogen atmosphere which contained oxygen less than 2 ppm and water less than 5 ppm.
• the reaction temperature was con- trolled within +0.3 P C by using a Lauda circulating bath.
• the slurry polymerizations were conducted in a 0.5 1 jacketed auto ⁇ clave equipped with a blade turbine stirrer. The dry glass autoclave was evacuated and flushed with nitrogen. This was repeated several times. Thereafter the first portion, i.e.
• a suitable amount of a phenolic stabilizer comonomer diluted in 15 ml of toluene was introduced into the reactor by means of gaseous propylene until the par ⁇ tial pressure of propylene reached 2 bar.
• the polymerization rate was determined by measuring the rate of propylene consump ⁇ tion, the total pressure- in the reactor remaining constant as gaseous propylene was added continuously.
• the polymerizations were quenched by removing the propylene rapidly and by adding 100 ml of methanol.
• the produced polyolefin was filtered and the catalyst residues were removed by a treatment with a 1 % methanol/HCl solution.
• the polyolefin was washed twice with ethanol, was dried under vacuum at 50 °C, and was weighed for the determination of the polymerization yield.
• the copolymer was extracted by refluxing with 2-propanol/cyclo- hexane for 24 h in a Soxhlet apparatus before the concentration of bound phenolic stabilizer comonomer was determined and thermo-oxidative tests were conducted.
• the proportion of bound phenolic stabilizer was determined by UV analysis, and the numeric values are based on polypropylene- /Irganox 1076 standards.
• the UV spectra were obtained by using a Schimadzu UV-240 spectrometer. The spectra were recorded between 220 and 350 nm.
• the phenolic stabilizer comonomer had a strong absorbance in this region at the wavelength 280 nm, and all of the measurements were performed at this wavelength.
• the melting and crystallization thermograms were recorded by a Perkin-Elmer DSC IV system, the temperature being increased from 50 °C to 200 °C at a rate of 10 °C/min.
• the sweeping gas used was nitrogen. The results of the second scan were reported in order to eliminate differences in sample history.
• Crystal- linity was determined from the DSC curves by using a fusion heat of 49.8 cal/g.
• the thermo-oxidative stability of the ex ⁇ tracted copolymers was investigated by means of oven aging, where the sample was at a temperature of 110 °C and in air, whereafter the oxidation products were detected by means of a Perkin-Elmer 1710-IR spectrometer.
• the increase of the absorb ⁇ ance peak at wave number 1720 cm is associated with products of hydrocarbon oxidation, such as acids, aldehydes and ketones.
• the formation time of the carbonyl peak was recorded. 13C NMR analyses were carried out with a Jeol 400 MHz spectrophotometer at 110 °C.
• the polymer samples were dissolved in 1,1,2,2-tetra- chloroethane-d2•
• the GVC chromatograms were obtained with a Waters model 150 C at 135 °C, the polymer samples being dis ⁇ solved in 1,2,4-trichlorobenzene.
• Copolymerizations of propylene and 6-tert.-butyl-(2-(l,l-di- methylhept-6-enyl) )-4-methylphenol in accordance with Scheme I were carried out by varying the concentrations of the monomers in relation to each other, the results obtained being shown in Table I.
• copolymerizations were carried out by varying the ratio Al/Zr while all of the other parameters re ⁇ mained constant, and the results of these copolymerizations are depicted graphically in Figure 1.
• the polymerization activity increased considerably when the molar ratio Al/phenol exceeded the value 4.4, whereafter the activity decreased gradually as the molar ratio Al/phenol de ⁇ creased.
• the molar masses of the copolymers increased as the concentration of the phenolic stabilizer comonomer increased, and the molar mass of copolymer produced using high concentra ⁇ tions corresponded to the molar mass of a polypropylene pre ⁇ pared under the same conditions, and therefore it is unlikely that the stabilizing phenolic comonomer served as a chain transfer agent.
• the molar mass distributions of the copolymers were in general within the range 1.9-2.1, which corresponds to the typical polymerization results of a catalyst which contains active centers of one type.
• thermo-oxidative stability of the copolymer was determined in an oven at 110 °C in the presence of air.
• the results were determined by the above-mentioned FT-IR analysis.
• the results are shown in Table III.
• the copolymers were kept in the oven they were extracted by refluxing for 24 hours in a Soxhlet apparatus by using 2-propanol/cyclohexane as the extraction liquid, to remove any monomer residues.
• a carbonyl peak appeared at 400-700 hours at 110 °C, whereas unstabilized polypropylene had a strong carbonyl peak already at 6 hours.
• the decrease in catalytic activity during copolymerization can be explained by a reduction, as a functiono of the polymerization time, of the strongly activating effect of the phenolic stabilizer, since approx. 60 % of the phenolic stabilizer monomer originally fed is incorporated into the copolymer within 20 min. That the polymerization rate increase from the initial value of 5 kg polymer / g catalyst • h to 28 kg polymer / g catalyst • h when polar 6-tert.-butyl-(2-(l,l- dimethylhept-6-enyl) )-4-methylphenol was added has been neither described not suggested previously.
• Crys. stands for polymer crystallinity, which was deter ⁇ mined from the DSC curves, the melting temperature of a folded-chain polypropylene crystal being assumed to be 49.8 cal/g.
• the bound phenolic stabilizer amount was determined by UV spectrometry after the copolymer had been extracted for 24 hours by refluxing with a 50:50 solution of 2- propanol and cyclohexane. Table II
• Thermo-oxidative stability results of extracted copolymers by using FTIR spectrometry after the samples had been stored in air and a temperature of 110 °C
• b copolymerization of propylene and 2-tert.-butyl-(2(l,l-di- methylhept-6-enyl) )-4-methylphenol. The phenolic stabilizer was added at 5 min after the starting of the propylene polymeriza ⁇ tion.
• Figure 4 a) FTIR spectrum of polypropylene, b) FTIR spectrum of co ⁇ polymer.
• a ) propylene poly ⁇ merization
• b) phenolic stabilizer (final concentration 0.0344 mol/1) was first precomplexed with MAO for 75 min before the adding of the metallocene catalyst.
• the non-precomplexed phenolic monomer (same final concentration) was added at c) 5 minutes, d) 20 minutes, and e) 40 minutes after the starting of the propylene polymerization.

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