MXPA98007910A - Using nitric oxide to reduce reactor fouling during polypropylene graft copolymerization - Google Patents

Abstract

Un copolímero injerto comprendiendo una cadena principal de material polímero propileno que tiene un monómero vinilo polimerizado aéste, se produce por medio de (1) tratar el material polímero propileno con un iniciador de la polimerización por radicales libres, (2) tratar el material polímero propileno con al menos un monómero injerto capaz de ser polimerizado por radicales libres y, (3) remover cualquier monómero injerto y reaccionar el material polímero propileno polimerizado por injerto, descomponiendo cualquier iniciador sin reaccionar, y desactivando cualquier residuo de radicales libres en el material, en donde (1) y (2) se lleva a cabo en presencia de continua alimentación deóxido nítrico. Elóxido nítrico reduce el desarrollo del polímero en paredes del reactor, espiral de circulación de gas, mientras casi no tiene efecto en la reacción de copolimerización por injerto.

Description

USE OF NITRIC OXIDE TO REDUCE DFL REACTOR CONTAMINATION DURING COPOLYMERIZATION BY POLYPROPYLENE GRAFTING This invention describes a process for the graft copolymerization of polypropylene materials. Contamination or embedding of the reactor in the graft copolymerization of propylene polymer materials and other vinyl monomers occurs in tank reactors with agitation for semilots and in spiral reactors with gas mixture. The polymer deposits that form on the walls of the reactor and the e ^ gas circulation in the spiral usually grow rapidly, after the initial deposit. The severe contamination of the reactor would affect the quality of the product, productivity and operability of a commercial plant. Since the primary reaction of a polymerization by free radicals using a peroxide and an initiator, any attempt to reduce reactor contamination by means of a monomer-soluble free radical scavenger will potentially interfere with the graft polymerization process. Therefore, such soluble scrubbers are not used in this process. It is known that polymerization inhibitors such as nitric oxide can be used to prevent the polymerization of vinyl aromatics during distillation, for example, as described in US Patent No. 3,964,979, US Patent No. 4,070,419 describes the addition of NO gaseous, for example during the purification of styrene by distillation and then subjecting the monomer under polymerization conditions, whereby the styrene is polymerized at an accelerated rate. Hungarian Patent 77-MA2891 discloses irradiated grafting of polypropylene with styrene in the presence of nitroxyl polymerization inhibitor to reduce side reactions, i.e., polystyrene products were not formed. US Patent No. 5,283,287 describes a process for producing a composition for thermoplastic resins having an excellent HCFC strength, which includes graft polymerizing a monomer mixture of a vinyl cyanide, an aromatic vinyl compound and an unsaturated carboxylic acid or ester thereof in the presence of a rubber latex and a polymerization inhibitor such as nitric oxide to control the sequence of polyacrylonitrile units. However, none of these references disclose the use of a continuous feed of nitric oxide to reduce reactor contamination during the production of polypropylene graft copolymers. The process of this invention for preparing a substantially non-oxidizable copolymer graft to the environment comprises: (a) treating a polymer or propylene material with an organic compound that is initiator of free radical polymerization, (b) treating the propylene polymer material. during a period of time coinciding with, or after (a), superimposed or not, about 5 to about 240 parts of at least one graft monomer capable of being free radical polymerized per one hundred parts of the propylene polymer material; c) removing any unreacted graft monomer from the resulting propylene grafted polymer material, decomposing any unreacted initiator and deactivating any free radical residue in the material, where (a) and (b) are carried out in the presence of nitric oxide which is added over the inert gas in an amount of about 0.05 parts to about 50 parts of oxide Nitric per million parts of the inert gas to reduce pollution in the reactor. The continuous feeding of nitric oxide significantly reduces the degree of contamination of the reactor while it hardly affects the percentage of monomer to polymer conversion or the efficiency of the graft. The propylene polymer material that is used as the main chain of the graft copolymerization can be: (a) a crystalline propylene homopolymer with an isotactic index greater than 80, preferably about 85 to about 99; (b) a variable crystalline propylene copolymer and an olefin selected from the group consisting of ethylene and C4-C α-olefin, this as long as the olefin is ethylene, the maximum polymerized ethylene content is 10. by weight, preferably about 4 oy when the olefin is an alpha-olefin of C4-Cn, the maximum polymerized content thereof is 20O by weight, preferably about 16 ^ and the copolymer has an isotactic index greater than 85; (c) a variable crystalline propylene terpolymer and two olefins selected from the group consisting of ethylene and C4-C8 α-olefin, provided that the content of polymerized C4-C8 α-olefin is 20% by weight, preferably by of 16 o, and, when ethylene is one of the olefins, the maximum polymerized ethylene content is 5'i by weight, preferably about 45, the termpolymer having an isotactic index greater than 85; (d) an olefin polymer composition comprising: (i) about 10 to 60 parts by weight, preferably about 15 parts to 55 parts, of a crystalline homopolymer having an isotactic index greater than 80, preferably about 85 up to about 98 or a copolymer selected from the group consisting of (a) propylene and ethylene, (b) propylene, ethylene and a C-Cß cleavage, and (c) propylene and a C4-α-olefin. Ce, the copolymer has a propylene content of more than 85% by weight, preferably close to 90% to about 99%, and an isotactic index greater than 85; (ii) about 5 parts up to about 25 parts by weight, preferably about 5 parts up to about 20 parts, of an ethylene-propylene copolymer or a C4-C-α-olefin, which is insoluble in xi 1 ene_ at room temperature; and (iii) about 30 parts up to about 70 parts by weight, preferably about 20 parts to 65 parts, of an elastomeric copolymer selected from the group consisting of (a) ethylene and propylene, (b) ethylene, propylene, and a C4-C6 α-olefin, and (c) ethylene and a C4-Cd α-olefin, the copolymer optionally contains about 0.5 'up to about 10 ° of a diene, and containing less than 70 °, preferably close to 10 up to about 60o, more preferably about 12% to about 55%, of ethylene and being soluble in xylene at room temperature and has an intrinsic viscosity of about 1.5 to about 4.0 dl / g; the total of (ii) and (iii), based on the total composition of the olefin polymer being from about -50o to about 90', and the weight reaction of (ii) /. { iii) being less than 0.4, preferably 0.1 to 0.3, wherein the composition is prepared by polymerization in at least two stages and has a flexural modulus of less than 150MPa: and (e) a thermoplastic olefin comprising: (i) about 10% to about 60 or preferably about 20O to about 50 of a propylene homopolymer having an isotactic index greater than 80, or a crystalline copolymer selected from the group consisting of (a) ethylene and propylene, (b) ethylene, propylene, and a C4-Cβ α-olefin, and (c) ethylene and a C4-Cι α-olefin, the copolymer having a propylene content greater than 85 and an isotactic index greater than 85; - (ii) about 20o to about 60o, preferably about 30o to about 50'O of an amorphous copolymer selected from the group consisting of (a) ethylene and propylene, (b) ethylene, propylene, and a -olefin of Cj-Cs, and (c) ethylene and a C4-Cß α-olefin, the copolymer optionally contains about O.S'O to about 10% of a diene, and contains less than 10% ethylene and being soluble in xylene at room temperature; and (iii) approximately 3 '? up to about 0%, preferably about 10% up to about 20%, of an ethylene-propylene copolymer or an α-olefin of C.-C. which is soluble in xylene at room temperature, wherein the composition has a flexural modulus of greater than 150 but less than 1200 MPa, preferably about 200 to about 1100 MPa, more preferably about 200 to about 1000 MPa. The temperature of the room or environment is ~ 25 ° C. The C4-C¿ α-olefin useful in the preparation of (d) and (e) includes, for example, 1-butene; 1-pentene; 1-hexene; 4-methyl-1-pentene and 1-octene. When the diene is present it is usually a butadiene; 1, hexadiene; 1, 5-hexadiene, or ethylene norbornene. The preparation of propylene propylene material (d) is described in more detail in U.S. Patent Nos. 5,212,246 and 5,406,922, the preparation of which was incorporated in the patent as a reference. The preparation of the propylene polymer material (e) is described in more detail in U.S. Patent Nos. 5,302,454 and 5,409,992, the preparation of which is incorporated herein by reference. The monomers that can be polymerized by grafting on the main chain of propylene polymer material can be any aromatic vinyl compound capable of being polymerized by means of free radicals wherein the vinyl radical, HC = CR, wherein R is H or methyl, it is attached to a linear or branched aliphatic chain or a ring, heterocyclic aromatic or substituted alicyclic or substituted nyl of a mono- or polycyclic compound.The common substituent groups may be alkyl, hydroxyalkyl, aryl, and halo. the vinyl monomer will be a monomer of the following vinyl substituted alicyclic heterocyclic aromatic classes or compounds including ethylene, vinyl naphthalene, vinyl pyridine, vinyl pyrrolidone, vinyl carbazole, and homologs thereof, for example, ally and para-methylstyrene, methylchlorostyrene, p-tert-butylstyrene, methylvinylpyridine, and ethylvinylpyridine; (2) vinyl esters of "saturated" aliphatic and aromatic carboxylic acids, including vinyl acetate, vinyl acetate, vinyl chloroacetate, vinyl cyanoacetate, vinyl propionate and vinyl benzoate, and (3) unsaturated aliphatic nitriles and carboxylic acids. and its derivatives, including acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, acrylic acid and acrylate esters, such as methyl, ethyl, hydroxyethyl, 2-ethylhexyl and acrylate butyl esters; methacrylic acid, ethacrylic acid, methacrylate esters, such as methyl, ethyl, butyl, benzyl, phenylethyl, phenoxyethyl, epoxypropyl and hydroxypropyl methacrylate esters; maleic anhydride and N-phenylmaleimide. Polymerizable dienes can also be used by free radicals, such as butadiene, isprene and its derivatives. Multiple monomers of the same or different classes can be employed. The preferred graft monomers are styrene and methyl methacrylate. The monomers are added in an amount of about 5 parts to about 240 parts per 100 parts of the propylene polymer material, preferably about 20 to about 100 ppc. The graft copolymer is made by forming active sites for grafting into the propylene polymer material by treatment with a peroxide, another chemical compound that is a free radical polymerization initiator. The free radicals produced in the polymer as a result of the chemical treatment initiate the polymerization of the monomers at those sites. During graft polymerization, the monomers are also polymerized to a certain amount of ungrafted or free copolymer or polymer. The morphology of the graft copolymer is such that the propylene polymer material is the continuous phase or matrix, and the polymerized monomers, both grafted and ungrafted are a dispersed phase. The treatment of the polymer with the initiator and with the graft monomer is carried out in a substantially non-oxidizing atmosphere, just like the next steps of the process. The expression "substantially non-oxidizing", when using and describing the environment or atmosphere to which the propylene polymer material is exposed, as it means an environment in which the concentration of active oxygen, ie the concentration of oxygen in a The form that reacts with free radicals in the polymeric material is less than about 15 ° or preferably less than about 5O and more preferably less than about 1% by volume The most preferred active oxygen concentration is 0.004% or less in volume. Within these limits, the non-oxidizing atmosphere can be any gas or gas mixture, i.e., oxidatively inert to the free radicals of the olefin polymer material for example inert gases such as nitrogen, argon, helium and carbon dioxide. contact copolymers of the propylene polymer material with a free radical polymerization initiator such as Such as an organic peroxide or a vinyl monomer is described in more detail in U.S. Patent No. 5,140,074, the preparation of which is incorporated herein by reference. In the process of this invention, the treatment of the propylene polymer material with the initiator of free radical polymerization and the vinyl monomer is carried out in the presence of a continuous feed of nitric oxide and an inert gas, which is added as A separate "feed stream to reduce reactor contamination." Better results were obtained when about 0.05 parts to about 50 parts, preferably about 0.1 parts to about 10 pair Les and more preferably about 0.2 parts to about 2 parts. Nitric oxide parts per million parts of the inert gas that was used Any gas or gas mixture, which is oxidatively inert towards free radicals in the propylene polymer material can be used, for example, nitrogen, argon, helium and dioxide The use of gaseous nitric oxide in the continuous fragmentation reaction does not produce a significant decrease in the Reactor Amination: The use of nitric oxide as a 'gaseous phase free radical scavenger useful for local protection of polymer deposition in the type of polymerization such as heaters, rupture discs and ventilation ducts, and will therefore increase greatly the operability and productivity of a commercial plant. The porosity of the propylene homopolymer used homopolymer main chain in the manufacture of the graft copolymers in the examples as described in Winslow, N.M. and Shapiro, J.J., * An Instrument for the Measurement of Pore-Size Distribution by Mercury Penetration, "ASTM Bull., TP 49, 39-44 (Feb. 1959), and Rootare, H.M., 'A Revie of Mercury Porosi etry,"? 5-r57 (In Hirshho, J.S., and Roll, K.H., Eds. Advanced Experimental Techniques in Powder Metallurgy, Plenum Press, New York, 1970). In this specification all parts and percentages are by weight unless otherwise specified.

Examples 1-4; Comparative Examples 1-5 These examples describe the contaminant effect of using continuous nitric oxide feed during a graft polymerization reaction of a reactor, compared to the discontinuous addition of nitric oxide or without nitric oxide at all. The graft copolymer was made of a propylene homopolymer as the main chain polymer, for which polystyrene was grafted. In this and the following examples, the homopolymer or propylene used as the main chain of the graft copolymer had the following properties: spherical shape, flow rate of (VFF) of 9 g / 10 min (ASTD D-1238 ° C, 2.16 kg) , a porosity of 0.46 cmJ / g, and weighted average molecular weight. { w) of 170,000. The styrene monomer was grafted onto the polypropylene backbone at a grafting temperature of 110 ° C using the peroxide graft polymerization process previously described, where the initiator and monomers are sprayed on particles of. polypropylene that have been heated to the reaction temperature in a one liter glass reactor for gas mixing. Seventy weight parts of styrene were added per hundred parts by weight of polypropylene. Lupersol PMS 50'-t-butylperoxy-2-ethyl hexanoate in mineral spirits commercially available from El Atochem, was used as initiator peroxide. The graft monomer was fed at a rate of 1 ppc / min, and a molar ratio of monomer to initiator used of 105. To quantify the degree of contamination of the reactor, it is tested in an in-line filter basket containing 10 g of spheres of propylene homopolymer, was placed in the recirculating gas stream. The percentage of inciement by weight of the test coupon during the reaction was an indicator of the contamination existing in the reactor. The greater the increase in weight, the greater contamination occurred in the reactor. Nitric oxide (NO) in nitrogen was -introduced by a separately fed stream and the amount of NO was expressed as parts per billion parts of nitrogen in Table 1. The temperature of the coupon for testing, the & of weight increase of the coupon, and the% conversion of monomer to polymer that is shown in the table. The term "filler gas" in comparative examples 4 and 5 refers to the feed of nitric oxide gas that was added only at the beginning of the reaction through a supply gas line. In Comparative Examples 1-3, NO was not added during the reaction. In Comparative Examples 4-5, the system was purged with NO in N and the NO flow was cut off at the beginning of the reaction, then the system pressure was increased with the addition of the monomer. In example 1, the temperature of the coupon was maintained at 97 ° C, while in example 2 the temperature of the coupon was maintained at 110 ° C, which was the reaction temperature. In Example 3 the flow rate of NO in nitrogen was 0.2 standard liters (LE) per minute. In Example 4, the flow velocity was increased to 0.4 LE / in, while the same concentration of NO continued.

The data show that there is significantly lower-coupon weight increase, which indicates that there is less contamination in the reactor, when a continuous NO feed is used during the reaction (2.5 and 2.9 or vs. 35.4? -43. ), While the conversion of monomer to polymer is comparable to that of the comparative examples. The examples and comparative examples show increased contamination with temperature. Examples 1.4 show that: pollution decreases when the concentration of NO increases. Although the increase in weight continued approximately equal when the flow rate was increased from 0.2 to 0.4 LE / in with the same concentration of NO, and the conversion of monomer to polymer decreased slightly at high flow rate. - - - Examples 5-7: Comparative Examples 6-7 The examples describe the effect of reactor contamination when using a continuous feed of nitric oxide during a graft polymerization reaction compared to the non-use of nitric oxide. A larger reactor than that of example 1 was used. The nitric oxide in "nitrogen was added in a separate feed stream and the amount of NO is expressed as parts per million nitrogen in table 2. The graft polymer was made to from a homopolymer propylene as the polymer of the main chain to which polyethylene was grafted The graft copolymer was prepared as described in example 1, except that a 2 gallon metal reactor was used to mix the gas, 45 parts of styrene per 100 parts of polypropylene were added, and the polymerization temperature was 120 ° C. The styrene feed rate, the ppm of NO added to the system: the percent increase in weight of the test coupon; the M ", the numerical average molecular weight (Mn) and the molecular weight distribution (MWD: Mw / Mn) of the polyethylene was grafted; graft efficiency and percent conversion of monomer to polymer for each experiment is shown in table 2. Molecular weight measurements were made by gel permeation chromatography.

The data shows that the percent increase in weight of the test coupon decreased significantly to 8.6 to -12.3 °, depending on the concentration of NO, compared to 27.2 to 36.0 ° without NO. The amount of contamination decreased when the amount of NO added was increased. The continuous NO feed did not significantly change the molecular weight or MWD of the polymerized monomer styrene indicating that NO does not act as an agent for transferring chains.

EXAMPLE 8 AND COMPARATIVE EXAMPLE 8 These examples describe the effect of contamination by a continuous feed of nitric oxide during the Δt-L v ^ -A- .imerization per inj erte n compared to the non-use of nitric oxide. The nitric oxide in nitrogen was added in a separate feed stream and the amount of NO is expressed as parts per million per parts of nitrogen in Table 3. The graft copolymer was prepared from a polypropylene homopolymer with the main chain polymer at which was grafted a copolymer of methyl methacrylate and methyl acrylate. The graft copolymer was prepared as described in example 1, except that 43.05 parts of methyl methacrylate and 1.95 parts of methyl acrylate were added per 100 parts of polypropylene, the grafting temperature was 115 ° C, and the molar ratio monomer / initiator was 120. A metallic reactor for two gallon gas mixture was used. The 'conversion of monomer to polymer, the? of increase in weight of the test coupon, the amount of poly (methyl methacrylate) (PMMA) in the product and the amount of PMMA in the test coupon is given in table 3.

The results show a significant decrease in the weight gain of the test coupon when the reaction was carried out in the presence of a continuous NO feed. Other features, advantages and embodiments of the invention described herein will be readily apparent to those who exercise ordinary skills after reading the above descriptions. In this regard while specific embodiments of the invention have been described in considerable detail as variations or modifications of these embodiments can be made without departing from the spirit and scope of the invention as described and claimed.

Claims (6)

REIVI DICACIONEí

1. A process for preparing a graft copolymer, in a substantially non-oxidizing environment comprising: (a) treating the polymer or propylene material with an organic compound that is a free radical polymerization initiator; (b) treating the propylene polymer material for a period of time that coincides with,? after (a;), overlapped or not, about 5 to about 240 parts of at least one graft monomer capable of being polymerized by free radicals per 100 parts of the propylene polymer material, and (c) removing any unreacted graft monomer from the material polymer grafted with resulting propylene, "decomposing any unreacted initiator and ~ deactivating any free radical residue in the material, where (a) and (b) are carried out in the presence of nitric oxide which is added to an inert gas in an amount of about 0.05 parts to about 50 parts of nitric oxide per million parts of the inert gas to reduce contamination in the reactor.

2. The process of claim I, in dwi. The polypropylene polymer material is selected from the group consisting of: (a) a crystalline propylene homopolymer having an isotactic index greater than 80, (b) a. crystalline copolymer of propylene and an olefin selected from the group consisting of ethylene and α-olefin of C4-CLÜ, provided that the olefin is ethylene, the maximum content of polymerized ethylene is 10o by weight, and when the olefin is a -olefin of C4-Cj.o, the maximum polymerized content thereof is 20 or by weight, and the copolymer has an isotactic index greater than 85; (c) a crystalline crystalline terpolymer of propylene and two olefins selected from the group consisting of ethylene and α-olefin of C4-Ca, provided that the maximum content of polymerized C4-Cs α-olefin is 20% by weight, and , when ethylene is one of the olefins, the maximum content of polymerized ethylene is 5 'by weight, the terpolymer having an isotactic index greater than 85; (d) an olefin polymer composition comprising: (i) about 10 to 60 parts per. weight, of a crystalline homopolymer having an isotactic index greater than 80, or a copolymer selected from the group consisting of (a) propylene and ethylene, (b) propylene, ethylene and an α-olefin of C4-Ce, and (c) ) propylene and an α-olefin of C-C6, the copolymer has a propylene content of more than 8. e weight, and an isotactic index greater than 85; (ii) about 5 parts up to about 25 parts by weight, of an ethylene-propylene copolymer or a C-Cß α-olefin, which is insoluble in xylene at room temperature, and (i i) about 30 parts to near 70 parts by weight, of an elastomeric copolymer "selected from the group consisting of (a) ethylene and propylene, (b) ethylene, propylene, and a C4-CQ α-olefin, and (c) ethylene and an a- C-Cd olefin, the copolymer optionally contains about 0.5 '? up to about 10% of a diene, and containing less than 70%, of ethylene and being soluble in xylene at room temperature and has an intrinsic viscosity of about 1.5 to about 4.0 dl / g; the total of (ii) and (iii), based on the total composition of the olefin polymer being from 50 'to about 90 °, and the weight reaction of (ii) / (iii) being less than 0.4, where the composition is prepared by polymerization in at least two stages and has a flexural modulus less than ISOMPa; and (e) an opal thermo olefin comprising: (i) about 10% to about 60'O of a propylene homopolymer having an isotactic index greater than 80, or a crystalline copolymer selected from the group consisting of (a) ethylene and prepiiene,) ethylene ^ e, propylene, and a C4-C6 α-olefin, and (c) ethylene and a C4-C α-olefin, the copolymer having a propylene content greater than 85'0 and an isotactic index greater than 85; (ii) about 20O to about 60 o, of an amorphous copolymer selected from the group consisting of (a) ethylene and propylene, (b) ethylene, propylene, and an α-olefin of C4-Ce, and (c) ethylene and an α-olefin of C, -C ?, the copolymer optionally contains about 0.5 to about 10O of a diene, and contains less than 70o of ethylene and being soluble in xylene at room temperature, and (iii) about 3. 'Up to about 40, of an ethylene-propylene copolymer or a CC-α-olefin, which is soluble in xylene at room temperature, - wherein the composition has a flexural modulus greater than 150 but less than 1200 MPa

3. The process according to claim 2, wherein the polymer material is propylene hompolymer

4. The process according to claim 1, wherein the graft monomer is selected from the group consisting of vinyl-substituted heterocyclic and alicyclic aromatic compounds; unsaturated and derivatives d e the same, unsaturated aliphatic natrils; vinyl esters of saturated carboxylic acids and saturated carboxylic acids, and mixtures thereof.

5. The process according to claim 4, -, -r ~ -J - -. 1-graft monomer is selected from the group consisting of ethylene, esters of acrylic acid; esters of methacrylic acid and mixtures thereof.

6. The process according to claim 1, wherein the amount of nitric oxide used is from about 0.1 parts to about 10 parts per million parts of inert gas.