METHOD OF PREPARING GRAFT COPOLYMER AND GRAFT COPOLYMER PREPARED BY THE SAME

Abstract

Provided are a method of preparing a graft copolymer and a graft copolymer, the method including: batch-adding a first molecular weight controlling agent, a diene-based rubber polymer, an aromatic vinyl-based monomer, and a vinyl cyanide-based monomer to a reactor to initiate polymerization; and after the initiation of polymerization, continuously adding a second molecular weight controlling agent, an aromatic vinyl-based monomer, and a vinyl cyanide-based monomer to the reactor to perform polymerization, wherein the second molecular weight controlling agent includes an alkyl styrene-based dimer and a mercaptan-based compound in a weight ratio of 40.0:60.0 to 70.0:30.0, and a weight ratio of the first molecular weight controlling agent and the second molecular weight controlling agent is 5.0:95.0 to 25.0:75.0.

Claims

1. A method of preparing a graft copolymer, comprising: initiating polymerization including batch-adding a first molecular weight controlling agent, a diene-based rubber polymer, an aromatic vinyl-based monomer, and a vinyl cyanide-based monomer to a reactor to initiate the polymerization; and after the initiation of the polymerization, performing the polymerization including continuously adding a second molecular weight controlling agent, the aromatic vinyl-based monomer, and the vinyl cyanide-based monomer to the reactor to perform the polymerization, wherein the second molecular weight controlling agent includes an alkyl styrene-based dimer and a mercaptan-based compound in a weight ratio of from 40.0:60.0 to 70.0:30.0, and a weight ratio of the first molecular weight controlling agent and the second molecular weight controlling agent is from 5.0:95.0 to 25.0:75.0.

2. The method of claim 1, wherein the second molecular weight controlling agent includes the alkyl styrene-based dimer and the mercaptan-based compound in a weight ratio of from 41.0:59.0 to 65.0:35.0.

3. The method of claim 1, wherein the batch addition includes adding the first molecular weight controlling agent in an amount of from 0.01 to 0.15 parts by weight with respect to 100 parts by weight of a sum of the diene-based rubber polymer, the aromatic vinyl-based monomer, and the vinyl cyanide-based monomer.

4. The method of claim 1, wherein the continuous addition includes adding the second molecular weight controlling agent in an amount of from 0.20 to 0.70 parts by weight with respect to 100 parts by weight of a sum of the diene-based rubber polymer, the aromatic vinyl-based monomer, and the vinyl cyanide-based monomer.

5. The method of claim 1, wherein the first molecular weight controlling agent is an alkyl styrene-based dimer.

6. The method of claim 1, further comprising: initiating the continuous addition of the second molecular weight controlling agent when a polymerization conversion rate reaches 10% or less, and terminating the continuous addition of the second molecular weight controlling agent when a polymerization conversion rate reaches from 80 to 97%.

7. The method of claim 1, wherein a weight ratio of the aromatic vinyl-based monomer added in the initiation of the polymerization and the aromatic vinyl-based monomer added in the performance of the polymerization is from 10.0:90.0 to 35.0:65.0.

8. The method of claim 1, wherein a weight ratio of the vinyl cyanide-based monomer added in the initiation of the polymerization and the vinyl cyanide-based monomer added in the performance of the polymerization is from 10.0:90.0 to 35.0:65.0.

9. A graft copolymer comprising a diene-based rubber polymer, onto which an aromatic vinyl-based monomer unit and a vinyl cyanide-based monomer unit are grafted, and has a weight-average molecular weight of from 70,000 to 80,000 g/mol or less, a degree of grafting of from 32 to 40%, and a molecular weight distribution of 2.0 or less.

10. A thermoplastic resin composition comprising the graft copolymer according to claim 9.

11. The thermoplastic resin composition of claim 10, wherein the thermoplastic resin composition has a particle dispersity of 5 or less as calculated by following Equation 1:
Particle dispersity (Np)=(Average particle diameter of insoluble content in turbid liquid).sup.3/(Average particle diameter of diene-based rubber polymer).sup.3  [Equation 1] in the Equation 1, the average particle diameter of insoluble content in turbid liquid is a value measured by a light scattering method after the thermoplastic resin composition is dissolved in acetone, stirring is performed, and an insoluble content that has not been dissolved in acetone is centrifuged for sorting according to a size, and the average particle diameter of diene-based rubber polymer is a value determined by a dynamic light scattering method measuring the diene-based rubber polymer added in polymerization.

Description

EXAMPLE 1

[0077] <Graft Copolymer>

[0078] A first mixed solution containing 100.0 parts by weight of ion exchanged water, 58.0 parts by weight (based on solid content) of a butadiene rubber polymer latex (average particle diameter: 300 nm), 7.5 parts by weight of styrene, 2.5 parts by weight of acrylonitrile, 0.10 parts by weight of potassium oleate, 0.050 parts by weight of tetrabutyl hydroperoxide, 0.080 parts by weight of dextrose, 0.050 parts by weight of tetrasodium pyrophosphate, 0.001 parts by weight of ferrous sulfate (II), and a first molecular weight controlling agent in an amount shown in Table 1 below was prepared.

[0079] In addition, a second mixed solution containing 12.0 parts by weight of ion exchanged water, 24.0 parts by weight of styrene, 8.0 parts by weight of acrylonitrile, 0.20 parts by weight of potassium oleate, 0.10 parts by weight of tetrabutyl hydroperoxide, and a second molecular weight controlling agent in an amount shown in Table 1 below was prepared.

[0080] Additionally, a third mixed solution containing 0.040 parts by weight of dextrose, 0.030 parts by weight of tetrasodium pyrophosphate, and 0.0005 parts by weight of ferrous sulfate (II) was prepared.

[0081] The first mixed solution was batch-added to a nitrogen-filled polymerization reactor, and then polymerization was initiated at 50° C. The temperature of the polymerization reactor was raised to 70° C., and polymerization was performed for 2 hours while continuously adding the second mixed solution so that a polymerization conversion rate reached 92%. Subsequently, the third mixed solution was batch-added to the polymerization reactor, the temperature was raised to 80° C. for an hour, and polymerization was terminated to obtain a graft copolymer latex. 0.4 parts by weight of an antioxidant (OW500 commercially available from LATON) was added to the graft copolymer latex, and the resultant was coagulated with 2.0 parts by weight of sulfuric acid. Afterward, dehydration and drying with hot air were performed to prepare graft copolymer powder with a moisture content of less than 1 wt %.

[0082] <Preparation of Thermoplastic Resin Composition>

[0083] 30 parts by weight of the prepared graft copolymer powder and 70 parts by weight of a styrene/acrylonitrile non-grafted copolymer (92HR commercially available from LG Chem.) were homogeneously mixed to prepare a thermoplastic resin composition.

EXAMPLES 2 TO 7 AND COMPARATIVE EXAMPLES 1 TO 10

[0084] Graft polymer powder and thermoplastic resin compositions were prepared in the same manner as in Example 1, except that a first molecular weight controlling agent and a second molecular weight controlling agent were added in amounts shown in Tables 1 to 5 below.

EXPERIMENTAL EXAMPLE 1

[0085] The physical properties of the graft copolymer latex or powder according to Examples and Comparative Examples were measured by methods shown below, and results thereof are shown in Tables 1 to 5 below.

[0086] (1) Polymerization conversion rate (%): calculated by the following equation.

Polymerization conversion rate (%)={(Total weight of monomers added until polymerization is completed)−(Total weight of monomers unreacted until polymerization is completed)}/(Total weight of monomers added until polymerization is completed)×100

[0087] (2) Degree of grafting (%): calculated by the following Equation 1 after 1 g of the graft copolymer powder was dissolved in 50 ml of acetone while stirring for 24 hours, centrifugation was performed to separate a supernatant and a precipitate, the precipitate was dried in a hot air dryer set at 50° C. for 12 hours, and then the obtained dry solid was weighed:

Degree of grafting (%)={(Weight of copolymer of grafted monomer mixture.sup.1))/(Weight of diene-based rubber polymer.sup.2))}×100  [Equation 1]

[0088] 1) Weight of copolymer of grafted monomer mixture=(Weight of dry solid)−(Weight of diene-based rubber polymer)

[0089] 2) Weight of diene-based rubber polymer=Weight (based on solid content) of theoretically added diene-based rubber polymer or Weight of diene-based rubber polymer as measured by analyzing a first copolymer through infrared spectroscopy

[0090] (3) Weight-average molecular weight (g/mol): measured as a relative value with respect to a standard polystyrene (PS) sample by gel permeation chromatography (GPC) after the dry solid obtained by drying the supernatant as described in the measurement method of the degree of grafting was dissolved in a tetrahydrofuran (THF) solution and then filtered through a 1-μm filter.

[0091] (4) Molecular weight distribution: it means a ratio (Mw/Mn) of a weight-average molecular weight (Mw) to a number-average molecular weight (Mn). The number-average molecular weight of the graft copolymer was also measured as described in the measurement method of the weight-average molecular weight of the graft copolymer.

[0092] (5) Glass transition temperature (° C.): measured using a dynamic mechanical analyzer (DMA) after the graft copolymer powder was compressed using a press at 200° C.

EXPERIMENTAL EXAMPLE 2

[0093] The thermoplastic resin compositions according to Examples and Comparative Examples were extruded and injected to prepare samples, the physical properties of the samples were measured by methods shown below, and results thereof are shown in Tables 1 to 5 below.

[0094] (1) Particle dispersity (Np): calculated by the following equation.

[0095] Particle dispersity is an index that indicates the degree of dispersion of the graft copolymer in the non-grafted copolymer in the thermoplastic resin composition, and a lower value indicates better dispersity of the graft copolymer.

Particle dispersity (Np)=(Average particle diameter of insoluble content in turbid liquid).sup.3/(Average particle diameter of diene-based rubber polymer).sup.3

[0096] The average particle diameter of an insoluble content in a turbid liquid was measured by a light scattering method after 0.2 g of the sample was dissolved in 50 ml of acetone, slow stirring was performed for 20 hours, and an insoluble content that had not been dissolved in acetone was centrifuged using a particle size analyzer (UHR 18000 commercially available from CPS Instruments) for sorting according to size.

[0097] The average particle diameter of the diene-based rubber polymer was determined by measuring a diene-based rubber polymer added in polymerization using a Nicomp 380 instrument (manufactured by PSS) by a dynamic light scattering method.

[0098] (2) Melt flow index (g/10 min): measured in accordance with ASTM D1238 under conditions of 220° C. and 10 kg.

[0099] (3) IZOD impact strength (kg.Math.cm/cm, ¼ inch): measured in accordance with ASTM D265.

[0100] (4) Surface protrusion (number): Among protrusions present in 1 m.sup.2 of the sample, only protrusions with a size of 50 μm or more were counted.

TABLE-US-00001 TABLE 1 Classification Example 1 Example 2 Example 3 Example 4 First molecular AMSD 0.05 0.05 0.05 0.05 weight controlling agent Second molecular AMSD 0.14 0.15 0.35 0.45 weight TDDM 0.20 0.20 0.20 0.20 controlling agent AMSD:TDDM about about about about (weight ratio) 41.2:58.8 42.9:57.1 63.6:36.4 69.2:30.8 Weight ratio of first and second about about about about molecular weight controlling agents 12.8:87.2 12.5:87.5  8.3:91.7  7.1:92.9 Graft copolymer Polymerization 97.3 97.8 97.7 95.2 conversion rate Degree of grafting 39 38 37 33 Weight-average 78,000 77,000 75,000 73,000 molecular weight Molecular weight 1.6 1.5 1.5 1.7 distribution Glass transition −90 −90 −93 −95 temperature Thermoplastic Melt flow index 21 21 22 23 resin Particle dispersity 3.9 3.8 2.7 2.5 composition IZOD impact 32 33 33 31 strength Surface protrusion 1,350 1,300 1,100 1,000 AMSD: α-methyl styrene dimer TDDM: t-dodecyl mercaptan

TABLE-US-00002 TABLE 2 Classification Example 5 Example 6 Example 7 First molecular AMSD 0.10 0.10 0.04 weight controlling agent Second molecular AMSD 0.15 0.30 0.35 weight TDDM 0.20 0.20 0.40 controlling agent AMSD:TDDM about 60.0:40.0 about (weight ratio) 42.9:57.1 46.7:53.3 Weight ratio of first and second about about about molecular weight controlling agents 22.2:77.8 16.7:83.3  5.1:94.9 Graft copolymer Polymerization 97.7 97.6 97.2 conversion rate Degree of 37 36 32 grafting Weight-average 76,000 74,000 72,000 molecular weight Molecular weight 1.5 1.3 1.5 distribution Glass transition −91 −94 −93 temperature Thermoplastic Melt flow index 22 23 24 resin Particle 3.5 2.5 2.2 composition dispersity IZOD impact 33 33 32 strength Surface 1,200 1,000 1,000 protrusion AMSD: α-methyl styrene dimer TDDM: t-dodecyl mercaptan

TABLE-US-00003 TABLE 3 Comparative Comparative Comparative Comparative Classification Example 1 Example 2 Example 3 Example 4 First molecular AMSD 0 0 0 0 weight controlling agent Second molecular AMSD 0.40 0 0 0 weight TDDM 0.20 0.10 0.20 0.30 controlling agent AMSD:TDDM about — — — (weight ratio) 66.7:33.3 Weight ratio of first and second — — — — molecular weight controlling agents Graft copolymer Polymerization 97.7 98.2 97.8 97.5 conversion rate Degree of 38 48 40 35 grafting Weight-average 77,000 93,000 81,000 68,000 molecular weight Molecular 2.1 2.1 2.2 2.3 weight distribution Glass transition −90 −87 −87 −87 temperature Thermoplastic Melt flow index 21 17 20 21 resin Particle 10 37 18 16 composition dispersity IZOD impact 31 32 32 27 strength Surface 1,700 8,500 4,700 4,000 protrusion AMSD: α-methyl styrene dimer TDDM: t-dodecyl mercaptan

TABLE-US-00004 TABLE 4 Comparative Comparative Comparative Comparative Classification Example 5 Example 6 Example 7 Example 8 First molecular AMSD 0.05 0.05 0.03 0.03 weight controlling agent Second molecular AMSD 0.12 0.60 0.60 0.12 weight TDDM 0.20 0.20 0.45 0.40 controlling agent AMSD:TDDM 37.5:62.5 75.0:25.0 about about (weight ratio) 57.1:42.9 23.1:76.9 Weight ratio of first and second about about about about molecular weight controlling agents 13.5:86.5  5.9:94.1  2.8:97.2  5.5:94.5 Graft copolymer Polymerization 97.6 93.1 92.5 97.3 conversion rate Degree of 38 31 28 37 grafting Weight-average 81,000 72,000 65,000 79,000 molecular weight Molecular 2.2 1.8 1.8 2.2 weight distribution Glass transition −85 −87 −87 −84 temperature Thermoplastic Melt flow index 19 22 24 20 resin Particle 25 20 17 17 composition dispersity IZOD impact 30 27 22 29 strength Surface 6,200 5,000 4,300 4,200 protrusion AMSD: α-methyl styrene dimer IDDM: t-dodecyl mercaptan

TABLE-US-00005 TABLE 5 Comparative Comparative Classification Example 9 Example 10 First molecular AMSD 0.34 0.30 weight controlling agent Second molecular AMSD 0.20 0.40 weight TDDM 0.60 0.40 controlling agent AMSD:TDDM about 50.0:50.0 (weight ratio) 25.0:75.0 Weight ratio of first and second about about molecular weight controlling agents 29.8:70.2 27.3:72.7 Graft copolymer Polymerization 94.7 93.0 conversion rate Degree of 29 30 grafting Weight-average 67,000 68,000 molecular weight Molecular weight 2.0 2.0 distribution Glass transition −86 −87 temperature Thermoplastic Melt flow index 23 23 resin Particle 16 13 composition dispersity IZOD impact 23 24 strength Surface 4,200 4,500 protrusion AMSD: α-methyl styrene dimer TDDM: t-dodecyl mercaptan

[0101] Referring to Tables 1 to 5, the graft copolymers according to Examples 1 to 7, in which an α-methyl styrene dimer and t-dodecyl mercaptan were added in a weight ratio of 40.0:60.0 to 70.0:30.0 as a second molecular weight controlling agent, and a weight ratio of the first molecular weight controlling agent and the second molecular weight controlling agent was 5.0:95.0 to 25.0:75.0, exhibited a weight-average molecular weight of 73,000 to 78,000 g/mol, a degree of grafting of 32 to 39%, a molecular weight distribution of 1.7 or less, and a glass transition temperature of −90 to −95° C. The samples according to Examples 1 to 7, which were prepared using the graft copolymers having the above properties, exhibited excellent processability due to having an appropriate melt flow index and few surface protrusions due to having a low particle dispersity, and thus surface characteristics and impact resistance were also excellent.

[0102] However, the graft copolymer according to Comparative Example 1, in which a first molecular weight controlling agent was not added, exhibited a degree of grafting of 38%, a weight-average molecular weight of 77,000 g/mol, a molecular weight distribution of 2.1, and a glass transition temperature of −90° C. Since the graft copolymer according to Comparative Example 1 had a high molecular weight distribution, the sample prepared using the same exhibited many surface protrusions due to having a high particle dispersity, and thus surface characteristics were degraded.

[0103] In addition, the graft copolymers according to Comparative Examples 2 and 3, in which a first molecular weight controlling agent was not added, and an α-methyl styrene dimer was not added as a second molecular weight controlling agent, exhibited a high degree of grafting, a high weight-average molecular weight, a high molecular weight distribution, and a high glass transition temperature. Also, the samples according to Comparative Examples 2 and 3, which were prepared using the graft copolymers having the above properties, exhibited many surface protrusions due to having poor particle dispersity, and thus surface characteristics were degraded.

[0104] The graft copolymer according to Comparative Example 4, in which a first molecular weight controlling agent was not added, an α-methyl styrene dimer was not added as a second molecular weight controlling agent, and an excessive amount of t-dodecyl mercaptan was added, exhibited a low weight-average molecular weight, a high molecular weight distribution, and a high glass transition temperature. The sample prepared using the graft copolymer having the above properties exhibited many surface protrusions due to having poor particle dispersity, and thus surface characteristics were degraded. Also, impact resistance was degraded.

[0105] In addition, the graft copolymer according to Comparative Example 5, in which an α-methyl styrene dimer and t-dodecyl mercaptan were added in a weight ratio of 37.0:63.0 as a second molecular weight controlling agent, exhibited a high weight-average molecular weight, a high molecular weight distribution, and a high glass transition temperature. The sample prepared using the graft copolymer having the above properties exhibited many surface protrusions due to having poor particle dispersity, and thus surface characteristics were degraded.

[0106] The graft copolymer according to Comparative Example 6, in which an α-methyl styrene dimer and t-dodecyl mercaptan were added in a weight ratio of 75:25 as a second molecular weight controlling agent, exhibited a low degree of grafting and a low glass transition temperature. The sample prepared using the graft copolymer having the above properties exhibited many surface protrusions due to having poor particle dispersity, and thus surface characteristics were degraded. Also, impact resistance was degraded.

[0107] The graft copolymer according to Comparative Example 7, in which a weight ratio of the first and second molecular weight controlling agents was about 2.8:97.2, exhibited a low degree of grafting, a low weight-average molecular weight, and a high glass transition temperature. The sample prepared using the graft copolymer having the above properties exhibited many surface protrusions due to having poor particle dispersity, and thus surface characteristics were degraded. Also, impact resistance was degraded.

[0108] The graft copolymer according to Comparative Example 8, in which an α-methyl styrene dimer and t-dodecyl mercaptan were added in a weight ratio of about 23.1:76.9 as a second molecular weight controlling agent, exhibited a high weight-average molecular weight, a high molecular weight distribution, and a high glass transition temperature. The sample prepared using the graft copolymer having the above properties exhibited many surface protrusions due to having poor particle dispersity, and thus surface characteristics were degraded.

[0109] The graft copolymer according to Comparative Example 9, in which an α-methyl styrene dimer and t-dodecyl mercaptan were added in a weight ratio of about 25.0:75.0 as a second molecular weight controlling agent, and a weight ratio of the first and second molecular weight controlling agents was about 29.8:70.2, exhibited a low weight-average molecular weight and a high glass transition temperature. The sample prepared using the graft copolymer having the above properties exhibited many surface protrusions due to having poor particle dispersity, and thus surface characteristics were degraded. Also, impact resistance was degraded.

[0110] The graft copolymer according to Comparative Example 10, in which an α-methyl styrene dimer and t-dodecyl mercaptan were added in a weight ratio of 50.0:50.0 as a second molecular weight controlling agent, and a weight ratio of the first and second molecular weight controlling agents was about 27.3:72.7, exhibited a low weight-average molecular weight and a high glass transition temperature. The sample prepared using the graft copolymer having the above properties exhibited many surface protrusions due to having poor particle dispersity, and thus surface characteristics were degraded. Also, impact resistance was degraded.