JPH07188454A - Expandable styrene polymer particle - Google Patents

Abstract

PURPOSE:To obtain a polymer particles which fuse well to each other on expansion molding and give a foamed molding with an excellent surface smoothness and a good appearance. CONSTITUTION:The wt.-average mol.wt. of the surface layer of this particle, which contains a volatile blowing agent, is made 3-30% higher than the wt. average mol.wt. of all the particles.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to expandable styrenic polymer particles. More specifically, the present invention relates to expandable styrenic polymer particles capable of obtaining a foamed molded product which does not adhere to the foamed particles during pre-expansion, has excellent foam moldability, and has a beautiful appearance.

[0002]

2. Description of the Related Art Expandable styrenic polymer particles are generally produced by suspending a styrenic monomer in water for polymerization and impregnating a foaming agent, or disclosed in JP-B-49-2994. As shown in the figure, styrene-based polymer particles are suspended in water, and styrene-based monomers are continuously or intermittently supplied to polymerize and polymerize, and a foaming agent is impregnated (seed polymerization method). Has been done.

The expandable styrenic polymer particles thus obtained are used as a raw material for producing a foamed molded product. Such a foamed molded product is obtained by temporarily foaming expandable styrenic polymer particles with steam or the like to form pre-expanded particles, filling the particles in a closed mold having a large number of small holes, and again heat-foaming with pressurized steam or the like. Then, the voids between the foamed particles are filled, and the foamed particles are fused to each other, then cooled and taken out from the mold.

However, conventionally, it was difficult to completely fill the voids existing between the pre-foamed particles during the in-mold foam molding, and it was difficult to obtain a foamed molded product having no voids between the foamed particles. Especially on the surface of the molded body that contacts the inner wall of the mold,
The pre-expanded particles may not be sufficiently filled, and usually a small amount of particle gaps will remain on the surface of the foamed molded product. Such a foam-molded product not only impairs the appearance but also causes a decrease in the strength of the molded product in some cases.

Therefore, in order to improve such problems, it has been proposed to add cyclohexane, a plasticizer, etc., which have a plasticizing and solvent effect, to the styrene polymer particles. However, since this plasticizer reduces the heat resistance of the styrene polymer particles, the foamed particles easily adhere to each other during the pre-foaming. Further, during in-mold foam molding, the mold is heated non-uniformly, or the heating conditions are only slightly changed, the resulting foam molded article has a particle gap, or the mutual fusion of particles is insufficient, Alternatively, there is a drawback that the surface of the molded body is melted.

[0006]

In order to solve the above drawbacks, in a method for producing expandable styrenic polymer particles by a seed polymerization method, a polymer having a weight average molecular weight obtained as a seed polymer particle is obtained. A method has been proposed in which one having a weight average molecular weight of 2/3 or less is used (JP-A-4-185616). According to this method, the expandable styrenic polymer particles obtained have a wide molecular weight distribution from low molecular weight to high molecular weight, and the above-mentioned problems are considerably solved. However, in this method, depending on the particle size of the desired expanded styrene polymer particles, since the usage rate of the seed polymer particles is different, the weight average molecular weight of the resulting polymer particles is not constant, As a result, there is a drawback in that it is necessary to change the impregnation prescription of the foaming agent and the foam molding conditions in correspondence with each other. Further, in this method, in order to obtain polymer particles having a wide molecular weight distribution, it is necessary to use polymer seed particles having a lower molecular weight than the weight average molecular weight of 200,000 or more suitable for ordinary foam molding (implementation). In the example, seed particles having a weight average molecular weight of 185,000 or less are used). However, the polymer particles having a lower molecular weight than the usual weight average molecular weight, when foam-molded,
Since the strength of the obtained molded article decreases, it cannot be used alone for ordinary foam molding. Therefore, in the above method, low molecular weight polymer particles have to be specially formulated to be used as the polymer seed particles, and the production efficiency is poor.

The present invention solves the above-mentioned conventional problems,
It is difficult for the expanded particles to adhere to each other during pre-expansion, while the expanded particles are well fused to each other during expansion molding, and the gaps between the particles are well filled in to obtain a foamed molded product with excellent smoothness and good appearance. The present invention provides expandable styrenic polymer particles.

[0008]

The expandable styrenic polymer particles of the present invention are the expandable styrenic polymer particles containing a volatile foaming agent, and the weight average molecular weight of the surface layer of the styrene-based polymer particles. Is 3 to 30% higher than the weight average molecular weight of the entire polymer particles.

That is, the feature of the present invention is that the internal weight average molecular weight which occupies the majority of the expandable styrenic polymer particles is within a normal range, and only the surface layer portion has a high molecular weight of 3 to 30%. Thus, during pre-expansion, it is difficult for the foamed particles to adhere to each other, while during foam molding, the foamed particles are well fused to each other, and the gaps between the particles are well filled to produce a foamed molded article having excellent smoothness and good appearance. To obtain expandable styrenic polymer particles.

In the case where the surface area of the polymer particles has a high molecular weight of less than 3% of the weight average molecular weight of the whole polymer particles,
It is not possible to obtain the effect of completely filling the gaps existing between the expanded particles during foam molding. On the other hand, when the surface layer has a high molecular weight of more than 30%, the thermal property becomes too strong as compared with the polymer inside the particles, and the foaming inside tends to be suppressed in the surface layer. As a result, the foaming performance is lowered, and a gap between particles tends to be left on the surface of the foamed molded product, which is not preferable.

In the present invention, the surface portion of the polymer particles means
Although the layer thickness from the surface of the polymer particles varies depending on the size of the polymer particles, it means the outer shell in the range of about 10% by weight from the surface of the polymer particles. The expandable styrene-based polymer particles in which the surface layer portion of the polymer particles of the present invention has a high molecular weight are styrene-based polymer particles (seed particles) dispersed in an aqueous medium, and styrene-based monomers are continuously added thereto. It can be obtained by a so-called seed polymerization method, in which the volatile blowing agent is impregnated by suspension polymerization in the presence of a polymerization initiator by intermittent or intermittent supply.
When the surface layer of the polymer particles is cross-linked using a cross-linking agent such as divinylbenzene or ethylene glycol dimethacrylate, the thermal properties of the particle surface layer become strong, but the gaps between the particles are sufficiently filled during foam molding. You can't get the effect of stretching out. Therefore, it is preferably produced by the above-mentioned seed polymerization method. The above-mentioned seed polymerization method is preferably used because of the problem.

The method for producing the expandable polystyrene polymer particles of the present invention by the seed polymerization method will be specifically described below. Examples of the styrene-based polymer seed particles used in the seed polymerization method include styrene homopolymers, copolymers of 50% by weight or more, preferably 80% or more of a styrene component and another polymerizable monomer. Used. Examples of the copolymerizable monomer include α-methylstyrene, acrylonitrile, an ester of acrylic or methacrylic acid and an alcohol having 1 to 8 carbon atoms, maleic anhydride, N-vinylcarbazole and the like.

If the particle size of the styrene-based polymer seed particles is within a certain narrow range, the resulting expandable styrene-based polymer particle size will be well aligned. Therefore, as the seed particles, polymer particles obtained by a suspension polymerization method are usually classified by sieving and adjusted so that the particle diameter is within a range of ± 20% of the average particle diameter. When obtained by a bulk polymerization method, pelletized to a desired particle size is used. Therefore, according to the seed polymerization method, the expandable styrenic polymer particles having a desired particle size range depending on the application can be produced at a yield of almost 100%. For example,
0.3-0.5 mm, 0.5-0.7 mm, 0.7-
1.2mm, 1.2-1.5mm, 1.5-2.5mm
The expandable styrenic polymer particles are obtained by being divided as follows.

The amount of the polymer seed particles used is 10 to 90% by weight, preferably 15 to 50% by weight, based on the total amount of the polymer at the end of the polymerization. Use amount of seed particles is 10% by weight
When the amount is less than the above, it becomes difficult to control the polymerization rate of the polymer particles within an appropriate range when supplying the styrene-based monomer, and the resulting polymer has a high molecular weight or generates a large amount of fine powdery polymer. It is industrially disadvantageous such as lowering manufacturing efficiency. If it exceeds 90% by weight, it is difficult to obtain excellent foam moldability.

As the styrene-based monomer, styrene and styrene derivatives such as α-methylstyrene and paramethylstyrene can be used alone or in combination. Further, difunctional monomers such as divinylbenzene and alkylene glycol dimethacrylate may be used in combination. Further, various monomers copolymerizable with styrene such as an ester of acrylic or methacrylic acid and an alcohol having 1 to 8 carbon atoms, acrylonitrile, and dimethyl fumarate can be used in combination.

As the above-mentioned polymerization initiator, a radical-generating type polymerization initiator generally used in suspension polymerization of styrene can be used. For example, benzoyl peroxide, lauryl peroxide, t-butyl peroxybenzoate, t-butyl. Peroxypivalate, t-butylperoxyisopropyl carbonate, t-butylperoxyacetate, 2,2-t-butylperoxybutane, t-butylperoxy 3,3,5 trimethylhexanoate, di-t- Examples thereof include organic peroxides such as butylperoxyhexahydroterephthalate and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These polymerization initiators may be used alone or in combination of two or more, but the decomposition temperature for obtaining a half-life of 10 hours is 50 in order to adjust the molecular weight and reduce the residual monomer. It is desirable to use together a polymerization initiator in the range of -80 ° C and a different polymerization initiator in which the decomposition temperature is in the range of 80-120 ° C.

These polymerization initiators are preferably added as a liquid because they need to be added during the polymerization or at the initial stage of the polymerization so that the polymer particles can uniformly absorb them. When the polymerization initiator is added directly to the aqueous suspension, it is difficult to be uniformly absorbed by the polymer particles, so the polymerization initiator is added in a state of being suspended or emulsified in an aqueous medium, or a small amount of It is desirable to dissolve in a styrene monomer, add an inorganic suspension stabilizer and an anionic surfactant, and add as an aqueous suspension.

As the suspension stabilizer used for dispersing the styrenic polymer particles in the aqueous medium, there are known polyvinyl alcohol, methyl cellulose, polyacrylamide and polyvinyl which have been generally used in suspension polymerization. Examples thereof include water-soluble polymers such as pyrrolidone and sparingly soluble inorganic compounds such as tricalcium phosphate and magnesium pyrophosphate. When using a sparingly soluble inorganic compound, an anionic surfactant such as sodium dodecylbenzene sulfonate is usually used together.

Examples of the above-mentioned volatile foaming agents have volatile properties such as propane, butane, pentane, cyclopentane, hexane having a boiling point not higher than the softening point of the polymer.
HCFC-141b, HCFC-142b, HCFC-
124, HFC-134a, HFC-152a, and the like. These foaming agents can be used alone or in combination of two or more kinds. The amount of easily volatile foaming agent used is
It is 1 to 10% by weight, preferably 2 to 7% by weight, based on 100 parts by weight of the polymer particles obtained. Further, in the seed polymerization method, the above-mentioned foaming agent is usually added by press-fitting after the polymerization or after the polymerization to impregnate the polymer particles.

In the above seed polymerization method, when the expandable styrenic polymer particles such as a solvent, a plasticizer, a foam cell nucleating agent, a filler, a flame retardant, a flame retardant aid, a lubricant and a coloring agent are produced. The additives used may be appropriately used if necessary. It is desirable to adjust the weight average molecular weight of the entire polymer particles to be adjusted within the range of 200,000 to 350,000, preferably 220000 to 300,000, which is suitable for ordinary foam molding. When the weight average molecular weight is less than 200,000, the strength of the foamed molded product is reduced, and when it is more than 350,000, the foaming performance is reduced. Also, as the polymer seed particles used in the seed polymerization method, it is preferable to use those whose weight average molecular weight is adjusted to a range suitable for the above foam molding.

In order to adjust the weight average molecular weight of the polymer particles to a range suitable for ordinary foam molding, it is important to make the polymerization initiator work efficiently, prevent unnecessary decomposition and generate radicals throughout the polymerization process. Therefore, it is necessary to adjust and control the distribution of the polymerization initiator, the polymerization temperature program, the feeding rate of the monomer, the polymerization rate during the polymerization and the like. In order for the polymerization initiator to work efficiently, it is important to diffuse the polymerization initiator not only at the surface layer portion of the polymer particles but also inside thereof during the polymerization. For that purpose, the polymer seed particles need to be appropriately softened with a styrene-based monomer, and the monomer content should be controlled so that the ratio of the monomer in the polymer particles does not exceed 35% by weight. It is effective to supply and to advance the reaction. When the proportion of the monomer is 10% by weight or less,
The polymerization initiator is wastefully consumed, and the resulting polymer has a high molecular weight, which is not preferable.

When the polymerization initiator is added in proportion to the amount of the monomer continuously supplied and the reaction is carried out at a constant temperature of 80 to 90 ° C., the polymerization initiator is scarce in the initial stage, and the polymerization progresses. Since it is accumulated and increased in the latter stage, the low molecular weight polymer is formed on the surface layer of the particle. When a low molecular weight polymer is formed in the surface layer of the particle as compared with the inside of the particle, the thermal properties of the surface layer of the expanded particle deteriorate, and the expanded particles are likely to coalesce with each other during pre-expansion, and foam molding is also performed. At times, the fusion of the expanded particles is hindered, and the expanded particles cannot be sufficiently filled. Furthermore, the surface of the foamed molded product is melted, the appearance of the molded product is deteriorated, and the strength of the foamed molded product is also reduced.

Specific examples of the method for increasing only the surface layer of the polymer particles to have a higher molecular weight than the average molecular weight of the polymer particles include the following methods. Ie 1
The polymerization initiator having a decomposition temperature of 50 to 80 ° C. for obtaining a half-life of 0 hours is set so as to almost disappear at the end of the supply of the styrene-based monomer, and the polymerization temperature is raised to a high temperature to obtain a surface layer of the polymer particles. The weight average molecular weight is increased. For example,
When performing the polymerization by adding the entire amount of the polymerization initiator first, set the polymerization initial temperature to a relatively low temperature so that the decomposition of the polymerization initiator works efficiently, and the polymerization radicals will be appropriately moderated when the monomer is supplied. It is effective to raise the temperature so as to generate a temperature gradient.

The expandable polystyrene-based polymer particles obtained in the above-mentioned manner in which the weight average molecular weight of the surface layer portion of the polymer particles of the present invention is 3 to 30% higher than the weight average molecular weight of the whole particles are the expanded particles at the time of pre-expansion. When the in-mold foam molding is performed without mutual adhesion of the foamed particles, the foamed particles are well fused to each other, the gaps between the particles are well filled, and a foamed molded article having excellent smoothness and good appearance is obtained. To be

[0025]

EXAMPLES Next, the present invention will be described more specifically by way of examples. However, the technical scope of the present invention is not limited to these examples. In the following examples, the surface condition of the foamed molded article depends on the degree of the gap between the particles,
It evaluated as follows.

1: Large with a gap, 2: Medium with a gap, 3: Small with a gap (currently ordinary commercial product), 4: Very small with a gap,
5: No gap The internal fusion bonding rate of the foamed molded product is the percentage of the surface where the foamed particles were broken when the foamed molded product was broken, in%. The weight average molecular weight of the polymer particles was measured by gel permeation chromatography (GPC) as follows. Measuring device: Toso Gel Permeation Chromatograph HLC-8020, Column: TSKgel GMH-XL-L 7.8 mm x
30 cm × 2, eluent: THF, flow rate: 1 ml / min, temperature: 40
° C, detection: RI.

The sampling of the surface layer of the particles for GPC measurement (in the range of about 10% by weight from the surface of the particles) was performed as follows.
First, the expandable styrene polymer particles obtained were expanded in saturated steam to a ratio of 80 times, and the surface layer of the expanded particles was peeled off with a razor blade into about 10% by weight of the particles in a thin skin sample. And GPC was measured with a solution of a sample collected from 20 to 30 particles.

Example 1 In a 5.6 l reactor, 1 part of pure water was added.
550 g, sodium dodecylbenzene sulfonate 0.7
g and 5 g of magnesium pyrophosphate were added, and the particle diameter was 0.
Polystyrene with 45 to 0.65 mm and a weight average molecular weight of 280000 (styrene is magnesium pyrophosphate,
In an aqueous medium using sodium dodecylbenzene sulfonate, 550 g of a product obtained by performing ordinary suspension polymerization) was added and stirred to suspend.

Then, in a previously prepared dispersion liquid of 280 g of pure water, 0.2 g of sodium dodecylbenzenesulfonate and 0.5 g of magnesium pyrophosphate, 4.5 g of benzoyl peroxide and 0.1 g of t-butylperoxybenzoate were added.
65 g was dissolved in 240 g of styrene and added, stirred with a homomixer to prepare a suspension, and this suspension was added to a reactor kept at 70 ° C.

After being kept for 1 hour so that the styrene and the polymerization initiator are absorbed in the polystyrene particles, styrene is continuously fed at a rate of 480 g / hr for 3 hours, and at the end of the styrene feeding, 105 ° C. The reactor was heated so that After heating to 120 ° C. and holding for 30 minutes, 40 g of cyclohexane was added to a solution of 120 g of pure water, 0.1 g of sodium dodecylbenzenesulfonate and 0.5 g of magnesium pyrophosphate, and stirred with a homomixer to react as a suspension. Butane 2 at 100 ℃
After press-fitting 10 g and holding for 2 hours, cool to normal
Expandable polystyrene particles having a particle diameter of 0.65 to 0.95 mm were obtained.

After washing, dehydrating and drying the expandable polystyrene particles, 2.2 g of zinc stearate, which is a commonly used surface treating agent, and 1.1 g of hydroxystearic acid triglyceride, are coated and steamed with a preliminary foaming machine. It was heat-expanded to obtain pre-expanded particles having a bulk ratio of 55 times. It was confirmed whether or not a coalesced mass of expanded particles was generated during the pre-expansion, but no coalescence was observed. Next, the pre-expanded beads were subjected to automatic foaming bead molding machine (manufactured by Sekisui Koki Mfg. Co., Ltd.) equipped with a mold having internal cavities of 300 × 400 × 100 mm.
Ace 3 type) was used for foam molding, and the obtained foam molded article was evaluated for surface condition (gap condition between particles), fusion degree between particles (internal fusion rate), and the like. The results are shown in Table 1.

Example 2 In a 5.6 l reactor, 1 part of pure water was added.
400 g, sodium dodecylbenzene sulfonate 0.7
g and 5 g of magnesium pyrophosphate were added, and the particle diameter was 0.
1100 g of polystyrene having a weight average molecular weight of 280000 and a size of 6 to 0.7 mm was added and stirred to suspend. Next, 400 g of pure water prepared in advance, 0.3 g of sodium dodecylbenzenesulfonate, and 1.5 g of magnesium pyrophosphate.
3 g of benzoyl peroxide and 0.4 g of t-butyl peroxybenzoate were added to styrene 530
It was dissolved in g and added, and stirred with a homomixer to prepare a suspension, and this suspension was added to a reactor kept at 76 ° C.

After being kept for 1 hour so that the styrene and the polymerization initiator are absorbed in the polystyrene particles, styrene is continuously fed at a rate of 620 g / hr for 1 hour, and at the end of the styrene feeding, 108 ° C. The reactor was heated so that After heating to 121 ° C. and holding for 15 minutes, 35 g of toluene is added to a solution of 100 g of pure water, 0.1 g of sodium dodecylbenzenesulfonate and 0.5 g of magnesium pyrophosphate, and stirred with a homomixer to react as a suspension. 145g of butane
After press-fitting and holding for 2 hours, it was cooled to room temperature to obtain expandable polystyrene particles having a particle diameter of 0.65 to 0.95 mm. Thereafter, the expandable polystyrene particles were pre-expanded in the same manner as in Example 1 and foam-molded to produce a foam-molded body. Table 1 shows the weight-average molecular weight of the particles, the degree of coalescence of the expanded particles during pre-expansion, the surface condition of the foamed molded product, and the measurement and evaluation results of the internal fusion rate.

Comparative Example 1 Pure water 1 was added to a 5.6 l reactor.
800 g, sodium dodecylbenzene sulfonate 0.7
g and 5 g of magnesium pyrophosphate were added, and the particle diameter was 0.
1300 g of polystyrene having a weight average molecular weight of 280000 and a weight average molecular weight of 6 to 0.7 mm was added and stirred to suspend. Next, 500 g of pure water prepared in advance, 0.4 g of sodium dodecylbenzene sulfonate, and 1.5 g of magnesium pyrophosphate.
3 g of benzoyl peroxide, 0.4 g of t-butylperoxybenzoate, and 32 g of toluene were dissolved in 530 g of styrene and added to the dispersion liquid of, and stirred with a homomixer to prepare a suspension liquid. Was added to the reactor held at.

After the styrene, toluene, and the polymerization initiator were held for a time until they were absorbed by the polystyrene, styrene was continuously fed at a rate of 730 g / hr for 30 minutes.
Next, 220 g of butane was press-fitted, the temperature was raised to 100 ° C., the temperature was maintained for 4 hours, the temperature was cooled to room temperature, and the particle size was 0.6
Expandable polystyrene particles of 0.9 mm were obtained. Thereafter, the expandable polystyrene particles were pre-expanded in the same manner as in Example 1 and foam-molded to produce a foam-molded body. Table 1 shows the weight-average molecular weight of the particles, the degree of coalescence of the expanded particles during pre-expansion, the surface condition of the foamed molded product, and the measurement and evaluation results of the internal fusion rate.

[Comparative Example 2] Pure water 1 was added to a 5.6 l reactor.
550 g, sodium dodecylbenzene sulfonate 0.7
g and 5 g of magnesium pyrophosphate were added, and the particle diameter was 0.
550 g of polystyrene having a weight average molecular weight of 280,000 and a weight of 45 to 0.65 mm was added and stirred to suspend.

Next, in a previously prepared dispersion liquid of 280 g of pure water, 0.2 g of sodium dodecylbenzenesulfonate and 0.5 g of magnesium pyrophosphate, 3.7 g of benzoyl peroxide and 0.6 g of t-butylperoxybenzoate.
5 g was dissolved in 240 g of styrene, added and stirred with a homomixer to prepare a suspension, and this suspension was added to a reactor kept at 72 ° C.

The polystyrene particles were held for 1 hour so that the styrene and the polymerization initiator were absorbed, and then styrene was fed at a rate of 360 g / hr for 4 hours, and the temperature was adjusted to 102 ° C. at the end of styrene feeding. The reactor was heated. After the temperature was raised to 120 ° C. and kept for 30 minutes, 40 g of cyclohexane was added to a solution of 120 g of pure water, 0.1 g of sodium dodecylbenzenesulfonate and 0.5 g of magnesium pyrophosphate, and stirred with a homomixer to form a suspension. Add to reactor and bring to 100 ° C butane 210g
After press-fitting and holding for 2 hours, it was cooled to room temperature to obtain expandable polystyrene particles having a particle diameter of 0.65 to 0.95 mm. Then, the obtained expandable polystyrene particles were used in Example 1
In the same manner as above, pre-foaming was performed and foam molding was carried out to produce a foam molded body. Table 1 shows the weight-average molecular weight of the particles, the degree of coalescence of the expanded particles during pre-expansion, the surface condition of the foamed molded product, and the measurement and evaluation results of the internal fusion rate.

[Comparative Example 3] The polystyrene particles used as seed particles in the seed polymerization method of Example 1 were sieved and classified to a particle size of 0.65 to 0.95 mm, and the same magnesium pyrophosphate and sodium dodecylbenzene sulfonate were used. According to Example 2, butane and toluene were impregnated using the aqueous medium prepared by using, to obtain expandable polystyrene particles.

The expandable polystyrene particles obtained were prefoamed in the same manner as in Example 1 and foam-molded to produce a foam-molded article. Table 1 shows the weight-average molecular weight of the particles, the degree of coalescence of the expanded particles during pre-expansion, the surface condition of the foamed molded product, and the measurement and evaluation results of the internal fusion rate.

[0041]

[Table 1]

[0042]

The expandable polystyrene polymer particles of the present invention, in which the weight average molecular weight of the surface layer of the particles is 3 to 30% higher than the weight average molecular weight of the entire particles, the foamed particles are coalesced with each other during pre-expansion. In addition, during foam molding, the foam particles are well fused to each other, the gaps between the particles are filled well, and a foam molded article having excellent smoothness and good appearance can be obtained. The expandable polystyrene polymer particles of the present invention are excellent in smoothness without melting the surface of the molded product, especially when molding a molded product foam molded product having a thin wall and a complicated shape. It is possible to obtain a foamed molded product having a unique appearance.

Claims (2)

[Claims] 1. In the expandable styrene polymer particles containing a volatile foaming agent, the weight average molecular weight of the surface layer of the styrene polymer particles is 3 to 30% higher than the weight average molecular weight of the entire polymer particles. Expandable styrenic polymer particles characterized by being contained. 2. The expandable styrenic polymer resin particles are obtained by suspending styrenic polymer particles in an aqueous medium, supplying a styrenic monomer thereto to polymerize, and impregnating a foaming agent. The expandable polystyrene polymer particles according to claim 1, which are obtained.