Photosensitive amphiphilic expansion microsphere and preparation method thereof

Abstract

The invention provides a photosensitive amphiphilic expanded microsphere and a preparation method thereof. The photosensitive amphiphilic expanded microsphere provided by the invention comprises a thermoplastic shell, alkane gas coated in the shell and an azide naphthoquinone group grafted on the surface of the shell. The photoisomerization reaction is utilized to enable the expanded microspheres to have the characteristics of photosensitivity and amphipathy, in the process of synthesizing the expanded microspheres, inorganic dispersants such as silicon dioxide, magnesium hydroxide and hydroxy calcium phosphate used in the synthesis of the expanded microspheres are not used, and the modifiability of the microspheres is improved; and the hydrophilic-oleophylic conversion of the microspheres can be realized by controlling the illumination time.

Description

Technical Field

[0001] The invention belongs to the field of polymer functional materials and relates to ultra-large thermal expansion microspheres and a preparation method thereof. Background Art

[0002] At present, people have prepared polymer microspheres with different functions according to usage conditions. The common form is solid polymer microspheres, such as PVC microspheres, polystyrene microspheres, PMMA solid microspheres, etc. The above microspheres can be used directly as raw materials, or they can be loaded and coated for functional modification. The preparation method of solid polymer microspheres is simple and has been widely used in various industries, such as printing, coatings, footwear, biomaterials, aerospace and other fields. In recent years, polymer hollow microspheres represented by expandable microspheres have become hot products. They are composed of a low-boiling point core material as the core and a thermoplastic polymer as the shell. When heated, they can expand and their density can be reduced to more than 1,000 times the original density. They are widely used in the research of lightweight technology.

[0003] Expanded microspheres are polymer plastic microspheres with a core-shell structure consisting of an airtight thermoplastic polymer shell and a hydrocarbon (C4-C12 alkane) core. At room temperature, hydrocarbons are restricted by the polymer shell and exist in the core in a two-phase coexistence state. When the microspheres are heated, the hydrocarbons vaporize and the pressure inside the microspheres increases. At the same time, when the polymer shell reaches its glass transition temperature (Tg), the shell becomes soft and ductile. When the internal pressure of the microspheres exceeds the yield strength of the polymer, the microspheres begin to foam. Since the mass remains unchanged and the volume increases sharply, the density drops significantly. Its foaming is controlled by factors such as the type and amount of hydrocarbons and the Tg of the polymer. After the microspheres are foamed, the thermoplastic shell changes from thick to thin, the volume increases by more than 80 times, the density decreases significantly, and most of the hydrocarbons escape from the core. At room temperature, the shell remains in the foamed state. Due to its thermal foaming and extremely low density after foaming, it is widely used as an excellent ultra-lightweight material as a lightweight filler in aerospace, high-speed rail, automotive and other industrial fields, coatings, insulation materials and sealing materials. The automotive industry uses ultra-lightweight materials in underbody coatings, tires, composite materials and adhesives.

[0004] Expandable microspheres have had many innovations in many fields, mainly used for lightweighting, and using the resilience of foamed microspheres to create some surface effects, but there are few studies on functional expandable microspheres. Functionalized microspheres can give expandable microspheres more possibilities, such as coating a layer of polyaniline on the surface of expandable microspheres, which has the function of conductive color change during printing; grafting glycidyl methacrylate on the surface of microspheres, so that the surface of microspheres has epoxy groups, and modification increases the functionality of the material surface. CN112430288A discloses a method for preparing expandable microspheres at normal pressure by visible light initiation, which is obtained by suspension polymerization reaction initiated by visible light; the expandable microspheres prepared by this method have the advantages of high expansion ratio, short polymerization time, high monomer conversion rate, low monomer residual rate, etc. It only replaces the initiator in different forms, and does not make the microspheres have functional characteristics.

[0005] Expanded microspheres can only exhibit uniphilic (lipophilic or hydrophilic) characteristics, which leads to problems in the selection of dispersion during use. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a photosensitive amphiphilic expanded microsphere and a preparation method thereof.

[0007] The characteristic of the present technology is that a kind of expandable microspheres with photosensitive groups are prepared. Under the action of light, the azide naphthoquinone groups in the microspheres will undergo obvious hydrophilic-hydrophobic changes before and after illumination, thereby realizing the change of the photosensitivity-amphiphilicity of the microspheres; in addition, since the substances with azide naphthoquinone groups cannot participate in suspension polymerization, the present invention uses a co-emulsification spheronization method to successfully prepare photosensitive-amphiphilic microspheres with expandable properties.

[0008] Traditional expanded microspheres need to be prepared by suspension polymerization, and monomers that are miscible with monomers such as acrylonitrile and methyl methacrylate must be selected for polymerization. Changes in the formula are often restricted by the monomers in the oil phase and the foaming agent. The functionalized structure of the functionalized microspheres is related to the surface structure of the microspheres. Therefore, it is difficult to achieve the functionalization of expanded microspheres by relying on traditional suspension polymerization.

[0009] On one hand, the present invention provides a photosensitive amphiphilic expandable microsphere, comprising a thermoplastic shell, an alkane gas encapsulated in the shell, and a azido naphthoquinone group grafted on the surface of the shell.

[0010] Furthermore, the thermoplastic shell includes an airtight monomer and an acrylic ester monomer.

[0011] Furthermore, the airtight monomer is one or more of acrylonitrile, methacrylonitrile, crotononitrile, fumaronitrile and vinylidene chloride, and the usage amount thereof is 20%-60%.

[0012] Furthermore, the acrylic acid ester monomer is one or more of methyl acrylate, acrylic acid, methacrylic acid, methyl methacrylate, butyl methacrylate, isopropyl methacrylate, vinyl acetate, and isobornyl methacrylate, and the usage amount thereof is 20%-60%.

[0013] Another aspect of the present invention provides a method for preparing photosensitive amphiphilic expandable microspheres, comprising the following steps:

[0014] (1) A copolymerization reaction is carried out with acrylonitrile, methyl methacrylate and hydroxypropyl methacrylate as main monomers to generate acrylonitrile copolymer resin AMH (AN-MMA-HPMA);

[0015] (2) The acrylonitrile copolymer resin AMH (AN-MMA-HPMA) is then reacted with sulfonyl chloride-naphthoquinone azide (S-DNQ) to generate the surface-grafted polymer resin AMHD (AN-MMA-HPMA-DNQ);

[0016] (3) AMHD was dissolved in DMF solution, and the photosensitive amphiphilic expanded microspheres hv-AMHD microspheres were prepared by a three-phase emulsification-salting-out process.

[0017] The principle of multi-stage emulsification spheronization

[0018] Salting out can make AMHD precipitate from water in solid form, but it cannot make it into spheres, so ethanol is added to increase phase separation. Since the foaming agent needs to be encapsulated inside the microspheres when the solid precipitates, Tween 60 dispersant is needed to help the foaming agent migrate inside the spheres, and finally form expanded microspheres. The Wolff rearrangement reaction makes it possible to prepare HV-AMHD microspheres.

[0019] Wolff rearrangement

[0020] The Walf rearrangement reaction refers to the nucleophilic rearrangement reaction of diazoketones to enones under the catalysis of silver oxide or light, and the ketocarbenes are generated in the rearrangement process. The enones generated by the Walf rearrangement reaction have high reactivity and can react with water, alcohol, ammonia, etc. to generate corresponding carboxylic acids or carboxylic acid derivatives.

[0021] The beneficial technical effects of the present invention are as follows:

[0022] The invention provides a photosensitive amphiphilic expandable microsphere and a preparation method thereof. The photoisomerization reaction is used to make the expandable microsphere have the characteristics of photosensitive-amphiphilicity. In the process of synthesizing the expandable microsphere, the use of inorganic dispersants such as silicon dioxide, magnesium hydroxide, calcium hydroxyphosphate, etc. used in the synthesis of the expandable microsphere is avoided, thereby improving the modifiability of the microsphere. The conversion of the microsphere between hydrophilicity and lipophilicity can be achieved by controlling the illumination time. The invention is a brand-new expandable microsphere synthesis technology. DETAILED DESCRIPTION

[0023] The present invention is further described below by way of examples. In the examples listed, unless otherwise stated, all parts and percentages in the examples are parts and percentages by weight.

[0024] The expanded microspheres prepared by the present invention are mainly tested for particle size, dispersibility, and foaming expansion. The particle size and dispersibility of the microsphere slurry and dry powder are tested by a laser particle size analyzer, and the expansion coefficient of the microspheres is tested by a thermomechanical analyzer (TMA).

[0025] (1) Particle size distribution characteristics analysis:

[0026] The particle size distribution of the microspheres was measured by a particle size distribution laser diffraction analyzer LS13320 produced by Bekman Coulter, and the average diameter was measured as the volume average particle size.

[0027] (2) Foaming characteristics analysis:

[0028] The characteristic of heat-expandable microsphere is measured by the thermomechanical analyzer TMA Q-400 produced by TA Instrument company.The 1.0mg heat-expandable microsphere prepared sample by the aluminum pan of diameter 6.7mm and depth 4.5mm.Then, the aluminum pan of diameter 6.5mm and depth 4.0mm is sealed.According to the TMA extended probe type, the sample temperature is increased to 280 ℃ from ambient temperature with the heating rate of 20 ℃ / min, and the power of 0.1N is applied by probe.Analysis is carried out by measuring the vertical displacement of probe.

[0029] - Expansion initial temperature (Tstart): The temperature at which the probe displacement starts to increase (°C);

[0030] - Maximum foaming temperature (Tmax): the temperature (°C) when the probe displacement reaches the maximum;

[0031] - Foaming density (Dmin): the ratio of the amount of microspheres added to the volume after foaming (kg / m 3 ).

[0032] Evaluation Method

[0033] Test methods and instruments:

[0034] (1) Measurement of contact angle using a contact angle analyzer

[0035] The change in the hydrophilicity and lipophilicity of the microspheres was verified by comparing the change in contact angle. If the contact angle is greater than 90, it is in a hydrophobic state, and if the contact angle is less than 90, it is in a hydrophilic state.

[0036] (2) Using TMA to test the foaming performance of microspheres

[0037] Place the asymmetric microspheres in a crucible and gradually heat them up at 2 degrees per minute. As the temperature rises, the microspheres will foam in the crucible, and a point Tstart will appear in the image. The probe on the top of the crucible will detect the change in height. As the temperature continues to rise, the microspheres reach the foaming peak and the first inflection point appears, which is recorded as Tmax.

[0038] (3) Use NMR to verify the characteristic group carboxyl (-COOH).

[0039] The addition amount of each component in Examples 1-4 and Comparative Examples 1-4 is recorded in Table 1, and the performance test results of the expandable microspheres prepared in Examples 1-3 and Comparative Examples 1-4 are also recorded in Table 1.

[0040] The preparation method of photosensitive amphiphilic expandable microspheres is as follows:

[0041] (1) Weigh 40-80 parts of acrylonitrile, 10-20 parts of methyl methacrylate, 20-30 parts of hydroxypropyl methacrylate, 0.1 parts of azobis(1-1-butylenenitrile), and 0.5 parts of divinylbenzene, and mix them to form an oil phase Omix; weigh 400 parts of deionized water, and then add 0.1-0.5 parts of polyvinyl alcohol, 0.05-0.1 parts of sodium lauryl sulfate, and 1-2 parts of nanocellulose to the water to form an aqueous phase Wmix; then emulsify the oil phase Omix and the aqueous phase Wmix under stirring in a homogenizer (500-10000 rpm) for 30 minutes, place them in a reactor at a constant temperature of 60 degrees for reaction for 36 hours, and after the reaction is completed; cool down to separate the solid and liquid, and then dry to obtain a white powder AMH.

[0042] (2) Weigh 20 parts of AMH powder, add 80 parts of DMF solution, stir in the dark until the powder is completely dissolved, then add 1 part of triethylamine, 0.01 parts of trimethylammonium hydrochloride, and 10 parts of sulfonyl chloride-naphthoquinone azide. After stirring at room temperature for 30 hours, a DMF solution of AMHD is obtained, which is kept for later use.

[0043] (3) Weigh 400 parts of 25% sodium chloride solution, then add 1 part of ethanol and 0.5 parts of Tween 60 as the continuous phase SM1; 10 parts of isooctane as OM1, and about 100 parts of AMHD solution as OM2; the sodium chloride solution, isooctane, and AMHD solution are passed through a multi-stage emulsification pump in a ratio of 40:1:10 and then enter a reactor containing a 400nm light source. After continuous irradiation for 10 hours, hv-AMHD microspheres are successfully prepared.

[0044] Table 1

[0045] The units of the components in the examples and comparative examples in Table 1 are in grams, wherein AN is acrylonitrile, MAN is methacrylonitrile, MMA is methyl methacrylate, DVB is divinylbenzene, AIBN is azobisisobutyronitrile, and S-DNQ is sulfonyl chloride-naphthoquinone azide.

[0046] The oil phase formula of Example 1 and Comparative Example 1 is exactly the same, the difference is whether or not light is irradiated. From the contact angle data, the contact angle of the microspheres of Example 1 is 95°, showing hydrophobic characteristics, while after the irradiation reaction of 400nm light, the contact angle of the microspheres of Example 2 is only 32°, showing obvious hydrophobic characteristics. In addition, by comparing the TMA data, it is found that the temperature of Tstart and Tmax of the microspheres of Example 2 are higher than that of the microspheres of Example 1, indicating that the microspheres have generated groups that improve the heat resistance of the microspheres. According to the synthesis experience of expandable microspheres, reference is made to the explanation of carboxyl (-COOH) in "Yasuhiro Kawaguchi, Yosuke Itamura, KenjiroOnimura, Tsutomu Oishi, Effects of the chemical structure on the heat resistance of thermoplastic expandable microspheres [J], Journal of Applied Polymer Science, 2005", indicating that under the action of light, the microspheres generate a carboxyl-containing structure.

[0047] The rules of Example 2 and Comparative Example 2 are the same as those of Examples 1 and 2, and will not be further described.

[0048] Compared with Comparative Example 3, Example 3 does not use HPMA containing hydroxyl (-OH) in the formulation, so the microspheres cannot be grafted with groups containing naphthoquinone azide, and therefore, even under light, they do not show amphiphilicity. Comparative Example 3 uses HPMA on the basis of Example 3, and the photosensitivity-amphiphilicity of the microspheres is confirmed.

[0049] After using 50% HPMA monomer in Example 4, photosensitive-amphiphilic microspheres were not successfully prepared, indicating that HPMA cannot be added to the expanded microspheres in a proportion of more than 50%, and the expandability of the microspheres requires a special combination of multiple monomers to prepare photosensitive-amphiphilic expanded microspheres; in Comparative Example 4, after using 25 parts of methyl methacrylate to replace part of the HPMA, the photosensitive-amphiphilic expanded microspheres were successfully prepared.

Claims

1. A photosensitive amphiphilic expandable microsphere, comprising a thermoplastic shell, an alkane gas encapsulated in the shell, and a azido naphthoquinone group grafted on the surface of the shell.

2. The expanded microsphere according to claim 1, characterized in that: The thermoplastic shell includes an airtight monomer and an acrylic ester monomer.

3. The expanded microspheres according to claim 1, characterized in that: The airtight monomer is one or more of acrylonitrile, methacrylonitrile, crotononitrile, fumaronitrile and vinylidene chloride, and the usage amount thereof is 20%-60%.

4. The expanded microspheres according to claim 1, characterized in that: The acrylic acid ester monomer is one or more of methyl acrylate, acrylic acid, methacrylic acid, methyl methacrylate, butyl methacrylate, isopropyl methacrylate, vinyl acetate, and isobornyl methacrylate, and the usage amount thereof is 20%-60%.

5. A method for preparing the expanded microspheres according to any one of claims 1 to 4, comprising the following steps: (1) A resin of acrylonitrile copolymer produced by copolymerization of acrylonitrile, methyl methacrylate and hydroxypropyl methacrylate as main monomers; (2) reacting the acrylonitrile copolymer resin with sulfonyl chloride-naphthoquinone azide to generate a surface-grafted polymer resin; (3) The polymer resin prepared in step (2) is dissolved in a DMF solution, and a three-phase emulsification-salting-out process is used to prepare photosensitive amphiphilic expanded microspheres.

Images