阅读说明：本技术 一种甲基丙烯酸甲酯聚合物及其制备方法 (Methyl methacrylate polymer and preparation method thereof ) 是由 刘波 刘铭 黄岐善 于 2019-10-10 设计创作，主要内容包括：本发明公开了一种甲基丙烯酸甲酯聚合物及其制备方法。本发明的甲基丙烯酸甲酯聚合物主要通过97-99.9质量份甲基丙烯酸甲酯与0.1-3质量份共聚单体进行连续本体聚合制备得到。通过选用两种具有不同分子结构的双官能度引发剂组成的复合引发体系,并控制这两种引发剂的比例,制备得到了一定分子量分布的聚合物。采用本发明的方法,可以在保持甲基丙烯酸甲酯聚合物耐热性及其它应用性能基本不变的条件下改善了树脂的加工流动性。(The invention discloses a methyl methacrylate polymer and a preparation method thereof. The methyl methacrylate polymer is mainly prepared by continuous bulk polymerization of 97-99.9 parts by mass of methyl methacrylate and 0.1-3 parts by mass of comonomer. The polymer with a certain molecular weight distribution is prepared by selecting a composite initiation system consisting of two bifunctional initiators with different molecular structures and controlling the proportion of the two initiators. The method of the invention can improve the processing fluidity of the resin under the condition of keeping the heat resistance and other application properties of the methyl methacrylate polymer basically unchanged.)

1. A methyl methacrylate polymer, the polymer having the following properties:

1) the weight average molecular weight is 80000-150000g/mol and the polydispersity is 2.5-3.0;

2) the thermal deformation temperature of the load is not lower than 100 ℃, and the test standard is ISO 75;

3) the non-notch impact strength of the simply supported beam is not lower than 22KJ/m²Test standard ISO 179;

4) melt index not less than 3g/10min, test standard ISO 1133.

2. A process for preparing the methyl methacrylate polymer of claim 1, comprising the steps of:

(1) preparing materials: adding 97-99.9 parts by mass, preferably 98-99.5 parts by mass of methyl methacrylate into a batching tank; 0.1-3 parts by mass, preferably 0.5-2 parts by mass of comonomer, and mixing uniformly;

(2) polymerization: simultaneously adding the mixture obtained in the step (1), a composite initiator and a chain transfer agent into a first-stage reactor to perform first-stage polymerization reaction to prepare first-stage slurry; then adding the first-stage slurry into a second-stage reactor to perform second-stage polymerization reaction to prepare second-stage slurry;

(3) devolatilizing: feeding the two-stage slurry obtained in the step (2) into a devolatilization device, and removing unreacted monomers and other volatile matters; and forming the devolatilized material to obtain a product.

3. The method according to claim 2, characterized in that the composite initiator comprises a bifunctional initiator ATA having two different functionalities and a bifunctional initiator ATB having two identical functionalities.

4. The method according to claim 3, wherein the initiator ATA has the following formula:

wherein R is₁、R₂、R₃May be a linear, branched or cyclic alkyl or alkoxy group or an aromatic group having 1 to 15 carbon atoms; preferably 4 carbon atoms-10 linear, branched or cyclic alkyl or aromatic groups; more preferably a branched alkyl group or aromatic group having 4 to 10 carbon atoms;

the initiator ATB has the following structural formula:

M₁-O-O-M₂-O-O-M₃and/or

Wherein M is₁、M₂、M₃、P₁、P₂、P₃May be a linear, branched, cyclic alkyl group or alkyl ester having 1 to 15 carbon atoms, and preferably a linear, branched or cyclic alkyl group having 4 to 10 carbon atoms.

5. The method according to claim 4, wherein the initiator ATA has the following formula:

wherein R is₂、R₃May be a linear, branched or cyclic alkyl group having 1 to 15 carbon atoms, preferably a branched alkyl group having 4 to 10 carbon atoms; r₄May be a hydrogen atom or a linear or branched alkyl group having 1 to 10 carbon atoms, and is preferably a hydrogen atom;

the initiator ATB has the following structural formula:

N-O-O-M-O-O-N, and/or

M, N, P, Q is a linear, branched or cyclic alkyl group having 1 to 15 carbon atoms, preferably a linear, branched or cyclic alkyl group having 4 to 10 carbon atoms.

6. The method according to claim 4 or 5, wherein the initiator ATA structure has a half-life ratio of 5-10, preferably 6-8, for the functional group with high decomposition temperature to the functional group with low decomposition temperature at a polymerization temperature.

7. The method according to any of claims 4 to 6, wherein the initiator ATA, at the temperature of the first stage polymerization, has a half-life of 1 to 15min, preferably 2 to 10min, for the functional group having a low decomposition temperature.

8. A process according to any one of claims 3 to 7, characterised in that the mass ratio between initiator ATA and initiator ATB is between 1 and 4, preferably between 1.5 and 2.5.

9. The method according to any one of claims 2-8, wherein the temperature of the first-stage polymerization reaction is 100-160 ℃, preferably 120-140 ℃; the temperature of the two-stage polymerization reaction is 140-200 ℃, and preferably 160-190 ℃.

10. The method according to any one of claims 2 to 9, characterized in that the amount of the complex initiator added is 10 to 500ppm, preferably 50 to 200ppm, based on the sum of the masses of methyl methacrylate and comonomer.

Technical Field

The invention relates to a methyl methacrylate polymer and a preparation method thereof, in particular to a method for preparing a methyl methacrylate polymer with a certain molecular weight distribution by adopting a mode of combining bifunctional initiators with different structures, and further improving the processing fluidity of the polymer on the premise of basically not losing other application properties.

Background

A methyl methacrylate polymer, i.e., polymethyl methacrylate (PMMA), is a polymer obtained by copolymerizing methyl methacrylate as a main monomer with other monomers, and has many excellent properties such as high light transmittance, good weather resistance, surface hardness, dimensional stability, and good electrical insulation. Therefore, the light-emitting diode is widely applied to the fields of automobiles, displays, electronic appliances, lighting, billboards and the like.

For the application fields of automobiles, illumination and the like, the polymethyl methacrylate has higher requirement on heat resistance. At present, the general-purpose heat-resistant polymethyl methacrylate products mostly limit the comonomer methyl acrylate in a lower range (the proportion of the comonomer in general polymers is less than 2wt percent) so as to meet the requirements of heat resistance and other application properties (such as mechanical strength). For the general-purpose polymethyl methacrylate, the processing fluidity (the main index is the melt index) and the application properties (such as heat resistance and mechanical strength) are often contradictory. Further improvements in polymer processing flowability are limited by heat resistance and other application property requirements.

From the published patent, the improvement of the processing fluidity of the methyl methacrylate polymer under the premise of keeping the basic performance of the methyl methacrylate polymer unchanged is realized by controlling the molecular weight and the distribution range of the polymer, and the method comprises the following steps:

1) polymers with different molecular weights are compounded, and different molecular weights and distributions are realized by controlling the molecular weight ranges and compounding ratios of high molecular weight polymers and low molecular weight polymers. Relevant patent reports are as in JP20050007663, JP20040324968, JP19990028890, JP20110080699, EP19990309488, WO2015JP 67919. The main problems existing in the technical scheme are that two polymers with different molecular weights are required to be prepared respectively and then compounded, the process flow is long, and the operation is complex.

2) And adding a chain transfer agent into the reactor in the subsequent polymerization stage, so that the molecular weight of the polymer in the subsequent reaction stage is obviously lower than that in the previous reaction stage, and obtaining the polymer with a certain molecular weight distribution. Related patents such as CN201680041007.5, CN 201580033739.5. The technical scheme has certain problems in implementation, firstly, when the conversion rate of reaction liquid is higher, the viscosity is high, and the chain transfer agent is added to cause mixing problems; on the other hand, a large amount of mercaptan chain transfer agent is added later, so that the residual quantity after devolatilization is increased, and the processing smell of the polymer is influenced.

3) In the compounding stage, a small amount of bi/multi-functionality monomer is added into the monomer, and the molecular weight and distribution of the polymer can be regulated and controlled through the proportion of the bi/multi-functionality monomer. Such as patents cn201110380403.x and CN 201010504215.9. The technical scheme has the problems that cross-linked polymers can be generated after bi/multi-functionality monomers are added into a reaction system, the optical performance of the polymers is influenced, and the application of the polymers is limited.

Disclosure of Invention

The invention aims to provide a methyl methacrylate polymer and a preparation method thereof. The methyl methacrylate polymer with a certain molecular weight distribution is prepared by adopting a composite initiation system consisting of bifunctional initiators with different structures, and the processing fluidity of the polymer can be improved on the premise of basically not influencing the heat resistance and the mechanical strength.

In order to solve the technical problems, the invention provides the following technical scheme:

a methyl methacrylate polymer, the polymer having the following properties:

1) the weight average molecular weight is 80000-150000g/mol and the polydispersity is 2.5-3.0;

2) the thermal deformation temperature of the load is not lower than 100 ℃, and the test standard is ISO 75;

3) the non-notch impact strength of the simply supported beam is not lower than 22KJ/m²Test standard ISO 179;

4) melt index not less than 3g/10min, test standard ISO 1133.

To meet processing and application requirements, methyl methacrylate polymers require a suitable molecular weight. The weight average molecular weight of the polymer of the invention is in the range of 8-15 ten thousand. When the molecular weight is too high, melt fluidity is poor and processing is difficult. When the molecular weight of the polymer is too low, it is difficult to satisfy the requirements in terms of application properties.

Polydispersity is a parameter that reflects the molecular weight distribution of a polymer. The polydispersity of the polymer is controlled in a certain range, the matching of polymers with different molecular weights is realized, and the fluidity of the polymer can be changed to a certain degree. The invention controls the polydispersity within the range of 2.5-3.0, can still have the melt index not less than 3g/10min on the premise of keeping the thermal deformation temperature of the load not less than 100 ℃, and the heat resistance and the processing fluidity of the polymer are well balanced.

The invention provides a preparation method of a methyl methacrylate polymer, which comprises the following steps:

(1) preparing materials: adding 97-99.9 parts by mass, preferably 98-99.5 parts by mass of methyl methacrylate into a batching tank; 0.1-3 parts by mass, preferably 0.5-2 parts by mass of comonomer, and mixing uniformly;

(2) polymerization: simultaneously adding the mixture obtained in the step (1), a composite initiator and a chain transfer agent into a first-stage reactor to perform first-stage polymerization reaction to prepare first-stage slurry; then adding the first-stage slurry into a second-stage reactor to perform second-stage polymerization reaction to prepare second-stage slurry;

(3) devolatilizing: feeding the two-stage slurry obtained in the step (2) into a devolatilization device, and removing unreacted monomers and other volatile matters; and forming the devolatilized material to obtain a product.

The comonomer of the invention can be selected from alkyl methacrylate except methyl methacrylate, preferably C2-C8 alkyl methacrylate, and can be one or more of ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate and isooctyl methacrylate; or selected from alkyl acrylate, preferably C1-C8 alkyl acrylate, which can be one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, and isooctyl acrylate; or from aromatic vinyl monomers, which may be styrene.

In terms of improving the thermal stability of the polymer and the ease of volatile removal, the preferred comonomers of the present invention are one or more of C1-C8 alkyl acrylates and styrene, more preferably C1-C4 alkyl acrylates, and particularly preferably methyl acrylate.

The molecular weight of the polymer can be adjusted by a chain transfer agent, and the chain transfer agent can be selected from one or more of n-butylmercaptan, tert-butylmercaptan, n-octylmercaptan, isooctylthiol, n-dodecylmercaptan and tert-dodecylmercaptan, and is preferably n-octylmercaptan.

To obtain the weight average molecular weight range according to the invention, the amount of chain transfer agent added is 0.1% to 0.5%, preferably 0.2% to 0.35%, based on the sum of the masses of methyl methacrylate and comonomer.

The invention selects the composite initiator with a specific structure to obtain the polymer with molecular weight distribution different from that of the conventional methyl methacrylate polymer, thereby effectively solving the contradiction between processing fluidity and heat resistance/mechanical strength. In the present invention, the polydispersity of the polymer is preferably in the range of 2.5 to 3.0 in order to improve the processing fluidity of the polymer, and when the polydispersity exceeds this range, the effect of the present invention is not sufficiently exhibited. When the polydispersity is less than 2.5, the improvement of the polymer processing flowability is insufficient, and when the polydispersity exceeds 3.0, the loss of the mechanical properties of the polymer is large.

Furthermore, in order to prepare the polymer with specific polydispersity, the composite initiator is a composition of bifunctional initiators, and further a composition of two bifunctional initiators with different structures. The "functionality" refers to the number of functional groups contained in one initiator molecule that can decompose to generate radicals. By difunctional initiator is meant that the initiator molecule contains two functional groups that can generate free radicals. The composite initiator selected by the invention comprises a bifunctional initiator ATA with two different functional groups and a bifunctional initiator ATB with two same functional groups from the aspects of polymer molecular weight control and production process control.

The initiator ATA has the following structural formula:

wherein R is₁、R₂、R₃May be a linear, branched or cyclic alkyl group or alkoxy group having 1 to 15 carbon atoms or an aromatic group; preferably a linear, branched or cyclic alkyl group or aromatic group having 4 to 10 carbon atoms; more preferably a branched alkyl group or aromatic group having 4 to 10 carbon atoms.

The initiator ATA of the present invention can decompose stepwise at the polymerization temperature. First, functional groups with low decomposition temperatures decompose to generate free radicals, which can initiate the reaction of monomers to give polymers of a certain molecular weight. After the polymerization reaction temperature is increased, the functional group with high decomposition temperature at the tail end of the polymer molecule starts to decompose again to generate free radicals, so that the growth of the polymer chain is further promoted, and the molecular weight of the polymer is obviously increased.

The initiator ATB has the following structural formula:

wherein M is₁、M₂、M₃、P₁、P₂、P₃May be a linear, branched, cyclic alkyl group or alkyl ester having 1 to 15 carbon atoms, and preferably a linear, branched or cyclic alkyl group having 4 to 10 carbon atoms.

The initiator ATB has two functional groups with different decomposition temperatures, and can decompose synchronously at polymer temperature to produce composition of diradical and single free radical, and initiate monomer polymerization to obtain polymer with different molecular weight.

In order to achieve the effects of the present invention better, it is preferable for the initiator ATA to have the following molecular structure:

wherein R is₂、R₃May be a linear, branched or cyclic alkyl group having 1 to 15 carbon atoms, preferably a branched alkyl group having 4 to 10 carbon atoms; r₄May be a hydrogen atom or a linear or branched alkyl group having 1 to 10 carbon atoms, and is preferably a hydrogen atom.

For the initiator ATB, it is preferable that the initiator has a symmetrical structure in the molecule, and further preferable is a formula as follows:

m, N, P, Q is a linear, branched or cyclic alkyl group having 1 to 15 carbon atoms, preferably a linear, branched or cyclic alkyl group having 4 to 10 carbon atoms. Alternative initiators ATB include, but are not limited to, one or more of 2, 2-di (t-butylperoxy) butane, 1-di-t-butylperoxy cyclohexane, 1-di-t-butylperoxy-3, 3, 5-trimethylcyclohexane.

For the initiator ATA, the reactivity of two different functional groups on its molecule needs to be particularly limited. In order to achieve the effects of the present invention, it is required that the half-life HP/LP ratio of the functional group (LP) having a low decomposition temperature and the functional group (HP) having a high decomposition temperature in the molecular structure is 5 to 10, preferably 6 to 8, at a certain polymerization temperature. When the half-life ratio is not in this range, the polydispersity of the polymer is difficult to control within the claimed range. With a half-life ratio in this range, the two functional groups on the initiator molecule can be decomposed stepwise. First, the LP functionality decomposes to produce free radicals that initiate polymerization to form polymers of a certain molecular weight. In the second polymerization stage, the polymer containing HP functional groups at the molecular chain ends can be decomposed continuously to generate free radicals, and further chain growth of the monomer is initiated to obtain a polymer with higher molecular weight. Polymers without HP at the end do not undergo further chain growth. The molecular weight and distribution of the polymer can be regulated and controlled by the proportion of the polymer containing the HP functional groups. When the half-life ratio of the two functional groups in the initiator molecule is not within this range or the two functional groups are the same, the stepwise polymerization is difficult to achieve or the effect is limited.

The half-life period of the functional group (LP) with low decomposition temperature of the initiator ATA in the invention at the temperature of one-stage polymerization reaction is 1-15min, preferably 2-10 min.

The initiator ATB has a half-life period of 1-15min, preferably 2-10min at the temperature of one-stage polymerization.

The amount of the composite initiator of the invention added is from 10 to 500ppm, preferably from 50 to 200ppm, based on the sum of the masses of methyl methacrylate and comonomer. When the initiator concentration is too low, the reaction rate is too slow, and the production efficiency is low. When the initiator concentration is too high, there is a problem that the polymerization reaction is too exothermic too quickly to remove heat, and on the other hand, the thermal stability of the polymethyl methacrylate is affected by a large amount of initiator fragments remaining in the polymer.

In the composite initiator, the mass ratio of the initiator ATA to the initiator ATB is in the range of 1-4, preferably 1.5-2.5. When the ratio of the two is out of this range, it is difficult to obtain a polymer having a desired molecular weight and molecular weight distribution, and it is difficult to achieve the effect of improving the processing fluidity of the present invention.

The reactor for preparing the methyl methacrylate polymer of the present invention may be a full mixed flow reactor, a plug flow reactor, or any combination thereof. Preferably a full mixed flow reactor, more preferably a stirred tank reactor with a jacket for temperature control. The reactor is provided with a supply port, a discharge port and a stirring device, and the stirring device preferably has mixing performance over the entire reaction zone. Besides the temperature control of the jacket, a flow guide pipe or a coil and the like can be arranged in the reactor, and the temperature is further controlled by the circulation of a heat carrier.

The temperature of the one-stage polymerization reaction is 100-160 ℃, and preferably 120-140 ℃.

The temperature of the two-stage polymerization reaction is 140-200 ℃, and preferably 160-190 ℃.

When the reaction temperature is lower than the lower limit for each stage of reaction, the viscosity of a reaction system is high, mass and heat transfer are influenced, and even the gel effect can occur to cause reaction runaway. When the reaction temperature is higher than the upper limit, the side reaction to produce methyl methacrylate dimer will be accelerated significantly, and the content of iso-isomers will be reduced, affecting the improvement of the heat resistance of the polymer.

The average residence time in the reactor is preferably from 0.5 to 4 h. The "average residence time" means the ratio of the amount of liquid in the reaction vessel to the feed rate of the reaction liquid. The average residence time mainly affects the conversion. The conversion is difficult to meet when the average residence time is too short. When the average residence time is too long, on the one hand, it is not economical to produce and, on the other hand, the amount of dimer produced increases. The mean residence time of the feed according to the invention in the reactor is more preferably from 0.5 to 3h, if appropriate in dependence on the conversion.

In the process according to the invention, the conversion at the outlet of the first reactor stage is from 35 to 55%, preferably from 40 to 50%.

In the process according to the invention, the conversion at the outlet of the secondary reactor is from 60 to 85%, preferably from 65 to 75%.

When the outlet conversion is too low, the production economy is not achieved. When the conversion rate at the outlet is too high, the viscosity of the materials in the kettle is too high, which is not beneficial to mass and heat transfer and is easy to cause gel effect. The conversion is regulated mainly by the initiator concentration, the residence time and the reaction temperature.

In the devolatilization stage, devolatilizers that may be used include, but are not limited to, flash tanks, falling bar devolatilizers, flight devolatilizers, or vented extruders, preferably vented extruders, and more preferably vented twin screw extruders.

In the devolatilization stage, the temperature in the devolatilization device is controlled at 220 ℃ and 280 ℃, and the temperature is preferably controlled by adopting a sectional temperature control and gradient temperature rise mode. Controlling the pressure in the devolatilization device to be 1-30 KPa. Preferably, two or more vacuum degrees are set, the former vacuum degree is lower to reduce foaming of the material, and the latter vacuum degree is higher to reduce resin residue.

In the devolatilization stage, the retention time of the materials in the devolatilization device is 5-15min, and when the retention time is too short, the volatile matters in the resin can not be removed fully. When the residence time is too long, the polymer is susceptible to thermal degradation resulting in cracking of the color. Unreacted monomers and impurities are removed in the devolatilizer. The monomer is fully condensed and recycled. And extruding and granulating the polymer to obtain finished particles.

According to the technical scheme of the invention, the added initiator basically cannot remain in the polymer after polymerization and devolatilization, and the purity and the application performance of the polymer cannot be influenced. In addition, compared with the method of adding a small amount of bi/multi-functionality monomers into the monomers in the burdening stage, the method of the invention can only produce linear polymers, can not form a cross-linking structure, and has little influence on the safety of polymerization reaction and the application performance of the polymers.

When the methyl methacrylate polymer is produced by the above-mentioned method, an auxiliary agent such as a mold release agent, an ultraviolet absorber, an antioxidant, a colorant and the like may be added as required, and the type and amount of these additives are well known to those skilled in the art.

The methyl methacrylate polymer prepared by the invention can be used in the application fields of display light guide plates, automobile tail lamps, lighting light guide plates, lenses, extruded bars, spectacle lenses and the like.

Drawings

FIG. 1 is an infrared spectrum of a peroxidation reaction product in the preparation process of ATA-1;

FIG. 2 is an infrared spectrum of a tert-butylation reaction product in the preparation of ATA-1;

FIG. 3 is an infrared spectrum of the acylation reaction product in the ATA-1 preparation process.

Detailed Description

Embodiments of the present invention will be further illustrated with reference to the following examples. The invention is not limited to the embodiments listed but also comprises any other known variations within the scope of the invention as claimed.