Process for the preparation of polyurethane toughened vinyl resins

Abstract

The present application relates to the technical field of high polymer composition, and particularly relates to a preparation method of polyurethane toughened vinyl resin, which comprises the following steps: mixing polyurethane prepolymer, vinyl resin, a catalyst and a polymerization inhibitor to obtain an initial system, and stirring; detecting the light transmittance of the initial system, determining a phase separation starting point according to the light transmittance change rate value and the light transmittance change acceleration value, and obtaining a homogeneous system; determining polymerization parameters according to phase separation characteristic parameters; adjusting the homogeneous system to an initial polymerization temperature and an initial polymerization shear rate, and adding initiators in batches according to the number of times of adding initiators; after all the initiators are added, detecting the viscosity and temperature distribution of the homogeneous system to obtain a polymerization state index, and adjusting the polymerization temperature and the polymerization shear rate to obtain high-toughness vinyl resin. The present application overcomes the problems of network structure defects caused by the difficulty in accurately determining the phase separation point and the uncontrollable polymerization process in the preparation of polyurethane toughened vinyl resin.

Description

Technical Field

[0001] This invention relates to the field of polymer composition technology, and more particularly to a method for preparing a polyurethane toughened vinyl resin. Background Technology

[0002] Polyurethane-toughened vinyl ester resins have significant application value in the field of composite materials due to their excellent mechanical properties and chemical corrosion resistance. Traditional preparation methods typically involve directly blending polyurethane prepolymers with vinyl ester resins and then initiating polymerization. However, this process has significant drawbacks: First, the initiation point of polyurethane phase separation relies on manual judgment. Since the phase change process is influenced by multiple factors such as raw material ratios, temperature, and shear force, the empirical method struggles to accurately capture the critical timing of phase separation, leading to insufficient or excessive phase separation in the homogeneous system, affecting the subsequent construction of interpenetrating network structures. Second, the static process employing fixed temperature, constant shear rate, and a one-time addition of the initiator cannot adapt to the dramatic increase in system viscosity and localized temperature fluctuations caused by exothermic polymerization. This easily leads to runaway reactions and inhomogeneous molecular chain structures, resulting in defects such as insufficient toughness and internal stress concentration in the product.

[0003] Chinese Patent Publication No. CN102532930A discloses a modified vinyl resin, comprising: 1-10 parts of acrylic polyurethane; and 10-150 parts of epoxy vinyl ester resin. The acrylic polyurethane resin is polymerized from acrylate compounds and polyurethane; the polyurethane is polymerized from isocyanate and polyester polyol or polyether polyol. The vinyl resin provided by this invention uses acrylic polyurethane-modified vinyl resin. Because acrylic polyurethane not only possesses high elongation but also, due to the introduction of unsaturated double bonds that allow for crosslinking with vinyl esters, it improves the resin's elongation at break while largely retaining the high mechanical strength, corrosion resistance, and good weather resistance of vinyl ester resins. This overcomes the shortcomings of traditional vinyl resins.

[0004] Therefore, the modified vinyl resin has the following problems: the phase separation point is difficult to determine accurately in the preparation of polyurethane toughened vinyl resin, and the uncontrollable polymerization process can easily lead to network structure defects. Summary of the Invention

[0005] Therefore, the present invention provides a method for preparing polyurethane toughened vinyl resin to overcome the problems in the prior art of accurately determining the phase separation point and network structure defects caused by the uncontrollable polymerization process in the preparation of polyurethane toughened vinyl resin.

[0006] To achieve the above objectives, the present invention provides a method for preparing polyurethane toughened vinyl resin, comprising:

[0007] Step S1: The polyurethane prepolymer, vinyl resin, catalyst and polymerization inhibitor are added to the reactor and mixed to obtain the initial system, and stirred at the initial shear rate.

[0008] Step S2: During the stirring process, the transmittance of the initial system is monitored in real time until the polyurethane phase separation starting point is reached, thus obtaining a homogeneous system.

[0009] The polyurethane phase separation initiation point is determined based on the transmittance change rate and transmittance change acceleration.

[0010] Step S3: Determine polymerization parameters based on phase separation characteristic parameters, wherein the polymerization parameters include initial polymerization temperature, initial polymerization shear rate, and number of initiator additions, and the phase separation characteristic parameters are the transmittance and the transmittance change acceleration corresponding to the polyurethane phase separation initiation point;

[0011] Step S4: Adjust the temperature of the homogeneous system to the initial polymerization temperature, control the shear rate of the homogeneous system to the initial polymerization shear rate, and simultaneously add free radical initiator in stages according to the number of times the initiator is added, so as to carry out free polymerization by shear stirring;

[0012] Step S5: After all the free radical initiator is added, the viscosity and temperature distribution of the homogeneous system are detected. The current polymerization state index of the homogeneous system is determined based on the viscosity and temperature distribution. The polymerization temperature and polymerization shear rate are adjusted based on the phase separation characteristic parameters and the polymerization state index to obtain a high-toughness vinyl resin with an interpenetrating network structure.

[0013] Further, step S2 includes:

[0014] Step S21: Continuously acquire the transmittance data of the initial system at a preset sampling frequency;

[0015] Step S22: Calculate the transmittance change rate based on the transmittance difference between adjacent sampling time points;

[0016] Step S23: When the rate of change of transmittance is less than or equal to the first preset threshold for the first time, the acceleration monitoring window is activated, and the acceleration of the transmittance change is calculated based on the change of the rate of change of transmittance within the acceleration monitoring window.

[0017] Step S24: When the acceleration of the change in transmittance is greater than or equal to the second preset threshold, it is determined that the initial system has reached the phase separation start point, and the transmittance and the acceleration of the change in transmittance at the time when the initial system is determined to have reached the phase separation start point are recorded as phase separation characteristic parameters.

[0018] Furthermore, in step S24, the transmittance of the initial system when it reaches the phase separation initiation point is determined to be the minimum transmittance within the current acceleration monitoring window.

[0019] Further, step S3 includes:

[0020] Step S31: Determine the initial polymerization temperature based on the transmittance in the phase separation characteristic parameters;

[0021] Step S32: Determine the initial polymerization shear rate based on the transmittance change acceleration in the phase separation characteristic parameters;

[0022] Step S33: Determine the number of times the initiator is added based on the initial polymerization temperature and the initial polymerization shear rate.

[0023] Further, step S5 includes:

[0024] Step S51: After all the free radical initiators are added, the temperature data of multiple locations in the homogeneous system are acquired in real time, and the temperature uniformity index is determined based on the temperature distribution differences.

[0025] Step S52: Based on the viscosity change rate and the temperature uniformity index, the polymerization state index is obtained;

[0026] Step S53: Adjust the polymerization temperature and polymerization shear rate according to the polymerization state index and the phase separation characteristic parameters.

[0027] Further, in step S53, adjusting the polymerization temperature and polymerization shear rate includes:

[0028] If the polymerization state index is less than or equal to the first state threshold, then the polymerization temperature is increased and the polymerization shear rate is decreased.

[0029] If the polymerization state index is greater than or equal to the second state threshold, the polymerization temperature is reduced and the polymerization shear rate is increased, wherein the adjustment range of the polymerization temperature and the polymerization shear rate is determined according to the phase separation characteristic parameter.

[0030] Further, in step S1, the initial shear rate is determined based on the mass ratio of polyurethane prepolymer to vinyl resin.

[0031] Furthermore, in step S4, the number of times the initiator is added ranges from 3 to 10 times, and the time interval between each initiator addition is determined based on the acceleration of the transmittance change.

[0032] Furthermore, the time interval between each initiator addition is negatively correlated with the acceleration of the transmittance change.

[0033] Furthermore, the temperature distribution difference is determined based on multiple temperature sensors evenly distributed around the circumference of the reactor in which the homogeneous system is located. When the temperature difference between any two temperature sensors is greater than or equal to the set tolerance, the current polymerization temperature is maintained until the temperature difference falls back to the set tolerance.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention accurately determines the initiation point of polyurethane phase separation and records phase separation characteristic parameters (transmittance and transmittance change acceleration) by real-time monitoring of the dynamic changes in the transmittance of the mixed system. Based on these characteristic parameters, the initial polymerization temperature, shear rate and initiator addition sequence are dynamically set. During the polymerization process, the polymerization state index is calculated by combining the viscosity change rate and temperature distribution, and the process parameters are adjusted in real time in conjunction with the phase separation characteristic parameters. This achieves accurate capture of the phase separation initiation point and adaptive closed-loop control of the polymerization process, solving the network structure defects caused by the reliance on experience in determining the phase separation point and the uncontrollable polymerization process in traditional processes. It significantly improves the toughness and phase region uniformity of vinyl resin and forms a dense interpenetrating network structure.

[0035] Furthermore, this invention uses a dual-threshold determination mechanism of transmittance change rate and transmittance change acceleration to capture the phase separation initiation point in real time. When the transmittance change rate first exceeds the negative threshold, the acceleration monitoring window is triggered. When the transmittance change acceleration exceeds the positive threshold, the phase separation point is confirmed. This effectively eliminates misjudgments caused by temperature fluctuations and bubble interference, providing accurate initial state parameters of the phase structure for subsequent polymerization.

[0036] Furthermore, this invention dynamically sets the initial polymerization temperature based on the transmittance value at the phase separation initiation point: the high transmittance system is moderately heated to accelerate the reaction, while the low transmittance system is cooled to suppress phase region coarsening; at the same time, the initial shear rate is set according to the transmittance change acceleration value, and the high acceleration system increases shear to suppress phase region growth, ensuring that the polymerization conditions are strictly matched with the phase separation characteristics and avoiding network structure instability.

[0037] Furthermore, this invention determines the number of initiator additions based on the initial polymerization temperature and shear rate, and dynamically calculates the interval between each addition by using the acceleration value of the change in transmittance. In high-temperature systems, the number of additions is increased to disperse the heat of reaction, while in high-shear systems, the number of additions is reduced to protect the integrity of the phase region. In high-acceleration systems, the interval is shortened to quickly stabilize the phase structure, while in low-acceleration systems, the interval is extended to promote the orderly arrangement of the phase region, thereby achieving synchronous control of reaction rate and structural evolution.

[0038] Furthermore, in the later stages of polymerization, this invention calculates the polymerization state index using viscosity change rate and temperature uniformity index, and adjusts the temperature and shear rate in real time in conjunction with phase separation characteristic parameters: when the index is too low, the temperature is increased and the shear rate is decreased to enhance the reaction kinetics; when the index is too high, the temperature is decreased and the shear rate is increased to suppress reaction runaway, thus balancing the reaction exothermic and heat dissipation efficiency, eliminating local hot spots and unreacted monomer residues, and ensuring the uniform formation of the interpenetrating network. Attached Figure Description

[0039] Figure 1 This is a flowchart of the preparation method of the polyurethane toughened vinyl resin of the present invention;

[0040] Figure 2 This is a flowchart of step S2 in the preparation method of polyurethane toughened vinyl resin of the present invention;

[0041] Figure 3 This is a flowchart of step S3 in the preparation method of polyurethane toughened vinyl resin of the present invention;

[0042] Figure 4 This is a flowchart of step S5 in the preparation method of the polyurethane toughened vinyl resin of the present invention. Detailed Implementation

[0043] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0044] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0045] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0046] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0047] Please see Figure 1 As shown, it is a flowchart of the preparation method of the polyurethane toughened vinyl resin of the present invention;

[0048] This invention provides a method for preparing a polyurethane toughened vinyl resin, comprising:

[0049] Step S1: The polyurethane prepolymer, vinyl resin, catalyst and polymerization inhibitor are added to the reactor and mixed to obtain the initial system, and stirred at the initial shear rate.

[0050] Specifically, in step S1, the initial shear rate is determined based on the mass ratio of polyurethane prepolymer to vinyl resin.

[0051] In this embodiment of the invention, polyurethane prepolymer and vinyl resin are added to a reactor at a preset mass ratio, along with a catalyst and polymerization inhibitor. The mixture is then stirred at a low speed of 30 rpm for 10-30 seconds to form a uniformly colored initial system. The mixture is then stirred at the initial shear rate, with a stirring temperature of 70°C-80°C. In actual control, the stirring speed is adjusted using a frequency converter to control the stirring shear rate. The specific formula for calculating the initial shear rate is as follows:

[0052] ,

[0053] Where y is the initial shear rate, in seconds. -1 ; 'a' represents the shear strength coefficient, in units of s. -1 The value range is 80s. -1 ~120s -1 Preferably, a is 100s -1 ;m PU The mass of the polyurethane prepolymer is expressed in kilograms (kg); m VE y0 represents the mass of vinyl resin, in kilograms (kg); b is the rheological response index, dimensionless, ranging from 0.7 to 0.9, preferably 0.8; y0 is the basic shear rate, in seconds (s). -1 Preferably, 40s is taken. -1 .

[0054] The shear strength coefficient 'a' is calibrated by fitting the rheological curve, which will not be elaborated here; the rheological response index 'b' is a non-Newtonian fluid characteristic parameter calibrated by numerical simulation of the stirred flow field, which will not be elaborated here either.

[0055] It is understandable that the phase separation point is difficult to determine precisely during the preparation of polyurethane-toughened vinyl resin in this invention, and the polymerization process is uncontrollable. Therefore, the network structure of products prepared based on traditional fixed process parameters often has unpredictable structural defects. This invention directly determines the compatibility boundary between the two phases through the mass ratio of polyurethane prepolymer to vinyl resin, and the initial shear rate is the key kinetic lever driving the phase separation process. When the proportion of polyurethane increases, the thermodynamic compatibility between the two phases decreases, and the shear rate needs to be appropriately reduced to avoid premature phase separation. Conversely, when vinyl resin is dominant, the shear rate needs to be increased to accelerate the initiation of phase separation. The shear field directly controls the activation energy barrier of phase separation nucleation by affecting molecular chain orientation and diffusion rate. A higher shear rate can reduce the activation energy of phase separation, accelerate the rearrangement of molecular chain segments, and enable the system to reach the phase separation critical point more quickly, while a lower shear rate delays the phase separation process, allowing time for molecular-level mixing. This dynamic shearing strategy based on mass ratio avoids both premature phase separation leading to uneven dispersion and delayed phase separation causing reaction lag. Simultaneously, the compatibility of the polyurethane prepolymer and vinyl resin has a decisive influence on subsequent phase separation behavior, and the mass ratio directly determines the system's rheological properties. When the polyurethane proportion increases, the system viscosity exhibits a non-linear increase. A traditional fixed shear rate leads to two risks: insufficient shearing at low proportions easily causes uneven dispersion, while excessive shearing at high proportions easily induces prepolymer chain breakage. Therefore, dynamically adapting the shear rate according to the mass ratio ensures the formation of a molecularly uniform dispersion in the initial mixing stage, laying the foundation for subsequent phase separation monitoring and avoiding side reactions caused by improper mechanical energy input.

[0056] In this embodiment of the invention, the polyurethane prepolymer is obtained from polyether diol and diisocyanate, and the vinyl resin is obtained from epoxy resin and methacrylic acid. The polyether diol is at least one of polyoxypropylene diol PPG600, PPG1000, and PPG2000; the epoxy resin is at least one of E42, E44, E51, and E54; and the diisocyanate is at least one of toluene diisocyanate, diphenylmethane-4,4'-diisocyanate, 1,6-hexane diisocyanate, isophorone diisocyanate, and phenylmethylene diisocyanate.

[0057] In embodiments of the present invention, the polymerization inhibitor is one or more of hydroquinone, p-tert-butylcatechol, 2,6-di-tert-butyl-p-methylphenol, p-benzoquinone, p-hydroxysemibenzoquinone, and 2,3-dichloro-1,4-naphthoquinone, and the catalyst is one or more of benzyldimethylamine, benzyltrimethylammonium chloride, benzyltriethylammonium chloride, triphenylphosphine, and triphenylphosphine chloride.

[0058] In this embodiment of the invention, the free radical initiator is one of benzoyl peroxide, dicumyl peroxide, di(4-tert-butylcyclohexyl) peroxide dicarbonate, and azobisisobutyronitrile.

[0059] In one specific embodiment, the raw materials for the polyurethane toughened vinyl resin are formulated in the following proportions by weight: 30 parts polyurethane prepolymer, 100 parts vinyl resin, 0.3 parts catalyst, 0.02 parts polymerization inhibitor, and 1.5 parts free radical initiator.

[0060] Step S2: During the stirring process, the transmittance of the initial system is monitored in real time until the polyurethane phase separation starting point is reached, thus obtaining a homogeneous system.

[0061] The polyurethane phase separation initiation point is determined based on the transmittance change rate and transmittance change acceleration.

[0062] In this embodiment of the invention, the transmittance detection device uses a visible light transmittance meter. Its light source module uses an infrared 850nm light source, an infrared 940nm light source, and a visible light 550nm light source. The light is perpendicularly incident on the initial system through a quartz window (thickness 8mm~10mm, transmittance ≥95%) embedded in the side wall of the reactor. The incident light path avoids the stirring blades of the reactor. The sensor detects the incident light intensity and the light intensity after passing through the initial system of the three light sources respectively. The transmitted light signal is received in real time and converted into a current signal. The ratio of the transmitted light intensity to the incident light intensity is the transmittance, expressed as a percentage.

[0063] Please see Figure 2 The diagram shows a flowchart of step S2 in the preparation method of the polyurethane toughened vinyl resin of the present invention; specifically, step S2 includes:

[0064] Step S21: Continuously acquire the transmittance data of the initial system at a preset sampling frequency;

[0065] In this embodiment of the invention, the preset sampling frequency is denoted as f, with the unit being Hertz (Hz), and the value range is from 1Hz to 5Hz. Preferably, f is 2Hz.

[0066] Step S22: Calculate the transmittance change rate based on the transmittance difference between adjacent sampling time points;

[0067] In this embodiment of the invention, the formula for calculating the rate of change of transmittance is as follows:

[0068] ,

[0069] Where i is the transmittance sampling sequence number, i = 1, 2, 3...; r i R represents the transmittance at the i-th order, expressed in %; iThe transmittance change rate is expressed in % / s; Δt is the time interval, which is the reciprocal of the preset sampling frequency, i.e., f. -1 The unit is seconds (s).

[0070] Understandably, this formula quantifies the instantaneous change trend of transmittance, when R... i A value <0 indicates a decrease in transmittance, a precursor to phase separation. i A value greater than 0 indicates a momentary increase in transmittance, requiring continued stirring.

[0071] Step S23: When the rate of change of transmittance is less than or equal to the first preset threshold for the first time, the acceleration monitoring window is activated, and the acceleration of the transmittance change is calculated based on the change of the rate of change of transmittance within the acceleration monitoring window.

[0072] In this embodiment of the invention, the first preset threshold is denoted as R. th The value range is -2.5% / s to -1.5% / s. Preferably, R... th Take -2% / s, first preset threshold R th Based on calibration using several historical experimental data, this will not be elaborated further.

[0073] In this embodiment of the invention, the formula for calculating the acceleration of the change in transmittance is as follows:

[0074] ,

[0075] Among them, A i The acceleration of the change in transmittance is expressed in % / s. 2 m is the acceleration monitoring window width coefficient, which is dimensionless and ranges from 3 to 10. Preferably, the acceleration monitoring window width coefficient m is 3.

[0076] Understandably, the value of m determines the sensitivity of acceleration detection. The smaller the m value, the narrower the acceleration monitoring window, and the more sensitive the acceleration detection, but the more prone it is to false positives. i >0 indicates accelerated phase separation, A i <0 indicates that the separation trend has slowed down.

[0077] Step S24: When the acceleration of the change in transmittance is greater than or equal to the second preset threshold, it is determined that the initial system has reached the phase separation start point, and the transmittance and the acceleration of the change in transmittance at the time when the initial system is determined to have reached the phase separation start point are recorded as phase separation characteristic parameters.

[0078] Specifically, in step S24, the transmittance of the initial system when it reaches the phase separation starting point is determined to be the minimum transmittance within the current acceleration monitoring window.

[0079] In this embodiment of the invention, the second preset threshold is denoted as A. th The value ranges from 0.8% / s to 1.2% / s. Preferably, A th Take 1% / s, second preset threshold A th Based on calibration using several historical experimental data, this will not be elaborated further.

[0080] In this embodiment of the invention, the transmittance in the phase separation characteristic parameter is denoted as r. s The acceleration of the transmittance change in the phase separation characteristic parameters is denoted as A. s .

[0081] Understandably, in the early stages of stirring, the polyurethane prepolymer and vinyl resin form a homogeneous, transparent system that is molecularly miscible, maintaining a stable high transmittance. As shearing continues, polyurethane segments begin to migrate and aggregate directionally. When microphase regions larger than the wavelength of light (approximately 50 nm to 200 nm) are formed, Rayleigh scattering occurs, causing a sharp drop in transmittance. Traditional methods only monitor the absolute value of transmittance, but the actual onset of phase separation is located at the inflection point of the transmittance change curve. A sudden increase in the rate of change at this point indicates the establishment of a phase separation trend, while a sudden increase in the acceleration of change indicates that phase separation has entered an irreversible stage. The dual-threshold condition design effectively eliminates false positive signals caused by local temperature fluctuations or bubble interference. This real-time monitoring method based on optical dynamic response, compared to offline detection methods such as DSC and electron microscopy, offers improved sensitivity and eliminates hysteresis, laying the foundation for precise control of subsequent polymerization parameters and ultimately ensuring the uniform formation of the interpenetrating network structure.

[0082] Step S3: Determine polymerization parameters based on phase separation characteristic parameters, wherein the polymerization parameters include initial polymerization temperature, initial polymerization shear rate, and number of initiator additions, and the phase separation characteristic parameters are the transmittance and the transmittance change acceleration corresponding to the polyurethane phase separation initiation point;

[0083] Please see Figure 3 The diagram shows a flowchart of step S3 in the preparation method of the polyurethane toughened vinyl resin of the present invention; specifically, step S3 includes:

[0084] Step S31: Determine the initial polymerization temperature based on the transmittance in the phase separation characteristic parameters;

[0085] In this embodiment of the invention, the formula for calculating the initial polymerization temperature is as follows:

[0086] ,

[0087] Where T0 is the initial polymerization temperature, in degrees Celsius (°C); T refThe reference polymerization temperature is expressed in degrees Celsius (°C). Preferably, the reference polymerization temperature T is... ref The temperature is set at 75℃, determined based on the polymerization activation energy of vinyl resins, which will not be elaborated further here; s The transmittance at the point where polyurethane phase separation begins is expressed in percentage (%). ref The transmittance reference value is expressed in percentage (%). Preferably, the transmittance reference value r is... ref The value is 77.5%, which is based on the transmittance calibration of a completely homogeneous system, and will not be elaborated here; c is the temperature response coefficient, in ℃ / %, with a value range of -1.2℃ / % to -0.8℃ / %, preferably, the temperature response coefficient c is -0.8℃ / %, which is based on calibration of several historical experiments, and will not be elaborated here.

[0088] It is understandable that the transmittance value at the phase separation initiation point directly reflects the microscopic phase region size distribution at the phase separation initiation point. The higher the value, the more slight the phase separation. At this time, increasing the initial polymerization temperature can accelerate the free radical reaction and establish a polymer network skeleton before the phase region coarsens further. Conversely, when the transmittance is low, it indicates that a large phase region has been formed, and the temperature needs to be reduced to prevent the exothermic reaction from causing excessive growth of the phase region.

[0089] Step S32: Determine the initial polymerization shear rate based on the transmittance change acceleration in the phase separation characteristic parameters;

[0090] In this embodiment of the invention, the formula for calculating the initial polymerization shear rate is as follows:

[0091] ,

[0092] Where g0 is the initial polymerization shear rate, in units of (s). -1 ); g b Minimum shear rate, in units of (s) -1 Preferably, the minimum shear rate g b Take 20 seconds -1 It is calibrated based on several historical experimental data to prevent phase region settlement; p is the shear response coefficient, with units of (s). -1 The value range is 15s. -1 ~25s -1 Preferably, the shear response coefficient p is 20s. -1 Its calibration is based on rheological experiments, which will not be elaborated here.

[0093] It is understandable that the acceleration of the transmittance change at the initiation point of phase separation characterizes the dynamic process of phase separation. The larger the value of the transmittance change acceleration, the more rapid the phase separation development. By increasing the shear rate, convective mixing can be enhanced, phase region coarsening can be suppressed, and nanoscale phase domain formation can be promoted.

[0094] Step S33: Determine the number of times the initiator is added based on the initial polymerization temperature and the initial polymerization shear rate.

[0095] Specifically, the number of times the initiator is added ranges from 3 to 10, and the time interval between each initiator addition is determined based on the acceleration of the change in transmittance.

[0096] Specifically, the time interval between each initiator addition is negatively correlated with the acceleration of the transmittance change.

[0097] In this embodiment of the invention, the formula for calculating the number of times the initiator is added is as follows:

[0098] ,

[0099] Where n represents the number of times the initiator is added, in units of 3 to 10 times; T m This is a temperature scaling factor, in °C, used as a normalization reference; preferably, it is set to 100 °C; g m Shear rate scaling factor, in seconds. -1 This is used as a normalization benchmark, preferably 100s. -1 α is the temperature weighting coefficient, in units of times, and its value ranges from 2.5 to 3.5. Preferably, the temperature weighting coefficient α is 2.5. β is the shear rate weighting coefficient, in units of times, and its value ranges from 1.5 to 2.5. Preferably, the shear rate weighting coefficient β is 1.5.

[0100] In this embodiment of the invention, the calculation formula for the time interval between each addition of the initiator is as follows:

[0101] ,

[0102] Where △t is the time interval, in seconds (s); t z The total aggregation time is expressed in seconds (s), ranging from 14400s to 28800s. Preferably, the total aggregation time t is... z 14400s is selected; λ is a time adjustment factor, which is dimensionless and ranges from 0.3 to 0.5. Preferably, the time adjustment factor λ is 0.5.

[0103] Understandably, when the initial polymerization temperature is high, the molecular chain segments move violently, and the free radical reactivity is significantly enhanced. If all the initiator is added at once, it will cause localized heat accumulation, creating a temperature gradient that disrupts the phase structure. Therefore, the number of additions needs to be increased to avoid localized heat buildup, thus dispersing energy input and allowing the polymerization reaction to proceed smoothly. The initial shear rate, on the other hand, affects the phase morphology. Higher shear forces will enhance interfacial disturbances, requiring fewer additions to prevent excessive fragmentation of the phase structure. The addition time interval is determined by the acceleration of the transmittance change, a parameter that characterizes the intensity of the phase separation process: a larger acceleration indicates rapid phase separation, requiring a shorter interval to quickly establish a stable polymer network phase; a smaller acceleration allows for a longer interval, providing a time window for the orderly arrangement of the phase regions. This timing control mechanism ensures that the polymerization reaction and phase separation process proceed synchronously under optimal kinetic paths, achieving a continuous, interpenetrating network structure between the two phases.

[0104] This invention transforms the transient characteristics of phase separation into precise control commands for the polymerization process through a multi-parameter collaborative mapping mechanism, ensuring that the interpenetrating network is formed under the optimal dynamic path.

[0105] Step S4: Adjust the temperature of the homogeneous system to the initial polymerization temperature, control the shear rate of the homogeneous system to the initial polymerization shear rate, and simultaneously add free radical initiator in stages according to the number of times the initiator is added, so as to carry out free polymerization by shear stirring;

[0106] In this embodiment of the invention, temperature adjustment is performed through the heat transfer oil circulation system of the reactor jacket, raising / lowering the system from the mixing temperature to the initial polymerization temperature determined in step S3 at a rate of 1.5°C to 2.5°C per minute. The rotational speed is linearly transitioned from the initial mixing rate to the initial polymerization shear rate within 10 seconds.

[0107] According to the number of additions and time intervals determined in step S33, the servo metering pump system is started, and the free radical initiator is radially sprayed through the atomizing nozzle (orifice diameter 0.2mm) in the reactor, with a nozzle pressure of 0.3MPa to 0.5MPa.

[0108] Step S5: After all the free radical initiator is added, the viscosity and temperature distribution of the homogeneous system are detected. The current polymerization state index of the homogeneous system is determined based on the viscosity and temperature distribution. The polymerization temperature and polymerization shear rate are adjusted based on the phase separation characteristic parameters and the polymerization state index to obtain a high-toughness vinyl resin with an interpenetrating network structure.

[0109] Please see Figure 4 The diagram shows a flowchart of step S5 in the preparation method of the polyurethane toughened vinyl resin of the present invention; specifically, step S5 includes:

[0110] Step S51: After all the free radical initiators are added, the temperature data of multiple locations in the homogeneous system are acquired in real time, and the temperature uniformity index is determined based on the temperature distribution differences.

[0111] Specifically, the temperature distribution difference is determined based on multiple temperature sensors that are evenly distributed around the periphery of the reactor in which the homogeneous system is located. When the temperature difference between any two temperature sensors is greater than or equal to the set tolerance, the current polymerization temperature is maintained until the temperature difference falls back to the set tolerance.

[0112] In this embodiment of the invention, temperature data is collected every 30 seconds and the average temperature is calculated by using 5 to 15 sets of temperature sensors (accuracy ±0.1℃) evenly distributed around the reactor axis.

[0113] The specific formula for calculating the temperature uniformity index is as follows:

[0114] ,

[0115] Where U is the temperature uniformity index, which is dimensionless; T p The average temperature is expressed in degrees Celsius (°C); T j Temperature data obtained from each temperature sensor, in degrees Celsius (°C); j is the temperature sensor number; △T max To set the tolerance, the unit is degrees Celsius (°C). Preferably, the tolerance is set to ΔT. max The temperature is set at 5℃, which is based on a safety threshold calibrated from several historical experiments, and will not be elaborated here.

[0116] When the temperature difference between any two temperature sensors is ≥ ΔT max At this time, no polymerization temperature adjustment is performed, and the current polymerization temperature is maintained until the temperature difference falls back to the set tolerance.

[0117] Understandably, when the temperature difference between any two adjacent sensors is greater than or equal to the set tolerance, maintaining the current polymerization temperature without active adjustment aims to avoid introducing new temperature disturbances and ensure that the reaction system restores thermal homogeneity through a self-balancing mechanism. When a local temperature difference exceeds the tolerance threshold, it indicates that the system is in a dynamic thermal equilibrium reconstruction process. Maintaining a constant temperature at this time provides stable boundary conditions for heat conduction, allowing excess heat from high-temperature regions to naturally diffuse to low-temperature regions. If the overall temperature is increased or decreased at this time, it will disrupt the existing heat transfer path and exacerbate temperature oscillations between regions. Therefore, when the temperature difference of the system is greater than or equal to the set tolerance, the relaxation characteristics of the polymerization reaction itself are utilized to allow the system to release internal stress through molecular chain rearrangement under constant temperature conditions, thereby achieving microstructural homogenization.

[0118] Step S52: Based on the viscosity change rate and the temperature uniformity index, the polymerization state index is obtained;

[0119] In this embodiment of the invention, a vibratory online viscometer at the bottom of the reactor, with a range of 10 cP to 10000 cP, is used to measure the dynamic viscosity at certain time intervals; the polymerization state index is the ratio of the viscosity change rate to the temperature uniformity index U, denoted as S.

[0120] The specific formula for calculating the viscosity change rate is as follows:

[0121] ,

[0122] Where H is the viscosity change rate, which is dimensionless; η t The dynamic viscosity measured in this instance is expressed in Pa·s; η t-△t The previous measurement was of dynamic viscosity, in Pa·s; Δt η The viscosity measurement time interval is measured in seconds (s), with a range of 10s to 120s. Preferably, Δt η Take 60s; △T η The viscosity measurement time normalization constant is expressed in seconds (s). Preferably, ΔT η Set the time to 60 seconds.

[0123] Understandably, the polymerization state index integrates the reaction progress and thermal equilibrium state. The viscosity change rate directly reflects the speed of molecular chain growth and cross-linking network formation, making it a core indicator of the reaction progress. The temperature uniformity index characterizes the internal heat transfer efficiency of the system, reflecting the balance between exothermic reaction and external cooling. When viscosity rises rapidly while temperature distribution is uneven, it indicates that the reaction is concentrated in a localized area, potentially forming hotspots that broaden the molecular weight distribution. Conversely, when viscosity changes gradually but temperature is uniform, it reflects insufficient overall reaction kinetics and the risk of unreacted monomer residue.

[0124] Step S53: Adjust the polymerization temperature and polymerization shear rate according to the polymerization state index and the phase separation characteristic parameters.

[0125] Specifically, in step S53, adjusting the polymerization temperature and polymerization shear rate includes:

[0126] If the polymerization state index is less than or equal to the first state threshold, then the polymerization temperature is increased and the polymerization shear rate is decreased.

[0127] If the polymerization state index is greater than or equal to the second state threshold, the polymerization temperature is reduced and the polymerization shear rate is increased, wherein the adjustment range of the polymerization temperature and the polymerization shear rate is determined according to the phase separation characteristic parameter.

[0128] In this embodiment of the invention, the first state threshold is 0.05; the second state threshold is 0.3, which is calibrated based on several historical experimental data, and will not be described in detail here.

[0129] When S≤0.05, increase the polymerization temperature ΔT=d×(0.05-S), and at the same time decrease the shear rate Δy=-w×(0.05-S).

[0130] When S≥0.3, the polymerization temperature is decreased by ΔT=-d×(S-0.3), while the shear rate is increased by Δy=w×(S-0.3).

[0131] Where d is the polymerization temperature adjustment coefficient, d = 5 × (r s / 2); w is the polymerization shear rate adjustment coefficient, w=20×(A s / 1.2); △T is the polymerization temperature adjustment range, in degrees Celsius (°C); △y is the shear rate adjustment range, in seconds. -1 .

[0132] Single adjustment range limits: |ΔT|≤5℃, |Δy|≤10s -1 .

[0133] When 0.05 < S < 0.3, maintain the current polymerization temperature and shear rate.

[0134] Understandably, transmittance, as a direct optical record of the initiation point of phase separation, reflects the scale and distribution density of the initial phase region structure; the acceleration of transmittance change characterizes the intensity of the phase separation process. These two historical parameters form a spatiotemporal correlation with the current polymerization state index through adjustment coefficients: when the polymerization state index is low, increasing the temperature enhances the mobility of molecular chain segments, while decreasing the shear rate reduces convective disturbances, creating conditions for molecular recombination in the reaction lag region; when the index is high, cooling operations suppress excessive reactions, while increasing the shear rate enhances mass and heat transfer. The essence of this adjustment mechanism is that transmittance determines the sensitivity of temperature regulation (high transmittance systems require gentler temperature changes), and the acceleration of transmittance change determines the intensity of shear regulation (high acceleration history systems require more significant shear intervention), thus forming an adaptive control system with process memory capabilities, ensuring that the phase region structure stably evolves into an ideal interpenetrating network in the later stages of polymerization.

[0135] Example 1:

[0136] Raw material ratio: 30 kg of polyurethane prepolymer (PPG2000 and 2,4-diisocyanate-1-methylbenzene), 100 kg of vinyl resin (E44 and methacrylic acid type), 0.3 kg of catalyst (benzyl dimethylamine), 0.02 kg of polymerization inhibitor (hydroquinone), and 1.5 kg of free radical initiator (azobisisobutyronitrile).

[0137] Step S1: Add the raw materials to the twin-shaft stirred reactor, and set the initial shear rate to 68 s. -1 Stir at 70°C for 20 seconds until the system is homogeneous.

[0138] Step S2, record the phase separation characteristic parameters: r s =78%, A s =1.2% / s 2 .

[0139] Step S3, initial polymerization temperature 74.6℃; initial shear rate 38s. -1 The initiator was added 4 times; the time interval between additions was 324 seconds.

[0140] Step S4: Heat to 74.6℃ and adjust the shear rate to 38s. -1 The calculation showed that the free radical initiator (azobisisobutyronitrile) was added in four separate additions, with each addition occurring every 324 seconds.

[0141] Step S5: Based on the phase separation characteristic parameters and polymerization state index, the polymerization temperature and polymerization shear rate are adjusted. The final polymerization temperature is 78.8℃, and the final polymerization shear rate is 32s. -1 The total aggregation time was 14400s.

[0142] The performance test results of the toughened vinyl resin are shown in Table 1.

[0143] Example 2

[0144] 20 kg of polyurethane prepolymer and 100 kg of vinyl resin were used, with the remainder identical to that in Example 1. The performance test results of the toughened vinyl resin are shown in Table 1.

[0145] Example 3

[0146] 50 kg of polyurethane prepolymer and 100 kg of vinyl resin were used, with the remainder identical to that in Example 1. The performance test results of the toughened vinyl resin are shown in Table 1.

[0147] Example 4

[0148] In step S2, the change in light transmittance was not monitored, and the mixture was stirred for a fixed period of 30 minutes before proceeding directly to step S3. The rest of the steps were exactly the same as in Example 1. The performance test results of the toughened vinyl resin are shown in Table 1.

[0149] Example 5

[0150] With a fixed initial polymerization temperature of 80℃ and a shear rate of 50s, -1 The initiator was added twice, and the rest was exactly the same as in Example 1. The performance test results of the toughened vinyl resin are shown in Table 1.

[0151] Example 6

[0152] The initiator was added only once, and everything else was exactly the same as in Example 1. The performance test results of the toughened vinyl resin are shown in Table 1.

[0153] Example 7

[0154] In step S5, the temperature and shear rate are kept constant in the later stages without dynamic adjustments, and the rest is exactly the same as in Example 1. The performance test results of the toughened vinyl resin are shown in Table 1.

[0155] Example 8

[0156] In step S1, a fixed shear rate of 50s is used. -1 Everything else was exactly the same as in Example 1. The performance test results of the toughened vinyl resin are shown in Table 1.

[0157] The performance test results of the products obtained from the above embodiments and comparative examples are shown in Table 1 below:

[0158] Table 1. Performance test results of the vinyl ester resin (VER) prepared according to the embodiments of the present invention.

[0159] ;

[0160] The experimental results show that Examples 1-3, which used different raw material ratios but followed the preparation process of this invention completely, produced products with balanced and excellent comprehensive performance in terms of volume shrinkage control, interfacial bonding strength, tensile properties, ductility, and impact resistance. This indicates that the method has good adaptability to changes in the ratio. Among them, Example 1, with a moderate polyurethane content, showed the best phase region penetration effect. Its interpenetrating network structure effectively suppressed internal stress concentration, enabling the material to achieve uniform stress distribution when subjected to external loads.

[0161] Example 4, by omitting the phase separation point monitoring step, resulted in inaccurate determination of the initial phase structure state, leading to deviations in subsequent polymerization parameter settings. The product exhibited significant phase region coarsening and interface defects, manifested as a marked decrease in interfacial bonding strength, prominent brittleness, and severe deterioration in impact resistance, confirming that accurately capturing the phase separation initiation point is a prerequisite for constructing an ideal network structure. Example 5, using fixed polymerization parameters instead of a dynamic setting mechanism, could not adapt to the differences in phase separation characteristics, causing a mismatch between reaction rate and phase region evolution. The product exhibited excessive cross-linking and broadened molecular weight distribution, resulting in a comprehensive decline in mechanical properties.

[0162] In Example 6, the one-time addition of the initiator led to concentrated exothermic reaction, causing localized temperature rise, molecular chain breakage, and unreacted monomer residue. This resulted in increased volume shrinkage, a sharp drop in ductility, and deterioration in impact strength, highlighting the crucial role of the staged addition strategy in controlling reaction equilibrium. In Example 7, the lack of a dynamic adjustment step in the later stages of polymerization meant that the uneven heat distribution in the reaction system was not corrected in time, leading to localized hotspots that damaged phase integrity and resulted in significant performance dispersion in the product. In Example 8, a fixed initial shear rate was used without adjusting the mixing intensity according to the mass ratio, resulting in uneven dispersion during the premixing stage, disordered subsequent phase separation, and a wide distribution of phase sizes in the final product, with a simultaneous decrease in interfacial bonding strength and toughness.

[0163] In summary, the overall process control mechanism of this invention effectively overcomes the structural control defects of traditional processes through the synergistic effects of precise phase separation point determination, dynamic mapping of polymerization parameters, sequential addition of initiators, and closed-loop feedback adjustment. This method ensures the formation of a dense, interconnected interpenetrating network between the polyurethane phase region and the vinyl resin matrix, significantly improving the material's dimensional stability, interfacial bonding strength, load-bearing capacity, deformation absorption energy, and impact resistance, providing a reliable preparation route for high-performance composite materials.

[0164] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a polyurethane toughened vinyl resin, characterized in that, include: Step S1: The polyurethane prepolymer, vinyl resin, catalyst and polymerization inhibitor are added to the reactor and mixed to obtain the initial system, and stirred at the initial shear rate, which is determined according to the mass ratio of polyurethane prepolymer to vinyl resin. Step S2: During the stirring process, the transmittance of the initial system is monitored in real time until the polyurethane phase separation starting point is reached, thus obtaining a homogeneous system. Step S2 includes: Step S21: Continuously acquire the transmittance data of the initial system at a preset sampling frequency; Step S22: Calculate the transmittance change rate based on the transmittance difference between adjacent sampling time points; Step S23: When the rate of change of transmittance is less than or equal to the first preset threshold for the first time, the acceleration monitoring window is activated, and the acceleration of the transmittance change is calculated based on the change of the rate of change of transmittance within the acceleration monitoring window. Step S24: When the transmittance change acceleration is greater than or equal to the second preset threshold, it is determined that the initial system has reached the phase separation start point. The transmittance and the transmittance change acceleration when the initial system has reached the phase separation start point are recorded as phase separation characteristic parameters. The transmittance is the minimum transmittance within the current acceleration monitoring window. The first preset threshold ranges from -2.5% / s to -1.5% / s, and the second preset threshold ranges from 0.8% / s. 2 ~1.2% / s 2 ; Step S3 includes: Step S31: Determine the initial polymerization temperature based on the transmittance in the phase separation characteristic parameters, wherein the initial polymerization temperature is positively correlated with the transmittance; Step S32: Based on the transmittance change acceleration in the phase separation characteristic parameters, determine the initial polymerization shear rate, wherein the initial polymerization shear rate is positively correlated with the transmittance change acceleration. Step S33: Determine the number of times the initiator is added based on the initial polymerization temperature and the initial polymerization shear rate. The number of times the initiator is added ranges from 3 to 10. Step S4: Adjust the temperature of the homogeneous system to the initial polymerization temperature, control the shear rate of the homogeneous system to the initial polymerization shear rate, and simultaneously add free radical initiator in stages according to the number of times the initiator is added, so as to carry out free polymerization by shear stirring; Step S5: After all the free radical initiators are added, the viscosity and temperature distribution of the homogeneous system are detected, and temperature data at multiple locations of the homogeneous system are acquired in real time. The temperature uniformity index is determined based on the temperature distribution difference. The current polymerization state index of the homogeneous system is determined based on the viscosity change rate and the temperature uniformity index. The polymerization temperature and polymerization shear rate are adjusted based on the phase separation characteristic parameters and the polymerization state index to obtain a high-toughness vinyl resin with an interpenetrating network structure. The polymerization state index is the ratio of the viscosity change rate to the temperature uniformity index. If the polymerization state index is less than or equal to the first state threshold, then the polymerization temperature is increased and the polymerization shear rate is decreased, where the first state threshold is 0.

05. If the polymerization state index is greater than or equal to the second state threshold, the polymerization temperature is reduced and the polymerization shear rate is increased, where the second state threshold is 0.

3.

2. The method for preparing polyurethane toughened vinyl resin according to claim 1, characterized in that, In step S5, the adjustment range of the polymerization temperature and the polymerization shear rate is determined based on the phase separation characteristic parameters.

3. The method for preparing polyurethane toughened vinyl resin according to claim 2, characterized in that, In step S4, the time interval between each initiator addition is determined based on the acceleration of the transmittance change.

4. The method for preparing polyurethane toughened vinyl resin according to claim 3, characterized in that, The time interval between each initiator addition is negatively correlated with the acceleration of the transmittance change.

5. The method for preparing polyurethane toughened vinyl resin according to claim 4, characterized in that, The temperature distribution difference is determined based on multiple temperature sensors that are evenly distributed around the periphery of the reactor in which the homogeneous system is located. When the temperature difference between any two temperature sensors is greater than or equal to the set tolerance, the current polymerization temperature is maintained until the temperature difference falls back to the set tolerance.

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