Aliphatic oligocarbonates, uses and methods of preparation

Abstract

This invention discloses an alicyclic oligomeric carbonate, its uses, and a preparation method. The preparation method includes the following steps: adding an alicyclic dihydroxy compound and a carbonate esterifying agent to a reaction vessel, and causing a polycondensation reaction in the system under the action of a mixed catalyst, while continuously removing reaction byproducts; during the reaction, the alicyclic oligomeric carbonate is obtained by controlling the molar ratio of the reactants, the reaction time, and the ratio of the mixed catalysts, wherein the molar ratio of the alicyclic dihydroxy compound to the carbonate esterifying agent is 0.98–1.05:1; the reaction time is 3–6 hours; and the ratio of the mixed catalysts is 2–4:1. This invention achieves stable molecular weight control within the optimal optical function range of 900–1800 in oligomeric carbonates. Through the synergistic effect of the feed ratio, reaction time, and the ratio of the mixed catalysts, stable molecular weight, controllable molecular weight distribution, and good batch-to-batch reproducibility are achieved.

Description

Technical Field

[0001] This invention relates to the field of oligocarbonate preparation technology, specifically to an alicyclic oligocarbonate, its uses, and preparation methods. Background Technology

[0002] Cellulose triacetate (TAC) optical films are widely used in fields such as protective films for display polarizers. To improve their water vapor barrier properties, dimensional stability, and damp heat reliability, a certain amount of optical additives is usually introduced into TAC.

[0003] In existing technologies, commonly used optical additives are prone to increased haze and decreased optical performance under high temperature and high humidity conditions.

[0004] Currently, almost all polycarbonates on the market are high-molecular-weight polycarbonates. For example, CN 103204987A discloses a method for synthesizing high-molecular-weight aliphatic polycarbonates. This method involves a multi-level transesterification reaction between aliphatic or alicyclic diols and diphenyl carbonate. During the process of removing the reaction byproduct phenol, high-molecular-weight aliphatic polycarbonates are formed by condensation. Furthermore, polycarbonates with different structures can be obtained by adjusting the type of diol or the ratio of mixed diols. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a method for preparing alicyclic oligocarbonate optical additives. This method enables stable and controllable control over the molecular weight and molecular weight distribution of alicyclic oligocarbonates through regulation of the molar ratio of reactants, reaction time, and catalyst type, thereby solving the problems of precise molecular weight control and large batch-to-batch performance fluctuations in existing technologies. Another objective of the present invention is to provide an application of alicyclic oligocarbonates as optical film additives to enhance the synergistic optimization of the moisture-blocking and optical properties of optical films.

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing an alicyclic oligocarbonate includes the following steps:

[0008] Alicyclic dihydroxy compounds and carbonate esterifying agents are added to a reactor, and a polycondensation reaction is carried out in the system under the action of a mixed catalyst, while reaction by-products are continuously removed. During the reaction, the molar ratio of reactants, reaction time, and the ratio of mixed catalyst types are controlled to obtain alicyclic oligocarbonates. The molar ratio of the alicyclic dihydroxy compound to the carbonate esterifying agent is 0.98–1.05 : 1; the reaction time is 3–6 hours; and the mass ratio of catalyst A to B in the mixed catalyst system is 2–4 : 1. In the mixed catalyst system, catalyst A is at least one of zinc acetylacetonate (Zn(Acac)2), stannous octoate (Sn(Oct)2), tetrabutyl titanate (Ti(OBu)4), and yttrium acetylacetonate (Y(acac)3), and catalyst B is at least one of cesium carbonate (Cs2CO3), potassium carbonate (K2CO3), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD). Catalyst A (Zn(Acac)2, Sn(Oct)2, Ti(OBu)4, Y(acac)3, etc.) acts as a Lewis acid, which significantly reduces the activation energy of nucleophilic attack by coordinating and activating the carbonyl oxygen atom of the carbonate esterification reagent; Catalyst B (strong base / organic base such as Cs2CO3, K2CO3, DBU, TBD, etc.) greatly enhances the nucleophilicity of alicyclic dihydroxy compounds by deprotonation. The two form a synergistic catalytic system, which not only ensures the rapid start-up of the transesterification reaction, but also precisely balances the chain growth and chain termination rates, so that the reaction reaches dynamic equilibrium within 3–6 hours. The synergistic effect of the mixed catalyst in this application is manifested in the following ways: in the early stage of the reaction, by controlling the chain growth rate, the chain ends are "captured" by intermolecular reactions before cyclization, reducing the probability of intramolecular ester exchange, thereby inhibiting the formation of low molecular weight cyclic oligomers; in the later stage of the reaction, by controlling the increase in system viscosity, the reaction is stopped in a specific molecular weight range, thereby achieving high batch reproducibility of alicyclic oligocarbonates with a stable number average molecular weight Mn falling within the optical functional window of 900–1800 and a molecular weight distribution Mw / Mn of 1.8–2.5.

[0009] The alicyclic dihydroxy compound is one or more of 1,4-cyclohexanediethanol (CHDM), hydrogenated bisphenol A, and norbornenediethanol.

[0010] The carbonate esterifying agent is one or more of diphenyl carbonate, dimethyl carbonate, and diethyl carbonate. The reaction temperature is 120–160 °C.

[0011] The molar ratio of the alicyclic dihydroxy compound to the carbonate reagent is 1:1, the reaction time is 5 hours, and the mass ratio of catalyst A to B is 4:1.

[0012] Existing literature and patents primarily focus on whether carbonates can be produced, but rarely address how to stably control the number-average molecular weight (Mn) within a specific functional window range, how to control the molecular weight distribution (Mw / Mn), and how to avoid batch-to-batch performance fluctuations. A common problem in actual industrial production is the large molecular weight fluctuations between different batches of the same formulation, leading to non-reproducible moisture barrier properties and haze stability when used in TACs, severely impacting product consistency and reliability. The preparation method of this invention actively inhibits the formation of low-molecular-weight cyclic oligomers and prevents high-molecular-weight gels generated in the later stages of the reaction due to localized overheating or side reactions, achieving stable and controllable molecular weight and molecular weight distribution of alicyclic oligocarbonates. This solves the problem of precise molecular weight control in existing technologies for oligocarbonates.

[0013] An alicyclic oligocarbonate prepared by the above method has a number-average molecular weight Mn of 900–1800 and a molecular weight distribution Mw / Mn of 1.8–2.5.

[0014] This invention discloses the use of an alicyclic oligocarbonate as an additive in optical films to enhance the synergistic optimization of moisture-blocking and optical properties. Through extensive systematic experiments, this invention reveals that only within the specific molecular weight and distribution range described above can this alicyclic oligocarbonate simultaneously achieve multiple core advantages in a rigid cellulose triacetate (TAC) matrix, including uniform molecular-level dispersion, long-term thermodynamic stability and compatibility, excellent moisture-blocking pathways, and high batch-to-batch reproducibility. Specifically, when Mn is between 900 and 1800, the degree of polymerization is moderate, and the mixing entropy is highly matched with the TAC chain segment length, thus achieving perfect molecular-level dispersion and zero-phase separation. Simultaneously, a moderate chain entanglement effect significantly improves the tortuosity of the water vapor diffusion path. Based on free volume theory, the diffusion coefficient is greatly optimized, resulting in consistently excellent water vapor permeability and superior moisture-blocking performance. Furthermore, precisely controlling the molecular weight distribution Mw / Mn within 1.8–2.5 completely eliminates the influence of end-molecule components, thereby achieving extremely low migration rates and extremely high consistency in moisture-blocking performance and haze between batches, with stable haze changes after damp heat aging.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0016] This invention achieves stable molecular weight control within the optimal optical function range of 900–1800 for oligocarbonates. Through the synergistic effect of feed ratio, reaction time, and the proportion of mixed catalysts, it achieves stable molecular weight, controllable molecular weight distribution, good batch-to-batch reproducibility, effectively reduces by-products, and improves the selective conversion rate of the reaction.

[0017] The alicyclic oligocarbonate prepared by this invention has good solubility, excellent compatibility with TAC, and exhibits excellent moisture barrier properties and haze stability when used as an optical additive. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0019] Figure 1 This is a synthetic route diagram of alicyclic oligocarbonates based on 1,4-cyclohexanediethanol (CHDM) according to the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0021] In the following examples and comparative examples, the reaction was carried out in a reactor equipped with a stirrer, condenser, and vacuum device. The temperature was raised to 140 °C under nitrogen protection, and a vacuum was gradually applied to remove reaction byproducts. After the reaction, the product was cooled and discharged to obtain an alicyclic oligocarbonate product. The number-average molecular weight (Mn) and molecular weight distribution (Mw / Mn) of the obtained product were determined by gel permeation chromatography (GPC). A portion of the product was added as an additive to cellulose triacetate to prepare optical films, and its water vapor transmission rate (WVTR) and haze change after damp heat aging were tested.

[0022] Example 1: 1,4-Cyclohexanediethanol (CHDM) and diphenyl carbonate (DPC) were weighed and added to a reaction vessel at a molar ratio of 1.00:1. Catalyst A (Zn(Acac)2, 0.2 wt% of the total reactants) and catalyst B (Cs2CO3, 0.05 wt% of the total reactants) were then added, with a catalyst ratio of A to B of 4:1. The mixture was heated to 140 °C under nitrogen protection and reacted under reduced pressure for 3.0 h. After the reaction was completed, the mixture was cooled and discharged to obtain 1,4-cyclohexanedimethylene carbonate with a number-average molecular weight (Mn) of 920 and a molecular weight distribution (Mw / Mn) of 1.9.

[0023] The following preparation method was used to prepare cellulose triacetate optical films:

[0024] (1) The additive was introduced into a cotton glue solution containing cellulose triacetate (20 wt%) as a solute and dichloromethane and ethanol (volume ratio 9:1) as solvents at an addition amount of 8 wt% (relative to cellulose triacetate);

[0025] (2) Cotton glue treatment: Heat the cotton glue solution to 90°C for high-temperature dissolution, maintain for 30 min and then cool to 35°C, and remove impurities by filtration multiple times.

[0026] (3) Casting film: The treated cotton glue solution is pumped to the casting machine and cast on a stainless steel strip.

[0027] (4) Stretching and drying: After the wet film is peeled off, it is stretched and dried until the solvent content is below 3%.

[0028] (5) Post-processing: After edge trimming and balanced winding, cellulose triacetate optical film is obtained.

[0029] The water vapor transmission rate of the thin film was measured to be 620 g / m²·24 h at 40 ℃ and 90% RH. After treatment at 85 ℃ and 95% RH for 120 h, the haze change was 0.09%. The synthesis route is as follows. Figure 1 As shown.

[0030] Example 2: The method for preparing 1,4-cyclohexanedimethyl carbonate in Example 1 was followed, but the reaction time was adjusted to 4.0 h.

[0031] The resulting 1,4-cyclohexanedimethyl carbonate has a Mn of 1250 and a Mw / Mn ratio of 2.1.

[0032] The optical film preparation method in Example 1 was used to prepare a cellulose triacetate optical film. The water vapor transmittance of the prepared cellulose triacetate optical film was measured to be 510 g / m²·24 h, and the haze change was 0.06%.

[0033] Example 3: The method for preparing 1,4-cyclohexanedimethyl carbonate in Example 1 was followed, but the reaction time was adjusted to 5.0 h.

[0034] The resulting 1,4-cyclohexanedimethyl carbonate has a Mn of 1650 and a Mw / Mn ratio of 2.3.

[0035] The optical film preparation method in Example 1 was used in the preparation of TAC optical films. The resulting cellulose triacetate optical film had a water vapor transmittance of 470 g / m²·24 h and a haze change of 0.05%.

[0036] Example 4: The method for preparing 1,4-cyclohexanedimethyl carbonate in Example 1 was followed, but the reaction time was adjusted to 6.0 h.

[0037] The resulting 1,4-cyclohexanedimethyl carbonate has a Mn of 1790 and a Mw / Mn ratio of 2.5.

[0038] The optical film preparation method in Example 1 was used in the preparation of TAC optical films. The resulting optical film had a water vapor transmittance of 530 g / m²·24 h and a haze change of 0.08%.

[0039] Example 5: The method of Example 3 was followed, except that 1,4-cyclohexanediethanol (CHDM) and diphenyl carbonate (DPC) were replaced with hydrogenated bisphenol A and dimethyl carbonate, and the molar ratio was adjusted to 1.05:1.

[0040] The resulting hydrogenated bisphenol A carbonate has a Mn of 1050 and a Mw / Mn ratio of 2.0.

[0041] Using the optical film preparation method in Example 1, the film was added to cellulose triacetate to form a film. The water vapor transmittance of the resulting optical film was 560 g / m²·24 h, and the haze change after wet heat treatment was 0.08%.

[0042] Example 6: The method of Example 3 was followed, except that CHDM and DPC were replaced with norbornanediethanol and diethyl carbonate, and the molar ratio was adjusted to 0.98:1. The mixed catalyst was replaced with stannous octanoate (Sn(Oct)2) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in a mass ratio of 3:1.

[0043] The resulting norbornene dimethyl carbonate has a Mn content of 1780 and a Mw / Mn ratio of 2.4.

[0044] Using the optical film preparation method in Example 1, the film was added to cellulose triacetate to form a TAC optical film. The resulting TAC optical film had a water vapor transmittance of 490 g / m²·24 h and a haze change of 0.06%.

[0045] Example 7: The method of Example 3 was followed, except that the mixed catalyst was replaced with tetrabutyl titanate (Ti(OBu)4) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) in a mass ratio of 2:1.

[0046] The resulting 1,4-cyclohexanedimethyl carbonate has a Mn of 1480 and a Mw / Mn ratio of 2.2.

[0047] The prepared optical thin film had a water vapor transmittance of 480 g / m²·24 h under humid and hot conditions, and a haze change of 0.05%.

[0048] Comparative Example 1

[0049] The procedure was carried out as in Example 3, except that the molar ratio of CHDM to DPC was adjusted to 1.10:1.

[0050] The number-average molecular weight of the obtained product was only 620, and the molecular weight distribution was 1.7.

[0051] The product has a low molecular weight and is prone to migration, making it unsuitable for use in TAC optical films. No further testing of its application effect was conducted.

[0052] Comparative Example 2

[0053] The procedure was carried out as in Example 3, except that the molar ratio of CHDM to DPC was adjusted to 0.90:1.

[0054] During the reaction, the system rapidly thickened and gelled, with the final product having an Mn content of approximately 3100 and a Mw / Mn ratio of 3.8. This makes it unsuitable for use in optical thin film systems, and no further testing of its application performance was conducted.

[0055] Comparative Example 3

[0056] The method described in Example 3 was followed, except that the reaction time was shortened to 2.0 h.

[0057] The resulting alicyclic carbonate product had a molecular weight of approximately 480, mainly consisting of low molecular weight components. When used as an optical additive, its stability was insufficient, and its application effect was not further tested.

[0058] Comparative Example 4

[0059] The method was carried out as in Example 3, except that the reaction time was extended to 8.0 h.

[0060] The reaction resulted in significant overpolymerization, with the product having a Mn content of 5200 and a Mw / Mn ratio of 4.2. The molecular weight distribution was severely out of control and could not meet the processing requirements, so no further testing was conducted on its application effects.

[0061] Comparative Example 5

[0062] The procedure was carried out according to Example 3, except that the mass ratio of A to B in the mixed catalyst was 1:1.

[0063] The obtained product has an Mn content of approximately 2600 and an Mw / Mn ratio of 3.5. It has a wide molecular weight distribution, but its performance fluctuates significantly when used as an optical additive, making it unsuitable for application. No further testing was conducted on its application effect.

[0064] Comparative Example 6

[0065] The procedure was carried out according to Example 3, except that the mass ratio of A to B in the mixed catalyst was 1:0.

[0066] The obtained product has a Mn content of approximately 2800 and a Mw / Mn ratio of 2.5. The target product has low selectivity and lacks industrialization potential. No further testing of its application effects was conducted.

[0067] Comparative Example 7

[0068] The procedure was carried out according to Example 3, except that the mass ratio of A to B in the mixed catalyst was 0:1.

[0069] The obtained product has a Mn content of approximately 2400 and a Mw / Mn ratio of 2.9. The conversion rate of the target product is low, and it does not have industrialization potential. Therefore, no further testing of its application effect was conducted.

[0070] Comparative Example 8

[0071] The procedure was carried out according to Example 3, except that no catalyst was used.

[0072] The resulting product has a Mn content of approximately 3500 and a Mw / Mn ratio of 3.9. The reaction rate is slow, and it is prone to forming polymers, which cannot meet the processing requirements. Therefore, no further testing was conducted on its application effects.

[0073] The specific numerical comparisons of the above embodiments and comparative examples are shown in Table 1.

[0074]

[0075] As can be seen from the above examples and comparative examples, when the molar ratio of alicyclic dihydroxy compound to carbonate esterification reagent, the reaction time, and the ratio of mixed catalyst types are controlled within the range defined by this invention, alicyclic oligocarbonates with a molecular weight of 900–1800 and a controllable molecular weight distribution can be stably prepared. This product exhibits good moisture barrier properties and haze stability when used as an additive for cellulose triacetate optical films. However, when the range is exceeded, the molecular weight and distribution are difficult to control.

[0076] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an alicyclic oligocarbonate, characterized in that, Includes the following steps: Alicyclic dihydroxy compounds and carbonate reagents are added to a reactor, where a polycondensation reaction occurs under the action of a mixed catalyst, and reaction byproducts are continuously removed. During the reaction, the molar ratio of reactants, reaction time, and the ratio of different types of mixed catalysts are controlled to obtain alicyclic oligocarbonates. The molar ratio of the alicyclic dihydroxy compound to the carbonate reagent is 0.98–1.05 : 1; the reaction time is 3–6 hours; and the mass ratio of catalyst A to catalyst B in the mixed catalyst is 2:

1. The ratio is 4:

1. Catalyst A is at least one of zinc acetylacetonate Zn(Acac)2, stannous octoate Sn(Oct)2, tetrabutyl titanate Ti(OBu)4, and yttrium acetylacetonate Y(acac)3. Catalyst B is at least one of cesium carbonate Cs2CO3, potassium carbonate K2CO3, 1,8-diazabicyclo[5.4.0]undec-7-ene DBU, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene TBD. The number-average molecular weight Mn of the alicyclic oligocarbonate is 900–1800, and the molecular weight distribution Mw / Mn is 1.8–2.

5.

2. The preparation method according to claim 1, characterized in that, The alicyclic dihydroxy compound is one or more of 1,4-cyclohexanediethanol, hydrogenated bisphenol A, and norbornanediethanol.

3. The preparation method according to claim 1, characterized in that, The carbonate esterifying agent is one or more of diphenyl carbonate, dimethyl carbonate, and diethyl carbonate.

4. The preparation method according to claim 1, characterized in that, The reaction temperature is 120–160 ℃.

5. The preparation method according to claim 1, characterized in that, The molar ratio of the alicyclic dihydroxy compound to the carbonate esterifying agent was 1:1, and the reaction time was 5 hours.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the mixed catalyst A to B is 4:

1.

7. The use of the alicyclic oligocarbonate prepared by the preparation method according to any one of claims 1-6 as an optical film additive to enhance the synergistic optimization of the moisture barrier properties and optical properties of optical films.

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