Composite catalytic initiators and methods for reducing the odor of ε-caprolactone homopolymers

Abstract

This invention belongs to the field of polymers, specifically relating to a composite catalytic initiator for reducing the odor of ε-caprolactone homopolymers, comprising component A and component B; wherein component A is a compound having a structure of formula 1 and / or formula 2; and component B is a compound having a structure of formula 3. R1 to R3 are individually C1 to C6 alkyl groups; R4 is H or a C1 to C3 alkyl group; and n is an integer from 1 to 3. This invention also includes a method for preparing low-odor polycaprolactone homopolymers using the aforementioned composite catalytic initiator. The method of this invention can effectively improve the homopolymerization effect and, moreover, effectively reduce the odor.

Description

Technical Field

[0001] This invention relates to a method for preparing a low-odor ε-caprolactone homopolymer, belonging to the field of biodegradable resin synthesis technology. Background Technology

[0002] Thermoplastic polycaprolactone (PCL) has many advantages such as good biodegradability, biocompatibility, and shape memory properties, and can be used as medical orthopedic splints, medical positioning membranes, absorbable surgical sutures, medical bone screws, and implantable stents.

[0003] Currently, the catalysts reported in domestic and international literature for the ring-opening polymerization of caprolactone mainly include tin-based, titanium-based, rare earth metal compound systems, active hydrogen, and enzyme catalytic systems. However, existing reports have the following shortcomings: ① Polycaprolactone products have a strong odor, mainly a sour smell, originating from organic acids introduced during the preparation process, making them unsuitable for high-end medical applications. ② They have low catalytic activity, requiring large amounts of catalyst, and the conversion rate of ε-caprolactone is slow and low. ③ The catalysts are expensive (such as rare earth metal catalysts). ④ The required polymerization reaction time is long. ⑤ The reaction conditions are harsh, often carried out in a vacuum drying oven.

[0004] Chinese patent (application number CN200910165299.5) discloses a method for synthesizing polycaprolactone, which is completed in one step. Specifically, it involves the bulk ring-opening polymerization of caprolactone initiated by first- to third-generation alkynylated poly(amide-amine) to prepare terminally alkynylated linear or fan-shaped polycaprolactone. The polymerization reaction temperature is 130℃, and the reaction time is 24 hours. This method requires a relatively long reaction time and has a low yield.

[0005] Chinese patent (application number CN201610186268.8) discloses a metal complex for efficient and controllable ring-opening of ε-caprolactone, specifically involving a thiourea metal salt, which is suitable for bulk polymerization and melt polymerization processes of ε-caprolactone, as well as slow and controllable polymerization in solution. However, the raw material cost required to synthesize this thiourea metal salt is relatively high.

[0006] Chinese patent (application number CN201810980422.8) discloses the synthesis of a β-pyridineneamine bidentate aluminum complex and its catalytic ring-opening polymerization of ε-caprolactone. 2-(2-pyridyl)-acetophenone undergoes a condensation reaction with aromatic amines containing different substituents to obtain a ligand containing two nitrogen atoms, which is then coordinated with an alkyl aluminum to synthesize a β-pyridineneamine bidentate aluminum metal complex. This complex can be used to catalyze the ring-opening polymerization of ε-caprolactone at a polymerization temperature of 70–80 °C and a reaction time of 20–240 min. This method involves several steps.

[0007] Mary F. Mahon et al. (Inorganic Chemistry 2006, 45(5):2282–2287.) reported the synthesis, X-ray structure, and application of a novel compound, aryloxytitanium, in the ring-opening polymerization of ε-caprolactone. They prepared a series of catecholtitanium compounds, characterized them by single-crystal X-ray diffraction, investigated the electronic and steric effects of the ligands, and used the novel aryloxytitanium compound in the ring-opening polymerization of ε-caprolactone to obtain polycaprolactone with a maximum yield of 79% at room temperature. However, the polycaprolactone yield obtained by this method is relatively low. Summary of the Invention

[0008] In view of the problems of existing ε-caprolactone homopolymers containing carboxylic acids, having a strong odor, and having a low homopolymer molecular weight, the primary objective of this invention is to provide a composite catalytic initiator for reducing the odor of ε-caprolactone homopolymers, aiming to effectively reduce the odor of the product and improve the homopolymerization effect.

[0009] The second objective of this invention is to provide a method for preparing a low-odor ε-caprolactone homopolymer, which aims to reduce the odor of the polycaprolactone product and improve the molecular weight of the product.

[0010] A third objective of this invention is to provide a low-odor polycaprolactone prepared by the aforementioned method.

[0011] A composite catalytic initiator for reducing the odor of ε-caprolactone homopolymer, comprising component A and component B;

[0012] Component A is a compound having the structure of Formula 1 and / or Formula 2;

[0013] Component B is a compound having the structure of Formula 3;

[0014]

[0015] R1 to R3 are individually C1 to C6 alkyl groups; R4 is H or a C1 to C3 alkyl group; and n is an integer from 1 to 3.

[0016] This invention innovatively discovers that the combination of components A and B in the aforementioned structure can unexpectedly achieve synergy, improving the efficiency and effect of ε-caprolactone homopolymerization, helping to improve the homopolymerization conversion rate and the molecular weight of the homopolymer product. Moreover, it can also reduce or even avoid the residue of odor substances in the product.

[0017] In this invention, the combination of components A and B in the described structure is key to synergistically reducing odor and simultaneously improving homopolymerization. Thanks to the synergistic effect of components A and B, excellent polymerization results can be achieved even at low catalytic concentrations, while odor is synergistically reduced.

[0018] Preferably, in Formula 1, R1 is a C3-C4 straight-chain or branched alkyl group, preferably isopropyl.

[0019] Preferably, in Formula 2, R2 is a straight-chain or branched alkyl group of C1 to C2, preferably methyl;

[0020] The R3 is a C3-C5 straight-chain or branched alkyl group, preferably n-butyl.

[0021] Preferably, in Formula 3, n is 2 and R4 is H.

[0022] Preferably, the molar ratio of component A to component B is 1:3 to 3:1, more preferably 1:2 to 2:1, and even more preferably 1:2 to 1:1.

[0023] In this invention, the composite catalytic initiator is composed of component A and component B.

[0024] The present invention also provides a method for reducing the odor of ε-caprolactone homopolymer (the present invention is also referred to as a method for synthesizing low-odor polycaprolactone), wherein ε-caprolactone is ring-opened polymerized under the catalysis of the aforementioned composite catalytic initiator to obtain a polycaprolactone homopolymer with reduced odor.

[0025] In this invention, the molar ratio of component A or component B to ε-caprolactone in the composite catalytic initiator is 1:5000 to 1:700. Preferably, considering the treatment effect and cost, the molar ratio of component A to ε-caprolactone is 1:950 to 1100, and the molar ratio of component B to ε-caprolactone is 1:700 to 1000.

[0026] Preferably, the ring-opening polymerization temperature is 145–180°C, and more preferably 155–165°C.

[0027] Preferably, the ring-opening polymerization time is not less than 150 min.

[0028] Preferably, when the composite catalytic initiator includes formula 1 and formula 3, the ring-opening polymerization time is preferably 150-180 min;

[0029] Preferably, when the composite catalytic initiator includes Formula 2 and Formula 3, the ring-opening polymerization time is preferably 2.5 to 10 hours, and more preferably 6.5 to 10 hours.

[0030] The present invention also provides a caprolactone homopolymer—polycaprolactone—prepared by the method.

[0031] Beneficial effects

[0032] This invention innovatively combines components A and B of the aforementioned structure, thereby achieving synergy and obtaining good catalytic conversion effects at lower dosages. Furthermore, it can effectively reduce odor substances in the product, thus possessing positive industrial value.

[0033] The technical solution of this invention employs a special catalytic initiation system that is safe and efficient. At a temperature of 155–165°C, the reaction rate is fast, resulting in rapid ε-caprolactone conversion and a low-odor polycaprolactone product. Compared with other methods for producing polycaprolactone, the catalytic initiation system used in this invention has advantages such as high activity, low dosage, fast reaction rate, short reaction time, rapid ε-caprolactone conversion, and low-odor polycaprolactone product.

[0034] The technical solution of this invention can be achieved using a bulk polymerization method, which has a simple production process and low cost. Attached Figure Description

[0035] Figure 1 The 1H NMR spectrum of the product in Example 1;

[0036] Figure 2 The GPC spectrum of the product in group D of Example 1;

[0037] Figure 3 The GPC spectrum of the E group product of Example 1;

[0038] Figure 4 The 1H NMR spectrum of the product in Example 2;

[0039] Figure 5 The GPC spectrum of the product in group E of Example 2;

[0040] Figure 6 The GPC spectrum of the product of group F in Example 2;

[0041] Figure 7 The GPC spectrum of the product of group G in Example 2;

[0042] Figure 8 The 1H NMR spectrum of the product in group D of Example 1 (highlighting 11-12 ppm);

[0043] Figure 9 The 1H NMR spectrum of the product in group E of Example 1 (highlighting 11-12 ppm);

[0044] Figure 10 The 1H NMR spectrum of the product in group E of Example 2 (highlighting 11-12 ppm);

[0045] Figure 11The 1H NMR spectrum of the product in group F of Example 2 (highlighting 11-12 ppm);

[0046] Figure 12 The 1H NMR spectrum of the product in group G of Example 2 (highlighting 11-12 ppm); Detailed Implementation

[0047] The present invention will be described in detail below with reference to the embodiments. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operating procedures.

[0048] As an example, the composite catalytic initiator described in this invention can be a combination of Formula 1 and Formula 3, or a combination of Formula 2 and Formula 3.

[0049] When the composite catalytic initiator is a combination of Formula 1 and Formula 3 (also known as composite catalyst A), as a typical example, Formula 1 can preferably be Formula 1-A, which is a Formula 1 compound where R1 is isopropyl; Formula 3 can be Formula 3-A. It is a compound of formula 3 with R4 being H and n being 2. Preferably, in this scheme, the molar ratio of formulas 1 to 3 is 1:2 to 2:1, more preferably 1:1.

[0050] When the composite catalytic initiator is a combination of Formula 2 and Formula 3 (also constituting composite catalyst B), as a typical example, Formula 2 can preferably be Formula 2-A, which is a Formula 2 compound where R2 is methoxy and R3 is n-butyl; Formula 3 can be Formula 3-A, which is a Formula 3 compound where R4 is H and n is 2. Preferably, in this scheme, the molar ratio of Formula 1 to Formula 3 is 1:3 to 3:1, preferably 7:10.

[0051] In this invention, the components of the composite catalyst can be mixed and contacted with ε-caprolactone in the form of a mixture, or each component can be mixed and contacted with ε-caprolactone independently in sequence, and then heated to carry out a ring-opening homopolymerization reaction to reduce the odor of the synthesis, thereby obtaining low-odor polycaprolactone.

[0052] In this invention, when the composite catalyst is composite catalyst A, the molar ratio of Formula 1 to ε-caprolactone is 1:5000 to 1:700, more preferably 1:950 to 1100. The molar ratio of Formula 1 to ε-caprolactone is 1:5000 to 1:700, more preferably 1:700 to 1000. The temperature of the ring-opening polymerization stage is 140 to 175°C, preferably 155 to 165°C. Considering the preparation efficiency and effect, the polymerization time is preferably 150 to 180 min.

[0053] In this invention, when the composite catalyst is composite catalyst B, the molar ratio of Formula 2 to ε-caprolactone is 1:5000 to 1:700, more preferably 1:950 to 1100. The molar ratio of Formula 3 to ε-caprolactone is 1:5000 to 1:700, more preferably 1:700 to 1000. The ring-opening polymerization temperature of caprolactone is 145 to 170°C, preferably 155 to 165°C. Considering the preparation efficiency and effect, the polymerization time is preferably 5 to 10 hours, more preferably 6.5 to 8.5 hours.

[0054] Example 1

[0055] Weigh 200.18 g of ε-caprolactone, 0.12 g of Formula 1-A, and 0.05 g of Formula 3-A, and add them separately to 500 ml three-necked flasks. Install thermometers and condensers, introduce nitrogen gas, open the condenser inlet and outlet, start the stirrer, and after confirming the system is sealed, heat the heating mantle until the liquid temperature in the three-necked flasks reaches 160 °C. React for different times (Group A: 30 min; Group B: 60 min; Group C: 120 min; Group D: 150 min; Group B: 154 min). Perform NMR analysis on the products at different times. The results are shown in [Figure number missing]. Figure 1 The results for different processing times are as follows:

[0056] Group A: Caprolactone conversion rate was 4.85%;

[0057] Group B: Caprolactone conversion rate was 5.94%;

[0058] Group C: Caprolactone conversion rate was 24.63%;

[0059] Group D: Caprolactone conversion rate was 85.21%, polycaprolactone number-average molecular weight was 78490, distribution was 1.38, and the product's 1H NMR spectrum is attached. Figure 1 The GPC spectrum is attached. Figure 2 The characteristic peak of the -COOH hydrogen proton of typical odorous organic carboxylic acids is found at 11–12 ppm. This product did not exhibit this characteristic peak at 11–12 ppm, indicating that it does not contain the typical odorous organic carboxylic acid. The NMR spectrum is attached. Figure 8 As shown.

[0060] Group E: Caprolactone conversion rate was 88.64%, polycaprolactone number-average molecular weight was 90,111, distribution was 1.33, and the product's 1H NMR spectrum is attached. Figure 1 The GPC spectrum is attached. Figure 3 The characteristic peak of the -COOH hydrogen proton of typical odorous organic carboxylic acids is found at 11–12 ppm. This product did not exhibit this characteristic peak at 11–12 ppm, indicating that it does not contain the typical odorous organic carboxylic acid. The NMR spectrum is attached. Figure 9 As shown.

[0061] Example 2

[0062] Weigh 200.80 g of ε-caprolactone, 0.16 g of formula 2-A, and 0.07 g of formula 3-A, and add them separately to 500 ml three-necked flasks. Install thermometers and condensers, introduce nitrogen gas, open the condenser inlet and outlet, start the stirrer, and after confirming the system is sealed, heat the heating mantle until the liquid temperature in the three-necked flask reaches 160 °C. React at different times (t1), and analyze and identify the products at different reaction times. The 1H NMR spectra of the products at different reaction times are shown in the appendix. Figure 4 The conversion rates and properties of the products at different times are as follows:

[0063] Group A: t1 is 1 hour, and the reaction time is 1 hour later. The conversion rate of caprolactone is 15.52%.

[0064] Group B: t1 was 2 hours, and the caprolactone conversion rate was 28.54%.

[0065] Group C: t1 was 3 hours, and the caprolactone conversion rate was 43.74%.

[0066] Group D: t1 was 4 hours, and the caprolactone conversion rate was 58.82%.

[0067] Group E: t1 was 5 h, caprolactone conversion was 71.48%, product number-average molecular weight was 37788, distribution was 1.55, and the product 1H NMR spectrum is attached. Figure 1 The GPC spectrum of the product is attached. Figure 5 The characteristic peak of the -COOH hydrogen proton of typical odorous organic carboxylic acids is found at 11–12 ppm. This product did not exhibit this characteristic peak at 11–12 ppm, indicating that it does not contain the typical odorous organic carboxylic acid. The NMR spectrum is attached. Figure 10 As shown.

[0068] Group F: t1 was 6 h, caprolactone conversion was 75.70%, product number-average molecular weight was 54953, distribution was 1.31, and the product 1H NMR spectrum is attached. Figure 1 The GPC spectrum of the product is attached. Figure 6 The characteristic peak of the -COOH hydrogen proton of typical odorous organic carboxylic acids is found at 11–12 ppm. This product did not exhibit this characteristic peak at 11–12 ppm, indicating that it does not contain the typical odorous organic carboxylic acid. The NMR spectrum is attached. Figure 11 As shown.

[0069] Group G: t1 was 7 h, caprolactone conversion was 90.16%, product number-average molecular weight was 53778, distribution was 1.43, and the product's 1H NMR spectrum is attached. Figure 1 The GPC spectrum of the product is attached. Figure 7The characteristic peak of the -COOH hydrogen proton of typical odorous organic carboxylic acids is found at 11–12 ppm. This product did not exhibit this characteristic peak at 11–12 ppm, indicating that it does not contain the typical odorous organic carboxylic acid. The NMR spectrum is attached. Figure 12 As shown.

[0070] This invention was funded by the Hunan Provincial Science and Technology Innovation Program, project number: 2021RC3138.

Claims

1. A method of reducing the odor of epsilon-caprolactone homopolymer characterized in that, ε-caprolactone was ring-opened polymerized under the catalysis of a composite catalyst initiator to obtain a polycaprolactone homopolymer with reduced odor. The composite catalytic initiator consists of component A and component B; Component A is a compound having the structure of Formula 1 and / or Formula 2; Component B is a compound having the structure of Formula 3; Formula 1 Formula 2 Formula 3 R1 is a C3-C4 straight-chain or branched alkyl group; R2 is a C1~C2 straight-chain or branched alkyl group; R3 is a C3-C5 straight-chain or branched alkyl group; In Equation 3, n is 2, and R4 is H; The molar ratio of component A to component B is 1:3 to 3:1; The molar ratio of component A or component B in the composite catalytic initiator to ε-caprolactone is 1:5000 to 1:700, respectively. The ring-opening polymerization temperature is 145~180°C; The ring-opening polymerization time should be no less than 150 min.

2. The method of claim 1, wherein, In Formula 1, R1 is isopropyl. In Formula 2, R2 is a methyl group; R3 is n-butyl.

3. The method of claim 1, wherein, The molar ratio of component A to component B is 1:2 to 2:

1.

4. The method as described in claim 1, characterized in that, The molar ratio of component A to component B is 1:2 to 1:

1.

5. The method of claim 1, wherein The ring-opening polymerization temperature is 155~165°C.

6. The method of claim 1, wherein, When the composite catalytic initiator includes formulas 1 and 3, the ring-opening polymerization time is 150~180 min.

7. The method of claim 1, wherein, When the composite catalytic initiator includes formulas 2 and 3, the ring-opening polymerization time is 2.5~10h.

8. The method of claim 7, wherein, When the composite catalytic initiator includes formulas 2 and 3, the ring-opening polymerization time is 6.5~10h.

9. A polycaprolactone homopolymer prepared by the method according to any one of claims 1 to 8.

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