Synthesis method of polycaprolactone

Abstract

The invention discloses a synthesis method of polycaprolactone, and belongs to the technical field of polyester synthesis. The method comprises the following steps: heating epsilon-caprolactone, tin dichloride dehydrate and trihydric alcohol, and carrying out ring-opening polymerization reaction, so as to obtain polycaprolactone; according to the method, tin dichloride dehydrate and trihydric alcohol are utilized to generate a metal alcohol compound with high catalysis and initiation activity in caprolactone to rapidly initiate epsilon-caprolactone ring opening polymerization, high-component polycaprolactone is obtained, and compared with an existing polycaprolactone synthesis method, the adopted metal alcohol compound is high in initiation activity and low in cost, and the method is suitable for industrial production. According to the method, the conversion rate of epsilon-caprolactone can be rapidly increased, the generated polycaprolactone is high in molecular weight and narrow in distribution, and the method is beneficial to large-scale use.

Description

Technical Field

[0001] This invention relates to a method for synthesizing polycaprolactone, and more particularly to a method for synthesizing polycaprolactone by initiating and catalyzing the ring-opening polymerization of polycaprolactone using metal alcohols, belonging to the field of polyester 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 titanium-based, aluminum-based, rare earth metal compound systems, active hydrogen, and enzyme catalytic systems. However, existing reports have the following shortcomings: ① Low catalytic activity, requiring large amounts of catalyst, resulting in slow and low conversion rates of ε-caprolactone. ② Expensive catalysts (such as rare earth metal catalysts). ③ Long polymerization reaction time required. ④ Harsh reaction conditions, often carried out in vacuum drying ovens. ⑤ Generally employing solution polymerization processes, which are cumbersome and require solvent recovery.

[0004] Chinese Patent (Publication No. CN101628971A) 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 °C, the reaction time is 24 h, and the highest yield of polycaprolactone is 92.2%. This method requires a long reaction time and has a low yield. Chinese Patent (Publication No. CN105968036A) discloses a metal complex for efficient and controllable ring-opening of ε-caprolactone, specifically involving a thiourea metal salt. This is suitable for bulk polymerization and melt polymerization processes of ε-caprolactone, and also for slow, controllable polymerization in solution. However, the raw material cost for synthesizing this thiourea metal salt is high. Chinese Patent (Publication No. CN109336916A) discloses the synthesis of a β-pyrideneamine bidentate aluminum complex and its catalytic effect on the ring-opening polymerization of ε-caprolactone. 2-(2-pyridyl)-acetophenone undergoes a condensation reaction with aromatic amines containing different substituents to obtain ligands containing two nitrogen atoms, which are then coordinated with alkyl aluminum to synthesize β-pyridineneamine bidentate aluminum metal complexes. This 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. 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, studied 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. The highest yield was 79% at room temperature. The polycaprolactone yield obtained by this method was relatively low. Chinese patent (publication number CN114605630A) discloses a rapid synthesis method for thermoplastic polycaprolactone. The catalyst used in this method needs to be synthesized separately, and the catalyst is a liquid catalyst that is easily oxidized, which will affect the color of the subsequent polycaprolactone product. At the same time, its catalytic conversion rate of ε-caprolactone is low. Summary of the Invention

[0005] To address the shortcomings of existing methods for ring-opening polymerization of polycaprolactone (ε-caprolactone), this invention aims to provide a method for synthesizing ε-caprolactone. This method utilizes tin dichloride dihydrate and triols to generate a metal alcohol compound with high catalytic and initiation activity as a catalytic and initiation system, which can rapidly improve the conversion rate of ε-caprolactone. Compared with existing methods for synthesizing ε-caprolactone, this method has the following advantages: ① Low dosage of additives and low cost; ② Fast conversion rate and high final conversion rate of ε-caprolactone; ③ Short reaction time required for the ring-opening polymerization of ε-caprolactone to prepare ε-caprolactone; ④ Mild reaction conditions, constituting bulk polymerization; ⑤ Good catalyst stability, resulting in a better color of the synthesized ε-caprolactone product.

[0006] To achieve the above-mentioned technical objectives, the present invention provides a method for synthesizing polycaprolactone, which involves heating ε-caprolactone with tin dichloride dihydrate and a triol to carry out a ring-opening polymerization reaction, thereby obtaining the product. The triol has the following structure: ; Where n is an integer from 1 to 7.

[0007] As a preferred embodiment, the tin dichloride dihydrate and the triol react in ε-caprolactone to generate a metal alcohol compound with catalytic and initiating activity; the metal alcohol compound has the structure of Formula 1: ; Where n is an integer from 1 to 7.

[0008] The key to the synthesis method of polycaprolactone provided by this invention lies in the generation of a special structure of metal alcohol compound active species in polycaprolactone using tin dichloride dihydrate and triol. This species has particularly high initiation and catalytic activity for the ring-opening polymerization of ε-caprolactone, which not only reduces the amount of auxiliary agents, shortens the polymerization reaction time, and improves the conversion rate of ε-caprolactone monomer, but also has significant technical advantages over existing catalytic initiation systems.

[0009] As a preferred option, n in the structure of Equation 1 is an integer from 1 to 3.

[0010] As a preferred embodiment, the metal alcohol compound has the structure of Formula 2:

[0011] The metal alcohol compounds of this invention do not require separate synthesis but are directly synthesized during the ε-caprolactone polymerization reaction, simplifying the operation and avoiding catalyst oxidation that could affect the color of the polycaprolactone product. Particularly noteworthy is that the reaction process of converting stannous dichloride dihydrate and glycerol into active species of metal alcohol compounds takes place within ε-caprolactone. Once the active species are formed, they can rapidly initiate and catalyze the ring-opening polymerization reaction of ε-caprolactone. The preferred terol is glycerol.

[0012] As a preferred embodiment, the molar ratio of tin dichloride dihydrate to triol is 0.46:1 to 1.04:1.

[0013] As a preferred embodiment, the molar ratio of ε-caprolactone to tin dichloride dihydrate is 3034:1 to 5958:1.

[0014] As a preferred embodiment, the molar ratio of ε-caprolactone to triol is 2746:1 to 3130:1.

[0015] The metal alcohol compounds of the present invention have the advantage of low addition amount, which reduces the cost of catalyst use.

[0016] As a preferred embodiment, the ring-opening polymerization reaction conditions are: under nitrogen protection, a temperature of 130~180°C, and a time of 30min~120min. The ring-opening polymerization temperature is further preferably 158~177°C. The ring-opening polymerization time is further preferably 30min~60min. Under the premise of using a special metal alcohol compound as the initiator and catalyst system, the ring-opening polymerization reaction of the present invention can achieve a conversion rate of over 92% for ε-caprolactone within 30 minutes, and a conversion rate of over 99% within 60 minutes, significantly shortening the ring-opening polymerization reaction time.

[0017] Compared with existing technologies, the technical solution of this invention brings beneficial technical effects.

[0018] The technical solution of this invention employs a special catalytic and initiation system, which is safe and efficient, with a fast conversion rate and high final conversion of ε-caprolactone. Compared with other methods for producing polycaprolactone, the technical solution of this invention uses highly active species, requires less basic additives, has a fast polymerization reaction rate, short reaction time, low cost, fast ε-caprolactone conversion rate, high final conversion rate, and high molecular weight of the product polycaprolactone.

[0019] 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

[0020] Figure 1The images show the 1H NMR spectrum (a) and GPC spectrum (b) of the polycaprolactone product obtained from the ring-opening polymerization reaction in Example 1 after 90 min.

[0021] Figure 2 The images show the 1H NMR spectrum (a) and GPC spectrum (b) of the polycaprolactone product obtained from the ring-opening polymerization reaction in Example 1 after 90 min.

[0022] Figure 3 The images show the 1H NMR spectrum (a) and GPC spectrum (b) of the polycaprolactone product obtained by the ring-opening polymerization reaction for 73 min in Example 3. Detailed Implementation

[0023] 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.

[0024] Example 1 Weigh 297.39 g of ε-caprolactone and pour it into a three-necked flask. Weigh 0.13 g of tin dichloride dihydrate and 0.08 g of glycerol and add them to the three-necked flask. Install the thermometer, condenser, metal stir bar, etc., introduce nitrogen gas, open the condensate inlet and outlet, start the stirring device, and after confirming that the system is sealed, raise the temperature of the heating mantle from 31°C to 160°C in 25 minutes. During this heating process, the active species with the structure of Formula 1 is formed and rapidly initiates the ring-opening polymerization reaction of ε-caprolactone.

[0025] After reacting at 160°C for 30 min, the conversion rate of ε-caprolactone was 93.29%, and the number-average molecular weight of the product (M) was [missing information]. n The weight-average molecular weight (M) is 54114. w The value is 72242, and the polydispersity index (PDI) is 1.33.

[0026] After reacting at 160°C for 60 min, the conversion rate of ε-caprolactone was 99.15%, and the number-average molecular weight of the product (M) was [missing value]. n The weight-average molecular weight (M) is 66673. w The value is 92311, and the Proportional Dispersion Index (PDI) is 1.38.

[0027] After reacting at 160°C for 90 min, the conversion rate of ε-caprolactone was 99.67%, and the number-average molecular weight of the product (M) was [missing information]. n The weight-average molecular weight (M) is 62548. w The product's NMR spectrum is 91703, and its polydispersity index (PDI) is 1.47. The 1H NMR spectrum of the product is attached. Figure 1 a. See attached GPC test chart for the product. Figure 1 b.

[0028] After reacting at 160°C for 120 min, the conversion rate of ε-caprolactone was 99.69%, and the number-average molecular weight of the product (M) was [missing information]. n The weight-average molecular weight (M) is 63210. w The value was 94154, and the polydispersity index (PDI) was 1.49.

[0029] Example 2 Weigh 197.41 g of ε-caprolactone and pour it into a three-necked flask. Weigh 0.0655 g of tin dichloride dihydrate and 0.058 g of glycerol and add them to the three-necked flask. Install the thermometer, condenser, metal stir bar, etc., introduce nitrogen gas, open the condensate inlet and outlet, start the stirring device, and after confirming that the system is sealed, heat the heating mantle from 27°C to 160°C in 25 minutes. During this heating process, the active species with the structure of Formula 1 is formed and rapidly initiates the ring-opening polymerization reaction of ε-caprolactone.

[0030] After reaching 160°C and reacting for 0 min, the conversion rate of ε-caprolactone was 51.53%, and the number-average molecular weight of the product (M) was [missing information]. n The weight-average molecular weight (M) is 18801. w The value is 22631, and the Multiple Dispersion Index (PDI) is 1.20.

[0031] After reacting at 160°C for 30 min, the conversion rate of ε-caprolactone was 96.74%, and the number-average molecular weight of the product (M) was [missing information]. n The weight-average molecular weight (M) is 41565. w The value is 57360, and the Proportional Dispersion Index (PDI) is 1.38.

[0032] After reacting at 160°C for 60 min, the conversion rate of ε-caprolactone was 99.42%, and the number-average molecular weight of the product (M) was [missing information]. n The weight-average molecular weight (M) is 45202. w The value was 67918, and the Proportional Dispersion Index (PDI) was 1.50.

[0033] After reacting at 160°C for 90 min, the conversion rate of ε-caprolactone was 99.68%, and the number-average molecular weight of the product (M) was [missing information]. n The weight-average molecular weight (M) is 51872. w The p-value was 75125, and the polydispersity index (PDI) was 1.45. The proton NMR spectrum of the product is shown in the appendix. Figure 2 a. See attached GPC test chart for the product. Figure 2 b.

[0034] After reacting at 160°C for 120 min, the conversion rate of ε-caprolactone was 99.64%, and the number-average molecular weight of the product (M) was [missing information]. n The weight-average molecular weight (M) is 43877.w The value is 69353, and the Proportional Dispersion Index (PDI) is 1.58.

[0035] The hydrogen NMR spectrum of the product is attached. Figure 2 a. See attached GPC test chart for the product. Figure 2 b.

[0036] Example 3 Weigh 200.16 g of ε-caprolactone and pour it into a three-necked flask. Weigh 0.1313 g of tin dichloride dihydrate and 0.0516 g of glycerol and add them to the three-necked flask. Install the thermometer, condenser, metal stir bar, etc., introduce nitrogen gas, open the condensate inlet and outlet, start the stirring device, and after confirming that the system is sealed, raise the temperature of the heating mantle from 24°C to 160°C in 21 minutes. During this heating process, the active species with the structure of Formula 1 is formed and rapidly initiates the ring-opening polymerization reaction of ε-caprolactone.

[0037] After reacting at 160°C for 3 minutes, the conversion rate of ε-caprolactone was 97.98%, and the number-average molecular weight of the product (M) was [missing information]. n The weight-average molecular weight (M) is 93608. w The value is 134384, and the Multiple Dispersion Index (PDI) is 1.44.

[0038] After reacting at 160°C for 33 min, the conversion rate of ε-caprolactone was 99.34%, and the number-average molecular weight of the product (M) was [missing information]. n The weight-average molecular weight (M) is 87739. w The value is 121398, and the Proportional Dispersion Index (PDI) is 1.38.

[0039] After reacting at 160°C for 63 min, the conversion rate of ε-caprolactone was 99.37%, and the number-average molecular weight of the product (M) was [missing information]. n The weight-average molecular weight (M) is 75332. w The value is 114688, and the Proportional Dispersion Index (PDI) is 1.52.

[0040] After reacting at 160°C for 73 min, the conversion rate of ε-caprolactone was 99.57%, and the number-average molecular weight of the product (M) was [missing information]. n The weight-average molecular weight (M) is 74531. w The p-value was 111572, and the polydispersity index (PDI) was 1.50. The proton NMR spectrum of the product is attached. Figure 3 a. See attached GPC test chart for the product. Figure 3 b.

Claims

1. A method for synthesizing polycaprolactone, characterized in that: The ε-caprolactone is obtained by ring-opening polymerization of stannous chloride dihydrate and triol under heating. The triol has the following structure: ； Where n is an integer from 1 to 7.

2. The method for synthesizing polycaprolactone according to claim 1, characterized in that: The tin dichloride dihydrate and the triol react in ε-caprolactone to generate a metal alcohol compound with catalytic and initiating activity; the metal alcohol compound has the structure of Formula 1: ； in, n is an integer from 1 to 7.

3. The method for synthesizing polycaprolactone according to claim 1, characterized in that: n is an integer from 1 to 3.

4. The method for synthesizing polycaprolactone according to claim 3, characterized in that: The metal alcohol compound has the structure of Formula 2:

5. The method for synthesizing polycaprolactone according to claim 1, characterized in that: The molar ratio of tin dichloride dihydrate to triol is 0.46:1 to 1.04:

1.

6. The method for synthesizing polycaprolactone according to claim 1, characterized in that: The molar ratio of ε-caprolactone to tin dichloride dihydrate is 3034:1 to 5958:1; The molar ratio of ε-caprolactone to triol is 2746:1 to 3130:

1.

7. A method for synthesizing polycaprolactone according to claim 1, 2, 4, 5 or 6, characterized in that: The conditions for the ring-opening polymerization reaction are: under nitrogen protection, the temperature is 130~180°C, and the time is 30min~120min.

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