Search

CN-121801061-B - Preparation method of cyclic poly (L-lactide)

CN121801061BCN 121801061 BCN121801061 BCN 121801061BCN-121801061-B

Abstract

The invention relates to a preparation method of cyclic poly (L-lactide), belonging to the technical field of polymer preparation. According to the method, L-lactide is used as a polymerization monomer, salallen type rare earth metal alkoxy complex is used as a catalyst, and cyclic poly (L-lactide) with high molecular weight is successfully prepared through solvent-free ring-opening polymerization reaction at the reaction temperature of 110-180 ℃. The method has the advantages of higher catalytic efficiency, high molecular weight of the obtained polymer, cyclic structure of the polymer and the like, and is green and solvent-free, and the product is the polymer only containing the cyclic topological structure.

Inventors

  • YAO YINGMING
  • ZHAO WENWEI

Assignees

  • 苏州大学

Dates

Publication Date
20260512
Application Date
20260311

Claims (6)

  1. 1. The preparation method of the cyclic poly (L-lactide) is characterized by comprising the following steps of mixing and sealing the L-lactide and a catalyst Salallen type rare earth metal alkoxy complex in an inert atmosphere, and carrying out solvent-free bulk ring-opening polymerization reaction to obtain the cyclic poly (L-lactide); the Salallen type rare earth metal alkoxy complex has the structural formula: Wherein RE is samarium, ytterbium or yttrium; the mol ratio of the Salallen type rare earth metal alkoxy complex to the L-lactide is 1:1000-3500; The temperature of the ring-opening polymerization reaction is 130-180 ℃.
  2. 2. The method according to claim 1, wherein the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.
  3. 3. The preparation method according to claim 1, wherein the ring-opening polymerization reaction time is 10 min to 12 h.
  4. 4. The method of claim 1, wherein the cyclic poly (L-lactide) has the structure: wherein n is more than or equal to 195.
  5. 5. The preparation method according to claim 1, wherein the molecular weight of the cyclic poly (L-lactide) is 28.3 kg/mol to 60.6 kg/mol.
  6. 6. The process according to claim 1, wherein the ring-opening polymerization reaction is followed by a separation and purification step of dissolving the polymerization reaction product in an organic solvent, adding a precipitant for precipitation, separating and drying.

Description

Preparation method of cyclic poly (L-lactide) Technical Field The invention relates to the technical field of polymer preparation, in particular to a preparation method of cyclic poly (L-lactide). Background Compared to linear polymers, cyclic polymers have no chain ends and thus exhibit many different properties, such as higher glass transition temperature, smaller hydrodynamic radius, and smaller intrinsic viscosity (see ：Josse, T.; Winter, J. D. ; Gerbaux, P.; Coulembie, O. Angew. Chem. Int. Ed. 2016, 55, 13944-13958.）.. Thus, cyclic polymers may exhibit unique properties distinguished from linear polymers, especially in emerging technical fields of drug delivery, surface modification, and hierarchical assembly (see Chen, c. J.; weil, t.j. Nanoscale horiz. 2022, 7, 1121-1135.) the current methods of synthesizing cyclic polymers are mainly two types of closed-loop methods (see Haque, f. M.; grayson, s. M. Nat. Chem. 2020, 12, 433-444.). Traditional closed-loop methods require highly diluted conditions, reaction conditions are difficult to scale-up, are limited by thermodynamic entropy adverse factors, the methods are capable of synthesizing cyclic polymers having a relatively low molecular weight (see Chen, c. J. Nanoscale horiz. 2022, 7, 1121-1135.; cyclic initiator (see 24. M.; grayson. Nat. Chem. 2020, 12, 433-444.; linear cyclic initiator) and the like, the cyclic initiator is further limited by the linear-loop-closure strategies such that the cyclic-closure methods are easily carried out by the linear-closure strategies of linear-up-down-cycle methods, and the cyclic-down-up-cycle methods of three-cycle systems are not required to be satisfied, so that the synthesis of the cyclic polymer can be carried out at conventional concentrations. The method enables mass production of cyclic polymers from milligrams to grams in a wide reaction time window of several seconds to several days, and enables efficient obtaining of cyclic polymers of high molecular weight (refer: kricheldorf, H.R.; lee, S.R. Macromolecules 1995, 28, 6718-6725.). However, most of the existing methods for preparing cyclic poly (L-lactide) by the ring-expanding method have the defect of impure products (see Hadjichristidis, N.; PITSIKALIS, M.; pispas, S.; iatrou, H. Chem. Rev. 2001, 101, 3747-3792.). In 2007, culkin, d.a. and Waymouth, r.m. et al reported for the first time a method for preparing cyclic (poly-L-lactide) by ring opening polymerization of L-lactide in tetrahydrofuran solution using N-heterocyclic carbene as an organic catalyst. However, the catalyst system has the disadvantages of low molecular weight of the product (up to only about 26 kg/mol), insufficient purity of the ring topology structure and the like (see ：Culkin, D. A.; Jeong,W.; Csihony, S.; Gomez, E. D.; Balsara, N. P.; Hedrick, J. L.; Waymouth, R. M. Angew. Chem., Int. Ed. 2007, 46, 2627-2630.）. In 2011 Weil et al reported an aluminum-based catalyst that can be used to prepare cyclic (poly L-lactide) by melt bulk or solution ring-expanding polymerization of lactide. The catalyst has high activity and can obtain cyclic polymer with high molecular weight and narrow distribution. However, MALDI-TOF mass spectrometry characterization showed that there was clearly a methoxy-terminated linear polymer in the product, with insufficient purity of the cyclic topology (see: weil, J.; matthers, R.T.; getzler, Y.D.Y.L. Macromolecules 2012, 45, 1118-1121.). In 2015, bonnet, f. catalyzed bulk polymerization of L-lactide with Ln (BH 4)3(THF)3) as a catalyst at 130 ℃ without solvent, to give cyclic poly (L-lactide), but the molecular weight of the resulting polymer was only 18 kg/mol, and linear poly (L-lactide) was present in the polymer (see: bonnet, f.; stoffelbach, f.; fontaine, g.; bourbigot, s.rsc adv. 2015, 31303-31310.). In 2017, kricheldorf, H.R. it was found that penta-cyclic dibutyltin as catalyst (DSTL) can catalyze the melt polymerization of L-lactide bulk at high temperature to form cyclic poly (L-lactide). However, the catalyst has low catalytic activity and linear poly (L-lactide) formation occurs in the product (see: kricheldorf, H.R.; weidner, S.M.; scheliga, F. Polym. Chem. 2017, 8, 1589-1596.). Thus, the cyclic poly (L-lactide) prepared by the conventional method for preparing the cyclic poly (L-lactide) has the problems of low molecular weight of the polymer, linear polymer generation and the like. Thus, developing a process for high activity catalytic polymerization of L-lactide to produce high molecular weight, pure cyclic poly (L-lactide) is a challenging problem. Disclosure of Invention In order to solve the technical problems, the invention provides a preparation method of cyclic poly (L-lactide), in particular to a method for preparing cyclic poly (L-lactide) under bulk polymerization conditions. The method is green and solvent-free, the product is a polymer only containing a ring topological structure, and the method has the advantages of higher cat