One-step Synthesis Of Cyclic Phosphazene Catalyst And Its Application In Ring-opening Polymerization

A current hot subject in polymer synthetic chemistry is the use of organic small molecules to catalyze the synthesis of controlled polymerization processes.Researchers have focused on creating effective and highly selective organocatalysts,and phosphazene catalysts in particular have gained popularity as polymerization catalysts because of their high catalytic activity and low toxicity.Unfortunately,there are currently few phosphazene catalysts available,and their synthesis is complex and expensive,limiting their application.To overcome the issues with phosphazene catalysts and broaden the range of phosphazene catalysts,a low-cost and straightforward method for making phosphazene catalysts was conceived and created in this thesis.the phosphazene catalysts were applied to the ring-opening polymerization of various cyclosiloxane monomers to investigate the impacts of various polymerization settings as well as the mechanism and kinetics of the polymerization reaction.Establishment of a novel route for the organocatalytic polymerization of cyclosiloxane monomers.Secondly,the stereoselective ring-opening polymerization of racemic lactide（rac-LA）was effectively carried out using the newly synthesized phosphazene catalyst HTGCP in combination with a urea catalyst.This resulted in the successful preparation of a polylactide with a high level of regularity.The main contents of the thesis are as follows:（1）Hexachlorotrimethylphosphonitrile（HCCP）and 1,1,3,3-tetramethylguanidine（TMG）served as the reaction feedstock for the effective production of a novel hexasubstituted phosphazene catalyst（HTGCP）.FTIR absorption spectroscopy（FTIR）,high resolution mass spectrometry（ESI-IS）,and NMR spectroscopy(¹H,¹³C,³¹P)all provided evidence of the product’s structure and purity being HTGCP.The acid-base equilibrium method was used to compute the p Ka^{Me CN}=27.2 of HTGCP.HTGCP is simple synthesis steps and low price when compared to other phosphazene catalysts that are already on the market.（2）The newly prepared HTGCP exhibited extremely high catalytic performance for hexamethylcyclotrisiloxane（D₃）in toluene,with conversions of more than 99%(M_n=10～836 kg·mol^-1)in 10～60 min under mild conditions.At high monomer dosage,the molecular weight M_n of the product can increase to 1136 kg·mol^-1 in 120 min.The structure and molecular weight and molecular weight distribution of the polymers were characterized by GPC,¹H NMR,²⁹Si NMR,and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry（MALDI-TOF MS）.The ionic reaction between the initiator and HTGCP ensured that the polymerization proceeded in a primary reaction kinetic form.Meanwhile,the polymerization rate constant increased significantly with increasing HTGCP concentration,and the clear linear relationship between M_n and[M]/[I]indicated that the polymerization of D₃ was controllable.In addition,the polymerization of octamethylcyclotetrasiloxane（D₄）and tetramethyltetravinylcyclotetrasiloxane（V₄）can still obtain high molecular weights under a wide molecular weight distribution.HTGCP as a new type of phosphazene catalyst,has outstanding application prospects in organic polymerization.（3）To address the challenges of the stringent reaction conditions（low temperature conditions）and the existence of ester exchange side reactions in the rise-selective ring-opening polymerization of rac-LA monomer,this thesis utilized a two-component organocatalytic system consisting of HTGCP and a urea catalyst to achieve the rise-selective ring-opening polymerization of rac-LA at room temperature and to prepare a higher-regularity polylactic acid material.It was found that the two-component catalytic system exhibited higher catalytic activity compared with HTGCP alone,and the regularity polymers were characterized by ¹³C NMR,and it was calculated that the degree of regularity of polylactic acid could reach P_m=0.85,and the melting point of polylactic acid could reach T_m=163℃,as measured by DSC,showing excellent thermal properties.The predictable molecular weight of polylactic acid was found by GPC,and the narrow molecular weight distribution indicated that the ester exchange of the reaction system was suppressed.The structure of PLA was characterized by ¹H NMR and ¹³C NMR.