Study On The Ring-opening Polymerization Of Lactones By A Mono (Phosphinoamide) Yttrium Complex

Aliphatic polyester is becoming more and more popular for its excellent properties such as excellent mechanical properties and biodegradability in biobased polymers.One of the in-novative strategies to obtain aliphatic polyester is by ring-opening polymerization.When it comes to the ROP of lactones and lactides,the drawbacks of the traditional catalysts were that the reaction temperature was high and the obtained polyesters have low molecular weights and poor mechanical properties.However,the emerging rare-earth metal complexes have re-ceived great interest due to their high activity,controllability and stereoselectivity.But up to nowadays,the polymerization of macrolactones using rare-earth metal complexes has been barely studied.In this work,a novel rare-earth yttrium complex?2,4,6-Me₃C₆H₂NPPh₂?Y?CH₂C₆H₄NMe₂-o?₂ was synthesized and fully characterized,and its application in the polymerization of lactones and macrolactone?ethylene brassylate?EB??was explored.Then the copolymerization of EB with?-CL and?-VL at room temperature was studied.The average sequence lengths and randomness characters of the copolymers were an-alyzed.Furthermore,the crystallization behaviors and thermal properties were investigated.?1?The mono?phosphinoamide?alkyl yttrium complex?2,4,6-Me₃C₆H₂NPPh₂?Y?CH₂C₆H₄NMe₂-o?₂?Cat Y?was synthesized and fully characterized by ¹H-NMR,¹³C-NMR,HSQC and X-ray diffraction analyses.The results showed that the complex has a mononuclear structure and the central rare-earth metal atom yttrium is six-coordinated.Cat Y was an efficient catalyst for _L-LA??-VL??-CL polymeriza-tions(TOF>1900 h^-1)and for EB polymerization(TOF=16 h^-1)at room temperature.All prod-ucts had a unimodal and narrow molecular weight distribution in the GPC curves and it is a reasonably well-controlled polymerization.?2?Based upon Cat Y,the EB/?-VL copolymerization and the EB/?-CL copolymeriza-tion were realized respectively at room temperature.All products had a high molecular weight?M_n=2.5?10⁴⁸.0?10⁴?and a narrow molecular weight distribution?PDI=1.4².4?in the GPC curves and the comonomer unit composition in this series of copolyesters can be con-trolled by adjusting the feed molar ratio of diacids.It is found that the sequence structure of resulting copolymers was different with the random copolymers obtained in traditional cata-lyst systems,which may have a block structure and presented a deviation from the random distribution of sequences.It demonstrated the transesterification rate is extremely slow and the complex we used as a catalyst is efficient with slight transesterification in the copolymer-ization process.?3?DSC and TGA was carried out to measure the basic thermal properties of poly?EB-co-?-CL?and poly?EB-co-?-VL?.The copolyesters showed a gradual increase of T_m and T_d with increasing EB content in the copolymer which indicating that the existence of EB sequences had a significant effect on the thermal stability of the copolymers.The crystalliza-tion behaviors were investigated by WAXD as well and the results indicated that the copoly-mers were able to crystallize over the entire range of composition and the isodimorphism be-havior can be observed.