Synthesis Of Bdmaxt And Research On St Polymerization Mediated By BDMAXT

Controlled free radical polymerization is an important tool for polymer synthesis.,which achieves control towards the molecular weight,molecular weight distribution,composition,topology and end groups of polymers.In order to meet the needs of applications,eastablishment of new controlled/living radical polymerization systems becomes hotpot.Our group proposes a cyclo-thioketone mediated radical polymerization system,mainly using xanthene-9-thione/thioxanthene-9-thione as mediator,which has good control over the polymerization of methacrylates.In order to optimize the control ability of xanthene-9-thione,the xanthene-9-thiotone substituted by dimethylamino,2,7-bis(dimethylamino)-xanthene-9-thione(BDMAXT),was synthesized via the four-step reaction of nitrification,reduction,methylation and sulfidation with xanthone as a substrate.BMDAXT was characterized by 1H NMR,mass spectrometry,infrared spectrometry and ultraviolet spectrometry.St polymerization mediated by BDMAXT,the effects of solvent,thione/initiator ratio,design molecular weight,monomer mass fraction,and temperature were explored.The results show that there are two stages in the process of BDMAXT-regulated St polymerization—the low-speed period and the growth period.When the reaction is in the low velocity phase,the polymerization rate is slower,Mn increases slowly with the conversion rate,the conversion rate is lower than 20%,Mn is less than 2k,PDI is less than 1.5;when the reaction is in the growth phase,the polymerization rate is accelerated,and the Mn with the conversion rate Increase and increase.When the ratio of thione/initiator was decreased from 1.00 to 0,Mn showed an increasing trend under the same conversion rate,and the time for polymerization in a low-speed period continued to shorten.When the monomer concentration was reduced from 80 wt%to 10 wt%,the Mn and PDI of the polymerized product showed a tendency to decrease at the same conversion rate.When the designed molecular weight was reduced from 4k to 1k,Mn showed a downward trend with the same conversion rate,PDI gradually decreased,and the control ability of the system increased.When the polymerization temperature was decreased from 80 ? to 70 ?,there was no significant difference between Mn and PDI at the same conversion rate.There are two basic dimethylamine groups in BDMAXT,and the dimethylamino group in protonated BDMAXT(acid BDMAXT)accepts protons to fonn dimethylammonium groups,and the substituents are changed from strong chargeability to strong electron absorption.The effect of different substituents on the polymerization behavior of St was investigated.The results showed that compared with unsubstituted xanthene-9-thione,BDMAXT and acid BDMAXT had better ability to control St polymerization.Strong;however,compared with BDMAXT,acid BMDAXT showed no significant difference in the ability to regulate St polymerization.The mass spectrometry analysis of polymer products in the low polymerization stage of St polymerization under the control of BDMAXT shows that the polymer in this stage is mainly the adducts obtained by the addition of C=S addition coupling of two PSt chains with initiator fraction and BDMAXT.In order to carry out cyclo-thioketone mediated polmerization in water system,thioketones with carboxyl groups and polyethylene glycol chains were synthesized.The products were characterized by 1H NMR.Thioketones with carboxyl groups,polyethylene glycol chains,and dimethylamino groups have good water solubility under different conditions.The thioketone with dimethylamine dissolves well in acidic condition,.The thioketone with PEG group dissolves well at suitable temperature with suitable ion concentration.The thioketone with carboxyl group dissolves well in basic condition.