A Solid-state NMR Study On The Structure And Segmental Motion Of Polycarbonates

Polycarbonates synthesized from the asymmetric copolymerization of CO₂ with meso-epoxides mediated by racemic isotactic catalyst systems,have the advantages of higher crystallinity,higher glass transition temperature and wider application prospect.However,the relationship between properties and microstructure,segmental motion is still unclear.In this thesis,the structures and segmental motions of polycarbonates such as PCOPC,PCHC,PCXC and PCEBC were investigated by multiple solid-state NMR techniques.The main findings are as follows:?1?¹³C CP/MAS NMR spectra were employed to study the differences in the stuctures of various polycarbonates.The results indicate that the half peak widths of the stereocomplexed polycarbonates are much narrower than those of the amorphous polycarbonates.Moreover,the signals of CH groups split into doublet for the stereocomplexed polycarbonates.It means that the interaction between the chains with opposite configuration leads to the change of the chemical environment.?2?The static broad-line ¹H NMR and 2D ¹H-13 C WISE NMR experiments were conducted to investigate the segmental motion of polycarbonates.It is demonstrated that the segmental mobility of the amorphous polycarbonate increases comparing to the stereocomplexed counterpart.?3?¹³C and ¹H spin-lattice relaxation time?T1?and ¹H T1? time in rotating frame are much longer for the stereocomplexed polycarbonates,indicating its less flexibility,more sterically hindered segment motion than the amorphous counterparts.Besidies,the spin-lattice relaxation time of the carbonyl and methine groups are shorter than other branched chain region groups,which proves that the interactions mainly exist in the main chain regions.?4?2D ¹H-13 C HETCOR and ¹H-¹H DQ MAS NMR spectra reveal that the structre features differ from each other for stereocomplexed and amorphous polycarbonates.The distance between chain segments with opposite configuration is much shorter in the stereocomplexed-PCXC due to the strong interactions.This results in the less mobility of the chains.