New Approaches To Characterize Phase Structure Of Multiphase Polymers By NMR Spin-diffusion Spectroscopy

In this dissertation, the phase structures of HDPE were investigated by employing solid-state high-resolution NMR spectroscopy. Some new methods with the potential of quantitatively studying the phase structures of multiphase polymers were proposed, basing on the spin-diffusion, cross-polarization (CP) and magic angle spinning (MAS) techniques. The works finished can be summarized as follows:1) A new pulse sequence which combines the "dipolar filter", Goldman-Shen, T₂ as well as CP sequence segments was suggested to selectively measure the mobility of different domains in HDPE. The domain sizes and spin diffusivity were obtained from second moment calculation. With a detailed analysis of NMR data, a new assignment of the ¹³C NMR resonance bands of HDPE was proposed.2) A novel method based on CP-MAS techniques was suggested, which can be used to quantitatively determine the phase content of multiphase phase polymers. This novel idea employs the conservation of magnetization during short time spin diffusion process. A new enhancement factor of different ¹³C resonance bands was introduced to quantify the relative intensities of ¹³C signals in the CP-MAS spectrum. With HDPE as a model sample, it was demonstrated that the crystallinity determined by the new method is in good consistence with the result obtained by the others. It was also demonstrated thatthe crystallinity determined keeps almost constant with the increase of the contact time (from 0.5ms to 6ms), indicating the new method is applicable under a wide range of conditions.3) The influence of fast magic angle spinning speed on the 1H spin-diffusion rate was studied with HDPE as a model sample. The spin diffusion rate does reduce with increasing spinning rate. Furthermore, it was found that under fast MAS condition, the line width of the spinning-bands of HDPE increases with its order. By employing the new pulse sequence which can be used to selectively measure 1H T2 of the crystalline region in different depths, it was demonstrated that there exist a distribution of mobility in the crystalline region of HDPE.