Popcorn Polymerization Of N-Vinylpyrrolidone

PVPP, the popcorn polymer of N-vmylpyrrolidone (NVP), was synthesized via two approaches: one is the popcorn polymerization with the in-situ-formed 1 -vinyl-3-ethylidene pyrrolidone (EVP) as a cross-linker; the other is with the external-added EVP, which was synthesized separately.EVP was synthesized and identified by GC/MS, NMR, IR, and DSC. The yield of EVP was found to be greatly dependent on reaction conditions. There is an optimal value for each reaction parameter studied: NVP level at 55wt%, NaOH level at 5wt%, reaction temperature at 140℃, and stirring rate at 600r/min. The highest yield of EVP of 26.53% was achieved with the purity over 99.9%.Acting as a cross-linker in popcorn polymerization of NVP, EVP was found to play a key role in the popcorn polymerization of NVP, as the popcorn polymerization of NVP occurred only when the level of EVP was in the range of 1 wt%~2 wt%, and within such a range of EVP level, the swelling degree of the popcorn polymer decreased with the increasing amount of EVP.The popcorn polymerization of NVP with the in-situ-formed EVP can be divided into 4 stages. Firstly, the system was held at a higher temperature for a period. Then, the temperature was lowered. After an induction period, the popcorn polymerization was initiating. The level of NVP and NaOH, reaction temperature, and duration of the first stage greatly affected the popcorn polymerization and the property of the product. The popcorn polymerization failed to process when the level of NVP was less than 40wt%. With the increasing level of NVP, the induction period became short. However, the product turned yellow and the yield of PVPP turned down since the reaction proceeded dramatically. As NaOH is the catalyst of the reaction, the polymerization proceeded so dramatically with the higher level of NaOH that the product turned yellow. Since thecross-linker was formed in the first stage of the reaction, reaction temperature and duration of the first stage greatly affected the polymerization process. It was found that the induction period could disappear when the initial pressure was 0.2MPa.In conclusion, the technique of popcorn polymerization of NVP with the in-situ-formed cross-linkers is advantageous in its simpler process. High quality product can be obtained with a high yield of PVPP. The studies is instructive for the PVPP commercial production.