| Supercritical CO2 has been broadly applied as a solvent to produce industrial polymers, because it provides intense advantages as an environmentally friendly, inexpensive and nonflammable alternative to the aqueous and organic solvents. In this dissertation, polymerizations of acrylonitrile and ethylene terephthalate in supercritical CO2 were investigated respectively. The main conclusions are as follows:(1) Utilizing 2, 2'-azo(bisisobutyronitrile) (AffiN) as the free radical initiator and under the condition of supercritical carbon dioxide, the precipitation polymerization of acrylonitrille (hereafter, referred as CO2-PAN) was successfully carried out in our laboratory. In addition, copolymer of (AN-co-MA) was also tried in supercritical CO2.(2) The meso and racemic sequence distribution of the polymer chain is a direct reflection of the characteristic feature of the polymerization reaction by which polymer is synthesized. In order to analyses CO2-PAN polymerization mechanism through sequence distribution of PAN chain, we evaluated the pentad tacticities of CO2-PAN from the intensities of cyano peaks splitting into ten peaks in 13C NMR spectra, all of which are assigned by Kamide et al, and tried to examine these values by statistical methods. It was found that the sequence distributions of CO2-PAN obey Bernoulli statistics.(3) The triad and pentad tacticties, (i.e. the content of mmmm, mmmr, rmmr, mmrm, mmrr, rmrm, rmrr, mrrm, mrrr, and rrrr(m, meso; r, racemic)), of the CO2-PAN were analyzed byC NMR spectra. It was found that CO2-PAN was completely random in stereoregularity. Compared with the aqueous phase suspension polymerization of AN, using AIBN as initiator, (hereafter, referred as S-PAN) and aqueous phase precipitation polymerization of AN, using redox type initiator, (hereafter, referred as R-PAN), it was found isotacticity of CO2-PAN was lower than those of S-PAN and R-PAN, although the three kinds of PAN were all random in stereoregularity. The (m) content of CO2-PAN was about 0.4, the (mm) content 0.153 and the (mmm) content 0.057, which is lower than those of the S-PAN or R-PAN by aqueous phase radical polymerization methods by 22%, 43%, 59% respectively. The lower isotacticity of CO2-PAN may be due to the non-polar property of CO2. Thepolymerization in supercritical CO2 seems helpful to repulsion between cyano groups, which reduce the chance of meso sequence on the propagation chain. The triad isotacticity (i.e. the content of mm) of CO2-PAN was also determined by IR method using Minagawa's equation of the quantitative relationship between intensity of IR bands and isotaticity percentage. The calculated result is accordant with the C NMR method used.(4) The effective linear molecular weight calibration curve of polyacrylonitrile was obtained using a copolymer standard with a single broad molecular weight distribution. The molecular weights and molecular weight distributions of PAN obtained from precipitation polymerization of acrylonitrile in supercritical CO2 were quantitated by the calibration curve. The viscosity -average molecular weight has also been determined and the results are accordant with the GPC results. TheMv of CO2-PAN was about 1.5X 104~1X 105g/mol and the MWD of PAN were around 3. It seems that the products obtained from precipitation polymerization in supercritical CO2 have slightly broader molecular weight distributions.(5) By varying the concentration of monomer and initiator, the total reaction time, the CO2 pressure as well as temperature, the effects on the molecular weight and MWD have been respectively studied. The molecular weight distribution became broad as the monomer concentration increased. There was no appreciable effect of initiator concentration on molecular weight distribution when AIBN concentration ranged from 1.0% to 2.5%. Changing the density of the continuous phase by manipulating the CO2 pressure had a dramatic effect on the reaction. The higher density CO2 at higher pressure has the greater solvency for the gro...
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