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236839923

铁杆木虫 (正式写手)
★ ★
ksq887: 金币+2, good job 2022-07-14 16:38:53
on Wednesday, July 13th, 2022
thermal analysis
The thermal behavior of material studied in this work was determined on a Dupont 990 differential scanning calorimeter. Samples of 5-10 mg were sealed in  aluminum sample pans. the temperature was programmed at 10Cmin-1. Other parameters used were according to the typical Dupont  990 operating procedure.
Material
the impact copolymer characterized in this work is a commercial impact polypropylene copolymer with the<a> melt flow rate MFR= 6 and designated PP/E1
Results
The molecular structure of commercial impact polypropylenes, which are typical produced gy multi-reactor systems, has been rarely reported in the literature. the primary reason for the scarcity of microstructure data on commercial impact polypropylene  is the difficulty of separating the many different components of the complex mixtures. identification and characterization of the components in unfractionated whole polymer is presently not possible, if definitive analysis is required.  one of the few   studies in the literature reported on the fractionation of impact polypropylene into two fractions, a xylene-soluble fraciton and a xylene-insoluble fraction. the xylene soluble fraction was found to contain ethylene-propylene copolymer. the xylene-insoluble was found to contain isotactic polypropylene homopolymer and a small amount of polyethylene. No evidence was seen for ethylene-propylene linkage due to block or graft ehtylene-propylene sequences. analysis was done by DSC and 13C NMR.
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十四万人齐解甲，竟无一个是男儿
41楼2022-07-13 08:28:53
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236839923

铁杆木虫 (正式写手)
on Friday, July 15th, 2022
the analytical TREF elution pattern of <for> the impact polypropylene copolymer studied in this work is shown in Figure 2. this impact compolymer was fractionated in the <a>preparative step to remove EPR component. the reminder <remainder> of the polymer was analyzed  by analytical TREF and this is shown in Figure 3. It can be seen that Figure 3 is similar to Figure 2, except that low-temperature- elution EPR component is absent in Figure 3. the polymer in Figure 3 was fractionated by a preparative TREF and separated into 12 fractions.  the analytical TREF chromatograms of each of the 12 fractions were shown in Figure4-7.  It can be observed in Figure4-7 that approximately peek elution temperatures increase as fraction number increases.  the increase in the peek elution temperature indicate the increase in the level of crystallinity. however, analytical TREF curves are rather braod and complex, and display significant overlap between fractions. this is indicative of the complexity of the mixture of components in the polymer, and  the limiitid separation efficiency of the preparative TREF.
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十四万人齐解甲，竟无一个是男儿
42楼2022-07-15 08:05:25
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236839923

铁杆木虫 (正式写手)
on Monday, July 18th, 2022
The elution temperature ranges of <the> room temperature and succeeding 12 preparative  TREF fractions are shown in Table 1. these fractions were characterized by differential scanning calorimetry and and 13C nuclear magnetic resonance spectroscopy.  compolymer compositon, monomer sequence distributions and stereoregularity of propylene units were determined by 13C by established techniques.  melting endograms from DSC analysis were used to determine the compolymer composition by comparision with DSC data of compolymer with known composition. these DSC and 13C NMR data were used to determined chemical composition  and stereoregularity of the components of each fraction. Table 1 shows the major and minor chemical composition  and stereoregularity of these 13 fractions.
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十四万人齐解甲，竟无一个是男儿
43楼2022-07-18 08:18:04
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236839923

铁杆木虫 (正式写手)
on Tuesday, July 19th, 2022
In Table 1, PP= polypropylene, PE=polyethylene, and LLDPE=polypropylene with a small concentration of propylene. the complex structure of impact propylenene compolymer can be rationalized on the basis of sequential polymerization process<used to these polymers>. the weight percentage of each fraction is given in Table 1. the polypropylene accounted for about 75%, the EPR about 17%, and the other compolymers about 8wt% of the total.
the results of the characterization of this impact compolymer show that impact compolymers is<are> typically  blends of polypropylene homopolymer, <EPR(with negligible crystallinity)>a high-density-like polyethylene component, and crystallizable copolymers of ethylene and propylene.  the presence of polypropylene homopolymer is obviously explained by the production of such homopolymer in the first reactor where only catalyst, propylene monomer and hydrogen is presented. the ethylene-propylene rubber(EPR) is present because of its deliberate production in the second reactor where ethylene, propylene, catalyst and hydrogen are all present in order to form this copolymer.
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十四万人齐解甲，竟无一个是男儿
44楼2022-07-19 08:39:21
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236839923

铁杆木虫 (正式写手)
on Wednesday, July 20th, 2022.
however, it is unexpected that crystallizable copolymers of ehtylene and propylene are <also> present besides the non-crystalliazble epr. the reason that  the presence of these crystallizable ethylene-propylene copolymers is unexpected is because the <monomer>ratio of ethylene to propylene in the second reactor is such that a copolymer rich in both ehtylene and propylene should be produced.  this copolymer is expected to be non-crystalliazble and rubber-like , which is the copolymer that is desired. the majority of copolymer produced in the second reactor, i.e. epr, fullfill these requirements.
however, it is initially surprising to find , in addition to per,  an apparent spectrum of crystallizable copolymer of ethylene and propylene, which contain small quantities of ethylene in a propylene-rich compolymer and small quantities of propylene in an ethylene-rich copolymer. the purpose of the next section is to give a  theoretical basis for the presence of crystallizable ethylene-propylene copolymers , as well as the epr.
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十四万人齐解甲，竟无一个是男儿
45楼2022-07-20 08:25:56
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236839923

铁杆木虫 (正式写手)
on Tuesday, July 21th, 2022
theoretical discussion
the theory that describes the expected composition of copolymers is well developed for copolymers produced with homogeneous catalysts system. in the case of copolymers made with heterogeneous catalysts, it is known that these systems often produce heterogeneous copolymers, i.e. copolymers with very broad compositional distributions.
this behavior is <has also been>observed in the fractionation studies on the LLDPE..  these LLDPE copolymers are made on the similar Ti based catalyst system as used in the production of impact copolymer. in these studies, it is<was> shown that copolymer of ethylene and propylene gives <gave>not only broad composition distribution, but also multimodal composition distributions. no theory exists for the calculation of the composition of the copolymers made on the heterogeneous catalyst. however, the calculation of the theoretical composition distribution function for copolymer made wtih homogeneous catalyst system is helpful in understanding the composition of the copolymers produced in  the secondary reactor in the production of impact copolymers.
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十四万人齐解甲，竟无一个是男儿
46楼2022-07-21 10:15:25
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236839923

铁杆木虫 (正式写手)
on Tuesday, July 26th, 2022
this function is <the > composition distribution of all chain lengths and is calculated from some basic polymerization parameters such as feed composition, reactive ratio, number-average chain length and average copolymer composition. the calculated composition distribution functions for several typical copolymers produced<formed as>  the second products are presented in Figure 8. these composition distribution are relative narrow, but they do exhibit the type of distribution of copolymer species expected for second reactor product. it is anticipated that the actual composition distribution produced in the second reactor are much broader than those presented in Figure 8. this is because heterogeneous catalysts may contain a spectrum of sites and processes in contrast to homogeneous catalysts. however, the distribution presented in Figure 8 is useful for qualitatively demonstrating the effect of these distribution on the structure of the copolymers produced.
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十四万人齐解甲，竟无一个是男儿
47楼2022-07-26 08:14:33
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236839923

铁杆木虫 (正式写手)
on Wednesday, July 27th, 2022
Figure 9 shows a qualitative representation of broad composition distribution for the second reactor in the production of impact  copolymer. the important point to illustrate is that the central portion highlighted with cross-hatching represents copolymer that contain a large fraction of ethylene and propylene and, therefore, are expected to be rubber-like and exhibit negligible crystallinity.  the extremities of the curve, on the other hand, represent copolymers that are rich in one of the monomer with only a small fraction of the other monomer. these copolymers are expected to be semicrystalline. Figure 2 shows temperature ranges in Figure 9 in which various copolymers elute in the TREF chromatogram of the impact copolymer. It has been observed that in these TREF chromatogram ehtylene-propylene copolymer elute from chromatogram in two different<distinct> regions. the EPR elutes immediately at room temperature, on  the other hand, crystallizable ethylene-propylene copolymers elute just before the elution of propylene homopolymer.  the order of the elution of these copolymer from TREF is governed by the melting point of the crystals as described iby the Flory equation.
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十四万人齐解甲，竟无一个是男儿
48楼2022-07-27 08:40:49
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236839923

铁杆木虫 (正式写手)
on Thursday, July 28th, 2022
previously, it was unclear why there should be effectively two regions of copolymer structure observed in the tref fractionation process. however, now it is clear, by consulting the figure 9, that it is to be expected that in the central region of copolymer distribution is rubber-like copolymers that elute at the room temperature. the copolymers represented by the extremities of the curve in figure 9 are semicrystalline and, therefore, are expected to elute at a much higher temperature from tref, as observed in figure 2.
this behavior was substantiated by fractionating an epr sythesized under conditions typical of the second reactor but without any propylene homopolymer present.  figure 10 shows the tref chromatogram for the epr. it can be seen that both an epr eluting at room temperature and a small peak round 85-105 are observed. this small hump, at higher temperature, would appear as a shoulder on <a> large polypropylene peak in the tref.  this can be observed by consulting figure 2 where the shoulders are identified as zone 3. the copolymers that elute at around 85-105 is much richer in ethylene than the epr or much richer in propylene than the epr, so that these copolymers are semicrystalline.
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十四万人齐解甲，竟无一个是男儿
49楼2022-07-28 08:23:29
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236839923

铁杆木虫 (正式写手)
on Friday, July 29th, 2022
the identity of the major peaks in the TREF of the impact copolymer is determined qualitatively according to the elution temperature of each major species. Table 2 presents the elution temperature <for>species present in the impact polypropylene.  the copolymers eluting around 93C are shown by C13 NMR and DSC data to be due to polyethylene containing 0-8wt% of propylene comonomer. this polymer is due to the ethylene-rich extremity of the broad copolymer  distribution shown in Figure 9. it is close to the large polypropylene peak, which elute later, and mixing of these two species is shown in Table 1. As shown in Figure 2, the copolymer rich in propylene and containing a small fraction of ethylene would elute towards the higher-temperature side of the 85-105 range. However,  a copolymer of propylene and a minor amount of ethylene was not observed., as shown in Table 1. A TREF of such a copolymer containing 96.1wt% propylene and 3.9wt% ethylene was analyzed by analytical TREF and this is shown in Figure 11. it, in fact,  does elute at a peak temperature of about 100C. However,  copolymers rich in propylene than the EPR were not observed in fraction numbers 2-7(Table 1) these copolymers are presented on the left side (low -ethylene)of the curve in Figure 9.
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十四万人齐解甲，竟无一个是男儿
50楼2022-07-29 08:57:06
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