Fractionation of Ethylene-Based Copolymers

McHugh and coworkers describe the fractionation of various poly(ethylene-co-methyl acrylate) copolymers using supercritical propane, propylene, 1-butene, and chlorodifluoromethane (Meilchen, Hasch, and McHugh, 1991 Pratt, Lee, and McHugh, 1993). The objective of their work was to extend the work of Krukonis and coworkers (Scholsky et al., 1987 Watkins and Krukonis, 1991) who demonstrated the ability of fractionating by chemical composition of the polymer as well as molecular weight. This concept is also described with other polymer-SCF solvent systems in the next few sections of this chapter. 

The fractionation and phase behavior data are presented in order of increasing polarity of the copolymer starting with EMA7o/3o- The phase behavior of EMA7o/3() in propane and propylene is shown in figure 9.6. The cloud point curves in butane and butene are not shown since they are at such low pressures that it is not possible to effectively fine-tune these solvents during 

Fractionation data are shown in table 9.7 for EMA70/30 fractionated with chlorodifluoromethane followed by propane, both at ISFC. Chlorodifluoromethane is only able to extract —68% of the copolymer charge to the fractionation columns. The polydispersities of the first seven fractions are about one half that of the parent material even though sample sizes of 1-2 g are obtained at each pressure level. The concentration of methyl acrylate in the backbone of the copolymer is about 4wt% greater than that in the parent material confirming that chlorodifluoromethane preferentially solubilizes the more polar oligomers. 

Fractions 8 through 13 in table 9.7 were obtained with propane. Again the polydispersities of the fractions are less than that of the parent material. The concentration of methyl acrylate in the backbone of the fractions is now about 4wt% less than that of the parent. Also, notice that molecular weights of the first few fractions obtained with propane are lower than those of the final fractions obtained with chlorodifluoromethane this indicates that chlorodifluoromethane can remove only fractions rich in acrylate even if the molecular weight is greater than available oligomers that have a higher ethylene content. 

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Figure 3.8 (a) Melting temperature TJ of rapidly crystallised fractions of PE-based copolymers as determined by DSC. A hydrogenated polybutadiene with ethyl groups ethylene-vinyl acetate copolymer diazoalkane copolymer with propyl side groups X ethylene-1-butene copolymer ethylene-1-octene copolymer, (b) Melting temperature (TJ of branched LDPE. 1 ethylene-propylene copolymer 2 ethylene-1-bntene copolymer 3 branched PE [23]... 

Figure 20 Melting temperature of rapidly crystallized fractions of polyethylene-based copolymers as determined by differential scanning calorimetry hydrogenated polybutadiene with ethyl groups A copoly(ethylene vinyl acetate) diazoalkane copolymer with propyl side groups A copoly(ethylene/l-butene) copoly(ethylene/l-octene)...

The previous sections in this chapter have tried to stress upon the significance of distribution of sequence lengths in polyethylene-based copolymers. The sequence length of interest in a system of ethylene-octene copolymers would be the number of methylene units before a hexyl branch point. As was discussed, this parameter has a greater impact on the crystallization behavior of these polymers than any other structural feature like branch content, or the comonomer fraction. The importance of sequence length distributions is not just limited to crystallization behavior, but also determines the conformational,... 

Cozewith and Ver Strate examined fractionation data of ethylene-propylene copolymers obtained with homogeneous or apparently homogeneous systems, based on vanadium compounds such as VCl and aluminum trialkyl, or VOCI3 and AKCjHjljCl. While some catalytic systems gave the expected narrow MWD with Q 2 and high composition uniformity concerning monomeric units distribution, others gave a wider composition distribution and multimodal and broader MWD with Q even >10. The authors attributed this last result to different active centres. 

Specific interactions in binary blends of ethylene-vinyl acetate copolymer with various low molecular weight terpene-phenol tackifying resins (TPR) were systematically investigated, as a function of the composition of the blend and of the electron acceptor ability of the resin, by using attenuated total reflection FTIR spectroscopy. Molecular acid-base were evidenced between TPR hydroxyl groups and EVA carbonyl groups. Quantitative information on the fraction of acid-base bonded entities, the enthalpy and equilibrium constant of pair formation were obtained. A crystalline transition of the EVA copolymer was observed and discussed in terms of enthalpy and entropy considerations based on FTIR and calorimetric DSC investigations. Fundamental results are then summarised to predict the interfacial reactivity of such polymer blends towards acid or basic substrates. 16 refs. 

The calibration curve, based on a series of standard copolymers prepared with Relabelled ethylene or propylene, is obtained by plotting the 7.25 absorbance 6.85 absorbance ratio against the C3 weight fraction. The basis for the calibration of many methods for the analysis of ethylene-propylene copolymers is the work published by Natta and co-workers [6], which involves measuring the IR absorption of polymer solntions at 7.25 pm (presumably due to methyl vibrations related to the propylene concentration in the copolymer). In some cases, the dissolution of copolymers with... 

V aisman et al. [52] reported the effect of bromination of the surface of commercial UHMWPE fibres in order to polarise the surface of the fibres. This bromination process was shown to result in an increase in the degree of order of the transcrystalline zone when these fibres were combined with HDPE to produce a self-reinforced polymer model composite. While these pubUcations report the use of different types of PE to create self-reinforced polymer composites, UHMWPE fibres have also been combined with ethylene-based copolymers. Kazanci et al. [53, 54] reported the creation of commercial UHMWPE fibre-reinforced ethylene-butene copolymers. Filament wormd structiues were produced, with fibre volume fractions of 65%, with the suggestirm of a potential application for these materials in unspecified medical devices. 

In order to increase the solubiUty parameter of CPD-based resins, vinyl aromatic compounds, as well as other polar monomers, have been copolymerized with CPD. Indene and styrene are two common aromatic streams used to modify cyclodiene-based resins. They may be used as pure monomers or contained in aromatic steam cracked petroleum fractions. Addition of indene at the expense of DCPD in a thermal polymerization has been found to lower the yield and softening point of the resin (55). CompatibiUty of a resin with ethylene—vinyl acetate (EVA) copolymers, which are used in hot melt adhesive appHcations, may be improved by the copolymerization of aromatic monomers with CPD. As with other thermally polymerized CPD-based resins, aromatic modified thermal resins may be hydrogenated. 

TABLE 16.9 Producers (TosoHaas) Specification of Fractionation Ranges of Ethylene Glycol/Methacrylate Copolymer-Based TSK PW Gels... 

RIS theory is used to predict values of the optical-configuration parameter Aa for ethylene - propylene copolymers as a function of chemical composition, chemical sequence distribution, and stereochemical structure of the propylene sequences. The calculations are based on information available for ethylene and propylene homopolymers, and on the model used to interpret the unperturbed dimensions of these copolymers. Values of Aa are generally found to decrease significantly with increase in the fraction of propene units, but to be relatively insensitive to chemical sequence distribution and stereochemical structure. Geometries and conformational energies are the same as those used for the interpretation of the unperturbed dimensions of these chains. The conformational energies used are E(q) = 0, EM 2.09, and E a>) = 0.37 kJ mol-1. 

The total crystal fraction, oriented crystal fraction (/oc). and unoriented crystal fraction (/uc) during extension and retraction have been analyzed. Results can be described as follows. At strain zero, the total crystal fraction was the same as the unoriented crystal fraction, which was about 14%, and both values decreased with strain. This indicates that a fraction of the original crystals was destroyed at the initial deformation stages. (This phenomenon was also reported in ethylene-based ethylene-propylene copolymer (34).) At strain 0.7, the total crystal fraction decreased about 4% (from 14% to 10%) at strains above 0.7, both total crystal fraction and oriented crystal fraction increased with strain, indicating the occurrence of strain-induced crystallization, whereas the unoriented crystal fraction decreased continuously with strain. The increase of the total crystal fraction was slower than that of the oriented crystal fraction, suggesting that some unoriented crystals were reoriented by... 

Kilburn et al. [2002] carried out a PALS study of free volume in semicrystalline poly(ethylene-co-l-octene) (PO) copolymers as well as high-density polyethylene (HDPF). The degree of crystallinity was characterized by DSC and WAXD analyses. A method was proposed to estimate the fractions of the RAF and MAF phases based on the observation that the mean thermal expansivity of free-volume holes, ea = d vh)/dt, varies as a function of Xc, which implies that the individual mean expansivities of holes in RAF and MAF phases are different. Thus, the thermal expansivity of the mean hole volume (i.e., averaged over the entire amorphous phase) may be expressed above To by... 

In blends of random copolymers, or in blends of a polymer with random copolymer, the presence of repulsive forces among segments (other than specific interactions discussed before) may lead to miscibility (Wang et al. 2006). The effect of ethylene-styrene cmitent on the miscibility and cocrystallization was studied extensively by Chen (2001). They showed that the miscibility of the system depends only oti the comonomer content with composition expressed as weight fraction. Based on the experimental observations, they constructed a miscibility map for binary blends (Fig. 10.34). 

In the literature many differences can be found in the temperature range used for the study of the crystalUzation and melting processes of PEO and PCL based AB diblock and ABA triblock copolymers. When the studies are performed above room temperature, an important fraction of the blocks may remain amorphous [8-11, 14, 16] however, most authors report that when the study is extended at temperatures below Tg, both blocks can crystallize [13-15,17]. In the case of ABA triblock copolymers, it has been found that the B-block remains amorphous when its content is lower than 10%, or its molecular weight is very low. Piao et al. [17] and He et al. [18,19] synthesized either poly(e-caprolactone)-6-poly(ethylene oxide)-6-poly(e-caprolactone) ABA triblock copolymers, as well as poly(ethylene oxide)-6-poly(e-caprolactone) AB diblock copolymers. They used poly(ethylene glycol) (PEG) as precursor and a calcium catalyst. Then, they characterized the materials by using NMR, DSC, WAXS and Polarized Optical Microscopy (POM). Cooling DSC scans carried out by He et al. [18] in AB diblock copolymers of different compositions are presented in Fig. 13.1. 

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