Fractionation Styrene-butadiene copolymers

Mastral et al.23,24 have also investigated the effect of the main components present in tyres (carbon black, styrene-butadiene copolymer and polybutadiene) on the liquefaction of coal. Coprocessing of coal and carbon black confirmed the catalytic role of the latter, as it promotes hydrocracking reactions leading mainly to the formation of gaseous products. The addition of SBR to coal improves the yield of gases, oil and asphalt fractions, even at relatively low temperatures (350-375 °C). It is proposed that SBR favours the stabilization of the radicals involved in the process through alkylation reactions... 

PE would have a low solubility even in hot toluene. In the case of styrene-butadiene copolymer, the uncrosslinked polymer is soluble in aromatic solvents, whilst the highly crosslinked (gel) fraction is completely insoluble and, indeed, this can be used as the basis of a method for separating gel from uncrosslinked polymer. Copolymers usually dissolve in a greater number of solvents than homopolymers. Thus, whilst PVC is only slightly soluble in acetone or methylene chloride, its copolymers with vinyl acetate or acrylates dissolve easily. 

TEC is a useful technique for separating polymers into molecular weight fractions on a fairly small scale. It has been used to fractionate PET [135, 136], styrene-butadiene copolymers [137], styrene acrylonitrile copolymers [138], polyoxypropylene glycols [136], Nylon-styrene graft copolymers and PMMA [139-141], styrene-methacrylate copolymers [142], poly-a-methylstyrene [143], polyvinyl acetate-styrene copolymers, and polyvinyl alcohol-styrene copolymers [144]. 

Ozonisation followed by GPC has been employed by Tanaka and co-workers [83] to study sequencing of vulcanised styrene-butadiene copolymers. Tanka and co-workers [83] carried out the ozonolysis in methylene dichloride and examined the fractions obtained after GPC by H-NMR. These workers found nonad, diad and triad styrene sequences flanked by 1,4 butadiene units and long styrene sequences ... 

By taking the resonance areas of the two gaussian peaks as a measure of block styrene , it was found that this agreed rather well with the fraction of styrene units in SSS and (SSB + BSS) triads, as is shown in Table 4. Mochel also noted that resonance at 6.5 in styrene-butadiene copolymers prepared by anionic techniques was a measure of styrene units in sequences of four or more styrene units. 

FIG. 12-8. Diffusion coefficient of n-hexadccane at 2S°C through random styrene-butadiene copolymers plotted against reciprocal of fractional free volume calculated from equation 8. Open circles, uncross-linked samples black circles, cross-linked. Lines drawn with slope of — 1/2.3Q3 as specified by equation 7. (Rhee and Ferry. ) Reproduced, by permission, from the Journal of Applied Polymer Science. 

Subsequently, the theory is applied to stepwise fi actionation using the crossfractionation procedure. After some model calculations to study the influence of different operative fractionation parameters on the fractionation efficiency, the theoretical results will be again compared with experimental data for the styrene-butadiene copolymer system in two different solvent systems, namely cyclohexane + isooctane and benzene + methyl ethyl ketone [75]. 

Teramachi S, Kato Y (1970) Cross fractionation of styrene-butadiene copolymer. J Macromol Sci A4 1785-1796... 

Crompton and Reid [113] have described procedures for the separation of high impact polystyrene, i.e., styrene-butadiene copolymer, into the free rubber plus rubber grafted polystyrene plus copolymerised rubber and a gel fraction and for estimating total unsaturation in the two separated fractions. To separate a sample into gel and soluble fractions it was first dissolved in toluene. Only gel remains undissolved. Methanol is then added, which precipitates the polystyrene - rubber graft, ungrafted rubber and polystyrene. Any styrene monomer, soap or lubricant remain in the liquid phase, which is separated from the solids and rejected. 

Styrene-butadiene copolymers have been fractionated by high performance liquid chrom-atography. ... 

Block copolymer chemistry and architecture is well described in polymer textbooks and monographs [40]. The block copolymers of PSA interest consist of anionically polymerized styrene-isoprene or styrene-butadiene diblocks usually terminating with a second styrene block to form an SIS or SBS triblock, or terminating at a central nucleus to form a radial or star polymer (SI) . Representative structures are shown in Fig. 5. For most PSA formulations the softer SIS is preferred over SBS. In many respects, SIS may be treated as a thermoplastic, thermoprocessible natural rubber with a somewhat higher modulus due to filler effect of the polystyrene fraction. Two longer reviews [41,42] of styrenic block copolymer PSAs have been published. 

Figure 3.6 Variation of retention with the composition of the stationary phase in GLC. Stationary phase styrene-butadiene polymer blends and copolymers, the butadiene fraction is plotted on the horizontal axis, (a) Specific retention volumes for three n-alkanes and benzene. V is proportional to the capacity factor, (b) the retention index for benzene. The solid line is calculated from the straight lines in figure 3.6a. The circles (polymer blends) and triangles (copolymers) represent experimental data. Figure taken from ref. [310], Reprinted with permission.

Structure and Composition of Diene Copolymers. One finds that most of the reported copolymerization studies on butadiene or isoprene involve styrene as comonomer. In part this is due to the early interest in styrene-butadiene synthetic rubbers. The free radical produced copolymers (GRS, usually about 20—25% styrene units) contain about 20% of its butadiene fraction in the 1,2 form. The ratio of 1,2 to 1,4 units is little affected by polymerization variables such as temperature, conversion and styrene content (39). Butadiene and styrene copolymers contain 50 to 60% 1,2-diene units when prepared by sodium catalysts at 50° (39). This behaviour is once more significantly different when lithium is used in place of sodium as can be seen in Table 3. 

The most important synthetic elastomer is styrene-butadiene (SBR) which accounts for 41% of the world market in elastomers. It is used predominantly for vehicle tires when reinforced with carbon black. Nitrile rubber (NBR) is a random copolymer of acrylonitrile (mass fraction 0.2 to 0.4) and butadiene, and it is used when an elastomer that is resistant to swelling in organic solvents is required. The range of properties can be extended when styrene is also incorporated in the chain. 

In experiments on immiscible blends, as noted by Dlubek et al. [2002], it is to be anticipated that the PALS parameters h and T3 will depend on the volume fractions and compositions of the three phases, as well as the effect of any interaction between the blend components. Such interactions have been identified in the studies of Wastlund et al. [1998] and Dlubek et al. [1999]. Thus, as pointed out above, the decrease in T3 observed by Wastlund et al. [1998] in 50 50 SMA24/SANx blends when the acrylonitrile content of the SANx increases from x=22% to x=33%, is interpreted as being due to increased interaction between the maleic anhydride and acrylonitrile groups. On the other hand, Dlubek et al. [1999] studied blends of an acrylonitrile-butadiene-styrene (ABS) copolymer and polyamide-6 (PA-6). This blend may be assumed to be quite heterogeneous, consisting of a two-phase structure having PA-6 crystals embedded in an amorphous ABS matrix and elastomeric... 

Natural rubber, synthetic cw-1,4-poly(isoprene), butadiene rubbers, and styrene-butadiene rubbers are all sensitive to oxidation because of their high carbon-carbon double bond fractions. Attempts to reduce sensitivity to oxidation with maintenance of the vulcanizability have lead to the development of what are known as the butyl rubbers, IIR, which are copolymers of isobutylene with a little isoprene. But butyl rubbers only have a small rebound elasticity. However, since they also have poor gas permeability, they are mostly used for tire inner tubes. 

MMD and CCD for styrene-butadiene block copolymers were determined by SEC followed by turbidimetric titration of the eluates [60]. The mobile phase was THF and methanol was added to the fractions in 7 minutes. The intensity of the scattered light was determined, and the point of inflection during titration indicated the precipitation of a new species of molecule. If the dependence of solubility on chemical composition and concentration is known for the particular retention volume, the chemical composition of each species may be evaluated from these inflection points. 

Figure 4.2 ReIatioi ship between (a) T of PVC and mass fraction of plastizer (IX5P) (%) and (b) of styrene-butadiene random copolymer and ma.ss fraction of styrene...

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