Molecular weights of polybutadiene

Chains of polybutadiene were trapped in the network formed by cooling a butadiene-styrene copolymer until phase separation occurred for the styrene, effectively crosslinking the copolymer. At 25°C the loss modulus shows a maximum which is associated with the free chains. This maximum occurst at the following frequencies for the indicated molecular weights of polybutadiene ... 

Using Alfin catalysts, butadiene polymers were already obtained in the 1940s. The Alfin catalytic system consists of three components (formed in statu nascendi from alkyl chloride, metallic sodium, alcohol and olefin) sodium salt of secondary alcohol (e.g. sodium isopropoxide), alkenylsodium (e.g. allyl-sodium) and finely dispersed sodium chloride (the name Alfin originates from a/cohol + olefin) [2,3], Since the molecular weight of polybutadiene obtained with Alfin catalysts is very high (it can reach a value of a few millions), 1,4-dihydronaphthalene is often added to the polymerisation system for the regulation of molecular weight [1],... 

Fig. 1.6. Dependence of molecular weight of polybutadiene and the monomer concentration 97). H202 (40% in H20) 5 g...

Effect of polymerization variables on molecular weight of polybutadiene from catalyst Co(acac)3/AlEt2Cl/H2 0 [168],... 

Effect of thiophene concentration on molecular weight of polybutadiene from catalyst CoClj/AICI3/thiophene [172] [Co] = 0.3X 10" molel AICI3. Thiophene = 0.34 x 10" mole 1 [M] =1.5 mole 1 ... 

Table 3 Influence of alkylaluminum compounds on the microstructure and molecular weight of polybutadiene afforded by NdV/ BuCl [63]...

Table 2.7 shows the maximum molecular weights of polybutadiene attainable at different polymerization temperatures, prior to gelation, expressed as the critical weight-average chain length, x, of the primary chains at the gel point. 

According to the mass process, polybutadiene rubber is dissolved in the mixed solution of styrene and acrylonitrile monomers, and then the reaction proceeds to prepare the ABS resin. For polybutadiene rubber, the method for grinding and then adding the rubber is utihzed. Contrary to the emulsion process, the particles of polybutadiene rubber are not present before the reaction, and therefore, the shape and distribution of particles appear to be different from those of the emulsion process. The molecular weight of polybutadiene rubber to be used is about 200,000, with the cis-1,4 ratio being about 40%. The amoimt of polybutadiene rubber used should be kept to 20% due to the problem related to a viscosity of polymerization solution. 

Carbon Cha.in Backbone Polymers. These polymers may be represented by (4) and considered derivatives of polyethylene, where n is the degree of polymeriza tion and R is (an alkyl group or) a functional group hydrogen (polyethylene), methyl (polypropylene), carboxyl (poly(acryhc acid)), chlorine (poly(vinyl chloride)), phenyl (polystyrene) hydroxyl (poly(vinyl alcohol)), ester (poly(vinyl acetate)), nitrile (polyacrylonitrile), vinyl (polybutadiene), etc. The functional groups and the molecular weight of the polymers, control thek properties which vary in hydrophobicity, solubiUty characteristics, glass-transition temperature, and crystallinity. 

The particle size of the dispersed phase depends upon the viscosity of the elastomer-monomer solution. Preferably the molecular weight of the polybutadiene elastomer should be around 2 x 10 and should have reasonable branching to reduce cold flow. Furthermore, the microstructure of the elastomer provides an important contribution toward the low-temperature impact behavior of the final product. It should also be emphasized that the use of EPDM rubber [136] or acrylate rubber [137] may provide improved weatherability. It has been observed that with an increase in agitator speed the mean diameter of the dispersed phase (D) decreases, which subsequently levels out at high shear [138-141]. However, reagglomeration may occur in the case of bulk... 

The crude product from the above reaction mixt was fractionated into a distilled product (bp 200°/0.3 Torr) with an average molecular weight of 514 and a residue with an average molecular weight of 940. These were evaluated as catalysts and compared to prior art ferrocenes in a standard carboxy-terminated polybutadiene formula cured with MAPO. The results are shown in Table 31... 

Polybutadiene-polydimethylsiloxane segmented copolymers were prepared by the reaction of epoxy-terminated PDMS and carboxy-terminated polybutadienes, in refluxing toluene under catalytic action of potassium hydroxide 243). Molecular weights of the copolymers obtained were usually in the low range. No other characterization data were available. 

Morphology. Observations with the light microscope, under polarized light, showed that the end blocks in the case of both types of polymers crystallized in the form of the usual spheru-lites, but not as well as the analogous homopolymer, H2-l,4-polybutadiene. The formation of the spherulites was improved with increasing end-block content and/or higher molecular weight of the end blocks. 

Even if a same azide is used as the sensitizer, such properties of the photoresist as photosensitivity, photocurability and adhesion to base surfaces differ depending on the property of the base polymer. That is, degree of cyclization, content of the unsaturated groups and molecular weight of the polymer affect the photoresist properties mentioned above. H.L.Hunter et al. have discussed the dependence of the sensitivity of polybutadiene photoresist on the polymer structure, and have concluded that a higher sensitivity was obtained when 1,2- and 3, -isomers were used( 7.) ... 

The degree of polymerization intervals of interest are, therefore, comprised of distinct regions determined by the initial molecular weight of the 1,2-polybutadiene, n. 

Figure 1. Stress relaxation curves for three different extension ratios. Uncross-linked high-vinyl polybutadiene with a weight average molecular weight of 2 million and a reference temperature of 283 K. G is the apparent rubber elasticity modulus calculated from classical affine theory. (Solid line is data from Ref. 1).

The effect of cross-linking in the unstrained state is shown in Figure 4 for a high-vinyl polybutadiene with a molecular weight of... 

Figures 1 and 2 show the dependence of polymer microstructure on the molecular weight of the polymer and therefore on the initial initiator concentration. The polymerization temperature also has an effect on the microstructure as can be seen in Figure 3 for polybutadiene. The overall heat activation energy leading to 1,2 addition is greater than that leading to 1,4 addition.2 IZ In summary, the stereochemistry of polymerization of butadiene and isoprene is sensitive to initiator level, polymerization temperature and solvent. The initiator structure (i.e., organic moiety of the initiator), the monomer concentration and conversion have essentially no effect on polymer microstructure.

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