Polyisoprene viscosity

Figure 2.15 Log of viscosity enhancement factor versus parameter measuring branch length for polyisoprene, [Data from W. W. Graessley, T. Masuda, J. E. I. Roovers, and N. Hadjichristidis, Afacromo/ecu/ej 9 127 (1976).]...

Specifications for soHd i7j -l,4-polyisoprenes are shown in Table 5 and include analyses for volatile matter, extractables, ash, and Mooney viscosity at 100°C. Standard method ASTM D1416 includes chemical analysis methods for volatile matter, extractables, and total ash, while ASTM D1646 includes Mooney viscosity (82). The Monsanto rheometer data for vulcanizates prepared by a standard recipe may also be specified. This formulation for vulcanizate (ASTM D3403) is mixed in a Banbury mixer in two passes with all but sulfur and accelerator added in first pass ... 

Other polymers used in the PSA industry include synthetic polyisoprenes and polybutadienes, styrene-butadiene rubbers, butadiene-acrylonitrile rubbers, polychloroprenes, and some polyisobutylenes. With the exception of pure polyisobutylenes, these polymer backbones retain some unsaturation, which makes them susceptible to oxidation and UV degradation. The rubbers require compounding with tackifiers and, if desired, plasticizers or oils to make them tacky. To improve performance and to make them more processible, diene-based polymers are typically compounded with additional stabilizers, chemical crosslinkers, and solvents for coating. Emulsion polymerized styrene butadiene rubbers (SBRs) are a common basis for PSA formulation [121]. The tackified SBR PSAs show improved cohesive strength as the Mooney viscosity and percent bound styrene in the rubber increases. The peel performance typically is best with 24—40% bound styrene in the rubber. To increase adhesion to polar surfaces, carboxylated SBRs have been used for PSA formulation. Blends of SBR and natural rubber are commonly used to improve long-term stability of the adhesives. 

Natural latex is polydisperse (size of individual particles may vary from 0.01 to 5 p.m). Flowever, synthetic latex has a relatively narrow particle size, and therefore the viscosity at a given rubber content is higher in synthetic rubber (polyisoprene) solutions. The average molecular weight is typically about I million g/mol, although it depends on the gel content. 

Fig. 2 a, b. Dependence of the maximum Newton viscosity (t/0) (a) and swelling ratio of the extrudate (D) (b) on the molecular mass of cis-1,4-polyisoprene, unfilled and filled to 33% by mass. Filler 1 — not 2 — CaC03 with specific surface areas 2-3 m2/g 3 — ash PM —15 with specific surface areas 12-18m2/g 4 — ash PM-100 with specific surface areas 90-100 m2/g... 

The heat of dissociation in hexane solution of lithium polyisoprene, erroneously assumed to be dimeric, was reported in a 1984 review 71) to be 154.7 KJ/mole. This value, taken from the paperl05> published in 1964 by one of its authors, was based on a viscometric study. The reported viscometric data were shown i06) to yield greatly divergent AH values, depending on what value of a, the exponent relating the viscosity p of a concentrated polymer solution to DPW of the polymer (q DP ), is used in calculation. As shown by a recent compilation 1071 the experimental a values vary from 3.3 to 3.5, and another recent paper 108) reports its variation from 3.14 to 4. Even a minute variation of oe results in an enormous change of the computed AH, namely from 104.5 KJ/mole for oe = 3.38 to 209 KJ/mole for oe = 3.42. Hence, the AH = 154.7 KJ/mole, computed for a = 3.40, is meaningless. For the same reasons the value of 99.5 KJ/mole for the dissociation of the dimeric lithium polystyrene reported in the same review and obtained by the viscometric procedure is without foundation. 

The same approach supposedly demonstrated the dimeric nature of lithium polyisoprene and polybutadiene. A tenfold decrease of viscosity was claimed 97), contrary to the findings of Worsfold and By water 115) who reported a 15 fold decrease of viscosity for lithium polyisoprene on protonation of their hydrocarbon solutions. 

With this choice of j8, the theoretical picture presented in this section is consistent, for example, with the range in MJM (from about 2 to about 20) explored by the polyisoprene (PI) data set of Fetters et al. [5] using a single value of Mg of 5000 g mol" The viscosities of these melts cover five decades in magnitude yet the current theory, together with values for Gq and Tg consistent with data on linear PI predicts the entire range of viscoelastic spectra (see Fig. 9). 

When the temperature is increased above the 0-temperature the enhanced local viscosity at higher concentration drops. The variation is the same as observed for the macroscopic viscosity [329]. In [328] polyisoprene (PI) and PS in different solvents have also been investigated and the authors observe that the slopes of the concentration dependence of the scaled local viscosities for PS and PI have a ratio of 1.7, which matches the value of the concentration ratio either on the Kuhn length (1.6) or the persistence length (1.7) for the two polymers. 

The general correlations of structure and properties of homopolymers are summarized in Table 2.13. Some experiments which demonstrate the influence of the molecular weight or the structure on selected properties of polymers are described in Examples 3-6 (degree of polymerization of polystyrene and solution viscosity), 3-15, 3-21, 3-31 (stereoregularity of polyisoprene resp. polystyrene), 4-7 and 5-11 (influence of crosslinking) or Sects. 4.1.1 and 4.1.2 (stiffness of the main chain of aliphatic and aromatic polyesters and polyamides). 

It is apparent from these data that all of the polymers, including butadiene, exhibit an association as dimers, and that there is no reason to expect any higher states of association for polyisoprene or polybutadiene. This is confirmed not only by the viscosity data on the active vs. terminated "capped" polymers, but also by the fact that there was no significant increase in viscosity when the polystyryl lithium was "capped" by butadiene or isoprene, i.e., all three types of chain ends are associated in the same way, as dimers. 

Bueche et al. (1952) derived that the coefficient for self-diffusion of poly(n-butyl acrylate) is inversely proportional to the bulk viscosity of this polymer. Also in the natural rubber (polyisoprene) diffusion system a clear connection appears to exist between diffusion coefficient and bulk viscosity. In general the following expression may be used as a good approximation ... 

The procedures used in polymer product isolation and evaluation were the same as presented earlier (13). Basically, the dried polymers were extracted with a 50 50 by volume mixture of hexane and isopropyl alcohol to remove low molecular-weight material, herein called extractables. Physical properties such as inherent viscosity, % gel, and polymer microstructure were determined on the solid polyisoprene residue. 

Physical properties such as inherent viscosity, % gel, and % cis-1,4 content of the polyisoprenes produced with the above catalysts are given in Table I. The differences from one system to another are small and do not suggest any particular trend. 

The physical properties of polyisoprenes produced with separated i-Bu3Al solids and their modified versions are listed in Table VI. These systems appear to give polymers with somewhat higher inherent viscosities than observed before with unseparated catalysts. No significant changes in micro-structure of the polymers were noticed between the various systems. 

Aminoalkylation of polyisoprene as viscosity index improvers for crankcase oil using (acetylacetonate)-dicarbonylrhodium with carbon monoxide and hydrogen with aminopropyl morpholine was used by Coolbaugh [3] to prepare oil dispersants. 

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