Polyisoprene cyclohexane

Tong, Z. Einaga, Y. Fujita, H., "Phase Equilibrium in Polymer + Polymer + Solvent Ternary Systems. III. Polystyrene + Polyisoprene + Cyclohexane System Revisited," Polym. J., 19, 965 (1987). 

T01 Tong, Z., Einaga, Y., Miyashita, H., and Fujita, H., Phase equilibrium in polymer + polymer + solvent ternary systems. 2. Phase diagram of polystyrene + polyisoprene + cyclohexane, Macroffro/ecw/ex, 20, 1888, 1987. 

HON Hong, J.-S. and Lee, D C., Phase equilibrium in poly(a-methylstyrene)/c/s-polyisoprene/cyclohexane system, Pollimo, 16, 470, 1992. 

To confirm these phenomena the UV absorption spectra of lithium polyisoprene of high and of low molecular weights dissolved in cyclohexane were re-examined over... 

Fig. 18. Microstructure of polyisoprene obtained in cyclohexane at 30 °C with sec. BuLi as initiator. Conversion 10% (D. J. Worsfold, S. Bywater, Ref. 12S )...

Fig. 1.24 Two examples of frequency-depen-dent relaxation times - 7"i is plotted as a function of the proton resonance frequency V = ou/2 JI, which was obtained from measurements at different magnetic fields strengths. Left polyisoprene (PI) melts and solutions of the same samples at 19wt-% concentration in cyclohexane. Numbers indicate the average molecular weight. The difference between the melt and solution increases towards lower magnetic fields strengths, the frequency dependence is more pronounced for melts.

Titanocene (Cp2Ti(C6H2(R1) PB, polyisoprene, SBS in cyclohexane (5 wt.%) Catalyst (di-p-tolyl- Asahi Kase Kogyo 32 (1987)... 

Figure 2. Microstructure of polyisoprene initiated with alkyllithium in cyclohexane...

A change from an aliphatic or aromatic hydrocarbon solvent (cyclohexane, benzene) to a polar solvent (THF) leads to a large increase in trans-1,4 and 3,4 microstructure (58). Organolithium compounds are highly associated sec-butyllithium in benzene or cyclohexane exists as a tetramer, and -butyllithium as a hexamer (64,65). This association in hydrocarbon solvents results pardy in the slow initiation observed between some organolitbiirms and isoprene (66). At low initiator concentrations, the polymerization rate of isoprene in alkyUithium polymerization is proportional to monomer and alkyUithium concentrations (67). 3,4-Polyisoprenes are obtained by modification of the lithium polymerization with ethers, such as the dialky] ethers of ethylene glycol or tertiary amines (68,69). 

The self-diffusion of benzene in PIB [36], cyclohexane in BR [37] and toluene in PIB [38-40] has been investigated by PFG NMR. In addition more recently Schlick and co-workers [41] have measured the self-diffusion of benzene and cyclohexane mixtures in polyisoprene. In the first reported study of this kind, Boss and co-workers [36] measured the self-diffusion coefficients of benzene in polyisoprene at 70.4 °C. The increase in Dself with increasing solvent volume fraction could be described by the Fujita-Doolittle theory which states that the rate of self-diffusion scales with the free volume which in turn increases linearly with temperature. At higher solvent volume fractions the rate of selfdiffusion deviates from the Fujita-Doolittle theory, as the entanglement density decreased below the critical value. 

At the end of polymerization the mixture was treated with an additional 100 ml of cyclohexane solvent to fluidify the medium, 1 ml of 1M acetylacetone in cyclohexane added to stop the reaction, and A-l,3-dimethylbutyl-A -phenyl-p-phenylenediamine (0.02 g) added as an antioxidant. Polyisoprene was then extracted by steam stripping for 30 minutes in the presence of calcium tamolate. Each extraction was then dried for approximately 18 hours in an oven at 50°C under 200 mmHg vacuum for 72 hours. Reaction scoping results are provided in Table 1. 

The polybutadienes and the -1,4-polyisoprenes used in this work were synthesized in house or obtained from commercial sources. The 1,2-polybutadienes were atactic. Blend compositions, prepared by dissolution in cyclohexane, precipitation into methanol, and vacuum drying, are listed by volume in Table II, along with the weight average degree of polymerization of the component. 

Cyclohexane as the mobile phase requires the use of polyisoprene standards, as polystyrene standards are not soluble in this solvent. It should be noted that calibration by polystyrenes results in an overestimation of molar masses by a factor of around 2, compared to the use of polyisoprene standards [10]. It is, therefore, necessary to carry out universal calibration or to convert molar masses using the Mark-Houvink coefficients relative to synthetic or natural polyisoprenes [4,5,8,11,12]. 

If a polymer is easily soluble in a solvent, by convention, the solvent is called a good solvent, and the converse, it is a poor solvent [6], Therefore, a solvent whose 8 value is close to the 8 value of a polymer family is a good solvent for this polymer family. As examples, the 8 value of polystyrene (PS) is about 18, which is closer to the 8 value of 18.6 of tetrahydrofuran (THF) than the 8 value of 16.8 of cyclohexane (CH). Therefore, THF is expected to be a better solvent for PS than CH. For polyisoprene (PIP), the situation is reversed CH is a better solvent than THF. 

In a previous publication 17, we compared the experimental anisotropies for dilute solutions of labeled polyisoprene in hexane and cyclohexane to several theoretical models. These results are shown in Table II. The major conclusions of the previous study are 1) The theoretical models proposed by Hall and Helfand, and by Bendler and Yaris provide good fits to the experimentally measured correlation function for both hexane and cyclohexane. The model suggested by Viovy, et al. does not fit as well as the other two models. 2) Within experimental error, the shape of the correlation function is the same in the two solvents (i.e, the ratio of t2/ti is constant). 3) The time scale of the correlation function decay scales roughly with the solvent viscosity. 

Figure 4. Time-dependent anisotropy for anthracene-labeled polyisoprene in dilute cyclohexane solution. The smooth curve through the data is the best fit to the Bendler-Yaris model(Ti=210 ps, t2=2750 ps, and r(0)=0.243).

The coefficients Xl>X2> etc., are determined from observed variation of X with 2. Very often x increases strongly with polymer concentration, particularly in the case of poor solvents. The systems benzene/polyisobutylene, cyclohexane/polystyrene, and methyl ethyl ketone/natural rubber constitute examples. In some cases, however, x seems to be independent of concentration, as proposed by the original Flory-Huggins theory. These findings mainly concern good solvents some examples are benzene/polyisoprene... 

Points measured values (from lonescu10) for a deuterated polystyrene-polyisoprene copolymer in solution in cyclohexane at 40° C. 

---