Poly-cis-isoprene

Al-Tl Catalyst for cis-1,4-Poly isoprene. Of the many catalysts that polymerize isoprene, four have attained commercial importance. One is a coordination catalyst based on an aluminum alkyl and a vanadium salt which produces />mf-l,4-polyisoprene. A second is a lithium alkyl which produces 90% j -l,4-p olyis oprene. Very high (99%) cis- 1,4-polyisoprene is produced with coordination catalysts consisting of a combination of titanium tetrachloride, TiCl4, plus a trialkylaluminum, R3A1, or a combination ofTiCl4 with an alane (aluminum hydride derivative) (86—88). 

Such differences in structure can have a profound effect on the physical properties of a polymer. Thus natural rubber, which comprises cis-1,4-poly(isoprene), is a soft rubbery material at room temperature, whereas guttapercha, which comprises the corresponding ftms-isomer, is semi-crystalline and hard. The method of polymerisation determines the isomeric form of the polymer. 

Comparison of results from the polymerizations of butadiene and isoprene with an AlR3-TiCl4 catalyst system reveals some interesting features. The 1 to 1 Al/Ti ratio yields a cis-l,4-polyisoprene and a mns-1,4-polybutadiene. Kinetic studies have, in fact, indicated that in both cases, the rate of polymerization at this ratio is proportional to the first power of the monomer pressure 6, 21). At lower Al/Ti ratios, higher trans-l,A- content is observed in both polyisoprene and polybutadiene. At comparable Al/Ti ratios, lower temperatures increase the trans-l,A-structure in both polymers. Although essentially all-cis-1,4-poly isoprene and all-... 

The chemiluminescence emission at 25-60° C was measured from films of cis-1,4-polybutadiene, 1,2-polybutadiene, and trans-polypentenamer. The polymers were autoxidized previously in air 100°C, or allowed to react with singlet molecular oxygen in solution, and then cast into films. Values of ft (or kaCOz -> 302)/K(102 + polymer -> products)) were determined in benzene for cis-1,4-polybutadiene and cis-1,4-poly-isoprene, and for model compounds cis-3-hexene and cis-3-meihyl-3-hexene by independent methods. The chemiluminescence emission from irradiated films of the polymers containing a dye sensitizer showed a complicated time dependence, and the results depended on the length of irradiation. 

Table 7-5. Permeability Coefficient P, Diffusion Coefficient D, and Solubility Coefficient S of Various Gases in Vulcanized cis-1,4-Poly isoprene) at 25° C...

Physical property Physical units cis-1,4- Poly(isoprenes) Styrene/butadiene copolymers Poly(urethanes) ... 

Several other elastic materials may be made by copolymerising one of the above monomers with lesser amounts of one or more monomers. Notable amongst these are SBR, a copolymer of butadiene and styrene, and nitrile rubber (NBR), a copolymer of butadiene and acrylonitrile. The natural rubber molecule is structurally a cis-1,4-poly isoprene so that it is convenient to consider natural rubber in this chapter. Some idea of the relative importance of these materials may be gauged from the data in Table 11.14. 

Synthetic cis- 1,4-poly(isoprene) (ANSI/ ASTM, BS, lUPAC) see also CPI, PIP Insect resistant treated Insoluble sulfur (WTR)... 

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