Polydiene

Anionic polymerization of vinyl monomers can be effected with a variety of organometaUic compounds alkyllithium compounds are the most useful class (1,33—35). A variety of simple alkyllithium compounds are available commercially. Most simple alkyllithium compounds are soluble in hydrocarbon solvents such as hexane and cyclohexane and they can be prepared by reaction of the corresponding alkyl chlorides with lithium metal. Methyllithium [917-54-4] and phenyllithium [591-51-5] are available in diethyl ether and cyclohexane—ether solutions, respectively, because they are not soluble in hydrocarbon solvents vinyllithium [917-57-7] and allyllithium [3052-45-7] are also insoluble in hydrocarbon solutions and can only be prepared in ether solutions (38,39). Hydrocarbon-soluble alkyllithium initiators are used directiy to initiate polymerization of styrene and diene monomers quantitatively one unique aspect of hthium-based initiators in hydrocarbon solution is that elastomeric polydienes with high 1,4-microstmcture are obtained (1,24,33—37). Certain alkyllithium compounds can be purified by recrystallization (ethyllithium), sublimation (ethyllithium, /-butyUithium [594-19-4] isopropyllithium [2417-93-8] or distillation (j -butyUithium) (40,41). Unfortunately, / -butyUithium is noncrystaUine and too high boiling to be purified by distiUation (38). Since methyllithium and phenyllithium are crystalline soUds which are insoluble in hydrocarbon solution, they can be precipitated into these solutions and then redissolved in appropriate polar solvents (42,43). OrganometaUic compounds of other alkaU metals are insoluble in hydrocarbon solution and possess negligible vapor pressures as expected for salt-like compounds. 

Aromatic radical anions, such as lithium naphthalene or sodium naphthalene, are efficient difunctional initiators (eqs. 6,7) (3,20,64). However, the necessity of using polar solvents for their formation and use limits their utility for diene polymerization, since the unique abiUty of lithium to provide high 1,4-polydiene microstmcture is lost in polar media (1,33,34,57,63,64). Consequentiy, a significant research challenge has been to discover a hydrocarbon-soluble dilithium initiator which would initiate the polymerization of styrene and diene monomers to form monomodal a, CO-dianionic polymers at rates which are faster or comparable to the rates of polymerization, ie, to form narrow molecular weight distribution polymers (61,65,66). 

In the early 1950s, Ziegler observed that certain heterogeneous catalysts based on transition metals polymerized ethylene to a linear, high density material at modest pressures and temperatures. Natta showed that these catalysts also could produce highly stereospecific poly-a-olefins, notably isotactic polypropylene, and polydienes. They shared the 1963 Nobel Prize in chemistry for their work. 

RITCHIE, p. D. (Ed.), Vinyl and Allied Polymers, Vol. 1 —Aliphatic Polyolefins and Polydienes Fluoro-olefin Polymers, Iliffe, London (1968)... 

As with most polyolefins and polydienes the presence of copper has a strong adverse effect and most antioxidants are relatively ineffective. In these instances quite good results may be achieved by the use of 1% of a 50 50 phenol alkane-dilauryl thiodiproprionate blend instead of the 0.1-0.2% of antioxidants more commonly used in polypropylene. 

Legge, N.R., Holden, G. and Schroeder, H.E., Thermoplastic elastomers based on polystyrene-polydiene block copolymers. Thermoplastic Elastomers, Hanser Publishers, New York, 1987. 

Modern assignment of polydiene structures is based on nmr results, including both 1H and I3C. A compilation of the pertinent data reported in the literature was published by Yudin l24). 

The aggregation of lithium polydienes is disrupted in ethereal solvents and their studies provide information about the conformation of the active centers. The stability of ethereal solutions of polydiene salts is greatly improved at low temperatures, especially in the presence of salts suppressing their dissociation 126). Under these conditions the cis-isomer is the most abundant in equilibrated THF solutions, although... 

An interesting approach to studies of the effects of coordination on the reactivity of lithium polydienes in hydrocarbon solvents was developed by Erussalimski and his colleagues 151 154 The polymerization of lithium polyisoprene in hexane is accelerated by the addition of TMEDA152), the rate levels off at a value of R = [TMEDA]/[li-thium polyisoprene] of 8, its final value giving the absolute rate constant of propagation of the polyisoprene coordinated with TMEDA, namely 0.17 M7l s at 20 °C. 

Finally it should be stressed that the complexation affects the microstructure of poly dienes. As was shown by Langer I56) small amounts of diamines added to hydrocarbon solutions of polymerizing lithium polydienes modify their structure from mainly 1,4 to a high percentage of vinyl unsaturation, e.g., for an equivalent amount of TMEDA at 0 °C 157) the fraction of the vinyl amounts to about 80%. Even more effective is 1,2-dipiperidinoethane, DIPIP. It produces close to 100% of vinyl units when added in equimolar amount to lithium in a polymerization of butadiene carried out at 5 °C 158 159), but it is slightly less effective in the polymerization of isoprene 160>. 

Polydienes. Polydienes that are modifled with organosilicons have been described and find application as antifoaming and/or deaeration agents for oil field treating of crude oil [170]. 

Atomic oxygen oxidation of polymers has been reported by a few authors (46,50). Experiments were limited to the measurements of weight-loss data and changing of the wetteability (46-48), and only two papers were devoted to the study mechanism of atomic oxygen oxidation of polydienes (49,50). 

The low temperature ene reactions of 4-substituted-l,2,4-triazoline-3,5-diones (RTD) were used to modify polydiene surfaces. Hydrophilic surfaces (contact angles with water of 30-50°) were obtained on polybutadiene, poly-isoprene and styrene-butadiene copolymers by first treating the polymer at room temperature with RTD (R=Ph,... 

Of particular interest to us was to find a method to surface modify elastomers. G. B. Butler and co-workers have demonstrated that 4-substituted-l,2,4-triazoline-3,5-diones, RTDs, readily undergo ene reactions with polydienes at ambient temperatures (13). They found that the solubility and solution properties of the modified... 

This investigation was undertaken to study the important variables in the hydrophilization of polydiene surfaces by ene reaction with triazolinediones (Step 1) followed by neutralization (Step 2) as shown below. These variables included the nature of the... 

Surface Modification. A polydiene film (supported on a microscope slide) was immersed in a stirred, room temperature, RTD-acetonitrile solution of known concentration contained in a large glass-stoppered test tube. After a specific reaction time, the film was removed from the solution, washed with acetonitrile, water, and acetonitrile again, and dried under vacuum (Step 1). Films subsequently treated with base were immersed in aqueous solutions for 5-15 min. They were then washed with water and CH3CN, and vacuum dried (Step 2). Some films were aged in air at room temperature. 

Table II. Contact Angles (H2O) of Treated Polydiene Films3...

When the reaction times for Step 1 are 5 min or longer, the samples severely crack, curl, or dissolve. These results suggest that substantial reaction is occurring in the bulk of the polymer. Significant hydrophilization can occur with reaction times as short as 5 s with RTD concentrations of 0.2-0.5 M. However, 0.002-0.02 M solutions of MeTD or PhTD do not allow sufficient reaction rates for surface hydrophilization at the shorter reaction times. Thus, diffusion of MeTD and PhTD into the polymer must occur readily from the acetonitrile solutions. Acetonitrile was used because it does not swell or dissolve the polymer or RTD-polymer adduct, and the RTDs are soluble and stable in it. This solvent is quite polar (dielectric constant, 38) (25), and this is probably a major factor in the partitioning of the relatively nonpolar RTDs between the polydiene film and the solvent. As noted below, more polar RTDs show less tendency to diffuse into the polymer. 

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