Polymerization results

LB Films of Polymerizable Amphiphiles. Stxidies of LB films of polymerizable amphiphiles include simple olefinic amphiphiles, conjugated double bonds, dienes, and diacetylenes (4). In general, a monomeric ampbipbile can be spread and polymerization can be induced either at tbe air—water interface or after transfer to a soHd substrate. Tbe former polymerization results in a rigid layer tbat is difficult to transfer. 

The prolonged polymerization resulted in the formation of a sufficiently high molecu-... 

Carbocations as reactive intermediates play an essential role in organic reactions and have been thoroughly researched 102, l0J). The individual quality of the cationic polymerization results from the reproduction of the cationic reactive intermediate in every propagation step during the addition of monomers. 

The primary attack of an electrophile takes place during both the electrophilic addition to olefines and the cationic polymerization resulting in the formation of a car-benium ion R—C+H—CH3 as a reactive intermediate from the olefine or monomer R—CH=CH2 72) (Eq. 16). In the simplest of cases, the electrophile is a proton. 

As the polymerization reaction proceeds, scosity of the system increases, retarding the translational and/ or segmental diffusion of propagating polymer radicals. Bimolecular termination reactions subsequently become diffusion controlled. A reduction in termination results in an increase in free radical population, thus providing more sites for monomer incorporation. The gel effect is assumed not to affect the propagation rate constant since a macroradical can continue to react with the smaller, more mobile monomer molecule. Thus, an increase in the overall rate of polymerization and average degree of polymerization results. 

This feature of the interfacial preparation of poIy(iminocarbon-ates) has an important consequence for the synthesis of copolymers if the dicyanate component is structurally different from the diphenol, partial hydrolysis of the dicyanate will lead to the presence of two structurally different diphenol components that will compete for the reaction with the remaining dicyanate. The interfacial copolymerization will therefore result in a random copolymer. On the other hand, during solution polymerization no hydrolysis can occur. Since the dicyanates can only react with diphenols and vice versa, solution polymerization results in the formation of a strictly alternating copolymer. 

Yin et al. [73,74] prepared new microgel star amphiphiles and stndied the compression behavior at the air-water interface. Particles were prepared in a two-step process. First, the gel core was synthesized by copolymerization of styrene and divinylbenzene in diox-ane using benzoylperoxide as initiator. Microgel particles 20 run in diameter were obtained. Second, the gel core was grafted with acrylic or methacryUc acid by free radical polymerization, resulting in amphiphilic polymer particles. These particles were spread from a dimethylformamide/chloroform (1 4) solution at the air-water interface. tt-A cnrves indicated low compressibility above lOmNm and collapse pressnres larger than 40 mNm With increase of the hydrophilic component, the molecnlar area of the polymer and the collapse pressure increased. 

Polymerization results for different end capped PDMS stabilizers... 

Table 1. Solution polymerization results for butadiene usir cobalt(II) pyridyl bis(imine) complexes. Polymerization conditions [l,3-butadiaie]= 1 mol/L [Cal.] = 2.00 x 10" mol/L ...

A challenging goal in this field, particularly from the synthetic point of view, is the development of general AB polymerization methods that achieve control over DB and narrow MWDs. Experimental results and theoretical studies mentioned above suggest that the SCV(C)P from surfaces, which are functionahzed with monolayers of initiators, permit a controlled polymerization, resulting structural characteristics (molecular weight averages, DB) of hyperbranched polymers. In particular, it is expected that the use of polyfunctional initiators with a different number of initiator functionahty, copolymerization, and slow monomer addition techniques lead to control the molecular parameters. 

The inhibitors more commonly used are molecules which in one way or another react with active chain radicals to yield product radicals of low reactivity. The classic example is benzoquinone. As little as 0.01 percent causes virtual total suppression of polymerization of styrene or other monomers. This is true of both thermal and initiated polymerizations. Results of Foord for the inhibition of thermal polymerization of styrene by benzoquinone are shown in Fig. 22. The... 

Fig. 100.—Network activity, r/RT ol — 1 o ) — veIVy of GR-S cross-linked with persulfate plotted against the effective degree of cross-linking. The values of yn indicated represent primary degrees of polymerization. (Results of Bardwell and Winkler. )...

Like many homogeneously catalyzed reactions, the overall cycle (or cycles) in these polymerization reactions probably contains too many steps to be easily analyzed by any single approach. Both kinetics and model compound studies have thrown light on some of the steps. However, as indicated above, many of the model compounds isolated from the reactions of primary silanes with metallocene alkyls and hydrides are too unreactive to explain the polymerization results. 

By using a transition metal chloride catalyst and an iodine modified cocatalyst, ring-opening polymerization of C5 and C8 monocyclic olefins is controlled to prepare either cis polymers or trans products that are crystallizable. In copolymerization, the cis/trans units in the copolymers are regulated by adjusting the C5/C8 olefin monomer ratio. As the comonomer is increased, the copolymer becomes less crystalline and then completely amorphous at equal amounts of cis/trans units. Polymerization results are reported from WC16 and MoCl5 catalysts. 

C for 20 hours. A catalyst system based on copper bromide, an amine, and oxygen was employed in these polymerizations, resulting in PPO yields as high as 83% and M s as high as 1.7 x 104 g/mol. 

Table 3 Ethylene polymerization results with Zr-FI catalysts 26-30...

Table 4 Ethylene polymerization results for Zr-FI catalysts 1 and 31 with MAO or MAO/tri-methylaluminum (TMA)... 

Table 5 Higher a-olefin polymerization results for Ti-FI catalyst 2 with i-Bu3Al/Ph3CB(C6F5)4 ... 

Table 6 Ethylene polymerization results with Ti-FI catalysts 40 and 44 17... 

Table 1 Selected polymerization results obtained with the catalysts 1 1 after MAO or borate activation...

There has been little insight into potential decomposition pathways for the Ni(II) system due to sparse experimental evidence. Polymerization results with catalysts bearing different alkyl and fluorinated substituents have suggested that a C-H activation process analogous to that occuring with the Pd(II) catalysts is unlikely with Ni(TT) [28], Instead, side reactions between Ni and the aluminum coactivator, present as it is in such large excess, have been implicated. The formation of nickel dialkyl species and their subsequent reductive elimination to Ni(0) is one possible deactivation mechanism [68]. 

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