Branched polymers living

Indeed, cumyl carbocations are known to be effective initiators of IB polymerization, while the p-substituted benzyl cation is expected to react effectively with IB (p-methylstyrene and IB form a nearly ideal copolymerization system ). Severe disparity between the reactivities of the vinyl and cumyl ether groups of the inimer would result in either linear polymers or branched polymers with much lower MW than predicted for an in/mcr-mediated living polymerization. Styrene was subsequently blocked from the tert-chloride chain ends of high-MW DIB, activated by excess TiCU (Scheme 7.2). 

The core first method starts from multifunctional initiators and simultaneously grows all the polymer arms from the central core. The method is not useful in the preparation of model star polymers by anionic polymerization. This is due to the difficulties in preparing pure multifunctional organometallic compounds and because of their limited solubility. Nevertheless, considerable effort has been expended in the preparation of controlled divinyl- and diisopropenylbenzene living cores for anionic initiation. The core first method has recently been used successfully in both cationic and living radical polymerization reactions. Also, multiple initiation sites can be easily created along linear and branched polymers, where site isolation avoids many problems. 

In the 1960 s, several groups of workers recognised that by modification of the Szwarc living polymer procedure of anionic polymerization it would be possible to synthesize polymers of fairly definitely known branched structure, which could be used to test existing theories of the effects of LBC on polymer properties, and a considerable amount of work has been published, which is summarised in Section 8. It may be said that the theories do not come very well out of comparison with experiment, and this work shows up the inadequacy of present understanding of the properties of branched polymers. 

Other synthetic possibilities provided by the living polymer technique may permit syntheses of star-shaped polymers, uniform networks of cross-linked polymers, regular branched polymers, etc. 

Star polymers are branched polymers consisting of several linear chains linked to a central core. The synthesis of star polymers has been the subject of numerous studies since the discovery of living anionic polymerization.7-10... 

MAO or MMAO also effectively activates late-transition metal halide a-olefin polymerization precatalysts such as 2,6- Pr-substituted aryl bulky di-imine Ni(II) dibromides for branched polymers and block copolymers by living polymerization at low temperatures,22 para- and unsubstituted aryl di-imine Ni(II) dibromides for production of linear... 

In some cases, it is necessary to use more than one subscript for the description of distributions in polymerization systems. One of such cases is the modeling of the bivariate distribution of chain length and number of branches resulting from polymerizations involving branched polymers. The extension of the method of moments to bivariate distributions is straightforward. Let us consider the bivariate distribution of live polymer of length n and number of branches ft for the sake of illustration of the method... 

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