Radical polymerization polymers, solution-based reactions

The very first reported PHOST that is transparent in the DUV was prepared by thermolysis or acidolysis of PBOCST, which is in turn prepared via radical polymerization of the BOCST monomer by 2,2-azobis(butyronitrile) (AIBN), benzoyl peroxide (BPO), or other radical initiators. The BOCST monomer can be prepared by the Wittig reaction on a protected 4-hydroxybenzaldehyde with a rather high yield due to the good stability of the t-BOC group toward a base cata-lyst. " The PBOCST polymer thus obtained is readily converted to PHOST by heating the polymer to 200°C or by treating the polymer with an acid such as acetic acid or HCl in solution. And PBOCST can be synthesized via cationic polymerization in liquid sulfur dioxide. ... 

A major milestone in the history of polymer science was the macromolecular hypothesis by Staudinger [1]. The molecular structure of polymers started to emerge and nowadays, almost 80 years later, a knowledge base of respectable size has been built by the contributions of thousands of researchers. Nevertheless, there are still many aspects of free-radical polymerizations that are not fully understood. The bimolecular free-radical termination reaction is one such example. The first scientific papers dealing in some detail with the kinetics of this reaction, can be traced back to the 40 s when the gel-effect was discovered [2-4]. From subsequent research it became apparent that this reaction has a very low activation energy and is diffusion controlled under almost all circumstances. A major consequence of this diffusion-controlled nature is that the termination rate coefficient kt) is governed by the mobility of macroradicals in solution and is thus dependent upon all parameters that can exert an effect on the mobility of these coils. Consequently, kt is a highly system-specific rate coefficient and benchmark values for this coefficient do not exist. 

The Smith and Ewart-Stockmayer-O Toole treatments [48-50] (see Chapter 4) that are widely used to calculate the average number of free radicals per particle (n) are based on the assumption that the various components of the monomer-swollen latex particles (e.g., monomer, polymer, free radicals, chain transfer agent, etc.) are uniformly distributed within the particle volume. A latex particle in emulsion homopolymerization of styrene involves uniform distribution of monomer and polymer within the particle volume except perhaps for a very thin layer near the particle surface. In the case of free radicals, this uniform distribution would only hold in a stochastic sense. However, as illustrated in Eq. (8.1), free radicals are not distributed uniformly in the latex particles when water-soluble initiators are used to initiate the free radical polymerization. The assumption of uniform distribution of free radicals in the latex particles would be valid only if the particles are very small or chain transfer reactions are the dominate mechanism for producing free radicals. If such a nonuniform free radical distribution hypothesis is accepted, the very basis of the Smith and Ewart-Stockmayer-O Toole methods might be questioned. Despite this potential problem, the Stockmayer-O Toole solutions for the average number of free radicals per particle have been used for kinetic studies of many emulsion polymerization systems. The theories seem to work reasonably well and have been tested extensively with monomers such as styrene. 

Early, in situ radical polymerization was used for the synthesis of poly(methyl methacrylate) (PMMA)-CNT composites [82]. In situ polymerization was performed using the radical initiator 2,2-azobisisobutyronitrile(AIBN). In this reaction, p-bonds in CNTs were initiated by AIBN, and therefore nanotubes could participate in PMMA polymerization to form a strong interface between the CNT and the PMMA matrix. PA6/CNT composites have been prepared by in situ polymerization of e-caprolactam in the presence of pristine and carboxylated CNTs. The e-caprolactam monomer was found to form an electron-transfer complex with CNTs and result in a homogeneous, polymerizable solution. The final composites can be spun into PA6/CNT fibers (Fig. 7) with excellent mechanical and electrical properties [83].This method is also suitable for the fabrication of thermosetting polymer composites with nanofillers. Bauhofer et al. [84] dispersed CNTs in an epoxy solution system based on a bisphenol-A epoxy resin and an amine hardener During nanocomposite curing, electric fields were used to induce the formation of aligned conductive nanotube networks. Recently, the in situ polymerization method... 

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