Polymerization pathway

Surprisingly, linalyl acetate (R = OAc) fails to undergo reduction under these conditions instead, it rapidly decomposes through cyclization and polymerization pathways.205 The same reaction conditions transform geranyl p-tolyl sulfone (R = S02C6H4Me-/ ) into a mixture of 7% reduced and 93% cyclized products within 20 hours, whereas geranyl acetate (R = OAc) gives only a 20% yield of cyclized and no reduced product (Eq. 95) 205... 

Ajayaghosh A, Francis R (1999) A xanthate-derived photoinitiator that recognizes and controls the free radical polymerization pathways of methyl methacrylate and styrene. J Am Chem Soc 121 6599-6606... 

The synthesis of the j>. newington O-antigenic polysaccharide by the chemical polymerization pathway will be discussed as an example (J 6 J 7) The first and the most difficult task consists in the preparation of the monomer itself, i. e. , the properly functionalized, oligosaccharide repeating unit. The most usual approach is to introduce the required functions into the already-existing oligosaccharide molecule. 

In the field of high thermomechanical performance polymers, linear and thermosetting systems offer complementary properties. Among the thermosetting materials, BMIs and BNIs have been extensively studied and are now commercially available. In this chapter, firstly the main preparation and characterization methods are reviewed, and then the chemistry of the polymerization processes is discussed for both families. For the BMIs, due to the electrophilic character of their double bond, different polymerization pathways have been published, which is not the case for BNIs. Special attention has been paid to thermal polymerization which has already been used in industrial achievements however, on the other hand, the structure of these materials has been considered for the purpose of establishing relationships between processability, stability and thermomechanical properties. 

The possibilities of amino acid thioesters in peptide synthesis have been demonstrated very early as well as the effect of carbon dioxide supporting the involvement of N-carboxyanhydrides in the hydrolysis and polymerization pathways [127,176,177]. Aminothioacids can also be converted into NCAs [152,178,179] but they can, in addition, be activated by oxidation into disulfides which are much more reactive [151]. 

The goal of this review is to summarize the results obtained in our laboratory regarding the concentrated emulsion polymerization pathway. This method was used to prepare polymers, copolymers, composites, tough polymers, as well as polymer supported catalysts. 

Concentrated Emulsion Polymerization Pathway to Hydrophobic and Hydrophilic Microsponge Molecular Reservoirs (44)... 

To draw the reaction model, separate experiments were performed with the decomposition products of cellulose. Cellulose was reacted in 300 C of hot-compressed water with 5 wt% of Na2C03 (Run 4) to obtain the water-soluble products and the oily products, which were easily separated by decantation. Then both were gasified with the nickel catalyst. As shown in Table 2, the water-soluble products could be gasified to H2, CO2 and CH4, while the oily, polymerized products could not be gasified. This result supports the competition of gasification pathway to polymerization pathway. The following total reaction model can be drawn. 

A combination of other polymerization pathways also results in some hyperbranched structures. Multifunctional hydroxyl groups in polyglycerol with hyperbranched structure, prepared by anionic polymerization of glycidol, were esterified with 2-bro-moisobutyroyl bromide and then employed as a hyperbranched multifunctional macroinitiator for the copper-catalyzed radical polymerization of MA to give products with 45—55 poly(MA) arms.449... 

The oxidative coupling uses a copper-catalysed system and a base, usually an aliphatic or heterocyclic amine, and oxygen as the oxidizing agent. In broad terms, free-radical processes are involved to explain the polymerization pathway which involves formation of the phenoxide radical, and coupling of two radicals through the attack by an oxygen-centred radical at the para position of another phenolic molecule (Scheme 25). 

SCHEME 25. Polymerization pathway of phenols under oxidation conditions... 

Norbornene monomers can be (co-)polymerized by a variety of polymerization pathways, offering significant diversity. 

Figure 2. The phase diagram for vinyl chlorlde/PVC/poly (butyl acrylate) mixtures showing polymerization pathways AB and CD.

Figure 2. Polymerization pathway of aqueous silicates according to Iler (2). Stages of growth recognized by Iler polymerization of monomer to form particles, growth of particles, and linking of particles together into branched chains, networks, and, finally, gels. (Reproduced with permission from reference 2. Copyright 1978.)...

Scheme 4.7-18 Different polymerization pathways for the coplymerization of ethene and 1,5-hexadiene using the zirconocene precursor 19 P = polymer chain [94].

The proposed polymerization pathway differs fundamentally from the coordination-insertion mechanism involving metal complexes, see Fig. 3.7 [5, 38]. Indeed, the nucleophilic catalyst only activates the monomer toward ring opening, whereas the metal complex activates the monomer, initiates the polymerization, and remains bound to the growing chain. The polymerization mechanism of a superbase or thiourea-amine catalyzed ROP will be discussed in more detail below. 

Figure 5. Polymerization pathway via ring-opening and vinyl addition.

A detailed simulation of the way in which the local interior environment of the channel of DCA induces direct asymmetric induction in the polymerization pathway of 2-methyl-trans-l,3-pentadiene was reported [17]. 

In general, electrochemically prepared conducting polymers (e.g., polypyrrole, polythiophene, and polyaniline, etc.) imdergo a. similar polymerization pathway. Figure 13.5 describes the electrochemical polymerization pathway for pyrrole [26,27]. 

Scheme 7.1 Radical/anionic polymerization pathways for PPV preparation.

Saturated solutions of acetylene in water were irradiated for several hours by a 125-W UV lamp [83]. Photopolymerization was followed by UV-vis spectroscopy and different polymerization pathways involving diacetylene, vinylacetylene, and cumulene formation were discussed. The evaporation of the solvent from the resulting milky white solution of photopolymer resulted in the isolation of a cream-colored powder of acetylene photopolymer that was insoluble in common solvents. This photopolymer was characterized by elemental analysis, FTIR, and UV spectroscopy and was found to incorporate about 18% oxygen (probably from water) in the form of ketone, carboxyl, hydroxyl, and ether derivatives. FTIR spectroscopy revealed the structural similarity of acetylene photopolymer and a linear PA oxi-... 

Figure 1.15 Polymerization pathways for the formation of (a) sols and (b) three-dimensional gel networks in the aqueous silica system. (From ller. )...

In conclusion, the intermolecular acylpalladation of alkenes is, so far, limited to specific substrates, and this is mainly due to certain strict requirements, that is, (i) acylpalladation faster than decarbonylation and (ii) a termination step faster than polymeric pathway, and yet slower than acylpalladion itself. Attempts to control this reaction by... 

Polyamide 6 [25,26], epoxy [27,28], poly(methylmethacrylate) [29,30], poly( -capro-lactone) [31], polyurethane [32], polyimide [33,34], and polyamide 12 [35] were prepared via polymerization pathway. 

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