Graft copolymer stabilization

Figure 1. Evolution of hydrogen chloride at 180° C (nitrogen as carrier gas) from suspension PVC (1), suspension FVC + stabilizer (2), ds-l,4-polybuta-diene-PVC (suspension) graft copolymer from monomeric butadiene (Type M) (3), Type M graft copolymer + stabilizer (4), and graft copolymer from cis-1,4-polybutadiene (Type P) (5)...

Block and Graft Copolymer Stabilizers in Dispersion Polymerization. A sterically-stabilized, nonaqueous, polymer dispersion is made simply by heating a solution of a free radical initiator (e.g., azobisisobutyronitrile), an appropriate monomer, and a suitable block or graft copolymer in an organic liquid which is a nonsolvent for the polymer product and acts as a diluent for the dispersion. The block or graft copoly-... 

Fig. 19.10 Schematic illustration of interfacial graft copolymers in polyamide/reactive rubber blends (Note Balanced end group PA (1-amine/chain) forms a mono-graft copolymer. A diamine terminated PA forms di-graft copolymers. The latter can lead to entanglement at interface. Both graft copolymers stabilize and strengthen the blend interface)...

The microemulsion polymerization and copolymerization of amphiphilic monomers and macromonomers can produce the fine polymer latex in the absence of emulsifier [98-100], The surface active block or graft copolymer stabilizes the latex particles. The chemically bound emulsifier (surface active copolymer) onto the particles surface is known to be much more efficient emulsifier than the emulsifier physically adsorbed onto the particle surface and, therefore, very stable and fine polymer latexes are formed. The similar behavior is expected with the transferred emulsifier radicals. For example, the surface-functionalized nanoparticles in the 12 - 20 nm diameter range can be prepared by a one-step or two-step microemulsion copolymerisation process of styrene (and/or divinylbenzene (DVB)) with the polymerisable macromonomer (Fig. 7) [93, 101]. 

Bailey, A.L, Cardenas-Valera, A.E., Doroszkowsi, A., Graft copolymers as stabilizers for oil-in-water emulsions. Part 1. Synthesis of the copolymers and their behaviour as monolayers spread at the air-water and oil-water interfaces. Colloids and Surfaces, v.96, pp.53-67, 1995. 

Figure 9 The schematical representation of dispersion polymerization process, (a) initially homogeneous dispersion medium (b) particle formation and stabilizer adsorption onto the nucleated macroradicals (c) capturing of radicals generated in the continuous medium by the forming particles and monomer diffusion to the forming particles (d) polymerization within the monomer swollen latex particles, (e) latex particle stabilized by steric stabilizer and graft copolymer molecules (f) list of symbols.

The success of the multifunctional initiators in the preparation of block and graft copolymers depends critically on the kinetics and mechanism of radical production. In particular, the initiator efficiency, the susceptibility to and mechanism of transfer to initiator, and the relative stability of the various radical generating functions. Each of these factors has a substantial influence on the nature and homogeneity of the polymer formed. Features of the kinetics of polymerizations initiated by multifunctional initiators have been modeled by O Driscoll and Bevington 64 and Choi and Lei.265... 

Such functionality can also be of great practical importance since functional initiators, transfer agents, etc. are applied to prepare end-functional polymers (see Section 7.5) or block or graft copolymers (Section 7.6). In these cases the need to maximize the fraction of chains that contain the reactive or other desired functionality is obvious. However, there are also well-documented cases where weak links formed by initiation, termination, or abnormal propagation processes impair the thermal or photochemical stability of polymers. 

Kennedy and co-workers 2 117) used the changing effect of the initiation ability of the Lewis acids according to Eq. (17) and the termination tendency of the anion formed according to Eq. (18) in order to obtain telechelic polymers , block copolymers and graft copolymers in a controlled manner. Quantum chemical calculations provide the possibility to discuss structural influences which work on the equilibrium Eq. (19) and therefore on the stability of the two adjacent ions. 

It should be pointed out that the addition of substances, which could improve the biocompatibility of sol-gel processing and the functional characteristics of the silica matrix, is practiced rather widely. Polyethylene glycol) is one of such additives [110— 113]. Enzyme stabilization was favored by formation of polyelectrolyte complexes with polymers. For example, an increase in the lactate oxidase and glycolate oxidase activity and lifetime took place when they were combined with poly(N-vinylimida-zole) and poly(ethyleneimine), respectively, prior to their immobilization [87,114]. To improve the functional efficiency of entrapped horseradish peroxidase, a graft copolymer of polyvinylimidazole and polyvinylpyridine was added [115,116]. As shown in Refs. [117,118], the denaturation of calcium-binding proteins, cod III parvalbumin and oncomodulin, in the course of sol-gel processing could be decreased by complexation with calcium cations. 

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