Grafting Kinetics of Polymer Chains

Keywords Pancake Mushroom Brush Electrostatic interaction Conformational change Grafting density Chain elasticity Adsorption 

Liu and G. Zhang, QCM-D Studies on Polymer Behavior at Interfaces, SpringerBriefs in Molecular Science, DOI 10.1007/978-3-642-39790-5 3, The Author(s) 2013 

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Another factor that determines the course of preferable grafting in one of the polymer phases is the so-called structural factor. This term implies effects of the chemical stmcture of polymer chains, molecular weight, conformation features, configuration, and mobility of hydrogen atoms in the chains on the reaction kinetics. 

The extent of chain transfer reactions in SI-ATRP could affect the polymerization kinetics and the resulting grafting density of polymers. However, further studies need to be conducted in order to fully understand the role of chain transfer reactions in the SI-ATRP mechanism. 

Molecules grafted to PDMS surface, due to the kinetic hindrance from the grafted chains against the new coming species, usually form brushes of low density. The film thickness is limited by the size of grafted molecule and it can have defects in surface uniformity. In grafting from technique the polymerization starts from the active initiation sites located on the modified surface. The growing species do not suffer from molecular hindrance and a dense layer of polymer chains can be formed. 

The preparation of polymer brushes by controlled radical polymerization from appropriately functionalized polymer chains, surfaces or particles by a grafting from approach has recently attracted a lot of attention.742 743 The advantages of growing a polymer brush directly on a surface include well-defined grafts, when the polymerization kinetics exhibit living character, and stability due to covalent attachment of the polymer chains to the surface. Most work has used ATRP or NMP, though papers on the use of RAFT polymerization in this context also have begun to appear. 

Tethering may be a reversible or an irreversible process. Irreversible grafting is typically accomplished by chemical bonding. The number of grafted chains is controlled by the number of grafting sites and their functionality, and then ultimately by the extent of the chemical reaction. The reaction kinetics may reflect the potential barrier confronting reactive chains which try to penetrate the tethered layer. Reversible grafting is accomplished via the self-assembly of polymeric surfactants and end-functionalized polymers [59]. In this case, the surface density and all other characteristic dimensions of the structure are controlled by thermodynamic equilibrium, albeit with possible kinetic effects. In this instance, the equilibrium condition involves the penalties due to the deformation of tethered chains. 

The mechanism and kinetics of RAFT-SIP were studied by Fukuda et al. [326]. Besides the expected linear increase of the molecular weight of the surface grafted polymer with the monomer conversion, they observed the appearance of a prominent low molar mass fraction which was attributed to a combination reaction of the propagating active chains. 

Any chemical reaction, whether involving the main chain or side groups, results in a change of composition of one or more groups and consequently in the IR spectrum. This makes it possible to study oxidation, thermal degradation, cyclization, grafting, and other reactions of polymers [2,4]. Evaluation of both qualitative and quantitative changes, as well as determination of kinetic constants of the reaction, is possible [2]. 

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