Polymer, branched Graft

Intentional hranching may improve the properties of the product polymer through grafting. A graft copolymer can he obtained by creating active sites on the polymer backbone. The addition of a different monomer then reacts at the active site and forms a branch. For example, polyethylene irradiated with gamma rays and then exposed to a reactive monomer, such as acrylonitrile, produces a polyethylene-polymer with acrylonitrile branches ... 

A copolymer in which chains or branches of one polymer are grafted on to the main chain of the other polymer. See Block Copolymer and Heveaplus. 

The completely cationic synthesis of comb or graft copolymers have yet to be realized [103]. However, numerous backbone polymers, branches and macromonomers have been prepared separately via cationic polymerization and these have been combined with other grafting and polymerization processes to prepare (co)polymers that cannot easily be prepared otherwise [103]. 

One method is to measure chain-transfer coefficients with low-MW analogues of the polymer. Thus Gilchrist (140) measured the rate at which 14C labelled decane was incorporated into polyethylene in the free-radical polymerization, and hence obtained an estimate of the transfer coefficient with methylene groups this was in fair agreement with another estimate obtained from the effect of the addition of fractions of linear polyethylene on the Mn of the branched polyethylene, which could be separated from linear polymer plus grafted branched polymer by column extraction. Low MW polymer may be used as a transfer agent Schulz and co-workers (189) obtained chain-transfer coefficients in styrene polymerization from the effect of added low MW polymer on Mn. 

Initiator Limiting y-values of fractional precipitation Weight content of polystyrene (in %) Weight % of graft copolymer compared to total polymer Branching fraction... 

Hydrolysis of Bamboo-Polyacrylonitrile Copolymer. In order to isolate the polymer branches of the graft copolymers and to check the accuracy of the grafting percentages... 

Infrared Spectra of Grafted Bamboo. It has been demonstrated that the occurrence of graft copolymerization of methyl methacrylate onto bamboo can be accertained by the presence of characteristic absorptions of polymer branches in the infrared spectrum (17-19), in addition to the weight increased in bamboo samples. In this study, similar procedures were conducted for the grafting of acrylonitrile. The formation of graft copolymer could easily be detected by the... 

In addition to the free polymer and grafted polymer systems shown here, iSAFT has been developed for branched and associating molecules (Bymaster 2010). For a homogeneous fluid, the iSAFT DFT has the advantage that it reduces to an accurate equation of state (SAFT) (Chapman, 1988 Chapman et al., 1989 Jackson et al., 1988 Mueller and Gubbins, 2001), which is widely applied in academia and industry. 

Figure 1 Macromolecular architectures linear macromolecular chains (homopolymer, block-copolymer and statistical copolymer [14]), brushed-polymer (= linear chains attached to a polymer-chain brush-polymer, brush-copolymers [14]), star polymer [4], mikto-star-polymer [16], arborescent graft polymer (=repeated grafting of linear chains on a macromolecule [17,18]), dendrimer (= maximally branched, regular polymer [15])...

The main feature of polymers is their MMD, which is well known and understood today. However, several other properties in which the breadth of distribution are important and influence polymer behavior (see Figure 1) include physical, the classical chain-length distribution chemical, two or more comonomers are incorporated in different fractions topological, polymer architecture may differ (e.g., linear, branched, grafted, cyclic, star or comb-like, and dendritic) structural, comonomer placement may be random, block, alternating, and so on and functional, distribution of chain functions (e.g., all chain ends or only some carry specific groups). Other properties the polymers may disperse (tacticity and crystallite dimensions) are not of the same general interest or cannot be characterized by solution methods. 

Macromolecules with nonlinear structure form a special group that includes branched, graft, comb, star, cyclic and network type macromolecules. Also, macromolecular assemblies are known, such as polymer blends, interpenetrating polymers, polymer networks, polymer-polymer complexes. The names of these types of macromolecules can be made using qualifiers such as -branch-, -blend-, -i- indicating crosslinked, etc. 

Graft polymers consist of a main polymer chain, the backbone, with one or more side chains attached to it through covalent bonds, the branches. Graft copolymers are comb-shaped polymers where the chemical nature of the backbone and the branches differs. The chemical nature and composition of the backbone and the branches differ in most cases. Branches are usually distributed randomly along the backbone, although recently advances in synthetic methods allowed the preparation of better defined structures.88,90... 

The molecular weight of an alternating copolymer depends on the concentration of polymerizable species, the comonomer charge-transfer complex, which in turn depends on the reaction temperature. At elevated temperatures, the copolymerization rate is rapid and the molecular weight of the alternating copolymer is low. When the polymerization is carried out under those conditions in the presence of a polymer, the grafted alternating copolymer is present as multiple short branches. 

New applications have been suggested to highlight the features of the grafted polymer branches. 

S. Tsuneda, K. Saito, S. Furusaki, T. Sugo and I. Ishigaki, Water/Acetone Permeability of Porous Hollow-Fiber Membrane Containing Diethylamino Groups on the Grafted Polymer Branches, J. Membrane Sci., 71 (1992) 1. 

Grafting is the branching of one type of polymer chain (graft) from another type of polymer chain (backbone), as shown in Figure 5.1. 

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