Polymeric comb/graft polymers

The anionic polymerization of methacrylates using a silyl ketene acetal initiator has been termed group-transfer polymerization (GTP). First reported by Du Pont researchers in 1983 (100), group-transfer polymerization allows the control of methacrylate molecular stmcture typical of living polymers, but can be conveniendy mn at room temperature and above. The use of GTP to prepare block polymers, comb-graft polymers, loop polymers, star polymers, and functional polymers has been reported (100,101). 

These inerts are mostly polymeric or oligomeric in nature and can be both nonionic and anionic. They have multiple binding / interaction sites to the interface, so that a displacement becomes improbable. Several materials have been made available to the industry [6d,ej. The chemistries range from sulfonic condensates (Morwet) or lignin sul-phonates (Reaxx) to EO-PO-block copolymers (Pluronics), comb graft polymers, acrylate based copolymers or various other block copolymers. 

When the polymeric initiator contains many halogens, there will be many grafted side chains, and the product is called a comb or brush polymer. A variety of polymers can be used as the polymeric initiator, including polymers containing vinyl chloride and 4-chloromethylstyrene units, and halogenated natural and butyl rubbers. Graft copolymers are discussed further in Chaps. 5, 6, and 9. 

The simultaneous hydrosilylation and ring-opening polymerization process provides a powerful method for the construction of a variety of novel polymer networks including comb, block and graft polymers, e.g. 272 (equation 102)271. 

This model was used in dispersion polymerization to predict the size of polymer particles stabilized through grafting on hydrophilic polymers such as PVPo. It provides a reasonable description of, for example, PVPo-stabilized polymerization of styrene in polar solvents. The present model does not apply to other types of dispersion polymerization where grafted comb or block copolymer stabilizers are active. The key controlling parameters in this model are the availability of graft and the minimum and maximum coverage, Qmin and Qmax. 

This review covered recent developments in the synthesis of branched (star, comb, graft, and hyperbranched) polymers by cationic polymerization. It should be noted that although current examples in some areas may be limited, the general synthetic strategies presented could be extended to other monomers, initiating systems etc. Particularly promising areas to obtain materials formerly unavailable by conventional techniques are heteroarm star-block copolymers and hyperbranched polymers. Even without further examples the number and variety of well-defined branched polymers obtained by cationic polymerization should convince the reader that cationic polymerization has become one of the most important methods in branched polymer synthesis in terms of scope, versatility, and utility. 

In the next section, therefore, we review recent studies of simpler cases, i.e., homopoly(macromonomers), star- and comb-shaped polymers, followed by some interesting properties of the graft copolymers to be used as polymeric surfactants, surface modifiers, and compatibilizers for blends. 

Comb or densely grafted polymers are defined as polymers that have at least one polymeric chains per monomer unit of the main chain, and Figure 29 shows examples obtained by metal-catalyzed living radical polymerization. Comb polymers possess physical properties similar to those of star polymers in solution. 

Quinn, J.F. Chaplin, R.P. Davis, T.P. Facile synthesis of comb, star, and graft polymers via reversible addition-fragmentation chain transfer (RAFT) polymerization. J. Polym. Sci. A 2002, 40 (17),... 

Metallocenes or late transition metal catalysts were iiKxeas-ingly utilized over the years for the (co)polymetization of olefins including the synthesis of graft copolymers. In this last case coordination polymerization had to be combined with other polymerization processes to give access to macromonomets. However, only a few examples of coordination homopolymer-ization or copolymerization of macromonomets aimed to design comb-shaped polymers were described in the literature. In the following these examples will be described briefly. 

Group transfer polymerization, first reported by DuPont in 1983 (103), allows the production of methacrylic esters with controlled architectures. This technique uses a silyl ketene acetal initiator to produce block polymers, comb-graft pol3uners, star polymers, and functional polymers (103,104). 

PLA and its random copolymer with glycolide have also been grafted onto poly(vinyl alcohol) to increase hydrophi-licity and manipulate the structure [88]. A novel comb-type PLA was prepared using a depsipeptide-lactide random copolymer having pendant hydroxyl groups as macroinitiator for graft polymerization of LA. The comb-type polymer had a lower Tg, and crystallinity than linear PLA [89]. 

Garti, N. (1998) A new approach to improved stability and controlled release in double emulsions, by the use of graft-comb polymeric amphiphiles. Acta Polymer., 49,606-616. 

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