Copolymerisation graft copolymers

An important class of copolymers made by chain copolymerisation is graft copolymers, synthesized in order to toughen brittle materials through inclusion of a rubber phase. Examples are the cases of styrenic copolymers called "HIPS" for High-Impact Polystyrene and ABS for Acrylonitrile-Butadiene-Styrene. Both are synthesized in two steps. 

Fig.5 Synthesis of the graft copolymers in two steps (/) copolymerisation of N-iso-propylacrylamide (NIPAM) and glycidylmethacrylate (GMA) or N-acryloylsuccinimide (NASI), and (2) grafting of PEO to the polymer backbone [170]... 

The phenomenon of graft copolymerisation dates back to the year 1933 but graft copolymer was officially defined in 1952 by IUPAC. 

Cross-linked graft-copolymers are prepared in a very simple manner by copolymerisation. In this an unsaturated polymer is dissolved in the monomer that is to be grafted on and the monomer is allowed to polymerise. The double bond of the polymer is incorporated into the growing chain of the polymerising monomer. 

An interesting example of this type of copolymer is the copolymerisation of butadiene and styrene in which first butadiene polymerises giving rise to polybutadiene. The polybutadiene formed then reacts with styrene to yield a graft copolymer as under ... 

Ionic polymerisation is a well-known technique for the preparation of graft copolymers but the fate of these reactions is determined by the reaction conditions. Since the discovery of living polymerisation , (anionic polymerisation) [67] it has become an excellent method for the synthesis of block and graft copolymers. In anionic polymerisation the graft copolymerisation is initiated by the anion generated by the reaction of bases with acidic protons in the polymer chain as shown in Scheme 2. 

The present volume is particularly concerned with the use of the different modes of controlled radical polymerisation for the preparation of copolymers such as random copolymers, linear block copolymers, as well as graft copolymers and star-shaped copolymers. It also presents the combination of controlled radical polymerisation with non-controlled radical copolymerisation, cationic and anionic polymerisation,both of vinyl monomers and cyclic monomers, and ringopening metathesis polymerisation. 

The preferred polyether used in this reaction is a higher molecular weight triol of 5000-6000 daltons (preferred MW is 6000 daltons). By copolymerisation of the macromer (structure 6.12) with ACN and styrene, a NAD is obtained in situ, which is in fact a graft copolymer ... 

CS-grafted copolymers Copolymerisation reactions Modifying the chemical and physical properties of chitin and CS to widen their practical use Tissue engineering, antibacterial and superoxide scavenging (antioxidant) activity... 

The sequential one-pot synthesis of the same graft copolymer also proved successful, but required the optimisation of some experimental parameters such as the reaction time for both the copolymerisation of norbomene and its brominated derivative, and the conversion of the copolymer growing chains (RuCl2[=CH-poly(NB-co-NB-Br)](PPh3)2) into the methylene-endcapped poly(NB-co-NB-Br) and the free RuCl2(=CHOEt)(PPh3)2 complex. 

Functionalised PO as block and graft copolymers used as compatibilisers or to increase interactions with other materials are prepared by free radical grafting (the simplest method), metallocene-catalysed copolymerisation of olefins with functional monomers, or anionic polymerisation (silane-containing PO). They are also produced by controlled/living polymerisation techniques such as nitroxide-mediated controlled radical polymerisation, atom transfer radical polymerisation (ATRP), and reversible addition-fragmentation chain transfer (RAFT). 

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]. 

The common feature of these materials was that all contained a high proportion of acrylonitrile or methacrylonitrile. The Vistron product, Barex 210, for example was said to be produced by radical graft copolymerisation of 73-77 parts acrylonitrile and 23-27 parts by weight of methyl acrylate in the presence of a 8-10 parts of a butadiene-acrylonitrile rubber (Nitrile rubber). The Du Pont product NR-16 was prepared by graft polymerisation of styrene and acrylonitrile in the presence of styrene-butadiene copolymer. The Monsanto polymer Lopac was a copolymer of 28-34 parts styrene and 66-72 parts of a second monomer variously reported as acrylonitrile and methacrylonitrile. This polymer contained no rubbery component. 

As already shown, it is technically possible to incorporate additive functional groups within the structure of a polymer itself, thus dispensing with easily extractable small-molecular additives. However, the various attempts of incorporation of additive functionalities into the polymer chain, by copolymerisation or free radical initiated grafting, have not yet led to widespread practical use, mainly for economical reasons. Many macromolecular stabiliser-functionalised systems and reactive stabiliser-functionalised monomers have been described (cf. ref. [576]). Examples are bound-in chromophores, e.g. the benzotriazole moiety incorporated into polymers [577,578], but also copolymerisation with special monomers containing an inhibitor structural unit, leading to the incorporation of the antioxidant into the polymer chain. Copolymers of styrene and benzophenone-type UV stabilisers have been described [579]. Chemical combination of an antioxidant with the polymer leads to a high degree of resistance to (oil) extraction. 

Alternating copolymers may be considered as homopolymers with a structural unit composed of the two different monomers. Random copolymers are obtained from two or more monomers, which are present simultaneously in one polymerisation reactor. In graft polymerisation a homopolymer is prepared first and in a second step one or two monomers are grafted onto this polymer the final product consists of a polymeric backbone with side branches. In block copolymerisation one monomer is polymerised, after which another monomer is polymerised on to the living ends of the polymeric chains the final block copolymer is a linear chain with a sequence of different segments. 

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