Graft-form polymerisation

The use of borane-containing monomers clearly presents an effective and general approach in the functionalisation of polyolefins, which has the following advantages stability of the borane moiety to coordination catalysts, solubility of borane compounds in hydrocarbon solvents (such as hexane and toluene) used as the polymerisation medium, and versatility of borane groups, which can be transformed to a remarkable variety of functionalities as well as to free radicals for graft-form polymerisations. The functionalised polymers are very effective interfacial modifiers in improving the adhesion between polyolefin and substrates and the compatibility in polyolefin blends and composites [518],... 

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 ... 

For the polymerisation of styrene (SnC -F O-PhNC -CC at 0°) kjkv for anisole was found [85] to be 1.62. It is highly probable that the big difference between this and the value for isobutene reflects mainly the difference between the ps for the two monomers. The very low value of kjkv in the polymerisation of isobutene - or the very large kv of isobutene - accounts for the observation [86] that, whereas styrene polymerising cationically in the presence of preformed poly-p-methoxystyrene will form grafts by reacting with pendent rings, isobutene will not do so. 

PolyHIPE, in granular form, has recently been employed as a support for bicatalyst systems [136]. Styrene/DVB porous polymers were prepared with free vinyl groups (acryloyl, allyl and vinylbenzyl) on the surfaces of the cavities. Impregnation with solutions of quaternary onium monomers, with subsequent polymerisation, resulted in grafting onto the pendant double bonds, to give a surface-quaternised material (Fig. 19). 

In the early 1970s, surface modification of most polymers was achieved using redox initiators. Ce+4-induced initiation was employed to achieve surface grafting of acrylamide onto LDPE film [117]. The film was first oxidised by chromic acid and then reduced with diborane to form a hydroxyl-rich surface which was then used to initiate graft polymerisation of acrylamide using Ce+4/HN03. The mechanism of chromic-acid-facilitated surface oxidation of LDPE surface is shown in Scheme 6a and that of free-radical generation is represented in Scheme 6b. 

Figure 5.26 Representation of the nanocomposite formed by graft-polymerisation of caprolactone on cellulose...

Other examples of solvent effects in casting blends include epoxy resin/copoly-ester/tetrachloroethane polyethersulphone/poly(ethylene oxide)/cyclohexanone and mixtures of PVC with various polyacrylates in solvents such as THF One particular pair of polymers PVC/poly(ethyl acrylate) appear to be miscible but no suitable solvent has been found as yet. Homogeneous blends can only be prepared by in situ polymerisation though it is possible that miscibility is enhanced by small amounts of graft copolymer which is inevitably formed by this technique. 

Poly(amino acid)s (PAAs) have also been used in drug delivery PEO-(l-aspartic acid) block copolymer nano-associates , formed by dialysis from a dimethyl acetamide solution against water, could be loaded with vasopressin. PLA-(L-lysine) block copolymer microcapsules loaded with fluorescently labelled (FITC) dextran showed release profiles dependent on amino acid content. In a nice study, poly(glutamate(OMe)-sarcosine) block copolymer particles were surface-grafted with poly(A-isopropyl acrylamide) (PNIPAAm) to produce a thermally responsive delivery system FITC-dextran release was faster below the lower critical solution temperature (LCST) than above it. PAAs are prepared by ring-opening polymerisation of A-carboxyanhydride amino acid derivatives, as shown in Scheme 1. 

Textile fibers consist of polymers. Polymers are long chain molecules which are formed by chemically joining the monomers and the process is known as polymerisation. The length of the chain is represented by degree of polymerisation (DP). If a polymer is formed from two or more monomers, it is called copolymer. To improve the properties of the fibre sometimes additional monomer is grafted on to the polymer chain. 

Initiation for grafting The free radicals formed on the surface of fibre by exposure to plasma can be used directly to initiate polymerisation, with new polymer bonded firmly to the surface by carbon linkages. Thus, a new polymer can be applied in the following manner ... 

During the radical polymerisation of vinylic monomers in liquid polyether media, graft species (carbocatenary vinylic polymer chemically linked on the polyether) are formed, by chain transfer reactions, which play the role of a true NAD. For grafting reactions on polyether triols, the graft species have the following idealised structure (Figure 6.3). 

PHD polymer polyols are a special class of filled polyols developed successfully by Bayer, PHD being the abbreviation of the German name polyharnstoff dispersion or polyurea dispersions [67-69]. PHD polyols contain organic urea, oligomeric or polymeric polyurea, finely dispersed in liquid polyether polyols [67-73]. The difference between PHD polyols and graft polyether polyols is the different nature of the solid polymer dispersed (it is a heterocatenary polymer - polyurea - instead of carbocatenary polymer) which is obtained by another synthetic procedure (polyaddition reaction between a diisocyanate and a diamine instead of radical polymerisation). The reaction between the diisocyanate and the diamine, takes place in situ (reaction 6.19), in liquid poly ether. The resultant polyurea being insoluble in polyether, precipitates in the form of very fine particles ... 

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