Acrylic polymers star-branched

GTP, on the other hand, offers good potential for the synthesis of star-and comb-branched polymers. The GTP chain ends are living even at temperatures as high as 70°C and, thus, are capable of participating efficiently in branching reactions. Both the arm-first and core-first approaches have been reported for the synthesis of multiarm star-branched acrylic polymers. However, very few details of experimental conditions and polymer characterization have been reported for star-branched pol)uners synthesized using the arm-first approach. 

The synthesis of A2B miktoarm star polymers has been discussed and exemplified using PIB as a component. The synthesis involves a quasi living cationic polymerization of isobutylene from a monofunctional cationic initiator. This initiator also contains a blocked hydroxyl group. Eventually, the blocked hydroxyl group of the initiator is deblocked, and functionalized with a branching agent. This activated reagent is then used for an atom transfer radical polymerization process of /erf-butyl acrylate (18). 

Hyperbranched polymers may be prepared by the self-condensing vinyl polymerization (SCVP) [257] of AB star monomers by a controlled free radical process, such as ATRP [258]. The result, under certain conditions, is a highly branched, soluble polymer that contains one double bond and, in the absence of irreversible termination, a large quantity of halogen end groups equal to the degree of polymerization which can be further functionalized [87] (Fig.35). Two examples explored in detail by ATRP are vinyl benzyl chloride (VBC, p-chlo-romethylstyrene) [258] and 2-(2-bromopropionyloxy)ethyl acrylate (BPEA) [259-261] both depicted in Fig. 35. Several other (meth)acrylates with either 2-... 

Polymers are normally classified into four main architectural types linear (which includes rigid rod, flexible coil, cyclic, and polyrotaxane structures) branched (including random, regular comb-like, and star shaped) cross-linked (which includes the interpenetrating networks (IPNs)) and fairly recently the dendritic or hyperbranched polymers. I shall cover in some detail the first three types, but as we went to press very little DM work has been performed yet on the hyperbranched ones, which show some interesting properties. (Compared to linear polymers, solutions show a much lower viscosity and appear to be Newtonian rather than shear thinning [134].) Johansson [135] compares DM properties of some hyperbranched acrylates, alkyds. and unsaturated polyesters and notes that the properties of his cured resins so far are rather similar to conventional polyester systems. 

Another significant application of the ADMET polymerisation relates to the preparation of star-shaped polymers, which are branched macromolecules in which several linear polymer chains are attached to a unique branching point or core [48]. Montero de Espinosa, Winkler and Meier [49] described an ADMET approach to obtain those architectures (three- and four-arm) using small tri-acrylates and tetra-acrylates. More recently, Unverferth and Meier [50] reported the synthesis of well-defined star-shaped polymers via a head-to-tail ADMET polymerisation whereby di(trimethylolpropane)tetra-acrylate (four-arm) and dipentaerythritol hexa-acrylate (six-arm) served as core units, and fatty acid-derived 10-undecenyl acrylate as asymmetric a,(0-diene monomers. In this case, star-shaped polymers containing arms of 10 or 20 monomer units with an a,(0-unsaturated ester backbone and their subsequent post-polymerisation via a base-catalysed Thia-Michael addition were prepared. 

It is desired to synthesize (a) AA -type triarm asymmetric polystyrene (PSt) stars with asymmetry in the molar mass of their branches, (b) AB2-type miktoarm star polymer core-(PSt)(PtBA)2 (where PtBA = poly(ten-butyl acrylate)), and (c) amphiphilic core-(PSt)(PAA)2 (where PAA = poly(acrylic acid)). Suggest a methodology to synthesize these polymers entirely by ATRP processes. 

A real synthetic strength of the TEC reaction is its versatility with respect to ene substrates that can be used and include both activated and nonactivaed species such as norbomenes, (meth)acryl-ates, maleimides, and allyl ethers to name but a few (Yu et al., 2009). Recent examples describing the application of the thiol-ene reaction in the polymer/materials eld include the use in thioether dendrimer synthesis (Killops et al., 2008), convergent star synthesis (Chan et al., 2008), synthesis of multifunctional branched organosilanes (Rissing and Son, 2008), and modi -cation/functionalization of wide range of polymers (Justynska and Schlaad, 2004 Killops et al., 2008). 

If the two kinds of branches are of different chemical nature, but of similar length, the resulting heterostar copolymer molecule is composed of a crosslinked core carrying equal numbers of branches of two different kinds. A variety of branches can be attached to a primary PS star molecule. Branches of poly(ethylene oxide) [68,83], poly(alkyl methacrylate) [84], poly(ter -butyl acrylate) (PtBA) [82], poly(2-vinylpyridine) [85], and others have been developed, with special emphasis on amphiphilic heterostar molecules. The presence of a population of linear precursors remains however, they can be easily removed by fractional precipitation. Since polymers of different chemical nature are usually incompatible, there is a question of the conformation of such... 

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