Copolymers, graft synthesis procedure

Synthesis. Graft copolymer was formed in aqueous solution by ceric-ion-initiated, radical polymerization of monomer on starch. Polymerization was conducted in an inert, atmosphere. Details of the synthesis procedure may be found in references 41 to 43 In recovering the polymer product, freeze drying was used with care since freeze drying produces a more dissolvable and useful product but can degrade polymers with molecular weights of 1 million or more. Poly(starch-g-(1-amidoethylene)) Poly(starch-g-(1-amidoethylene))... 

The architecture of copolymers can be controlled by the synthesis procedure, and it is possible to prepare diblock, triblock, multiblock, starblock and graft copolymers. These are illustrated in Fig. 1.1. Examples of other exotic architectures that have recently been synthesized are shown in Fig. 2.33. The possibilities for molecular design seem to be almost limitless, only being limited by the chemist s imagination. This book is concerned with block copolymers, and graft copolymers... 

Though their synthesis has not been pubUshed, it is probable that the triblock copolymers 138 and 139 [243] were prepared by a similar grafting onto procedure. 

Several groups have conducted graft copolymerizations on starch or its purified components, amylose and amylopectin. The syntheses are based on attack of the anhydroglucose unit of starch by cerium (+4) ion. The free radical produced from this attack is then immersed in a monomer solution polymerizable by free radical, chain polymerization and a graft copolymer is formed. A typical synthesis procedure (10,16) is as follows. 

An alternate approach was the synthesis [85,86] of PBZT copolymers (XIX) containing pendent 2,6-dimethylphenoxy graft sites. Such copolymers do not lead to any breaks within the rigid-rod backbone thereby, they have no adverse effects upon rod reinforcement efficiency. Using the conventional PBZT polymerization procedure, 2-(2,6-dimethylphenoxy)terephthaloyl chloride was substituted for terephthaloyl chloride up to 30 mol %. The pendent dimethylphenoxy copolymers were then reacted with m-phenoxybenzoic acid in PPMA. 

In the first part of this review we shall consider the various pathways that have been used (or attempted) to synthesize macromolecular monomers. We shall critically discuss the efficiency of the methods that have been proposed, together with the procedures used for the characterization of the species obtained. In the second part we shall describe the various attempts to homopolymerize macromonomers and to use them in copolymerization reactions to obtain graft copolymers. We shall include some potential applications of macromonomers as intermediates to the synthesis of new polymeric materials that have been proposed. 

N-Benzyl and iV-alkoxy pyridinium salts are suitable thermal and photochemical initiators for cationic polymerization, respectively. Attractive features of these salts are the concept of latency, easy synthetic procedures, their chemical stability and ease of handling owing to their low hygroscopicity. Besides their use as initiators, the applications of these salts in polymer synthesis are of interest. As shown in this article, a wide range of block and graft copolymer built from monomers with different chemical natures are accessible through their latency. 

In the following we would like to describe the synthesis of graft copolymers with silicone backbone based on polymeric initiators. These graft copolymers might find application as compatibilizers and, furthermore, the synthetic procedure allows broad combination possibilities. 

Styrene and butadiene also form copolymers known as high impact polystyrene, or rubber-modified polystyrene, when the content of butadiene is 10%. This type of material has excellent mechanical properties, and it is widely used in practice for the manufacturing of numerous objects, including parts for household appliances, furniture, etc. Rubber-modified polystyrene is commonly used as wood replacement and also for packaging. The synthesis of this material typically is done by dissolving polybutadiene in styrene monomer, followed by free radical polymerization achieved using a peroxide catalyst. This procedure leads to block or graft type copolymers. 

Well-characterized systems. This depends on the appropriate chemistry and subsequent characterization (typical issues here are the polydispersity, control of grafting density, reproducibility of procedure to obtain identical particles). One frequent problem here is that the price one pays for such systems is tlie availability of small amounts (sometimes only fractions of 1 g) of material. For example, multiarm star polymers are in many ways unique, clean, soft colloids [ 19,23], but their nontrivial synthesis makes them not readily available. On the other hand, recent developments witli block copolymer micelles from anionically synthesized polymers [54-58] and arborescent graft copolymer synthesis [40] appear to have adequately addressed this issue for making available different alternative star-like systems. 

Most of the known photochemical procedures for the synthesis of block and graft copolymers are based on the modification of already existing polymers with photolabile groups incorporated at defined positions, i.e. at the chain end, at side chains, or in the main chain (see Chart 11.13) [84]. 

Figure 11.28 Synthesis of graft copolymers made of EPDM rubber backbone and PMMA branches, using ATRP procedure and grafting from approach, the diene of the EPDM rubber being 4-ethylidene norbom-2-ene. (Adapted from Wang et al., 1999.)...

The extent of regioregularity has a marked impact on the properties of the material and it is reported that this procedure generates the highest molecular weight reported so far for a substituted poly(p-phenylene). Furthermore, these polymers have functional chain ends and/or side-groups which can be used in other functionalization reactions and in the synthesis of block and graft copolymers. 

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