Synthetic approaches copolymers

As the synthetic approach to polydichlorophosphazene put forward by R. De Jaeger has been already described in several recent review articles [10,38,57, 172], in this paper we will illustrate only the polycondensation approach proposed by I. Manners and H. R. Allcock, together with the consequences of this reaction on the preparation of chain phosphazene copolymers (block copolymers) [220,223,224,232-234,240], and star polymers [222]. 

The grafting from methodology was also utilized for the synthesis of poly(4-methylphenoxyphosphazene-g-2-methyl-2-oxazoline) graft copolymers [187]. The synthetic approach involved the thermal polymerization of hexachlorophosphazene, in the presence of aluminum chloride, to give low molecular weight poly(dichlorophosphazene). The chloro groups were subsequently replaced by 4-methylphenoxy groups, followed by partial bromi-... 

Well-defined nanoclusters (w 10-100 A diameter) of several metals have been prepared via the polymerization of metal-containing monomers. The synthetic approach involves the block copolymerization of a metallated norbornene with a hydrocarbon co-monomer which is used to form an inert matrix. Subsequent decomposition of the confined metal complex affords small clusters of metal atoms. For example, palladium and platinum nanoclusters may be generated from the block copolymerization of methyl tetracyclododecane (223) with monomers (224) and (225) respectively. 10,611 Clusters of PbS have also been prepared by treating the block copolymer of (223) and (226) with H2S.612 A similar approach was adopted to synthesize embedded clusters of Zn and ZnS 613,614... 

An unusual synthetic approach to PF copolymers was demonstrated by Bunz and coworkers [370], who prepared poly(fluorene ethynylene) 281a-e by metathesis polymerization reaction (Scheme 2.44) [370], The aggregation of polymers 281 in concentrated solutions and in solid state is manifested in slight (up to 10-20 nm) red shift of the absorbance and emission peaks, although solutions and films emit pure blue light. 

Regardless of the desired architecture, there are three main synthetic approaches to the preparation of diblock, dumbbell or dendronized hybrid copolymers. These involve grafting, polymerization or stepwise dendritic growth... 

As this brief overview demonstrates, novel copolymers obtained by hybridization of the linear and globular architectural states are readily prepared through a variety of synthetic approaches. In general the dendritic components of the hybrid copolymers are well defined, with unique molecular and structural characteristics. In contrast, all the linear components prepared polymerization are less precisely defined and are polydisperse. Only the very short linear components, themselves prepared by stepwise synthesis just like the dendrons, are monodisperse and can be used to prepare well-defined, monodisperse hybrids. While architectural and structural precision may be of great importance for the determination of ultimate properties, some degree of structural variation is quite acceptable for practical applications in many areas including, for example, surface modification, sensing, or encapsulated delivery. 

In this chapter, we will focus on the use of CLP techniques for the synthesis of systematic copolymer libraries using high-throughput approaches. Prior to that, automated parallel optimization reactions that have been performed for different CLP techniques will be discussed. At the end of this chapter there will be a highlight on the latest synthetic approaches to synthesize well-defined polymer libraries. 

The new synthetic approach being adopted for the preparation of the lignin-polystyrene graft copolymer involved three steps. 

Thus, N-pyrimidine phthalimide reacted with hexylamine at room temperature to form an amide-amide. The initial amide-amide formation proceeded more rapidly in chloroform as compared to dimethylsulfoxide (DM SO). However, the ring closure reaction to the imide was favored by the more polar, aprotic DMSO solvent, yielding the imide in nearly quantitative yield after 3 hours at 75 °C. The authors were able to utilize this synthetic approach to prepare well-defined segmented poly(imide-siloxane) block copolymers. It appears that transimidi-zation reactions are a viable approach to preparing polyimides, given that the final polyimide has a Tg sufficiently low to allow extended excursions above the Tg to facilitate reaction without thermal decomposition. Additionally, soluble polyimides can be readily prepared by this approach. Ultimately, high Tg, insoluble polyimides are still only accessable via traditional soluble precursor routes. 

Recently, cyclic diblock copolymers of styrene and butadiene were synthesized (Fig. 12). The synthetic approach of the cycles involved the reaction of (l,3-phenylene)bis(3-methyl-l-phenyl-pentylidene)diUthium initiator... 

In conclusion, with this synthetic approach a wide range of redox-active polymers can be obtained where factors such as the nature of the polymer backbone (e.g use of copolymers), the loading of the metal center, and the nature and coordination sphere of the metal center can be controlled systematically. This has been used to great effect in the design of electrochemically driven chemical and biochemical sensors. 

Figure 4.26 Illustration of the synthetic approach to producing diblock copolymers...

Scheme 8.4 Synthetic approach to block copolymers using sequential normal/living radical polymerization...

Gauthier et al.193 prepared highly branched arborescent graft copolymers of PS and polyethylene oxide). Their synthetic approach involved the reaction of living PS end-capped with DPE with chlorometh-... 

Ishizu et al.194 synthesized hyperbranched macromolecules that resemble dendrimers. The synthetic approach involved the preparation of poly(4-methyl-styrene-b-PS-b-poly(4-methylstyrene) triblock copolymer by using naphthalene lithium as difunctional initiator. The 4-methyl groups of the terminal blocks were metalated with s-BuLi/tetramethylethylenedi-amine (TMEDA) complex in a molar ratio of 1 2. After removal of the excess s-BuLi by repeated precipitation of the living polymer and transfer of supernatant solution to another flask under high vacuum conditions, the polymer was dissolved in THF and was used as the initiator of a-methylstyrene at —78 °C. After the polymerization of a-methylstyrene, a small amount of 4-methylstyrene was added. The procedure of metalation of the a-methyl groups and polymerization of a-methylstyrene can be repeated many times to form a dendritic type hyperbranched polymer (Scheme 99). The characterization of the inter-... 

Other synthetic approaches to the kinetic problem have been taken. Variations in catalyst concentration for the formation of each component network from linear polyurethanes and acrylic copolymers have been used along with a rough measure of gelation time (5) to confirm the earlier (2-3.) results. Kim and coworkers have investigated IPNs formed from a polyurethane and poly(methyl methacrylate) (6) or polystyrene (7) by simultaneous thermal polymerization under varied pressure increasing pressure resulted in greater interpenetration and changes in phase continuity. In a polyurethane-polystyrene system in which the polyurethane was thermally polymerized followed by photopolymerization of the polystyrene at temperatures from 0 to 40 C, it was found (8.) that as the temperature decreased, the phase-... 

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