Rational homopolymers

In the following, the phase behavior of copolymer-based blends will be illustrated by listing experimental results which have been published chiefly in the last five years. Phase behavior of homopolymer/copolymer and copolymer/copolymer Mends can be rationalized in temperature-copolymer composition and isothermal copolymer composition - copolymer composition plots, respectively, at fixed blend ratio. The blend systems will be classified as follows ... 

Lee and Char [93] studied the reinforcement of the interface between an amorphous polyamide (PA) and polystyrene with the addition of thin layers of a random copolymer of styrene-maleic anhydride (with 8% MA) sandwiched at the interface. After annealing above the Tg of PS, they found significantly higher values of Qc for samples prepared with thinner layers of SMA than for the thicker ones. They initially rationalized their results by invoking the competition between the reaction rate at the interface and the diffusion rate of the SMA away from the interface. For very thick layers, and therefore also for pure SMA, the reaction rate was much faster than the diffusion rate away from the interface and favored therefore a multiple stitching architecture, as shown schematically in Fig. 50. Such an interfacial molecular structure does not favor good entanglements with the homopolymer and is mechanically weak. 

Figure 20. Examples of/ amino acid homopolymers from racemic lactams and the conformational preferences as rationalized in 1968 by Bestian.lsy...

Living cationic sequential block copolymerization is one of the simplest and most convenient methods to provide well-defined block copolymers. The successful synthesis of block copolymers via sequential monomer addition relies on the rational selection of polymerization conditions, such as Lewis acid, solvent, additives, and temperature, and on the selection of the appropriate order of monomer addition. For a successful living cationic sequential block copolymerization, the rate of crossover to a second monomer ( ) must be faster than or at least equal to that of the homopolymerization of a second monomer (i p). In other words, efficient crossover could be achieved when the two monomers have similar reactivities or when crossover occurs from the more reactive to the less reactive monomer. When crossover is from the less reactive monomer to the more reactive one a mixture of block copolymer and homopolymer is invariably formed because of the unfavorable Rcr/Rp ratio. The nucleophilicity parameter (N) reported by Mayr s group might be used as the relative scale of monomer reactivity [171]. 

TG-DTA-MS has obvious synthetic polymer applications. TA-MS has been appHed to study the thermal behavior of homopolymers, copolymers, polymeric blends, composites, residual monomers, solvents, additives, and toxic degradation products. In the latter context, FICl evolution from heated polyfvinyl chloride) materials is readily quantified by TA-MS and such data are of major significance in the design of fire-resistant polymeric materials. Pyrotechnic materials have been studied by TA-MS. A complex sequence of thermal events relates to the decomposition of these materials involving interactions between the nitrocellulose, perchlorate, and metal components with periodic release of carbon dioxide and oxygen. Only by EGA is it possible to rationalize the thermal behavior of such materials. TA-FTIR has also been applied extensively to study the thermal characteristics of synthetic polymers... 

A simple, although originally empirical, way to reduce the band gap of a polymer was suggested by Kertesz and co-workers [296] and consists of obtaining a copolymer in which a comonomer provides a homopolymer with a lower gap. A rational basis has been given for this method [297]. Following this idea, compounds 68 [298], 69 [299], and 70 [299] have been employed as starting monomers. 

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