Ordered polymer synthesis by direct

UEDA OKADA Ordered Polymer Synthesis by Direct Polycondensaiion 443... 

It is well known that the less porous the polymer, the better is the barrier effect, and the better the metal is protected against corrosion [41,42]. Unfortunately, native conducting polymers prepared by electropolymerization of a monomer in aqueous media and deposited directly onto the metal are very porous [77]. Moreover, polymer synthesis in aqueous media leads to native films containing large amounts of water, which are detrimental [41,42]. In general, the films are dried in air, but, even after that, the water content remains high. Clearly, submitting the material to thermal treatment, in order to remove all the water inside the polymer and make it more compact, should improve the barrier effect. 

Thus, the studies of the directed synthesis of polyrotaxanes indicate the necessity of a preliminary ordering of the system (association, channel complexes of inclusion compounds). It should be pointed out that the above-described ways for the ordering are limited by a restricted choice of both macrocycles (p-cyclodextrin) and linear polymers (polyvinylidene chloride and its copolymer with allyl chloride and... 

Until about 40 years ago, the determination of the molar mass distribution was the prime objective of polymer fractionation by phase separation. Since the advent of size exclusion chromatography the need for such time consuming and essentially ineffective classic fractionation methods has disappeared. However, today chromatographic techniques are still incapable of producing large-size fractions of the order of 100 g and phase separation methods continue to be needed for the preparation of large amounts of narrow-distribution polymers that cannot be obtained by direct synthesis. The most important polyolefins, polyethylene and polypropylene, fall into this category and a discussion of fractionation by distribution between two... 

Our group has initiated a synthesis of ordered polymer from nonsymmetric monomers by direct polycondensation. In the previous papers, we reported a successful synthesis of ordered polyamides (head-to-head or tail-to-tail) from a synunetric monomer and a nonsynunetric monomer, (7,2), and ordered polyamides (head-to-tail) from a synunetric monomer and a nonsynunetric monomer or a pair of two synunetric monomers (3). 

Recently, we succeeded on the synthesis of ordered(-abcd-) poly(amide-thioether) by poly(addition-direct condensation) of a pair of two nonsynunetric monomers, 4-(actyloxy)benzoic acid (XabX) and 4-aminobenzenethiol (YcdY), where a polyaddtion was combined with a polycondensation to prepare the ordered polymer (4). Because, the selective amidation of carboxylic acids would be difficult using condensing agents due to the small difference of pKa values between carboxylic acids. An active ester is also useful as a substitute for a carboxylic acid component. 

On the basis of the above findings, we initiated the synthesis of ordered (-abedef-) polymer from three nonsymmetric monomers, XabX, YcdY and ZefZ by direct polycondensation. 

In many cases, these cyclic siloxanes have to be removed from the system by distillation or fractionation, in order to obtain pure products. On the other hand, cyclic siloxanes where n = 3 and n = 4 are the two most important monomers used in the commercial production of various siloxane polymers or oligomers via the so-called equilibration or redistribution reactions which will be discussed in detail in Sect. 2.4. Therefore, in modern silicone technology, aqueous hydrolysis of chloro-silanes is usually employed for the preparation of cyclic siloxane monomers 122> more than for the direct synthesis of the (Si—X) functional oligomers. Equilibration reactions are the method of choice for the synthesis of functionally terminated siloxane oligomers. 

---