Ladder copolymers

The copolymerization of multimonomers with vinyl monomers such as acrylic acid, styrene, or acrylonitrile results in semi-ladder copolymers soluble in many common sol-vents. Such products consist of ladder-type blocks created from multimonomer molecules and blocks of repeated units formed from vinyl monomer, both connected with branching points and fastened together by fragments of the molecule with ladder structure. Semi-ladder copolymer (multimethacrylate-acrylic acid, partially crosslinked) has the following structure ... 

Styrene-multimethacrylate ladder copolymers, varying in molecular weight and composition, were also synthesized from styrene and methacryloyl ester of... 

The condensation of trihydroxymethyl- and trihydroxyphenylsilanes takes place during the distillation of toluene, in which the synthesis occurs. As a result, we obtain ladder polymethyl(phenyl)silsesquioxane. Since there is a certain amount of the products of incomplete alcoholysis formed at the stage of alcoholysis, the process forms a ladder copolymer, i.e. a copolymer with a certain number of branched and linear elements in the chain. 

The ladder copolymers are preferentially formed (by the intermolecular reaction) because the formation of a tricyclic heterocycle by intramolecular cyclisa-tion is difficult for steric reasons [100]. 

Figure 3. Copolyamide approach to the synthesis of processible ladder copolymers.

These preliminary results indicate a dramatic improvement over previous ladder copolymer formulations, with increased processibility. However, preliminary attempts at optical quality film fabrication led to cloudy films, posably due to solvent incorporation and trapping in the film. Further studies with a wido- variety of solvents and different spin-coating conditions are currently underw , and we hope to report thin film values to compare to the calculated values based on percent of NLO-phore incorporation in the very near future. 

Sporopollenin Ladder copolymer of carotenoids and fatty adds ( )... 

Blue emission can also be produced in different conjugated polymer systems. Blue electroluminescence has been reported in poly(p-phenylene) (PPP) [62], polyal-kylfluorene [63], fluorinated polyquinoline [64], and PPP-based ladder copolymers [65]. One problem that is found for the larger gap polymers is that although the... 

Figure 9-2. Based on ihe conjugated backbone of a /H/ra-phenylcne the most common principle structures of conjugated molecules am described (a) the pure backbone (b) a backbone with attached side-groups R and R (e) a ladder type-eonjugaled backbone (d) and (c) represent different types of copolymers. where (d) represents a side cliain-gnill copolymer and (c) a single eliain-bloek copolymer.

The source-based nomenclature identifies the starting material(s) from which the ladder or spiro polymer is prepared. It is derived from the nomenclature system for copolymers [3]. The system is based on the following principles ... 

Point A deals with the case in which at least one of the comonomers is connected with the template hy covalent bonding. In particular A1 represents the reaction of multimonomer with free monomer B (not connected to the template). One type of units A with double bonds (for instance, acrylic groups) is connected by covalent bonds to the template units, T. As a result of polymerization, a copolymer with ladder blocks is formed. 

A2 shows the reaction between two different multimonomers. Two different type of units A and B, containing double bonds, are attached to two different templates. After polymerization, the ladder block copolymer can be formed. However, one cannot exclude formation of a mixture consisting two unconnected ladder homopolymers. 

IR analysis shows that double bonds were absent in the product within the range of an experimental error. The reaction product is composed of ladder blocks and the blocks of styrene units. In order to verify this structure, hydrolysis of the product was carried out in methanol-benzene and methanol solutions of KOH. After the hydrolysis, the product was esterified by diazomethane and styrene-methyl methacrylate copolymer was separated. The expected scheme of these reactions is as follows ... 

NMR study shows that the block copolymer of styrene-methyl methacrylate is present in the product of esterification. It confirms that the original copolymer consists of blocks of styrene units and the ladder type blocks. Analysis of a few fractions of the copolymer obtained from oligomeric multimonomer and styrene confirmed this type of structure. Data recalculated from publications are presented in Table 5.1. 

In the product, there should be a ladder-type blocks linked by segments composed of p-cresyl methacrylate units. This type of structure was confirmed by IR and NMR spectrometry. However, by preparation of such copolymers with labeled end-groups (using radioactive AIBN), and by fractionating and radiometric analysis, it was shown that copolymers obtained are slightly branched. There is slightly more branch points than in the case of copolymers with styrene. It could be an effect of chain transfer reaction. 

The copolymerization product was soluble in DMF and in chloroform. When the reaction was complete the product was precipitated with methanol, redissolved in chloroform, reprecipitated with methanol, and then dried. Hydrolysis of the copolymer followed by separation and analysis shows that one of the products of the hydrolysis is poly(vinyl alcohol) with molecular weight similar to that of the initial PVA. All these findings lead to the conclusion that by the copolymerization of two different multimonomers a copolymer with two ladder-type blocks can be obtained. However, the possibility that the copolymer is slightly branched cannot be excluded, and the assumption that mainly ladder-type, linear structure exists still needs confirmation. 

There is no information in the literature up to now on polymerization of multimonomer in which two different types of groups are connected with one template by covalent bonds. In principle, such polymerization should lead to the ladder-type product, and, after hydrolysis, to the copolymer with composition controlled by the composition of the initial template. 

On the basis of these examples, we can see that using templates connected by covalent bonds, we can produce a new class of copolymers - semi-ladder block copolymers -with blocks of ladder-type structure. By hydrolysis, the template can be removed and block copolymers with defined length of block can be obtained. Such synthesis by conventional copolymerization is very difficult and sometimes impossible. 

Production of materials in which the daughter polymer and the template together form a final product seems to be the most promising application of template polymerization because the template synthesis of polymers requiring further separation of the product from the template is not acceptable for industry at the present stage. Possible method of production of commonly known polymers by template polymerization can be based on a template covalently bonded to a support and used as a stationary phase in columns. Preparation of such columns with isotactic poly(methyl methacrylate) covalently bonded to the microparticulate silica was suggested by Schomaker. The template process can be applied in order to produce a set of new materials having ladder-type structure, properties of which are not yet well known. A similar method can be applied to synthesis of copolymers with unconventional structure. 

Template copolymerization seems to be applied to the synthesis of copolymers with unconventional sequences of units. As it was shown, by copolymerization of styrene with oligomers prepared from p-cresyl-formaldehyde resin esterified by methacrylic or acrylic acid - short ladder-type blocks can be introduced to the macromolecule. After hydrolysis, copolymer with blocks of acrylic or methacrylic acid groups can be obtained. Number of groups in the block corresponds to the number of units in oligomeric multimonomer. Such copolymers cannot be obtained by the conventional copolymerization. 

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