Reaction, degree polymer-analogous

To obtain PVA, PVAc is saponified in a polymer analogous reaction using methanolic sodium hydroxide. The reaction 5 in Fig. 2, which is better described as a transesterification rather than a simple basic hydrolysis, leads to PVAs with different degrees of saponification (see Fig. 4). 

In the above-mentioned example of the polymer-analogous saponification of poly(vinyl acetate) the reactant and the product differ in their properties, for example, in their solubility however, both compounds have the same average degree of polymerization. The poly(vinyl alcohol) obtained by saponification can, in principle, be esterified back to poly(vinyl acetate) with the original molecular weight the reacetylated polymer then has the same properties as the original material. The viscosity number may be used to check whether in fact any chain scission has occurred during the reaction sequence of saponification and reacetylation (see Example 5-1). 

This is as a rule not possible as these data are not available for high-molecular-weight samples. In order to be able to exclude the influence of the distribution of degree of polymerization for various polymer structures, polymer analogous reactions may be carried out, where polymers of differing chemical structures and molecular weights, but with the same distribution of degree of polymerization are obtained (e.g., Kulicke, Horl 1985). Of particular interest in this report are polyelectrolytes. 

Figure 7. Degree of polymerization ( , ) and polydispersity (O, n) of the precursor polymer resulting from the cationic polymerization of 6-chlorohexylvinyl ether ( , O) initialed by HI/Ij in toluene at -40 °C, and of the final poly 6-[(4 -n-ethoxy-4"-azobenzene)hexyl]vinyl ether)s prepared by polymer analogous reactions ( , )...

Figure 10. Dependence of the transition temperatures from the glass ( , O), SmC ( , O), SmA ( , ) and nematic (A, A) phases of poly 6-[(4 -cyanopheny]-4"-phenoxy)hexyl]vinyl ether prepared by directcation-ic polymerization (, , )[ 24] and by polymer analogous reactions (O, o, ) [212, 213] as a function of the GPC-determined degree of polymerization. Infinite molecular weight transitions G 31 SmC 81 SmA 122 I.

Macromolecular transformations are also of scientific and commercial interest. They can be used for the manufacture of new compounds, particularly in cases where no monomer exists (vinyl alcohol as the enolic form of acetaldehyde) or where the monomer polymerizes with difficulty or not at all (e.g., vinyl hydroquinone). In these cases, derivatives such as vinyl acetate or vinyl hydroquinone ester are polymerized and the polymers are then saponified to poly(vinyl alcohol) and poly(vinyl hydroquinone), respectively. Other processes of industrial importance are conversions of inexpensive macromolecular compounds such as cellulose into new materials (cellulose acetate, cellulose nitrate, etc.), manufacture of ion exchange resins, and dyeing with reactive dyestuffs. All of these reactions lead to a definite product. If the degree of polymerization is retained, they are called polymer analog reactions. 

The reactions and properties of macromolecules are determined by chemical structure and molecular size. Consequently, it is convenient to use these parameters instead of, for example, mechanisms to classify macro-molecular reactions. Distinction is made among catalyses, isomerizations, polymer analog conversions, chain extension, and degradation reactions according to whether the chemical structure, the molar mass and/or the degree of polymerization are retained or changed. 

Thus, the constitution and the molar mass are altered in polymer analog reactions, but the degree of polymerization remains unchanged. Chain analog reactions are a special case in which the end groups are transformed but the constitution of the monomeric units is retained. 

PAAm/AAcNa) which are prepared by polymer analogous reactions and therefore have the same degree of polymerization and chain length distribution. Figure 5 shows the viscosity behaviour at zero-concentration for co-polymer compositions between 0 and... 

Table 1-3. Degree of Polymerization X from Osmotic Measurements During Polymer-Analogous Reaction of Amylopectin Fractions"...

Fig. 5.21. Stabilization of acrylate-acrylamide-acrylate units via hydrogen bonds in the copolymer poly(acrylamide-co-acrylate).The copolymer can be synthesized via a copolymerization of acrylic acid and acrylamide or a partial hydrolyses of poly(acrylamlde) with sodium hydroxide (NaOH).The hydrolyses as a polymer analogous reaction leads to copolymers with the same degree of polymerization P. A hydrolysis to a copolymer with more than 66% of acrylic acid units is only possible at with extreme reaction conditions [31]...

The synthesis of a series of polyacrylates and methacrylates with pendant carbazole groups has been reported [587]. The polymers were prepared by the reaction of ffl-hydroxyalkylcarbazoles or the corresponding alkoholates with poly(acryloyl chloride) and poly(methacryloyl chloride) (43). GPC, H-NMR, and elemental analysis show that high-molecular weight polymers with an almost quantitative degree of substitution are obtained by this polymer analogous reaction. 

In many cases the functional or loading capacity is expressed in mmolg" polymer. For polymer-analogous derivatization reactions the definition of the degree of functionalization (DF) is useful. It is defined as the quotient of the content of new functional groups and that of original ftmctional groups [61]. 

To initiate the first step of the repetitive synthesis, the trityl chloride derivative of polystyrene was subjected to reaction with thymidine in pyridine (Scheme 6). It is note-worthy that unreacted trityl chloride groups were blocked as methyl ethers by addition of methanol [41], The thymidine content was found to be 60-340 jumol g" after polymer-analogous cleavage from the support. This capacity corresponds to a degree of functionalization of 15-85% and points to steric problems of this attachment to the polymer. 

---