Poly reaction sequence

The in situ process is simpler because it requires less material handling (35) however, this process has been used only for resole resins. When phenol is used, the reaction system is initially one-phase alkylated phenols and bisphenol A present special problems. As the reaction with formaldehyde progresses at 80—100°C, the resin becomes water-insoluble and phase separation takes place. Catalysts such as hexa produce an early phase separation, whereas NaOH-based resins retain water solubiUty to a higher molecular weight. If the reaction medium contains a protective coUoid at phase separation, a resin-in-water dispersion forms. Alternatively, the protective coUoid can be added later in the reaction sequence, in which case the reaction mass may temporarily be a water-in-resin dispersion. The protective coUoid serves to assist particle formation and stabUizes the final particles against coalescence. Some examples of protective coUoids are poly(vinyl alcohol), gum arabic, and hydroxyethjlceUulose. 

Polyurethane foams are formed by reaction with glycerol with poly(propylene oxide), sometimes capped with poly(ethylene oxide) groups with a reaction product of trimethylolpropane and propylene oxide or with other appropriate polyols. A typical reaction sequence is shown below, in which HO—R—OH represents the diol. If a triol is used, a cross-linked product is obtained. 

Multiblock copolymers of poly(L-lysine) and PEG were prepared following the reaction sequence illustrated in Scheme 66. N-carboxy-(AT -benzyloxy... 

Figure 25.2 Core-shell reaction sequence steps (a) alkylation and (b) amidation steps for preparation of G.5n and Gn. [NH2-(CH2>2 6-NH2l (G = 0-2.5)-der>dri-poly(amidoamines)...

Several examples of the binding of enzymes to poly(vinyl alcohol) are in the literature. These could possibly be used to treat enzyme deficiency diseases. In a recent example, trypsin was immobilized on poly(vinyl alcohol) fibers using maleic dialdehyde or bromal. While the reaction was more complete with bromal, the reaction with maleic dialdehyde gave a better support which showed decreasing activity with increasing enzyme content. The activity of the bromal activated system was independant of the enzyme content (52 ). Trypsin and papain were attached to poly(vinyl alcohol) by the reaction sequence shown in Equation 13. In this case, the crosslinked poly(vinyl alcohol) is treated by the 1,3-dioxalone derivative and then converted to either the isothiocyanate or the diazonium salt for coupling with the enzyme. The bound enzymes showed significant, altho reduced, activity in each case (53). 

The very high value of Cm for vinyl chloride is attributed to a reaction sequence involving the propagating center XVIII formed by head-to-head addition [Hjertberg and Sorvik, 1983 Llauro-Darricades et al., 1989 Starnes, 1985 Starnes et al., 1983 Tornell, 1988]. Intramolecular migration of a chlorine atom (Eq. 3-114) yields the secondary radical XIX that subsequently transfers the chlorine atom to monomer (Eq. 3-115) to yield poly(vinyl chloride)... 

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 reaction sequence is satisfactory although the overall yield is approximately 50%. A different route for the preparation of poly(p-acetoxystyrene) involves the direct acetylation of poly (p-hydroxystyrene) with acetic anhydride. The main problem with this approach is the lack of commercial availability of high purity poly(p-hydroxystyrene). 

The oxazolidine-2,5-dione heterocycle, perhaps better known as the N-carboxyanhydride of an amino acid, has been incorporated employing a modification of chloromethylated poly(styrene) (192) (76USP3985715). The reaction sequence involved utilization of a masked amino acid, ethyl acetamidocyanoacetate (205). The amino acid was liberated in a subsequent hydrolysis/decarboxylation step (Scheme 98). The cyclized, IV-carboxyanhydride-functional resins (206) were reported to be useful in solid phase peptide synthesis and as supports for enzyme immobilization. 

When dissolved in a suitable solvent, uncross-linked poly(dichlorophosphazene) (3.21) functioned as a remarkable macromolecular reactant (reaction sequence (3)). When treated with organic nucleophiles such as the sodium salts of alcohols or phenols, or with primary or secondary amines, all the chlorine atoms along the polymer chain could be replaced by organic units. This is all the more remarkable because an average of 30,000 chlorine atoms per molecule are replaced. 

The earliest synthesis method, which involves a ring-opening polymerization of a cyclic chlorophosphazene followed by replacement of the chlorine atoms in the polymer by organic groups, is the most extensively developed route to the preparation of poly(organophosphazenes). It is summarized in reaction sequence (3). 

Solutions of poly(dichlorophosphazene) (3.21) in benzene, toluene, or tetrahydrofuran react rapidly and completely with nucleophiles such as sodium trifluoroethoxide to yield derivative polymers as shown in reaction sequence (3). An impetus for this... 

As discussed, condensation reactions form the basis of the synthesis of the cyclic trimer, (NPC12)3. The reaction between phosphorus pentachloride and ammonia or ammonium chloride proceeds in a stepwise fashion, as shown in reaction sequence (18), by elimination of hydrogen chloride first to form a monomer (3.40), then a linear dimer (3.41), trimer (3.42), tetramer, and so on. Cyclization could occur to give cyclic chlorophosphazenes at any stage beyond the dimer, but in practice is less likely as the chains grow beyond a certain length. Several authors have extended this process to produce relatively low molecular weight poly(dichlorophosphazene).36-39... 

Enzymes have been linked covalently to the surface of a poly Mv(aryloxy)phosp-hazene].191 In the system to be described, the high surface area was ensured by depositing a thin film of poly[W.s(phenoxy)phosphazcne] (3.31) on to the surface of highly porous small particles of alumina powder. Provided the deposition of the polymer is controlled carefully so as not to block the microscopic pores, an enormous surface area of polymer can be generated (see Figure 3.19). Surface chemistry on the polymer was then carried out according to the reactions shown in reaction sequence (56). 

Figure 2.14. Possible reaction sequence of polymer formation from catechol by peroxidase. Reprinted from Dubey, S., Singh, D., and Misra, R. A. (1998). Enzymatic synthesis and various properties of poly(catechol). Enzyme Microb. Technol. 23, 432-437, with permission from Elsevier.

Anionic polymerization techniques and naphthalene chemistry were used by Teyssie et al. to prepare A2B miktoarm stars, where A is poly(ethylene oxide) (PEO) and B is PS, PI, poly(a-methyl styrene) or poly(tert-butyl styrene) [25]. The reaction sequence is shown in Scheme 7. 

Crosslinked poly(ortho esters) are prepared by a reaction sequence in which an excess of the diketene acetal 3,9-bis(ethylidene 2,4,8,10-tetraoxaspiro [5,5] undecane) is reacted with a diol, and the ketene acetal terminated prepolymer is then crosslinked with a triol. Because the prepolymer is a viscous liquid at room temperature, the therapeutic agent and any excipients used are incorporated into the prepolymer by mixing at room temperature and then cured at temperatures that can be as low as 40°C. 

The methoxy-substituted acetal C is isolated and is subjected to another two reactions (1) the acetal function is hydrolyzed under acidic conditions to provide the methoxylated aldehyde E. (2) With a catalytic amount of sodium methoxide, the methoxylated aldehyde E reacts via an Elcb elimination, which leads to the formation of the poly-unsaturated aldehyde D. The substrates A and B of the three-step reaction sequence in Figure 12.23 derive from crotonic aldehyde (E13C-CE[=CE[-CH=0) the respective methods of preparation are outlined in the figure. The final product, which is the highly unsaturated aldehyde D, displays the structure of an aldol condensation product, namely of the crotonic aldehyde mentioned above. 

Multi-polymer Materials. The literature for multi-polymer materials is extensive but is less than that for blends and grafts composed of two polymers. A ternary graft copolymer, semi-IPN is described by Rogers and Ostler (43, 44) an original crosslinked polyethylene graft-poly-(potassium acrylate) was swelled with styrene and radiation polmerized. The authors comment that most of the grafting of polymer 3 was on polymer 2, the poly (potassium acrylate). This reaction sequence can be described ... 

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