Polyaddition Type Polymers

Conj ugated Ladder Polymers. Since the 1930s double-stranded, ladder-type polymers have been prepared in a multistep process with limited success of cyclization (191,192). Other routes have also been explored such as those for poly(acrylonitrile) (193,194), poly(l,2-butadiene), poly(3,4-isoprene) (195), or poly(butadiyne)s (196). These materials were found to be poorly soluble and unworkable, with a considerable number of defects in the structure (incomplete cyclization, cross-linking, radical sites). The first successful synthesis of a ladder polymer with a completely defined structure was accomplished in 1991 by Sherf and Mullen (197). The first step was the AA/BB-t5q)e polycondensation of an aromatic diboronic acid with a substituted 2,5-dibromo-l,4-dibenzoylbenzene to give a single-stranded precursor PPP-type polymer, followed by cyclization to the ladder structure (Fig. 8). Several other examples exist that have resulted in ladder-type structures. These include angular polyacene (198,199), Diels-Alder polyaddition of AB-type diene-dienophiles (200), AA/BB-type Diels-Alder polyaddition of a bisdiene and a bisdienophile (201), thienylene imits (202),... 

General theory of gelation for polyaddition- and polycondensation-type polymers... 

In the manufacture of highly resident flexible foams and thermoset RIM elastomers, graft or polymer polyols are used. Graft polyols are dispersions of free-radical-polymerized mixtures of acrylonitrile and styrene partially grafted to a polyol. Polymer polyols are available from BASF, Dow, and Union Carbide. In situ polyaddition reaction of isocyanates with amines in a polyol substrate produces PHD (polyhamstoff dispersion) polyols, which are marketed by Bayer (21). In addition, blending of polyether polyols with diethanolamine, followed by reaction with TDI, also affords a urethane/urea dispersion. The polymer or PHD-type polyols increase the load bearing properties and stiffness of flexible foams. Interreactive dispersion polyols are also used in RIM appHcations where elastomers of high modulus, low thermal coefficient of expansion, and improved paintabiUty are needed. 

Another family of polyols is the filled polyols.llb There are several types, but die polymer polyols are die most common. These are standard polyether polyols in which have been polymerized styrene, acrylonitrile, or a copolymer thereof. The resultant colloidal dispersions of micrometer-size particles are phase stable and usually contain 20-50% solids by weight. The primary application for these polyols is in dexible foams where the polymer filler serves to increase foam hardness and load-bearing capacity. Other filled polyol types diat have been developed and used commercially (mainly to compete with die preeminent polymer polyols) include the polyurea-based PEID (polyhamstoff dispersion) polyols and the urethane-based PIPA (poly isocyanate polyaddition) polyols. 

Many reactions familiar to organic chemists may be utilized to carry out step polymerizations. Some examples are given in Table 2.2 for polycondensation and in Table 2.3 for polyaddition reactions. These reactions can proceed reversibly or irreversibly. Those involving carbonyls are the most commonly employed for the synthesis of a large number of commercial linear polymers. Chemistries used for polymer network synthesis will be presented in a different way, based on the type of polymer formed (Tables 2.2 and 2.3). Several different conditions may be chosen for the polymerization in solution, in a dispersed phase, or in bulk. For thermosetting polymers the last is generally preferred. 

Data on MMD (Table 14) indicate that cyclolinear polymers with the most homogeneous structure and composition are formed on the reduced catalyst. The more so, every particular case displays its own optimal type of the reduced form, i.e. catalytic system for synthesizing cyclolinear polymers should be selected with regard to activity of dihydrorganocyclosiloxane in polyaddition reaction. It should be noted that as yellow colloid is applied as the catalyst, the reaction temperature has no ef-fect on the shape of MMD curves for ethyl-substituted polymers with tetra- and hexasiloxane cyclic fragments. 

Functionalized polymers of the type B and C (Scheme 1) can be formed via polyaddition processes of bifunctional reactants, without splitting off of low molecular weight compounds. Most syntheses of stabilizers have been based on reactions of bis-isocyanates with H-acid nucleophiles. Some reactions of oxiranes may be listed here too (syntheses involving oxiranes are listed in Sect. 3.1.1.2 if polymerization aspects are more evident syntheses of stabilizers formed via reactivity of oxirane moieties attached to an oligomeric or polymeric chain are classified as reactions on polymers. Sect. 3.2.2.1... 

A polymeric matrix based on a silicone polyaddition composition is promising for the creation of magnetic control material. This type of polymer allows us to regulate the elastic properties of the ME in the range 1 - 500 kPa and elongation up to 1100%. In the magnetic field the elasticity increased by 800 %. 

The polymers were synthesized according to the base-catalyzed Michael-type polyaddition reaction of a,to-dimercaptoalkanes to (ft)-3-methylhexamethylene bis[4-[4-(acryloyloxy)benzoyloxy]benzoate] (9) (polymers I-n), as described in detail elsewhere (10), or of 1,2-dimercapto-benzene or 1,3-dimercaptobenzene to a a-alkylene bis[4-[4-(acryloyloxy)benzoyloxy]benzoate]s (1) (polymers II-m). 

As mentioned previously, the synthesis of polyurethanes, by the reaction of a diisocyanate (or polyisocyanate) with oligo-diols (or oligo-polyols), is a polyaddition reaction (or step-addition polymerisation), a particular type of polycondensation reaction. There is a great difference between the polycondensation and the polyaddition reactions and the classical radical polymerisation or ionic (living) polymerisation reactions. In radical polymerisations (typical chain reactions), the high MW polymer is formed at the beginning of polymerisation. The reaction system is constituted from monomer and high... 

In drying by polyaddition, low molecular mass reactive polymers such as alkyd resins, saturated polyesters, or polyacrylates react with polyisocyanates or epoxy resins to form cross-linked macromolecules. Because this reaction can take place at room temperature, the binder components must be mixed shortly before application. The period of time during which a coating of this type remains usable after mixing of the components is known as the pot life. These are known as two-pack coatings, differing from the one-pack systems, which can be stored for months or even years. 

Heterochain polymers of the type -(M-X) - contain polar M-X bonds (for reviews see [1,2,12-15]). Such polymers are often prepared by polycondensation of a bifimctional metal halide (M = B, Si, Ge, Sn, Pb, Sb, Ni, Pd, Pt, Ti, Hf) with a bifunctional Lewis base such as a diol, diamine, dihydrazine, dihydrazide, dioxime, diamideoxime, dithiol, diacetylene (Eq. 7-2). Another possibilitiy is the polyaddition of a bifunctional metal hydride to bifunctional alkenes (Eq. 7-3). Mn and mg containing poly(p-xylylenes) of the composition -(-CH2-C6H4-CH2-M-) - were produced by solid-state UV-photopolymerization of a cocondensated mixture of p-xylylene with Mn or mg at 80 K [16]. Prolonged storage of the polymers at ambient temperature under vacuum led to gradual decomposition. 

Polymerization plays a key role in chemical microencapsulation. The basic mechanism of this method is to put a polymer wall (can be multilayer) through polymerization on a core material, which is in a form of small liquid droplets, solid particles, or even gas bubbles or to embed the core material in a polymer matrix through polymerization. Interfacial polymerization is one of the most important methods that have been extensively developed and industrialized for microencapsulation. According to Thies and Salaun, interfacial polymerization includes live types of processes represented by the methods of emulsion polymerization, suspension polymerization, dispersion polymerization, interfacial polycondensation/polyaddition, and in situ polymerization. This chapter is only focnsed on interfacial polycondensation and polyaddition in a narrow sense of interfacial polymerization. 

Miniemulsion is a special class of emulsion that is stabilized against coalescence by a surfactant and Ostwald ripening by an osmotic pressure agent, or costabilizer. Compared with conventional emulsion polymerization process, the miniemulsion polymerization process allows all types of monomers to be used in the formation of nanoparticles or nanocapsules, including those not miscible with the continuous phase. Each miniemulsion droplet can indeed be treated as a nanoreactor, and the colloidal stability of the miniemulsion ensures a perfect copy from the droplets to the final product. The versatility of polymerization process makes it possible to prepare nanocapsules with various types of core materials, such as hydrophilic or hydrophobic, liquid or solid, organic or inorganic materials. Different techniques can be used to initiate the capsule wall formation, such as radical, ionic polymerization, polyaddition, polycondensation, or phase separation from preformed polymers. 

Poly(amidoamine)s (PAAs) can be easily synthesized by Michael-type polyaddition of primary or bis-secondary amines to give bis(aciylamide)s. These polymers are water soluble, biodegradable and biocompatible, and show significantly lower cytotoxicity than other usual polycationic vectors (>100-fold less toxic than PAAs have the advantage of degrading to... 

More recently, a series of linear PAAs with repetitive disulfide linkages in their backbone (SS-PAAs) has been developed as biodegradable carriers for gene delivery. These bioreducible SS-PAA polymers were synthesized via Michael-type polyaddition of the primary amine monomers to Nff -cystamine-bisactylamide (CBA) in equimolar monomeric ratios. These polymers have been designed to form nanocomplexes with nucleic acids, which remain relatively stable in extracellular media but are prone to fast degradation in the reductive intracellular environment due to cleavage of the... 

The aim of this chapter is to describe the possibilities offered by the miniemulsion process for performing chain polymerization, polyaddition, polycondensation, and modifications of polymers, and to outline the current trends in this field of research. Whilst the different polymerization types performed in miniemulsion are discussed in detail, descriptions of so-called secondary or artificial miniemulsions (i.e., miniemulsions with a preformed polymer) will not be included at this point... 

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