Ring-type monomers

The final group of solid state monomers which have been polymerized are ring type monomers. There polymerizations showns two favorable factors. On ring opening and polymerization the number of covalent bonds stays constant and the heat of reaction and the voliune change are smaller. It seems that in this group of reactions the only topotactic polymerization reactions have been discovered. 

Ring-type monomers such as cyclic ethers, lactams, and lactones can be polymerized via ring scission reactions to high-molecular-weight polymers. 

The cellulose derivatives are a class of naturally occurring binders. The polymer molecule is made up of a ring-type monomer unit having a modified a-... 

Traditional polymerizations usually involve AB-type monomers based on substituted ethylenes, strained small ring compounds using chain reactions that may be initiated by free radical, anionic or cationic initiators [20]. Alternatively, AB-type monomers may be used in polycondensation reactions. 

Over the past decade, literally dozens of new AB2-type monomers have been reported leading to an enormously diverse array of hyperbranched structures. Some general types include poly(phenylenes) obtained by Suzuki-coupling [54, 55], poly(phenylacetylenes prepared by Heck-reaction [58], polycarbosilanes, polycarbosiloxanes [59], and polysiloxysilanes by hydrosilylation [60], poly(ether ketones) by nucleophilic aromatic substitution [61] and polyesters [62] or polyethers by polycondensations [63] or by ring opening [64]. 

Fig. 34. Structural types for complexed lithium amides (RR NLixLi, L = a Lewis base (a) ladders with n = 2 and 3 (b) dimeric rings (c) monomers (CIPs and SSIPs). ...

The formation of triazole rings by the reactions of azides and acetylenes was first described by Huisgen and coworkers [48,49] and has recently been promoted as dick chemistry by Sharpless et al. [50,51]. This versatile [3 + 2] dipolar cycloaddition proved to be useful for the synthesis of hyperbranched polytriazoles via 1,3-dipolar polycydoaddition of AB2-type monomers 28 and 29 (Scheme 14) [52], The monomers exhibited very high reactivity the... 

Okumara et al. [10] were the first to attempt the enzyme-catalyzed synthesis of oligoesters from a reaction between dicarboxylic acids and diols. Gutman et al. [11] reported the first study on polyester synthesis by enzyme-catalyzed polymerization of A-B type monomers. Two independent groups in 1993 [12, 13] were first to report enzyme-catalyzed ring-opening polymerization (ROP). Their studies focused on 7- and 6-membered unsubstituted cyclic esters, e-caprolactone (e-CL) and 8-valerolactone (8-VL), respectively. 

Figure la. Free radical ring opening of a NVCA type monomer to an ester intemiediate. 

To produce polymer wood, wood is degassed and then loaded according to wood type with 35%-95% monomer. The monomer is then converted by polycondensation or addition polymerization to polymer. For polycondensation, monomers that do not eliminate volatile components during polyreaction are, of course, preferred. Ring-shaped monomers as well as monomers with carbon-carbon double bonds can be polymerized. In the latter case, polymerization can be induced by 7-rays, peroxides, redox systems, etc. Not all monomers, however, are suitable for the preparation of polymer wood. For example, acrylonitrile is not soluble in its own monomer. In wood, therefore, the precipitation polymerization leads to powdery deposits and not to a continuous phase. The same problem occurs with vinyl chloride, and in this case, the boiling point of the monomer is too low. Poly (vinyl acetate) has a glass transition temperature which is too low. In addition, monomers with G values (see Chapter 12) which are too low require high 7-ray doses to induce polymerization. Copolymers of styrene and acrylonitrile, poly (methyl methacrylate), and unsaturated polyesters are used commercially. 

Another publication describes formation of polyphenylene dendrimers that formed nanoparticles with 102 benzene rings [250]. In this preparation, an A—B type monomer, 2,3,4,5-tetrakis(4-triisopropylsilylethynylphenyl)-cyclopenta-2,3-dienone, is condensed in a [4 -i- 2]cycloaddition with 3,3 5,5 -tetraethynyl-biphenyl ... 

Other examples of self-polycondensation of an AB2-type monomer containing an imide-ring via etherification reactions can be found in the literature [7,10,77]. The selfpolycondensation can be performed though nucleophilic etherification of silylated phenol and aryl fluoride in diphenylsulfone at 240 °C under the presence of caesium fluoride... 

In the search of novel materials with low dielectric constants (e) and low water absorption for the electronics industry as well as transparent, high oxygen permeable and crosslinkable materials for the fast production of contact lenses, the Ring-Opening Metathesis Polymerization (ROMP) became an interesting opportunity for our company [1]. In 1988, it was shown, that strained (heterocyclic) monomers with or without pendant functionalities, especially 7-oxa-norbornene (7-oxabicyclo[2.2.1]hept-5-ene) type monomers, can be efficiently polymerized in aqueous solutions at moderate temperatures (Scheme 1) [2]. 

Monomers. Two broad types of monomers can be polymerized anionically vinyl, diene, and carbonyl-type monomers with diftmctionahty provided by one or more double bonds and cyclic (eg, heterocyclic) monomers with difunctionality provided by a ring that can open by reaction with nucleophiles. For vinyl monomers, there must be substituents on the double bond that can stabilize the negative charge that develops in the transition state for monomer addition, as shown in equation 8 ... 

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