Direct polymerization

There is a good amount of data on the transformations of natural polymers, but the literature concerning chemical modifications of natural monomers is rather scanty. However, there are a few natural monomers that have found applications. The monomers in these cases are either modified into other suitable monomers of industrial importance or are polymerized directly into polymers. A few examples are given below for illustration. 

Prerequisite for the formation of a network structure is the existence of distinct PVC globules of ca. 1 ym diameter generated in the polymerization directly as was shown by Berens and Folt.10... 

The most promising route towards variable isotacic PHB is a process in which PO is transferred to both enantiopure and racemic (3-BL in two parallel processes (Fig. 40). As mentioned, these monomers can be distilled off from the catalysts and polymerized directly. Thus, any degree of tacticity in the polymer can be adjusted by mixing racemic and enantiopure (3-BL, which would allow the preparation of tailor-made materials from the low-cost oil-based monomers PO and CO (cf. Sect. 8). 

This was conhrmed in 1967 by Kubin et al., who were the first to accomplish polymerization directly in a glass colnmn [13], The resulting swollen poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) gel, which was prepared in the presence of 1% cross-linker, was strongly compressed after pressnre application and consequently exhibited exceedingly low permeability (4.5mL/h for a 25 X 220 mm colnmn) and poor efficiency. 

Following route A (Fig. 1), Yan Xiao et al. reported the chemoenzymatic synthesis of poly(8-caprolactone) (PCL) and chiral poly(4-methyl-8-caprolactone) (PMCL) microparticles [5]. The telechelic polymer diol precursors were obtained by enzymatic polymerization of the corresponding monomers in the presence of hexanediol. Enzymatic kinetic resolution polymerization directly yielded the (R)-and (S )-enriched chiral polymers. After acrylation using acryloylchloride, the chiral and nonchiral particles were obtained by crosslinking in an oil-in-water emulsion photopolymerization. Preliminary degradation experiments showed that the stereoselectivity of CALB is retained in the degradation of the chiral microparticles (Fig. 2). 

PA-induced acrylate polymerization has also been used as a way of writing bits for high-density read-only memory devices. In early work, acrylates were polymerized directly, with the information readable through the different refractive indices of acrylate monomers and polymerized acrylates however, high-power excitation was required due to the low cross-sections of the materials employed [160], An alternative scheme involves resins incorporating effective 2 PA dyes similar to... 

Cationic Polymerization. Cationic polymerization is initiated by the transfer of a cation from the catalyst to the monomer. It allows a wider choice of monomers with double bonds, including carbonyls, cyclic ethers, and lactones. The ion may be within a carbonium or an oxonium ion. Friedel-Crafts halides, like AlCls or A CoHsJCL, are strong Lewis acids and initiate the polymerization directly. Weak Lewis acids need a... 

Ferroelectric liquid crystalline monomers (Fig. 21, XXXVII) bearing two terminal vinyl groups were polymerized directly from their smectic A" liquid crystal phase using a Grubbs-type initiator. 

As a photoinitiator for the polymerization of bulk methyl methacrylate, benzil was found to be considerably less efficient than benzoin or benzoin methyl ether (20), e,g. at photoinitiator concentrations of 10 M, the polymerization rate observed using benzoin was eight times that observed using benzil, despite the fact that the latter was found to absorb three times as much of the incident radiation (Fig. 1). The photo-initiating efficiency of benzil was improved by a factor of three on addition to the methyl methacrylate of 10% v/v tetrahydrofuran, whereas the same additive had no appreciable effect on rates of benzoin- and benzoin methyl ether-photoinitiated polymerizations direct evidence that photoinitiation by benzil proceeds by a hydrogen abstraction mechanism rather than by fragmentation. 

Electropolymerization Based on 4-Vinylpyrldlne and Related Ligands. The third technique for preparing electrode/film interfaces is in many ways the most interesting both in terms of the chemistry involved and the results so far obtained. The strategy is to induce polymerization directly at the electrode surface by oxidation or reduction and our emphasis has been on the reduction of coordinated 4-vinylpyridine and related compounds. It is known that 4-vinylpyridine is susceptible to anionic polymerization (38). 

The alkyl substituents of methacrylates are varied as methyl (M-l),27-84-100-132-133 176 ethyl (M-2),102198 isopropyl (M-3),199 n-butyl (M-4),102 132 176 198 isobutyl (M-5),102 sec-butyl (M-6),102 tot-butyl (M-7),63102 isobornyl (M-8),63 2-phenylethyl (M-9),195 benzyl (M-10),199 and 4-nitrophenyl (M-ll)166 methacrylates were also polymerized in a controlled way, and the polymer from M-ll can be converted easily into poly(methacrylic acid) via deprotection of the nitrophenyl group. Sodium methacrylate (M-12), an ionic monomer, can be polymerized directly into poly(methacrylic acid) sodium salt with controlled molecular weights and narrow MWDs (MJMn = 1.2—1.3) with a water-soluble bromide initiator and CuBr/L-1 in water under alkaline conditions (pH 8—9) at 90 °C, although the polymerization stopped around 70— 80%.200... 

Amino- and amido-functionalized monomers can also be polymerized directly with metal catalysts. Living radical polymerization of 2-(dimethylamino)-ethyl methacrylate (FM-5) was achieved with 1-31 (X = Br)/CuBr/L-29 in dichlorobenzene at 50 °C.314 Its ammonium salt (FM-6) was polymerized from the surface of a cross-linked polystyrene latex with CuBr/ L-l in water at 80 °C to generate hydrophilic shells, although there were no data for polymer molecular weight.248 As described above (section II.C.6), (methacrylamides with at least their amido protons unprotected (FM-7, FM-8, and FM-9) can be polymerized with copper-based systems,117168,217,218 but a further optimization seems to be necessary. 

There are numerous combinations of transition metal and ligand that can be used to tailor the ATRP catalyst system to specific monomers. The ATRP systems are tolerant of many impurities and can be carried out in the presence of limited amount of oxygen and inhibitors [216,217]. This approach is so simple that it has been proposed as undergraduate experiments to prepare block copolymers [218,219]. However, the ATRP catalyst can be poisoned by acids, but the salts of methacrylic and vinylbenzoic acids have been polymerized directly in aqueous media [206]. Also, the use of protecting groups [206], followed by a deprotection step to yield the acids, has been successful in organic media [220]. While ATRP cannot be used to prepared well-defined polymers of vinyl acetate [221 ] as of yet, these goals may be realized with further catalyst development. 

I-B group Oligostilbenes are polymerized directly from resveratrol monomers but do not contain any oxygen heterocyclic ring in their structures, such as ampelopsis D (21) [11]. Until now, 20 oligomers of this group have been found in plants. 

Latex-based polymer materials can be either nature-made, as natural rubber [Stern, 1967 White, 1995], or synthetically made. The synthetically made latexes are commonly based on recipes of monomer, water, surfactant, and free radical initiator to induce chain polymerization [Lovell and El-Aasser, 1997 Wickson, 1993], However, recipes based on step polymerization are also well known, often resulting in crossUnked films [Walker and Shaffer, 1996], The resulting latex material consists of small particles, usually spherical, of 50-500 nm in diameter, dispersed in water. Alternately, polymers are sometimes emulsified after polymerization (direct emulsification, the product sometimes called artificial latexes) via agitation of a melt in the presence of water and surfactant (emulsifier), and sometimes organic solvent or plasticizer [Piirma, 1989]. 

Quantitatively, the end-group intensity relative to the main-chain intensity gives the number-average degree of polymerization directly. 

For both filopods and lamellipods/pseudopods, stimulated actin polymerization directly under the membrane is thought to provide the driving force producing the protrusion [21,40,169,173]. Thus the regulation of the location of actin polymerization and the cross-linldng between actin filaments is critical for coordinating chemotactic responses. 

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