Monomer modification

Acryhc stmctural adhesives have been modified by elastomers in order to obtain a phase-separated, toughened system. A significant contribution in this technology has been made in which acryhc adhesives were modified by the addition of chlorosulfonated polyethylene to obtain a phase-separated stmctural adhesive (11). Such adhesives also contain methyl methacrylate, glacial methacrylic acid, and cross-linkers such as ethylene glycol dimethacrylate [97-90-5]. The polymerization initiation system, which includes cumene hydroperoxide, N,1S7-dimethyl- -toluidine, and saccharin, can be apphed to the adherend surface as a primer, or it can be formulated as the second part of a two-part adhesive. Modification of cyanoacrylates using elastomers has also been attempted copolymers of acrylonitrile, butadiene, and styrene ethylene copolymers with methylacrylate or copolymers of methacrylates with butadiene and styrene have been used. However, because of the extreme reactivity of the monomer, modification of cyanoacrylate adhesives is very difficult and material purity is essential in order to be able to modify the cyanoacrylate without causing premature reaction. 

Hawker et al. 2001 Hawker and Wooley 2005). Recent developments in living radical polymerization allow the preparation of structurally well-defined block copolymers with low polydispersity. These polymerization methods include atom transfer free radical polymerization (Coessens et al. 2001), nitroxide-mediated polymerization (Hawker et al. 2001), and reversible addition fragmentation chain transfer polymerization (Chiefari et al. 1998). In addition to their ease of use, these approaches are generally more tolerant of various functionalities than anionic polymerization. However, direct polymerization of functional monomers is still problematic because of changes in the polymerization parameters upon monomer modification. As an alternative, functionalities can be incorporated into well-defined polymer backbones after polymerization by coupling a side chain modifier with tethered reactive sites (Shenhar et al. 2004 Carroll et al. 2005 Malkoch et al. 2005). The modification step requires a clean (i.e., free from side products) and quantitative reaction so that each site has the desired chemical structures. Otherwise it affords poor reproducibility of performance between different batches. 

BASF s Ecoflex is based on a co-polyester from terephthalic acid, adipic acid and 1,4-butanediol. The content of terephthalic acid in the polymer is approximately 42-45 mol% (with regard to the dicarboxylic monomers). Modification of the basic co-polyester lead to a flexible material, which is especially suitable for film applications. 

Coming back to Table 7, it should be emphasized that the simple cases shown there are the most important. None of the numerous derivatives obtained hitherto via monomer modification, copolymerization or codeposition of dispersed solids to form composites [258] showed improved properties relevant to batteries. Therefore the basic systems shown in Table 7 represent the optimum in terms of redox capacity, potential and long-term stability. 

Choi et al. [9] also reported the synthesis of functional benzoxazine monomers and polymers containing phenylphosphine oxide. Phosphorus-containing group was introduced into polybenzoxazine via monomer modification. Three phosphorus-containing bisphenol compounds, bis(4-hydroxyphenyl)phenylphosphine oxide (BHPPO), bis(4-hydroxyphenoxyphenyl) phenylphosphine... 

The second way involves direct copolymerization of functionalized monomers. Modification of monomers is a fundamentally different approach from modification of polymer in that modification of monomer makes feasible control of the molecular structures. Both diphenols and dihalide aryl sulfones can be modified to incorporate functional groups or new counterparts. 

Various monomers impart characteristic film properties to the acrylic polymer (see Table 1). These monomer modifications also affect polymer polarity and solubility, as well as the glass transition temperature of the polymer. 

Chain-Growth Associative Thickeners. Preparation of hydrophobically modified, water-soluble polymer in aqueous media by a chain-growth mechanism presents a unique challenge in that the hydrophobically modified monomers are surface active and form micelles (50). Although the initiation and propagation occurs primarily in the aqueous phase, when the propagating radical enters the micelle the hydrophobically modified monomers then polymerize in blocks. In addition, the hydrophobically modified monomer possesses a different reactivity ratio (42) than the unmodified monomer, and the composition of the polymer chain therefore varies considerably with conversion (57). The most extensively studied monomer of this class has been acrylamide, but there have been others such as the modification of PVAlc. Pyridine (58) was one of the first chain-growth polymers to be hydrophobically modified. This modification is a post-polymerization alkylation reaction and produces a random distribution of hydrophobic units. 

Successful />Xylylene VDP Monomers. Within the limits mentioned above, it is frequentiy possible, and often desirable, to modify the /5-xylylene monomer by attaching to it certain substituents. Limitations on such modifications He ia three areas reactivity, performance ia the coater, and cost. 

Mitsui Toatsu Chemical, Inc. disclosed a similar process usiag Raney copper (74) shortiy after the discovery at Dow, and BASF came out with a variation of the copper catalyst ia 1974 (75). Siace 1971 several hundred patents have shown modifications and improvements to this technology, both homogeneous and heterogeneous, and reviews of these processes have been pubHshed (76). Nalco Chemical Company has patented a process based essentially on Raney copper catalyst (77) ia both slurry and fixed-bed reactors and produces acrylamide monomer mainly for internal uses. Other producers ia Europe, besides Dow and American Cyanamid, iaclude AUied CoUoids and Stockhausen, who are beheved to use processes similar to the Raney copper technology of Mitsui Toatsu, and all have captive uses. Acrylamide is also produced ia large quantities ia Japan. Mitsui Toatsu and Mitsubishi are the largest producers, and both are beheved to use Raney copper catalysts ia a fixed bed reactor and to sell iato the merchant market. 

The principal monomer is acrylamide [79-06-17, where R = H and R = NH2, made by the hydrolysis of acrylonitrile. The homopolymer [9003-05-8] of acrylamide, which in theory has no electrical charge, has some use as a flocculant however, the majority of acrylamide-based flocculants are copolymers with acryHc monomers containing charged functional groups, such as those shown in Figure 1, or polymers containing functional groups formed by modification of acrylamide homopolymers or copolymers (Fig. 2). The chemistry of polyacrylamides has been reviewed by several authors (18—20) (see... 

There are two main advantages of acrylamide—acryUc-based flocculants which have allowed them to dominate the market for polymeric flocculants in many appHcation areas. The first is that these polymers can be made on a commercial scale with molecular weights up to 10—15 million which is much higher than any natural product. The second is that their electrical charge in solution and the charge density can be varied over a wide range by copolymerizing acrylamide with a variety of functional monomers or by chemical modification. 

Etee-tadical reactions ate accompHshed using a variety of processes with different temperature requirements, eg, vinyl monomer polymerization and polymer modifications such as curing, cross-linking, and vis-breaking. Thus, the polymer industries ate offered many different, commercial, organic peroxides representing a broad range of decomposition temperatures, as shown in Table 17 (19,22,31). 

These products are useful for modification of alkyd resins (qv), preparation of paint vehicles, and copolymeri2ation with other monomers. Substitution on the amino group occurs readily, giving bases stronger than the parent amines. 

Processes that are essentially modifications of laboratory methods and that allow operation on a larger scale are used for commercial preparation of vinyhdene chloride polymers. The intended use dictates the polymer characteristics and, to some extent, the method of manufacture. Emulsion polymerization and suspension polymerization are the preferred industrial processes. Either process is carried out in a closed, stirred reactor, which should be glass-lined and jacketed for heating and cooling. The reactor must be purged of oxygen, and the water and monomer must be free of metallic impurities to prevent an adverse effect on the thermal stabiUty of the polymer. 

Complexation of the initiator and/or modification with cocatalysts or activators affords greater polymerization activity (11). Many of the patented processes for commercially available polymers such as poly(MVE) employ BE etherate (12), although vinyl ethers can be polymerized with a variety of acidic compounds, even those unable to initiate other cationic polymerizations of less reactive monomers such as isobutene. Examples are protonic acids (13), Ziegler-Natta catalysts (14), and actinic radiation (15,16). 

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