Comonomers, chemical structure

The DuPont Nafion materials, both sulfonate and carboxylate varieties, are not entirely unique, as similar perfluorinated ionomers have been developed by others such as the Asahi Chemical Company (commercial name Aciplex) and the Asahi Glass Company (commercial name Flemion). The comonomer chemical structures of and further information on these materials are given in the recent review article by Doyle and Rajendvan. Now commercially unavailable, but once considered a viable alternative, the Dow Chemical Company developed a somewhat similar perfluorinated ionomer that resembled the sulfonate form of Nafion except that the side chain of the former is shorter and contains one ether oxygen, rather than two ether oxygens, that is, —O—... 

Depending on the chemical structure of the MAI, a suitable solvent is sometimes needed to get a homogenous state of reaction mixture. Even if using the same combination of comonomers, for example, to prepare PMMA-b-poly(butyl acrylate) (PBA), the selection of the using order of comonomers for the first step or second step would affect the solvent selections, since PMMA is not easily soluble to BA monomer, while PBA is soluble to MM A monomer [28]. 

Short chain branches are frequently introduced into polymers by copolymerization. The chemical structure of the comonomer controls the type and length of the short chain branch. The polymerization catalyst, reaction conditions, and comonomer content in the reaction medium determine the probability of finding a branch at any particular location along a chain. Comonomers, and hence the short chain branches derived from them, can be introduced at random or as blocks. 

We can readily copolymerize styrene with a variety of comonomers. Commercially, the two most important random styrene copolymers are styrene co-acrylonitrile and styrene cobutadiene, the general chemical structures of which are shown in Fig, 21.3. 

The final class of polymers are copolymers containing one or more of the repeat units of classes 2 and 3 (15-18). Copolymer effectiveness would presumably be a function of the chemical structures of each comonomer, comonomer sequence distribution, and polymer molecular weight. The comonomer could be a relatively... 

Nafion ionomers were developed and are produced by the E. I. DuPont Company. These materials are generated by copolymerization of a perfluorinated vinyl ether comonomer with tetrafluoroethylene (TEE), resulting in the chemical structure given below. 

Postsulfonation of polymers to form PEMs can lead to undesirable side reactions and may be hard to control on a repeatable basis. Synthesis of sulfonated macromolecules for use in PEMs by the direct reaction of sulfonated comonomers has gained attention as a rigorous method of controlling the chemical structure, acid content, and even molecular weight of these materials. While more challenging synthetically than postsulfonation, the control of the chemical nature of the polymer afforded by direct copolymerization of sulfonated monomers and the repeatability of the reactions allows researchers to gain a more systematic understanding of these materials properties. Sulfonated poly(arylene ether)s, sulfonated poly-(imide)s, and sulfonated poly(styrene) derivatives have been the most prevalent of the directly copolymerized materials. 

Very interesting Diels Alder comonomers for BMI are the bis(benzocyclobutenes). Under appropriate thermal conditions, the strained four-membered ring of benzocyclobutene undergoes electrocylic ring opening to generate, in situ, o-quinodimethane, which, in the presence of BMI, reacts via a Diels-Alder reaction (83). The chemical structure of a bis(benzocyclobutene-imide) is provided in Fig. 28. The synthesis and properties of BCB and BMI/BCB blend systems is described in detail in chapter I of this book. 

Though MGI units have similar effects on the glass transition temperature as CMI comonomer, the specific features of the MGIMx copolymer chemical structure yield mechanical behaviours, in particular in fracture, quite different to the CMIM series (as described in [1]). For this reason, it is interesting to investigate the effect of MGI unit content on the p transition of the copolymers and compare it to that observed in the CMIM series. 

MACA as a hydrophobic comonomer can be used to modify PNIPAM. Copolymers, PNIPAM-co-MACA with different amounts of MACA can be synthesized by free-radical copolymerization of NIPAM and MACA in a mixture of methanol and chloroform with AIBN as the initiator. The resulting copolymers after purification can be dried in vacuum at 40 °C for 24 h. Hereafter, these copolymers are denoted as PNIPAM-co-x-MACA, where x denotes the molar percent of MACA. As expected, their solubility in water decreases as the MACA content or the solution temperature increases. It is also expected that the copolymer chains with a higher MACA content would have a lower LCST in comparison with PNIPAM homopolymer chains. In order to prepare a true solution, one has to dissolve these copolymers in water at low temperatures. The chemical structure of PNIPAM-co-MACA is as follows (Scheme 7). 

Nation ionomers are produced by copolymerization of a perfluorinated vinyl ether comonomer with tetrafluoroethylene resulting in the chemical structure shown in Figure 8.25 [162,166], This polymer and other related polymers consist of perfluorinated, hydrophobic, backbones that give chemical stability to the material. The material also contains sulfonated, hydrophilic, side groups that make hydration possible in the acidic regions, and also allow the transport of protons at low temperatures, since the higher limit of temperature is determined by the humidification of the membrane, since water is a sine qua non for conduction [166], The material exhibits a proton conductivity of 0.1 S/cm at 80°C [162], The membrane performance is then based on the hydrophilic character of the sulfonic acid groups, which allow proton transport when hydrated while the hydrophobic... 

Fig. 29 Chemical structures of comonomers used for copolymerization with parylenes.

Copolymers of type C offer an additional feature changing the composition of the hydrophilic and the hydrophobic comonomers, the hydrophilic/hydrophobic balance of the copolymers can be easily varied without changing the chemical structure of the starting material (28). Table 1 displays the results of non-ionic copolymers. In the case of a suitable monomer... 

Acrylics. Acrylics are produced by the polymerization of acrylonitrile. They have a chemical structure essentially comprising the repeating unit, [ —CH2—CH(CN)—]n, with up to 15 percent of the polymer comprising one or two other monomeric units. As comonomers, vinyl acetate and an acrylate or methacrylate ester is used to vary the properties of the polymer for both ease of processing into a fiber and for improved fiber properties [8]. 

Dow Chemical Company presented a series of PF copolymers, consisting of various charge-transport moieties and low band-gap chromophores on the backbone, for tuning the emission color of PLED to cover the whole visible range [63]. They claimed that their blue-, green-, and red-emitting copolymers (without disclosing chemical structures and ratios of comonomers) can exhibit acceptable device performance, as shown in Table 1. 

Nuclear magnetic resonance (NMR) spectroscopy is a popular direct measurement technique that provides quantitative information about the chemical structure of copolymers. and isotopes are the two commonly employed nuclei, but other isotopes ( N, F, F, Si, and P) can be used depending on the comonomers. Other spectroscopic techniques (e.g., infrared, ultraviolet, and Raman spectroscopy) are also used [129-132]. 

Chart 5.1 Chemical structures of comonomer moieties styrene (left) and 4-(methylacryloylami no) azobenzene (right). 

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