Reaction crosslinking

Haward et al.t have reported some research in which a copolymer of styrene and hydroxyethylmethacrylate was cross-linked by hexamethylene diisocyanate. Draw the structural formula for a portion of this cross-linked polymer and indicate what part of the molecule is the result of a condensation reaction and what part results from addition polymerization. These authors indicate that the crosslinking reaction is carried out in sufficiently dilute solutions of copolymer that the crosslinking is primarily intramolecular rather than intermolecular. Explain the distinction between these two terms and why concentration affects the relative amounts of each. 

Other crosslinking reactions may be triggered by a catalyzed reaction between different units of a copolymerized functional monomer, such as A -methylol acrylamide or a copolymerized silane compound [86]. 

Scheme 9. Crosslinking reaction of a two-part moisture cure silicone adhesive system.

Scheme 11. Basic crosslinking reaction by hydrosilylation catalyzed by a platinum complex.

In this reaction, no by-products are evolved, and the crosslinking reactions occur within the bulk of the material. A typical hydrosilylation crosslinking system is depicted in Scheme 11, where n and y can vary depending on the required viscosity of the uncured formulation and the final targeted properties of the cured adhesive. 

Fig. 8. Crosslinking reactions of carboxylated waterborne polyurethane dispersions.

BMI was also used as a crosslinking agent for poly(iminoethylene). The Michael addition takes place with the nucleophilic nitrogen of the imino group and the double bonds of the electrophilic BMI. The Michael addition of BMI is now adopted as a crosslinking reaction for polymers with amino end groups [2]. 

The crosslinking reaction is detectable without difficulty by spectroscopic and magnetic measurements. 

From the data of DTA and TGA analyses illustrated in Fig. 4, its evident that the visible exo-peaks in the range of 140-150°C appear in DTA curves (Fig. 4a), which can be taken as evidence of a crosslinking reaction of acylated macromolecules at the expense of side chain... 

A. Crosslinking reactions of two polymer chains of different types. 

The non-Newtonian index is plotted against the blend ratio in Fig. 2. There are three distinct stages of the change of value with %NBR in the preblend. First, a decrease of up to 40% of NBR, a rapid rise of up to 60% of NBR, and beyond this ratio a further decrease are observed. Heating of blends shows the only minimum at 50 50 ratio. It is obvious that 60-50% of Hypalon in the NBR-Hypalon blend is an optimum range where maximum extent of interchain crosslinking reaction is expected, and this blend is supposed to be more pseudoplastic. 

Interfacial adhesion and, thereby, compatibility can be enhanced by the selective crosslinking reaction in polymer blends. Inoue and Suzuki [26] reported the properties of blends dynamically crosslinked PP-EPDM blends. The crosslinking agent was yV,N -/w-phenylene-bismaleimide - poly(2,2,4 - trimethyl - 1,2-dihydroquino -line) system. Increase in interfacial adhesion leads to... 

Through the addition of a low-molecular weight component that may promote copolymer formation and crosslinking or co-crosslinking reactions. 

Idealised crosslinking reaction of UF resin with alkyd resin... 

From these, prepolymers are prepared where the diisocyanates may be completely reacted as in the case of the urethane oils which resemble the oil-modified alkyds but have urethane (—NHCOO—) links in place of the ester (—COO—) links of the alkyds, or where one only of the isocyanate groups is combined, leaving the other to participate in crosslinking reactions. Such a reactive prepolymer is the biuret that may be prepared from hexamethylene diisocyanate, has the following structure ... 

The different possible adducts formed between mitomycin C and DNA have been isolated by degradation of DNA after in vitro alkylation/crosslinking reactions and structurally characterized. Monoadduct 21 (Scheme 11.3), derived from alkylation at C-l only [53], and monoadducts 22 [54] and 23 [55, 56] (derived from C-10 alkylation by 16 at N-7 or N-2 of guanine, respectively) have been isolated, together with bisadducts 24 [57] and 25 [58], derived from interstrand and intrastrand crosslinks, respectively, and adduct 26 [59], formed by addition of a molecule of water to C-10 instead of the second guanine. All of these adducts have also been isolated from DNA after in vivo crosslinking [60, 61]. 

It was concluded that the crosslinking reaction proceeded through initial alkylation of N-7 of adenine by the aziridine ring, followed by guanine N-7 alkylation by the epoxide (Figure 11.12). This seems inconsistent with Armstrong s earlier conclusions, but the very short oligonucleotides used by Saito et al. may influence the DNA alkylation chemistry. 

For example, the molecular weight of unsaturated polyesters is controlled to less than 5000 g/mol. The low molecular weight of the unsaturated polyester allows solvation in vinyl monomers such as styrene to produce a low-viscosity resin. Unsaturated polyesters are made with monomers containing carbon-carbon double bonds able to undergo free-radical crosslinking reactions with styrene and other vinyl monomers. Crosslinking the resin by free-radical polymerization produces the mechanical properties needed in various applications. 

The final properties depend not only on unstaturated polyester structure but also on a number of other parameters, such as the nature and proportion of unsaturated comonomer, the nature of the initiator, and the experimental conditions of the crosslinking reaction. Moreover, since polyester resins are mainly used as matrices for composite materials, the nature and amount of inorganic fillers and of reinforcing fibers are also of considerable importance. These aspects have been discussed in many reviews and book chapters and are beyond the scope of this chapter.7-9... 

Quentin may have been the first to sulfonate (arylene ether sulfone).168 In this patent, it was demonstrated that the bisphenol A polysulfone could be sulfonated by chlorosulfonic acid to produce a sulfonated polyfarylene ether sulfone), which was used for desalination via reverse osmosis. However, the chlorosulfonic acid may be capable of cleaving the bisphenol A polysulfone partially at the iso-propylidene link or it might induce branching and crosslinking reactions by... 

Quinone methides are the key intermediates in both resole resin syntheses and crosslinking reactions. They form by the dehydration of hydroxymethylphenols or dimethylether linkages (Fig. 7.24). Resonance forms for quinone methides include both quinoid and benzoid structures (Fig. 7.25). The oligomerization or crosslinking reaction proceeds by nucleophilic attack on the quinone methide carbon. 

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