Functionality, crosslinking

Hydrosilation silicones or addition cure systems utilize a hydride functional crosslinker with a vinyl functional base polymer and a noble metal catalyst. While the cure can be initiated with UV [48,49], thermal cure versions dominate the commercial market [23,50]. In thermal cure systems, inhibitors are necessary for processing and anchorage additives are common. 

Hydroxybenzylamine intermediates, 392 Hydroxybenzylamines, 389, 391, 416 thermal decomposition of, 392 Hydroxy-ester interchange reactions, 62, 65, 69-74, 84, 111 Hydroxy-functional crosslinkers, 214 Hydroxyl endgroup chemical titration, 94-95... 

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This means that, as a result of the urea formation, higher functional crosslink molecules are formed, which may influence the physical properties of the paint during curing. 

Annexin V-functionalized crosslinked iron oxide (CLIO) was designed as a contrast agent for MRI, which was additionally labeled with Cy5.5 to allow colocalization with optical imaging techniques [98]. Alternatively, conjugation of multiple Gd-DTPA molecules or SPIO particles to the C2 domain of synaptotagmin I was shown to allow the detection of apoptotic cells in vitro [99]. Zhao et al. [100] were the first to apply a C2 domain-functionalized SPIO and showed very promising results for future in vivo applications of MR contrast agents for the detection of apoptotic sites. 

It is apparent that the mode of reaction of the hyperbranched polyesteramides must be distinctively different from those of the known commercial crosslinkers. In order to explain these results, the hyperbranched polyesteramides should in our view not be regarded as simply multifunctional polymeric crosslinkers but rather as precondensed forms of two-functional crosslinkers (the addition product of diisopropanolamine and the cyclic anhydride), as depicted in Fig. 22, left. Bearing in mind the chemical fate of benzoic acid (2.2.1, Fig. 11) which was condensed with a polyesteramide resin and which appeared to transesterify at least as fast as it esterified, the mode of reaction of polyesters comprising aromatic acid end groups must be in accordance and comprised of both transesterification and esterification. 

Figure 4.7 Synthesis of PNA-functionalized crosslinker molecule and association of a complementary PNA-terminated polymer synthesized by ATRP (Wang et al. 2005).

Usually, the Tg vs x relationship shows an upward curvature related to the shape of the curves describing the increase in the concentration of branching points and high-functional crosslinks as a function of conversion (Chapter 3). Theoretical equations relating the Tg increase to structural parameters of the polymer network have been proposed. But, in every case, adjustable parameters are required to fit experimental results. 

Polynadimides. The exact structure of the network crosslink is somewhat controversial but it could resemble the structure shown in Fig. 10.6. These polymers cumulate all the problems encountered in other polymers Is it really pertinent to consider that we are in the presence of hexa-functional crosslinks In this case, how do we take into account their copolymer effect In fact, if the black junctions in Fig. 10.6 connect one crosslink directly to another, we are in the presence of crosslink lines rather than dispersed individual crosslinks. Does this feature modify the whole glass transition behavior There is, to our knowledge, no satisfactory answer to these questions, and the research field remains largely open in this domain. 

Figure 2. (A) Growth curve for pristine sample showing results of one site fit (dotted line) and two site fit (solid line - components are shown underneath curve in red) (B) Schematic of network structure of typical engineering silicone with both short and long chain constituents and standard four site crosslinking species and highly functional crosslinking sites. (Figure 2B is reproducedfrom reference 17. Copyright 2005 American Chemical Society.) (See page 7 of color insert.)...

Burshe MC, Sawant SB, Joshi JB, and Pangarkar VG. Sorption and permeation of binary water-alcohol systems through PVA membranes crossUnked with multi-functional crosslinking agents. Sep. Purific. Tech. 1997 12(2) 145-156. 

For application as a functional crosslinker or coupling agent in a one-component waterborne coating, a silane has to meet two important demands it must (1) be stable in the formulation for the required shelf life, and (2) be reactive after the coating formulation is applied to the substrate. Both... 

Since epoxides are reactive compounds, the epoxy groups present in pre-polymers are used for crosslinking or curing purposes. Curing occurs when the pre-polymer is treated with a suitable multi-functional crosslinking agent, or with an accelerator. The... 

The fluctuations of junction points in a network are quite similar to those of the branch point of an /-arm star polymer. In order to calculate the amplitude of these fluctuations, start with/- 1 strands that are attached at one end to the surface of the network and joined at the other end by a junction point connecting them to a single strand [see the left-most part of Fig. 7.5(a)]. The strands attached to the elastic non-fluctuating network surface are called seniority-zero strands. Each of these /— 1 seniority-zero strands are attached to a single seniority-one strand by a /-functional crosslink [see the left-mostpart of Fig. 7.5(a)]. The seniority of a particular strand is defined by the number of other network strands along the shortest path between it and the network surface. The/- 1 seniority-zero strands... 

A host of crosslinkers have been employed, see Table 6.2. The mixed functionality crosslinkers often serve as grafting sites between networks of quite different nature, perhaps one network chain polymerized, and the other step polymerized. Then, each type of functionality reacts with each type of monomer during polymerization. 

The crosslink density is dependent on the crosslinker fimc-tionallty and concentration, the chain length of the polymer and the concentration of functional, crosslinkable filler (silica). 

Features Hydroxy-functional crosslinkable with polyisocyanates pigment compat. high film hardness, flexibility, abrasion resist. exc. diem, resist. 

Features Hydroxy-functional crosslinkable with polyisocyanates exc. 

Features Hydroxy-functional crosslinkable with polyisocyanates high gloss exc. mech. props., adhesion to steel and noniron metals (Al, Zn) Properties Hazen < 200 color dilutable with toluene, xylene, acetone, MEK, MIBK, methoxypropyl acetate, ethyl acetate, butyl acetate dens. = 1.0 g/cm (20 C) dynamic vise. 1100-2500 mPa s hyd. no. 40-50 flash pt. 28 C 58-62% NV... 

Chem. Descrip. Acrylic resin (65%) in methoxypropyl acetate Uses Acrylic for air-drying and stoving two-component industrial coatings, wood coatings, metal coatings, plastic coatings Features Hydroxy-functional crosslinkable with polyisocyanates exc. 

Uses Acrylic for fast drying two-pack coatings, industrial lacquers Features Hydroxy-functional crosslinkable with polyisocyanates Properties Hazen < 80 color dens. = 1.00 g/cm (20 C) dynamic vise. 

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