Crosslinking mode

Hydrogel Crosslinking mode Dissociation signal References... 

A new class of functional comonomers exemplified by acrylamidobutyraldehyde dialkyl acetals 1 and their Interconvertible cyclic hemlamidal derivatives 2 were prepared and their chemistry was Investigated for use In polymers requiring post-crosslInking capability. These monomers do not possess volatile or extractable aldehyde components and exhibit additional crosslinking modes not found with conventional am1de/forma1dehyde condensates, eg, loss of ROH to form enamides 9 or TO and facile thermodynamically favored reaction with diols to form cyclic acetals. 

Alternate Crosslinking Modes. In addition to the crosslinking modes previously described, (co)polymers containing 1 and 2 may be cured by other means. For example, under appropriate acidic conditions with limited availability of active hydrogen species cyclic hemiamidals 2 will lose ROH to form the enamide 9 (Scheme 5). This has been demonstrated on model systems, e.g., 2 where vinyl is replaced by methyl ). The product, N-acetylpyrroline, has in turn been converted to nonvolatile products (oligomers) under free radical catalysis. These systems may thus be considered for application in the UV/EB or catalyzed free radical cure field. 

While all of the materials discussed above contain standard covalent crosslinks, it is also possible to utilize a range of physical crosslinking modes. Three distinct types of physical crosslinks may be recognized. 

To help distinguish the different crosslink modes, mathematical notation may be called into play. A special advantage of the notational system to be described involves the completeness with which a set of known crosslinking modes can be described. Further, and perhaps more importantly, the possibility arises of generating new systems. 

Thus, a series of tables similar to Table IV may be generated, once the polymers and crosslinking modes have been specified. Several aspects of such reactions and their notation have been reviewed recently... 

In other cases, creep or flow could be suppressed by the addition of a second crosslinking mode, swelling decreased, etc. More generally, if the chemist or chemical engineer becomes aware of the possibility of introducing a second crosslink mode into a system as a method of modifying the polymer, the probability of discovering unique behavior profiles increases. 

T. J. Kistenmacher, J. D. Orbell, and L. G. Marzilli Conformational Properties of Purine and Pyrimidine Complexes of cis-Platinum Implications for Platinum(II)— DNA Crosslinking Modes (Platinum, Gold and Other Metal Chemotherapeutic Agents, ACS Symposium Series v. 209, Ed. S. J. Lippard), p. 191. ACS, Washington... 

There is not enough space here to give a detailed classification, but only to delineate the major families from which resins for industrial coatings may be selected. Resins may be divided into two groups according to their modes of film formation which may or may not involve a chemical reaction. In the first, the components must react together to form a crosslinked structure which may require heat, radiation or catalysis to effect the reaction. The bulk of resins used in industrial finishes are of this type. They are commonly referred to as chemically convertible or, simply, convertible. 

Although great progress has been made in study of the mode of action of the azinomycins, a full understanding of their interaction with DNA will require future structural characterization of azinomycin-DNA crosslinks by NMR or X-ray crystallography. 

Naphthalenedisulfonate-acetonitrile as the only mobile phase with a silica column coated with a crosslinked aminofluorocarbon polymer has proven to be an effective combination for the separation of aliphatic anionic surfactants. Indirect conductivity and photometric detection modes are used to monitor these analytes. The retention of these surfactants is found to depend on both the ionic strength and the organic solvent content of the mobile phase. The mechanism of retention is considered to be a combination of both reverse phase and ion exchange processes. Selective separation of both alkanesulfonates and... 

The fracture strength and mode of fracture of a material have been found to be related to a number of characteristics of the polymer molecules of which it is made up. These include, among others, constitution, molar mass, polydispersity, crystallinity, and degree of crosslinking. Other factors which also affect fracture strength and mode of fracture are temperature, strain rate, and geometry of the specimen, all of which are decided upon prior to testing the material. 

Glntaraldehyde also owes part of its mode of action to its ability to react with, and provide irreversible crosslinking in, the cell wall. As a result, other cell functions are impaired. This phenomenon is especially found in Gram-positive cells. 

The choice of a corrosion inhibitor as an additive in antifreezing agents is also dependent on the mode of operation. For instance, cars are operated intermittently. Here the corrosion inhibitors must also protect the system when it is idle. Film-forming silicates can protect the system while idle. This is especially true of aluminum parts, which are introduced in cars for the sake of weight reduction. But silicones can react with ethylene glycol to form crosslinked polymers. These gels may clog lines. 

Modes of attachment of functional groups to crosslinked polystyrene are discussed ( 1). Attention is drawn to improved stability and activity of polymer-bound reagents and catalysts incorporating dimethylene spacer between polystyrene aryl and functional group heteroatom, and the simplicity and versatility of their synthesis through high-conversion functional group modifications. 

To explain the formation of non-crosslinked polymers from the diallyl quaternary ammonium system, Butler and Angelo proposed a chain growth mechanism which involved a series of intra- and inter-molecular propagation steps (15). This type of polymerization was subsequently shown to occur in a wide variety of symmetrical diene systems which cyclize to form five or six-membered ring structures. This mode of propagation of a non-conjugated diene with subsequent ring formation was later called cyclopolymerization. 

As these experiments indicate, polysilanes can in some cases be converted to silicon carbide directly, without the necessity for formation of polycarbosilane, fractionation, or oxidation. For example, polysilastyrene copolymers can be formed into films or fibers and then crosslinked by irradiation with UV light. The crosslinked polysilane forms silicon carbide when heated to 1100°C in vacuum. (1U This method can be used in a "printing" mode, if a film of polysilane is cast onto a ceramic or metal substrate, then... 

Fig. 11. Schematic of relaxation time spectrum of the critical gel of PBD 44 (Mw = 44 000). The entanglement and glass transition is governed by the precursor s BSW-spectrum, while the CW spectrum describes the longer modes due to the crosslinking [60]. denotes the longest relaxation time of PBD44 before crosslinking...

The mode of polymerisation and crosslinking for coatings is very similar to that of bulk polymers. An important requirement is that premature polymerisation should not take place before application. In the presence of activators, e.g., cobalt naphthenate, many paints on exposure to air polymerise by radical oxidation resulting in crosslinked structures. Stepwise growth polymerisation, e.g., urethanes, is promoted by heat therefore storage at high temperatures (>50°C) should be avoided. 

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