Intramolecular crosslinking

StiU, our conclusion on the restricted overlapping of individual polystyrene coils in the hypercrossHnked network and in the initial polymer solution was further corroborated by a direct experiment, namely by the preparation of a hypercrossHnked material deHberately constructed from individual polystyrene macromolecules. The initial Hnear polystyrene was first crosslinked intramolecularly in a very ddute solution and then the individual intramolecularly crossHnked cods, nanosponges, were additionally crosslinked intermolecularly in a concentrated solution, thus giving a bulk hypercrossHnked material. Both the nanosponges and the final polymeric material were subjected to electron microscopic investigation. 

When ifickel coordinates to two pyridine ligands, there is no guarantee that these ligands reside on different macromolecular chains, producing effective crosslinks. Intramolecular loops form if both ligands originate from the same chain, and Tg should not increase much, if at aU, due to ineffective crosslinks. Hence p accounts for the fraction of effective intermolecular coordination crosslinks. 

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. 

Serious deviations of the polymer network structure from the ideal one can have several causes. One of them is the crosslinking agent involvement in intramolecular cycle formation. The contribution of this reaction grows with the system dilution as well as when the crosslinker units in the chain are close one to the other, i.e. its fraction in the copolymer increases. All this is in good agreement with the observed trend. 

Analysis of data pertaining to the modulus of PEO gels obtained by the polyaddition reaction [90] shows that even in this simplified case the network structure substantially deviates from the ideal one. For all samples studied, the molecular weight between crosslinks (M p) exceeds the molecular weight of the precursor (MJ. With decreasing precursor concentration the M xp/Mn ratio increases. Thus, at Mn = 5650 a decrease in precursor concentration from 50 to 20% increases the ratio from 2.3 to 12 most probably due to intramolecular cycle formation. 

Diene monomers with suitably disposed double bonds may undergo intramolecular ring-closure in competition with propagation (Scheme 4.12). The term cyclopolymcrization was coined to cover such systems. Many systems which give cyclopolymerization to the exclusion of normal propagation and crosslinking are now known. The subject is reviewed in a series of works by Butler.98 102... 

Some Bis reactions may lead to intramolecular cycles that will not affect the elasticity behavior of the gel, and pendant, unreacted, gronps may form where only the crosslinker reacts at one of its double bonds [315]. Tobita and Hamielec [393] found that primary cyclization, i.e., the formation of loop cycles, may consnme as much as 80% of... 

Modification of the ATPase by ATP-EDC occurred without significant incorporation of the nucleotide into the enzyme, suggesting that the inhibition of enzymatic activity is entirely due to intramolecular crosslinking by the carbodiimide moiety... 

A similar mechanism was postulated for the Ca " -dependent inactivation of Ca -ATPase by ATP-imidazolidate [380] that results in intramolecular crosslinking with the formation of a new protein band of 125 kDa. In both cases the reactive carboxyl group was suggested to be the phosphate acceptor Asp351. 

DNA, apsPtDNA, contains an overhanging G-residue that undergoes preferential inter-duplex crosslinking (4°C over a period of 2 months) to form 3 -crosslinked complementary strands. Duplex melting and intramolecular hybridization at pH 4.2 leads to the formation of parallel stranded DNA, psPtDNA. 

Funke, Wa Microgels-Intramolecularly Crosslinked Macromolecules with a Globular Structure. VoL 136, pp. 137-232. 

The inhibition of C a2+-ATPase at the active site by ATP-Im or ADP-Im with the participation of Ca2+ is illustrated by the following model. In the reaction of ATP-imidazolide with the carboxylate of Asp 351, a mixed anhydride is formed with the aspartate residue, followed by presumably nucleophilic attack of a lysine side chain, thereby displacing the nucleotide and leading to an intramolecular crosslink.[1]... 

A-chain immunotoxins, however, may not be quite as cytotoxic as conjugates formed from intact toxin molecules (Manske et al., 1989). In an alternative approach to A chain use, the intact toxin of two-subunit proteins is directly conjugated to a monoclonal without isolation of the A chain. Conjugation of an antibody with intact A-B chain toxins can be done without a cleavable linker, as long as the A chain can still separate from the B chain once it is internalized. Therefore, it is important to avoid intramolecular crosslinking during the conjugation process which can prevent release of the A-B complex. In addition, since the B chain... 

For a crosslinking polyreaction the functionality of the monomers is the basic parameter. However, it was found long ago that, after their reaction, not all functional groups are involved in intermolecular crosslinks but also in intramolecular and cyclic links. 

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