Acryl fragment

It is noteworthy that in the case of IV there is a unidirectional, regioselec-tive formation of the pyrazoline ring due to the more electrophilic character of the or carbon of the acrylate fragment than that of the /3-methyne. The regio-selectivity of this cycloaddition notwithstanding, pyrazolines usually collapse to cyclopropanes by exclusion of molecular nitrogen under the influence of moderate heat, such as in V leading to VI. 

The ethylene-acrylic polymer (H) produced A.2% by weight of total volatiles. The condensables were Identified as acrylic fragments or oxidized ethylene fragments (Table III). The noncondensables were not identifed, but were considered to be moisture if their concentration was less than 0.5% by weight. 

The acrylic terpolymer (I) produced 0.8% by weight of condensable material which was identified as acrylate fragments and/ or oxidized paraffinic oil. 

Pyrolysis of poly(methyl methacrylate) at low temperature produces monomer, whereas other acrylics fragment with loss of side chains, scission of the chain backbone, elimination or rearrangement of the products. Knowledge of the degradation pathways for particular polymer sequences is required to interpret the fragmentation patterns obtained from pyrolysis (65-70). 

P. Dowd, B. K. Trivedi, M. Shapiro, and L. K. Marwaha (1976), Vitamin Bj2 model studies. Migration of the acrylate fragment in the carbon-skeleton rearrangement leading to a-methyleneglutaric acid. J. Amer. Chem. Soc. 98, 7875-7877. 

The stracture of 13 is particularly suitable for an intramolecular cycloaddition since it eontains a 1,3-dipole (the nitronate fragment) and a dipolarophile (the acrylate fragment) linked by a two-methylene tether. The second step of the tandem reaetion is then clear. Once nitronate 13 is formed, an intramolecular [3+2] cycloaddition takes place to yield tricyclic nitroso acetal 9 (Scheme 22.9). 

The regio- and stereochemistry of the reaction will follow the patterns previously discussed. The a and p carbons of the acrylate fragment will become attached respectively to the oxygen and the C=N carbon in the nitronate moiety, and the preference for the exo approach of the alkene will lead to the reaction product 9 with the carboxylate group, the P-H and the bridged Me in a cw-arrangement. 

For the construction of the I ring, the vinylic group introduced to activate the y-hydroxy epoxide moiety of 28 towards cyclization is an acrylic ester residue, which concomitantly allows cyclization on the allylic position, with formation of the tricyclic compound 29 containing the IJK fragment of the natural product, and fur-... 

First, these copolymers undergo decarboxylation more readily than any of the homopolymers. Second, decarboxylation involves the units of acrylic add at temperatures which do not affect homopolymers of acrylic acid. In our view, the first phenomenon is accounted for by the effect of separation of conjugation blocks exemplified by this particular chemical reaction. As to the second observation, we believe that decarboxylation under relatively mild conditions (160—170 °C) affects, apparently, the fragments of acrylic acid located at the junctions of the blocks. 

The high temperature polymerization of acrylates with the backbiting-fragmentation process has been used to synthesize macromonomers based on acrylate esters. 277,312 Interestingly, fragmentation shows a strong preference for giving the polymeric macromonomer 64 and a small radical 65. 276.277 An explanation for this specificity has yet to be proposed. 

Chain transfer to polymer is reported as a major complication and is thought to be unavoidable in the polymerization of alkyl acrylates.200 202 The mechanism is believed to involve abstraction of a tertiary backbone hydrogen (Scheme 6.32). It has been proposed that this process and the consequent formation of branches may contribute to the early onset of the gel or Norrish-Trommsdorff effect in the polymerization of these monomers. At high temperatures the radicals formed may undergo fragmentation. 

Copolymerization of macromonomers formed by backbiting and fragmentation is a second mechanism for long chain branch formation during acrylate polymerization (Section 4.4.3.3). The extents of long and short chain branching in acrylate polymers in emulsion polymerization as a function of conditions have been quantified.20 ... 

Ring B of pyrimido[l,6-tf]pyrimidines has been most frequently synthesized from [3+3] atom fragments. The 6-aminopyrimidin-2-one derivative, cytidine 211, on reaction with acrylic acid under thermal conditions gave the pyrimido[l,6- ]pyrimidin-4,6-dione 212 <1996MI301> while reaction with 3-chloropropionaldehyde under base catalysis resulted in the pyrimido[l,6- ]pyrimidine-6-one 213 (Scheme 33) <1996MI501, 1996BAP209>. 

A number of new resist materials which provide very high sensitivities have been developed in recent years [1-3]. In general, these systems owe their high sensitivity to the achievement of chemical amplification, a process which ensures that each photoevent is used in a multiplicative fashion to generate a cascade of successive reactions. Examples of such systems include the electron-beam induced [4] ringopening polymerization of oxacyclobutanes, the acid-catalyzed thermolysis of polymer side-chains [5-6] or the acid-catalyzed thermolytic fragmentation of polymer main-chains [7], Other important examples of the chemical amplification process are found in resist systems based on the free-radical photocrosslinking of acrylated polyols [8]. 

More recently, such studies have been extended to nonhydrocarbon chiral comonomers, for example, menthyl acrylate and menthyl methacrylate (379, 382). Of notable interest, especially for microsequence investigation, are fluorescence studies combined with CD spectra carried out on copolymers containing the caibazole fragment (382). It is interesting to note that the induction of... 

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