Polyamides cyclic

Fig. 3.4 Polyamide-DNA binding motifs with equilibrium association constants K,). Hairpin amino-substitution at the a-position of the y-turn residue leads to enhanced binding affinity (10-fold) without loss of specificity, and with higher orientational selectivity and offers potential for further substitution. Cycle Cyclic polyamides show higher affinity than analogous hairpin molecules with the same number of cationic groups and eliminate all possibility of extended 1 1 binding. H-pin and U-pin compared to their non-linked analogs, H-pins and U-pins exhibit higher binding affinity. The black and open circles represent Im and Py rings, respectively diamonds repre-...

The acetolysis of hexamine has proven a diverse route to cyclic polyamides. 1,3,5-Triacetyl-... 

The nitrolysis of cyclic polyamides offers a possible alternative industrial synthesis of HMX. The nitrolysis of l,3,5,7-tetraacetyl-l,3,5,7-tetraazacyclooctane (TAT) (79) and 1,5-diacetyl-3,7-dinitro-l,3,5,7-tetraazacyclooctane (DADN) (80) with a solution of dinitrogen pentoxide in anhydrous nitric acid gives HMX in 79 % and 98 % yields, respectively. Interestingly, the same reactions with nitric acid-acetic anhydride fail at room temperature. 

Although rigid-rod poly(p-phenyleneterephthalamide) analogues having alkyl side chains did not contain cyclic polymers, the polycondensation of silylated m-phenylenediamine and aliphatic dicarboxyhc acid chloride afforded cyclic polyamides predominantly (Scheme 49) [187]. Furthermore, cyclic polymers were also produced in polycondensations for polyesters, poly(ether ketone)s, polyimides, and polyurethanes [183]. These examples are the products in polycondensation of AB monomers or in A2 + B2 polycondensations, but cyclization of oligomer and polymer was also confirmed in polycondensation of AB2 monomers [ 188-195] and in A2 + B3 [ 196-202] and A2 + B4 polycondensations [203-206], which afford hyperbranched polymers. 

Another interesting example from DSM is the synthesis of monomers for novel polyamides. In contrast to chemical routes, an enzyme (nitrilase) performs single hydrolysis of dinitrile to a mono-acid that can then be hydrogenated to novel cyclic polyamide (co)monomers (Figure 2.18). This is also an example of integration between bio- and chemo-catalysis. 

Further studies were devoted to syntheses of polyamides [60, 61] via KC polycondensations. The monomer combinations were selected so that polyamides having a moderate or good solubility in the reaction media were obtained, so that early precipitation of linear chains from the reaction mixture was prevented (e.g., (a) in Formula 7.3). From the best experiments spectra exclusively displaying mass peaks of cyclic polyamides up to 13 kDa were obtained. Similar results were found for soluble polyimides derived from the dianhydrides (b) and (c) (in Formula 7.3) and various aromatic diamines [62, 63]. 

The difunctionality of the enamines of cyclic ketones toward phenyl isocyanate provides the ideal situation for a potential polymer. The properties of the polyamides produced by addition of various diisocyanates to the enamines of cyclic ketones have been reported Ilia). 

The AB polyamides are made from either >-amino acids or cyclic lactams, derivatives of the oj-amino acids (Table 3.1). In these polymers, the amino and acid groups are inherently balanced and the polymer also contains one amino and one acid endgroup. There are a number of different routes available for polymerizing these AB-type polyamides ... 

In connection with studies on the ring-opening polymerization of cyclic acetals, we have undertaken investigations on the polymerization of bicyclic acetals, bicyclic oxalactone, and bicyclic oxalactam, which yield polysaccharide analogs, macrocyclic oligoesters, and a hydrophilic polyamide, respectively, some of which can be expected to be useful as novel speciality polymers. The monomers employed in the studies were prepared via synthetic routes presented in Scheme 1, starting from 3,4-dihydro-2H-pyran-2-carbaldehyde (acrolein dimer) I. 

Polymers with hetero-atoms in the chain are suitable for chemical recycling of waste materials. In addition to depolymerisation (nylon 6) and solvolysis (nylon 6,6, PETP, PU) the degradation of aliphatic polyamides with dicarboxylic acids, diamines and cyclic anhydrides, especially trimellitic anhydride, becomes more and more important. The utilisation of the obtained fragments is described. 

FIGURE 17.19 2D contour plot of a modified polyamide 6, first dimension LCCC, second dimension SEC. Area 1 unmodified chains, area 2 modified chains, area 3 cyclic oligomers. (See color plate.)... 

FIGURE 17.20 LCCC separation of low molar mass polyamide 6.6 samples. Top trace amine rich polyamide 6.6 (Mw = lOkg/mol), middle trace acid rich polyamide 6.6 (Mw = 6 kg/mol), lower trace cyclic polymer of polyamide 6.6 (Mw = 700) (Mengerink et al., 2002 with permission from Elsevier). 

A much better agreement between theory and experiment is found in the closely-related field of macrocyclisation equilibria. Investigations of the cyclic populations in ring-chain equilibrates set up in typical polymeric systems such as polyesters, polyethers, polysiloxanes, and polyamides take a major advantage from the relative ease with which the cyclic fraction can be separated from the linear fraction and analysed for the relative abundance of the individual oligomeric rings. This is conveniently done by means of modern analytical techniques such as gas-liquid and gel-permeation chromatography (Semiyen, 1976). 

A second major method of producing polyamides is by using an amino acid as a monomer (amine and acid group in the same molecule) or by a ring opening of cyclic amide (lactam). 

The presence of even small amounts of cyclic oligomers can be detrimental for the utilization of a polymer if the cyclics migrate out of the product during its use. Many commercial processes remove cyclic by extraction (e.g., with steam in polyamide production) or thermal devolatilization (polysiloxane). 

The polyamide-6 (Nylon-6) so obtained has a crystallite melting point around 216 °C. It still contains monomer and low-molecular-weight cyclic oligomers which can be removed by extraction with water or lower alcohols.These oligomers can be separated and identified chromatographically (see Example 4-9). 

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