DPP crystal

Differential Scanning Calorimetry. Some structural information is provided by the thermal behavior of the polymer. The homopolymer of DPP crystallizes when heated above the glass transition temperature. A crystallization exotherm at the appropriate temperature therefore indicates the presence of DPP blocks, either as the homopolymer or in a block copolymer. 

DSC traces of the polymers prepared in Procedures 1 and 2 are shown in Figure 3, along with that of a mixture of the two homopolymers. The polymer prepared by Procedure 2 shows the typical DPP crystallization exotherm, while that prepared by Procedure 1 does not crystallize and is therefore presumed not to contain DPP segments long enough to permit crystallization. 

DPP crystal 27 10000 HHHH/HDLL3, HDLL/DDLL4 HDLL/DDLL4 HHHH/DDDD 12 19 ... 

The intra- and intermolecular arrangements of the DPP molecules in a DPP crystal have been investigated by single X-ray structure analysis ". Angles and bond distances in the diphenyl DPP 2 are shown in Figure 11-3. 

Figure 11.4 Projection of diphenyl-DPP crystal 2 on the (b,c)-plane and illustration of the hydrogen bond interaction.

These studies were followed up by Ciba-Geigy and systematically developed into a synthetic route to a group of very fast red pigments, known as diketo-pyrrolopyrrole pigments (DPP pigments) [3, 4], since the brilliant red crystals of 141 turned out to be extremely insoluble. 

X-ray diffraction analyses revealed a practically planar crystal structure of diphenyl-DPP with the phenyl rings twisted by only 7° out of the plane of the... 

DPP/Quinacridone Mixed Crystal Phase ( Solid Solutions ) Pigments... 

From the reaction of the radical anion of l,2-bis[(2,6-diisopropylphenyl)imino]acen-aphthene (dpp-bian) with i -PrMgCl, the persistent radical complex isopropylmagnesium dpp-bian (253) was isolated in yields up to 60% (equation 20). An X-ray crystal-structure determination of 253 showed that the magnesium atom has distorted tetrahedral coordination geometry as the result of the cr-bonded isopropyl group, one coordinate-bonded diethyl ether molecule and A, A -chelate bonding of the dpp-bian radical anion. The radical anionic character of the dpp-bian moiety is indicated by the relatively long Mg—N bond distances [Mg-N 2.120(2) and 2.103(2) A]. 

Poly(arylene oxide) copolymers were prepared by simultaneous and sequential oxidation of 1 1 mixtures of 2, 6-dimethylphenol (DMP), 2-methyl-6-phenylphenol (MPP), and 2,6-diphenylphenol (DPP), and methods were developed for determination of their structure. DMP and DPP yielded either random copolymers or block copolymers with crystallizable DMP and DPP blocks, depending on the order of oxidation and reaction conditions. Four types of copolymers were produced from MPP and DPP random copolymers, block copolymers with crystallizable DPP blocks, short block copolymers with DPP segments too short to permit crystallization, and mixed block copolymers containing DPP blocks and randomized MPP-DPP segments. Redistribution is so facile in the DMP-MPP system that only random copolymers were obtained, even on oxidation of a mixture of the two homopolymers. 

The homopolymer of DMP dissolves readily in methylene chloride but precipitates on standing as a crystalline polymer-CH2Cl2 complex, providing a method for distinguishing between block copolymers and mixtures of homopolymers. Random copolymers prepared by methods a and b form stable solutions in methylene chloride. Copolymers with a 1 1 ratio of DMP and DPP prepared by methods c and d also yield stable methylene chloride solutions. Since the NMR spectrum shows that the DMP portion of these materials is present as a block and the solubility in methylene chloride shows that DMP homopolymer is absent, these copolymers have the block structure. They can be separated by crystallization from m-xylene into an insoluble DPP-rich fraction and a soluble DMP-rich fraction, both fractions having the NMR spectra characteristic of block copolymers. A typical 1 1 copolymer prepared by adding DMP to growing DPP polymer yielded 35% of insoluble material... 

Thermal Properties. The DPP portion of block copolymers crystallizes on heating at 290°C and then melts at 480°C. The DMP portion of block copolymers does not crystallize thermally but can be caused to crystallize by treatment with a suitable solvent, such as a mixture of toluene and methanol the crystallized DMP then melts at 258°C. The glass-transition temperatures of the homopolymers are too close (221°C for DMP, 228° for DPP) to permit observation of separate transitions, either in block copolymers or blends of the homopolymers. 

Oxidation of a mixture of equivalent weights of the two low-molecular-weight homopolymers at 25°C with a diethylamine-cuprous bromide catalyst yielded a copolymer that formed stable solutions in methylene chloride and could not be caused to crystallize by stirring with a 3 1 methanol/toluene mixture, a procedure that results in crystallization of DMP homopolymer or of the DMP portion of DMP-DPP block copolymers. The NMR spectrum was identical with that of the polymer obtained by simultaneous oxidation of the two monomers. 

Sequential Oxidation at 25° C. Because of the slow polymerization rate of DPP at 25°C, most sequential polymerizations at this temperature were carried out with isolated homopolymers, separately prepared under conditions appropriate for the homopolymerization. Oxidation at 25°C of a 1 1 mixture of DPP and MPP homopolymer yielded a copolymer that did not crystallize, formed stable solutions in m-xylene, and had the NMR spectrum characteristic of a random copolymer. 

The product of oxidation of a mixture of MPP and DPP homopolymer crystallized on heating. No clear glass transition was observed on the first heating, but on reheating, the transition occurred at 172°C. The NMR spectrum shows some randomization but resembles that of a mixture of homopolymers much more closely than that of a random copolymer (Figure 6). The product dissolves readily in m-xylene, but partially precipitates on standing overnight on a steam bath. 

Addition of DPP to growing MPP at 60° C produced still another type of copolymer. Solvent-cast films of this material are transparent. The copolymer does not crystallize on heating, forms stable solutions in m-xylene, and has a single glass transition, at 190°C. The thermal behavior is similar to that of a random copolymer, but the NMR spectrum (Figure 7) is more nearly that expected of a block copolymer. The methyl proton peak is rather sharp with the chemical shift expected for... 

Block copolymers of this composition are completely amorphous when isolated in the usual manner, by adding the polymer solution to a large volume of methanol or other antisolvent. They show a single Tg = 226°C. The T/s of the two homopolymers are too close (225° for DMP (17) and 230°C for DPP (11)) to permit the observation of separate transitions for the DMP and DPP portions of the blocks. The DPP portion of the block crystallizes when heated to approximately 290°C, as does the DPP homopolymer. Melting of the crystalline DPP, which occurs at 480°C in the homopolymer, could not be observed in the copolymer because of the onset of decomposition at approximately 450°C. 

DMP homopolymer, unlike that from DPP, does not crystallize thermally, and no evidence of such crystallinity has been observed in thermally... 

Fig. 2 Structure drawing of saxagliptin. Binding region of DPP-IV showing saxa-gliptin (ball-stick model) interactions with key amino acid residues (stick model) from X-ray crystal structure (3BJM) (produced with Pymol)...

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