Hydrogen bonding complex composition

Bajoras and Makuska investigated the effect of hydrogen bonding complexes on the reactivities of (meth)acrylic and isotonic acids in a binary mixture of dimethyl sulfoxide and water using IR spectroscopy (Bajoras and Makuska, 1986). They demonstrated that by altering the solvent composition it was possible to carry out copolymerization in the azeotropic which resulted in the production of homogeneous copolymers of definite compositions at high conversions. Furthermore, it was shown that water solvent fraction determines the rate of copolymerization and the reactivity ratios of the comonomers. This in turn determines the copolymer composition. 

The question as to whether hydrogen-bonded complexes are miscible with normal covalently bonded liquid-crystalline compounds arises for their application. Binary phase diagrams of a hydrogen-bonded mesogenic complex with normal liquid crystals have been prepared to examine the miscibility of two different classes of liquid crystals [67], Compound 16 or 4 -heptyl-4-cyanobi-phenyl was mixed with complex 14, These are miscible over the whole range of composition, A smectic C phase is induced for a mixture of 16 and the cyanobiphenyl. 

Variation with solvent composition explained in terms of formation of a 1 1 hydrogen bonded complex and further solvent effects. 

Remarks Finding ionization conditions under which both the rotaxane and the hydrogen-bonded complex are formed with sufficient intensity may be difficult, and optimization may be necessary. Since both anions have the same elemental composition, make sure that no memory effect occurs when both are measured one after the other. 

It is important to note that these data can be retrieved from measurements of IR spectra at room temperature in solution or even in the soUd state and need just a comparative analysis of the spectra of proton donor with and without base (Fig. 10). Application of Eqs. 12 does not require the knowledge of concentrations, but one should keep in mind that the base excess makes it easier to observe. Measurements at different temperatures provide not only the enthalpy (AHhb) but entropy (AShb) of hydrogen bond formation as the parameters of the temperature dependenee of hydrogen bond formation eonstant AThr. The AThr values (Eq. 4) can be obtained from the intensity drop of vah band (Fig. 10). In this case the knowledge of proton donor and proton acceptor concentrations is vital. In the absence of proton donor self-association (relatively low HA concentrations) the hydrogen bonded complexes have 1 1 composition (one HA molecule interacts with one molecule of proton acceptor) and calculations are straightforward. 

Table 7 IR data in the range of vco and Vno vibrations (in cm ) for ReHX(CO)(NO)(PR3) hydrides (3) and their hydrogen bonded complexes 4 and 5 (of 1 1 and 2 1 composition.

Philippova and Starodubtzev have also extensively studied the complex-ation behavior of polyacids and PEG, especially, the system of crosslinked of poly(methacrylic acid) and linear poly(ethylene glycol) (Philippova and Starodubtzev, 1995 Philippova et al., 1994). They observed that decreasing the molecular weight of PEG from 6000 to 1500 resulted in its slower diffusion into the swollen network of PMAA, and a drastic decrease in both the stability and equilibrium composition of the intermacromolecular complex. Analysis of dried polymer networks of PMAA with absorbed PEG chains by FT-IR spectroscopy revealed the presence of two types of hydrogen bonded structures (1) dimers of methacrylic acid at absorption frequency of 1700 cm-1 and (2) interpolymer complexes of PMAA and PEG at 1733 cm-1. In addition, they also suggested as a result of their studies, that the hydrogen bonded dimer of PMAA forms preferentially to the intermacromolecular complex between the PMAA network and PEG chains. 

---