Influence of the Stereochemical Structure on The Physicochemical Properties of Polymers Prepared by Ring-Opening Polymerization of Chiral Heterocyclic Monomers

Physico-chemical properties of polymers prepared by ringopening polymerization of heterocyclic chiral monomers with different enantiomeric composition are compared. Two general kinds of behaviour were observed for products with a monosubstituted carbon in the chain: when the substituent group is not bulky the properties of polyenantiomers and their racemic mixture are very similar ; when the substituent is a bulky group, e. g. t-butyl, many of the properties (m.p., crystalline structure, solubility, etc.) are very different for the same polymers. The corresponding statistical stereocopolymers are amorphous. For polymers with disubstituted asymmetric carbon atoms the statistical stereocopolymers are crystalline and their melting behaviour varies with the enantiomeric purity. In some cases a strong dependence of the mechanical and biological properties on the enantiomeric purity of stereocopolymers is reported

Influence of the Stereochemical Structure on The Physicochemical Properties of Polymers Prepared by Ring-Opening Polymerization of Chiral Heterocyclic Monomers

Physico-chemical properties of polymers prepared by ringopening polymerization of heterocyclic chiral monomers with different enantiomeric composition are compared. Two general kinds of behaviour were observed for products with a monosubstituted carbon in the chain: when the substituent group is not bulky the properties of polyenantiomers and their racemic mixture are very similar ; when the substituent is a bulky group, e. g. t-butyl, many of the properties (m.p., crystalline structure, solubility, etc.) are very different for the same polymers. The corresponding statistical stereocopolymers are amorphous. For polymers with disubstituted asymmetric carbon atoms the statistical stereocopolymers are crystalline and their melting behaviour varies with the enantiomeric purity. In some cases a strong dependence of the mechanical and biological properties on the enantiomeric purity of stereocopolymers is reported

Rheokinetic study of crosslinking of a,w-dihydroxy oligo(alkylene maleate)s with a trisisocyanate

The crosslinking reaction of three series of a,w-dihydroxy oligo(alkylene maleate)s with a trifunctional isocyanate was followed by dynamic mechanical analysis and FTIR spectroscopy. The evaluation of rheological parameters, such as storage G and loss modulus G", was recorded. A typical G versus time curve has a characteristic S shape, indicating autoacceleration of the crosslinking reaction. The whole curing process starting from G equal G" or the beginning of gelation is described by a second - order phenomenological rheokinetic equation which takes into account the autoacceleration effect, the latter being a consequence of the superposition of both the chemical reaction and phase segregation. It appears that the crosslinking reaction rate depends on the concentration of the functional groups, i.e., on the molecular weight of the polyester prepolymer and on the length of the aliphatic sequence in the repeating unit or the segmental mobility. The crosslinking rate decreases in the order: poly(octamethylene maleate) > poly(hexamethylene maleate) > poly(butylene maleate)

300 MHz 1H-NMR study of poly(propylene sulfide)

An 1H 300-MHz NMR spectroscopic study of deuterated poly(propylene sulfide) shows that methylene protons are sensitive to triad effects. It was possible to distinguish i, hi, s, and hs triads. Experimental values found for different polymers are in good agreement with theoretical amounts obtained from statistical probability calculation. The methyl groups are also slightly stereosensitive. By using optically active deuterated monomers with different R/S ratios it was possible to confirm the assignment of peaks and the tacticity. Nondeuterated polymers give very complicated spectra, and only the highly stereoregular polymer could be analyzed through its ABCX3 spin system