Microstructure and properties of poly(vinyl alcohol-co-vinyl acetate)-g-ε-caprolactone

Microstructural studies of Poly(vinyl alcohol-co-vinyl acetate)-g-polycaprolactone (PVA-Ac)-g-(PCL) were realized principally using NMR. Initial PVA-Ac has a rather blocky structure with an average sequence length of PVA units equal to 12.5. During the synthesis of the studied (PVA-Ac)-g-(PCL), alcoholysis and transesterification reactions led to PCL grafts with acetate end groups. These reactions typically concern 2-5.5% of the total acetate groups. The influence of the local tacticity on the alcohol triad reactivity was evidenced and explained the incomplete functionalization of the PVA-Ac hydroxyl groups. Alcoholysis reactions were also evidenced but with a very low rate in the tested conditions. Caprolactone homopolymerization was not observed. Other properties of the final synthesized copolymers were also presented. Crystallinity totally disappeared in the (PVA-Ac)-g-(PCL). The glass transition temperature was perfectly adjustable by the Fox law without significant modification of the viscoelastic properties characterized by dynamic rheology.     

Heterogeneous anionic coordinated polymerization of propylene oxide: A quantitative 13c NMR analysis of the regio- and stereo-selectivity of the catalyst via microstructure analysis of polymers

Poly(propylene oxide)s synthesized with an heterogeneous catalytic system have been analyzed by ¹³C NMR spectroscopy by using DEPT experiments and sub-spectrum editing techniques. The results have been compared with those obtained from commercial products, in order to reach a greater insight into the selectivity of the catalytic system. A quantitative and reliable determination of the inversion ratio is proposed, which implies each type of carbon as well. This inversion ratio was found to be much higher than that observed in commercial PPO. It is shown that when the inversion ratio is no longer negligeable, its accurate determination is a prerequisite to a reliable approach of the tacticity distribution in regular sequences. So, a quantitative determination of the configurational diad and triad distribution is proposed which takes into account the fraction of “defect” resonances (consequence of inverted addition) overlapping with “normal” resonances (unaffected by the inverted addition) in the different sub-spectra. The main features of the catalyst activity are outlined and compared with results obtained with commercial PPO.     

NMR techniques in emulsion polymer investigation

This paper is a brief survey showing the versatility and unicity of NMR spectroscopy for characterizing the macromolecular architecture in copolymers originated from an emulsion process. Three cases are more particularly described using various NMR techniques i) to carry out high resolution ¹³ C NMR in order to investigate the microstructure (mainly the monomer sequence distribution as a function of process variables, ii) to perform direct analysis of latex particles by ¹³ C NMR so as to get insight on the surface morphology of functional particles, iii) to deal with solid-state NMR on as-dried particles (or films) in order to obtain quantitative information on the internal morphology of composite latexes.     

Functionalization of poly(ethylene terephthalate) in the melt state: Chemical and rheological aspects

This article deals with a new way of improving the melt viscosity of linear poly(ethylene terephthalate) (PET) chains through the reaction of the PET end groups (alcohol and acid) with new chain extenders, 3‐(triethoxysilyl)propylsuccinic anhydride (ASSI) and 3‐glycidoxypropyltrimethoxysilane, during the melt processing of PET. The reactions, investigated with model compounds monomethylterephthalate and triethylene glycol monomethylether for PET? COOH and ? OH end groups, respectively, by multinuclear NMR spectroscopy (¹H, ¹³C, and ²⁹Si), provided evidence of well‐known acid–epoxide and alcohol–anhydride reactions, respectively. In addition, numerous other species appeared because of the presence of alkoxysilane groups, such as alcohol–alkoxysilane exchange reactions, acyloxysilane formation, and hydrolysis–condensation reactions of alkoxysilane. All these reactions led to the formation of branched chains when transposed to PET melt modification. A size exclusion chromatography analysis and the rheological behavior confirmed the presence of branched structures embedded in shorter linear PET chains. The rheological behavior of this blend was drastically modified in comparison with that of neat PET; consequently, there was an important increase in the zero‐shear viscosity, with a maximum concentration of branched structures of about 17 vol % obtained with an ASSI/PET molar ratio of 4. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2207–2223, 2005