Characterization of the structure of the stereocomplex of poly(methyl methacrylate) in solution from NMR relaxation data

Abstract

From the values of relaxation times Tz determined on a pulse spectrometer, and from the shape of bands in high resolution (HR-) and broad line (BL-) NMR spectra, two types of protons, different in mobility, were found to exist in the associated stereocomplex of isotuctic (it-) and spdiotactic (sr-) poly(methy1 methacrylate) (PMMA). From the analysis of NMR spectra, measured at magic angle rotation (MAR-NMR), the mobility of the ester groups in the stereocomplex is shown to be greatly hindered. Temperature changes of HR-NMR spectra of mixed solutions of it-and st-PMMA in benzene indicate that the associated segments of the stereocomplex can be characterized as junctions of a network of nonassociated sequences. ZUSAMMENFASSUNG:Mit dem lmpulsspektrometer bestimmte Relaxationszeiten T,, sowie Linienformen in Hochauflosungs-und Breitband-Kernresonanzspektren (HR-und BL-NMR) haben gezeigt. daR im assoziierten Stereokomplex von isotakrischem (it-). und synrliotaktischem (st-) Poly(methylmethacry1at) (PMMA) zwei Protonentypen vorkommen, die sich durch ihre Beweglichkeit unterscheiden. Aus der Analyse der unter dem magischen Winkel aufgenommenen Kernresonanzspektren (MAR-NMR) wurde gezeigt, daB die Beweglichkeit von Estergruppen im Stereokomplex weitgehend behindert ist. Aus der Temperaturabhangigkeit der HR-NMR Spektren der gemischten Losungen von it-und sr-PMMA in Benzol konnen die assoziierten Stereokomplexsegmente als Vernetzungspunkte eines Geriistes von nichtassoziierten Sequenzen charakterisiert werden.

Stereocomplex formation between enantiomeric poly(lactic acid)s. 2. Stereocomplex formation in concentrated solutions

“…Complex formation for isotactic (it) and syndiotactic (st) poly(methyl methacrylate) (PMMA) is most widely known among the polymeric stereocomplexes and has intensively been investigated using various techniques. [15][16][17][18][19][20][21][22][23][24][25] It has been found that when itand st-PMMA form a stereocomplex in dilute solution with a strongly complexing solvent, the solution viscosity decreases, while in a concentrated solution of complexing solvent, an increase in viscosity is observed accompanying gelation. 15 In a previous paper, we reported that a stereocomplex is formed when a ternary dilute chloroform solution of PDLA and PLLA is poured into methanol, although no change in viscosity of the dilute chloroform solution could be detected.11 Therefore, the complex seems to form not in the dilute solution but during the precipitating process.…”