Solid-State NMR Study of Miscibility and Phase Separation in Blends and Semi-Interpenetrating Networks of ¹³C-Labeled Poly(styrene-co-acrylonitrile) and Poly(styrene-co-maleic anhydride)

Abstract

Site-directed isotopic enrichment and solid-state 13 C spin-diffusion NMR techniques were employed to characterize miscibility at the molecular level and phase separation in blends of amorphous polymers. Using 2D proton-driven spin-diffusion techniques on a mixture of 13 C-labeled poly(styreneco-maleic anhydride), [ 13 CH2, 13 CO]SMA (27 wt % MA, Mw ∼ 4 × 10 4 g mol -1 ), and poly(styrene-coacrylonitrile), [ 13 CN]SAN (27 wt % ACN, Mw ) 1.3 × 10 5 g mol -1 ), it is demonstrated that SMA and SAN are miscible on the molecular level. However, a specific orientation of the nitrile moieties in SAN with respect to the carbonyl groups in SMA is unlikely. This suggests that the miscibility of SAN and SMA copolymers is associated mainly with a decrease of intramolecular repulsion upon mixing, as opposed to a specific exothermic binary interaction. In addition, spin-diffusion experiments show that upon selective cross-linking of the SMA phase semi-interpenetrating networks are formed. Increasing the degree of cross-linking results in increasing degrees of phase separation.

Specific13C Isotope Enrichment of Isoprene

“…Isoprene (1) and (4-13 C)isoprene (1a) were prepared from methyl methacrylate using this scheme. We have prepared various other monomers in 13 C-labelled form, like acrylates, [7] acrylonitrile, [3] maleic anhydride, [2,3] styrene [3] and methyl methacrylate. [8] With the addition of isoprene, methacrolein and methallyl alcohol, we are able to prepare even more polymers and copolymers.…”

“…[2Ϫ6] In our group a number of important labelled monomers have already been prepared with 99% 13 C enrichment, namely acrylonitrile, [3] styrene, [3] ethyl acrylate, [7] maleic anhydride, [2,3] and methyl methacrylate. [8] Our purpose of preparing 13 C-labelled isoprene is to use it in anionic block copolymer synthesis.…”

Cross-Linking Induced Phase Separation in SAN/SMA Semi-interpenetrating Polymer Networks Observed by Solid State NMR and Site Specific Isotope Enrichment

“…6 The MA content of the copolymer is 27.0 wt %, as was determined from the ratio of the FT-IR intensities of the 13 CO stretch absorption at 1807 cm -1 and the 13 CH2 bend † Leiden Institute of Chemistry. ‡ DSM Research.…”

“…In Figure 5 this fraction of the various blends is plotted versus the amount of 4,4′-methylenedianiline cross-linking agent added. From the study in ref 6 we learned already that a substantial fraction of the material remained intimately mixed upon cross-linking. In contrast to the present investigation, these 13 C spin diffusion experiments yielded no quantitative information about the relative amount of material that was involved.…”

“…13 C spin diffusion experiments with such semi-interpenetrating (semi-IPN) blends of labeled SAN and SMA clearly showed phase separation, but the domain sizes could not be quantified. 6 The observation of structural features and distances of the order of 100 nm and less in noncrystalline, organic compounds without long-range order can be performed successfully using NMR spin diffusion techniques. [7][8][9][10][11][12][13] In principle, neutron and X-ray scattering techniques can be used for similar purposes, provided there is sufficient contrast.…”