Unique Interphase and Cross-Linked Network Controlled by Different Miscible Blocks in Nanostructured Epoxy/Block Copolymer Blends Characterized by Solid-State NMR

Abstract

A variety of multiscale solid-state NMR techniques were used to characterize the heterogeneous structure and dynamics of the interphase and cross-linked network in nanostructured epoxy resin/block copolymer (ER/BCP) blends, focusing on the role of ER-miscible blocks containing poly(ε-caprolactone) (PCL) or poly(ethylene oxide) (PEO) blocks having different intermolecular interactions with ER. 1H spin-diffusion experiments indicate that the interphase thickness of PEO-containing blends is obviously smaller than that of PCL-containing blends. High-resolution 1H fast magic-angle spinning (MAS) spin-exchange experiments reveal detailed interfacial mixing between ER and BCPs for the first time, and two different types of interphase structure are found. 1H fast MAS double-quantum filter experiments provide a fast and convenient detection of interphase composition, including immobilized BCPs and partially cured or local damaged ER network. The driving force for the interphase formation and miscibility in PCL-containing blends was successfully determined by high-resolution 13C CPMAS experiments, demonstrating the formation of hydrogen bonds between PCL and ER; competing hydrogen bonding interactions were also found when ER was blended with PEO-b-PCL (EOCL). A new calculation method is proposed to quantitatively determine the distribution of different blocks in the interphase and dispersed phase for PCL-containing blends in combination with 13C CPMAS and 1H spin-diffusion experiments. A 13C T 1 spin–lattice relaxation experiment provides a quantitative determination of the amount of local destroyed network in the interphase. Furthermore, it is found that incorporation of BCPs induces unexpected enhanced rigidity of the cross-linked network. On the basis of NMR results, we propose a model to describe the unique structure and dynamics of the interphase and cross-linked network as well as their underlying formation mechanism in ER/BCP blends.

Heterogeneous Dynamics and Microdomain Structure of High-Performance Chitosan Film as Revealed by Solid-State NMR

“…17,31 For multiphase polymers with distinct componential dynamics, a 1 H dipolar filter or a double quantum filter with 1 H spin-diffusion have been widely used to determine domain sizes. 16,36 Herein, 1 H double quantum (DQ) filter was selected to create a magnetization gradient by suppressing the weak dipolar couplings of the signals of the mobile component due to the high content of rigid component for CTS sample (Table 2). After a certain mixing time (t m ) of spin-diffusion, the reserved magnetization of the rigid component was gradually transferred to the suppressed mobile component through spin diffusion.…”

Toughening of epoxy by nanostructures with ABA triblock copolymers: An influence of organosilicon modification of block copolymer

“…Over the past decades, numerous block copolymer–modified nanostructured thermosets have been reported and the formation mechanisms of nanophases follow either self‐assembly or RIMPS. [ 12–23 ] By changing the composition of the thermosetting blends, architectures, and molecular weights of block copolymers as well as the type of curing agent, investigators have obtained the nanostructured thermosets with various morphologies. It is realized that the thermomechanical properties of the thermosetting blends are quite contingent on morphological types of nanostructures.…”

“…Over the past decades, numerous block copolymermodified nanostructured thermosets have been reported and the formation mechanisms of nanophases follow either self-assembly or RIMPS. [12][13][14][15][16][17][18][19][20][21][22][23] By changing the composition of the thermosetting blends, architectures, and molecular weights of block copolymers as well as the type of curing agent, investigators have obtained the Lei Li and Wenjun Peng contributed equally.…”

Rapid Structural Analysis of Minute Quantities of Organic Solids by Exhausting 1H Polarization in Solid-State NMR Spectroscopy Under Fast Magic Angle Spinning

“…Instead, there is considerable interest in developing proton-based solid-state NMR spectroscopy that fully utilizes the high sensitivity of protons afforded by its highest gyromagnetic ratio and nearly 100% natural abundance. − Fortunately, by virtue of the tremendous advances in magic angle spinning (MAS) probe technologies, spinning can be up to 170 kHz now using a small rotor with a diameter of less than 0.5 mm, , and the probe with the capability of spinning beyond 60 kHz has indeed become common in many NMR laboratories. Under such fast MAS conditions, the strong proton–proton dipolar couplings can be significantly averaged, leading to a dramatic enhancement of proton spectral resolution particularly when combined with an ultrahigh magnetic field. − Indeed, we have previously fully exploited multidimensional single channel proton solid-state NMR experiments at fast MAS conditions in order to fully explore the benefits of high sensitivity of protons for structural analysis of minute amounts of organic solids. − Particularly, homonuclear 1 H/ 1 H single-quantum/single-quantum (SQ/SQ) and double-quantum/single-quantum (DQ/SQ) correlation experiments are widely adapted for probing the proximity of protons, enabling revealing the hydrogen bonding interactions, intermolecular compatibility, and chain packings. − Nevertheless, it should be noted that the spectral resolution of proton is not comparable to that of 13 C spectra, and a proton-detected 13 C/ 1 H heteronuclear correlation (HETCOR) experiment is typically required for accurate proton resonance assignments and thus enabling rapid structural analysis. − Notably, in the conventional proton-detected HETCOR experiment (Figure a), , only around 1% of 1 H polarization is transferred to 13 C via the first cross-polarization (CP) period for the natural abundance organic solids since the natural abundance of 13 C is only around 1%, while 99% of 1 H polarization is actually destroyed and wasted by the heteronuclear decoupling or homonuclear rotary resonance (HORROR) period to fully eliminate the residual proton polarization before second CP transfer for proton detection. In the previous study, we have well demonstrated that those residual 99% 1 H polarization can be further utilized for subsequent multiple CP polarization transfer at fast MAS conditions if the proton T 1ρ is long enough, even enabling the direct acquisition of natural abundant 13 C NMR spectra using only ∼2 mg compounds .…”