Tuning Polymer Blends to Cocontinuous Morphology by Asymmetric Diblock Copolymers as the Surfactants

Post-chemical grafting poly(methyl methacrylate) to commercially renewable elastomer as effective modifiers for polylactide blends

A novel poly(epichlorohydrin-co-ethylene oxide)-g-poly(methyl methacrylate) copolymer (ECO-g-PMMA) was successfully synthesized from a commercially renewable elastomer via the ATRP method. The graft copolymer was investigated as a toughening agent and compatibilizer for polylactide (PLA) and PLA/ECO blends, respectively. Binary blending PLA with the copolymers (5-15 wt%) significantly improved the strain at break of PLA above 200% without a great strength loss. More importantly, the ternary PLA/ECO/ECO-g-PMMA copolymer blends exhibited a remarkably high impact strength of 96.9 kJ/m² with non-broken behaviors. An interesting phase structure transformation from a typical sea-island structure to a unique quasi-continuous network structure was observed with varying the content of ECO-g-PMMA from 0 to 15 wt% in the ternary blends. The native toughening mechanism analysis indicated the synergistic toughening effect of the good interfacial adhesion and unique quasi-continuous morphology endowed the ternary blends with excellent mechanical performance.

Distinctive Morphology Modifiers for Polymer Blends: Roles of Asymmetric Janus Nanoparticles during Phase Separation

Janus nanoparticles (JPs), which are anisotropic nanoparticles with multiple constituting parts, have been recognized as superior compatibilizers for polymer-blend-based nanocomposites. However, so far, most studies focused on the effects of symmetric JPs on the phase separation dynamics of polymer blends, while the roles of asymmetric JPs during phase separation remain unclear. In this work, the phase separation dynamics of symmetric blends compatibilized by JPs with various compositions was studied by using dissipative particle dynamics (DPD) simulations. It was found that the blends compatibilized by asymmetric JPs tend to undergo morphological transitions from bicontinuous networks to droplets-in-matrix structures at the late stage of phase separation, which is due to the influence of asymmetric JPs on the energetically favored curvature of the interfaces between polymer domains. Such a mechanism is absent for symmetric JPs and other compatibilizers (e.g., triblock copolymers and homogeneous particles) because they lack the unique combination of chemical asymmetry with the particulate nature like the asymmetric JPs. Moreover, it was observed that the asymmetric JPs can stably localize at the interfaces and act as efficient compatibilizers only when the fraction of the minor constituent part exceeds a critical value. These findings not only shed light upon the roles of asymmetric JPs as compatibilizers but also indicate a promising strategy for designing polymer-blend-based nanocomposites with tailor-made structures.

Controlling the kinetics of viscoelastic phase separation through self-assembly of spherical nanoparticles or block copolymers

Viscoelastic phase separation (VPS) can produce a network structure of the minor phase, which needs to be stabilized for designing a heterogeneous structure with desired mechanical and electrical functions. In this work, we investigate the stabilization of the VPS-induced network structure in a dynamically asymmetric PS/PVME blend by incorporation of a SEBS-g-MA block copolymer or dimethyldichlorosilane modified nanosilica. The addition of SEBS-g-MA retards the volume shrinking process and slows down the kinetics of phase separation due to its localization at the PS/PVME interfaces. Consequently, in the later stage of VPS, phase inversion occurs at longer times with respect to the neat blend due to the decreased interfacial tension. In contrast, hydrophobic nanoparticles self-assemble in the bulk of PS-rich phase and restrain the dynamics of polymer chains enhancing the dynamic asymmetry of the system. The efficiency of nanoparticles in controlling the kinetics of phase separation is found to be superior compared to block copolymer-based compatibilizers indicating the significance of chain dynamics. Moreover, beyond a critical nanoparticle volume fraction, phase separation is pinned due to particle percolation within the PS-rich phase, yielding a kinetically trapped VPS-induced network structure.

Simulation of conformational properties of end-grafted diblock copolymers

The conformational properties of end-grafted diblock copolymers XA_nB_n and XB_nA_n are dependent on the position of the grafted end X.

Triple shape memory effects of cross-linked polyethylene/polypropylene blends with cocontinuous architecture

In this paper, the triple shape memory effects (SMEs) observed in chemically cross-linked polyethylene (PE)/polypropylene (PP) blends with cocontinuous architecture are systematically investigated. The cocontinuous window of typical immiscible PE/PP blends is the volume fraction of PE (v(PE)) of ca. 30-70 vol %. This architecture can be stabilized by chemical cross-linking. Different initiators, 2,5-dimethyl-2,5-di(tert-butylperoxy)-hexane (DHBP), dicumylperoxide (DCP) coupled with divinylbenzene (DVB) (DCP-DVB), and their mixture (DHBP/DCP-DVB), are used for the cross-linking. According to the differential scanning calorimetry (DSC) measurements and gel fraction calculations, DHBP produces the best cross-linking and DCP-DVB the worst, and the mixture, DHBP/DCP-DVB, is in between. The chemical cross-linking causes lower melting temperature (Tm) and smaller melting enthalpy (ΔHm). The prepared triple shape memory polymers (SMPs) by cocontinuous immiscible PE/PP blends with v(PE) of 50 vol % show pronounced triple SMEs in the dynamic mechanical thermal analysis (DMTA) and visual observation. This new strategy of chemically cross-linked immiscible blends with cocontinuous architecture can be used to design and prepare new SMPs with triple SMEs.