All-Methacrylic Stereoregular Triblock Co-polymer Thermoplastic Elastomers Toughened by Supramolecular Stereocomplexation

One-Step Synthesis of Lignin-Based Triblock Copolymers as High-Temperature and UV-Blocking Thermoplastic Elastomers

This work utilizes frustrated Lewis pairs consisting of tethered bis-organophosphorus superbases and a bulky organoaluminum to furnish the highly efficient synthesis of well-defined triblock copolymers via one-step block copolymerization of lignin-based syringyl methacrylate and n-butyl acrylate, through di-initiation and compounded sequence control. The resulting thermoplastic elastomers (TPEs) exhibit microphase separation and much superior mechanical properties (elongation at break up to 2091 %, tensile strength up to 11.5 MPa, and elastic recovery up to 95 % after 10 cycles) to those of methyl methacrylate-based TPEs. More impressively, lignin-based tri-BCPs can maintain TPEs properties up to 180 °C, exhibit high transparency and nearly 100 % UV shield, suggesting potential applications in temperature-resistant and optical devices.

Epoxidized Block and Statistical Copolymers Reinforced by Organophosphorus-Titanium-Silicon Hybrid Nanoparticles: Morphology and Thermal and Mechanical Properties

Glycidyl methacrylate (GMA) and a mixture of alkyl methacrylates (average chain length of 13 carbons; termed C13MA; derived from vegetable oils) were copolymerized by nitroxide-mediated polymerization to form epoxidized statistical and block copolymers with similar compositions (F GMA ∼0.8), which were further cross-linked by a bio-based diamine. Hybrid plate-like nanoparticles containing organophosphorus-titanium-silicon (PTS) with an average size of ∼130 nm and high decomposition temperature (485 °C) were synthesized via a hydrothermal reaction to serve as additives to simultaneously enhance the thermal and mechanical properties of the blend. Nanocomposites filled with PTS were prepared at different filler-loading levels (0.5, 2, 4 wt %). Transmission electron microscopy (TEM) of the cured block copolymer displayed reaction-induced macrophase-separated domains. TEM also showed an effective dispersion of PTS hybrids in the matrix without intense agglomeration. Thermogravimetric analysis at different heating rates revealed the activation energy of poly (GMA-stat-C13MA) at maximum decomposition increased from 143.5 to 327.2 kJ mol-1 with 4 wt % PTS. Decomposition temperature and char residue improved 12 °C and ∼7 wt %, respectively, and T g increased 12 °C by adding 4 wt % PTS. Targeting various PTS concentrations enabled tuning of the tensile modulus (up to 75%), tensile strength (up to 46%), and storage modulus in both glassy state (up to 59%) and rubbery plateau regions (up to 88%). Oscillatory frequency sweeps indicated that PTS makes the storage modulus frequency dependent, suggesting that the inclusion of the nanoparticles alters the relaxation of the surrounding matrix polymer.

Helix-Sense-Selective Encapsulation of Helical Poly(lactic acid)s within a Helical Cavity of Syndiotactic Poly(methyl methacrylate) with Helicity Memory

We report a highly enantio- and helix-sense-selective encapsulation of helical poly(lactic acid)s (PLAs) through a unique "helix-in-helix" superstructure formation within the helical cavity of syndiotactic poly(methyl methacrylate) (st-PMMA) with a one-handed helicity memory, which enables the separation of the enantiomeric helices of the left (M)- and right (P)-handed-PLAs. The M- and P-helical PLAs with different molar masses and a narrow molar mass distribution were prepared by the ring-opening living polymerization of the optically pure l- and d-lactides, respectively, followed by end-capping of the terminal residues of the PLAs with a 4-halobenzoate and then a C₆₀ unit, giving the C₆₀-free and C₆₀-bound M- and P-PLAs. The C₆₀-free and C₆₀-bound M- and P-PLAs formed crystalline inclusion complexes with achiral st-PMMA accompanied by a preferred-handed helix induction in the st-PMMA backbone, thereby producing helix-in-helix superstructures with the same-handedness to each other. The induced helical st-PMMAs were retained after replacement with the achiral C₆₀, indicating the memory of the induced helicity of the st-PMMAs. Both the C₆₀-free and C₆₀-bound helical PLAs were enantio- and helix-sense selectively encapsulated into the helical hollow space of the optically active M- and P-st-PMMAs with the helicity memory prepared using chiral amines. The M- and P-PLAs are preferentially encapsulated within the M- and P-st-PMMA helical cavity with the same-handedness to each other, respectively, independent of the terminal units. The C₆₀-bound PLAs were more efficiently and enantioselectively trapped in the st-PMMA compared to the C₆₀-free PLAs. The enantioselectivities were highly dependent on the molar mass of the C₆₀-bound and C₆₀-free PLAs and significantly increased as the molar mass of the PLAs increased.

100th Anniversary of Macromolecular Science Viewpoint: The Past, Present, and Future of Stereocontrolled Vinyl Polymerization

The thermomechanical properties exhibited by synthetic macromolecules can be directly linked to their tacticity, or the relative stereochemistry of repeat units. The development of stereoselective coordination-insertion polymerization, for example, led to the discovery of isotactic polypropylene, now one of the most widely produced commodity plastics in the world. Widespread interest in controlling polymer tacticity has led to a variety of stereoselective polymerization methodologies; however, this area of polymer science has lagged behind when compared to the ability to control molecular weight, dispersity, and composition. Despite decades of advancements, many stereoregular vinyl polymers remain unknown, particularly those comprised of polar functionality or derived from renewable resources. This Viewpoint provides an overview of recent developments in stereocontrolled polymerization, with an emphasis on propagation mechanism, and highlights successes, limitations, and future challenges for continued innovation.