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The growing environmental pollution and the expected depleting of fossil resources have sparked interest in recent years for polymers obtained from monomers originating from renewable sources. Furthermore, nature can provide a variety of building blocks with special structural features (e. g. side groups or stereo‐elements) that cannot be obtained so easily via fossil‐based pathways. In this context, terpenes are widespread natural compounds coming from non‐food crops, present in a large variety of structures, and ready to use as monomers with or without further modifications. The present review aims to provide an overview of how chemists can stereospecifically polymerize terpenes, particularly the acyclic ones like myrcene, ocimene, and farnesene, using different metal catalyst systems in coordination‐insertion polymerization. Attention is also paid to their copolymers, which have recently been disclosed, and to the possible applications of these bio‐based materials in various industrial sectors such as in the field of elastomers. © 2021 The Authors. ChemPlusChem published by Wiley‐VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution Non‐Commercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. Examples of stereoregular polymerizations of acyclic terpenes (myrcene, ocimene, and farnesene) promoted by catalysts based on transition metal complexes are reported. Their copolymers and interesting applications as elastomers in the industrial sector are also discussed.

Polar 2D Polymer Crystals In article 2300214, Hiroshi Sakaguchi and co‐workers develop a vectorial on‐surface synthesis method to produce polar materials. Using “compass” precursors that have three separate vectors for bonding, edges, and dipoles, the process involves isotactic polymerization, ultimately resulting in two‐dimensional polar crystalline structures due to the CH‐π interaction at hetero‐edges.

The asymmetric introduction of functional groups into polymers is promising due to its potential to provide novel electronic and magnetic properties. Though traditional on‐surface bottom‐up synthesis has succeeded in creating various types of polymers, it struggles at realizing asymmetry due to the difficulty of stereoregular polymerization and the tendency for overall polarity cancellation during agglomeration. Here, enabled by the low halogen‐contaminated metal surfaces provided by two‐zone chemical vapor deposition, “compass” precursors possessing three independent bonding, edge, and dipole vectors undergo isotactic polymerization via the vectorial self‐assembly of chiral precursor diradicals without the need for chiral catalysts required in conventional in‐solution polymerization. The isotactic polymers exhibit polar 2D crystalline structures due to the hetero‐edge CH–π interaction between the standing phenyl and butoxy group surpassing the homo‐edge interactions of π–π and CHCH. The developed vectorial on‐surface synthetic technique not only paves the way to the realization of stereoregular control but also unlocks unprecedented crystal engineering. Vectorial on‐surface synthesis using newly designed compass precursors possessing three independent bonding, edge and dipole vectors, is capable of aligning their reaction intermediates in the same 2D vectorial direction that leads to isotactic polymers with the polar 2D crystalline structures.

Linear poly(methylphenylsiloxane) (PMPS) was prepared by the living anionic ring-opening polymerization of cis -2,4,6-trimethyl-2,4,6-triphenylcyclotrisiloxane ( cis -P 3 ). The resulting linear PMPS was shown by NMR to be highly stereoregular and remarkably high in meso-meso fraction and proposed isotactic content (~80%). Tetrahydrofuran (THF) was used as the solvent and it is noted that THF also acts as a promoter for the system by increasing the reactivity of the silanolate nucleophile at the end of the propagating chain. It is proposed that this increase in the reactivity occurs preferentially in the intermolecular (propagating) reaction. The evidence for this proposed hypothesis is the exclusive production of meso-meso and meso-racemic triads in the linear PMPS as evidenced by NMR. As the reaction temperature was increased, the rate of polymerization increased and yet the tacticity of the polymer was not affected. It is therefore clear that there was no significant amount of back-biting (intramolecular) reaction for the temperatures and time intervals studied here, despite the fact that ring-chain equilibration is commonly observed in ring-opening siloxane polymerizations. Had the reversion reaction been present, then scrambling of the chain stereoregular sequences would have been observed by an equilibration mechanism. It is well established that phenyl-phenyl interactions ( π – π stacking) can stabilize certain local conformations in PMPS chains and hence we propose that these phenyl-phenyl interactions may prevent back-biting reactions for PMPS under the kinetic conditions employed here.

Some syndiotactic-rich polyolefins, generally difficult to synthesize through stereospecific polymerization of the corresponding monomers, were prepared by homogeneous non-catalytic hydrogenation of syndiotactic 1,2 poly(1,3-diene)s with diimide, arising from thermal decomposition of p-toluene-sulfonyl-hydrazide. All the polymers synthesized were structurally characterized by means of several analytical techniques, such as FT-IR, NMR (1H, 13C and 2D), DSC, and GPC, and herein illustrated.

Isotactic poly[methyl α-(hydroxymethyl)acrylate] was prepared via anionic polymerization of the respective monomer protected with trimethylsilyl group ( 1-TMS ) initiated with isopropyl α-lithioisobutyrate (Li- i PrIB) in toluene at −78 °C. The polymerization proceeded in high isotactic specificity similarly to the case of α-(alkoxymethyl)acrylate, although the monomer conversion was low (~18 %) due to the self-terminating reaction accompanying the elimination of trimethylsilanolate anion. The monomer conversion could be improved to ca. 75 % in the polymerizations with an excess amount of LiOSiMe 3 , which would interact with and stabilize the propagating species to suppress the self-terminating reaction. This was a sharp contrast to the polymerization of α-(methoxymethoxymethyl)acrylate ( 1-MOM ), an acetal protected monomer, where the addition of LiOSiMe 3 enhanced the self-termination. Consequently, the structure of protective group affects the polymerization behavior. For the resulting poly(1-TMS) , the deprotection by acid hydrolysis quantitatively afforded isotactic poly[methyl α-(hydroxymethyl)acrylate].

Two poly(3-hexylthiophene) (P3HT) macromers containing a donor polymer with a polymerizable methacrylate (MA) end group, P3HT-CH2-MA and P3HT-(CH2)2-MA, have been synthesized, and P3HT-(CH2)2-MA has been successfully homopolymerized and copolymerized with methyl methacrylate (MMA) into stereoregular brush polymers and graft copolymers, respectively, using chiral ansa-zirconocene catalysts. Macromer P3HT-CH2-MA is too sterically hindered to polymerize by the current Zr catalysts, but macromer P3HT-(CH2)2-MA is readily polymerizable via either homopolymerization or copolymerization with MMA in a stereospecific fashion with both C2-ligated zirconocenium catalyst 1 and Cs-ligated zirconocenium catalyst 2. Thus, highly isotactic (with mm% ≥ 92%) and syndiotactic (with rr% ≥ 93%) brush polymers, it-PMA-g-P3HT and st-PMA-g-P3HT, as well as well-defined stereoregular graft copolymers with different grafted P3HT densities, it-P(M)MA-g-P3HT and st-P(M)MA-g-P3HT, have been synthesized using this controlled coordination-addition polymerization system under ambient conditions. These stereoregular brush polymers and graft copolymers exhibit both thermal (glass and melting) transitions with Tg and Tm values corresponding to transitions within the stereoregular P(M)MA and crystalline P3HT domains. Acceptor molecules such as C60 can be effectively encapsulated inside the helical cavity of st-P(M)MA-g-P3HT to form a unique supramolecular helical crystalline complex, thus offering a novel strategy to control the donor/acceptor solar cell domain morphology.

By contrast to traditional free radical emulsion polymerization, catalytic polymerization allows for polymer microstructure control. In terms of polymerizable monomers, both techniques are largely complementary. Since the beginning of this decade, an increasing number of reports on polyolefin, polybutadiene, polyalkenamer, polynorbornene, polyketone, and polyacetylene dispersions prepared by catalytic polymerization in disperse aqueous systems has appeared. This contribution reviews the preparation of these dispersions, their colloidal properties, particle formation mechanisms, particle morphologies, and polymer microstructures.[PUBLICATION ABSTRACT]

Highly efficient stereoregular polymerizations within template nanospaces using free radical initiators, based on stereocomplexes formed between isotactic and syndiotactic methacrylate polymers are reviewed. Ultrathin films composed of double-stranded helical or van der Waals contacted stereocomplex nanostructures were successfully prepared by the layer-by-layer assembly method, and fundamental aspects of film preparation were summarized. Template nanospaces were prepared by the selective solvent extraction of a single component from stereocomplex films composed of it-poly(methyl methacrylate) and st-poly(methacrylic acid). The resulting porous films with designed nanospaces were used for template polymerizations. Methacrylate polymers with high iso- and syndiotacticities were synthesized within nanospaces. Structural information not only of template stereoregularity but also of template chain length was efficiently transferred to synthesized polymers.