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End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: xxxxxxxxx@xxx.xx.xx. You will be contacted as soon as possible. University Library Radboud University ~~THz Electric Field~~8892 Macromolecules 2010, 43, 8892–8903 DOI: 10.1021/ma101792v Rhodium-~~induced Second Harmonic Generation in Ferroelectric Thin Film BaSrTiO3 K. A. Grishunin1~~Mediated Stereospecific Carbene Polymerization: From Homopolymers to Random and Block Copolymers ) ) Xxxxx Xxxxxxx,† Xxxx X. Xxxxxxxxx,† Xxxx Xxxxxxx xxx Xxxxxxxxx,‡ Xxxxxx X. Xxxxxxxx,§ Xxxx X. Xxxxxxxxx,§ Xxx X. Xxxxxxxxxx, ~~N. A. Ilyin1~~,# Xxxxxxxxxx Xxxxxxxxx, ~~N. E. Sherstyuk1~~Xxxxx X. Xxxxxxxxxxxx, ~~E. D. Mishina1, A. Kimel2, V. M. Mukhortov3, A. V. Ovchinnikov4, O. V. Chefonov4~~Xxx Xxxxxxxxx,^ Xxxxx X. X. xxx Xxx,^ Xxxxx X. X. Xxxx,† and Xxx xx Xxxxx*,† ) †Homogeneous and Supramolecular Catalysis Group, and ~~M. B. Agranat4 1MIREA~~‡Zernike Institute for Advanced Materials, ~~Moscow Technological University~~University of Groningen, ~~Xxxxxxxxx Xxx. 00~~Xxxxxxxxxx 0, ~~Xxxxxx 000000~~0000 XX Xxxxxxxxx, ~~Xxxxxx 2Institute~~ Xxx Xxxxxxxxxxx, §Faculty of Aerospace Engineering, Delft University of Technology, Xxxxxxxxxx 0, 2629 HS Delft, The Netherlands, and ^Institute for Molecules and Materials, Radboud University Nijmegen, ~~6525 AJ~~Xxxxxxxxxxxxxx 000, ~~Nijmegen~~0000 XX Xxxxxxxx, Xxx Xxxxxxxxxxx. #Current address: Institute of Analytical Chemistry, Xxxxxxxx Xxxxxx University, 0000 Xxxx, Xxxxxxx. ABSTRACT: New stereoregular homo- and copolymers with an ester group at every backbone carbon atom were prepared from ethyl, benzyl and tert-butyl diazoacetate (Mw of homopolymers up to 690 kDa and copolymers up to 430 kDa). With polarizing optical microscopy we found that the homopolymers poly- (ethyl 2-ylideneacetate) and poly(benzyl 2-ylideneacetate) are able to form stable and accessible thermotropic and lyotropic nematic phases. Both two polymers show relatively high storage moduli up to the glass transition temperature (Tg), as evidenced by dynamic mechanical thermal analysis. The ~~Netherlands 3Southern Scientific Center~~ materials retain quite decent storage moduli in a broad elevated temperature range between Tg and Tm. The formation of ~~Russian Academy~~ (block) copolymers was confirmed by a combination of ~~Sciences~~NMR spectroscopy, ~~Chehova 41~~differential scanning calorimetry and size-exclusion chromatography. 2D-solubility-gradient chromatography-SEC as well as pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) showed a clear difference in the composition of the random and block copolymers with benzyl and ethyl ester groups. Thermal analysis showed that the homopolymers and block copolymers are semicrystalline, ~~Rostov~~while the random copolymers are completely amorphous. The polymers are thermally stable toward decomposition up to 300 °C (and polymers containing tert-onbutyl ester groups up to 200 °C). The formation of cross-~~Don 344006~~linked polymer was achieved by heating copolymers containing tert-butyl ester groups. Introduction A long-standing challenge in polymer synthesis is the con- trolled synthesis of highly stereoregular, ~~Russia 4Joint Institute~~ high molecular weight carbon-chain polymers with a controllable amount of polar functionalities. Over the past years, several new approaches have been developed to reach this goal. Considerable progress in this field has been achieved with lanthanide metallocene complexes, group 4 early transition metal metallocenes, and alike, which polymerize polar vinyl monomers via coordination-addition polymerization mechanisms (metal-controlled anionic poly- merization), allowing the controlled synthesis of both syndiotac- tic and isotactic (rich) polymers from methylacrylates, acrylates, (meth)acrylamides, acrylonitriles, and vinylketones.1,2 High triad selectivities can be reached with these methods, but generally low temperatures are required to achieve high stereospecificities. These reactions bear some similarities with anionic polymeriza- tion of (meth)acrylates at low temperatures, which also allow a decent stereocontrol.3 The living character of both anionic and coordination-addition polymerization reactions provides inter- esting opportunities to prepare block copolymers. Progress in the development of new late transition metal catalysts for ~~High Temperatures~~ coordination-insertion-type polymerization reac- + + *Corresponding author. Telephone: 00 00 000 0000. Fax: 31 20 000 0000. E-mail: x.xxxxxxx@xxx.xx. tions has made it possible to prepare (random) copolymers of ~~Russian Academy~~ polar vinyl monomers and (aliphatic) alkenes, hence producing interesting new materials with varying microstructures (e.g., side- chain functionalized, main-chain functionalized, random, and block copolymers).1,4 These catalytic systems produce more than one chain per metal ion (chain transfer), and the most recently developed catalysts even allow a decent control over the amount of ~~Sciences~~ the incorporated functionalities. So far there are no reported examples of late transition metal catalysts capable of stereospe- cific polymerization of polar vinyl monomers or stereospecific copolymerization of polar vinyl monomers with olefins.1 Fascinating new developments in the field of radical-type polymerization reactions show the possibility to gain excellent control over polymer lengths and polydispersities, and modern radical polymerization techniques even make it possible to gain some (~~JIHT~~albeit still limited) ~~Izhorskayast~~control over the polymer tacticities.5 Despite all these intriguing new developments, the problem is by no means solved and many important challenges are still remaining.1 For example, the synthesis of stereoregular carbon- chain polymers which are functionalized at every carbon-atom of the polymer backbone has proven to be difficult using olefinic monomers, and even the formation of atactic polymers by radical polymerization of 1,2-difunctionalized olefins is nontrivial in some cases.6 In this respect, C1 polymerization (or “carbene” polymerization) techniques may offer valuable alternative syn- thetic methods for the synthesis of new materials that are not so xxxx.xxx.xxx/Xxxxxxxxxxxxxx Published on Web 10/07/2010 Ⓒ 2010 American Chemical Society Article Macromolecules, Vol. 1343, BdNo. 21, 2010 8893 Scheme 2. Synthesis of Catalyst Precursors 1 and 2 easily accessible by the more common polymerization of CdC double bonds.7-9 We recently contributed to this field by show- ing that Rh-mediated carbene polymerization, using diazoesters (ROC(dO)CHdN2) as carbene precursors, allows the prepara- tion of fully functionalized, high molecular weight, and highly syndiotactic carbon-chain polymers,10-13 in good yields.13 Pre- sently, this is the only available method to prepare such densely functionalized, sp3-hybridized14 polymers in a stereoregular manner. The reaction follows a migratory carbene insertion chain propagation mechanism (Scheme 1), and the high syndio-specificity is most likely determined by chain-end control.11 With a method in hand to prepare high molecular weight and highly stereoregular fully functionalized polycarbenes, we decided to expand the scope of this new reaction toward the pre- paration of random and block-type copolymers using three different carbene precursors. The results are described in this paper. Another important goal of this paper is to address the unusual thermal and thermo-mechanical properties of the new highly functionalized, stereoregular polycarbenes. Polar side- chain functionalities of carbon-chain polymers in general have a large and important influence on the polymer material properties (e.g., toughness, paintability/printability, solvent resistance, mis- cibility).4a However, their influence has so far only been investi- gated for materials in which the mutual influence of the dipole moments of the applied functionalities have a poorly defined (atactic materials)6,8 and/or diluted effect (C2-polymerization of monofunctionalized olefins in general). In this paper we present for the first time efforts to unravel the influence of multiple dipolar interactions in close proximity along a fully functiona- lized and stereoregular carbon-chain polymer chain on the material properties of these poly carbenes. As a result we here dis- close the unusual material properties of new poly carbene materials, which includes a broad end-use temperature range as well as thermotropic (and lyotropic) liquid crystalline behavior in a broad temperature range (rigid rod behavior). Results and Discussion Catalyst Precursors. Previously, we reported different [(diene)RhI(N,O-ligand)] complexes (diene =1,5-cycloocta- diene (cod) (1 in Scheme 2), endo-dicyclopentadiene (dcp), or 2,5-norbornadiene (nbd)) for polymerization of carbenes from ethyl diazoacetate (EDA).10,11 We showed that the diene ligand plays an important role during the propagation steps, while the N,O-ligand is likely involved in the initiation Figure 1. Carbene precursors: ethyl, benzyl, and tert-butyl diazo- acetate. of the polymerization. The highest yields were obtained with [(L-prolinate)RhI(1,5-cyclooctadiene)] (1) (50%)10,11 and [(L-prolinate)RhI(1,5-dimethyl-1,5-cyclooctadiene)] (2) (up to 80%) and therefore these catalyst precursors were selected for copolymerization reactions. Complex 2 was stored for several days in air prior to its use in the polymer- ization reactions in order to obtain higher polymer yields, following the procedures described in one of our previous papers.13 Complexes 1 and 2 are easily prepared by reacting the corresponding [{RhI(diene)(μ-Cl)}]2 (diene=1,5-cyclooc- tadiene (cod) or 1,5-dimethyl-1,5-cyclooctadiene (dmcod)) with deprotonated L-proline in methanol at room tempera- ture (Scheme 2). Homopolymerization of Different Diazoesters. We first investigated the behavior of catalyst precursors 1 and 2 in the homopolymerization of different diazoesters. The sub- strates are ethyl diazoacetate (EDA), a diazoester with an aromatic substituent: benzyl diazoacetate (BnDA) and one with a sterically demanding side group: tert-butyl diazoace- xxxx (tBuDA) (Figure 1). EDA and tBuDA are commercially available and BnDA was prepared by published proce- dures.15,16 The homopolymerization reactions were performed by addition of 50 equiv of diazoester to a solution of catalyst precursor 1 or 2 in chloroform.10,11 The solution was stirred for 14 h at room temperature. The polymer was obtained by evaporation of the solvent and subsequent precipitation with methanol. After washing with methanol and drying, a white solid was obtained. Carbenes from EDA and BnDA are polymerized to poly- (ethyl 2-ylidene-acetate) (poly(EA)) and poly(benzyl 2-yli- dene-acetate) (poly(BnA)), respectively, of high molecular weight (up to 690 kDa) and in moderate to good yields (entries 1, 2, ~~Moscow 125412~~4, ~~Russia Abstract— Strong modulation~~ and 5 in Table 1). EDA and BnDA are completely converted into polymers (major fraction), and some dimeric (dialkyl fumarate and maleate) and oligomeric byproducts. The byproducts are soluble in methanol and are separated from the polymer during the precipitation step, as described before.10-12 Precatalyst 2 gives higher yields than precatalyst 1 for both substrates. The bulky diazoester tBuDA is polymerized to poly(tert- butyl 2-ylidene-acetate) (poly(tBuA)) in only low yields by both catalyst precursors 1 and 2 (Table 1, entries 3 and 6). ∼ ∼ ∼ ∼ The conversion is not complete (65% for 1 and 50% for 2) and unreacted tBuDA was recovered after the reaction. Most of the ~~Second Harmonic Generation~~ reacted tBuDA was converted into oligomers ( 80%, Mw 1500 Da, PDI 1.4) and a small amount of dimeric products, di-tert-butyl fumarate and maleate ( 15%). Dur- ing the polymerization reaction the polymeric poly(tBuA) product precipitates from the reaction mixture in chloro- form, which in part explains the low yields (~~SHG~~and probably low molecular weights) ~~signal by THz nearly single cycle pulse~~ obtained in ferroelectric thin film BaSrTiO3 was observed. As the employed THz pulses pumps the medium in the range of phononic excitations, the THz electric field induced ferro- electric polarization is due to the ionic contributionthese reactions. The ~~proposed model describes this effect~~ isolated white solid is insoluble in ~~terms~~ most organic solvents, such as chloroform (with and without trifluoroacetic acid), dichlor- omethane, methanol, toluene, and benzene. Because of ~~electric polarization induced in the plane of the film~~its poor solubility, poly(tBuA) was analyzed by solid state IR spectroscopy (see Supporting Information). The ~~net SHG signal responds to~~ solubility behavior of poly(tBuA) contrasts markedly with the ~~THz excitation as if the THz pulse induces a 90-degrees switching~~ polymer obtained by radical polymerization of ~~the polarization in parts~~ 8894 Macromolecules, Vol. 43, No. 21, 2010 Xxxxxxx et al. Table 1. Homopolymerization of ~~the sample on the time scale of the period of the soft mode~~EDA, BnDA, and tBuDA with 1 and 2a entry catalyst precursor diene substrate polymer polymer yield (%)b Mw (kDa)c PDIc 111 1 cod EDA poly(EA) 50 150 3.6 213 1 cod BnDA poly(BnA) 20 80 6.3 3 1 cod tBuA poly(tBuA) <5 n.d. ~~According to the proposed model, under action of the THz pulse the latter acquires an in-plane component up to 6% of the net polarization.~~n.d. 413 2 dmcod EDA poly(EA) 80 670 3.3 513 2 dmcod BnDA poly(BnA) 50 690 2.7

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