Anionic Self-alternating Polymerization of 1‑(4-Vinylphenyl)-1-phenylethylene

A new AB-type difunctional monomer, 1-(4-vinylphenyl)-1-phenylethylene (1), was subjected to anionic polymerization using sec-butyllithium (s-BuLi), diphenylmethyllithium (Ph2CHLi), and diphenylmethylpotassium (Ph2CHK) in tetrahydrofuran at 0 °C. Soluble poly­(1)­s with predicted molecular weights and relatively narrow molecular weight distributions (Mw/Mn = 1.1–1.3) were quantitatively obtained. 1H and 13C NMR measurements revealed that two carbon–carbon double bonds in the styrene (A) and 1,1-diphenylethylene (DPE, B) frameworks in 1 were alternately consumed to construct the polymer main chain carrying unsaturated A and B units, respectively. This unique reaction mechanism of 1 was coined “self-alternating polymerization”. Quantitative hydrogenation of the unsaturated pendant groups in poly­(1) with p-toluenesulfonyl hydrazide afforded a saturated polymer suitable for structural characterization. Poly­(1) carrying the residual styrene and DPE pendant groups underwent heat-induced cross-linking to give an insoluble polymer

Precise Synthesis of New Exactly Defined Graft Copolymers Made up of Poly(alkyl methacrylate)s by Iterative Methodology Using Living Anionic Polymerization

An iterative methodology using living anionic polymerization with a 1,1-diphenylethylene disubstituted with trimethylsilyl (TMS) and <i>tert</i>-butyldimethylsilyl (TBS) ethers has been developed in order to synthesize new exactly defined graft copolymers made up of poly­(alkyl methacrylate)­s. During each reaction sequence, the TMS and TBS ethers were transformed into α-phenyl acrylate (PA) functions one by one at the different reaction stages. The first PA function derived from the TMS ether was utilized to introduce the graft chain, while the main chain with the TMS and TBS ethers was introduced via the second PA function derived from the TBS ether. Thus, the same chain-end functionalities (both TMS and TBS ethers) were reintroduced after construction of the graft unit. In practice, the reaction sequence involving “the introduction of the graft chain” and “the introduction of the main chain with the two silyl ethers” was iterated three times, leading to the synthesis of poly­(benzyl methacrylate) (PBnMA)-<i>exact graft</i>-poly­(methyl methacrylate) (PMMA) with three PMMA graft chains. Similarly, the synthesis of PBnMA-<i>exact graft</i>-poly­(2-vinylpyridine) (P2VP) with two P2VP graft chains was successfully carried out. With the use of the α,ω-chain-end-difunctionalized PBnMA as the starting material, two graft units could be constructed at the same time by iterating the reaction sequence once. The graft copolymers with up to six graft chains were obtained by only three repeated reaction sequences. Thus, the reaction steps could be significantly reduced. The graft copolymers synthesized in this study were perfectly controlled in structure from a viewpoint of the following three parameters defining the structure of the graft copolymer: (1) molecular weight of the main chain, (2) molecular weights of the graft chains, and (3) number and placement of the graft chains. Furthermore, these three parameters can also be intentionally changed as required

Formation of Alternating Copolymers via Spontaneous Copolymerization of 1,3-Dehydroadamantane with Electron-Deficient Vinyl Monomers

Copolymerizations of 1,3-dehydroadamantane, 1, and various vinyl monomers were carried out in THF at room temperature. On mixing 1 with electron-deficient vinyl monomers, such as acrylonitrile and methyl acrylate, in the absence of any initiator, the copolymerization spontaneously proceeded to give alternating copolymers in 28−88% yield. By contrast, no reaction of 1 occurred at all when isobutyl vinyl ether or styrene was mixed under similar conditions. These contrastive results indicate the high electron density of a central σ-bond in a strained [3.3.1]propellane derivative, 1. Alternating sequences of the resulting copolymers were characterized by NMR and MALDI-TOF-MS measurements. DSC and TGA measurements revealed the high thermal stability of the alternating copolymers containing bulky, stiff, and strain-free adamantane skeletons

Selective Anionic Polymerization of 2,5-Divinylthiophene Derivatives

Selective anionic polymerization of 2,5-divinylthiophene was conducted at one of its two vinyl groups in a living manner using oligo­(α-methylstyryllithium) (αMSLi) and a 10-fold excess of tBuOK as a binary initiator system in tetrahydrofuran at −78 °C. 2-Isopropenyl-5-vinylthiophene (iPrVT), an asymmetric divinyl monomer, also underwent selective anionic polymerization under the initiation of αMSLi/tBuOK to yield a polymer with a predictable molecular weight (Mn < 9.0 kg/mol)) and a narrow molecular weight distribution (Mw/Mn < 1.15). In each case, the binary initiator system of αMSLi/tBuOK effectively prevented the side reactions of the propagating anion with the residual vinyl or isopropenyl groups. A weak 1H NMR signal (∼5%) of the residual vinyl groups was observed for the resulting poly­(iPrVT) along with dominant signals of the isopropenyl group, suggesting that the isopropenyl group of iPrVT also participated in the polymerization but to a significantly lesser extent. The obtained polymers exhibited glass-transition temperatures (∼75 °C) as well as typical exothermic peaks (>120 °C) owing to thermal cross-linking, confirming the reactivity of the residual vinyl groups in the repeating unit of the polymer

Synthesis of Sequence-Controlled Homopolymer via Anionic Self-Alternating and Chemoselective Polymerization of 4‑Vinyl-1,1-diphenylethylene Derivatives

Anionic polymerization of AB-type difunctional monomers derived from 4-vinyl-1,1-diphenylethylene (VD) bearing styrene and 1,1-diphenylethylene (DPE) frameworks was examined using diphenylmethylpotassium (Ph2CHK) in THF at −78 to 0 °C. A series of substituents including chloro (ClVD), methyl (MeVD), methoxy (MeOVD), and dimethylamino (Me2NVD) groups were introduced at the 4′-position of the VD framework to vary the polymerizability of VD. In each case, the resulting polymer was soluble and possessed the predicted molecular weight and a narrow molecular weight distribution (Đ, Mw/Mn = 1.1–1.3). The 1H and 13C NMR measurements and MALDI-TOF-MS analysis revealed that a “self-alternating polymerization” of ClVD, MeVD, and MeOVD yielded a linear homopolymer with an (AB)n-type alternating sequence through the intermolecular cross-propagation chain-growth mechanism. In particular, the resulting poly(ClVD) exhibited only an odd-numbered degree of polymerization, indicating a mechanism of exclusive initiation and subsequent self-alternating polymerization of the VD derivative. In contrast, Me2NVD underwent the usual chemoselective polymerization in the styrene framework to yield an (A)n-type sequence because the electrophilicity of the DPE unit of Me2NVD was highly reduced. Thus, the electronic effect of the substituents determines the polymerization behavior of the VD derivatives

Stereospecific Anionic Polymerization of <i>N,N</i>-Dialkylacrylamides

N,N-Dimethylacrylamide (DMA), N,N-diethylacrylamide (DEA), N,N-dipropylacrylamide (DPA), N-ethylmethylacrylamide (EMA), N-acryloylpyrrolidine (APY), N-acryloylpiperidine (API), and N-acryloylmorpholine (AMO) were polymerized with 1,1-bis[(4‘-trimethylsilyl)phenyl]-3-methylpentyllithium (1) and with 1,1-bis[(4‘-trimethylsilyl)phenyl]-3,3-diphenylpropylpotassium (2) in THF in the presence of additives. Although the polymers produced directly with 1 or 2 have broad molecular weight distributions, the addition of Et2Zn to the polymerization systems leads to slow propagation reaction and narrow molecular weight distributions of the polymers. The poly(N,N-dialkylacrylamides) produced with 1 are rich in isotactic configuration, while the addition of Et2Zn reduces isotacticity and increases the degree of syndio- and heterotacticity. In particular, the poly(DEA)s generated with 1/Et2Zn and 1/LiCl are highly syndiotactic and isotactic, respectively. Although the broad distributions of triad sequence are observed for the polymers produced with 2, the highly heterotactic poly(DEA) is formed with 2/Et2Zn at 0 °C. The additive effects of Et2Zn on the molecular weight and tacticity are supposed to be caused by the coordination of Et2Zn with the propagating enolate anion

Living Anionic Polymerization of Benzofulvene: Highly Reactive Fixed Transoid 1,3-Diene

Anionic polymerization of benzofulvene (<b>BF</b>, α-methyleneindene), an exomethylene monomer having a fixed transoid 1,3-diene moiety, quantitatively proceeded with <i>sec</i>-BuLi or diphenylmethylpotassium in THF at −78 °C for 1 h. The resulting poly­(<b>BF</b>)­s possessed the predicted molecular weights based on the molar ratios between monomer and initiators and narrow molecular weight distributions (<i>M</i>_w/<i>M</i>_n = 1.1). High anionic polymerizability of <b>BF</b> was realized by the fact that a well-defined diblock copolymer, poly­(methyl methacrylate)-<i>block</i>-poly­(<b>BF</b>), was obtained by the sequential copolymerization of <b>BF</b> with a low nucleophilic enolate anion of living poly­(methyl methacrylate) in quantitative efficiency. NMR analyses indicated that the repeating units of poly­(<b>BF</b>) consisted of a 1,2-addition unit (41%) and a 1,4-addition unit (59%) without a 3,4-addition unit, suggesting that the exomethylene group of <b>BF</b> always participated in the polymerization. Thus, <b>BF</b> acted as a novel polymerizable transoid 1,3-diene in the anionic polymerization

Synthesis of Well-Defined Novel Reactive Block Polymers Containing a Poly(1,4-divinylbenzene) Segment by Living Anionic Polymerization

In order to synthesize a variety of block polymers having poly­(1,4-divinylbenzene) (PDVB) segments, the living anionic block polymerizations of DVB with styrene, 2-vinylpyridine (2VP), <i>tert</i>-butyl methacrylate (^tBMA), methyl methacrylate (MMA), <i>N</i>-(4-vinylbenzylidene)­cyclohexylamine (<b>1</b>), 2-(4′-vinylphenyl)-4,4-dimethyl-2-oxazoline (<b>2</b>), or 2,6-di-<i>tert</i>-butyl-4-methylphenyl 4-vinylbenzoate (<b>3</b>) were conducted in THF at −78 °C with the anionic initiator bearing K⁺ in the presence of a 10-fold excess of potassium <i>tert</i>-butoxide. With the sequential addition of DVB and each of these monomers, the following block polymers having PDVB segments were successfully synthesized: PS-<i>b</i>-PDVB, P2VP-<i>b</i>-PDVB, PDVB-<i>b</i>-P2VP, PDVB-<i>b</i>-P^tBMA, PDVB-<i>b</i>-P­(<b>1</b>), PDVB-<i>b</i>-P­(<b>2</b>), PDVB-<i>b</i>-P­(<b>3</b>), PS-<i>b</i>-PDVB-<i>b</i>-P^tBMA, PS-<i>b</i>-P2VP-<i>b</i>-PDVB-<i>b</i>-P^tBMA, and PS-<i>b</i>-PDVB-<i>b</i>-P2VP-<i>b</i>-P^tBMA. The resulting polymers are all novel block polymers with well-defined structures (predictable molecular weights and compositions and narrow molecular weight distributions) and possess reactive PDVB segments capable of undergoing several postreactions. Based on the results of such sequential block polymerizations, the anionic random copolymerization of DVB and 2VP, the polymerizability with (C₄H₉)₂Mg, and some other addition reactions, it was found that the comparable reactivity of the chain-end anions follows the sequence of PS^– > PDVB^– > P2VP^– > P^tBMA^–. Accordingly, the reactivity of the corresponding monomers increases as follows: styrene < DVB < 2VP < ^tBMA

Living Anionic Polymerization of 1,4-Divinylbenzene

We have successfully realized for the first time the living anionic polymerization of 1,4-divinylbenzene (1) with the use of a specially designed initiator system prepared from oligo(α-methylstyryl)lithium and a 11-fold or more excess of potassium tert-butoxide. The polymerization was very fast and complete at −78 °C for 1 min. Soluble polymers having a pendant vinyl group in each monomer unit were always quantitatively obtained under such conditions. The resulting poly(1)s possessed predictable molecular weights (Mn = 11 000–26 400 g/mol) and narrow molecular weight distributions (Mw/Mn 1)-block-poly(tert-butyl methacrylate), was also successfully synthesized with the same initiator system by the anionic block copolymerization where 1 and tert-butyl methacrylate were sequentially added in this order

Living Anionic Polymerization of 1,4-Diisopropenylbenzene

The anionic polymerization of diisopropenylbenzene (DIPB) derivatives was conducted in THF at −78 °C with a specially designed initiator system prepared from oligo­(α-methylstyryl)­lithium and an excess potassium <i>tert</i>-butoxide (KOBu^t) (2.7–5.0 equiv to the Li salt). Among the <i>ortho</i>-, <i>meta</i>-, and <i>para</i>-isomers of DIPB derivatives, it was found that the <i>para</i>-isomer (<i>p</i>-DIPB) successfully underwent the living polymerization in a selective manner through one of the two isopropenyl groups under the above stated conditions. With this living polymerization system, soluble polymers with controllable <i>M</i>_n values ranging from 7620 to 31 500 g/mol and near monodisperse distributions (<i>M</i>_w/<i>M</i>_n ≤ 1.03) were obtained for the first time. The obtained living polymers were stable at −78 °C even after 168 h and at −40 °C after 6 h, in which the intermolecular addition reaction of the chain-end anion to the pendant isopropenyl group could be completely suppressed. In contrast, the living polymerization of either the <i>ortho</i>- or <i>meta</i>-isomer was not successful under the same conditions. The block copolymerization of <i>p</i>-DIPB with either styrene (S), 2-vinylpyridine (2VP), or <i>tert</i>-butyl methacrylate (^tBMA) by the sequential addition of such monomers was conducted. Four new PS-<i>block</i>-P­(<i>p</i>-DIPB), P2VP-<i>block</i>-P­(<i>p</i>-DIPB), P­(<i>p</i>-DIPB)-<i>block</i>-P2VP, and P­(<i>p</i>-DIPB)-<i>block</i>-P^tBMA containing reactive P­(<i>p</i>-DIPB) segments were synthesized. On the basis of the block copolymerization results, it is understood that <i>p</i>-DIPB is comparable to 2VP and located between S and ^tBMA in monomer reactivity. The reactivity increases as follows: S < 2VP ∼ <i>p</i>-DIPB < ^tBMA, while the nucleophilicity of the living chain-end anion decreases in the following order: PS^– > P2VP^– ∼ P­(<i>p</i>-DIPB) ^– > P­(^tBMA) ^–