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

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

Precise Synthesis of Miktoarm Star Polymers by Using a New Dual-Functionalized 1,1-Diphenylethylene Derivative in Conjunction with Living Anionic Polymerization System

The general utility of a 1,1-diphenylethylene (DPE) derivative substituted with trimethylsilyl- and <i>tert</i>-butyldimethylsilyl-protected hydroxyl functionalities, as a new dual-functionalized core agent in conjunction with a living anionic polymerization system, has been demonstrated by the successful synthesis of various well-defined 3-arm ABC and 4-arm ABCD μ-star polymers. Two different protected hydroxyl functionalities were progressively deprotected to generate hydroxyl groups, followed by conversion to α-phenyl acrylate (PA) functions at separate stages, and the PA functions were reacted with appropriate living anionic polymers to result in the above μ-stars. In order to further synthesize μ-star polymers with five or more arms, a new iterative methodology using a functional DPE anion derived from the above DPE derivative has been developed. The reaction system of this methodology is designed in such a way that the PA function used as the reaction site is regenerated after the introduction of an arm segment in each reaction sequence, and this sequence, consisting of “arm introduction and regeneration of the PA reaction site”, is repeatable. With this methodology, a series of new well-defined μ-star polymers up to a 5-arm ABCDE type, composed of all different methacrylate-based polymer segments, were successfully synthesized for the first time

Precise Synthesis of Dendrimer-like Star-Branched Poly(<i>tert</i>-butyl methacrylate)s and Their Block Copolymers by a Methodology Combining α-Terminal-Functionalized Living Anionic Polymers with a Specially Designed Linking Reaction in an Iterative Fashion

A new stepwise iterative methodology was developed for the synthesis of well-defined high-generation and high-molecular-weight dendrimer-like star-branched poly­(<i>tert</i>-butyl methacrylate)­s (P^tBMA)­s and block copolymers composed of P^tBMA and polystyrene (PS) segments. The methodology involves the following two reaction steps in an iterative process: (1) a linking reaction based on a 1:1 addition reaction of an α-terminal-(3-<i>tert</i>-butyldimethylsilyloxymethylphenyl (SMP))₂-functionalized living polymer with a core compound or α-terminal-(α-phenyl acrylate (PA))₂-functionalized polymers linked to the core and (2) a conversion of the SMP group to the PA function, to be used as the next reaction site. Repetition of the two reaction steps, (1) and (2), allows for the synthesis of high-generation and high-molecular-weight dendrimer-like star-branched polymers. In practice, a series of dendrimer-like star-branched (P^tBMA)­s up to the fifth generation (5G) were successfully synthesized. The resulting polymers, whose arm segments were four-branched at the core and two-branched at each layer, were all well-defined in branched architecture and precisely controlled in chain length, and the final 5G dendrimer-like star-branched P^tBMA possessed a predictable <i>M</i>_n value of 1.07 × 10⁷ g/mol and an extremely narrow molecular weight distribution of 1.03 in <i>M</i>_w/<i>M</i>_n value. The synthetic possibility of similar dendrimer-like star-branched polymers composed of functional polymer segments bearing acid-labile and/or basic groups by the same methodology was also demonstrated. Furthermore, 4G dendritic architectural block copolymers with hierarchic layer structures composed of P^tBMA (and poly­(methacrylic acid)) and PS segments were synthesized

Successive Synthesis of Miktoarm Star Polymers Having up to Seven Arms by a New Iterative Methodology Based on Living Anionic Polymerization Using a Trifunctional Lithium Reagent

A new stepwise iterative methodology based on living anionic polymerization using a trifunctional lithium reagent substituted with trimethylsilyl (TMS), <i>tert</i>-butyldimethylsilyl (TBDMS), and tetrahydropyranyl (THP) ethers of protected hydroxyl functionalities has been developed in order to obtain synthetically challenging many-armed μ-star polymers. In each reaction sequence of the new methodology, these three ether functions were selectively deprotected in turn under carefully selected conditions as designed, followed by conversion to three α-phenyl acrylate (PA) reaction sites step by step at different reaction stages. They were used for the introduction of two different arm segments and the reintroduction of the above same three ethers. This reaction sequence was repeated three times to successively synthesize 3-arm ABC, 4-arm ABCD, 5-arm ABCDE, 6-arm ABCDEF, and 7-arm ABCDEFG μ-star polymers with well-defined structures. Herein, the A, B, C, D, E, F, and G arms were poly­(cyclohexyl methacrylate), polystyrene, poly­(4-methoxystyrene), poly­(4-methylstyrene), poly­(methyl methacrylate), poly­(ethyl methacrylate), and poly­(2-methoxyethyl methacrylate) segments, respectively. The trifunctional lithium reagent was also demonstrated to satisfactorily function as a convenient and useful core agent access to the general synthesis of 4-arm ABCD and 6-arm A₂B₂C₂ μ-star polymers

Interplay between the Phase Transitions at Different Length Scales in the Supramolecular Comb–Coil Block Copolymers Bearing (AB)_<i>n</i> Multiblock Architecture

We introduced the concept of comb–coil supramolecule into linear (AB)_<i>n</i>-type multiblock copolymer and investigated the self-assembly behavior of the copolymers as a function of the unit number <i>n</i>. Linear (polystyrene-<i>block</i>-poly­(2-vinylpyridine))_<i>n</i> (denoted as (PS-<i>b</i>-P2VP)_<i>n</i>, where <i>n</i> = 1, 2, 3) was complexed with a surfactant, dodecylbenzenesulfonic acid (DBSA), to yield the comb–coil multiblock copolymers, in which DBSA bound stoichiometrically with P2VP block via physical bonds. All three comb–coil block copolymers, including diblock (<i>n</i> = 1), tetrablock (<i>n</i> = 2), and hexablock (<i>n</i> = 3), self-organized to form cylinder-<i>within</i>-lamellae morphology at the lower temperature, where the cylindrical microdomains formed by the PS block embedded in the matrix composed of the lamellar mesophase organized by the P2VP­(DBSA) comb block. The disordering of the smaller-scale lamellar mesophase formed by the comb block occurred upon heating; at the same time, the larger-scale cylindrical domains transformed to body-centered cubic-packed spheres in the diblock complex and to another hexagonally packed cylinder structure with smaller domain spacing in tetrablock and hexablock complexes, indicating that the order–disorder transition (ODT) of the smaller-scale structure drove an order–order transition (OOT) of the larger-scale structure irrespective of <i>n</i>. The transition temperatures were found to increase with increasing <i>n</i> due to the introduction of more interfacial area in the microphase-separated state of the multiblock with larger unit number

Precise Synthesis of Novel Star-Branched Polymers Containing Reactive Poly(1,4-divinylbenzene) Arm(s) by Linking Reaction of Living Anionic Poly(1,4-divinylbenzene) with Chain-(α-Phenyl acrylate)-Functionalized Polymers

We have synthesized several star-branched polymers having poly­(1,4-divinylbenzene) (PDVB) segment(s) by quantitatively linking the 1,1-diphenylethylene-stabilized living anionic PDVB with the chain-(α-phenyl acrylate)-functionalized polymers. The synthesized polymers were the A₃ regular star PDVB, A₂B, AB₂, ABC, ABCD, and A₄B μ-star polymers. The A arm is the PDVB segment, while the B, C, or D arm is either a polystyrene, poly­(methyl methacrylate), poly­(α-methylstyrene), or poly­(2-vinylpyridine) segment. These polymers are the first successful highly reactive PDVB-containing well-defined star-branched polymers, whose pendant vinyl groups are capable of undergoing various postfunctionalization reactions to introduce additional functionalities

Side-Chain-Controlled Self-Assembly of Polystyrene–Polypeptide Miktoarm Star Copolymers

We show how the self-assembly of miktoarm star copolymers can be controlled by modifying the side chains of their polypeptide arms, using A₂B and A₂B₂ type polymer/polypeptide hybrids (macromolecular chimeras). Initially synthesized PS₂PBLL and PS₂PBLL₂ (PS, polystyrene; PBLL, poly­(ε-<i>tert</i>-butyloxycarbonyl-l-lysine)) miktoarms were first deprotected to PS₂PLLHCl and PS₂PLLHCl₂ miktoarms (PLLHCl, poly­(l-lysine hydrochloride)) and then complexed ionically with sodium dodecyl sulfonate (DS) to give the supramolecular complexes PS₂PLL­(DS) and PS₂(PLL­(DS))₂. The solid-state self-assemblies of these six miktoarm systems were studied by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and small- and wide-angle X-ray scattering (SAXS, WAXS). The side chains of the polypeptide arms were observed to have a large effect on the solubility, polypeptide conformation, and self-assembly of the miktoarms. Three main categories were observed: (i) lamellar self-assemblies at the block copolymer length scale with packed layers of α-helices in PS₂PBLL and PS₂PBLL₂; (ii) charge-clustered polypeptide micelles with less-defined conformations in a nonordered lattice within a PS matrix in PS₂PLLHCl and PS₂PLLHCl₂; (iii) lamellar polypeptide–surfactant self-assemblies with β-sheet conformation in PS₂PLL­(DS) and PS₂(PLL­(DS))₂ which dominate over the formation of block copolymer scale structures. Differences between the 3- and 4-arm systems illustrate how packing frustration between the coil-like PS arms and rigid polypeptide conformations can be relieved by the right number of arms, leading to differences in the extent of order

Synthesis and Characterization of Multicomponent ABC- and ABCD-Type Miktoarm Star-Branched Polymers Containing a Poly(3-hexylthiophene) Segment

The new series of ABC-type miktoarm star polymer (<b>ABC star</b>, A = polyisoprene (PI), B = polystyrene (PS), and C = poly­(3-hexylthiophene) (P3HT)) and ABCD-type miktoarm star polymer (<b>ABCD star</b>, A = PI, B = PS, C = poly­(α-methylstyrene) (PαMS), and D = P3HT) could be synthesized by the combination of the controlled KCTP, anionic linking reaction, and Click chemistry. By the copper­(I)-catalyzed Huisgen 1,3-dipolar cycloaddition click reaction of the azido-chain-end-functional P3HT (<b>P3HT-N</b>_<b>3</b>) with the alkyne-in-chain-functional AB diblock copolymer (A = PI and B = PS) (<b>AB-alkyne</b>) or alkyne-core-functional ABC miktoarm star polymer (A = PI, B = PS, and C = PαMS) (<b>ABC-alkyne</b>), the target <b>ABC star</b> and <b>ABCD star</b>, respectively, were obtained, as confirmed by size exclusion chromatography (SEC) and proton nuclear magnetic resonance (¹H NMR). The thermal and optical properties of these star polymers were examined by thermal gravimetric analysis (TGA) and UV–vis spectroscopy. The dynamic scattering calorimetry (DSC), atomic force micrograph (AFM) image, and grazing incidence small-angle X-ray scattering (GISAXS) results showed that the periodic P3HT fibril nanostructures rather than microphase separation occurred in the <b>ABCD star</b> film. In addition, it was found that highly crystalline P3HT domains aligned in the “edge-on” orientation, as supported by grazing incidence wide-angle X-ray scattering (GIWAXS)

Complex Self-Assembled Morphologies of Thin Films of an Asymmetric A₃B₃C₃ Star Polymer

An asymmetric nine-arm star polymer, (polystyrene)₃-(poly­(4-methoxystyrene))₃-(polyisoprene)₃ (PS₃-PMOS₃-PI₃) was synthesized, and the details of the structures of its thin films were successfully investigated for the first time by using in situ grazing incidence X-ray scattering (GIXS) with a synchrotron radiation source. Our quantitative GIXS analysis showed that thin films of the star polymer molecules have very complex but highly ordered and preferentially in-plane oriented hexagonal (HEX) structures consisting of truncated PS cylinders and PMOS triangular prisms in a PI matrix. This HEX structure undergoes a partial rotational transformation process at temperatures above 190 °C that produces a 30°-rotated HEX structure; this structural isomer forms with a volume fraction of 23% during heating up to 220 °C and persists during subsequent cooling. These interesting and complex self-assembled nanostructures are discussed in terms of phase separation, arm number, volume ratio, and confinement effects