Synthesis and properties of the addition polymer of benzenedithiol with divinylbenzene

Polyaddition of 1,4-benzenedithiol (BDT) to 1,4-divinylbenzene (DVB) was carried out with 2,2′-azobisisobutyronitrile initiator in toluene at 75°C under a nitrogen atmosphere. The polymerization proceeded without an induction period, to give a white polymer with a high molecular weight (M?_w = 110,000) in ca. 90% yield for 2 hr. It was confirmed by ¹H-NMR (nuclear magnetic resonance), IR (infrared) and sulfur contents that the polymer had an alternating structure of DVB and BDT units. The end-capping reaction of the polymer was also achieved by addition of thiophenol and/or styrene to the polymerization solution at a final stage of the polymerization. The polymer film exhibited a reversible phase transition between a transparent state and an opaque one by thermal mode. The thermal property of the polymer was studied by differential scanning calorimetry (DSC) analysis and polarized optical microscope observation with the polymer film. The detailed DSC analysis showed that the end-capped polymer with a relatively low molecular weight (M?_W = 4400–9600) exhibited similar to liquid crystalline behavior. A diffuse reflectance spectrum of the polymer coated on an aluminum plate showed a marked difference in reflective light intensity in the ultraviolet and visible regions: the reversible phase transition between an opaque and a transparent polymer layers was induced by thermal mode. The light transmittance of the polymer film, which was measured by depolarized light intensity method, was very sensitive toward the temperature variation.     

Tetradentate schiff base ligand/MCln initiating systems for the controlled cationic polymerization of isobutyl vinyl ether: Effects of the ligand framework

We investigated the cationic polymerization of vinyl ethers using metal complex catalysts with salen and salphen ligands. Metal complexes were generated in situ from the reaction of a ligand and a metal chloride. The choice of a ligand and a central metal was crucial for tuning the catalyst function such as catalytic activity and controllability of the polymerization. Among metal chlorides employed, ZrCl₄ was the most efficient for controlled polymerization. Cationic polymerization of isobutyl vinyl ether (IBVE) proceeded using the salen and salphen‐type ligand/ZrCl₄ initiating systems, yielding polymers with predetermined molecular weights and narrow molecular weight distributions. Importantly, the structural effects of the complex catalysts were responsible for the polymerization behavior. For example, the polymerization using the salen‐type ligand/ZrCl₄ system was much slower than that using the salphen‐type ligand/ZrCl₄ system. In addition, the polymerization of IBVE using the salen‐type ligand/FeCl₃ system proceeded in a controlled manner, which was in contrast to uncontrolled polymerization using the salphen‐type ligand/FeCl₃ system. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 989–996     

Living cationic polymerization of vinylnaphthalene derivatives

The living cationic polymerization of 6‐tert‐butoxy‐2‐vinylnaphthalene (tBOVN), a vinylnaphthalene derivative with an electron‐donating group, was achieved with a TiCl₄/SnCl₄ combined initiating system in the presence of ethyl acetate as an added base at –30 °C. The absence of side reactions at low temperature was confirmed by ¹H NMR analysis of the resulting polymer. In contrast to this controlled reaction at –30 °C, reactions performed at higher temperature, such as 0 °C, frequently involved unwanted intramolecular or intermolecular Friedel–Crafts reactions of naphthalene rings due to the high electron density of these rings. The cationic polymerization of 6‐acetoxy‐2‐vinylnaphthalene, a derivative with an acetoxy group, was also controlled under similar conditions, but chain transfer reactions were not completely suppressed during the polymerization of 2‐vinylnaphthalene. The glass transition temperature (T_g) of the obtained poly(tBOVN) was 157 °C, a value higher by 94 °C than that of the corresponding styrene derivative. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4828–4834     

Precise synthesis of pH‐responsive copolymers with naphthoic acid side groups via living cationic polymerization

pH‐Responsive homopolymers and copolymers with naphthoic acid side groups were synthesized via base‐assisting living cationic polymerization. To this end, the feasibility of the living cationic polymerization of ethyl 6‐[2‐(vinyloxy)ethoxy]‐2‐naphthoate (EVEN) was first examined using a base‐assisting initiating system. Et_1.5AlCl_1.5 as a Lewis acid catalyst induced the living cationic polymerization of EVEN in the presence of ethyl acetate or 1,4‐dioxane in CH₂Cl₂ at 0 °C. In contrast, the use of naphthoxyethyl vinyl ether (NpOVE), which is a nonsubstituted counterpart, resulted in a poorly controlled polymerization under these conditions. The presence of the carboxy ester was most likely critical in preventing side reactions. A subsequent alkaline hydrolysis of the side‐chain esters quantitatively yielded a carboxy‐containing polymer. Aqueous solutions of this polymer underwent pH‐driven phase separation at pH 7.0. Well‐defined random and block copolymers were also prepared with various functional segments, and their stimuli‐responsive behaviors were investigated in terms of solution transmittance and aggregate size. Block copolymers containing two different pH‐responsive segments formed micelle‐like structures between the two phase‐separated pH values, and dual stimuli‐responsive copolymers containing a pH‐responsive polyacid segment and a thermosensitive segment self‐assembled in the water in response to both the pH and temperature. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5239–5247     

Thermosensitive gradient copolymers by living cationic polymerization: Semibatch precision synthesis and stepwise dehydration‐induced micellization and physical gelation

Thermosensitive forced gradient copolymers with various sequence distributions were synthesized by living cationic polymerization in the presence of an added base. The synthesis was conducted using a semibatch reaction method, which is unfavorable for ionic polymerization, especially when a simple apparatus is employed. Polymerization of 2‐ethoxyethyl vinyl ether (EOVE) was initiated using a conventional syringe technique. Immediately after initiation, 2‐methoxyethyl vinyl ether (MOVE) was continuously added using a syringe pump at regulated feed rates, which allowed control of the sequence distribution. The resulting gradient copolymers of EOVE and MOVE underwent thermally induced association in water, forming micelles with a hydrophobic core derived from EOVE‐rich segments. Interestingly, the size of the micelles obtained from gradient copolymers decreased monotonously with increasing solution temperature, while the micelles of the corresponding block copolymers were unchanged in size. This self‐association behavior can be controlled by designing the gradient pattern of the instantaneous composition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6151–6164, 2008     

Living cationic polymerization of dihydrofuran and its derivatives

Cationic polymerization of 2,3‐dihydrofuran (DHF) and its derivatives was examined using base‐stabilized initiating systems with various Lewis acids. Living cationic polymerization of DHF was achieved using Et_1.5AlCl_1.5 in toluene in the presence of THF at 0 °C, whereas it has been reported that only less controlled reactions occurred at 0 °C. Monomer‐addition experiments of DHF and the block copolymerization with isobutyl vinyl ether demonstrated the livingness of the DHF polymerization: the number–average molecular weight of the polymers shifted higher with low polydispersity as the polymerization proceeded after the monomer addition. Furthermore, this base‐stabilized cationic polymerization system allowed living polymerization of ethyl 1‐propenyl ether and 4,5‐dihydro‐2‐methylfuran at ?30 and ?78 °C, respectively. In the polymerization of 2,3‐benzofuran, the long‐lived growing species were produced at ?78 °C. The obtained polymers have higher glass transition temperatures compared to poly(acyclic alkyl vinyl ether)s. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4495–4504, 2008     

Thermosensitive diblock copolymers with designed molecular weight distribution: Synthesis by continuous living cationic polymerization and micellization behavior

The synthesis of diblock copolymers with designed molecular weight distributions (MWDs) was successfully demonstrated in a continuous living cationic polymerization system using simple equipment. The control of MWDs was achieved by gradually feeding a polymerization reaction mixture into a terminating agent. As thermosensitive diblock copolymers, poly(vinyl ethers) containing a thermosensitive segment with oxyethylene side chains and a hydrophilic segment were prepared. The polymerization was carried out in a gas‐tight microsyringe, and the polymerization mixture was added continuously into methanol during the second‐stage polymerization. The self‐association behavior of the resulting diblock copolymers was evaluated by dynamic light scattering in water. MWD‐designed polymers with thermosensitive segments that varied continuously in length and hydrophilic segments of nearly uniform lengths formed micelles with a broad size distribution. Conversely, polymers with nearly uniform thermosensitive segments and hydrophilic segments of different lengths formed micelles with a narrow size distribution, as observed with conventional narrow MWD diblock copolymers. Thus, the MWD of the thermosensitive segment proved a decisive factor in achieving fine control of self‐association. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2212–2221, 2008     

Stimuli‐responsive reversible physical networks. II. Design and properties of homogeneous physical networks consisting of periodic copolymers synthesized by living cationic polymerization

The design and precision synthesis of physical networks consisting of copolymers with crystallizable pendant groups are described in this work. Amphiphilic periodic, statistical, and gradient copolymers consisting of octadecyl vinyl ether (ODVE) units were synthesized via living cationic polymerization. The synthesis involved the copolymerization of ODVE and 2‐methoxyethyl vinyl ether (hydrophilic) with an 1‐(isobutoxy)ethyl acetate [CH₃CH(OiBu)OCOCH₃]/Et_1.5AlCl_1.5 initiating system in the presence of a weak Lewis base to yield copolymers with very narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight ? 1.2). All aqueous solutions of the copolymers behaved as a viscous liquid above 50 °C. When cooled below 25 °C, the solutions turned into transparent, transient physical gels (exhibiting terminal flow), regardless of the sequence distribution. Viscoelastic studies showed that a periodic copolymer gave a hard gel that was more brittle than the gels obtained from the corresponding statistical and gradient copolymers. This difference and the differences in the relaxation time and relaxation mode distribution of the copolymer gels were consistent with the sequence distributions of ODVE in the respective copolymers. These results indicate that the mechanical properties of a physical network can be controlled by the primary polymer structures. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2712‐2722, 2005