Akikazu Matsumoto

Thermochromism and Structural Change in Polydiacetylenes Including Carboxy and 4-Carboxyphenyl Groups as the Intermolecular Hydrogen Bond Linkages in the Side Chain

We investigated the thermochromic behavior of polydiacetylenes including the carboxy and 4-carboxyphenyl groups as the side-chain substituents adjacent to the conjugated main chain, and then, the thermal stability and the thermochromism reversibility of the polymers were related to changes in the polymer conformations monitored by IR and Raman spectroscopies and powder X-ray diffractions. The polydiacetylenes with no or a phenylene spacer between the main chain and the carboxylic acid moiety were revealed to exhibit a thermal resistance for maintaining reversible thermochromism in a high temperature range, rather than polydiacetylenes with a conventional structure with a flexible alkylene spacer. The molecular stacking structures of the diacetylenes and the corresponding polymers in the crystals were discussed based on the results of an X-ray single-crystal structure analysis as well as the powder X-ray diffraction measurements.

Facile Synthesis of Main-Chain Degradable Block Copolymers for Performance Enhanced Dismantlable Adhesion

Block copolymers consisting of readily degradable polyperoxides and non-degradable vinyl polymers as the block segments were successfully synthesized by reversible chain transfer catalyzed polymerization, which is one of living radical polymerization techniques. The block copolymers showed characteristic morphology and wettability being different from the polymer blends. When block copolymers containing polyperoxide and polymethacrylate blocks were heated below 150 °C, the polyperoxide blocks were completely degraded and the polymethacrylate blocks were recovered without degradation. Block copolymers containing a poly(2-ethylhexyl methacrylate) block were then investigated as a dismantlable adhesion material, which requires adequate bonding strength during use and easy debonding on demand. Among the several block copolymers, the one consisting of poly(2-ethylhexyl methacrylate) and polyperoxide from methyl sorbate (PPMS) (M(n) = 4900) exhibited good performance as a pressure-sensitive adhesive (PSA). After heating the test specimens in a temperature range from 60 to 100 °C, PSA performance, which was evaluated by 180° peel strength and shear holding power measurements, was significantly diminished. Especially, after heating at 100 °C for 1 h, spontaneous debonding of some test specimens was observed because of the evolution of volatile acetaldehyde from PPMS.

Self-Assembly and Cellular Uptake of Degradable and Water-Soluble Polyperoxides

Water-soluble polyperoxides (PPs) as a new type of degradable and polymeric material were synthesized by the radical alternating copolymerization of sorbic derivatives containing a tetra(ethylene oxide) unit in the ester group using molecular oxygen. The obtained PPs showed a lower critical solution temperature (LCST)-type phase separation, and the transition temperature decreased according to the content of the hydrophobic ester group in the PPs. The PPs formed nanoaggregates with a diameter of 250-370 nm in water under the LCST. These PP aggregates were revealed to include 1-anilinonaphthalene-8-sulfonic acid as the fluorescence probe and epirubicin as the anticancer drug in their hydrophobic compartment. We evaluated the cytotoxicity and cellular uptake of the PPs in order to test their ability as a carrier used for the delivery of anticancer drugs. The cell viability in the presence of the PPs was comparable to those for the other biodegradable polymers, and epirubicin was taken up into the A549 efficiently with the PPs via an endocytosis mechanism.

Facile synthesis of functional polyperoxides by radical alternating copolymerization of 1,3-dienes with oxygen.

We have developed a facile synthesis of degradable polyperoxides by the radical alternating copolymerization of 1,3-diene monomers with molecular oxygen at an atmospheric pressure. In this review, the synthesis, the degradation behavior, and the applications of functional polyperoxides are summarized. The alkyl sorbates as the conjugated 1,3-dienes gave a regiospecific alternating copolymer by exclusive 5,4-addition during polymerization and the resulting polyperoxides decomposed by the homolysis of a peroxy linkage followed by successive beta-scissions. The preference of 5,4-addition was well rationalized by theoretical calculations. The degradation of the polyperoxides occurred with various stimuli, such as heating, UV irradiation, a redox reaction with amines, and an enzyme reaction. The various functional polyperoxides were synthesized by following two methods, one is the direct copolymerization of functional 1,3-dienes, and the other is the functionalization of the precursor polyperoxides. Water soluble polyperoxides were also prepared, and the LCST behavior and the application to a drug carrier in the drug delivery system were investigated. In order to design various types of degradable polymers and gels we developed a method for the introduction of dienyl groups into the precursor polymers. The resulting dienyl-functionalized polymers were used for the degradable gels. The degradable branched copolymers showed a microphase-separated structure, which changed owing to the degradation of the polyperoxide segments.

High-molecular-weight polar acrylate block copolymers as high-performance dismantlable adhesive materials in response to photoirradiation and postbaking

We synthesized high-molecular-weight acrylate block copolymers as high-performance dismantlable adhesives consisting of a poly(tert-butyl acrylate) (PtBA) sequence as the reactive segment and a random copolymer sequence of n-butyl acrylate (nBA) or 2-ethylhexyl acrylate (2EHA) with 2-hydroxyethyl acrylate (HEA) as the adhesive segment, using an organotellurium-mediated living radical polymerization (TERP). The adhesion strength of PtBA/P2EHA and PtBA/PnBA block copolymers containing polar HEA repeating units in their soft segments was sufficiently high for use as a pressure-sensitive adhesive. A quick change in the adhesion properties was observed in response to the dual external stimuli of photoirradiation and postbaking during the dismantling process. We discuss the adhesion strength and failure mode as a function of the HEA content, the sequence structure of the copolymers, and the external stimulus conditions.

Dismantlable adhesion properties of reactive acrylic copolymers resulting from cross-linking and gas evolution

ABSTRACT The acrylic copolymers involving 2-hydroxyethyl acrylate (HEA) and tert-butyl acrylate (tBA) units as reactive units behave as pressure-sensitive adhesive type dismantlable adhesive materials. In order to clarify the individual role of HEA and tBA units on dismantlability, the 180° peel behavior after the dismantling treatment, i.e., heating in the presence of given amount of acid catalysts, was systematically investigated using the acrylic copolymers involving different amounts of the reactive units. It was revealed that transesterification of HEA units resulted in an increase in the cohesive force and modulus due to an increase in the molecular weight and cross-linking. Deprotection of tBA units, i.e., transformation of tBA to acrylic acid (AA) unit with isobutene evolution, promoted cross-linking by the esterification of AA units and tended to reduce a cohesive force by forming voids in the adhesive layer due to the evolution of isobutene gas. Interfacial failure in the peel tests corresponded with a high degree of cross-linking and increased modulus of the adhesive. Conversely, cohesive failure was associated with reduced cohesive strength of the adhesive layer and a low peel strength.

Polymer Crystal Engineering for Control of Stereochemical Structure of Polymers: Stereospecific Monomer Synthesis and Stereospecific Solid-State Polymerization

ABSTRACT We have successfully synthesized diisotactic and disyndiotactic polymers of (Z,Z)- and (E,E)-muconates with various benzyl ester groups. Muconic acid was conveniently converted into its corresponding ester derivatives without EZ isomerization when reacted with benzyl bromides in the presence of potassium carbonate in hexamethylphosphoramide (HMPA) at room temperature. Several monomers undergo photopolymerization in the crystalline state to give stereoregular polymers according to the monomer configuration and the ester substituents. X-ray single crystal structure analysis of the monomer and polymer crystals has revealed the process of the topochemical polymerization. In the monomer crystals with 4-alkoxybenzyl groups as the ester substituents, a columnar structure is formed by the alternate stacking of monomer molecules with the aid of weak hydrogen bonds such as CH/π and CH/O intermolecular interactions. The alternate stacking is appropriate for syndiotactic polymerization, being different from the crystal structures of many other ester monomers which provide a diisotactic polymer due to the translational monomer stacking in a column, as is seen in the crystals of the 4-chloro-, 4-bromo-, and 4-nitro-substituted benzyl esters. Weak and flexible intermolecular interactions provide a variety of crystal structures and different type of molecular stacking leading to the different tacticity of the polymers.

Dissimilar Materials Bonding Using Epoxy Monolith

The epoxy monolith with a highly porous structure is fabricated by the thermal curing of 2,2-bis(4-glycidyloxyphenyl)propane and 4,4′-methylenebis(cyclohexylamine) in the presence of poly(ethylene glycol) as the porogen via polymerization-induced phase separation. In this study, we demonstrated a new type of dissimilar material bonding method for various polymers and metals coated with the epoxy monolith. On the basis of scanning electron microscopy (SEM) observations, the pore size and number of epoxy monoliths were evaluated to be 1.1–114 μm and 8.7–48u2009200 mm–2, respectively, depending on the ratio of the epoxy resin and cross-linking agent used for the monolith fabrication. Various kinds of thermoplastics, such as polyethylene, polypropylene, polyoxymethylene, acrylonitrile–butadiene–styrene copolymer, polycarbonate bisphenol-A, and poly(ethylene terephthalate), were bonded to the monolith-modified metal plates by thermal welding. The bond strength for the single lap-shear tensile test of stainless steel and copper plates with the thermoplastics was in the range of 1.2–7.5 MPa, which was greater than the bond strength value for each bonding system without monolith modification. The SEM observation of fractured test pieces directly confirmed an anchor effect on this bonding system. The elongated deformation of the plastics that filled in the pores of the epoxy monolith, was observed. It was concluded that the bond strength significantly depended on the intrinsic strength of the used thermoplastics. The epoxy monolith bonding of hard plastics, such as polystyrene and poly(methyl methacrylate), was performed by the additional use of adhesives, solvents, and a reactive monomer. The epoxy monolith sheets were also successfully fabricated and applied to dissimilar material bonding.

Control of adhesive strength of acrylate polymers containing 1-isobutoxyethyl and isobornyl esters in response to dual stimuli for dismantlable adhesion

BackgroundTo develop an adhesion system satisfying both constant adhesion strength during use and quick debonding ability during a dismantling process.MethodsAdhesive properties were investigated for the random and block copolymers consisting of 1-isobutoxyethyl acrylate (iBEA), 2-ethylhexyl acrylate (2EHA), and 2-hydroxyethyl acrylate (HEA) as the dismantlable pressure-sensitive adhesives in the presence of a photoacid generator in response to dual external stimuli of photoirradiation and post baking.ResultsThe use of LED combined with a new photoacid generator SIN-11 was enable us to achieve a rapid dismantling process during UV irradiation within several minutes. The protection of the ester alkyl group in the iBEA repeating unit to give an acrylic acid unit was suppressed by the introduction of isobornyl acrylate (IBoA) as the additional unit into the copolymer of iBEA, 2EHA, and HEA. While IBoA‐containing block copolymer showed a constant adhesive strength during photoirradiation as the single external stimulus, deprotection was immediately induced by the subsequent heating, leading to a significant decrease in the adhesive strength.ConclusionThe copolymer including the iBEA and IBoA units was revealed to function as the highly sensitive adhesive materials for dual-locked dismantlable adhesion.

Metal-resin bonding mediated by epoxy monolith layer

An epoxy monolith layer with porous structure is fabricated on the surface of a stainless steel (SUS) plate by polymerization induced phase separation process as the mediator for the bonding of SUS and various thermoplastic resin plates. Bonding strength is evaluated in the presence and absence of the epoxy monolith layer by a tensile lap shear test. The morphology of fracture surfaces is observed by scanning electron microscopy (SEM) in order to clarify the anchor effect of molten resins into the pores of the epoxy monoliths. The bonding strength values are calculated to be 1.2‒2.7xa0MPa based on an apparent adhesion area for the bonding of SUS with polyethylene, polypropylene, polyoxymethylene and acrylonitrile–butadiene–styrene copolymer in the presence of the epoxy monolith mediator. These values are 2‒30 times higher than those for direct metal-resin bonding. By the SEM observation, stretched needle-like structures were detected on the both fracture surfaces of the resins and the epoxy monoliths. The direct observation of the stretched debris out of the holes located at the monolith surfaces indicates the significant anchor effect for the present metal-resin bonding system. The bonding system mediated by the epoxy monolith layer is conveniently used for the bonding of dissimilar materials such as metals and resins without any special process and apparatus.