Network Polymer Precursors Research Articles

A11 多官能アリル架橋重合における高架橋密度ネットワークポリマー前駆体からなるゲルの超音波照射分解(口頭発表)

A11 多官能アリル架橋重合における高架橋密度ネットワークポリマー前駆体からなるゲルの超音波照射分解(口頭発表)

Synthesis and properties of novel network polymers containing castor oil and silsesquioxane moieties

Novel network polymer precursors were synthesized with castor oil or branched poly(l-lactic acid) and 3-(triethoxysilyl)propyl isocyanate. The network polymer precursors were cross-linked at 120 °C for 24 h to obtain network polymer films. The film formed from castor oil was easily broken when peeled off of a polytetrafluoroethylene petri dish, while the film formed from branched poly(l-lactic acid) was obtained as a self-supporting film. Thermal stabilities of the obtained films were measured by thermogravimetric analysis. The temperature at which 10% weight loss (Td10) occurred was 298 °C for the film derived from castor oil, and the Td10 of the film made from branched poly(l-lactic acid) was 200 °C. The film obtained using branched poly(l-lactic acid) exhibited elastomeric properties owing to a relatively low glass transition temperature of 3 °C and the onset of a rubbery plateau region at approximately 20 °C, as measured by dynamic mechanical analysis. Furthermore, we also prepared a film using the precursor material together with tetraethyl orthosilicate. The obtained film exhibited a higher thermal stability (Td10=223 °C) than that of the film using branched poly(l-lactic acid). Finally, the cross-linked films were subjected to degradation by exposure to porcine pancreas lipase. The observation of weight loss after 30 days confirmed the degradability of the films. In this study, we were synthesized novel biomass network polymer containing silsesquioxane as inorganic moiety. First, novel network polymer precursors were synthesized with castor oil or branched poly(l-lactic acid) (PLLA) and 3- (triethoxysilyl) propyl isocyanate. Precursors were carried out to cross-link reaction at 120 °C for 24 h, and obtained network polymer films. Furthermore, we were synthesized cross-linked film, which was increased inorganic moiety using tetraethyl orthosilicate.

Characterization of resulting network polymer precursors in stepwise crosslinking diepoxide/diamine polymerization

Our previous mechanistic discussion of network formation in chainwise crosslinking multiallyl polymerization was extended to stepwise crosslinking diepoxide/diamine polymerization, typically including bisphenol-A diglycidyl ether (BADGE) and 4,4′-diaminodiphenylmethane (DDM). In allyl polymerization a monomer chain transfer is an essential termination reaction, providing only oligomeric primary polymer chains. Therefore, crosslinking multiallyl polymerization could be in the category of a classical gelation theory. Thus, the gelation behavior was discussed by comparing the actual gel point with the theoretical one. Then the resulting network polymer precursors (NPPs) were characterized by size-exclusion chromatography-multiangle laser light scattering-viscometry to clarify the stepwise crosslinking BADGE/DDM polymerization mechanism. Notably, the intrinsic viscosity ratio [η]NPP/[η]Linear tended to decrease with the progress of crosslinking and finally, it reached less than 0.2. This suggests that the structure of resulting NPP becomes dendritic at a conversion close to the gel point. These dendritic NPPs can collide with each other to form crosslinks between NPPs, eventually leading to gelation as a reflection of the high concentration of NPP. The dilution effect on gelation was marked in polar solvent; no gelation was observed at a dilution of 1/5. However, in nonpolar solvent the gelation was promoted by dilution; this is ascribed to enhanced crosslink formation between NPPs through hydrogen bonding due to abundant hydroxyl groups in the NPP generated by the polyaddition reaction. Finally, the subject of “Is cured epoxy resin inhomogeneous?” is briefly discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Microgel-like network polymer precursor formation in free-radical cross-linking multiallyl polymerization

The present study is an extension of our preceding work on gelation behavior. We observed no substantial difference in the actual gel points among three isomeric diallyl phthalates: diallyl phthalate, diallyl isophthalate and diallyl terephthalate. The resulting network polymer precursors (NPPs) were characterized by size-exclusion chromatography with both multiangle laser light scattering and viscometry. It is of note that the structure of NPP, consisting of oligomeric primary polymer chains, becomes core-shell type dendritic or nanogel-like with the progress of polymerization. The nanogel-like NPPs can then collide with one another to form cross-links, eventually leading to gelation. Although the concentration of NPP should be high at the conversion close to the gel point, the dilution of NPP by adding monomer could prevent the cross-link formation among NPPs, and consequently lead to the successive growth of high-molecular-weight NPP from a nanogel to a microgel. The further growth of the microgel as an inhomogeneous NPP with high cross-link density could eventually reach an extremely inhomogeneous network polymer. These processes were pursued as typical examples using the bulk polymerization of DAT.

Mechanistic discussion of cationic crosslinking copolymerizations of 1,2‐epoxycyclohexane with diepoxide crosslinkers accompanied by intramolecular and intermolecular chain transfer reactions

AbstractOur previous mechanistic discussion of the free‐radical crosslinking monoallyl/diallyl copolymerizations was extended to the cationic crosslinking monoepoxide/diepoxide copolymerizations, typically including 1,2‐epoxycyclohexane (ECH) as a monoepoxide and bis[3,4‐epoxycyclohexylmethyl] adipate (BECHMA) as a diepoxide crosslinker. In the cationic polymerization, oligomer is usually obtained because of the occurrence of characteristic chain‐forming reactions. Therefore, cationic crosslinking monoepoxide/diepoxide copolymerizations could be in the category of the network formation through free‐radical crosslinking monoallyl/diallyl copolymerizations. Thus, the gelation behavior was discussed by comparing the actual gel points with the theoretical ones; the greatly delayed gelation from theory was observed. Then, the resulting network polymer precursors (NPPs) were characterized by SEC‐MALLS‐viscometry to clarify the cationic crosslinking ECH/BECHMA copolymerization mechanism. Notably, the correlation lines of molecular weight versus elution volume were specific for the NPPs obtained at a high conversion close to the gel point as compared with those obtained by the free‐radical crosslinking monoallyl/diallyl copolymerization. This may be ascribed to the occurrence of intramolecular and intermolecular chain transfer reactions characteristic of cationic polymerization; the chain transfer reactions involve the intramolecular and intermolecular nucleophilic attack of ether oxygen or terminal hydroxyl oxygen in the NPPs to a terminal growing cation that leads to the formation of not only the loop‐ but also the crosslink‐structures containing NPPs, providing fragile ultrahigh‐molecular‐weight NPP in the SEC columns. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Discussion of substantially identical gel points among multiallyl monomers based on characterization of resultant network polymer precursors consisting of oligomeric primary polymer chains

AbstractNo difference in the actual gel points was substantially observed among three isomeric diallyl phthalates such as diallyl phthalate (DAP), diallyl isophthalate, and diallyl terephthalate (DAT); this interesting gelation behavior was discussed further in terms of the correlation between gelation and the difference in cyclization modes, and also, the difference in reactivity between the uncyclized and cyclized radicals for cross‐linking. In the present work, we tried to extend the preceding discussion to the polymerization of triallyl trimellitate (TAT) because the molecular structure of TAT is presumed to essentially involve the characteristics of three isomeric diallyl phthalates and, therefore, the enhanced gelation was expected in TAT polymerization. However, no enhancement of gelation was observed. For a full understanding of the gelation in multiallyl cross‐linking polymerization, we explored further the polymerizations of DAP, DAT, and TAT, especially focusing on the characterization of resultant network polymer precursors (NPPs) using SEC‐MALLS‐viscometry providing the correlation of [η] versus Mw of fractionated samples. Notably, the structure of NPP consisting of oligomeric primary polymer chains generated from specific allyl polymerization would become core‐shell type dendritic with the progress of polymerization. The correlation between delayed gelation and decreased reactivity of dendritic NPP for intermolecular cross‐linking is discussed. Conclusively, the reactivity for intermolecular cross‐linking between NPPs decreased with the progress of polymerization leading to a delayed gelation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2871–2881, 2009

Further Discussion on Correlation between Brittleness and Inhomogeneous Network Structure of Cross-Linked Resins Originating in Specific Polymerization Behavior of Triallyl Isocyanurate

Nonfilled triallyl isocyanurate (TAIC) cured resin obtained directly by polymerization of TAIC monomer was too brittle for practical use. The brittleness of cross-linked resins has been thought to be due to the inhomogeneity of their network structures, which consist of colloidal particles as evidenced by electron microscopy. However, the complete loss of flexibility of poly(TAIC) chain does not satisfy the prerequisite of locally enhanced occurrence of intramolecular cross-linking reaction inducing microgelation to form a colloidal particle. Therefore, the correlation between brittleness and network structure of TAIC resins was further discussed, especially focusing on the characterization of resulting TAIC network polymer precursors (NPPs) by size-exclusion chromatography (SEC)−multiangle laser light scattering (MALLS)−viscometry since the ordinary explanation for the brittleness of cross-linked resin does not appear to be the true explanation for TAIC resin’s extreme brittleness. Thus, an alternative explanation for the brittleness of TAIC resins is provided: insufficient growth of the network structure of TAIC resin because of steric hindrance of the cross-linking reaction between sterically crowded growing polymer radical and pendant allyl groups belonging to the rigid primary polymer chain. This imperfection of cross-linking, providing not only insufficient network structure formation but also incorporation of abundant dangling chains into network polymer, could be one of the principal causes of brittleness, even for common cross-linked resins.

A Cleavable Network Based on Crosslinked Star Polymers Containing Acid-Labile Diacetal Crosslinks: Synthesis, Characterization and Hydrolysis

A hydrolyzable model network comprising interconnected star polymers was prepared by the sequential group transfer polymerization of methyl methacrylate and the acid-labile diacetal-based dimethacrylate crosslinker bis[(2-methacryloyloxy)ethoxymethyl] ether. In contrast to other polymer networks previously synthesized by our group, all the branching points of this polymer network were found to hydrolyze under mildly acidic conditions, giving a linear copolymer with the theoretically expected molecular weight and composition. The ease of hydrolysis of this polymer network renders it a good candidate for use in the biomedical field. The characterization of the synthesized network, its linear and star polymer precursors and the hydrolysis products of the network and its precursors, by a variety of techniques, established the successful synthesis and hydrolysis of this well-defined polymer nanostructure.

Molecular Design of Patchwork-Type Network Polymers Utilizing Network Polymer Precursors Consisting of Oligomeric PrimaryPolymer Chains Originated in Multiallyl Crosslinking Polymerization

Molecular Design of Patchwork-Type Network Polymers Utilizing Network Polymer Precursors Consisting of Oligomeric PrimaryPolymer Chains Originated in Multiallyl Crosslinking Polymerization

Approach to Ideal Simultaneous Interpenetrating Network Formation via Topological Cross-Links between Polyurethane and Polymethacrylate Network Polymer Precursors

The equimolar polyaddition cross-linking reaction of poly(methyl methacrylate-co-2-methacryloyloxyethyl isocyanate) with tri(oxytetramethylene) glycol leading to polyurethane (PU) networks was carried out in methyl benzoate at a 0.1 mol/L concentration of functional groups at 80 °C. Simultaneously, the free-radical cross-linking copolymerization of methyl methacrylate with tri(oxytetramethylene) dimethacrylate leading to polymethacrylate (PM) networks was progressed at a dilution of 1/10 in the presence of CBr4 as a chain transfer agent. The simultaneous interpenetrating networks (SINs) were formed via the topological cross-links between PU and PM network structures introduced by the respective intramolecular cross-linking reactions. Under the same polymerization conditions, no gelation was observed for respective cross-linking homopolymerizations leading to PU and PM homo-networks because respective intramolecular cross-linking reactions would be enhanced at a diluted solution. The topological cross-link...

Influence of structural parameters on the degradation of ultrahigh-molecular-weight vinyl-type network-polymer precursors during elution through size exclusion chromatography columns

Network-polymer precursors obtained in various crosslinking monovinyl/divinyl copolymerization systems, including benzyl methacrylate/1,6-hexanediol dimethacrylate, benzyl acrylate (BzA)/1,6-hexanediol diacrylate (HDDA), and vinyl benzoate/divinyl adipate, were subjected to degradation during elution through size exclusion chromatography (SEC) columns, although the copolymerizations were conducted under specified conditions where the factors for the greatly delayed gelation from the Flory–Stockmayer gelation theory were reduced. The most remarkable degradation was observed for the BzA/HDDA copolymerization, which provided prepolymers with the most flexible backbone chains. Thus, the BzA/HDDA precopolymers were chosen, and their degradation behavior during elution through SEC columns was explored in detail as one of the representatives of vinyl-type network-polymer precursors. The results were correlated with the structural parameters of network-polymer precursors, including primary polymer chain length, branched structure, and multiple crosslink or network structure. The degradation became more remarkable with decreased primary polymer chain length, that is, the increment of branching, whereas reduced degradation was observed with the incorporation of loop and network structures into the prepolymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 577–582, 2003

Degradation of Ultrahigh Molecular Weight Poly(styrene-co-m-divinylbenzene)s as Network-Polymer Precursors in SEC Columns

Degradation of Ultrahigh Molecular Weight Poly(styrene-co-m-divinylbenzene)s as Network-Polymer Precursors in SEC Columns

Amphiphilic polymethacrylates as crosslinked polymer precursors obtained by free‐radical monomethacrylate/dimethacrylate copolymerizations

As an extension of our work on the elucidation of the mechanism and control of 3-dimensional network formation in the free-radical crosslinking polymerization and copolymerization of multivinyl compounds with the aim to molecularly design vinyl-type network polymers, novel amphiphilic polymers were prepared as crosslinked polymer precursors. Thus, benzyl methacrylate, a nonpolar monomer, was copolymerized radically with 5 mol % of triicosaethylene glycol dimethacrylate [CH2C(CH3)CO(OCH2CH2)23OCOC(CH3)CH2], a polar monomer, in the presence of lauryl mercaptan as a chain transfer agent. The resulting prepolymers (i.e., vinyl-type network-polymer precursors or amphiphilic polymers) were characterized mainly by viscometry using t-butylbenzene (t-BB) and a t-BB/MeOH (80/20) mixture as solvents. The viscosities in the t-BB/MeOH (80/20) mixture were quite high compared with those in t-BB, and completely reversed concentration dependencies were observed in the solvents. These are discussed by considering the difference in conformation and the shrinkage of polar, flexible polyoxyethylene units or the entanglement of nonpolar, rigid primary chains. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4396–4402, 2000

Amphiphilic polymethacrylates as crosslinked polymer precursors obtained by free-radical monomethacrylate/dimethacrylate copolymerizations

As an extension of our work on the elucidation of the mechanism and control of 3-dimensional network formation in the free-radical crosslinking polymerization and copolymerization of multivinyl compounds with the aim to molecularly design vinyl-type network polymers, novel amphiphilic polymers were prepared as crosslinked polymer precursors. Thus, benzyl methacrylate, a nonpolar monomer, was copolymerized radically with 5 mol % of triicosaethylene glycol dimethacrylate [CH2C(CH3)CO(OCH2CH2)23OCOC(CH3)CH2], a polar monomer, in the presence of lauryl mercaptan as a chain transfer agent. The resulting prepolymers (i.e., vinyl-type network-polymer precursors or amphiphilic polymers) were characterized mainly by viscometry using t-butylbenzene (t-BB) and a t-BB/MeOH (80/20) mixture as solvents. The viscosities in the t-BB/MeOH (80/20) mixture were quite high compared with those in t-BB, and completely reversed concentration dependencies were observed in the solvents. These are discussed by considering the difference in conformation and the shrinkage of polar, flexible polyoxyethylene units or the entanglement of nonpolar, rigid primary chains. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4396–4402, 2000