Two‐dimensional polymer synthesis through the topochemical polymerization of alkylenediammonium muconate as a multifunctional monomer

Here we demonstrate a unique two‐dimensional polymer synthesis through topochemical polymerization via polymer crystal engineering, which is useful for controlling and designing the polymerization reactivity as well as the polymer chain and crystal structures. We have succeeded in the synthesis of a sheet polymer through the polymerization of alkylenediammonium (Z,Z)‐muconate as a multifunctional 1,3‐diene monomer in the crystalline state under the irradiation of UV and γ‐rays or upon heating in the dark. The photopolymerization reactivity of several muconates and the structural control of the obtained polymer are described. The stereochemical structure of the polymer and the polymerization mechanism are discussed on the basis of the results of IR and NMR spectroscopy, thermogravimetric measurements, and solid‐state hydrolysis for the transformation into poly(muconic acid). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3922–3929, 2004     

A novel organic intercalation system with layered polymer crystals as the host compounds derived from 1,3-diene carboxylic acids

A new type of organic intercalation system using poly(muconic acid) and poly(sorbic acid) crystals as the host compounds is described. The layered polymer crystals as the host are derived from benzyl-, dodecyl-, or naphthylmethylammonium salts of (Z,Z)-muconic or (E,E)-sorbic acids by topochemical polymerization. The subsequent solid-state hydrolysis of the resulting ammonium polymer crystals provides the corresponding carboxylic acid polymer crystals. When alkylamines are reacted with poly(muconic acid) or poly(sorbic acid) crystals dispersed in methanol at room temperature for a few hours, the intercalation proceeds to give layered ammonium polymer crystals via solid-state reactions, in which the polymers maintain a layered structure throughout. The interplanar spacing value of the polymer crystals changes according to the size of the guest molecules; that is, it exactly depends on the carbon number of the alkylamines used for each reaction of poly(muconic acid) or poly(sorbic acid) crystals. The stacking structure of alkyl chains with a tilt in the intercalated alkylammonium layers exists irrespective of the chemical and crystal structures of the host polymers. The intercalation of higher alkylamines into poly(muconic acid) crystals proceeds fast and quantitatively, while the conversion is dependent on the reaction conditions such as the structure and amount of the amine and the reaction time during the intercalation with poly(sorbic acid) crystals, due to the difference in the repeating layered structures of these polymer crystals. Some functional amines are also used as the guest molecules for this organic intercalation system.     

Crystal engineering for topochemical polymerization of muconic esters using halogen-halogen and CH/pi interactions as weak intermolecular interactions

We now report the molecular and crystal structure design of muconic ester derivatives on the basis of crystal engineering using halogen-halogen contacts and CH/pi interactions. The solid-state photoreaction pathway of the dibenzyl (Z,Z)-muconates as the 1,3-diene dicarboxylic acid monomers depends on the structure of the ester groups. The substitution of a halogen atom for the aromatic hydrogen of a benzyl group induces topochemical polymerization to produce stereoregular polymers in a crystalline form, whereas the unsubstituted benzyl derivative isomerizes to yield the corresponding E,E isomer under similar conditions. The topochemical polymerization process is directly confirmed by the fact that the single-crystal structures before and after the polymerization are very similar to each other. From the crystal structure analysis for a series of substituted benzyl (Z,Z)- and (E,E)-muconates, it has been revealed that the planar diene moieties are closely packed to form a columnar structure in the crystals. The stacking of the polymerizable monomers is characterized by a stacking distance of 4.9-5.2 A along the columns. This structure is supported by a halogen-halogen interaction between the chlorine or bromine atoms introduced at the p position of the benzyl groups in addition to an aromatic stacking due to the CH/pi interaction between the benzylic methylene hydrogens and aromatic rings. The design of a monomer packing corresponds to the type and position of the introduced halogen atom and also the polymorphs. To make a stacking distance of 5 A using both halogen-halogen and CH/pi interactions as supramolecular synthons is important for the molecular design of muconic ester derivatives appropriate for topochemical polymerization.     

Crystal‐to‐Crystal Synthesis of Helically Ordered Polymers of Trehalose by Topochemical Polymerization

The synthesis of crystalline helical polymers of trehalose via topochemical azide–alkyne cycloaddition (TAAC) of a trehalose‐based monomer is presented. An unsymmetrical trehalose derivative having azide and alkyne crystallizes in two different forms having almost similar packing. Upon heating, both the crystals undergo TAAC reaction to form crystalline polymers. Powder X‐ray diffraction (PXRD) studies revealed that the monomers in both the crystals polymerize in a crystal‐to‐crystal fashion; circular dichroism (CD) studies of the product crystals revealed that the formed polymer is helically ordered. This solvent‐free, catalyst‐free polymerization method that eliminates the tedious purification of the polymeric product exemplifies the advantage of topochemical polymerization reaction over traditional solution‐phase polymerization.     

First example of the topochemical polymerization of the (E,E)‐muconic acid derivative

The 1‐naphthylmethylammonium salts of not only (Z,Z)‐ but also (E,E)‐muconic acid were found to polymerize upon photoirradiation in the crystalline state to provide a stereoregular polymer in a high yield. The stereochemical structure of both polymers obtained from the monomers with different configurations was identical, i. e., a meso‐diisotactic‐trans‐2,5‐structure. The stereochemistry of the polymers obtained is discussed on the basis of the monomer configuration and the molecular packing in the crystals.     

Crystal-to-Crystal Synthesis of Helically Ordered Polymers of Trehalose by Topochemical Polymerization

The synthesis of crystalline helical polymers of trehalose via topochemical azide–alkyne cycloaddition (TAAC) of a trehalose-based monomer is presented. An unsymmetrical trehalose derivative having azide and alkyne crystallizes in two different forms having almost similar packing. Upon heating, both the crystals undergo TAAC reaction to form crystalline polymers. Powder X-ray diffraction (PXRD) studies revealed that the monomers in both the crystals polymerize in a crystal-to-crystal fashion; circular dichroism (CD) studies of the product crystals revealed that the formed polymer is helically ordered. This solvent-free, catalyst-free polymerization method that eliminates the tedious purification of the polymeric product exemplifies the advantage of topochemical polymerization reaction over traditional solution-phase polymerization.     

Single-crystal-to-single-crystal synthesis of a pseudostarch via topochemical azide–alkyne cycloaddition polymerization

There is high demand for polysaccharide-mimics as enzyme-stable substitutes for polysaccharides for various applications. Circumventing the problems associated with the solution-phase synthesis of such polymers, we report here the synthesis of a crystalline polysaccharide-mimic by topochemical polymerization. By crystal engineering, we designed a topochemically reactive crystal of a glucose-mimicking monomer decorated with azide and alkyne units. In the crystal, the monomers arrange in head-to-tail fashion with their azide and alkyne groups in a ready-to-react antiparallel geometry, suitable for their topochemical azide–alkyne cycloaddition (TAAC) reaction. On heating the crystals, these pre-organized monomer molecules undergo regiospecific TAAC polymerization, yielding 1,4-triazolyl-linked pseudopolysaccharide (pseudostarch) in a single-crystal-to-single-crystal manner. This crystalline pseudostarch shows better thermal stability than its amorphous form and many natural polysaccharides.

Prudent crystal engineering allows head-to-tail arrangement of inositol monomer molecules pre-organizing azide and alkyne units of adjacent monomers in a ready-to-react manner. On heating regiospecific SCSC polymerization yields a starch-like polymer.     

Perfluorophenyl–Phenyl Interactions in the Crystallization and Topochemical Polymerization of Triacetylene Monomers

A series of symmetrically and unsymmetrically substituted octa‐2,4,6‐triyne‐1,8‐diol derivatives with benzoyl, 4‐dodecyloxybenzoyl, as well as perfluorobenzoyl substituents were prepared and investigated with respect to their crystal structures and topochemical polymerizability. Single‐crystal structures for several of these triacetylene monomers have been obtained and proved that the perfluorophenyl–phenyl interactions played a decisive role in the molecular packing. As a consequence of the geometric requirements imposed by the perfluorophenyl–phenyl interactions, packing parameters appropriate for a topochemical triacetylene polymerization in the sense of either a 1,6‐ or a 1,4‐polyaddition along different crystallographic axes were observed in two cases, and UV irradiation led to successful polymerization. Raman as well as solid‐state ¹³C NMR spectra of the obtained polymers revealed that the polymerization had predominantly proceeded in the form of a 1,4‐polyaddition.     

Spontaneous Single‐Crystal‐to‐Single‐Crystal Evolution of Two Cross‐Laminated Polymers

Two cases of spontaneous evolution of monomers to linear polymers having novel cross‐laminated topology are reported. We synthesized two peptide monomers N₃‐Gly‐Gly‐NH‐CH₂‐CCH and N₃‐Gly‐Gly‐Gly‐CH₂‐CCH and solved their crystal structures by single‐crystal X‐ray diffraction. They adopt H‐bonded crisscrossed layered packing in their crystals such that: (a) the monomers are aligned head‐to‐tail in 1D‐chain‐like arrays and parallel arrangement of such arrays forms a layer; (b) the proximally placed azide and alkyne motifs are in an orientation apt for their regiospecific cycloaddition; (c) each monomer having x peptide bonds is H‐bonded with 2x monomers disposed in intersecting arrangement, which pre‐organize 1D‐chain‐like arrays in adjacent layers in perpendicular orientation. These crystals underwent spontaneous single‐crystal‐to‐single‐crystal (SCSC) polymerization via azide–alkyne cycloaddition reaction to form triazolyl‐polyglycines, at room temperature. The crisscrossed arrangement of monomers in adjacent layers ensured the formation of cross‐laminated polymers.     

Preparation and thermal behavior of poly-p-phenylene diacrylic acid dimethyl ester

The photopolymerization behavior of p-phenylene diacrylic acid dimethyl ester (p-PDA Me) crystal and the thermal behavior of the resultant poly-p-PDA Me were investigated. From the kinetic study of polymerization at various temperatures a topochemical process via a stepwise mechanism was observed. Continuous change from monomer to polymer crystals was demonstrated by x-ray diffraction pattern and DSC analysis. Crystallinity of the reacting phase was maintained at an extremely high degree during the polymerization process in support of monomer crystal lattice control. Thermal study on as-polymerized poly-p-PDA Me crystal confirmed that the thermal reaction was a polymer crystal lattice-controlled depolymerization, which was followed by miscellaneous processes that involved vaporization, sublimation, and deterioration of the oligomeric or monomeric units of p-PDA Me. Thermal stability was dependent on the molecular weight. All the results are compared with those of four-center-type photopolymerization in the crystalline state.     

Solid‐state polymerization of 2,3,6,7,10,11‐hexa(methacrylate) triphenylene

A new monomer, 2,3,6,7,10,11‐hexa(methacrylate) triphenylene (HMTP), and its crystals have been successfully synthesized, and the solid‐state polymerization under UV irradiation has been investigated. The photo polymerization of HMTP in solid was confirmed by the reduction of vinyl bonds in the FT‐IR and UV spectra of PHMTP in comparison with the corresponding spectra of its precursor. Thus, IR spectroscope was used to follow the polymerization of HMTP crystals under UV irradiation, and kinetic studies show a first‐order reaction with rate constant of 6.12 × 10^?3 min^?1. This value is slightly larger than that measured by the weight method. The polarizing optical microscope and X‐ray diffraction were used to study the crystal structure difference between the polymers and its monomer. The results show that the polymers' crystals obtained from photo polymerization kept the monomer crystal lattice. Because of strong overlap between the π‐electron of the triphenylene, the monomer and polymer crystals showed different fluorescence properties. All these results proved that the photo polymerization of HMTP crystals is governed by the packing structure of monomer molecules; in other words, this reaction is just lattice controlled polymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1526–1534, 2005     

Stereocontrol of diene polymers by topochemical polymerization of substituted benzyl muconates and their crystallization properties

We report the stereocontrol of diene polymers by the topochemical polymerization of alkoxy-substituted benzyl muconates in the solid state. A monomer stacking structure is controlled by the weak intermolecular interactions in the monomer crystals, depending on the structure and position of the alkoxy-substituent. The translational and alternating types of molecular stacking structures in a column provide diisotactic and disyndiotactic polymers, respectively, by the solid-state polymerization under UV and γ-ray irradiation. On the other hand, the meso and racemo structures of the resulting polymers are determined by the molecular symmetry of the used muconate monomers. The various substituted benzyl ester polymers are transformed into the same ethyl ester polymers with the four types of tacticities. The structure and crystallization behavior of the substituted benzyl ester polymers as well as the ethyl ester polymers have been revealed in detail. We clarify the effects of the tacticity on the crystallization property of the stereoregular polymuconates. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4952–4965, 2006     

Solid state polymerization of butadienes. Polymerization of long chain derivatives of sorbic and muconic acid

The polymerization of long chain derivatives of sorbic and muconic acid was studied in the solid state. Crystals of sorbic acid n-octadecylester (1), sorbic acid n-octadecylamide (2), and 6-n-octadecanoylamino sorbic acid (3) were found to rapidly polymerize upon UV- or-irradiation. A 1,4-trans-polymer was obtained in a high yield. Crystals of muconic acid di-n-octadecylester (4) and muconic acid di-n-octadecylamide (5) were completely photoinactive.Polymerization of3 was also investigated in monomolecular layers at the air-water interface and in Langmuir-blodgett type multilayers. The polymer formed upon UV- irradiation of mono- and multilayers was identified by infrared spectroscopy as the 1,4-trans-adduct.     

Solid‐Phase Radical Polymerization of Halogen‐Bond‐Based Crystals and Applications to Pre‐Shaped Polymer Materials

Liquid vinyl monomers were converted into solid crystals via halogen bonding. They underwent solid‐phase radical polymerizations through heating at 40 °C or ultraviolet photo‐irradiation (365 nm). The X‐ray crystallography analysis showed the high degree of monomer alignment in the crystals. The polymerizations of the solid monomer crystals yielded polymers with high molecular weights and relatively low dispersities because of the high degree of the monomer alignment in the crystal. As a unique application of this system, the crystalized monomers were assembled to pre‐determined structures, followed by solid‐phase polymerization, to obtain a two‐layer polymer sheet and a three‐dimensional house‐shaped polymer material. The two‐layer sheet contained a unique asymmetric pore structure and exhibited a solvent‐responsive shape memory property and may find applications to asymmetric membranes and polymer actuators.     

Structural study of the solid-state photoaddition reaction of arylidenoxindoles

The photochemistry of isomeric 2-furyliden- and benzylidenoxindoles (2H-indol-2-ones) is examined. In solution E-Z isomerization is the only process via the excited singlet state (which fluoresces in glassy solution at 77 K and not at room temperature). In the crystalline state, the two (Z) derivatives are photostable, in accordance with the prediction based on the structural determination of the furylidene derivative, which adopts the unreactive Schmidt's gamma type arrangement. The (E) furylidene derivative (1a) gives efficiently (Phi = 0.3) the head-to-tail dimer, as indicated by the crystal structure, which is of the reactive alpha type, in full accord with the topochemical principles. In contrast, the corresponding benzylidene (1b) derivative reacts sluggishly (Phi < 0. 01) and mainly gives polymers, despite the fact that crystal structure determination shows that it likewise pertains to the alpha type and complies with the topochemical rules. The difference in reactivity is explained on the basis of (i) the twist of the phenyl ring with respect to the indole plane, and (ii) the higher overall cohesion energy and the lower interaction energy between facing molecules, as found from the charge density analysis for the crystals of 1b in comparison to those of 1a. This evidences a further stringent requirement for the occurrence of topochemical photodimerizations.     

Vinyl‐terminated side‐chain liquid‐crystalline polyethers containing mesogenic benzylideneaniline moieties

The synthesis of two vinyl‐terminated side‐chain liquid‐crystalline polyethers containing benzylideneaniline moieties as mesogenic cores was approached in two different ways: by chemically modifying poly(epichlorohydrin) with suitable mesogenic acids or by polymerizing analogous glycidyl ester or glycidyl ether derivatives. In all the conditions tested, the first approach led to materials in which the imine group was hydrolyzed. The second approach led to the desired polymers PG2a and PG2b , but only from the glycidyl ether derivatives and when the initiator was the system that combined polyiminophosphazene base t‐Bu‐P₄ and 3,5‐di‐t‐butylphenol. These polymers were chemically characterized by IR and ¹H and ¹³C NMR spectroscopies. The estimated degrees of polymerization ranged from 30 to 36. The liquid crystalline behavior of the synthesized polymers was studied by differential scanning calorimetry, polarized optical microscopy (POM) and X‐ray diffraction. Both polymers behave like liquid crystals and exhibited a single mesophase, which was recognized as a smectic C mesophase, probably with a bilayer arrangement, i.e., a smectic C₂ mesophase. The crosslinking of both polymers was performed with dicumyl peroxide as initiator, which led to liquid crystalline thermosets. POM and X‐ray diffraction confirmed that the mesophase organization mantained on the crosslinked materials. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1877–1889, 2006     

Four-center type photopolymerization in the crystalline state. VI. Kinetic and structural study of the polymerization of p-phenylenediacrylic acid diethyl ester

The effect of temperature on the four-center type photopolymerization has been investigated for p-phenylenediacrylic acid diethyl ester over a wide temperature range including crystal transition point (56°C) and melting point (96°C) of monomer. With the elevation of temperature between ?50 and 15°C, the polymerization rate in the initial stage increased and the degree of polymerization decreased monotonously, while the rate in the later stage decreased above ?25°C. With irradiation at above 25°C, the monomer crystals became sticky, and the polymerization was suppressed at the stage of oligomerization with low conversion. This tendency was enhanced above the crystal transition point, giving mainly dimer in low yield. Above the melting point, only radical polymerization occurred with the aid of oxygen. The steric configuration of the products in the crystalline state was 1,3-trans with respect to the cyclobutane ring. Peaks in NMR spectra of all products were assigned to the protons involved in four compounds up to tetramer. Various results obtained have been interpreted in terms of the change, as a function of temperature, from a topochemical polymerization which proceeds under a control of the monomer lattice to a photoinitiated vinyl-type polymerization in the disordered state. It is concluded that a rigid crystal lattice is indispensable for the four-center type photopolymerization to proceed smoothly.     

Synchronized propagation mechanism for crystalline-state polymerization of p-xylylenediammonium disorbate.

We describe the results of the topochemical polymerization of p-xylylenediammonium disorbate as the bifunctional monomer in the crystalline state via a radical chain polymerization mechanism. The structure and properties of the resulting double-stranded polymer are investigated by X-ray crystal structure and thermal analyses as well as IR spectroscopy. The stereochemical structure of the polymer is confirmed by NMR spectroscopy after the solid-state transformation of the polymer side chain to give the single-stranded chains that are soluble in methanol. We propose a model for the reaction mechanism to provide a ladder polymer in the crystalline state on the basis of the results of single-crystal structure analysis and the observation of the alpha-methyl and alpha-carboxylate propagating radicals by ESR spectroscopy. The two reaction parts of the monomer are synchronized to simultaneously react with the conformational change in a sorbate moiety that is transformed into another sorbate through the diammonium part as the linker.     

Identification of Molecular Crystals Capable of Undergoing an Acyl‐Transfer Reaction Based on Intermolecular Interactions in the Crystal Lattice

Investigation of the intermolecular acyl‐transfer reactivity in molecular crystals of myo‐inositol orthoester derivatives and its correlation with crystal structures enabled us to identify the essential parameters to support efficient acyl‐transfer reactions in crystals: 1) the favorable geometry of the nucleophile (? OH) and the electrophile (C?O) and 2) the molecular assembly, reinforced by C? H???π interactions, which supports a domino‐type reaction in crystals. These parameters were used to identify another reactive crystal through a data‐mining study of the Cambridge Structural Database. A 2:1 co‐crystal of 2,3‐naphthalene diol and its di‐p‐methylbenzoate was selected as a potentially reactive crystal and its reactivity was tested by heating the co‐crystals in the presence of solid sodium carbonate. A facile intermolecular p‐toluoyl group transfer was observed as predicted. The successful identification of reactive crystals opens up a new method for the detection of molecular crystals capable of exhibiting acyl‐transfer reactivity.     

Designed Synthesis of a 1D Polymer in Twist‐Stacked Topology via Single‐Crystal‐to‐Single‐Crystal Polymerization

To synthesize a fully organic 1D polymer in a novel twist‐stacked topology, we designed a peptide monomer HC≡CCH₂‐NH‐Ile‐Leu‐N₃, which crystallizes with its molecules H‐bonded along a six‐fold screw axis. These H‐bonded columns pack parallelly such that molecules arrange head‐to‐tail, forming linear non‐covalent chains in planes perpendicular to the screw axis. The chains arrange parallelly to form molecular layers which twist‐stack along the screw axis. Crystals of this monomer, on heating, undergo single‐crystal‐to‐single‐crystal (SCSC) topochemical azide–alkyne cycloaddition (TAAC) polymerization to yield an exclusively 1,4‐triazole‐linked polymer in a twist‐stacked layered topology. This topologically defined polymer shows better mechanical strength and thermal stability than its unordered form, as evidenced by nanoindentation studies and thermogravimetric analysis, respectively. This work illustrates the scope of topochemical polymerizations for synthesizing polymers in pre‐decided topologies.