Four-center type photopolymerization in the solid state. III. Polymerization of phenylene diacrylic acid and its derivatives

The solid-state photopolymerization of phenylene diacrylic acid (PDA) and its derivatives was studied as an application of solid-state photodimerization of cinnamic acid to photopolymerization of corresponding bifunctional molecule which has two cinnamic units in a single molecule. p- and m-PDA, and their esters and amides were prepared and investigated with respect to their photopolymerizability. Many of them have been found to polymerize into linear high polymers with the cyclobutane rings in the main chain on irradiation by ultraviolet or visible light. The polymerization process, the structure of the polymers, and their general properties were investigated in several ways. All the polymers are very similar to poly-2,5-distyrylpyrazine and poly-1,4-bis(β-pyridyl-2-vinyl) benzene with respect to their polymerization behavior, polymer structure, and some polymer properties: these polymers are soluble in a limited number of solvents, they have a high melting point and an extremely high crystallinity. On the basis of chemical behavior of poly-PDA and its phenyl ester the possible steric configurations of these polymers are discussed. It is demonstrated for the PDA series that solid-state dimerization can be generally extended to solid-state photopolymerization of the compound having two dimerizable units in a single molecule, although the crystal structure renders polymerization impossible in certain cases.     

Crystallization during polymerization of poly-p-xylylene. II. Polymerization at low temperature

The polymerization of p-xylylene was followed with a newly designed differential thermal analysis system at temperatures between ?196°C and ?20°C. It was found that at the lower temperatures the monomer condenses first to the crystalline monomer before simultaneous polymerization and crystallization. At the higher temperatures, polymerization and crystallization are successive. The data are in agreement with the morphology and crystal structure data derived in Part I of this series of papers on crystallization during polymerization of poly-p-xylylene.     

Four-center type photopolymerization in the solid state. VII. Photochemical reaction of m-phenylene diacrylic acid dimethyl ester

The photochemical reaction of m-phenylene diacrylic acid dimethyl ester (m-PDA Me) crystals and solutions has been studied to clarify the effects of the molecular shape on four-center type photopolymerization of diolefins. On irradiation, m-PDA Me crystals were converted into amorphous oligomers having more than two kinds of cyclobutane rings with respect to steric configuration. The characteristic oligomer formation is explained by considering a two-step mechanism: topochemical dimer formation in an ordered crystal lattice and subsequent random cycloaddition in a disordered crystal lattice. In m-PDA Me solution, reversible cyclobutane ring formation and cis–trans isomerization take place, depending on the concentration of m-PDA Me in solution and the wavelength of the irradiating light. The multiplicity of reactivity in various states has been established.     

Four-center type photopolymerization in the solid state. IV. Polymerization of α,α′-dicyano-p-benzenediacrylic acid its derivatives

The solid-state photopolymerization of α,α′-dicyano-p-benzene diacrylic acid (p-CBA) series has been studied. p-CBA, its esters, amide, and a few other cyano derivatives were prepared and new polymers were obtained from p-CBA alkyl esters on irradiation of ultraviolet or visible light. Though the polymerization behavior differs with each monomer, polymerization proceeds in essentially the same manner as in the 2,5-distyrylpyrazine (DSP) and p-benzenediacrylic acid (BDA) series: the reaction proceeds topochemically forming polymer with a cyclobutane ring in the main chain. Properties of high polymer are typical of cyclobutane-containing polymer. That is, they are highly crystalline with high melting temperature and a limited solubility. The study on this series of compounds, as well as the DSP and p-BDA series, supports the generalization that solid-state dimerization can be extended to solid-state photopolymerization of compound having two dimerizable units in a molecule.     

A new type of photodegradable polymer having a pyrazine moiety in the chain

Photooxidative degradation of poly-2,5-distyrylpyrazine (poly-DSP) has been studied in detail. Both amorphous poly-DSP film and poly-DSP solution were photooxygenated and degraded by irradiation by sunlight in the air. The nitrile group was formed, together with carbonyl groups and hydroxyl group. The photodegradation of a pyrazine derivative to a nitrile derivative is a new reaction. Next, photodegradation behavior of polymers having a cyclobutane moiety in the main chain, poly-1,4-bis[2-(2-pyridyl)-vinyl]benzene (poly-P2VB) and polydiethyl p-phenylenediacrylate (poly-p-PDA Et), was studied. The photodegradability of these polymers decreases in the order: poly-DSP > poly-P2VB ? poly-p-PDA Et. Further, the photodegradation behavior of various vinyl polymers containing a vinylpyrazine or vinylpyridine component and polyamides having pyrazine or pyridine ring in the main chain, was investigated. Of these, polyvinylpyrazine has the largest photodegradability.     

Cationic photopolymerization of liquid fullerene derivative under visible light

We describe the synthesis and cationic photopolymerization of a C₆₀ derivative bearing a 2,4,6‐tris(epoxynonyloxy)phenyl moiety (FB9ox). Rheological analysis of monomer indicates that temperature of 130 °C yields sufficiently low viscosity for polymerization. A thin film of the liquid monomer has been cationically photopolymerized with a photoinitiator system of curcumin and p‐(octyloxyphenyl)phenyliodonium hexafluoroantimonate, which harvests 424 nm light instead of commonly used ultraviolet light. The degree of polymerization was determined with ATR‐IR. The reaction is the first recorded photopolymerization of a fullerene derivative thin film. The polymer exhibits good mechanical and chemical stabilities. The polymerization can also be achieved by annealing at 150 °C without illumination, but with a smaller degree of polymerization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5194–5201, 2008     

The role of dislocations in the solid-state polymerization of monomers having conjugated triple bonds: A study of 2,4-hexadiyne-1,6-diol bis(p-toluene sulfonate)

The crystal structure of the monomer bis(p-toluene sulfonate) ester of 2,4-hexadiyne-1,6-diol (pT) is conducive from the viewpoint of both the separation distances and molecular configuration, to polymerization, irrespective of whether initiation is thermal, photochemical, or mechanical. The dislocations present in the monomer and polymer structures have been characterized by employing optical microscopic techniques. The slip system (102)[010] is found to be present in both monomer and polymer crystals but the (010)[001] system is found only in the monomer. On this basis a crystal structure for the monomer is proposed based on existing crystallographic information relating to the structure of the polymer. Dislocations are thought, on energetic grounds, to facilitate nucleation of product in the thermal polymerization but have no observable influence on the photoinduced reaction which proceeds homogeneously through the bulk.     

Thermal properties and ionic conductivity of a polymer prepared by the in situ photopolymerization of a vinylimidazole monomer containing a mesogenic group

We have synthesized liquid crystalline polymers containing an imidazolium salt moiety and a mesogenic group by the in situ photopolymerization of a liquid crystalline vinylimidazole monomer in order to investigate the relationship between their thermal properties and ionic conductivity. A smectic phase was shown by the vinylimidazole monomer. The in situ photopolymerization of the monomer was carried out in the temperature range of the smectic phase. The polymer thus prepared displayed a highly ordered smectic phase in the temperature range between room temperature and about 200°C. The ionic conductivity of the polymer increased with increasing temperature. Anisotropic ionic conductivity behavior was observed for the polymer. The ionic conductivity of the polymer aligned homogeneously is larger than when homeotropically aligned.     

Raman spectroscopic studies of the solid-state polymerization of diacetylenes. II. Thermal polymerization of 1,6-di-p-methoxybenzene-sulfonyloxy-2,4-hexadiyne

The Raman spectra of 1,6-di-p-methoxybenzene-sulfonyloxy-2,4-hexadiyne (MBS) have been recorded during thermal polymerization. The spectra are similar to those of the related p-toluene-sulfonyloxy monomer but indicate a higher strain in the initially formed MBS polymer chains. Despite this similarity, the polymerization kinetics for the two monomers are markedly different. The polymerization behavior of MBS shows that the polymer chain initiation and propagation are practically independent of lattice strain. Possible causes for this independence are discussed.     

Four-center photopolymerization. A heterogeneous topochemical solid-state reaction

The four-center solid-state photopolymerization of distyrylpyrazine (DSP) and of 2,6-naphthalene bis(acrylic acid-2,4-dichloro phenyl ester) (NBA–DCP) was investigated by x-ray and microscopic techniques. In both cases the polymer grows as a separate product phase topotactically well arranged with respect to the monomer matrix. In the case of polymerization of DSP the space group of the monomer (Pbca) is not maintained but the polymer phase has space group P2₁ca. Nucleation and growth of the polymer phase was observed by light and electron microscopy. Nucleation occurs at defect sites. The polymer grows at different rates in different crystallographic directions which were identified by electron diffraction in the case of DSP. Polymerization thus occurs in the transition region between monomer crystal and product phase and not in the bulk of the crystal so that the four-center-type photopolymerization is best described as a heterogeneous solid-state reaction.     

Synthesis,polymerization, and thermal properties of a new acetylene-terminated schiff base

A new acetylene-terminated Schiff base monomer, N,N′-(1,4-phenylenedimethylidyne)-bis-(4-ethynylaniline) (PPP), was synthesized and was characterized by nuclear magnetic resonance and infrared spectroscopy. This monomer was then polymerized to yield a new polymer (PPPP) with alternating units of aromatic imine and diacetylene via an oxidative coupling polymerization of the acetylenic terminal groups. The monomer was also polymerized by thermal curing at elevated temperatures up to 400°C to afford a crosslinked polymer network without significant structural decomposition. Thermal properties and thermal reactions of the monomer and the polymers were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The polymers exhibit excellent thermal stabilities in an inert atmosphere. Electronic properties of the polymers are also discussed.     

Photopolymerization of poly(ethylene glycol) dimethacrylates: The influence of ionic liquids on the formulation and the properties of the resultant polymer materials

The photo‐initiated polymerization of poly(ethylene glycol)dimethacrylates [PEGDM(n)] in the presence of various ionic liquids (ILs) is reported. The influence of ILs concentrations as well as of their nature upon the photopolymerization kinetics was studied in detail. It was found that according to reactive ability in bulk and in solution photopolymerization, the investigated monomers can be divided into two groups: PEGDM(1)–PEGDM(2)–PEGDM(3) and PEGDM(4)–PEGDM(7‐8). ILs slightly influence the photopolymerization of monomers from the first group and greatly change kinetics of those from the second. Such behavior was explained by the theory of “kinetically favorable or unfavorable monomer associations.” It was demonstrated that certain ILs accelerate the photopolymerization of the highest PEGDMs and offer access to the polymers derived from low reactive monomers. Relying on the obtained data, the attempt to predict the structure of the “best” ionic additive for the given monomer photopolymerization was performed and proved. Finally, the influence of both residual and specially added ILs quantities upon the properties of obtained polymer materials was investigated. It was revealed that ILs can physically interact with polymer networks increasing their thermal stability, plasticizing films, and blocks, imparting ionic conductivity equal up to 3.62 × 10^?3 Sm/cm at 25 °C. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2388–2409, 2010     

Mass spectral and pyrolysis/gas-chromatographic studies of the monomer and polymer of bis(p-toluenesulfonate) of 2,4-hexadiyne-1,6-diol

The thermal degradation of the monomer and polymer of bis(p-toluenesulfonate) of 2,4-hexadiyne-1,6-diol has been investigated. Decomposition during the latter stages of solid-state thermal polymerization at 80°C and of 100% polymer at 112°C was observed by mass spectrometry and the decomposition fragments identified. Mechanisms for this low-temperature degradation are suggested. Pyrolysis of the monomer and polymer between 400 and 1000°C was studied by gas chromatography and mass spectrometry. The principal pyrolysis products are triacetylene and p-toluenesulfonic acid. The fragmentation routes leading to and derived from these products are discussed.     

Four-center-type photopolymerization in the crystalline state. IX. Characteristic features of topochemical process and polymer properties thus obtained

Changes in TG-DSC diagrams and X-ray diffraction patterns in the course of four-center-type photopolymerization of 2,5-distyrylpyrazine (DSP) and thermal depolymerization of poly-DSP were investigated. It has been found that as-polymerized poly-DSP crystal with high molecular weight does not melt but depolymerizes into the oligomer in the crystalline state. The crystal change found in the depolymerization was just the reverse of that in the polymerization. From the results a reversible topochemical process, which comprises monomer lattice-controlled photopolymerization and polymer lattice-controlled thermal depolymerization, has been established between DSP and poly-DSP. Quantitative thermal analysis reveals that both of the two endotherms of poly-DSP crystal include the heat of crystallization as well as that of depolymerization. Several specific properties of a topochemical product of as-polymerized poly-DSP crystal, such as nonreproducibility of the original crystal structure by recrystallization and superior stabilities to thermal depolymerization and photooxidation, are discussed in comparison with natural cellulose.     

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     

Monitoring ultrathin film photopolymerization of tetra‐alkylepoxyporphyrin by UV‐Vis spectroscopy

Cationic photopolymerization is a convenient in situ polymerization method for organic thin film preparation. In this work, the polymerization mechanisms is applied for highly viscous cross‐linking monomers, using tetra‐alkylepoxyporphyrin (TAEP) as a case study. By comparing the UV‐Vis spectra of the polymerized sample before and after the unreacted monomers have been dissolved, it is possible to estimate the polymerization yield. An IR spectrum of a reference thick film confirms full polymerization. Scanning fluorescence lifetime microscopy and AFM show the uniformity of the polymer. It was shown that photopolymerization is highly dependent on the substrate nature and requires at best case a 10 min illumination at 90 °C. Thermal polymerization of the same sample requires 10 min heating at 150 °C in dark. It was also shown that TAEP works as a self‐sensitizer for cationic photopolymerization. The proposed method is a mild and versatile technique for in situ preparation of thin polymeric films directly from chromophore monomers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6095–6103, 2009     

Study on functionalization of metal surfaces. III. Photopolymerization of monomer films on metal surfaces

The three kinds of monomer films on metal surfaces were deposited by adsorption from a solution of 6-polymerizable substituents-1,3,5-triazine-2,4-dithiol monosodium salts (RTDN); the polymerizable substituents such as cis-9-octadecenylamino, di(cis-9-octadecenyl)amino, and p-vinylbenzyl(cis-9-octadecenyl)amino groups were selected in view of the polymerization activity of unsaturated groups in the substituents and the packing degree of monomer molecules. The monomer films were estimated to consist of mainly 6-substituents-1,3,5,-triazine-2,4-dithione (3H, 5H) and to be multimolecular layers that are considerably cross-packed and ordered. The monomer films on metal surfaces were polymerizable under a UV light irradiation in air atmosphere to give polymer films. In the photopolymerization, azobis(isobutyronitrile) (AIBN) was very effective for increasing the monomer conversion and the polymerization rate. The optimum concentration of AIBN in monomer films was very small, about 0.025 mol %. The monomer conversion was influenced by the kind of monomers, namely, the polymerization activity and the packing degree. The effect of the packing degree was especially remarkable. The monomer conversion decreased with an increase in the thickness of monomer films. This is because the polymerization was initiated by oxygen and AIBN, which were diffused into the inner of monomer films. The possibility of polymerization of the unsaturated groups and the thione groups in monomer molecules under UV light irradiation is discussed.     

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.     

Photopolymerization kinetics in and of self‐assembling lyotropic liquid crystal templates

Photopolymerization in and of lyotropic liquid crystal (LLC) template phases shows great promise for generating nanostructure in organic polymers. Interestingly, the order imposed on the polymerization system in LLCs significantly alters polymerization kinetics. The rate of polymerization of hydrophilic monomers increases with increasing LLC order, primarily due to monomer/polymer association with surfactant and the resulting decrease of growing polymer chain diffusion. Conversely, as LLC order increases, hydrophobic monomers become less segregated as nonpolar volume increases, which decreases polymerization rate. The efficiency of initiators is also dependent on LLC template order, further contributing to polymerization rate changes. When reactive surfactants are used, LLC mesophase, location of reactive group, and aliphatic tail length also affect polymerization kinetics. Overall, these photopolymerization kinetics directly relate to the segregation behavior and local order of reactive groups and thus can be used to probe nanostructure evolution, facilitating understanding and control of ultimate polymer nanostructure. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 471–489     

A New,General Synthetic Method for the Preparation of Linear Poly-p-xylylenes

A new, general synthetic route to poly-p-xylylene and substituted poly-p-xylylenes is described. The key intermediate in the new process is di-p-xylylene [(2,2)p-cyclophane]. It has been found that di-p-xylylene is quantitatively cleaved by vacuum vapor-phase pyrolysis at 600°C. to two molecules of p-xylylene. p-Xylylene spontaneously polymerizes on condensation to form high molecular weight, linear poly-p-xylylene. The conversion of di-p-xylylene to poly-p-xylylene is quantitative. The process is adaptable to the preparation of a wide variety of substituted poly-p-xylylenes by pyrolysis of ring-substituted di-p-xylylenes and polymerization of the resultant substituted p-xylylenes. Many of these polymers are not attainable by any other route. All are linear and free of crosslinking. Evidence supporting the proposed mechanism of pyrolytic cleavage of every molecule of di-p-xylylene to two molecules of p-xylylene is presented. Tough, transparent polymeric films are obtained from the process when the polymerization of the p-xylylenes is conducted on glass or metal surfaces. Outstanding combinations of physical, electrical, and chemical properties are displayed by poly-p-xylylene, polychloro-p-xylylene, and other substituted polymers. A comparison of the relative merits of the original Szwarc route and the new di-p-xylylene route to poly-p-xylylenes is presented.