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Summary Photosensitive microcapsules that reversibly switch upon visible light irradiation are attractive targets for drug delivery, fragrance release and pesticide delivery. In this study we report the development of visible light triggered microcapsules and demonstrate the concept of protection and remote release of a model, non-toxic perfume oil. Polyamide microcapsule shells containing visible light-sensitive ortho-substituted azobenzene moieties in the main chain of the polymer were prepared by oil-in-water interfacial polymerization method. Microcapsules surface and cross-section morphologies were observed by SEM. Triggered perfume release during light irradiation was monitored by means of GC/MS. We suggest that the mechanism of perfume release from the microcapsules shell is based on decrease of modified azobenzene length during light illumination. This visible light-induced compression of microcapsules offers a new way to modulate the release of encapsulated materials.

Controlled release of photosensitive systems is widely studied because of its numerous applications. However, just a few descriptions of the mechanism of this phenomenon have been reported. The aim of this study was to investigate the behaviour of a real system based on light-sensitive α-methylstilbene-based copolyester microcapsules with vanillin as an upload under UV irradiation. For this purpose we aimed to elucidate some of the structural features of the chains by means of quantum chemical calculations applying periodic boundary conditions. Additionally, the excitation energy of an approximated model was used to verify the influence of large size and various functionalities of attached groups on the system. From the optimized structure of trans and cis isomers, it was proved that trans-to-cis isomerization can be responsible for a main chain length reduction by 20% in comparison to the initial state, thus confirming the experimental findings. Moreover, the major influence of double bonds on photoactivity of the system was justified by comparison of the calculated UV-visible spectra of both forms with empirically obtained data which were in good agreement. © 2015 Society of Chemical Industry

A liquid crystal polyester and two liquid crystal copolyesters containing α-methylstilbene moieties and aliphatic or aromatic spacers in the backbone were synthesized in good yields, with the aim of using them for photosensitive microcapsule preparation.Thesynthesizedpolymerswerefullycharacterizedwithrespecttothermalstability,typeofmesophase,molecular weight and E–Zphotoisomerization. Combination of monomers with different structures allowed adjustment of the polymer characteristics such as degree of crystallinity and glass transition temperature, as verified using X-ray diffraction, polarized optical microscopy and differential scanning calorimetry. Quantitative 1 H NMR and UV-visible experiments were performed in order to investigate E–Zphotoisomerization after photoirradiation at 364 nm. Finally, a membrane based on one of these polymers was prepared and it was found that its wettability increased on photoirradiation. c � 2013 Society of Chemical Industry Supporting information may be found in the online version of this article.

A new family of liquid crystalline columnar polyethers was obtained by modification of Poly(epichlorohydrin-co-ethylene oxide) (P(ECH-co-EO)) with the dendron 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoate, under different conditions. The highest modification degree that we could achieve was 69%. The copolymers were fully characterized by 1H and 13C nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction (XRD). All copolymers exhibited liquid-crystalline columnar behavior whose range of stability depended on the modification degree. X-ray diffraction experiments on oriented samples showed that the dendrons are approximately perpendicular to the column axis and that their average number per unit cell ranged from 5 to 6. The formation of a stable columnar mesophase in the polyether should determine the presence of a continuous ion channel along the column axis. Therefore, these copolymers are suitable candidates for the preparation of membranes for small cation transport, in agreement with the results that we obtained by using poly(oxy-1-chloro methylethylene) (PECH) modified with the same dendron. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Acrylic microspheres bearing a dense shell were successfully prepared by aninsitu microemulsion photoinduced polymerization. Experiments following a fractional factorial design were performed for assessing the effect of the main reaction parameters (surfactant concentration in the aqueous phase, stirring rate, organic to water volume ratio, irradiation time) on the morphology of the microspheres and on their encapsulation yield. Environmental scanning electron microscopy and porosity measurements were carried out. Finally, the drug-delivery features of the obtained products were investigated, evaluating the release of vanillin, chosen as a reference compound. The diffusion coefficients were found to be almost unvaried despite the increase in BET area. Such products show promising potentialities for home and personal care applications. c � 2012 Society of Chemical Industry

Liquid-crystalline thermosets (LCTs) have received considerable attention since they exhibit many interesting properties. However, some aspects concerning LCTs are still unexplored. In particular, the structure–property relationships, as far as the organization of liquid-crystalline (LC) domains in cured thermosets is concerned, have not been fully elucidated yet. We investigated the effect of the presence of a nematic mesophase on the thermal and dynamic mechanical behaviour of p-(2,3-epoxypropoxy)phenyl-p-(2,3-epoxypropoxy)benzoate cured with 2,4-diaminotoluene. Fourier transform infrared spectral analysis showed that epoxy group conversion was complete in both LC and isotropic (ISO) systems; moreover, a greater amount of intermolecular hydrogen bonding in the LC material was found. Thermogravimetric analysis evidenced similar thermal stability for the two systems, but a kinetic analysis of the data showed that the degradation process is more complex for the LC sample, and is characterized by higher activation energy. Dynamic mechanical thermal analysis (DMTA) showed lower glass transition temperature values for the LC system. Solid-state NMR analysis evidenced lower paramagnetic oxygen absorption for this system. DMTA results show that the ISO material possesses a larger number of physical crosslinks, which act as extra constraints on the molecular motions. In the case of the LCT, the formation of a locally more dense structure is postulated, where the presence of more extended macromolecular segments leads to a smaller number of physical crosslinks, as also confirmed by solid-state NMR analysis. A more compact molecular packing also leads to an increase of the activation energies of the thermal degradation process of the LC system. Copyright © 2010 Society of Chemical Industry

Two new polyethers, bearing azobenzene moiety in the side chain, were synthesized in excellent yields by means of anionic polymerization of 4-glycidyloxyazobenzene and 4-cyano-4′-glycidyloxyazobenzene (leading to azo-P1 and azo-P2 polymers, respectively) with the system polyiminophosphazene base t-Bu-P4/3,5-di-tert-butylphenol as initiator. The polymers were characterized with respect to their molecular weights, structure, and calorimetric features. The polyether bearing cyanoazobenzene group in the side chain was found to exhibit nematic phase up to 200 °C. E–Z isomerization of both polymers in tetrahydrofuran solution, after irradiating with UV light at 364 nm for 15 min, was investigated by means of UV–visible absorption spectroscopy. In the case of glycidylic monomers as well as the resulting polymers, E–Z isomerization was also investigated by means of 1H NMR, by direct irradiation in the NMR probe in deuterated 1,1,2,2-tetrachloroethane solution. By this technique, in the case of 4-cyano-4′-glycidyloxyazobenzene, it was found that irradiation led to a photostationary state corresponding to an amount of Z isomer equal to 25%. For azo-P1 polymer, Z–E or “reverse” isomerization was investigated at 60, 70, or 80 °C directly in the NMR probe; as expected, the process followed a first-order rate law. The kinetic constants as well as the activation energy for the process were determined in this temperature range. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5426–5436, 2009

BACKGROUND: Microencapsulation technology promises new applications such as intelligent microstructures, phase change materials and self-healing composites. Microcapsule synthesis and characterization have been researched extensively; however, the well-known polymerization between epoxy resins and carboxylic acids has not been used to prepare microcapsules. RESULTS: Microcapsules were prepared by interfacial polymerization of an oil-in-water emulsion which contained a commercial epoxy resin and multifunctional carboxylic acids. The microcapsules obtained were characterized using optical microscopy and scanning electron microscopy. Experiments performed at lower stirring rates led to larger microcapsules, in the range 100–400 µm, while higher stirring rates resulted in microcapsules in the range 10–50 µm. CONCLUSIONS: Microcapsules can be prepared by interfacial polymerization of epoxy resins, an extensively studied and widely used class of polymers. By means of NMR characterization we gained insight into the mechanism of polymerization at the interface wherein products coming from the more hindered ring opening as well as from intermolecular transesterification are identified. The presence of a crosslinker affects the morphology of the external microcapsule surface. Copyright © 2008 Society of Chemical Industry

We reacted various dimeric, liquid-crystalline epoxy–imine monomers, differing in the length of the central aliphatic spacer or the dipolar moments, with heptanedioic acid. The resulting systems showed a liquid-crystalline phase in some cases, depending on the dimer and on the reaction conditions. The systems were characterized with respect to their mesomorphic properties and then were submitted to dynamic mechanical thermal analysis in both fixed-frequency and frequency-sweep modes in the shear sandwich configuration. The arrangement in the liquid-crystalline phase seemed to be mainly affected both by the polarization of the mesogen and by the reaction temperature, which favored the liquid-crystalline arrangement when it was lying in the range of stability of the dimer mesophase. In agreement with other recent literature data, dynamic mechanical thermal analysis results suggested that the presence of the mesogen directly incorporated into the main chain increased the lifetimes of the elastic modes both in the isotropic phase and in the liquid-crystalline phase with respect to side-chain liquid-crystalline elastomers and that the time–temperature superposition principle did not hold through the liquid-crystalline-to-isotropic transition. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44:6270–6286, 2006

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

We investigated the dynamics and structure of the aliphatic side chains of a randomly grafted copolymer, obtained through the chemical modification of poly(epichlorohydrin) with potassium 3,4,5-tris(dodecyloxy)benzoate, with solid-state 13C NMR. Below 283 K, the aliphatic chains partially crystallized in an all-anti conformation. The calorimetric data were compatible with an orthorhombic packing. Below 323 K, the polymer exhibited a columnar mesophase. Spin–lattice relaxation times were determined in this temperature range and at 333 K, that is, in the isotropic phase. In the liquid-crystalline state, some carbons exhibited a double decay in the spin–lattice relaxation, and this was attributed to presence of the liquid-crystalline phase. This hypothesis was supported by a conformational analysis performed by molecular modeling. The activation energies of the relaxation processes in the mesophase were also estimated. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2099–2111, 2005

A set of high-molecular-weight new side-chain liquid-crystalline polyethers was obtained by chemical modification of poly(epichlorohydrin) with potassium 3,4,5-tris(dodecyloxy)benzoate. The degree of modification ranged from 48 to 70% depending on the reaction conditions, and the upper value was an apparent modification plateau. NMR characterization indicated that no side reactions of any kind occurred (e.g., deshydrohalogenation). All copolymers had a nematic columnar mesophase whose range of stability depended on the modification degree. X-ray diffraction experiments performed on mechanically oriented samples showed that tapered groups were tilted with respect to the column axes. Also X-ray experiments and density measurements demonstrated that the number of disks per unit cell decreased as the modification degree increased. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2918–2929, 2003

Novel epoxy-terminated monomers based on imine groups were synthesized and their mesogenic properties studied. Aliphatic spacers of different lengths were introduced between the rigid unit and the glycidylic group, and their liquid-crystalline behavior was examined. They were reacted with primary aromatic diamines inside a magnetic field so that the formation of anisotropic networks could be investigated. The influence of curing conditions and the structure of monomers and amines on the formation of liquid-crystal thermosets were investigated. Thermosets with locked nematic textures were obtained in all cases. The influence of a 7.1 T magnetic field on the macroscopic orientation of these materials was studied, and mechanical properties of the resulting networks were evaluated by dynamic mechanical analysis. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1–12, 2003

The synthesis and physical characterization of a novel liquid crystalline epoxy resin, used as a matrix for carbon fiber-reinforced composites, is presented in this paper. The curing reaction was monitored by means of calorimetric and rheological measurements. Calorimetric analysis indicates that the presence of carbon fibers does not affect the reaction rate. A conventional isotropic epoxy resin in used as a model compound in the rheological analysis. According to the patent literature, two different formulations of the model compound were used, characterized by a stoichiometric ratio of epoxy and an epoxy excess, respectively, with respect to the curing agent.

The dynamic-mechanical characterization and fracture resistance of composites, prepared by using a liquid crystalline epoxy resin and continuous carbon fibers, are presented and compared with conventional composites. In the case of the LC matrix, a higher T g was found; similarly, a superior fracture resistance, higher elastic modulus and higher T g were found for the LC-based composites. These results allow to consider these materials as potential candidates for advanced composites.

The authors describe the features of liquid crystalline epoxy resins having both high and low crosslinking densities. These materials seem to be very promising as matrices in advanced composites and in optical and electro-optical applications because of their peculiar properties. The importance of factors like molecular rigidity, nature of the curing agent, and curing temperature for the development of such properties are analyzed. The authors showed that amines produce thermosets having high T g s and high fracture toughness. In particular, the enhancement of this last parameter is very promising if a new generation of matrices is to be sought for manufacturing composites. In the case of acids as curing agents, thermosets having lower T g s and more ordered mesophases can be obtained. In this case, LC elastomers can be prepared that can find applications in the optical industry as waveguides or electro-optical devices.

The glycidyl (Gly)-terminated liquid crytalline (LC) monomer GlyOPhC(Me)=CHPhOGly is cured with aromatic amines. A nematic structure suddenly develops during the curing reaction and is related to the molecular weight increase of the developing network. An unusual exothermal double peak is observed in the isothermal curves obtained in a defined temperature range. The calorimetric analysis is used to evaluate the kinetic parameters and is related to the initial formation of a linear prepolymer and to the subsequent development of the tridimensional network

By reacting a rigid rod epoxy terminated molecule (p-bis(2,3-epoxypropoxy)-α-methylstilbene) with an aliphatic carboxylic acid (decanedioic acid), a lightly crosslinked liquid crystalline network is obtained. This network exhibits a smectic-like phase. While the mesophasic structure resulted “frozen” by the crosslinks in the case of higly crosslinked liquid crystalline epoxy resins, in this case a reversible transition from the liquid crystalline to the isotropic phase is observed. Moreover, while curing the same rigid rod epoxy molecule with amines resulted in a thermoset with a nematic structure, in this case a more ordered mesophase can be obtained. Preliminary results show that it is possible to orient macroscopically the mesogenic chains by stretching thin films above the glass transition temperature (Tg) and then quickly cooling down to the glassy state. This makes this material very attractive in the field of optical applications.

Water sorption tests have been carried out for a novel epoxy resin having liquid crystalline character. The sorption isotherm. Relative to the expoxy resin cured in the nematic phase, does not indicate any substantial difference from the resin cured in the isotropic state. This is an indication that, as far as this class of thermosets is considered, the liquid crystalline order does not affect mechanism and equilibrium values of water uptake.

A novel glycidyl-terminated benzaldehyde azine was synthesized and subsequently cured with an aromatic diamine. The resulting liquid-crystalline network was characterized by means of optical microscopy, X-ray analysis and dynamic-mechanical analysis. The influence of the curing temperature on the nematic textures is pointed out. The curing reaction was followed by means of differential scanning calorimetry and dielectric analysis.