L. O. Vretik

Polymethacryloylaminoarylmethacrylates: New Concept of Photoalignment Materials for Liquid Crystals

New class of highly efficient polymers for liquid crystal (LC) photoalignment is proposed. These polymers are based on methacryloylaminoarylmethacrylates having two methacryloyl groups of different reactivity. The more active O-methacryloyl group is subjected to polymerization, while the less active NH-methacryloyl group undergoes photocrosslinking reaction in combination with Fries rearrangement. The latter process is anisotropic in case of polarized light irradiation that results in LC photoalignment with readily controlled pretilt angle and anchoring energy. The induced alignment shows high thermal and photo-stability.

New Photoalignment Materials in LCD's Development: Liquid Crystal Pretilt Angle Variations By Using Fluoroalkylmethacrylates

Fluorinated copolymers based on 4-(N-methacryloylamino)phenyl methacrylate are proposed as materials for the liquid crystal (LC) photoalignment with a wide range of variations of a pretilt angle. As fluorinated chains, 2,2,3,3-tetrafluoropropylmethacrylate and 2,2,3,3,4,4,5,5-octafluoropenthylmethacrylate are used. The growth of a pretilt angle with the concentration of fluorinated chains, more pronounced in a series with longer fluorinated chain, is observed. The pretilt angle of TN LC ZLI 2293 is smoothly varied in the range 0°–20°. Additionally, the uniform high pretilt angle (89°–90°) alignment is realized for VA LC MJ961180.

Photochemistry of Bis-Methacrylic Polymers and Alignment of Liquid Crystals

Photochemical processes leading to the photoinduced anisotropy and the excellent photoaligning properties of bis-methacrylic polymers are discussed. Comparing the data for bis-methacrylic polymers and a series of model compounds, we conclude that Fries rearrangements and crosslinking reactions taking place in bis-methacrylic polymers cause the photoinduced ordering in films of these polymers via the mechanism of photoselection. Thus, all of these photochemical processes contribute to the liquid crystal photoalignment. The induced alignment is thermally stable due to the crosslinking of methacryloyl groups which fix the induced anisotropy in aligning polymer films.

Problem of Photoalignment in the LCD's Development: Synthetic Routes in Its Solving

Hereinafter we discuss our last five years investigations in the field of new highly efficient polymers for liquid crystal (LC) photoalignment. New polymers finally proposed are based on methacryloylaminoarylmethacrylates with two methacryloyl groups of different reactivity. Fries rearrangement and photocrosslinking/photopolymeryzation are such photochemical reactions which take place in their films under the action of UV light. In a case of polarized light irradiation rearrangement results in LC photoalignment. The problem of pretilt angle and anchoring energy control as well as thermal stability of the induced alignment are discussed.

Naphthalene containing polymers as new photoaligning materials for LCs

Abstract Polynaphtylmethacrylates (PNMA) are considered as a new class of liquid crystal (LC) photoaligning polymers. The films of PNMA irradiated with polarized UV light provide high quality LC alignment with the easy axis oriented perpendicularly to polarization direction of the exciting light. A maximal value of the azimuthal anchoring energy was estimated as 5 × 10−6 J/m2. It is close to the best photoaligning materials. Fries rearrangement is considered as a main photochemical reaction leading to anisotropy of PNMA layers.

Photochemical Transformations in Bis-Methacrylic Polymers for Liquid Crystal Photoalignment: IR Spectroscopy Studies

Fourier transform infrared spectroscopy (FTIR) is applied to study photochemical transformations in poly(p-methacryloylaminophenyl methacrylate), a material with pronounced liquid crystal photoalignment capability. The characteristic bands corresponding to photosensitive groups of this polymer are identified by comparing its FTIR spectra with the spectra of model compounds having a reduced number of photochemical transformations. The changes in FTIR spectra of this material under ultraviolet illumination give evidence of two Fries rearrangements (in arylamide and arylester groups) and a conversion of C˭CH2 methacrylic bonds. This allows one to refine the microscopic model of photoinduced ordering in this class of polymers.

Polystyrene-diphenyloxazole-chlorin e6 nanosystem for PDT: Energy transfer study

ABSTRACT As the step to design nanosystems for X-ray excited sensitizing of singlet oxygen, nanoparticles of polystyrene and polystyrene with encapsulated 2,5-diphenyloxazole were synthesized. Binding of the photosensitizer chlorin e6 molecules to both kinds of nanoparticles was shown. Excitation energy transfer from styrene chromophores of polystyrene to the bound chlorin e6 molecules occurs in the case of both kinds of nanoparticles. Efficiency of the energy transfer in 2,5-diphenyloxazole-mediated case is higher (0.17) as compared to the non-mediated one (0.12).

LC Photoaligning Polymer Prepared via Selective Polymerization of Bifunctional Monomer with O-Methacryloyl and Styrene–Type Double Bonds

Phenylene-containing monomer 1 possessing O-methacryloyl and styrene double bonds with different reactivities in radical polymerization was designed as new type of bifunctional monomers suitable for preparation of LC photoaligning alkene-functionalized polymers. To elucidate an individual contribution of double bond of each type into kinetics of bifunctional monomers polymerization, thermo- and photo-induced polymerization of model monomers were investigated and compared. Polymer poly-1 obtained by thermo-induced radical polymerization demonstrated high efficiency of LC ZLI 2293 photoalignment.

The photochemical behavior of polyhydroxy styrene with azofragments containing free methacrylic double bounds

ABSTRACT Polymer material which combines advantages of photoaligning azo-compounds with thermal stability of the induced anisotropy provided by free methacryloyl groups was synthesised. FTIR spectroscopy was employed for clarification its photochemical behavior. Two Fries rearrangements in arylester groups and photoinitiated cross-linking in methacryloyl functional groups were established after the action of UV-irradiation.

Poly(Methacrylamidoaryl Methacrylate)’s Surface Morphology

Possible morphological changing onto poly(methacrylamidoaryl methacrylate)’s surface before and after irradiation with polarized ultraviolet (UV) light was investigated. We examined the possibility of that the polymer alignment occurred through grooves induced on the photoactive polymer surface by the linearly polarized UV (LPUV) illumination of photoactive polymer surface. While such a mechanism may be applicable to some situations, we find unsatisfactory explanation for it in the case of poly(methacrylamidoaryl methacrylates).