Cholesteric and photoreactive polyesters

Several classes of cholesteric and photoreactive homo- and copolyesters were synthesized and characterized. Most of these polyesters were prepared in such a way that a chiral spacer (e.g. isosorbide) was polycondensed with a photoreactive dicarboxylic acid, such as 4-carboxycinnamic acid, benzene- 1,4-bisacrylic acid, 4-(4′-carboxyphthalimido)cinnamic acid. In several cases other dicarboxylic acids, such as naphthalene-2,6-dicarboxylic acid or 4-aminobenzoic acid trimellitimide were cocondensed to favor the formation of a Grandjean texture. When ‘sugar diols’ such as isosorbide or isomannide were used as chiral building blocks, suitable diphenols were required as comonomers to stabilize the LC phase. Most polyesters were capable of forming a selectively reflecting Grandjean texture, which can be fixed by crosslinking using UV light. An alternative synthetic strategy based on chiral, substituted terephthalic acids is discussed.     

Photoactive Polyesters Containing o-Nitro Benzyl Ester Functionality for Photodeactivatable Adhesion

The fabrication of modern microelectronic silicon devices mechanically challenges these thin silicon substrates during manufacturing operations. Melt and solution polyesterification enabled the synthesis of polyesters containing photoreactive o-nitro benzyl ester units for use as a potential photocleavable adhesive. Melt transesterification provided a solvent-free method for synthesis of 2-nitro-p-xylylene glycol (NXG)-containing polyesters of controlled molecular weights. ¹H NMR spectroscopy confirmed the chemical composition of the photoactive polyesters. Size exclusion chromatography (SEC) determined the number-average molecular weights (M_n) of the polyesters synthesized in the range of 6000 to 12000 g/mol. ¹H NMR spectroscopy confirmed increasing levels of photocleavage of the o-nitro benzyl ester functionality with increasing exposure to broad wavelength UV irradiation, and exposure levels ranged from 0–187 J/cm² UVA. Photocleaveage of approximately 90% of the o-nitro benzyl ester (ONB) units within the backbone of the polymer occurred at maximum dosage. Wedge fracture testing revealed approximately a two-fold decrease in fracture energy upon UV irradiation, suggesting that these structural adhesives offer potential for commercial “flip bonding” applications.     

丙烯酰化环氧大豆油光敏涂料的研究

由于光敏涂料具有固化速度快、节省能量和无污染等优点,因此在现代涂料工业中占有重要位置。本文对环氧大豆油(ESBO)新型紫外光固化涂料进行了研究,并讨论了光敏涂料的优化配方、光固化工艺以及固化膜的动态粘弹行为。研究结果表明:谊光敏涂料具有固化速度快、表面硬度高、柔韧性好等优点,可用作金属和木制品的保护性涂层。     

Application of selected 2-methylbenzothiazoles AS cationic photoreactive crosslinkers for pressure-sensitive adhesives based on acrylics

Since their introduction half a century ago, acrylic pressure-sensitive adhesives have been successfully applied in many fields. They are used in self-adhesive tapes, label signs, marking films and protective films as well as in medical pharmaceutical applications for plaster, in dermal dosage systems and in a wide range of biomedical electrodes. In the last 15 years or so, the UV technology, especially UV-crosslinking, is well established in the market and allows the production of UV-crosslinkable pressure-sensitive adhesives (PSA) based on acrylics with interesting performance. So much so that the larger manufacturers of pressure-sensitive adhesive materials and their suppliers now use very expensive equipment to study pressure-sensitive adhesive behavior: tack, peel adhesion and shear strength. The balance between adhesive and cohesive strength after the crosslinking process is very important and critical for properties of acrylic PSA in form of self-adhesive films. In this work the cationic UV-crosslinking of acrylic PSA containing epoxy groups in their structure and additionally cationic photoinitiators based on 2-methylbenzothiazoles as photoreactive crosslinkers have been investigated using UV-lamp as ultraviolet sources. The investigated acrylic PSA were synthesized from 80 wt% of butyl acrylate, and 20 wt% of glycidyl methacrylate. The use of selected photoreactive crosslinkers: 1,5-bis[N,N׳-(2-methylbenzothiazolium)]pentane diiodide and 1,10-bis[N,N׳-(2-methylbenzothiazolium)]decane diiodide allows manufacturing of high quality PSA materials with interesting properties, such as high tack, high peel adhesion, and excellent shear strength.     

Studies on the interaction of photoreactive light stabilizers and UV-absorbers

Coatings, like all organic substances, are submitted to photoageing during their life time. Ultraviolet light absorbing additives (UVAs) and hindered amine light stabilizers (HALS) often are added to improve their performance. These additives can be lost by migration to the surface, where they are exposed to physical depletion, as well as through photodegradation of the molecule itself. Modifying hindered amine light stabilizers by introducing a photoreactive site gives the possibility to fix the stabilizing molecule onto the polymer matrix. The influence of the presence and the type of UV absorbers onto the photografting reaction will be discussed.     

UV reactive polymers for refractive index modulation based on the photo-Fries rearrangement

In this study we report on the synthesis and characterization of photoreactive polymers which display large changes in their refractive index upon UV irradiation. These polymers contain aromatic ester groups which undergo a photo-Fries rearrangement from aryl esters to hydroxyketones. The polymers under investigation were poly(4-acetoxystyrene) and two derivatives of polynorbornene, poly(bicyclo[2.2.1]hept-5-ene-2-carboxylic acid, phenyl ester) and poly(bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, diphenyl ester). The kinetics of the photoreaction was studied by FTIR spectroscopy. Ellipsometric measurements of thin films showed that the photo-Fries rearrangement causes a large increase of the refractive indices in these polymers (between +0.03 and +0.05). The modulation of the refractive index is of interest for applications in the field of optics and data storage. The photoreaction also leads to an increase in surface energy as evidenced by contact angle measurements with water and diiodomethane as test liquids.