Synthesis of main chain polymeric benzophenone photoinitiator via thiol‐ene click chemistry and Its use in free radical polymerization

Main chain polymeric benzophenone photoinitiator (PBP) was synthesized by using “Thiol‐ene Click Chemistry” and characterized with ¹H NMR, FTIR, UV, and phosphorescence spectroscopies. PBP as a polymeric photoinitiator presented excellent absorption properties (ε₂₉₄ = 28,300 mol^?1L^?1cm^?1) compared to the molecular initiator BP (ε₂₅₂ = 16,600 mol^?1L^?1cm^?1). The triplet energy of PBP was obtained from the phosphorescence measurement in 2‐methyl tetrahydrofurane at 77 K as 298.3 kJ/mol and according to phosphorescence lifetime, the lowest triplet state of PBP has an n‐π* nature. Triplet–triplet absorption spectrum of PBP at 550 nm following laser excitation (355 nm) were recorded and triplet lifetime of PBP was found as 250 ns. The photoinitiation efficiency of PBP was determined for the polymerization of Hexanedioldiacrylate (HDDA) with PBP and BP in the presence of a coinitiator namely, N‐methyldiethanolamine (MDEA) by Photo‐DSC. The initiation efficiency of PBP for polymerization of HDDA is much higher than for the formulation consisting of BP. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

N‐Methyl‐N‐phenylaminomethyl 2‐naphthyl ketone: an X‐ray diffraction and density functional theory study

The crystallographically observed molecular structure of the title compound, C₁₉H₁₇NO, and its inverted counterpart are compared with that calculated by density functional theory (DFT) at the B3LYP/6‐311++G(d,p) level. The results from both methods suggest that the observed molecular conformation of the title compound is primarily determined by intermolecular interactions in the crystal structure. The periodic organization of the molecules is stabilized by weak C—H...O and C—H...π hydrogen bonds and thus a two‐dimensional puckered network consisting of R₄⁴(22) and R₄⁴(38) ring motifs is established. The title molecule has a (+)‐antiperiplanar conformation about the C—C bond in the aminoacetone bridge. The pyramidal geometry observed around the vertex N atom is flattened by the presence of bulky phenyl and naphthylethanone fragments.     

Thioxanthonation of fluorenone: Visible photoinitiator for radical polymerization

Thioxanthonation of fluorenone resulted in a new visible light initiator namely, indeno [1,2‐b]thioxanthene‐7,13‐dione (TX–FN). The detailed photophysical properties of the singlet and the triplet excited states of TX–FN are reported using steady‐state absorption, fluorescence, and phosphorescence, as well as laser flash photolysis techniques. Photoinitiated polymerization of MMA with TX–FN and CQ has been investigated in the presence and absence of a co‐initiator (MDEA). Additionally, Photo‐DSC studies were performed both in mono‐ and multiacrylate systems with TX–FN and parent compounds TX and FN. The obtained results were compared for formulations consisting of CQ. At low initiator concentrations, the conversions were lower than those obtained with TX–FN. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1012–1019     

Thermal and morphological investigation of the effect of POSS-(PEG2000)8 addition to UV curable PEGMEA/PEGDA formulation and simultaneously in situ formed silver nanoparticles

In this study, hybrid nanocomposites were synthesized by photo-crosslinking of poly (ethylene glycol) methyl ether acrylate/poly (ethylene glycol) diacrylate monomer system using 2- (carboxymethoxy) thioxanthone and POSS-(PEG₂₀₀₀)₈. Additionally, AgNO₃ was added to this formulation and in situ formation of silver nanoparticles onto hybrid nanocomposites were achieved in one-step. UV–Vis spectroscopy technique was used as a very useful tool for surface plasmon resonance band detection of silver nanoparticles. In addition to thermogravimetric analyses which were performed in nitrogen atmosphere to determine the thermal stability of the nanocomposites, dynamic light scattering, and scanning electron microscopy techniques were also used for size and morphology of silver nanoparticles in a hybrid network. TGA analyses proved that even the addition of a very low amount of POSS-(PEG₂₀₀₀)₈ made noteworthy contribution to thermal stability especially in the presence of silver nanoparticles in the hybrid network. The swelling capacities of the prepared films were examined at 1, 3 and 24 h in phosphate buffer solution (pH = 7.4). It was found that film containing only POSS-(PEG₂₀₀₀)₈ had the highest swelling ratio in the shortest time.     

The effect of an aminoalcohol on the polymerization of acrylates with type II initiators

In this study, the authors report the use of an aliphatic amine and an aromatic aminoalcohol as synergists with various Type II initiators by using Photo-DSC (Photo-differential scanning calorimetry) technique. The photopolymerization of triacrylate and diacrylate was performed under nitrogen atmosphere in the presence of an amine or aminoalcohol with type II initiators, which allowed us to compare the efficiency of the initiating radicals. The oxygen scavenging role of the amine was left out.     

Synthesis of block and star copolymers by photoinduced radical coupling process

The general design for the synthesis of AB diblock, and A₂B and AB₂ star copolymers based on the statistical coupling of poly(styrene) (PSt) and poly (methyl methacrylate) (PMMA) macromolecules containing photoreactive benzophenone is presented. For this purpose, mono- and bifunctional initiators for Atom Transfer Radical Polymerization (ATRP) bearing benzophenone group were synthesized and characterized. End- and mid-chain benzophenone functional PSt and PMMA with low molecular weights were obtained by ATRP using these initiators in the presence of CuBr/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) catalytic complex. Poly(styrene-block-methyl methacrylate) (PSt-b-PMMA) copolymers were prepared by photolysis of the solutions containing end functional PSt and PMMA in THF at λ = 350 nm for 60 min in the presence of a hydrogen donor such as N-methyldiethanolamine (NMDEA). The proposed mechanism assumes hydrogen abstraction of photoexcited benzophenone moiety by NMDEA. Ketyl radicals resulting from abstraction reaction undergo radical-radical coupling to form benzpinacol structure at the core. Formation of A₂B and AB₂ type star copolymers upon irradiation of solutions containing appropriate combinations of end- and mid-chain functional polymers was also demonstrated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2938–2947, 2009     

Optical dilution and feedback cooling of a gram-scale oscillator to 6.9 mK

We report on the use of a radiation pressure induced restoring force, the optical spring effect, to optically dilute the mechanical damping of a 1 g suspended mirror, which is then cooled by active feedback (cold damping). Optical dilution relaxes the limit on cooling imposed by mechanical losses, allowing the oscillator mode to reach a minimum temperature of 6.9 mK, a factor of approximately 40 000 below the environmental temperature. A further advantage of the optical spring effect is that it can increase the number of oscillations before decoherence by several orders of magnitude. In the present experiment we infer an increase in the dynamical lifetime of the state by a factor of approximately 200.     

An all-optical trap for a gram-scale mirror

We report on a stable optical trap suitable for a macroscopic mirror, wherein the dynamics of the mirror are fully dominated by radiation pressure. The technique employs two frequency-offset laser fields to simultaneously create a stiff optical restoring force and a viscous optical damping force. We show how these forces may be used to optically trap a free mass without introducing thermal noise, and we demonstrate the technique experimentally with a 1 g mirror. The observed optical spring has an inferred Young's modulus of 1.2 TPa, 20% stiffer than diamond. The trap is intrinsically cold and reaches an effective temperature of 0.8 K, limited by technical noise in our apparatus.     

Frequency-resolving spatiotemporal wave-front sensor

We report on a high-resolution wave-front sensor that measures the complete spatial profile of any frequency component of a laser field containing multiple frequencies. This probe technique was developed to address the necessity of measuring the spatial overlap of the carrier field with each sideband component of the field exiting the output port of a gravitational-wave interferometer. We present the results of an experimental test of the probe, where we were able to construct the spatial profile of a single radio-frequency sideband at the level of -50 dBc.     

Water makes it hydrophobic: contraphilic wetting for polyurethanes with soft blocks having semifluorinated and 5,5-dimethylhydantoin side chains

A series of polyurethanes with novel copolymer soft blocks display a new surface phenomenon, contraphilic wetting, in which the dry surface is hydrophilic and the wetted surface is hydrophobic. A precursor polymer was prepared with copolymer soft blocks containing semifluorinated (trifluoroethoxy, 3FOx, or pentafluoropropoxy, 5FOx) and bromomethyl functional pendant groups with 2:1, 1:1, and 1:2 semifluorinated/bromomethyl ratios. The hard block consists of isophorone diisocyanate (IPDI) and 1,4-butanediol (BD). 5,5-Dimethylhydantoin was introduced by the substitution of Br via reaction-on-polymer. The composition, structure, and percent of 5,5-dimethylhydantoin substitution for both the precursor and the 5,5-dimethylhydantoin-substituted polyurethanes were analyzed by 1H NMR. The difference between the advancing contact angle on the wetted surface and that on the dry surface (deltaC) is highest (38 degrees ) for the polyurethane with the highest ratio of semifluorinated/hydantoin soft block side chains. A model is proposed according to which contraphilic wetting is driven enthalpically by hydrogen bonding. For the dry surface, hydrogen bonding of 5,5-dimethylhydantoin amide carbonyl groups to methylene hydrogens of semifluorinated groups disrupts the normal surface concentration of semifluorinated groups, whereas the geometric arrangement of hydantoin N-H results in availability for hydrogen bonding with water. Upon exposure to water, amide groups switch from hydrogen bonding to -CH2CF2CF3 to stronger hydrogen bonding with water. As a result, semifluorinated groups are "released", and the surface becomes hydrophobic. Drying the coating (50 degrees C) reversibly restores hydrophilic character. Coatings stored at ambient temperature and humidity have deltaC values intermediate between dry and wet states.