FREE-RADICAL PHOTOINITIATORS AND USES OF SAME IN SILICONE COMPOSITIONS

Abstract

The present invention concerns type II photoinitiators for the free-radical crosslinking of silicone compositions, in particular acrylic silicone compositions. The present invention concerns a silicone composition C1 that can be crosslinked by exposure to radiation with a wavelength of between 300 and 450 nm, comprising:—at least one organopolysiloxane A comprising at least one methacrylate group bonded to a silicon atom, at least one organohydrogenopolysiloxane H comprising at least two, and preferably at least three hydrogen atoms each bonded to different silicon atoms, and—at least one free-radical photoinitiator P. The present invention also concerns the provision of a silicone composition that can be polymerized or crosslinked by free-radical process comprising a type II photoinitiator system suitable for crosslinking silicone compositions, in particular by exposure to radiation, and absorbing light radiation with a wavelength greater than 300 nm.

Claims

1. Compound of formula (20): ##STR00026##

Description

EXAMPLES

[0330] In the following examples, different photoinitiators, organohydrogenopolysiloxanes and polyorganosiloxanes with acrylate functions were used according to the invention and their structures are indicated in the tables given below.

TABLE-US-00001 TABLE 1 Photoinitiators Molecular weight Name (g .Math. mol.sup.−1) Structure Benzophenone BP from Rahn Comparative 182 [00012] Isopropyl- thioxanthone ITX Comparative 254.35 [00013] Xanthone XT Comparative 196.19 [00014] Thioxanthone TX Comparative 212.27 [00015] 2- hydroxy- thioxanthone 2 OH-TX Invention 228 [00016] 2-hydroxy- anthone 2 OH-XT Invention 212 [00017] 2 Hex-XT(1) Invention 296 [00018] 2 Dod-XT (4) Invention 380 [00019] 2 neodeca-XT (19) Invention 366 [00020] 2 Hex-TX (5) Invention 312 [00021] 2 Dod-TX (8) Invention 396 [00022] 2 neodeca-TX (20) Invention 382 [00023]

[0331] Among these photoinitiators, compounds (1), (4), (5), (8), (19) and (20) were synthesized according to the protocols explained hereunder.

Synthesis of 2-hydroxyxanthone (2 QH-XT)

Reagents

[0332] 2-iodobenzoic acid [0333] 4-m ethoxyphenol [0334] cesium carbonate [0335] copper(I) chloride [0336] tris[2-(2-m ethoxyethoxy)ethyl]amine (TDA-1) [0337] 1,4-dioxane [0338] concentrated sulfuric acid

[0339] Charge a single-necked flask with 1 equivalent of 2-iodobenzoic acid, 1.4 equivalents of 4-methoxyphenol and 2.8 equivalents of cesium carbonate in 6 mL of 1,4-dioxane per mmol of 2-iodobenzoic acid. Stir for 10 min at room temperature, under argon. Then add 0.1 equivalent of copper(I) chloride and 0.1 equivalent of TDA-1. Leave to react for 20h under reflux under argon.

[0340] Once the reaction has ended, evaporate the 1,4-dioxane in a rotary evaporator. Dissolve the residue with 10 wt % solution of Na.sub.2CO.sub.3 and filter the solution. Then put the filtrate in a separating funnel and wash it with a toluene/ethyl acetate 50/50 mixture. Recover the aqueous phase and acidify before filtering to obtain the reaction intermediate. (Yield: 75%)

[0341] Charge a single-necked flask with 1 equivalent of the intermediate in 1.25 mL of concentrated sulfuric acid per mmol of reagent. Leave to react until the spot of the product with a methoxy disappears in TLC (about 3 h). Once the reaction has ended, leave the reaction mixture to cool before pouring it into 10 times the volume of acid in ice. Then extract the solution obtained 3 times with ethyl acetate. The organic phases are collected, dried and evaporated. The product obtained is a white solid. It is possible to recrystallize it in acetone (Yield: 48%). The NMR spectrum corresponds to 2-hydroxyxanthone.

Synthesis of 2-hydroxythioxanthone (2 OH-XT)

Reagents

[0342] thiosalicylic acid [0343] phenol [0344] sulfuric acid

[0345] Slowly charge a single-necked flask with 1 equivalent of thiosalicylic acid in 1 mL of sulfuric acid per mmol of thiosalicylic acid. Stir vigorously for 10 minutes. Then add 5 equivalents of phenol in the course of 30 minutes. Then leave the mixture to react for 1 h at room temperature, then 2 h at 80° C. and leave to stand overnight at room temperature.

[0346] Once the reaction has ended, pour the reaction mixture into 10 times the volume of sulfuric acid in boiling water, and leave to boil for 10 min. Filter the solution once it has cooled. The product obtained is a yellow powder (Yield: 62%). The NMR spectrum corresponds to 2-hydroxythioxanthone.

Synthesis of the Ethers of Xanthone and Thioxanthone, Compounds (1), (4), (5), (8)

Reagents

[0347] 2-hydroxyxanthone and 2-hydroxythioxanthone [0348] iodoalkane (1-iodohexane and 1-iodododecane) [0349] potassium carbonate [0350] dimethylsulfoxide DMSO

Balanced Equation

[0351] ##STR00024##

FIG. 1: Synthesis of Ethers of Xanthone and Thioxanthone (X=O, S)

Protocol

[0352] Charge a single-necked flask with 1 equivalent of 2-hydroxyxanthone (or of 2-hydroxythioxanthone) and 2 equivalents of potassium carbonate in 5 mL of DMSO per mmol of product. Stir for 10 min at room temperature under argon. Then add the iodoalkane (1-iodohexane or 1-iodododecane) dropwise, and then leave to react at 100° C. under argon for 48 h. Once the reaction has ended, add 10 times the volume of the reaction mixture to water and extract the mixture 3 times with n-hexane. The organic phases are then collected, dried and evaporated. The crude product obtained is then purified on silica gel with an eluent of 90/10 cyclohexane/ethyl acetate (Yield: about 66%).

Synthesis of the Compounds 2 neodeca-XT (19) and 2 neodeca-TX (20)

[0353] Charge a single-necked flask with 1 equivalent of 2-hydroxyxanthone (or of 2-hydroxythioxanthone), 1 equivalent of neodecanoic acid and 1 ml of concentrated sulfuric acid per mmol of product. Stir for 2 hours at room temperature under argon. Then leave to react at 120° C. under argon for 12 h.

[0354] Once the reaction has ended, add 10 times the volume of the reaction mixture to water and extract the mixture 3 times with n-hexane. The organic phases are then collected, neutralized with sodium carbonate, dried and evaporated. The crude product obtained is then purified on silica gel with an eluent of 90/10 cyclohexane/ethyl acetate.

TABLE-US-00002 TABLE 2 Organohydrogenopolysiloxane Content of Position of the Si—H Compound Name/Supplier Si—H units (mol/100 g) Hyd 1 AB 112087 ® Company middle of chain 1.41 ABCR Chemical Hyd 2 BLUESIL ® FLD end and middle 0.707 626V25H7 Company of chain Bluestar Silicones

[0355] The compounds Hyd 1 and Hyd 2 specified in the above table are linear organohydrogenopolysiloxanes with SiH units arranged in the middle and/or end of chain.

Acrylic Silicones

A Polyorganosiloxane Acryl 1 of Formula

[0356] ##STR00025##

[0357] with x=85 and n=7 is used in the compositions.

Silicone Compositions Crosslinking by Irradiation

[0358] Tests were carried out to illustrate the use of the type II photoinitiators according to the invention with an organohydrogenopolysiloxane as photoinitiator for polymerizing acrylic silicones. The preparations are carried out as follows: weigh and add 1.2 10-4 mol of the photoinitiator to 2 g of polyorganosiloxane Acryl 1. Stir the whole for 12 hours. Then add 1 wt % of the organohydrogenopolysiloxane Hyd 1.

Two Types of Crosslinking by Irradiation Were Tested

[0359] 90 seconds of UV radiation with a mercury-xenon lamp. The lamp power is fixed at 510 mW/cm.sup.2, and [0360] 90 seconds of LED radiation 365 nm with a power of 750 mW/cm.sup.2 for the xanthone derivatives or under LED radiation 395 nm with a power of 680 mW/cm.sup.2 for the thioxanthone derivatives.

[0361] The manipulations were performed in laminate in order to avoid any effect of inhibition of the reactive species by oxygen. When the manipulations are performed in laminate, the formulation is placed between two sheets of polypropylene, and then between two pellets of CaF.sub.2.

[0362] The polymerization kinetics is monitored by real-time Fourier transform infrared (RT-FTIR, Vertex 70 from Brucker Optik). This spectroscopy technique consists of exposing the sample simultaneously to light and to infrared radiation in order to monitor the changes in the IR spectrum at 1636 cm.sup.−1, which is a characteristic band of the C═C bond of the acrylic functions.

[0363] The degree of conversion of C═C to C—C during polymerization is directly linked to decrease in calculated area under the peak at 1636 cm.sup.−1 according to the following equation: conversion (%)=(A.sub.0−A.sub.t)/A.sub.0×100, where A.sub.0 is the area under the peak before irradiation and A.sub.t is the area under the peak at each timepoint t of irradiation.

[0364] For the tests carried out with the mercury-xenon lamp, the plot as a function of time makes it possible to find the final degree of conversion, but also other important parameters, such as the maximum rate of conversion Rp expressed in the following tables as Rp/[M].sub.0×100 where [M].sub.0 is the initial concentration of acrylate function. The maximum rate of conversion Rp is determined from the slope of the curve conversion(%)=f(time) at its inflection point.

[0365] The results are presented in Tables 3 and 4 below.

TABLE-US-00003 TABLE 3 UV-LED radiation Solu- LED (365 LED(395 bility Ab- nm) % nm) % of PI sorp- conversion conversion in com- tion λ of acry- of acry- Photo- pound max lates lates Example initiator PI A1* (nm) after 90s after 90s Comp 2 Thio- − 378 16 xanthone TX Ex-1 2 OH-TX − 400 24 Ex-5 2 Hex-TX (5) + 400 55 Ex-6 2 Dod-TX (8) ++ 400 63 Comp 1 Xanthone XT − 340 24 Ex-2 2 OH-XT − 360 71 Ex-3 2 Hex-XT(1) + 360 75 Ex-4 2 Dod-XT (4) + 360 89 *−: low solubility < 50%; +: partial solubility > 50%, ++: soluble Observations made after stirring for 12 h with a magnetic stirrer

[0366] The photoinitiators according to the invention give a better degree of conversion after 90 s of irradiation with LEDs.

TABLE-US-00004 TABLE 4 Results with Hg—Xe lamp Absorp- Conver- Photo- tion λ Rp[M].sub.0 × sion Example initiator max (nm) 100 (%) Comp 3 Xanthone XT 340 1.2 55 Ex-7 2 OH-XT 360 2.6 90 Ex-8 2 Hex-XT (1) 360 3.5 93 Ex-9 2 Dod-XT (4) 360 7.7 100 Ex-10 2 neodeca-XT (19) 345 4.4 100

[0367] The photoinitiators according to the invention give a better degree of conversion after 90 s of irradiation with an Hg-Xe lamp.

[0368] Silicone compositions crosslinking by irradiation and thermally:

[0369] The formulations tested are detailed in Table 5 below.

[0370] The formulations are prepared by simple mixing of all of the constituents in a high-speed mixer, mixing at 1000 rev/min for one minute.

[0371] In addition to the compounds already described above, the following compounds are used:

Oil Vinyl 1: polydimethylsiloxane oil blocked at each chain end with a (CH.sub.3).sub.2ViSiO.sub.1/2 unit, having a viscosity of 60000 mPa.Math.s.
Resin Vinyl 2: polyorganosiloxane of formula MM.sup.ViQ containing 1.1 wt % of vinyl groups.
Hydrosilylation catalyst: platinum metal, added in the form of an organometallic complex at 10 wt % of platinum metal, known by the name Karstedt catalyst,
Inhibitor: ethynyl-1-cyclohexanol-1 or ECH,
Filler: Aerosil®200 from the company Evonik,
Polydimethylsiloxane PDMS of viscosity 50 mPa.Math.s

TABLE-US-00005 TABLE 5 Silicone compositions crosslinking with free radicals and by polyaddition A1 A2 B parts by parts by parts by weight weight weight Formulation Comparative Invention Invention Acryl 1 20 20 0 Vinyl 2 16.1 16.1 14.7 Vinyl 1 27.7 27.7 25.6 Aerosil ®200 1.5 1.5 1.5 PDMS 5.54 5.54 0 Pt 100 ppm 100 ppm 0 Isoprylthioxanthone ITX 0.35 ITX 0 0 diluted in xylene 0.70 Xylene 2 Dod-XT (4) 0 0.35 0 Hyd 2 0 0 8.2 Ethynyl Cyclohexanol 0 0 500 ppm Total 71.9 71.2 50

Two Compositions are Obtained

[0372] Composition 1 by mixing A1+B, which is a comparative example.

[0373] Composition 2 by mixing A2+B, which is an example according to the invention. At 23° C., the dynamic viscosity of composition 2 is equal to 15400 mPa.Math.s.

3D Printing Test

[0374] 100 g of composition is put in the reservoir of a 3D printer using tank photopolymerization with 365 nm LEDs. It is a DLP Prodway® 3D printer with a twin-cartridge system equipped with a static mixer. The bath life or “potlife” of the composition obtained in the dark (away from the light) is 24 hours before undergoing gelation.

[0375] The results for the crosslinking conditions necessary for the first layer with a thickness of 250 μm deposited on a plate and exposed for 5.5 s to UV LED radiation of 365 nm and with an intensity of 75.5 mW/cm.sup.2 are presented in Table 6 below.

TABLE-US-00006 TABLE 6 Energy required for radiation crosslinking of a 250-μm layer of the silicone compositions Composition1 Composition 2 Optical properties Comparative Invention Ec(mJ/cm.sup.2) 270 110 E.sub.4 (mJ/cm.sup.2) (100 μm) 355 140 E.sub.8 (mJ/cm.sup.2) (200 μm) 416 178 E.sub.10 (mJ/cm.sup.2) (250 μm) 515 225
In the following table, Ec represents the critical surface energy measured in mJ/cm.sup.2.

[0376] The composition according to the invention has a lower critical surface energy. Less energy will have to be supplied to it to reach the gel point. This composition therefore offers the advantage of requiring less energy for crosslinking and consequently it will be possible to print the successive layers more quickly.

E4 is the energy to be supplied to achieve crosslinking on a thickness of 100 microns, E8 to achieve 200 microns and E10 to achieve 250 microns.

TABLE-US-00007 TABLE 7 Mechanical properties measured according to standard NF EN ISO 527 on the silicone elastomers obtained after crosslinking by irradiation and thermally Mechanical Composition 1 Composition 2 properties Comparative Invention Breaking strength (MPa) 1.65 1.65 Elongation at break (%) 65 65 Tension modulus (MPa) 2.54 2.54