Photoinitiators made from bifunctional silane

Abstract

The present invention relates to a compound of formula (I) below: ##STR00001##
in which: R.sub.1 represents, in particular, an alkylene group comprising from 1 to 6 carbon atoms; R.sub.2 and R.sub.3 are, in particular, H; n is 0, 1, 2 or 3; and R.sub.4 is chosen from the group consisting of: NO.sub.2, OR.sub.a, SR.sub.a and NR.sub.aR.sub.b, wherein R.sub.a and R.sub.b are as defined above; R.sub.5 and R.sub.6, identical or different, represent an alkyl or alkoxy group comprising from 1 to 6 carbon atoms; and R.sub.7, R.sub.8 and R.sub.9, identical or different, represent an alkyl group comprising from 2 to 6 carbon atoms.

Claims

1. Compound of formula (I) below: ##STR00011## in which: R.sub.1 represents an alkylene group comprising from 1 to 6 carbon atoms or an —O-alkylene group comprising from 1 to 6 carbon atoms; R.sub.2 and R.sub.3, identical or different, are chosen from the group consisting of: H, NO.sub.2, OR.sub.a, SR.sub.a and NR.sub.aR.sub.b, wherein R.sub.a and R.sub.b, identical or different, represent H or an alkyl group comprising from 1 to 6 carbon atoms, or R.sub.2 and R.sub.3 may together form a phenyl group with the carbon atoms carrying them; n is 0, 1, 2 or 3; R.sub.4 is chosen from the group consisting of: NO.sub.2, OR.sub.a, SR.sub.a and NR.sub.aR.sub.b, wherein R.sub.a and R.sub.b are as defined above; R.sub.5 and R.sub.6, identical or different, represent an alkyl group comprising from 1 to 6 carbon atoms or an alkoxy group comprising from 1 to 6 carbon atoms; and R.sub.7, R.sub.8 and R.sub.9, identical or different, represent an alkyl group comprising from 2 to 6 carbon atoms or an alkoxy group comprising from 2 to 6 carbon atoms.

2. A compound according to claim 1, wherein n=0.

3. A compound according to claim 1, wherein R.sub.5 and R.sub.6 represent a methyl group.

4. Compound according to claim 1, wherein R.sub.7, R.sub.8 and R.sub.9 represent an ethyl group.

5. Compound according to claim 1, corresponding to the following formula (I-1): ##STR00012## in which: R.sub.1, R.sub.2 and R.sub.3 are as defined in claim 1.

6. Compound according to claim 1, wherein R.sub.1 represents an alkylene group.

7. Compound according to claim 1, wherein R.sub.2 and R.sub.3 represent H.

8. Compound according to claim 1, wherein R.sub.2 represents H, while R.sub.3 represents an OR.sub.a group as defined in claim 1.

9. Compound according to claim 1, wherein R.sub.2 and R.sub.3 together form a phenyl group with the carbon atoms which carry them.

10. Process for the preparation of a compound of formula (I) according to claim 1, comprising: the reaction of a compound of formula (II) below: ##STR00013## in which: n, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are as defined in claim 1; with a compound of formula (III) CH.sub.2=CH-A.sub.1-X, X representing a halogen atom such as I or Br, A.sub.1 representing an alkylene radical comprising from 1 to 5 carbon atoms; to obtain a compound of the following formula (IV): ##STR00014## and the reaction of the compound of formula (IV) with a compound of formula (V) below: ##STR00015## in which: R.sub.7, R.sub.8 and R.sub.9 are as defined in claim 1.

11. Use of a compound of formula (I) according to claim 1 as a photoinitiator.

12. Use of a compound of formula (I) according to claim 1 to modify a silica surface.

13. Process for modifying a silica surface comprising: bringing together a silica surface comprising free Si—OH groups with at least one compound of formula (I) according to claim 1, to obtain a silica surface grafted with groups of the following formula (VI) below: ##STR00016## in which: n, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7 and R.sub.9 are as defined in claim 1; and photopolymerization of the grafted silica surface obtained in the previous step with at least one monomer M, to obtain a modified silica surface comprising at least one group of formula (VII) below: ##STR00017## in which: R.sub.1, R.sub.5, R.sub.6, R.sub.7 and R.sub.9 are as defined in claim 1; and P′ is a polymer derived from the monomer M.

14. Silica surface comprising at least one group of formula (VI) or (VII) as defined in claim 13.

Description

FIGURES

(1) FIG. 1 represents the organic matter content (estimated by thermogravimetric analysis) in silica samples grafted with: SPI-I (columns on the left), 3-methacryloxy propyltrimethoxysilane (MPTS) (98%) (columns in the center), and vinyl triethoxysilane (VTES) (columns on the right) after 5 minutes of photopolymerization of trimethylolpropane triacrylate (TMPTA) in the presence of silica suspension grafted with different silica/monomer ratios. In the case of MPTS and VTES, 1% by mass (relative to the amount of monomer) of an external photocell (isobutyrophenone; IBP) was used. After photopolymerization, the silica powders are collected by centrifugation, washed three times (with AcN)/EtOH/H.sub.2O), and dried at 70° C. for more than 24 hours.

(2) FIG. 2 represents HAADF-STEM images of a sample of SPI-1/silica after ex-situ photopolymerization of TMPTA/AcN (silica/monomer ratio 1:5 wt/wt). (a) The primary silica particles of 20-40 nm are visible (brilliant contrast), but are all strongly agglomerated and covered with amorphous organic matter (gray contrast). The amorphous gray contrast envelope surrounding the single silica nanoparticles is clearly distinguished in (b) and (c). The figure shows a homogeneous covering of the silica by the polymers.

(3) FIG. 3 represents the UV-visible spectra of SPI-1, SPI-2 and SPI-3 in acetonitrile. The insert in this figure shows a zoom on the absorbance of these compounds between 290 nm and 390 nm.

(4) FIG. 4 represents the TG analysis of silica samples before (dotted curves) and after grafting with SPI-1 and SPI-2.

(5) FIG. 5 represents the TG analysis of zeolite (Faujasite X) samples (prepared without organic structuring agents) before (dashed curves) and after grafting with SPI-1, SPI-2 and SPI-3.

(6) FIG. 6 represents the DR-UV-visible spectra of SPI-1, SPI-2 and SPI-3 grafted onto the zeolite (ZX).

(7) FIG. 7 represents the DR-UV-visible spectra of SPI-2 grafted on a zeolite (SPI-2/ZX) and on a silica (SPI-2/silica).

(8) FIG. 8 represents the FTIR spectra of the zeolite samples (Faujasite X) (synthesized without an organic structuring agent) before grafting (ZX) and after grafting with

(9) SPI-1, SPI-2 and SPI-3 (degasification of the samples in in situ mode at 150° C. under vacuum (10.sup.−6 torr)).

(10) FIG. 9 represents the kinetics of the photopolymerization in situ of the TMPTA monomer in the presence of grafted zeolite (ZX) with SPI-1, SPI-2 and SPI-3 (10% by mass) under polychromatic UV irradiation (Hg-Xe lamp, Irradiance=150 mW/cm.sup.2) and under a controlled atmosphere (Ar).

EXAMPLES

(11) The reagents used hereinafter are obtained from Aldrich and without additional purification: isobutyrophenone (IBP) (97%), triethoxysilane (95%), trimethylolpropane triacrylate (TMPTA), ethyl vinyl ether (99%), 3-methacryloxy propyltrimethoxysilane (3-MPTS) (98%) and vinyl triethoxysilane (VTES) (97%).

Example 1: Preparation of a Photoinitiator According to the Invention

(12) ##STR00010##

(13) 1. Synthesis of 2,2-Dimethyl-1-phenylpent-4-en-1-one

(14) 2.10 g of potassium tert-butoxide (18.70 mmol) was added to a solution of isobutyrophenone (2.02 ml, 17.00 mmol) in anhydrous tert-butanol (25.0 ml). The mixture is stirred at room temperature for 5 minutes. Then, 1.64 ml of allyl bromide (18.70 mmol) is added by syringe to the solution and the mixture is heated to 90° C. for 24 hours. After cooling, 5 ml of water are added and the product is extracted with diethyl ether Et.sub.2O (2×100 ml). The organic phases are then dried over magnesium sulfate and the solvent is evaporated in vacuo.

(15) The .sup.1H proton NMR of the reaction mixture shows that the desired product is contaminated with approximately 10% of the starting product. Purification on a column on silica using a toluene/hexane mixture (1:1) provides the pure final product, with a yield of 94% (3.01 g; yield=94%) in the form of a colorless oil.

(16) 1H NMR (500 MHz, CDCl.sub.3): 7.70-7.62 (m, 2H, ArH), 7.50-7.36 (m, 3H, ArH), 5.80-5.67 (m, 1H, HC=CH.sub.2), 5.08-4.98 (m, 2H, HC=CH.sub.2), 2.50 (dt, J=7.5 and 1.0 Hz, 2H, CH.sub.2CH=CH.sub.2), 1.33 (s, 6H, (CH3)2).

(17) 1. Summary of SPI-1

(18) A solution of triethoxysilane (0.192 g; 1.17 mol) and 2,2-dimethyl-1-phenylpent-4-en-1-one (0.2 g; 1.06 mmol) is stirred without solvent in a tube sealed under an argon atmosphere, without prior purification.

(19) A platinum on Al.sub.2O.sub.3 (5% by mass) was added to the solution and the tube was sealed and heated to 85° C. for 20 hours. After cooling to room temperature, the raw product is filtered on active carbon with anhydrous ethanol. The filtrate is concentrated and then dried under reduced pressure. The .sup.1H NMR analysis of the reaction mixture clearly shows the formation of the hydrosilylation product with conversions ranging from 40 to 62%. However, this adduct was found to be unstable on a column of silica or alumina, which made it impossible to obtain in pure form (the maximum degree of purity obtained being 82%). However, the residues do not contain the functional group necessary for grafting (EtOSi) and have no impact on this latter process. It should be noted that other methods of catalytic hydrosilylation, namely that recently reported by Chirik et al., were also tested and gave comparable results in terms of conversion (Schuster, C. H.; Diao, T.; Pappas, I.: Chirik, P J ACS Catal. 2016, 6, 2632).

(20) .sup.1H-NMR (500 MHz, CDCl.sub.3): 6 0.13 (s, 3H, CH.sub.3—Si); 0.63 (m, 2H, SiCH.sub.2); 1.22 (t, 6H, J =7.1 Hz, OCH.sub.2CH.sub.3); 1.70 (m, 2H, SiCH.sub.2CH.sub.2CH.sub.2); 2.05 (s, 3H, CH.sub.3COO); 3.77 (q, 4H, J=7.1 Hz, OCH.sub.2CH.sub.3); 4.03 (t, 2H, J=7.0 Hz, SiCH.sub.2CH.sub.2CH.sub.2).

(21) .sup.13C NMR (150 MHz, CDCl.sub.3): δ 11.0; 18.21; 18.26; 26.1; 30.9; 44.5; 48.0; 58.3; 127.5; 128.0; 130.7; 139.2; 209.2.

(22) The aforementioned SPI-2 and SPI-3 compounds were also prepared by applying the same protocol as that described in Example 1.

Example 2: Immobilization of SPI-1 on the Surface of Silica Nanoparticles

(23) Ultrasil 7000 GR (Evonik) was used as the silica model, with a specific surface area of 175 m.sup.2/g and a primary particle size of around 14 nm. The silica is first dried at 150° C. and 1 g is then dispersed in 20 ml of decane at 120° C. with vigorous stirring. After 10 min, 100 mg of SPI-1 is added and stirred continuously for 30 minutes. The product is then washed by centrifugation and dispersed in water/ethanol three times, then dried at 50° C. for 12 hours and stored at the end in the dark.

(24) Characterizations through in-situ FTIR, NMR, UV-visible and thermogravimetry of the grafted silica confirm the grafting of SPI-1 on the surface, and show a 30% increase in the hydrophobicity of the silica after grafting and thermal stability up to 200° C. (FIGS. 3 to 8).

(25) In particular, the characterizations by thermogravimetry (FIG. 5) show that the “SPI” coupling agents (compounds according to the invention) may also be grafted onto materials based on zeolite with a relatively high content. The mass contents of SPI on the zeolite are found respectively in the order of 8.0%, 8.3% and 7.5% for SPI-1, SPI-2 and SPI-3. The results demonstrate a relatively high thermal stability of the SPI structure (up to 250° C.).

(26) The UV spectra of FIG. 6 show the stability of the structure after the grafting process on the zeolite and their absorbance in the solid state. The three structures have a different UV absorbance, which is useful and allows an increase in the choice of light sources used to initiate the photopolymerization.

(27) The UV spectra of FIG. 7 show that the nature of the supports (for example zeolite or silica) has no influence on the absorbances of the SPI compounds.

EXAMPLE 3: Photopolymerization Tests

(28) The grafted silica was tested via photopolymerization, in mass (without solvent) and in solution (acetonitrile), of an acrylic (TMPTA) and vinyl (VE) monomer in the absence of an external photoinitiator and under UV irradiation.

(29) The two monomers chosen respectively present a monomer poor and rich in electrons. The in-situ and ex-situ characterization of the product shows an interesting efficiency of the grafted silica in radical polymerization. Comparison with conventional systems (silicas grafted with monomers in which an external photoinitiator is used) shows a greater effectiveness of the new structure (FIG. 1). The difference is more significant for photopolymerization in solution (using a solvent) (FIG. 2). Unlike conventional systems, the SPI-1-silica product is non-selective with respect to the monomer used, so there is no need to modify/change the structure by changing the monomer. A significant improvement in the mechanical property (+180%), adhesion (−30%) and hydrophobicity (+−5-13%) was observed in comparison with the pure polymer or the composite prepared with the non-grafted silica.