Uv adhesive composition for photocuring silicone and difficult-to-bond materials

Abstract

The application discloses a photocuring organic silicon and UV glue composition for difficultly-bonded materials, and comprises the following steps: hydrogen-containing double-sealing heads and AGE are subjected to a silicon-hydrogen addition reaction in the presence of a platinum catalyst to obtain epoxy double-sealing heads; then, the epoxy double-sealing heads are subjected to ring-opening esterification reaction with excessive acrylic acid in the presence of a catalyst to obtain hydroxyl acryloyloxy double-sealing heads; then, the hydroxyl acryloyloxy double-sealing heads are subjected to esterification dehydration reaction with excessive acrylic acid in the presence of cyclohexane water-carrying agent and an acidic catalyst to obtain double-acryloyloxy double-sealing heads; finally, the double-acryloyloxy double-sealing heads are subjected to reaction with polydimethylsiloxane under the action of linear phosphorus chloride catalyst to synthesize photocuring organic silicon oligomers. The UV glue composed of the oligomers, acrylate monomers and free radical photoinitiators has excellent bonding strength for low-surface-energy substances.

Description

Technical Field

[0001] This invention belongs to the field of ultraviolet (UV) curable adhesives, and specifically relates to a UV adhesive composition that has good adhesion and bonding strength to difficult-to-bond materials. Background Technology

[0002] Bonding low surface energy materials (such as PE, PP, PET, POE, etc.) has always been a challenge and pain point in the adhesive industry. These materials are generally considered difficult to bond. Although hot melt adhesives have been developed for these low surface energy materials, hot melt adhesives themselves are thermoplastic resins, and their operating temperature is difficult to exceed 100°C, which greatly limits their application in the electronics and electrical appliance industries where heat resistance is required.

[0003] UV adhesives (ultraviolet-curing adhesives) are increasingly favored by industry due to their fast curing speed, energy efficiency, and environmental friendliness, especially in electronic component assembly lines. UV adhesives can cure in seconds, significantly accelerating assembly speed and improving production efficiency. The oligomers used in UV adhesives typically have two or more functional groups, forming a cross-linked network with good heat resistance. Therefore, UV adhesives are used for potting and bonding many electronic components. However, ordinary UV adhesives composed of polyurethane acrylate compounds do not provide sufficient adhesion strength to low surface energy materials, and cationic curing systems of alicyclic epoxy resins also lack good adhesion to these materials. To obtain good adhesion strength, physical treatments (surface roughening by mechanical grinding, short-wavelength ultraviolet irradiation, corona treatment, plasma treatment, etc.) or chemical treatments (silane coupling agents, primers, etc.) are necessary. Sometimes, even with surface treatment, sufficient adhesion strength is not achieved. These treatment processes are not only time-consuming and labor-intensive, increasing process costs, but also polluting the working environment. Therefore, industry has been searching for a UV adhesive that can be applied directly without surface treatment.

[0004] Japanese Patent Application No. 2008-31307 discloses a photocurable organosiloxane composition that exhibits good adhesive strength to PET, PBT, PC, ABS, and LCP (liquid crystal polymer). The synthesis method involves a dealcoholization reaction of hydroxyl-terminated polydimethylsiloxane (107 silicone oil) and an aminosilane coupling agent, followed by reaction with 2-isocyanatoethyl methacrylate to form methacryloyloxy-terminated polydimethylsiloxane. Combined with some acrylate monomers compatible with organosilicon, a UV adhesive is formed. The shear strength of PET / PET can reach 2.8 MPa, basically meeting the adhesive strength requirements of most applications. However, the methacryloyloxy-terminated polydimethylsiloxane is very expensive, resulting in a high price for the synthesized methacryloyloxy-terminated polydimethylsiloxane, limiting its use to high-end applications. In addition, this methacryloyloxy-terminated polydimethylsiloxane has a fatal flaw: after long-term storage, it will undergo trace hydrolysis, producing a foul-smelling substance that causes great discomfort to customers during use. Currently, no effective solution has been found. Summary of the Invention

[0005] The purpose of this invention is to provide a photocurable silicone adhesive for materials that are difficult to bond (such as PE, PP, PET, POE, etc.).

[0006] The technical solution to achieve the purpose of this invention is:

[0007] In a first aspect, the present invention provides a photocurable silicone, which is an acrylic acid-modified polydimethylsiloxane, having the following structure:

[0008]

[0009] Where n is an integer from 40 to 2000.

[0010] In a second aspect, the present invention provides a method for synthesizing the photocurable organosilicon described in the first aspect, comprising:

[0011] (1) The step of performing a hydrosilylation reaction with a hydrogen-containing double-ended agent (tetramethyldisiloxane) and allyl glycidyl ether (AGE) in the presence of a platinum catalyst to generate a double-ended agent with an epoxy group at each end.

[0012]

[0013] (2) The step of performing a ring-opening esterification reaction of a bi-terminant containing an epoxy group at each end and excess acrylic acid in the presence of a ring-opening esterification catalyst to obtain a bi-terminant with an acryloyloxy group and a hydroxyl group at each end.

[0014]

[0015] (3) A dual-terminator with one acryloyloxy group and one hydroxyl group at each end is subjected to an esterification and dehydration reaction with excess acrylic acid in the presence of cyclohexane dehydrating agent and acidic catalyst to generate a dual-terminator with two acryloyloxy groups at each end.

[0016]

[0017] (4) The step of reacting a dual-end capping agent containing two acryloyloxy groups at each end with polydimethylsiloxane in the presence of a linear phosphorocyanine chloride catalyst to obtain high molecular weight acrylic acid-modified polydimethylsiloxane, i.e., photocurable organosilicon.

[0018]

[0019] Preferably, in order to prevent acrylic acid from undergoing self-polymerization during the ring-opening esterification and esterification dehydration reactions, a free radical polymerization inhibitor needs to be added in both the ring-opening esterification and esterification dehydration reactions, with the amount added being 0.01% to 1% of the total mass of the reactants.

[0020] Specifically, the free radical polymerization inhibitor is any one or more of p-methoxyphenol (MeHQ), hydroquinone (HQ), and 2,6-di-tert-butyl-4-methylphenol (BHT).

[0021] Preferably, the ring-opening esterification catalyst is selected from tertiary amines and quaternary ammonium salts, commonly including any one of triethylamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, trimethylbenzylammonium chloride, triphenylphosphine, triphenylantimony, chromium acetylacetone, chromium isooctanoate, stannous octoate, and tetraethylammonium bromide, and its amount is 0.1% to 5.0% of the reactants.

[0022] Preferably, the acidic catalyst is selected from any one of concentrated sulfuric acid, sodium bisulfate, methanesulfonic acid, methylbenzenesulfonic acid, trifluoromethanesulfonic acid, strong acid ion exchange resin and solid superacid, and preferably any one of methanesulfonic acid, trifluoromethanesulfonic acid, strong acid ion exchange resin and solid superacid, and its addition amount is 0.1% to 5.0% of the total mass of the reactants.

[0023] Preferably, the amount of linear phosphonium chloride catalyst added is 0.005 to 1.0% of the total reactants.

[0024] Preferably, after the rearrangement reaction is completed, a passivating agent is used to deactivate the linear phosphorocyanine chloride, and the amount of the passivating agent added is 1.1 to 4.0 times the amount of linear phosphorocyanine chloride added.

[0025] Specifically, the passivating agent can be selected from the following: First, amine compounds, such as triethylamine, propylamine, triethylenenonamine, hexamethyldisilazane, hexamethylcyclotrisilazane, etc. Second, lithium salts, such as n-butyllithium in hexane solution, hexamethyldisilazane lithium salt, trimethylsiloxane, and lithium hydroxide in polydimethylsiloxane alkaline gel, etc. Third, epoxy compounds, such as compounds containing one or more epoxy groups in the molecule, such as propylene oxide, glycidyl ether, bisphenol A diglycidyl ether, phenyl glycidyl ether, cyclohexene oxide, etc. Fourth, salts of magnesium, aluminum, calcium, zinc, barium, and sodium, such as magnesium oxide, magnesium carbonate, magnesium hydroxide, aluminum oxide, zinc oxide, barium carbonate, sodium carbonate, etc. Triethylamine and hexamethyldisilazane are preferred.

[0026] Thirdly, the present invention provides a UV adhesive composition for difficult-to-bond materials comprising the photocurable silicone described in the first aspect, comprising, by weight, 100 parts of photocurable silicone, 10 to 80 parts of acrylate monomer and 0.5 to 5.0 parts of free radical photoinitiator.

[0027] Preferably, the acrylate monomer is selected from any one or two of isobornyl acrylate (IBOA), cyclohexyl acrylate, tetrahydrofuran acrylate (THFA), tricyclodecyl acrylate, dicyclopentadiene acrylate, acrylmorpholine (ACMO), and N,N-dimethylacrylamide (DMAA), with isobornyl acrylate, tetrahydrofuran acrylate (THFA), acrylmorpholine (ACMO), and N,N-dimethylacrylamide (DMAA) being more preferred.

[0028] Preferably, the free radical photoinitiator is selected from one or more of the following: 2-hydroxy-2-methylphenylpropanone (Darocure 1173), 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), ethyl 2,4,6-trimethylbenzoylphenylphosphonate (TPO-L), a mixture of 2,4,6-trimethylbenzophenone and 4-methylbenzophenone, benzoin dimethyl ether, benzophenone (BP), 1-hydroxy-cyclohexylbenzophenone, α,α′-ethoxyacetophenone (DEAP), or α-aminealkylbenzophenone.

[0029] Preferably, considering water resistance, the UV adhesive composition of the aforementioned difficult-to-bond materials may also contain various epoxy silane coupling agents, titanate coupling agents, zirconate coupling agents, aluminate coupling agents, etc.

[0030] Preferably, the UV adhesive composition of the difficult-to-bond material further includes hydrophobic fumed silica.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] (1) This invention uses a linear phosphorocyanine chloride catalyst to rearrange polydimethylsiloxane with bisacryloyloxy-terminated polydimethylsiloxane in the presence of the linear phosphorocyanine chloride catalyst to obtain high molecular weight photocurable organosilicon. The reaction conditions are mild and the reaction rate is relatively fast. No siloxane rings are generated during the entire reaction process, and the volatile matter is minimal. This effectively solves the problems of low target product activity, low content of effective components, low-boiling-point residues, and excessive rings in traditional acid-catalyzed equilibrium reactions. It also eliminates the cumbersome process of high vacuum and nitrogen purging for long-term high-temperature devolvation in the later stages of the reaction.

[0033] (2) The photocurable silicone adhesive composition of the present invention has excellent bonding strength to low surface energy materials (such as PE, PP, PET, POE, etc.). Detailed Implementation

[0034] The present invention will now be described in detail with reference to the embodiments.

[0035] One effective method for attaching (meth)acryloyloxy groups to both ends of polydimethylsiloxane is to use a hydrosilylation reaction. First, hydrosilylation is performed on a hydrogen-terminated silicone oil and a bifunctional compound with allyl and epoxy or hydroxyl groups to generate a polydimethylsiloxane with terminal epoxy or hydroxyl structures. Then, the polydimethylsiloxane with terminal epoxy or hydroxyl structures is reacted with (meth)acrylic acid to introduce (meth)acryloyloxy groups into the end groups of the polydimethylsiloxane, giving it photocurable properties.

[0036] The purpose of this invention is to incorporate two acryloyloxy functional groups at each end of a polydimethylsiloxane, thereby improving its photocurability compared to polydimethylsiloxanes with only one acryloyloxy group at each end. Especially for high molecular weight polydimethylsiloxanes, if there is only one acryloyloxy group at each end, the photocurability is weak due to the very low proportion of photocurable functional groups. Having two acryloyloxy groups at each end significantly improves photocurability, resulting in higher crosslinking density and correspondingly greater adhesive strength.

[0037] If high-molecular-weight terminal hydrogen silicone oil (with extremely low hydrogen content) is used directly as the initial reactant and allyl glycidyl ether (AGE) to synthesize high-molecular-weight terminal functional organosilicon oligomers, the low SiH content leads to incomplete hydrosilylation, meaning fewer active substances are attached to the end groups. This is detrimental to obtaining organosilicon oligomers with good photocurability in the next step. Furthermore, allyl glycidyl ether (AGE) and low-hydrogen silicone oil (i.e., high-molecular-weight terminal hydrogen silicone oil) have poor compatibility, making the reaction difficult. A common industrial method is to synthesize low-molecular-weight terminal active polydimethylsiloxanes via hydrosilylation, followed by chain extension through D4 equilibrium telomerization to obtain high-molecular-weight terminal active polydimethylsiloxanes. However, this method suffers from drawbacks such as low equilibrium conversion, the need to remove low-boiling-point residues and small-molecule rings after the reaction, poor yield, and complex processes.

[0038] The synthesis method of this invention first synthesizes a bisacryloyloxy group, each end-capped with two acryloyloxy groups, and then reacts it with polydimethylsiloxane in the presence of a linear phosphorocyanine chloride catalyst to obtain a high molecular weight photocurable polydimethylsiloxane. Throughout the reaction process, no siloxane rings are formed, and the volatile matter is minimal, effectively solving the problems of low target product activity, low effective component content, low-boiling-point residues, and excessive rings in traditional acid-catalyzed equilibrium reactions. After the reaction, a passivating agent is used to deactivate the linear phosphorocyanine chloride.

[0039] The synthesized photocurable silicone, combined with acrylate monomers, free radical photoinitiators, coupling agents, and hydrophobic fumed silica, forms a UV adhesive with excellent adhesion strength to low surface energy materials.

[0040] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0041] The following section details the synthesis and formulation examples of photocurable polydimethylsiloxane.

[0042] Synthesis of epoxy-based double-ended agents.

[0043] 160g of allyl glycidyl ether (AGE) and 0.01g of chloroplatinic acid were added to a three-necked glass flask equipped with an oil bath and condenser. The mixture was stirred and heated to 70°C. 100g of hydrogen-containing double-ended head (1,1,3,3-tetramethyldisiloxane) was added dropwise over one hour. The mixture was then heated to 80°C and the reaction was continued for 4 hours. The unreacted hydrogen-containing double-ended head was removed under vacuum to obtain a colorless and transparent double-ended head agent with an epoxy group at each end (referred to as epoxy double-ended head agent), with a molecular weight of 362.7.

[0044] Synthesis of hydroxyacryloyloxy bicapsulant.

[0045] 100g of epoxy-based double-ended agent, 0.5g of triethylamine, and 0.05g of MeHQ free radical polymerization inhibitor were added to a three-necked glass flask equipped with an oil bath and condenser. The mixture was stirred and heated to 70°C, and 50g of acrylic acid was added dropwise over one hour. The temperature was then raised to 80°C and the reaction continued for 6 hours. Excess sodium carbonate was added to neutralize the residual acrylic acid and triethylamine. The precipitate was filtered, washed with water several times, and then vacuum dried to obtain a pale yellow, transparent double-ended agent containing one hydroxyl group and one acryloxy group at each end (referred to as hydroxyacryloyloxy double-ended agent), with a molecular weight of 506.8.

[0046] Synthesis of bisacryloyloxy dicapping agent.

[0047] In a three-necked glass flask equipped with an oil bath and condenser, 100g of hydroxyacryloyloxy dual-heading agent, 0.05g of MeHQ free radical inhibitor, 0.05g of BHT free radical inhibitor, 0.5g of trifluoromethanesulfonic acid, and 100g of cyclohexane dehydrating agent were added. The mixture was stirred and heated to 85°C under reflux. 35g of acrylic acid was added dropwise, completing the addition within one hour. The water carried over was periodically released using a separatory tube. The amount of water retained in the separatory tube was carefully observed until no more excess water was distilled off, indicating that the reaction was complete. The mixture was cooled to room temperature, and excess sodium carbonate was added to neutralize the residual acrylic acid and trifluoromethanesulfonic acid. The precipitate was filtered, washed repeatedly with water, and then vacuum dried to obtain a pale yellow, transparent dual-heading agent containing two acryloyloxy groups at each end (referred to as bisacryloyloxy dual-heading agent), with a molecular weight of 614.9.

[0048] Example 1 of the synthesis of modified organosilicon.

[0049] 85g of polydimethylsiloxane with a viscosity of 1000 mPas and 0.1g of linear phosphonium chloride catalyst were added to a three-necked glass flask equipped with an oil bath and condenser. Under nitrogen protection, the mixture was stirred and heated to 80°C. 10g of bisacryloyloxy dual-end-capping agent was gradually added dropwise, completing the addition within one hour. The temperature was then raised to 110°C and the reaction continued for 4 hours. After cooling to room temperature, 0.2g of triethylamine passivating agent was added to obtain a colorless, transparent polydimethylsiloxane containing two acryloyloxy groups at each end, i.e., a photocurable organosilicon with a molecular weight of approximately 6520. This product was named Modified Organosilicon Synthesis Example-1.

[0050] Example 2 of modified organosilicon synthesis.

[0051] 1000g of polydimethylsiloxane with a viscosity of 500mPas and 0.5g of linear phosphorocyanine chloride catalyst were added to a three-necked glass flask equipped with an oil bath and condenser. The mixture was stirred and heated to 80°C, and 19g of bisacryloyloxy group-capping agent was gradually added dropwise over half an hour. The temperature was then raised to 110°C and the reaction continued for 4 hours. After cooling to room temperature, 1.0g of hexamethyldisilazane passivating agent was added to obtain a colorless and transparent polydimethylsiloxane containing two acryloyloxy groups at each end, i.e., a photocurable organosilicon with a molecular weight of approximately 36900. The product was named Modified Organosilicon Synthesis Example-2.

[0052] The UV adhesive composition was prepared by combining the above-prepared photocurable silicone with acrylate monomers, etc. The specific formulation is shown in Table 1.

[0053] Table 1

[0054] Example 1 of the synthesis of modified organosilicon 100 100 Example 2 of modified organosilicon synthesis 100 100 100 Baojun Chemical 2900 100 Zhongshan Qianyou 3001 100 100 BOA 40 40 40 30 40 40 40 DMAA 5 5 5 ACMO 5 5 5 5 THFA 5 10 5 TS720 20 25 20 15 R972 20 15 15 15 Darocure1 173# 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 TPO-L 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 KBM403 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 KBM5103 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Shear strength (MPa) PE / PE 1.0 1.5 1.2 1.5 0.4 0.3 0.4 0.5 PP / PP 17 2.7 2.9 2.6 1.1 0.5 0.9 1.0 PET / PET 2.0 3.4 3.8 3.5 1.0 2.5 2.7 2.6 POE / POE 3.1 4.2 4.3 4.4 0.9 0.9 1.1 1.2

[0055] Note: TS720 is Cabot's hydrophobic silica (USA); R972 is Evonik's hydrophobic silica (Germany); KBM403 is Shin-Etsu γ-glycidyl etheroxypropyltrimethoxysilane (Japan); KBM5103 is Shin-Etsu 3-(acryloyloxy)propyltrimethoxysilane (Japan); Baojun Chemical 2900 is a polyurethane-type acrylate oligomer with good adhesion strength to PET film; Zhongshan Qianyou 3001 is a polyurethane-type acrylate oligomer with good adhesion strength to PET film; IBOA is isobornyl acrylate; DMAA is N,N-dimethylacrylamide; ACMO is acrylmorpholine; THFA is tetrahydrofuran acrylate; PE is polyethylene; PP is polypropylene; PET is polyethylene terephthalate; POE is polyolefin elastomer.

[0056] Preparation of shear strength test specimens: The test specimens were wiped with alcohol to remove surface oil and dust. After adhesive application and bonding, they were fixed with butterfly clips, and then cured with ultraviolet light. The ultraviolet irradiation dose was 1000 mJ / cm on both sides. 2 The shear strength was tested after being placed at room temperature for 30 minutes, and the test method was in accordance with GB / T 7124-2008.

[0057] According to Table 1, comparative examples 1-4 show that the UV-curable silicone adhesive of the present invention, formulated with acrylate monomers, exhibits good adhesion strength to PE, PP, PET, POE, etc. Comparative Example 1, using only UV-curable polydimethylsiloxane without acrylate monomers, shows lower adhesion strength. Comparative Examples 2-4 use commercially available UV adhesives formulated with polyurethane acrylate oligomers that exhibit good adhesion strength to PET films. While these adhesives show good adhesion to PET films, their adhesion strength to low surface energy materials such as PE, PP, and POE is very low, failing to meet practical application requirements.

Claims

1. A UV adhesive composition for difficult-to-bond materials, characterized in that, By weight, it comprises 100 parts of photocurable silicone, 10-80 parts of acrylate monomer and 0.5-5.0 parts of free radical photoinitiator; Photocurable silicone has the following structure: ； Where n is an integer from 40 to 2000; Photocurable silicone is prepared using the following steps: (1) The step of performing a hydrosilylation reaction with hydrogen-containing double-ended agents and allyl glycidyl ether in the presence of a platinum catalyst to generate a double-ended agent with an epoxy group at each end. ； (2) The step of performing a ring-opening esterification reaction of a bi-terminant containing an epoxy group at each end and excess acrylic acid in the presence of a ring-opening esterification catalyst to obtain a bi-terminant with an acryloyloxy group and a hydroxyl group at each end. ； (3) A dual-terminator with one acryloyloxy group and one hydroxyl group at each end is subjected to an esterification and dehydration reaction with excess acrylic acid in the presence of cyclohexane dehydrating agent and acidic catalyst to generate a dual-terminator with two acryloyloxy groups at each end. ； (4) The step of reacting a dual-end capping agent containing two acryloyloxy groups at each end with polydimethylsiloxane in the presence of a linear phosphazene chloride catalyst to obtain high molecular weight acrylic acid-modified polydimethylsiloxane, i.e., photocurable organosilicon. 。 2. The UV adhesive composition for difficult-to-bond materials as described in claim 1, characterized in that, Free radical polymerization inhibitors were added in both the ring-opening esterification and esterification dehydration reactions, with the amount added being 0.01% to 1% of the total mass of the reactants.

3. The UV adhesive composition for difficult-to-bond materials as described in claim 1, characterized in that, The ring-opening esterification catalyst is selected from any one of tertiary amines, quaternary ammonium salts, triphenylphosphine, triphenylantimony, chromium acetylacetone, chromium isooctanoate, and stannous octoate.

4. The UV adhesive composition for difficult-to-bond materials as described in claim 1, characterized in that, The ring-opening esterification catalyst is selected from any one of triethylamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, trimethylbenzylammonium chloride, and tetraethylammonium bromide.

5. The UV adhesive composition for difficult-to-bond materials as described in claim 1, characterized in that, The acid catalyst is selected from any one of concentrated sulfuric acid, sodium bisulfate, methanesulfonic acid, methylbenzenesulfonic acid, trifluoromethanesulfonic acid, strong acid ion exchange resin and solid superacid, and its addition amount is 0.1% to 5.0% of the total mass of the reactants.

6. The UV adhesive composition for difficult-to-bond materials as described in claim 1, characterized in that, The acid catalyst is selected from any one of methanesulfonic acid, trifluoromethanesulfonic acid, strong acid ion exchange resin, and solid superacid.

7. The UV adhesive composition for difficult-to-bond materials as described in claim 1, characterized in that, After the rearrangement reaction is completed, a passivating agent is used to deactivate the linear phosphazene chloride.

8. The UV adhesive composition for difficult-to-bond materials as described in claim 1, characterized in that, The acrylate monomer is selected from any one or two of isobornyl acrylate, cyclohexyl acrylate, tetrahydrofuran acrylate, tricyclodecyl acrylate, and dicyclopentadiene acrylate.

9. The UV adhesive composition for difficult-to-bond materials as described in claim 1, characterized in that, The acrylate monomer is selected from any one or two of isobornyl acrylate and tetrahydrofuran acrylate.

10. The UV adhesive composition for difficult-to-bond materials as described in claim 1, characterized in that, The free radical photoinitiator is selected from one or more of 2-hydroxy-2-methylphenylpropanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, a mixture of 2,4,6-trimethylbenzophenone and 4-methylbenzophenone, benzoin dimethyl ether, benzophenone, 1-hydroxy-cyclohexylbenzophenone, α,α-diethoxyacetophenone and α-aminealkylbenzophenone.

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