WO2019037016A1

WO2019037016A1 - Silicone polymeric photoinitiator and uses thereof

Info

Publication number: WO2019037016A1
Application number: PCT/CN2017/098789
Authority: WO
Inventors: Bo Xu; Yuxia Liu; Matthew AHEARN; Wenjuan Tan
Original assignee: Henkel IP & Holding GmbH; Henkel Ag & Co. Kgaa
Priority date: 2017-08-24
Filing date: 2017-08-24
Publication date: 2019-02-28
Also published as: KR20200044732A; TW201920302A; JP2020531594A

Abstract

Silicone polymeric photoinitiators formed by covalently bonding polysiloxane polymers with terminal or pedant photobleachable photoinitiator moieties are disclosed. The liquid silicone optically clear adhesive compositions containing the silicone polymeric photoinitiators are particularly suitable for sealing and bonding cover glasses, touch panels, and polarizers in display devices.

Description

SILICONE POLYMERIC PHOTOINITIATOR AND USES THEREOF

FIELD OF THE INVENTION

The invention relates to silicone polymeric photoinitiators suitable for optically clear silicone based coating and adhesives. The silicone polymeric photoinitiator are particularly suitable in optical display applications, e.g., LCD displays, LED displays, touch screens.

BACKGROUND OF THE INVENTION

There is a growing demand for optical display applications for smarter phones, mobile devices, automobile displays, outdoor displays, flexible and foldable displays, and wireless reading devices. Optically clear adhesives, both as film (OCA) and in liquid (LOCA) , are silicone-based adhesives that bond substrate layers in optical display applications, such as transparent cover, touch panel, diffuser, rigid compensator, heater, polarizer, retarder, and the like, in an optical display device. In addition to bond these substrates together, the OCA or LOCA fills the air gaps between the various layers and improves image quality and display durability.

The LOCA faces numerous challenges. One key challenge is compatibility of most commercial photoinitiators that are not soluble in silicone-based adhesive compositions. Incorporating commercial photoinitiators in silicone-based adhesives will reduce light transmittance and cause haze of the LOCA films. This phenomenon becomes exacerbated with heat and humidity. Also, curing the LOCA film with UV light becomes problematic since transparent plastic like PET films and UV filter films block some UV radiation, particularly at less than about 400 nm wavelengths. However, traditional none-photobleachable red-shifted photoinitiators generate color fragments after UV photolysis, and as a result, the LOCA is no longer optically colorless.

Some efforts have been made to provide silicone-based coatings and adhesives with soluble or compatible photoinitiators. For example, U.S. Patent Nos. 4,534,838 and 4,536,265 disclose organopolysiloxane photoinitiators having an average of at least two siloxane units. However, the organopolysiloxane photoinitiator does not have any UV absorbance above 400nm, and is unable to UV cure through PET films or other plastic cover films.

U.S. Patent No 4,507,187 discloses a polyorganosiloxane photoinitiators containing aryoyl formate photomoieties bonded to silicone via non-hydrolyzable Si-C bonds. While they are effective photoinitiators for photocurable silicone resins and for ethylenically unsaturated monomers, they are not photobleachable. The color fragments after photolysis is not acceptable to display applications.

Similarly, WO 2004/108799 discloses a polyorganosiloxane polymeric photoinitiators with methylene group in between two oxygens. Again, these photoinitiators are not photobleachable.

WO 2011/053615 discloses silane and siloxane containing photochromic materials that include an indeno-fused naphthopyran photochromic compound. The photochromic materials improve compatibility with urethane coating compositions； however, they generate a strong color fragment of indeno-fused naphthopyran after photolysis.

U.S. Patent No. 6,399,805 discloses photobleachable photoinitiators, bisacylphosphine oxides (BAPO) and monoacylphosphine oxides (MAPO) . These photoinitiators are not compatible with silicone adhesive compositions.

J. Organomet. Chem. 2004, 689, 3258-3264 and CN103333276 disclose an alkoxysilane containing long-wave-absorbing photoinitiator； however, silanes are not compatible with silicone-based adhesive compositions, and they form a hazy mixture.

Therefore, there is a need in the art for photobleachable photoinitiators that are fully compatible to silicone optically clear adhesive compositions without any haze and color, and that are fully transparent to visible light after photolysis and after aging at high temperature and high humidity conditions. The current invention fulfills this need.

BRIEF SUMMARY OF THE INVENTION

The invention provides polymeric photoinitiators compatible with silicone-based adhesive or coating compositions. The polymeric photoinitiators are useful in optical devices, particularly to seal and adhere various substrates. The cured composition enhances light transmission and optical efficiency for a prolonged time in a wide range of temperatures, and provides adhesive bonding between layers in display devices.

One aspect of the invention is directed a photoinitiator having a structural formula:

where,

each M is independently, alkyl, aryl, alkoxy, H, vinyl, or combination thereof；

each R is independently alkyl, aryl, fluoroalkyl, trialkylsiloxy, triarylsiloxy, or combination thereof；

X is a linear, cyclic, or branched link having a divalent alkylene, arylene, oxyalkylene, oxyarylene, ester, imide, amide, alcohol, carbonate, urethane, urea, sulfide, ether, or a derivative or combination thereof；

Y is alkyl, aryl, alkoxy, benzoxy, acyl or benzoyl；

Z is alkyl or aryl；

N and Q are different and is independently alkyl, aryl, trialkylsiloxy, triarylsiloxy, alkoxy, amine, ester, epoxy, acrylate, methacrylate, H, vinyl, or derivative thereof；

n ≥ 1；

m, q, r ≥ 0 and

the average molecular weight (Mw) of the polymeric photoinitiator is from 100 to 300,000 g/mol.

Another aspect of the invention is directed a polymeric photoinitiator having a structural formula:

where,

wherein,

R and R’are independently alkyl, or aryl；

N and Q are independently alkyl, aryl, fluoroalkyl, alkoxy, benzoxy, or H；

X is a linear, cyclic, or branched link comprising alkylene, arylene, oxyalkylene, oxyarylene, ester, imide, amide, alcohol, carbonate, urethane, urea, sulfide, ether or a derivative or combination thereof；

Y is alkyl, aryl, alkoxy, benzoxy, acyl, or benzoyl；

Z is alkyl or aryl；

m and n are independently ≥ 1； and

the weight average molecular weight (Mw) of the polymeric photoinitiator is from 100 to 300,000 g/mol.

Another aspect of the invention is directed to the method of preparing a polymeric photoinitiator, including the steps of reacting a monoacylphosphinic acid (MAPO acid) , and/or (meth) acrylic acid with epoxy polydimethylsiloxane polymers comprising either pedant or terminal epoxy functional group to produce the silicone polymeric photoinitiator.

Another aspect of the invention is directed to the method of preparing a polymeric photoinitiator. A silane modified monoacylphosphate (MAPO-TMS) is reacted with a sinanol terminated polysiloxane polymer in the presence of an acid or base catalyst to produce the terminal silicone polymeric photoinitator.

Yet another aspect of the invention is directed to the method of preparing a polymeric photoinitiator. A allyl modified monoacylphosphate (MAPO-TMS) is reacted with a H terminated polysiloxane polymer in the presence of platinum catalyst to produce the terminal silicone polymeric photoinitator.

Yet another aspect of the invention is directed to a UV curable silicone adhesive composition comprising the silicone polymeric photoinitiator of the above. The adhesive composition may further comprise a (meth) acryloxyalkyl terminated siloxane polymer and/or a (meth) acryloxyalkyl alkoxy functional silane. The cured adhesive has a transmittance, measured in accordance with ASTM E903 at 500nm, of greater than 90％.

In another aspect, the invention is directed to an article comprising the silicone polymeric photoinitiator of the above. The article is a display panel, touch panel or other optical device.

In a further aspect, the invention is directed to a method of making an electronic device comprising the steps of: (1) preparing a first substrate； (2) preparing a UV curable silicone adhesive composition comprising the polymeric photoinitiator of the above； (3) coating the adhesive composition onto the first substrate； (4) laminating a second substrate onto the coating at room temperature； and (5) curing the adhesive composition by UV light through one of the two substrates at 380-410nm.

These and other aspects of the invention are described in the detailed description below. In no event should the above summary be construed as a limitation on the claimed subject matter which is defined solely by the claimed as set forth herein.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 is a graph of UV-vis absorbance versus wavelength of the polymeric photoinitiators Example 3 and the epoxy functional PDMS starting material.

Figure 2A is a GPC refractive index (RI) chromatogram of the polymeric photoinitiator Example 3 and the epoxy functional PDMS starting material.

Figure 2B is a GPC UV chromatogram of the polymeric photoinitiator Example 3 and the epoxy functional PDMS starting material.

DETAILED DESCRIPTION OF THE INVENTION

All documents cited herein are incorporated in their entireties by reference. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention.

As used herein, the term "alkyl" refers to a monovalent linear, cyclic or branched moiety containing C1 to C24 carbon and only single bonds between carbon atoms in the moiety and including, for example, methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, heptyl, 2, 4, 4-trimethylpentyl, 2-ethylhexyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-hexadecyl, n-octadecyl and n-eicosyl.

As used herein, the term "aryl" refers to an monovalent unsaturated aromatic carbocyclic group of from 6 to 24 carbon atoms having a single ring (e.g., phenyl) or multiple condensed (fused) rings, wherein at least one ring is aromatic (e.g., naphthyl, dihydrophenanthrenyl, fluorenyl, or anthryl) . Preferred examples include phenyl, methyl phenyl, ethyl phenyl, methyl naphthyl, ethyl naphthyl, and the like.

As used herein, the term "alkoxy" refers to the group -O-R wherein R is alkyl as defined above.

As used herein, the term "alkylene" refers to a divalent linear, cyclic or branched moiety containing only single bonds between carbon atoms in the moiety and including, for example, methylene, ethylene, propylene, isopropylene, n-butylene, sec-butylene, isobutylene, tert-butylene, n-pentylene, n-hexylene, n-heptylene, 2, 4, 4-trimethylpentylene, 2-ethylhexylene, n-octylene, n-nonylene, n-decylene, n-undecylene, n-dodecylene, n-hexadecylene, n-octadecylene and n-eicosylene.

As used herein, the term "arylene" refers to a divalent unsaturated aromatic carbocyclic group of from 6 to 20 carbon atoms having a single ring (e.g., phenylene) or multiple condensed (fused) rings, wherein at least one ring is aromatic (e.g., naphthylene, dihydrophenanthrenylene, fluorenylene, or anthrylene) . Preferred examples include phenylene, naphthylene, phenantrenylene and the like.

As used herein, the term " (meth) acryloxy group" represents both acryloxy and methacryloxy group.

As used herein, the above groups may be further substituted or unsubstituted. When substituted, hydrogen atoms on the groups are replaced by substituent group (s) that is (are) one or more group (s) independently selected from alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, cycloalkynyl, aryl, heteroaryl, heteroalicyclyl, aralkyl, heteroaralkyl, (heteroalicyclyl) alkyl, hydroxy, protected hydroxyl, alkoxy, aryloxy, acyl, ester, mercapto, alkylthio, arylthio, cyano, halogen, carbonyl, thiocarbonyl, O-carbamyl, N-carbamyl, O-thiocarbamyl, N-thiocarbamyl, C-amido, N-amido, S-sulfonamido, N-sulfonamido, C-carboxy, protected C-carboxy, O-carboxy, isocyanato, thiocyanato, isothiocyanato, nitro, trialkylsilyl, triarylsily, trialkylsiloxy, triarylsiloxyl, sulfenyl, sulfinyl, sulfonyl, haloalkyl, haloalkoxy, trihalomethanesulfonyl, trihalomethanesulfonamido, and amino, including mono-and di-substituted amino groups, and the protected derivatives thereof. In case that an aryl is substituted, substituents on an aryl group may form a non-aromatic ring fused to the aryl group, including a cycloalkyl, cycloalkenyl, cycloalkynyl, and heterocyclyl.

All percentages, parts and ratios are based upon the total weight of the compositions of the present invention, unless otherwise specified. All such weights as they pertain to listed ingredients are based on the active level and, therefore, do not include carriers or by-products that may be included in commercially available materials.

As used herein, a polymer or an oligomer is a macromolecule that consists of monomer units greater than about 5 monomer units. Polymer and oligomer, or polymeric and oligomeric, are used interchangeably here in the invention.

As used herein, the term “optically clear” or “optical clarity” refers to transmission of a film of 90％or greater measured in accordance with ASTM E903 at 500nm.

As used herein, the terms “optically clear adhesive, ” and “OCA, ” used interchangeably, refer to an adhesive that has optical clarity. The term OCA is well established in the art. OCA films are usually cast as a film, optically clear adhesive film.

As used herein, the terms “liquid optically clear adhesive, ” and “LOCA, ” used interchangeably, refer to a liquid adhesive that has optical clarity. The term LOCA is well established in the art.

As used herein, the terms “display device” and “electronic device, ” used interchangeably, refer to an article that has various components such as, inks, print circuits or active light emitting layers in between a cover front sheet and a substrate back sheet, and operates by manipulating the flow of electrons, e.g., displays, including flexible and foldable displays, automobile displays, outdoor displays, LCD displays, LED displays； touchscreens； mobile phone； tablet PC； TV； notebook PC； digital camera； photo frame； car navigation； and the like.

The invention provides the art with a novel class of polymeric photoinitiators that have good solubility and compatibility in silicone OCA and LOCA compositions, and improve optical properties like low haze and high percent T (％T) under 1000-hour aging conditions of QUV, QSun, and high temperature and high humidity. The polymeric photoinitiators comprise both polysiloxane polymer backbone chain with photoinitiator moiety. In particular, the polymeric photoinitiator provides polysiloxane polymers having photoinitiator moiety as the pedant or terminal groups covalently linked to the polymer chains.

Various photoinitiator moieties may be used to form the polymeric photoinitiator. Examples include benzophenone and derivatives, acetophenone and derivatives, acylphosphine oxide and derivatives, benzoin ether derivatives, anthraquinone, thioxanthone, triazine or fluorenone derivatives, and the like. In general, UV photoinitiators may be divided into Norrish Type I and Type II photoinitiators. For the purposes of the invention, the Norrish type I photoinitiators also include those where instead of the carbonyl group another functional group is present and where cleavage relates to the bond between this group and an α carbon atom. The Type I initiators include aromatic carbonyl compounds, such as benzoin derivatives, benzil ketals and acetophenone derivatives. The Type II photoinitiators include aromatic ketones, such as benzophenone, benzil and thioxanthones. The Norrish Type II photoinitiators break down on exposure to light in accordance with Norrish Type II reaction with hydrogen abstraction； this is an intramolecular reaction. In the case of aliphatic ketones, a hydrogen may be eliminated from the γ-position to one corresponding to the functional group shown above. Furthermore, there also exist photoinitiators based on triazine, hexaarylbisimidazole, and dye. Many Norrish type I photoinitiators exhibit photobleaching, in which the absorbance decreases with illumination time when exposed to proper wavelength. This occurs because the absorption characteristics of the photolysis products are different than the original initiator molecule. Two classes of α-cleavable photoinitiators for which photobleaching is particularly pronounced are aryl phosphine oxides in the 365 nm region of the spectrum, and substituted titanocenes in the 450 nm region. Photobleaching is particularly important for photopolymerization of thick polymer parts and pigmented coatings.

While both Norrish types of photoinitiator can be used for the polymeric photoinitiator in the invention, the photoinitiators preferred in the invention are those, which on exposure to light, decompose in accordance with a Norrish Type I reaction, where the photo fragmentation of a carbonyl compound of the photoinitiator produces an acyl radical and an alkyl radical. In particular, the photoinitiators preferred in the invention are those that exhibit photobleaching properties.

In one embodiment, Si LOCA is cured through an optical clear cover sheet or front sheet, and the photoinitiator must be capable of absorbing radiation at wavelengths for which the cover or substrate sheets are transparent. For example, if an adhesive is to be cured through a sodalime glass coverplate, the photoinitiator must have significant UV absorbance above 320 nm. UV radiation below 320 nm will be absorbed by the sodalime glass coverplate and cannot reach the photoinitiator in the adhesive films. If an adhesive is to be cured through a PET film with cut-off absorbance at 400nm and below, the photoinitiator must have UV absorbance above 400 nm or include a red shifted photosensitizer. In one embodiment, the photoinitiator moieties of the polymeric photoinitiators are acyl phosphine oxides. Examples of the acyl phosphine oxides are monoacyl phosphine oxides (MAPO) and bis (acyl) phosphine oxides (BAPO) . While MAPO and BAPO can be incorporated though chemical modification into the polymeric photoinitiators, commercially available photoinitiators can also be incorporated through chemical modification. Such commercially available photoinitiators include

819,

TPO (2, 4, 6-trimethylbenzoyldiphenylphosphine oxide) ,

TPO-L (ethyl 2, 4, 6-trimethylbenzoylphenyl phosphinate) , available from BASF.

Polysiloxane polymers useful as a polymeric component in the polymeric photoinitiators of the invention are also compatible with LOCA compositions. In general, such polysiloxane polymers are polydiorganosiloxane polymers having α, ω-endcapped functional group of hydroxy (silanol) , alkoxy, hydride, vinyl, amine, epoxy, (meth) acryloxyalkyl, or mixtures thereof, wherein the polydiorganosiloxane polymers are those having at least two monomer units of (RR’S iO) , wherein R and R’a re independently alkyl or aryl. Preferred polydiorganosiloxane polymers are polydimethylsiloxane polymers (PDMS) with endcapped functional groups of hydroxy, alkoxy, hydride, vinyl, amine, epoxy, (meth) acryloxyalkyl, or a mixture thereof.

Another useful polydiorganosiloxane polymers as the polymeric backbone in the polymeric photoinitiator of the invention include polydialkylsiloxane, polydiaryysiloaxane, and polyalkylarylsiloaxane having some of organic substitutes R or R’of the monomeric unit (RR’S iO) being replaced with vinyl, hydride, alkoxy, fluoroalkyl, aminoalkyl, epoxyalkyl, (meth) acryloxyalkyl, or a mixture thereof. A preferred example of such polymers include polydimethylsiloxane polymers (PDMS) with some of the monomer units containing pedant functional groups of hydride, alkoxy, epoxyalkyl, or (meth) acryloxyalkyl, or a mixture thereof.

The chemical structure of the polysiloxane polymers in the backbone comprises pendant UV or moisture curable functional groups, such as (meth) acrylic C＝C, alkoxy Si (OR) 4-n, or a mixture thereof. These functional groups undergo further crosslinking during the silicone OCA or LOCA curing process in the presence of UV light or moisture, which decreases bleeding out of the photoinitiator from the polymer resin. In addition, the presence of amine and epoxy functional groups in the polymeric photoinitiator further enhances the adhesion of silicone OCA or LOCA to various substrates in the display devices.

The chemical covalent spacer between the polysiloxane backbone and the photoinitiator moiety is chosen to minimize any interference of the decomposition of photoinitiator moiety upon UV irradiation. Also, the spacer should not affect the thermal stability of the polymeric photoinitiators. Useful spacer include linear, cyclic, or branched organic moieties and have the chemical structures of divalent alkylene, arylene, oxyalkylene, oxyarylene, carbonate, carbamate, urea, or a derivative or combination thereof.

One aspect of the invention is directed a photoinitiator with the structural formula:

where,

each M is independently, alkyl, aryl, fluoroalkyl, alkoxy, H, vinyl, or combination thereof；

each R is independently alkyl, aryl, trialkylsiloxy, triarylsiloxy, or combination thereof；

Y is alkyl, aryl, alkoxy, benzoxy, acyl or benzoyl；

Z is alkyl or aryl；

n ≥ 1；

m, q, r ≥ 0 and

In another embodiment, the above polymeric photoinitiator structure has

M is alkyl, aryl, alkoxy, or H；

R is alkyl or aryl；

N is a cycloaliphatic 1, 2-epoxide, 1, 2-propylene oxide, 1, 3-propylene oxide, glycidyl epoxide；

Q is a derivative of an acrylate or methacrylate； and

n, m, q, r ≥ 1.

In one preferred embodiment, the photoinitiator has the following structural formula:

wherein M is independently alkyl, aryl, alkoxy, or H

R is independently, alkyl or aryl

N and Q are a cycloaliphatic 1, 2-epoxide, 1, 2-propylene oxide, 1, 3-propylene oxide, glycidyl epoxide, acrylate, methacrylate, H, or derivative thereof； and

m, n, q and r ≥ 1.

Another aspect of the polymeric photoinitiator has a structure of:

In another embodiment, the photoinitiator has the following structural formula:

where Me is a methyl group.

In another preferred embodiment, the photoinitiator has the following structural formula:

where R is alkyl or aryl, X is a combination of linear, cyclic, or branched link of alkylene and oxyalkylene, n and m ≥ 1.

One preferred embodiments include photoinitiators with the following structural formula:

where Me is methyl, R is alkyl or aryl, n and m ≥ 1.

In another embodiment, the photoinitiator has the following structural formula:

where R is alkyl or aryl, X is a combination of linear, cyclic, or branched link of alkylene and oxyalkylene, m, n and q ≥ 1.

Preferred embodiments include photoinitiators with the following structural formulas:

where M is independently alkyl, aryl, alkoxy, or H

R is independently, alkyl or aryl；

N is a cycloaliphatic 1, 2-epoxide, 1, 2-propylene oxide, 1, 3-propylene oxide, glycidyl epoxide, acrylate, methacrylate, H, or derivative thereof, and

In one embodiment of the invention, the polymeric photoinitiators above have average molecular weight from 100 to 300,000 g/mol.

where,

R and R’are independently alkyl, or aryl；

N and Q are independently alkyl, aryl, alkoxy, benzoxy, or H；

Y is alkyl, aryl, alkoxy, benzoxy, acyl, or benzoyl；

Z is alkyl or aryl；

n and m are independently ≥ 1.

The weight average molecular weight of the polymeric photoinitiator of the above from 100 to 300,000 g/mol.

One preferred polymeric photoinitiators have the following structural formula:

wherein X is a combination of linear, cyclic, or branched link of alkylene and oxyalkylene.

Particularly preferred polymeric photoinitiators have the following structural formula:

Another embodiment of the invention is directed to the method of making the polymeric photoinitiators. Monoacylphosphinic acid (MAPO acid) , made in accordance to J. Am. Chem. Soc., 1950, 72 (9) , pp 4292–4293, “The Synthesis of Phosphonic and Phosphinic Acids” , Gennady M. Kosolapoff, Mar. 2011, by Organic Reactions, Inc., John Wiley &Sons, Inc., or by using other synthetic methods known by those skilled in the art, is reacted with an epoxyalkoxysilane, and forms an intermediate of silane modified monoacylphosphate oxide (MAPO) to produce MAPO-TMS. An example of MAPO acid is benzoylphenyl phosphinic acid. An example of MAPO-TMS is trimethoxysilyl benzoylphenyl phosphinate. The silane modified MAPO-TMS is reacted with sinanol terminated polysiloxane polymer to form a silicone polymeric photoinitator in the presence of an acid or base catalyst. Preferred catalyst has a pKa value equal to or less than -6 or equal to or greater than 15 in a hydrocarbon solvent.

One preferred catalyst is a base catalyst. Examples of the base catalyst are KOH, NaOH, LiOH, organolithium reagents, Grignard reagents, and mixtures thereof. Other catalysts include organometallic salts of metals such as tin, titanium, aluminum, bismuth. Combination of above catalysts can also be used. The preferred organolithium reagents includes an alkyl lithium, such as methyl, n-butyl, sec-butyl, t-butyl, n-hexyl, 2-ethylhexyl and n-octyl lithium. Other useful catalysts include phenyl lithium, vinyl lithium, lithium phenylacetylide, lithium (trimethylsilyl) acetylide, lithium silanolates and lithium siloxanolates. Generally, the amount of lithium in the reaction mixture is from 1 ppm to about 10,000 ppm, preferably from about 5 ppm to about 1,000 ppm based on the weight of the reactants. The amount of the organolithium catalyst used in the catalyst system depends on the reactivity of the silanol group-containing reactant and the reactivity of the alkoxysilane containing the polymerizable ethylenically unsaturated group. The amount chosen may be readily determined by those persons skilled in the art. After the reaction, the organolithium catalyst can be reacted with carbon dioxide, precipitated as lithium carbonate and removed from the reaction mixture by liquid-solid separation means such as centrifuging, filtration and the like.

More specifically, the process for preparing the polymeric photoinitiators includes (1) forming a mixture of a silanol-terminated polydiorganosiloxane polymer, an alkoxysilane having (meth) acryloxy group, and organolithium catalyst, and (2) reacting the mixture with agitation in the absence of moisture until the desired amount of silanol capping has occurred. Where substantially complete capping is desired, the equivalent ratio of silanol groups to alkoxysilane is preferably from about 1 : 0.95 to about 1 : 1.5, and more preferably from about 1: 1 to about 1: 1.2. Any volatile materials remaining in the reaction mixture after the capping has reached the required level can be removed by a mild heating under reduced pressure. An inert gas can be passed through the reaction mixture during the removal of the volatile materials.

In another embodiment, the synthesis of polymeric photoinitiator starts with a reaction of MAPO-acid with epoxy polysiloxane polymers comprising either pedant or terminal epoxy functional group, forming the silicone polymeric photoinitiator. The epoxy polysiloxane polymers can be made according to U.S. Patent Nos. 4,313,988, 6,187,834 or other methods known in the art. Some of the epoxy polysiloxane polymers are also commercial available from Gelest, Dow Corning, Wacker, etc.

Another embodiment of the invention is directed to the method of making the polymeric photoinitiators. Allyl or vinyl modified monoacylphosphinic acid (MAPO acid) , made by reacting MAPO acid with a C3-C24 alkene containing both halogen and C＝C functional groups, is reacted with terminal or pendant hydride (SiH) polysiloxane polymer, under the catalysis of a transition metal complex of Pt, Rh, Ru. The preferred catalyst is platinum meta complex, like Speier's catalyst H₂PtCl₆, or Karstedt’s catalyst, or any alkene-stabilized platinum.

In one embodiment, the preparation of the polymeric photoinitiator is carried out in an organic solvent at about room temperature to the reflux temperature of the organic solvent. Suitable organic solvents or mixtures of solvents are alkanes, such as hexane, heptane, octane, and isooctane； aromatic hydrocarbons, such as toluene, and xylene； esters, such as ethyl, propyl, butyl acetate； halogenated hydrocarbons, such as chlorobenzene, chloroform methylene chloride； alkanols, such as methanol, ethanol, iso-propanol, ethylene glycol, and ethylene glycol monomethyl ether； ethers such as diethyl ether and dibutyl ether； or mixtures thereof. Preferred solvents include hexane, heptane, xylene, toluene, tetrahydrofuran, and mixtures thereof.

In another embodiment, the preparation of silicone polymeric photoinitiator can be carried out in neat at room temperature and up to 150℃.

The suitable range of the molecular weight of the polysiloxane polymers used to make the polymeric photoinitiators in the invention depends upon the desired final properties and contemplated end uses of the silicone OCA or LOCA compositions. The acceptable range of weight average molecular weight (Mw) is from about 100 to about 1,000,000g/mol； the preferably range is from about 500 to about 300,000 g/mol； even more preferable range is from about 1,000 to 100,000g/mol. The average molecular weight is determined by gel permeation chromatography (GPC) , using polystyrene standards.

The polymeric photoinitiator generates free radicals by UV and/or visible light and cures any silicone adhesive compositions containing any free radical reactive functional groups. The term UV curable herein refers to crosslinking, toughening, hardening or vulcanization of the curable portion of the adhesives through actinic radiation exposure. Actinic radiation is electromagnetic radiation that induces a chemical change in a material, including electron-beam curing. In most cases, such radiation is ultraviolet (UV) or visible light. The initiation of radiation cure is achieved through the addition of the photoinitiator. The cure of the adhesive is achieved by direct exposure to ultraviolet (UV) or visible light or by indirect exposure through transparent cover sheet that are made of polyester, polycarbonate, polyimde, glass, and the like. The polymeric photoinitiators of the invention are particularly useful to prepare a wide variety of UV curable silicone pressure sensitive adhesive, ink and coating compositions. More particularly, the polymeric photoinitiators of the invention is useful in silicone OCA and LOCA compositions because the compositions require optically clarity. In fact, the compositions have prolonged stability under high temperature and high humidity conditions, e.g., 85％RH (relative humidity) and 85℃ over 1000 hours.

In another embodiment, the invention provides UV curable silicone LOCA compositions comprising (a) the polymeric photoinitiator of the invention, (b) (meth) acryloxy functional polysiloxane liquid polymers, and (c) optionally, functional silanes as UV crosslinkers, adhesion promoters, and/or chains extenders.

Yet in another embodiment, the invention provides UV and moisture curable silicone LOCA compositions comprising (a) about 0.1 to about 30 ％of the polymeric photoinitiator of the invention； (b) about 60 to about 99.9 ％of a (meth) acryloxy and alkoxy functional polysiloxane polymer having a weight average molecular weight (Mw) of about 100 to about 500,000 g/mol； (c) optionally, up to about 10 ％of a moisture curing catalyst； and (d) optionally, up to 10 ％of silanes as UV crosslinkers, moisture crosslinkers, adhesion promoters, and/or chains extenders.

The components in the above compositions are mixed together at about 10℃ to about 100℃ in a mixer to form the silicone LOCA. The mixer is equipped with a mechanical stirrer, condenser, thermometer, heating mantle, nitrogen inlet, and an addition funnel is charged with components (a) , (b) , (c) , and (d) , and heated up to 100℃. The contents are mixed at 120 rpm under vacuum for about 3 hours, then cooled under vacuum to room temperature.

The amount of polymeric photoinitiator incorporated into the silicone LOCA must be sufficient to provide enough reactive and cure speed to crosslink and maintain an excellent balance of optical properties over aging. This amount depends on the compositions, the source of radiation, the dosage of radiation, and the thickness of the adhesive coating on the substrate. In general, this amount will be in the range of about 0.001, preferably from about 0.1 to about 30％by weight in the silicone LOCA compositions.

The (meth) acryloxyalkyl or (meth) acryloxyalkyl alkoxy functional polysiloxane polymers may be (meth) acryloxyalkyl or (meth) acryloxyalkyl alkoxy terminated or pendant polydiorganosiloxane polymers. A preferred (meth) acryloxyalkyl or (meth) acryloxyalkyl alkoxy functional silicone polymers are (meth) acryloxyakyl or (meth) acryloxyalkyl alkoxy terminated polydiorganosiloxane polymers having α, ω-endcapped RR’_nR”_2-nSiO groups, wherein R is (meth) acryloxyethyl, or (meth) acryloxypropyl, R’is alkoxy, and R”is alkyl and 0≤ n ≤2. In a preferred embodiment, the (meth) acryloxyalkyl alkoxy terminated polysiloxane polymer is polydimethylsiloxane with terminal functional groups of (meth) acryloxypropyldimethoxysilyl, (meth) acryloxypropylmethylmethoxysilyl, (meth) acryloxyethyldimethoxysilyl, (meth) acryloxyethylmethylmethoxysilyl, or mixtures thereof. A particularly preferred (meth) acryloxyalkyl alkoxy terminated polysiloxane polymer is methacryloxypropyldimethoxy terminated PDMS. The average weight molecular weight of the (meth) acryloxyalkyl or (meth) acryloxyalkyl alkoxy functional polysiloxane polymers ranges from about 100 to 300,000 g/mol. The (meth) acryloxyalkyl or (meth) acryloxyalkyl alkoxy functional polysiloxane polymers are available from Henkel Corporation, or made in accordance with U.S. Patent Nos. 5,300,608 and 6,140,444.

The addition of the moisture curing catalyst initiates moisture curing of the LOCA adhesive composition in the presence of moisture. The moisture curing catalysts include metal and non-metal catalysts. Examples of the metal portion of the metal catalysts useful in the present invention include tin, titanium, zirconium, lead, iron cobalt, antimony, manganese, bismuth and zinc compounds. In one embodiment, the tin compounds useful for facilitating the moisture curing of the composition include but are not limited to dibutyltindilaurate, dibutyltindiacetate, dibutyltindimethoxide, tinoctoate, isobutyltintriceroate, dibutyltinoxide, solubilized dibutyl tin oxide, dibutyltin bisdiisooctylphthalate, bis-tripropoxysilyl dioctyltin, dibutyltin bis-acetylacetone, silylated dibutyltin dioxide, carbomethoxyphenyl tin tris-uberate, isobutyltin triceroate, dimethyltin dibutyrate, dimethyltin di-neodecanoate, triethyltin tartarate, dibutyltin dibenzoate, tin oleate, tin naphthenate, butyltintri-2-ethylhexylhexoate, tinbutyrate, d ioctyltin d idecylm ercapt ide, bis (neodecanoyloxy) d ioctylstannane, dimethylbis (oleoyloxy) stannane. In one preferred embodiment, the moisture curing catalyst is selected from the group consisting of dimethyldineodecanoatetin (available from Momentive Performance Materials Inc. under the trade name of FOMREZ UL-28 A) , dioctyltin didecylmercaptide (FOMREZ UL-32) , bis (neodecanoyloxy) dioctylstannane (FOMREZ UL-38) , dimethylbis (oleoyloxy) stannane (FOMREZ UL-50) , and combination thereof. In the moisture and UV curable adhesive composition according to the present invention, the moisture curing catalyst is present in an amount from 0.1 to 5％by weight, preferably 0.1 to 1.0％by weight, based on the total weight of all components.

The optional UV and/or moisture crosslinkers and chain extenders of the LOCA compositions are (meth) acryloxyalkyl alkoxy functional silanes with a formula of R_aR’_bSi (OR”) _4- _(a+b) , wherein a and b are independently is 0 to 3, R is (meth) acryloxyalkyl group and R’R”is alkyl or aryl group. Examples of (meth) acryloxyalkyl alkoxy functional silanes useful in the invention are (γ-acryloxymethyl) phenethyltrimethoxysilane, (γ-acryloxymethyl) trimethoxysilane, (γ-acryloxypropyl) methylbis (trimethylsiloxy) silane, (γ-acryloxypropyl) methyldimethoxysilane, (γ-acryloxypropyl) methyldiethoxysilane, (γ-acryloxypropyl) trimethoxysilane, (γ-acryloxypropyl) tris (trimethylsiloxy) silane, (γ-methacryloxypropyl) bis (trimethylsiloxy) methylsilane, (γ-methacryloxymethyl) bis (trimethylsiloxy) methylsilane, (γ-methacryloxymethyl) methyldimethoxysilane, (γ-methacryloxymethylphenethyl) tris (trimethylsiloxy) silane, (γ-methacryloxymethyl) tris (trimethylsi loxy) silane, (γ-methacryloxypropyl) methyldimethoxysilane, (γ-methacryloxypropyl) methyld iethoxys i lane, (γ-methacryloxypropyl) triethoxysilane, (γ-methacryloxypropyl) triisopropoxysilane, (γ-methacryloxypropyl) trimethoxysilane, (γ-methacryloxypropyl) tris (methoxyethoxy) silane, (γ-methacryloxypropyl ) tris (trimethylsiloxy) silane. Preferably, the (meth) acryloxyalkyl alkoxy functional silanes having (meth) acryloxy group is selected from (γ-acryloxymethyl) phenethyltrimethoxysilane, (γ-acryloxypropyl) trimethoxysilane, (γ-acryloxymethyl) trimethoxysilane, (γ-methacryloxypropyl) trimethoxysilane, (γ- methacryloxyethyl) trimethoxysilane； (γ-methacryloxypropyl) dimethoxymethylsilane, or a mixture thereof.

Moisture crosslinkers and adhesion promoters of moisture hydrolyzable silanes and polymeric and/or oligomeric adhesion promoters may further be added to the curable adhesive. Examples of silane adhesion promoters that are useful include, but are not limited to, C3-C24 alkyl trialkoxysilane, (meth) acryloxypropyltrialkoxysilane, chloropropyltrialkoxysilane, vinyltrialkoxysilane, aminopropyltrialkoxysilane, vinyltriacetoxysilane, glycidoxypropyltrialkoxysilane, beta. - (3, 4-epoxycyclohexyl) ethyltrimethoxysilane, mercaptopropyltrialkoxysilane, and the like. However, silane adhesion promoters that reacts and degrades any active organic component in the LOCA composition or display devices should not be added to adhesives intended for use in electronic device. Examples of functional polymeric and/or oligomeric adhesion promoters that are useful include, but are not limited to, hydrolysable PDMS polymer or oligomer, e.g., PDMS that is endcapped with trialkoxysilyl (meth) acrylates, dialkoxysilyl (meth) acrylates or methacrylates groups. The adhesion promoter will typically be used in amounts of from 0.2 to 40 weight percent, more preferably, 1 to 20 weight percent of the whole curable silicone LOCA.

The amount of the optional silanes or siloxane polymer as UV crosslinkers, moisture crosslinkers, adhesion promoters, or chains extenders will typically be used in amounts of from 0 to 20 weight percent, more preferably, 1 to 15 weight percent of the acrylic polymer.

The liquid silicone LOCA compositions in the invention have Brookfield viscosity range of from about 100 to about 100,000 cps in the ranges of about 20-60℃, preferably about 1,000 to about 40,000 cps at 25-60℃. The liquid adhesive composition in such range of viscosity has a good flowing property which makes it easy to be applied or injected onto a substrate. The Brookfield viscosity is measured by using a Brookfield rotational viscometer (digital Brookfield viscometer, DV-II+, available from BROOKFIELD, US) with spindles at 25℃, according to ASTM 01084-1997. The selection of spindle for testing will depend on the level of the viscosity of the adhesive composition.

To prepare an optical device, the liquid adhesive is coated onto a glass or a substrate. The coating procedure is well-known to those skilled in the art. The coated film is then laminated onto a substrate, and UV cured (Fusion Systems or LED UV light) with a dosage of UVA&V 1-5J/cm².

Optical properties (T％, haze％and yellow index b*) of the cured adhesive film can be measured with Cary 300 from Agilent, in accordance with ASTM E903 and ASTM D1003. The adhesive is considered to be optically clear, if the cured silicone adhesive film exhibits an optical transmission of at least 90％, preferably > 99％between glass slides, over 500-900nm range, and with haze and yellowness b*< 1％.

The silicone LOCA compositions of the invention are useful for bonding display devices that require optical clarity and/or touch sensory. In one embodiment, LOCA is used to bond the cover lens, plastic or other optical materials to the display module substrate. LOCA is generally used to improve the optical characteristics of the device, including minimizing Mura, as well as to improve durability and process efficiency. Major applications of LOCA also include capacitive touch panels, LED/OLED televisions.

There are several ways to incorporate the silicone LOCA of the invention in the display devices between the cover lens and the display module substrate in LCD, LED, touch panel display devices. In one embodiment, the LOCA adhesive of the invention is applied on either the back-substrate or the front cover lens of the device by coating and laminating in one direction by a blade. The back-substrate or the cover lens is then laminated to the LOCA surface, preferably under vacuum (< 0.1MPa) and/or pressure in autoclave (<0.5MPa) . Vacuum condition is preferred for a bubble-free bonding.

In another embodiment, the LOCA is coated on the first substrate, and then laminated onto the second substrate of either front coversheet or the back-substrate. The LOCA of the invention is cured through the clear, top substrate by exposure to electromagnetic irradiation comprising a wavelength ranging from 200 nm to 700 nm, preferably from 380 to 410 nm.The curing degree can be determined by measuring the decrease of the IR absorption at an absorption peak which is characteristic to the corresponding formulation chemistry. This is well established to the person skilled in the art. UV-irradiation can be supplied with a continuous high intensity emitting system, such as those available from Fusion UV Systems. A metal halide lamp, LED lamp, high-pressure mercury lamp, xenon lamp, Xenon flash lamp etc. can be used for UV cure, with an energy range of about 1 to about 5 J/cm².

In a preferred embodiment, the top substrate is selected from glass or polymer film, preferably plastic films, including in particular polyethylene terephthalate, polymethyl (meth) acrylate, polyimide film, and/or triacetate cellulose (TAC) . In another embodiment, the top substrate is a reflector, coverlens, touch panel, retarder film, retarder glass, LCD, lenticular lens, mirror, anti-glare or anti-reflective film, anti-splinter film, a diffuser or an electromagnetic interference filter. For 3D-TV applications, a glass or film retarder will be bonded onto a LCD for passive 3D-TV, or a TN LCD or lenticular lens is bonded a regular TFT LCD for naked eye 3D. The base substrate is a LCD module with polarizer film on top. The base substrate can be a display panel, preferably selected from a liquid crystal display, a plasma display, a light-emitting diode (LED) display, an electrophoretic display, and a cathode ray tube display.

Yet in another embodiment, the display panel has a touch functionality. The adhesive of the invention can be used to bond touch panel sensors that require two layers of indium-tin-oxide coated glass. The adhesive can be used for cover lens bonding, in particular to fill the air gap in the touch panel sensors that utilize a cover lens, such as clear plastic polymethyl (meth) acrylate, and the glass touch panel sensor. The adhesive can be used for directly bonding the cover lens to a LCD module. In another embodiment, the invention comprises the possibility of two or more top substrates stacked onto the base substrate with the LOCA of the invention in between layers.

Many modifications and variations of this invention can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. The specific embodiments described herein are offered by way of example only, and the invention is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled.

EXAMPLES

Optical properties (％T, haze％and yellow index b*) were measured with a spectrometer, Cary 300 from Agilent, in accordance with ASTM E903 and ASTM D1003.

The percent transmission (％T) was measured as follows: (1) place a small film of adhesive on a 75mm by 50mm plain micro slide (aglass slide from Corning Co) , that had been wiped three times with isopropanol； (2) attach a second glass slide onto the adhesive under a force； (3) cure the adhesive with a D-bulb (Fusion Systems) at UVA&V 1-5J/cm²； and (4) measure the optical transmission from 300 to 900nm with the spectrometer.

Terminal or pendant epoxy functional polydimethylsiloxane (Mw 20,000-30,000 g/mol) , hydride terminated polysiloxane (Mw 5,000 g/mol) , Pt catalyst, methacryloxypropyl trimethoxysilane, and glycidylpropyl trimethoxysilane were commercially available from Gelest.

(Meth) acryloxypropyldimethoxy terminated polydimethylsiloxane was made according to U.S. Patent No. 5,300,608 at Henkel Corporation.

MAPO acid was prepared in accordance with J. Am. Chem. Soc., 1950, 72 (9) , pp 4292–4293 and “The Synthesis of Phosphonic and Phosphinic Acids” , Gennady M. Kosolapoff, Mar. 2011, by Organic Reactions, Inc., John Wiley &Sons, Inc.

MAPO acid

Heptane, acrylic acid, acetone, toluene, K₂CO₃ and n-butyl lithium (1.6M in hexane) were commercially available from Aldrich.

Comparative Example 1. Preparation of silane modified photoinitiator (I)

A solution of MAPO acid (10.0g, 34.7 mmol) and glycidylpropyl trimethoxysilane (8.20 g, 34.7 mmol) in heptane (anhydrous, 60 mL) was stirred at room temperature for 12 hours under nitrogen gas. The solvent was then removed under vacuum at room temperature and the product was collected as a light yellow liquid with a quantitative yield. The identity of this compound was confirmed by 1 H NMR to have the following structure (I) :

Comparative Example 2. Preparation of silane and acrylate modified photoinitiator (II)

A solution of MAPO acid (10.0g, 34.7 mmol) and glycidylpropyl trimethoxysilane (8.20 g, 34.7 mmol) in heptane (anhydrous, 60 mL) was stirred at room temperature under nitrogen gas. 2-Isocyanatoethyl methacrylate (8.0 g, 0.05 mol) and triethylamine (1.0 g, 10.0 mmol) were added subsequently to the solution. The solvent was then removed under vacuum at room temperature and the product was collected as a light yellow liquid with a quantitative yield. The identity of this compound was confirmed by 1 H NMR to have the following structure (II) :

Example 3. Preparation of Polymeric Photoinitiator (III)

A solution of MAPO acid (2.3 g, 8.0 mmol) and polydimethylsiloxane with pendant epoxy functional groups (Mw 20,000g/mol, 150 g) in heptane was stirred at 60℃ for 4 hours. The solvent was then removed under vacuum at 60℃. The product was collected as a light yellow liquid with a quantitative yield. The identity of this compound was confirmed by 1 H NMR to have the following structure:

Example 4. Preparation of Polymeric Photoinitiator (IV)

A solution of MAPO acid (2.3 g, 8.0 mmol) and terminal epoxy functional polydimethylsiloxane (Mw20,000g/mol, 150 g) in heptane was stirred at 60℃ for 4 hours. The solvent was then removed under vacuum at 60℃. The identity of this compound was confirmed by 1 H NMR to have the following structure (IV) :

Example 5. Preparation of Polymeric Photoinitiator (V)

A solution of MAPO acid (1.0 g, 0.35mmol) , K₂CO₃ (0.5g, 3.6mmol) , allyl bromide (1.0g, 8.3mmol) in toluene (20mL) , acetone (20mL) and water (20mL) was stirred at reflux for 4 hours. The aqueous layer was removed. Hydride terminated polysiloxane (Mw5000g/mol, 50g, 10mmol) , Pt catalyst were added and stirred for 48hr at 60℃. The product was collected as a clear liquid after organic solvent was removed. The identity of this compound was confirmed by ¹H NMR to have the following structure:

Figure 1 is a UV-vis spectrum of Example 3. The dash line is the starting material epoxy functional PDMS, the solid line is the polymeric photoinitiator of Example 3. Example 3 has UV absorbance at greater than 400 nm, whereas the starting material has no any UV absorbance greater than 250 nm. Thus, Example 3 is a polymeric photoinitiator that can be cured at a wavelength greater than 400nm.

Figure 2A is GPC refractive index (RI) chromatogram and Figure 2B is GPC UV chromatogram of Example 3. The dash line is the starting material epoxy functional PDMS, and the solid line is the polymeric photoinitiator of Example 3. The RI and UV curves of the starting material epoxy functional PDMS shows that it has no UV absorbance. However, once the UV chromophore moiety of the MAPO was chemically attached to the PDMS polymer backbone, it has UV absorbance, and thus, the GPC UV detector can detect the signal. Also, the UV chromatogram shows that the molecular weight remains almost identical after the MAPO moiety is attached to the PDMS chain.

Example 6. Preparation of Liquid Optically Clear Adhesive

Table 1 shows ten LOCA formulations: Sample 1-2 and Comparative Samples A-D. The components and the amounts are listed in the Table. Various photoinitiators were added and tested for haze, ％transmission and yellow index b. Comparative Samples A-D were prepared with commercially available Irgacure TPO, TPOL, 819； and exemplary samples 1-2 were made with Example 3 polymeric photoinitiator.

As showed in Table 1. Commercial photoinitiators in Samples A to D, were initially compatible with acrylate terminated polydimethylsiloxane resins with either Mw 20,000 or 30,000 g/mol, as indicated by the 0 haze, when freshly made. However, after aging at 85℃ and 85％relative humidity, haze％were all increased for Samples A-D. Haze for Samples 1 and 2, made with the instant inventive photoinitiators, remained as zero even after aging at 85℃ and 85％relative humidity for 500hr.

Claims

A polymeric photoinitiator having the structural of:

wherein,

each M is independently, alkyl, aryl, alkoxy, H, vinyl, or combination thereof；

each R is independently alkyl, aryl, fluoroalkyl, trialkylsiloxy, triarylsiloxy, or combination thereof；

X is a linear, cyclic, or branched link having a divalent alkylene, arylene, oxyalkylene, oxyarylene, ester, imide, amide, alcohol, carbonate, urethane, urea, sulfide, ether, or a derivative or combination thereof；

Y is alkyl, aryl, alkoxy, benzoxy, acyl or benzoyl；

Z is alkyl or aryl；

N and Q are different and is independently alkyl, aryl, trialkylsiloxy, triarylsiloxy, alkoxy, amine, ester, epoxy, acrylate, methacrylate, H, vinyl, or derivative thereof；

n ≥ 1；

m, q, r ≥ 0 and

the average molecular weight (Mw) of the polymeric photoinitiator is from 100 to 300,000 g/mol.
The polymeric photoinitiator of claim 1 wherein

M is independently alkyl, aryl, alkoxy, or H；

R is independently alkyl or aryl；

N is a cycloaliphatic 1, 2-epoxide, 1, 2-propylene oxide, 1, 3-propylene oxide, glycidyl epoxide；

Q is a derivative of an acrylate or methacrylate； and

n, m, q, r ≥ 1.
The polymeric photoinitiator of claim 2 having the structural of:
The polymeric photoinitiator of claim 1, having the structural formula:

wherein n ＝ 1.
The polymeric photoinitiator of claim 4, having the structural of:

wherein Me is methyl.
The polymeric photoinitiator of claim 1, having the structural formula:

where Me is methyl；

R is alkyl or aryl；

n and m ≥ 1.
The polymeric photoinitiator of claim 1 having the structural formula:

wherein m, n and q ≥ 1.
The polymeric photoinitiator of claim 7 having the structural of:

wherein M is independently alkyl, aryl, alkoxy, or H

R is independently, alkyl or aryl； and

N is a cycloaliphatic 1, 2-epoxide, 1, 2-propylene oxide, 1, 3-propylene oxide, glycidyl epoxide, acrylate, methacrylate, H, or derivative thereof.
A polymeric photoinitiator having the structural formula:

wherein,

R and R’ are independently alkyl, or aryl；

N and Q are independently alkyl, aryl, fluoroalkyl, alkoxy, benzoxy, or H；

X is a linear, cyclic, or branched link comprising alkylene, arylene, oxyalkylene, oxyarylene, ester, imide, amide, alcohol, carbonate, urethane, urea, sulfide, ether or a derivative or combination thereof；

Y is alkyl, aryl, alkoxy, benzoxy, acyl, or benzoyl；

Z is alkyl or aryl；

m and n are independently ≥ 1； and

the weight average molecular weight (Mw) of the polymeric photoinitiator is from 100 to 300,000 g/mol.
The polymeric photoinitiator of claim 9 having the structural formula of:

wherein

R and R’ are alkyl or aryl；

N and Q are alkyl, acryl, or alkoxy.
The photoinitiator of claim 10 having the structural formula of:
The photoinitiator of claim 10 having the structural formula of:
A method of making polymeric photoinitiator of claims 1 to 8 comprising the step of reacting monoacylphosphinic acid with polysiloxane polymers having pedant epoxy functional groups.
A method of making polymeric photoinitiator of claims 9 to 11 comprising the step of reacting monoacylphosphinic acid with polysiloxane polymers having terminal epoxy functional groups.
A method of making polymeric photoinitiator of claims 9-11 comprising the step of reacting a trialkoxysilane modified MAPO with silanol terminated polysiloxane polymers in the presence of an acid or base catalyst.
A method of making polymeric photoinitiator of claim 12 comprising the step of reacting allyl modified MAPO with hydride terminated polysiloxane polymers in the presence of platinum catalyst.
A UV curable, optically clear silicone adhesive composition comprising:

(a) about 0.1 to about 30％of the polymeric photoinitiator of claims 1-12；

(b) about 60 to about 99.9％of a (meth) acryloxyalkyl or (meth) acryloxyalkyl alkoxy functional polysiloxane, with weight average molecular weight from about 100 to 500,000 g/mol； and

(c) about 0 to about 20％of a (meth) acryloxyalkyl functional silane, silane UV crosslinker, moisture crosslinker, silane adhesion promoter, hydrolyzable polydimethylsiloxane polymer and/or chains extender；

wherein the cured adhesive has a transmittance of greater than 90％, as measured in accordance with ASTM E903 at 500nm.
The UV curable, optically clear silicone adhesive compositions of claims 17, wherein the (meth) acryloxyalkyl or (meth) acryloxyalkyl alkoxy terminated polysiloxane polymer has α, ω-endcapped RR’_nR”_2-nSiO groups,

wherein R is (meth) acryloxyethyl, or (meth) acryloxypropyl； and

wherein R’ is alkoxy and R” are alkyl, 0≤ n ≤2.
An article comprising UV curable optically clear silicone adhesive composition of claims 17-18.
A method of forming an electronic device comprising the steps of:

(1) preparing a UV curable silicone adhesive composition of claims 17-18 comprising the polymeric photoinitiator of claims 1-12；

(2) preparing a first substrate；

(3) coating the adhesive composition onto the first substrate；

(4) laminating a second substrate onto the coating；

(5) curing the adhesive composition by UV light through either the first substrate or the second substrate at 380-410nm.