Debondable compositions

Abstract

Dual-cure compositions for use in high temperature adhesive applications, and particularly for temporarily adhesively attaching one substrate to another substrate, are provided. These dual-cure adhesives are silicone-based compositions that can be B-staged by exposure UV radiation to provide initial green strength, followed by a C-stage cure to give adhesives that can survive high temperature processes above 200 C., especially above 300 C., yet easy to debond afterwards to allow separation of the top and bottom substrates.

Claims

1. A composition radiation curable to form a pressure sensitive adhesive, comprising: at least one photoinitiator selected from an acyl phosphine oxide photoinitiator, an alpha-hydroxyl ketone photoinitiator and a phenylglyoxalate photoinitiator; and a mixture of polysiloxane resins including: a polysiloxane resin (a) having a vinylsiloxane unit, a molecular weight (Mw) of 2323 to 242352 and a structure represented by: ##STR00014## a polysiloxane resin (b) having at least two (meth)acrylate groups and a structure selected from at least one of: ##STR00015## wherein the composition is free of hydridosilane and hydridopolysiloxane; and the weight ratio of polysiloxane resin (a) to polysiloxane resin (b) in the composition is within the range of 97:3 to 40:60 and the vinyl functionality to acrylate functionality in the composition is within the range of 21:1 to 0.29:1; or the weight ratio of polysiloxane resin (a) to polysiloxane resin (b) in the composition is within the range of 99:1 to 90:10 and the vinyl functionality to acrylate functionality in the composition is within the range of 19:1 to 1.4:1.

2. The composition of claim 1; wherein the composition further comprises a thermal initiator.

3. The composition of claim 1; wherein the polysiloxane resins therein consist of polysiloxane resin (a) and polysiloxane resin (b).

4. The composition of claim 1; wherein: 1) the composition further comprises a thermal initiator; and 2) the polysiloxane resins therein consist of polysiloxane resin (a) and polysiloxane resin (b).

5. The composition of claim 1 wherein exposure in a photorheometer to UVA radiation at 230 mW/cm.sup.2 for 5 minutes forms a pressure sensitive adhesive having a storage modulus (G) of less than or equal to 3.010.sup.5 Pa, at 25 C. and 1 Hz.

6. The composition of claim 1, wherein the polysiloxane resin (a) has a mole % of vinylmethylsiloxane units in the range of 4.0-13.0%.

7. The composition of claim 1, wherein (i) the photoinitiator is a combination of ##STR00016## and further comprising 1,1-di-(t-amylperoxy)-cyclohexane as a thermal initiator, or (ii) the photoinitiator is ##STR00017## and the composition further comprises 3,5-dimethyl-hexyn-3-ol.

8. The composition of claim 1, wherein the polysiloxane resin (a) has a mole % of vinylmethylsiloxane units in the range of 1-99%.

9. Cured reaction products of the composition of claim 1.

10. An assembly comprising: a substrate, a carrier, and the composition of claim 1 disposed between the carrier and the substrate.

11. A method for bonding a substrate to a carrier comprising: (a) providing a substrate; (b) providing a carrier; (c) disposing the composition of claim 1 onto at least one of the substrate or the carrier; (d) contacting the substrate and carrier so that the composition is disposed between the carrier and the substrate, forming an assembly; and (e) radically curing the composition by (i) exposing the assembly to radiation in the electromagnetic spectrum; (ii) exposing the assembly to elevated temperature conditions, or (iii) (i) followed by (ii).

12. A method for debonding a substrate from a carrier to which the substrate is adhesively bonded, comprising: (a) providing an assembly comprising the substrate and the carrier with the composition of claim 1 therebetween; and (b) separating the substrate from the carrier.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1: Storage modulus development of photoinitiated vinylsiloxane (VDT-731)-radical photoinitiator (Irgacure 2100) compositions with and without acrylate-functional silicone (UMS-182).

(2) FIG. 2: Storage modulus development of photoinitiated vinylsiloxane (VDT-731)-radical photoinitiator (Irgacure 2100) compositions with different levels of acrylate-functional silicone (UMS-182).

(3) FIG. 3: Storage modulus development of photoinitiated vinylsiloxane (VDT-731)-radical photoinitiator (Irgacure 2100) compositions using acrylate-functional silicone (UMS-182) versus methacrylate-functional silicone (RMS-083).

(4) FIG. 4: Storage modulus development of photoinitiated vinylsiloxane (VDT-731)-acrylate-functional silicone (UMS-182) compositions using different radical photoinitiators.

(5) FIG. 5: Storage modulus development of thermally-initiated vinylsiloxane (VDT-731)-radical photoinitiator (Irgacure 2100)/peroxide initiator (Luperox 531M80) compositions.

(6) FIG. 6: Storage modulus development of dual cure UV/thermally-initiated vinylsiloxane (VDT-731) acrylate-functional silicone (UMS-182)/-peroxide initiator (Luperox 531M80) compositions.

(7) FIG. 7: Depicts a schematic of the peel strength test specimen.

(8) FIG. 8: Depicts a schematic of the peel strength test specimen showing the force F recorded as peel force on a 180 degree peel tester.

DETAILED DESCRIPTION

(9) As used within this specification and the claims, substrate refers to the target component for the fabrication processes, and carrier refers to the support structure for the substrate. A B-stage process generally involves partial curing, solvent evaporation, or both, of the adhesives system, oftentimes using UV or heat. This typically allows easy handling of the adhesives, or provides initial adhesives strength as in the case of debondable adhesives described above. When the adhesive system is then heated at elevated temperatures, more complete cross-linking of the adhesive system can occur and a C-Stage cure is reached.

(10) The vinyl silicone resins are linear or branched polysiloxane compounds having SiCHCH.sub.2 groups.

(11) A representative structure for the vinyl silicone resins is shown below:

(12) ##STR00001##
where R.sub.1, R.sub.2, R.sub.3, and R.sub.4 are independently selected from hydrogen, C.sub.1-10 aliphatic or C.sub.6-10 aromatic hydrocarbons with or without heteroatoms or unsaturation, and w, x, y, and z are molar fractions of the repeating units (w+x+y+z=1, w>0). Generally, the chain-ends of these resins are terminated by trimethylsilyl group or vinyldimethylsilyl groups. Exemplary vinyl silicones are available from Gelest under VDT product designation.

(13) The (meth)acrylate silicone resins are linear or branched polysiloxane compounds having (meth)acrylate groups either at the backbone or chain-ends.

(14) A representative structure for the (meth)acrylate silicone resins is shown below:

(15) ##STR00002##
where R.sub.1, R.sub.2, and R.sub.3 are independently selected from hydrogen, C.sub.1-10 aliphatic or C.sub.6-10 aromatic hydrocarbons with or without heteroatoms or unsaturation, X is a linking group selected from C.sub.1-10 aliphatic or C.sub.6-10 aromatic hydrocarbons with or without heteroatoms or unsaturation, x.sub.1, x.sub.2, y.sub.2, and z are molar fractions of the repeating units (where x.sub.1+x.sub.2+y.sub.1+y.sub.2+z=1), and A is either a hydrogen, or (meth)acrylate group. Exemplary (meth)acrylate silicones include products available commercially from Gelest Inc. under the trade designations DMS-R, RMS, and UMS, and TEGO RC silicone resins for release coating available commercially Evonik. More details on each of these is provided in the Examples section. In addition, acrylate silicones are also available from Siltech Corporation under the Silmer ACR product line, such as Silmer ACR D208, Silmer ACR D2, Silmer ACR Di-10, Silmer ACR Di-50, Silmer ACR Di-1508, Silmer ACR Di-2510, Silmer ACR Di-4515-O, and Fluorosil ACR C7-F.

(16) The radical thermal initiators are substances that can produce radical species under heat to initiate radical reactions. Typical thermal initiators are azo compounds, and organic/inorganic peroxides that have weak bonds and small bond dissociation energies.

(17) Suitable radical thermal initiators are well known and may be chosen from dicumene peroxide, cumene hydroperoxide, and perbenzoates, such as t-butyl perbenzoate. Organic peroxides available commercially from Arkema under the Luperox trade name, such as Luperox 531M80 [1,1-di-(t-amylperoxy)-cyclohexane], are particularly useful herein.

(18) The hydridosilane and hydridosiloxane resins are compounds having SiH group capable of hydrosilation reaction with the double bond on the vinyl silicone resin structure. Exemplary compounds include, but not limited to the following structures:

(19) ##STR00003##

(20) ##STR00004##
where R.sub.1, R.sub.2, R.sub.3, and R.sub.4 are independently selected from hydrogen, C.sub.1-10 aliphatic or C.sub.6-10 aromatic hydrocarbons with or without heteroatoms or unsaturation, and w, x, y, z are molar fractions of the repeating units (w+x+y+z=1, w>0).

(21) The hydridosilane and hydridosiloxane resins may also exist in a cyclic siloxane structure, examples of which are cyclotrisiloxane (D3), cyclopentasiloxane (D5), or even higher.

(22) Hydrosilation catalysts (also called hydrosilylation catalysts) promote the addition of SiH bonds across unsaturated double bonds. These are typically metal catalysts such as platinum and rhodium compounds.

(23) In another embodiment, this invention is an assembly of a substrate and carrier, in which the adhesive composition is disposed between the substrates.

(24) In a further embodiment, a method of debonding a substrate from a carrier is provided. The method comprises the steps of: (a) providing a substrate and a carrier, (b) disposing a debondable adhesive on the substrate and/or the carrier, (c) contacting the substrate and carrier so that the debondable adhesive is disposed between, forming an assembly, (d) exposing the assembly to conditions favorable to adhere the substrate to the carrier, such conditions being heating at an elevated temperature, exposure to radiation in the electromagnetic spectrum, or exposure to radiation in the electromagnetic spectrum followed by heating, and (e) separating the substrate from the carrier.

(25) When step (d) involves heating, the temperature should be in the range of 100 C. to 175 C. for a period of time of 1 to 30 minutes. When step (d) involves radiation exposure, radiation may be generated and applied using a 400 Watt lamp for about 1 to 4 minutes. When a combination of radiation and heat is used to obtain the desired cure, suitable conditions can be determined by one skilled in the art without undue experimentation.

EXAMPLES

(26) Gel Permeation Chromatography was used to determine the molecular weight of the silicone materials. A Waters model 717GPC, equipped with an autosampler and a refractive index detector, was used with polystyrene of various molecular weights as standards (1.1 M-162 Da) and tetrahydrofuran as solvent.

(27) In the tables below, averaged molecular weights (Mn and Mw in Daltons) and (relative to polystyrene standards) and polydispersivity (Mn/Mw) calculations are shown for the various silicone materials.

(28) TABLE-US-00001 Mn Mw Polydispersity Sample (Da) (Da) (Mw/Mn) VDT-131 17646 33365 1.9 VDT-431 15543 35534 2.3 VDT-731 18540 40153 2.2 599 635 1.1 VDT-954 42613 242352 5.7 587 608 1.0

(29) The data above is illustrative for the VDT series, vinylmethylsiloxane-dimethylsiloxane copolymers, trimethylsiloxy terminated, which is represented by the

(30) ##STR00005##

(31) TABLE-US-00002 Mn Mw Polydispersity Sample (Da) (Da) (Mw/Mn) DMS-V05 1486 2323 1.6 DMS-V21 6047 10963 1.8 DMS-V25 12097 26432 2.2 DMS-V31 15087 36028 2.4 DMS-V41 42938 80479 1.9 DMS-V51 76987 162933 2.2

(32) The data above is illustrative for the DMS series, vinyl terminated polydimethylsiloxanes, which is represented by the

(33) ##STR00006##

(34) TABLE-US-00003 Mn Mw Polydispersity Sample (Da) (Da) (Mw/Mn) PDV-0346 63671 145752 2.3 2066 2444 1.2 498 515 1.0 PDV-0541 25703 74421 2.9 552 573 1.0 PDV-1625 7363 13386 1.8 497 512 1.0 PDV-1641 21127 102786 4.9 496 511 1.0 TEGO RC-90 7524 17532 2.3 UMS-182 7591 12286 1.6 676 713 1.1 UMS-992 1924 2183 1.1 775 796 1.0

(35) The data above is illustrative for the PDV series, diphenylsiloxane-dimethylsiloxane copolymers, which are represented by

(36) ##STR00007## TEGO RC-902, which is an acrylated silicone having the following CAS No.: 155419-56- and is described by the manufacturer as siloxanes and silicones, di-Me, hydrogen-terminated, reaction product with acrylic acid and 2-ethyl-2[(2-propenyloxy)methyl]-1,3-propanediol; and For the UMS series, (acryloxypropyl)methylsiloxane-dimethylsiloxane copolymers,

(37) ##STR00008## UMS-182: 15-20% (acryloxypropyl)methylsiloxane repeating unit UMS-992: 99-100% (acryloxypropyl)methylsiloxane repeating unit.

Example 1: Impact of Acrylated Polysiloxane on UV Cure of Vinyl Silicone Resin

(38) A 100:0.9 (by weight) blend of vinyl silicone resin VDT-731 (Gelest) having 7-8% vinyl groups and Irgacure 2100 was cured under 230 mW/cm.sup.2 UVA. Curing was monitored with an Anton Paar Physica MCR501 photorheometer using 8 mm plate, 1 mm gap at 1 Hz. UV curing started at 60 seconds. This sample was compared with a 90:10:0.9 blend (by weight) of VDT-731:UMS-182:Irgacure 2100, in which UMS-182 (Gelest) is a silicone resin having 15-20% acrylate groups along the silicone polymer chain. As shown in FIG. 1, the use of small amounts of acrylated silicone resulted in dramatically improved cure speed and roughly two orders of magnitude increase in storage modulus. Considering that the level of acrylate functional group is very low (2%) among all siloxane repeating units in the composition, the improvement in curing is extremely efficient. Most importantly, the storage modulus exceeded 10.sup.4 Pa. It was also noted that the formulation containing UMS-182 gelled at only 1.5 seconds according to Tan Delta, the ratio of loss modulus to storage modulus. Without the acrylated silicone, the gelation process took over 2 minutes.

(39) Irgacure 2100 has the following structure

(40) ##STR00009##

(41) This was repeated with a 94.6:5.4:0.9 blend (by weight) of VDT-731:UMS-182:Irgacure 2100. Again, a very efficient modulus buildup was observed even at extremely low levels of acrylate functionality. (See FIG. 2.)

Example 2: Model Studies of Vinyl Siloxane and Acrylate Monomers

(42) A 90:0 (by weight) blend of SIV9082:butyl acrylate was photopolymerized using 2 weight percent Darocur 1173. The mixture was sealed in a quartz NMR tube and irradiated under 50 mW/cm.sup.2 UVA for 5 minutes. SIV9082 (Gelest) is a vinyl siloxane monomer having the following structure:

(43) ##STR00010##

(44) Darocur 1173 has the following structure

(45) ##STR00011##

(46) The SIV9082:butyl acrylate blend has a molar ratio of 4.6:1. This blend helps to promote the co-polymerization reaction between two monomers instead of homopolymerization of the fast acrylate monomer.

(47) .sup.1H NMR analyses before and after UV irradiation were conducted. Further, residual monomers were removed from the UV polymerized sample under 400 micron vacuum at 95 C., and .sup.1H NMR confirms the formation of polymers incorporating both vinyl siloxane SIV9082 and butyl acrylate monomers.

Example 3: Comparison of Acrylate and Methacrylate Silicones

(48) In this example, methacrylated silicone RMS-083 (Gelest) having 7-9% methacrylate groups in the silicone repeating units was tested. VDT-731:RMS-083:Irgacure 2100 blends at a 90:10:0.9 ratio as well as a 80:20:0.9 ratio were compared with the acrylated silicone formulation made and evaluated above in Example 1. Although slower curing was observed, both samples were eventually cured to 510.sup.3 Pa region. (See FIG. 3.)

Example 4: Use of High Functional Acrylate Silicone

(49) In this example, UMS-992 (Gelest), an acrylate silicone with 99-100% acrylate groups on all siloxane repeating units was tested. A blend of VDT-731:UMS-182:UMS-992:Irgacure 2100 in a 90:10:5:0.9 ratio was cured by photorheometry, and was found to have a storage modulus was 10.sup.4 Pa.

Example 5: Comparison of Different Photoinitiators

(50) In this example, a resin blend of VDT-731:UMS-182:photoinitiator was prepared at a 90:10:0.9 ratio. Three different types of photoinitiators were evaluated: Irgacure 2100, Darocur 1173, and Irgacure MBF. Irgacure 2100 is an acylphosphine oxide type initiator, Darocur 1173 is alpha-hydroxyl ketone type initiator, and Irgacure MBF is phenylglyoxylate initiator. Irgacure MBF has the structure shown below:

(51) ##STR00012##

(52) When cured using photorheometry, all three yielded a cured product having a storage modulus exceeding 510.sup.3 Pa after cure. However, Irgacure 2100 was found to be the fastest photoinitiator. (See FIG. 4.) On the other hand, Darocur 1173 resulted in higher storage modulus after cure.

(53) Further, TEGO Al 8 (Evonik) was tested as a less volatile replacement for Darocur 1173 and similar performance was observed. Structures of this initiator is shown below where R is an alkyl group having C10-13 alkyl chains:

(54) ##STR00013##

Example 6: Thermal Cure of VDT 731

(55) An important attribute of a debondable adhesive is the ability to easily peel off after processing. Generally speaking, adhesives having storage modulus above 10.sup.6 Pa are beyond the pressure sensitive adhesive region and are tack-free. VDT-731 was blended with 2 and 4 weight percent Luperox 531M80 and cured on a rheometer. The samples were cured by exposure to elevated temperature conditions, which ramped from room temperature to a temperature of 150 C. at 10 C./minute intervals and then held at a temperature of 150 C. for a period of time of 1 hour. As shown in FIG. 5, the cured samples resulted in storage modulus exceeding 10.sup.6 Pa. This example demonstrates that samples based on this chemistry are suitable for thermally induced C stage cure.

Example 7: Dual-Cure Formulation

(56) VDT-731 (9.0 g), UMS-182 (1.0 g), Irgacure 2100 (0.1 g), and Luperox 531M80 (0.2 g) were mixed together, and dispensed onto a glass die (4 mm.sup.2) over which a microscope glass slide was positioned. Radiation in the electromagnetic spectrum (50 mw/cm.sup.2 UVA) was directed toward the glass die/glass slide assembly for a period of time of 30 seconds. The assembly was then exposed to elevated temperature conditions of 150 C. for a period of time of 60 minutes. Next, the assembly was subjected to 30 minutes of baking either at 350 C. or 400 C. to mimic a TFT/ITO processes. At these two baking conditions, the die adhered to the glass slide. The die however was observed to be easily debonded, using the peel strength evaluation technique described herein.

(57) With reference to FIG. 6, the photorheometry measurements indicate the development of modulus initially after exposure to electromagnetic radiation and then to exposure to elevated temperature conditions.

Example 8: Preparation of Three Master Batches

(58) Master batch A contains 20.0 g VDT-731, 0.20 g Irgacure 2100, and 0.40 g Luperox 231. Master batch B contains 10.0 g UMS-182, 0.10 g Irgacure 2100, and 0.20 g Luperox 231. Master batch C contains 10.0 g Tego RC-902 acrylate silicone resin (Evonik), 0.10 g Irgacure 2100, and 0.20 g Luperox 231. Various blended samples were prepared from these master batches, and are set forth below in Table 1. The blended samples were cured in the photorheometer using the conditions of Example 1 for a period of time of 5 minutes. The G values for each of the blended samples are also recorded in Table 1.

(59) TABLE-US-00004 TABLE 1 Classification A:B Mixtures A:C Mixtures according to A:B (wt) G (Pa) A:C (wt) G (Pa) Dahlquist criterion 100:0 1.95 10.sup.3 Non-PSA Region 97:3 1.32 10.sup.4 97:3 1.19 10.sup.4 PSA Region 95:5 2.10 10.sup.4 PSA Region 90:10 4.04 10.sup.4 90:10 5.47 10.sup.4 PSA Region 85:15 5.23 10.sup.4 PSA Region 80:20 5.37 10.sup.4 80:20 8.03 10.sup.4 PSA Region 70:30 9.61 10.sup.4 PSA Region 60:40 60:40 2.87 10.sup.5 PSA Region 50:50 1.18 10.sup.5 50:50 4.00 10.sup.5 PSA Region 40:60 4.04 10.sup.5 40:60 5.49 10.sup.5 PSA Region (borderline) 30:70 7.63 10.sup.6 Non-PSA Region 10:90 1.12 10.sup.7 Non-PSA Region 0:100 1.25 10.sup.7 Non-PSA Region

(60) From these data, it seems that in order to achieve pressure sensitive adhesive properties for the inventive compositions, a vinyl silicone to acrylate silicone ratio desirably is within the range of 97:3 to 40:60 so that the vinyl functionality to acrylate functionality falls roughly within the range of 21:1 to 0.29:1.

Example 9: Preparation of Three Master Batches

(61) UMS-992, an acrylate silicone resin having 99-100 mole % (acryloxypropyl)methylsiloxane units, was evaluated as a blended with VDT-731 and the initiator package. One drop of each sample was placed between two microscope slides, and exposed to radiation in the electromagnetic spectrum (50 mW/cm.sup.2 UVA) for a period of time of 60 seconds. Then the so-formed assembly was exposed to elevated temperature conditions of 150 C. for a period of time of 1 hour. The results are summarized in Table 2.

(62) TABLE-US-00005 TABLE 2 Constituents After UV Cure G (Pa) Sample VDT-731 UMS-992 Initiator (50 mw/cm.sup.2 After 5 minutes After Thermal Cure Nos. (part) (part) Package UVA), 60 s in Photorheometer (150 C./1 h) 1 99 1 IP Tacky PSA 1.0 10.sup.4 Easy debond CF 2 97 3 IP Tacky PSA 7.0 10.sup.3 Easy debond CF 3 95 5 IP Tacky PSA 6.0 10.sup.3 Easy debond CF 4 90 10 IP Tacky PSA 4.4 10.sup.3 Easy debond CF 5 80 20 IP Not tested, 2.8 10.sup.3 Not tested formulation phase separated IP (Initiator Package): 1 part Irgacure 2100 plus 2 parts Luperox 231 CF: cohesive failure during debonding

(63) Here, the desired vinyl silicone to acrylate silicone ratio is within the range of 99:1 to 90:10, and the vinyl functionality to acrylate functionality is approximately within the range of 19:1 to 1.4:1.

Example 10: Various Vinyl Silicone Resins

(64) A variety of vinyl silicones having different levels of vinyl group along the polymer chains were formulated. One drop of each sample was placed between two microscope slides, and exposed to radiation in the electromagnetic spectrum (50 mW/cm.sup.2 UVA) for a period of time of 60 seconds. Then the so-formed assembly was exposed to elevated temperature conditions of 150 C. for a period of time of 1 hour. The results are summarized in Table 3.

(65) TABLE-US-00006 TABLE 3 Constituents After UV Cure G (Pa) Sample Acrylate Silicone Initiator (50 mw/cm.sup.2 After 5 minutes After Thermal Cure Nos. Vinyl Silicone UMS-182 Package UVA, 60 s) in Photorheometer (150 C./1 h) 1 90 parts 10 parts IP Tacky PSA 2.1 10.sup.5 Easy debond AF VDT-954 (11-13% VMS) 2 90 parts 10 parts IP Tacky PSA 4.0 10.sup.4 Easy debond AF VDT-731 (7.0-8.0% VMS) 3 90 parts 10 parts IP Tacky PSA 5.0 10.sup.3 Easy debond CF VDT-431 (4.0-5.0% VMS) 4 90 parts 10 parts IP Not cured 17 Not tested VDT-131 (0.8-1.2% VMS) VMS: vinylmethylsiloxane repeating unit IP: 1 part Irgacure 2100 plus 2 parts Luperox 231 AF: adhesive failure during debonding CF: cohesive failure during debonding

Example 11: Dual-Cure Formulation Using Hydridosiloxane Thermal Cure

(66) VDT-731 (9.0 g), UMS-182 (1.0 g), Darocur 1173 (0.1 g), HMS-993 (0.6 g), 3,5-dimethyl-hexyn-3-ol (0.05 g), and SIP6830.3 (0.0062 g) were mixed together. HMS-993 (Gelest) is a hydridosiloxane resin having SiH group in all repeating units (according to the manufacturer, Gelest, it is a polymethyl hydrosiloxane, trimethylsiloxyterminated having a molecular weight of 2100-2400), 3,5-dimethyl-hexyn-3-ol is a hydrosilation inhibitor for potlife stability, SIP6830.3 (Gelest) is a platinum catalyst for catalyzing hydrosilaton cure of the vinyl siloxane resin and hydridosiloxane resin. More specifically, the platinum catalyst may be described as platinum-divinyltetramethyldisiloxane complex or Karstedt catalyst, where a 3-3.5% platinum concentration in vinyl terminated polydimethylsiloxane is present, and the complex is described as Pt[O(SiMe.sub.2CHCH.sub.2).sub.2].sub.1.5. The samples were cured between a glass die (4 mm.sup.2) and a microscope glass slide under exposure to radiation of 50 mW/cm.sup.2 UVA for 60 seconds, followed by heating at a temperature of 150 C. for a period of time of 60 minutes. The cured assemblies were then subjected to 30 minutes of baking either at 350 C. or 400 C. At these two baking conditions, the die adhered to the glass slide. The die however was observed to be easily debonded.

(67) The peel test evaluation was conducted on a Cheminstrument 180 degree peel adhesion tester. Peel test samples were prepared by adhering in an off set manner 50 mm75 mm glass substrate (0.12 mm thickness) on 5075 mm glass substrate (1 mm thickness) as shown in FIG. 7. The overlap is 50 mm. The glass substrates were adhered by a composition having a thickness control to be 0.125 mm. FIG. 8 shows the force being applied to separate the bonded assembly. An average peel force of over 2N/25 mm is considered not debondable, as substrate failure will ordinarily be observed under such conditions. An average peel force between 1.5-2N/25 mm is considered semi-debondable, and an average peel force of less than 1.5N/25 mm is considered debondable.

Comparative Example 1: Vinyl-Terminated Polydimethylsiloxane

(68) A series of alpha, omega-vinyl terminated linear polydimethylsiloxanes were cured in the presence of 1 weight percent Darocur 1173 under exposure to radiation of 50 mw/cm.sup.2 UVA for a period of time of 60 seconds. The results are summarized in Table 4.

(69) TABLE-US-00007 TABLE 4 Base Viscosity Molecular Vinyl- State After Resin (cSt) Weight Eq/kg UV Cure DMS-V05 4-8 800 2.4-2.9 Liquid DMS-V21 100 6000 0.33-0.37 Liquid DMS-V25 500 17,200 0.11-0.13 Liquid DMS-V31 1000 28,000 0.07-0.10 Liquid DMS-V41 10,000 62,700 0.03-0.04 Liquid + sticky gel DMS-V51 100,000 140,000 0.016- Sticky Gel 0.018

(70) As shown in the table, only those alpha, omega-vinyl terminated linear polydimethylsiloxanes with molecular weights above 60,000 daltons were found to gel or show the potential to be useful as a pressure sensitive adhesive after cure. DMS-V51 was mixed with 1 weight percent Darocur 1173 and 2 weight percent Luperox 231, and a drop placed between two microscope slides. The slide assembly was exposed to radiation in the electromagnetic spectrum in the UV range (50 mw/cm.sup.2 UVA) for a period of time of 60 seconds. Next, the slide assembly was heated at a temperature of 150 C. for a period of time of 1 hour. The cured sample showed good adhesion to the slides but was observed to be hazy and non-uniform. It was difficult to separate the microscope slides by hand and thus not suitable for a debondable adhesive.

Comparative Example 2: Vinyl Terminated Diphenylsiloxane-Dimethylsiloxane Copolymers

(71) A series of alpha, omega-vinyl terminated linear diphenylsiloxane-dimethylsiloxane copolymers were mixed with 1 weight percent Irgacure 2100 and 2 weight percent Luperox 231. One drop of each sample was placed between two microscope slides, and exposed to electromagnetic radiation (50 mW/cm.sup.2 UVA) for a period of time of 60 seconds, and then heated at a temperature of 150 C. for a period of time of 1 hour. The results are summarized in Table 5.

(72) TABLE-US-00008 TABLE 5 Base Mole % Viscosity Mol. Vinyl- State After State After Resin SiPh.sub.2O (cSt) Wt. Eq/kg UV Cure Thermal Cure PDV-0346 3.0-3.5 60,000 78,000 0.017-0.021 Liquid Cured CF PDV-0541 4-6 10,000 60,000 0.027-0.038 Liquid Cured AF PDV-1625 15-17 500 9,500 0.19-0.23 Liquid Not completely cured PDV-1641 15-17 10,000 55,000 0.033-0.040 Liquid Almost cured CF AF: adhesive failure during debonding CF: cohesive failure during debonding

(73) None of these resins contributed to a composition having pressure sensitive adhesive properties after UV cure. And after thermal cure, all the sample slides were difficult to separate by hand.

(74) Rheology studies were conducted on formulations in Table 5 by ramping from room temperature to 150 C. at 10 C./minutes and then held at 150 C. for a period of time of 1 hour. The final storage modulus is tabulated in Table 6.

(75) TABLE-US-00009 TABLE 6 Final Modulus After Base Resin 150 C./1 h (Pa) VDT-731 in Example 6 1.61 10.sup.6 PDV-0346 4.0 10.sup.4 PDV-0541 1.1 10.sup.5 PDV-1625 3.6 10.sup.4 PDV-1641 1.6 10.sup.4