AC YLA IDE OPOL YM FOE PRESSURE SENSITIVE ADHESIVES OO013 This application claims the priority of U.S. Provisional Patent Application

61/892,509, filed October I S, 2013, which Is incorporated herein by reference,

FIELD OF TEE INVENTION

0002] The present invention relates to copolymer compositions tor making pressure sensitive adhesives,

BACKGROUND OF THE INVENTION

[0003] Acrylic polymers have advantages and superior qualities to other polymer based adhesives for use in pressure sensitive adhesives (PSA), Acrylics are transparent and chemically and oxi ative! ^' }' stable. They are less irritating to skin and often used for biomedical applications. Commercial PSAs commonly use - permanent cross linking to improve the cohesive strength and to. obtain clean peeling. Noneovalent interactions can also provide a physically crosslinked ^" polyiner .network while incorporating reversibility, Noneovalent interactions include van der Waais force, hydrogen bonding, pi. stacking, and ionic interaction. Physically crossiinked polymers are responsive to heat, moisture, solvent, salt concentration, etc., depending on. the specific noneovalent interaction,

£0004] Histamin serves a wide range o-f biological functions, including allergic reactions to antigens and ne on regulation etc. The imidazole ring has both hydrogen bonding donor and acceptor to form noneovalent Interactions. The aromaticity sustains the thermal and chemical stability of Imidazole rings. Imidazoie-containing polymers also exhibit anti-int nn ^' natory responses. The polarity of histamine also contributes ^' k> its potential in designing waler-sohib!e adhesive;? and coatings.

0δ¾ However, there remains a need for PSAs based on hydro-gen bonding. The reversible nature of noncovaient interaction in hydrogen bonding provides an opportunity to design thermal ^' or .solvent reversible adhessves and recyclable adhessves ma erials, Hydrogen bonding introduces physical crosslinks to enhance mechanical properties;, especially cohesive strength of adhesive materials and maintains proeessahihty above the hydrogen bonding dissociation t-emperaiure..

SUMMARY OF THE INVENTION

0008 The present ioventson provides copolymers for making pressure semi-live adhesives (PSAs), The copolymer cont ns a first comonomer and a second com nomer. The first comonomer s he structure of Formula I

Formula 1

wherein Rl is an alkykrre having 1 to 3 carbons, preferably 1 to 2 carbons; and R2 is hydrogen or an alkyl having I to 3 carbons. s preferably, Rl is an ethylene. Most preferably, R2 is hydrogen or a methyl,

[0007] The second comonomer has the structure of Formula If, 111 or iV, or combinations t ereoE Formula f I Is given as follows:

R3

Formula 11 herein R3 is an alky! having i to 16 carbons or alcohol or acids thereof; and R4 is hydrogen o an alkyi having 1 to 3 carbons. Preferably, R3 is a butyl - Preferably, R4 is hydrogen or a m ethyl.

[0008] Formula .1 II is given as follows;

Formula ill

wherein 5 Is an alkyi having 1 to 12 carbons, preferably 1 io 3 carbons; and K.6 s hydrogen or an alky! having 1 io 3 carbons. Preferably, R5 is a methyl. Preferably, R6 is hydrogen or a methyl,

0009| Formula IV is given as follows:

Formula IV

wherein ? is an alkylene having 0 to 2 carbons; each of R8 to R 12 is hidependeniiy hydrogen, a halogen., or an alkyi having 1 to 3 carbons; and R 13 is hydrogen or an alkyi having 1 to 3 carbons, Preferabl , R ^' 7 has 0 carbon atom. Preferably, 8 to ^' Rl 2 arc ail hydrogen. Preferably, RJ 3 is hydrogen.

[00101 The copolymer may be a random copolymer or a block copolymer. A random ^' copolymer is preferred. Additionally,, the second monomer may contain any combinations of Formulas 1 1 to IV, For example, the copolymer may eonta a monomer of formula I anrl a com.onom.er or several conienomers of orm rlar II k> IV.

BRIEF DESCRIPTION OF THE DRAWINGS

£00 1] Figure 1 is a dr ing showing chemical structures of some preferred second conronomers,

[0012| Figure 2 is a graph sho ng an NMR analysis of Poly(HA-c<?→iBA) copolymers, [0013] Figure 3 is a graph showing a TO A analysis of 1.1 mol% HA-coniaining poiyacTylate which depicts a 5% wei ht loss at temperature: of 2 /2 °€,

|0014| Figure 4 is a graph showing a iff rential scanning ea ri etry (DSC) of 1 i mol%, lA-containing poiyacry!ate which depicts a broad glass transition around temperature of -30 [0015] Figure 5 is ¾· graph showing a stee exc sion drrornaiography analysis of 1 1 mol% HA -containing polyaery!ate which depicts a weight average molecular weight of 101 k.Da.

[0018] Figure 6 is a graph showin the storage and loss modulus master curves of poiyaerylates containing 1 1 moi% HA.

[0017] Figure 7 is a graph showing peel strength of 1 1 mof% BA-eomammg poiyacrylaie compared to poiyi?BA and 3M Scotch* ^"' Magic ^{: M} tape,

[0018J Figure § is a picture showing that Mylar backing of scotch tape and HA-containing copolymer curls alter pee! and Mylar backing of poly nB A remai s flat

[0019] Figure 9 is a graph showing the thermodynamic mechanical properties of solvent easted poiyaeryiates films containing 13 mol HA and 28 mol¾ HA.

[0020] Figure 1 are a series of picture showing the property changes of poi aerylates containing 0, 1 k 28 πχ>1% HA from left to right. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The present invent on relates to compositions for pressure sensitive adhesive (PSA), The compositions provide physical crosslinfcing through hydrogen bonding. The compositions contain a copolymer having a first eomonomer and a second ce-monomer. The first eomonomer has the structure of Formula 1; and the second, comonomer has the structure of Formula Π, 111 or IV. live copolymer may be a random or block copolymer, in the copolymer, the first comonomer serves to provide tackiness .for the adhesive through hydrogen bonding between the imidazole rings; and the second, copolymer Is used to tunc the desired properties of the PSA. Preferably, the copolymer c ntains about 3-28 raol %, more preferably 5-15%, of the first comononteL and about 72-97 mol ¾, more preferably 85-9 moi %, of the seco d comonomer, [0022] In an embodiment, the first comonomer may be made by reacting a suitable amino substituted imidazole {Formula V, where Rl is as described above) wit an aery to ! hah ^' de (Formula VI, where R2 is as described above and X is a hahde, such- s fluoride, chloride, bromide, and iodide, preferably chloride and bromide)

Formula V Formula VI

Preferably, R2 is hydrogen or methyl, and X is chloride. The reaction between Formulas V and

VI is preferably carried out in a solvent in the presence of a base. The base used can be inorganic, such as sodium hydroxide, potassium hydroxide, and sodium carbonate; and organic, such as triethylarrsine. The solvent ears, be, but is not limited to, water, dichloromeihane (DCM), cldo oform, and ethyl acetate, wi th the preferred solvent being a mixture of■ water arsd DCM. An iaterifccial reaction was carried out at 0 °C, When R2 is methyl crystallization occurs at the interface of DCM and ater, allowing min mized purification process, hi a preferred

embodiment, histamine dihydroehloride is reacted with acryloyl chloride to forat histamine aerytemide as shown in Scheme 1

Scheme 1

Alternatively, if ^' histamine (met ^' h^crylamide is desired, the histamine di hydrochloride can be reacted with meth(acryloyl) chloride to .form the hisiamine fmeth)acrylannde.

[0023] The second eomono ers are well-known i the art and may be obtained using previously described methods. Indeed, the second comonomers are available commercially from many sources, for example, butyl acrylate has CAS Number 141 -32-2 and is available from Dow; butyl methacrylate has CAS Number 97-88-1 and is available from Dow; 2-ethylhexyl methacrylate has CAS Number 688-84-6 and is available from Sigma Aldrich; 2-ethylhexyl acrylate has CAS Number 03- 1 1-7 and is available from Sigma Aldrich; methyl acrylate has CAS Number 96-33-3 and is available from Dow; and methyl methacrylate has CAS Number 80-62-6 and is available from Sigma Akirich; styrene and its ftmetiona!ixe monomers are also available through Sigma Aldrich. Specific examples of the second monomer may be. but are not limited to, acry!ates or metbacryktes, such as methyl, acrylate, methyl methacrylate, ethyl

S crylaie, ethyl eth aerylate, Isopropyl acryiate, isopropyl methacrylate, n-butyl acrylaie, n~butyineihaeryiate, i-butyl acryiaie, -butyl raethaerylate, i-buiyi aerylate, i-hutyl methaerylaie, hexyi aerykte. hexyl methaerylaie ethylhexyl aerylate, ethylhexyl methacfylate, 3,3 dimethylbutyl meihaerylaie, lauryl acrylaie; sivrene and mnetionalixed styrenes, such as brotriostyrene, chlorostyrenes, butoxysiyteo.es,, butylsiyrenes, methyistyrencs, and propyIstryreri.es, The preferred second comomoners are n-bistyl. acrylaie, ri-buiyl methaerylaie, 2-ethylhexyi aerylate, iso~oetyi aerylate, methyl aerylate, methyl methaerylaie, vinyl acetate, styrene, 2-hyd xy ethyl acrylaie, or combinations thereof. The structures of some of those second eomonomers are shown In Figure 1. The tt st preferred second comonomer is n-butyi acryiaie, ethylhexyl aerylate, n-butyl rneihacryhrie, lauryl aerylate, or combinations- thereof

|0024| The first and second monomers are reacted to Ibrm the copolymer of the present invention, Preferably, the reaction takes place in a solvent with the presence of an. initiator. Preferably, the reaction is carried em at about 6d-?0°C for about 18-30 hours, more preferably 20-24 hours, unde inert gas, su h as argon or nitrogen,. The solvent can be, but is noi limited to, dimethyl sulfoxide (DMSO), dinieihylmrmamide D F), and methanol, with DMSO being the preferred solvent. The initiator can be, but is not limited to, axohtsssobmyronltrile (ΛΙΒΝ), 4,4'- Azobi3(4-cyanovaierie acid), and organic peroxides, such as dhtert-boty! peroxide and benzoyl peroxide, with AIBN being the preferred initiator.

[002$] In a preferred embodiment, the adhesive composition contains a copolymer of histamine aer la lde (Fonnula IA) -and re-butyl aerylate. In another preferred embodiment, the adhesive composition contains a copolymer of histamine aerylarmde (Formula Ϊ Α) and n-bntyl methaerylate,

Formula 1 A

Formula lA is preferably obtained by reacting histamine with aeryioy! chloride at condit.io.ns descr bed above.

00 61 i.n a further preferred embodiment, , the adhesive composition contains a copolymer of histamine niethacrylamide (Formula IB) and rt-hm l acrylale. la yet another preterred embodiment the adhesive composition contains a copolymer oX histamine methacrylamide (Formula IB) and n -but l methaeryiate,

Formula IB

Formula IS preferably obtained by reacting histamine with (meth aeroy chloride at the conditions described above,

£0027J Without further description, it is believed that one of ordinary skill In the art can. using the preceding description and the following illustrative example, make and utilise the compounds of the present invention and practice the claimed methods. The following example is given io illustrate th present invention, It should be understood ihat the invention is not to he limited to the specific conditions or details described in the example.

Id Kxaotple

[ 2SJ Method*

[00281 Synthesis of Histamine A&yfamitk Monomer, In a three-necked 250 mi, flask equipped with a stirrer and two 200 ml, dripping mnnelst histamine dihydroehloride i S.OO , 43,6 mmol) was dissolved h 40 oil, of distilled water. The solution was- ooled to 0-S "C in ice bath. A solution of acryloyi chloride (3.932g. 43.6 mmol) in anhydrous dichloro ethaae (40 nil) and t aqueous NaGH solmion (3.27M, 40 mL 130,9.romol) were simultaneou ly added dropwise while stirring vigorously for 1 h. The reaction was allowed to he warmed to room temperature and stirred for an additional 4 h. The aqueous layer was collected and iree:se~dried. The residue was re-suspended in 200 mL of isopropanol and filtered. The filtrate was concentrated by rotary evaporation. The crude product was purified with coluron

chromatography us ng 3 : 1 cblorofom ed-anoi as an eloen The collected fractions were evaporated through, rotary evaporation and dried in a vacuum oven at room temperature.

|OO301 Synthesis of Histamine Meikxavkmide. in a three-necked 100 mL flask including a stirrer and two 25 ml, dripping funnels, histamine dihydroehloride (2,00g, 10.9 mmoi) was dissolved in 10 mL of disti lled water. The solution was cooled to 3°C in an ice bath, A solution of methacryioyl chloride ( 1.14g, 10.9 mraol) in anhydrous diehi.oron5et.hane (10 ml.,} and an aqueous NaOrl solution (3-; ^' 2?M, 1 0 mL, 32,7 rnmof) were simultaneously added dropwlse while stirring vigourously over I h, The .reaction, was allowed to be warmed 10 room temperature and stirred for an additional 4h, The flask was left in a 4 ^U C refrigerator for 72 h to collect crystals. {00311 Synthesis f Hist mne-Cooiain g Copolymers. Btstannne-cofitaining random copolymers were prepared using solution tree radical eopoiymerizaiioo in DM SO or N ,N- djtwihyjformamide (OMF) with Ai ^' B as initiator. Typical synthesis was conducted as/follows. Poly(hista ifse aerylamide o.fob¾tY! aery I ale) poly(IL eo~.nBA) polymers were prepared by radical polymerization of hi tamisre acrylatnlde (HA) in the presence of 0, 1 moi% A.I.B (3∑ng) in DM SO at 65°C. Under an argon, atmosphere, HA (0.5 3.02 m o!), ^' DMSO (2.85g, 17. ! mrnol), and Al!B ( 3.3 mg, 20.2 μηιο]) were added i to a 10 mL Schlenk flask equipped with a magnetic stirrer. The flask was purged with argon tor 2.0.mm. The flask was then sealed and placed in an oil bath at 5*C, After stirring for 24 h, the polymer was precipitated using a 2; 1 ratio of. .eOH: distilled ¾0. After precipitation,, the solid, was collected and l e it in a vacuum oven at room temperature for 24h. The polymer was then dissolved in 10 wt%

then east by evaporating the DMF at 50°C exposed to air for 72 h and then 4CFC n a vacuum oven Ibr 2411.

[0032] Analytical Methods. ⁵ H NMR and ^{5 i} C ^' NMR spectra spectroscopy was performed on a Variari Unity 400 at 400 MM¾ In deuterated eldomfornt or DMSO. Themmgravimetrie analysis was completed using a TA Instruments TO A Q500 under at Hi °C mitt ^* '. DSC was executed using a TA Instruments DSC Q2000 under j us n a heat/eool/heai cycle at J0 *C mm '. All T ₈ $ were obtained fr m the second heat.. Size exclusion chromatography (SEC) was performed using a Waters size exclusion ehromatograph. The Instrument was equipped with an auto sampler, three 5 u.m Pi, gel Mtxed-C columns, a Waters 2410 retractive index (I I) detector operating at 880 nra, a Wyati Technologies mini DAWN mufti-angle laser light scattering (MALL-S) detector operating at 690 MI, and a Viscolek 270 viscosity detector with a flow rate of I niL/mln at 50 °C in DMF with 0,05 M lithium, bronsi.de (l.iBr), Reported molecular weights are relative to polystyrene, Prior to SEC analysis, ail polymers were analyzed by DLS to confirm no aggregation, in the utilized SEC solvent.. DSC was performed tinde a nitrogen .flush of 50 mL/mln at a he-atmg rate of 10 *Cmti« on a ΤΛ instruments Qi 000· DSC, which was calibrated using indium Imp ~ 156.60 ⁵ C) and ¾inc imp =* 419,47 C) standards. Glas iransulon temperatures were measured as the midpoint of the transition in the second heating amp.

Dynamic mechanical analysis (DMA) wa conducted on a TA Instruments Q800 Dynamic Mechanical Analyzer in tension mode at a frequency of ! Ez, an oscillatory amplitude of 13 urn, ana a static force of 0,01 R The temperature ramp wa 3 /mim Pol mers were dissolved in D F and cast into a Teflon® Petri dish, fo l lowed by slow evaporation of the sol vent and drying of the film in vacuo, Disposable 8 mm diameter -aluminum p rallel plates were used for rheometry. All measurements were strain-controlled at a constant noramal strain value within the linear viseoe!as lg range, determined with strain sweeps. Master curves were obtained from temperature/frequency sweep measurements using t me -temperature superposition (TT ^' S), which were described with the Williams-I.ai?dehFerry equation. <F curves were used, as the reference curves for ITS. The peel force per unit width was measured In accordance with ASTM-D330O standard. The polymer coated Mylar film was adhered to a ethyl acetate cleaned stainless steel substrate and rolled down once with a 1 kg roll. Adhesive strength wa measured at 1 80 ^β using a Cheminstrivments A - 1000 Peel Tester, The cross-head speed was maintained at 12 in/mm, and four measurements were performed on four different specimens to ensure reproducibility, 100331 Results and Discusssion

03 | We prepared two hisiamme-eomaimng monomers (Formulas 1A and IB) and hisiamsne-eomain g copolymers through free radical polymerizations (the histamine containing aerylamide is abbreviated herein as HA) The (meth)acrylanfide monomers (FormuialA and IB) provide facile synthesis to incorporate imidazole and histamine function groups in an adhesive ibr niatiom offering reversible erosslinktng sites to increase the apparent molecular wei ht and to enhance mechani al strength.. Aerykmide and met aerykmide monomers have different reactivity ratios; and corresponding homopo!ymers have different _ξ due to the methyl, group on the polymer backbone. For each histamiue-eontammg monomer, a wide variety of commercial eomononiers can be used in formulation to tune copolymer properties, in particular,, sof acrylic monomer serve as the polymer matrix to mainta the tacki ess and lower the cost fo PSA applications. ^' We can also utilize living . radical polymerization to produce copolymers with well- defined architectures such as block or branched ^' copolymers, Currently, we focus on. the -synthesis and. characterisation of -random copolymers of histamine aerylate with ??~butyi aery te t A) for PSA fabrication to examine d e structure-property relationships with histamine incorporation, £803SJ A DMF and MeOH mixiure solvent with specific ratio or dimethyl sulfoxide (D S0) as required to obtain a homogeneous pol Ymerixa on solution with specific monomer feed ratio. Pol (HA-oo-fiBA.} with 1 1 mo % I lA is an example, which was polymerized in a DMF~MeOH 5:2 solvent mixture, ¾ M M showed incorporated histamine composition m the copolymer in Figure 2. DM F SEC confirmed histamine-coutsinmg copolymers with high molecular weights were achieved in -Figure 5. A polytn-hotyi aerylate) homopoiymer with comparable molecular weight was synthesized as a control. Table I lists molecular weights of histamine-eontainmg copolymers and polynBA (relative to polystyrene standard). We can tune the histamine composition and molecular weight of copolymers through varying the monomer teed ratio, initiator concentration, and. solution concentration.

Table t

Sample j

1 1 mol% HA. I 49 k 1 101 k I 2.07 polv «BA 1 39k 1 102k ! 2 06 [0036] Polymer morpholog and behavior change significantly with increasing HA contest in a copolymer (Figure 10), Hi hornopoiymer of poIytrBA with comparable molecular weight is a slieky liquid. Histam ne-contairang polyaerylates with 1 1 moi%, 13 mol¾, and 28 mol% were tacky soft film, tacky free standing f¾m ₅ and tree standing film., respectively. Thermograyimetrie analysis demonstrated that the thermal stability of poiyaerylates remained with histamine incorporaiion (Figure 3), which proved the potential oi ^' hist mine containing po ymers in hot melt PSA fabrication. The glass transition temperature increased w t more histamine content, which was attributed to additional chain mobility restriction from Ime tolecular and

. teRolec«kr-physic.ai--cro& iinking. 11 mol% I lA-containing copolymer has a glass transition temperature around -3( ^* C (Figure 4), which is in the range o -20·-- 0 ^* C for typical PSA. i !istamiue-containing copolymers showed broad glass transitions in DSC and DMA (Figure 4 and 9).

[0037] In Figure 9, 13 mol.% and 28 mol% HA -containing copolymers are free standing films to enable dynamic mechanical analysis. Lower tan delta peak of 28 mol% HA shows thai higher density of histamine leads to less chain mobility. However, flow temperatures of 1.3 moI¾ and 28 mof% HA copolymers are the same due to similar hydrogen bonding dissociation temperature. Thermo-reversibih y of hydrogen bondin of the imidazole groups can also maintain proeessab hty of adhesive materials as well as enhance mechanical strength.

0038J Figure 6 shows the theological characterization of Po!y(H A-«w?B A) using time- temperature superposition. The master curves of storage and loss modulus versus frequency for 1 1 mol% hi A polyaerylate were referenced to 25 °G and overlaid. One step decrease of modulus elicited the absence of phase separation morphology. Bisiamine-contahuug poiyacrylsies exhibited slower molecular dynamics compared t polynilA, Histamine incorporation also ^• contributed to higher shear modulus over the ^' entire frequency range tested. The master curves demonstrate a marked improvement of cohesive strength upon introduction of histamine into pol cryiates.

[603SJ Figure 7 shows- the peel strength of 11 mo1% HA-coniatning copolymer, polynBA, and 3. Scotch* Magic ^~'M tape. Adhesive layer thickness of 1 1 mof% HA containing copolymer and polynBA. was 0.103*0.006 mm and (1125*0,030 mm. With comparable adhesive thickness, poly(I fA-co-nB A) has over i 00 times higher peel strength than polynBA. Histamine

incorporation introduces hydrogen bonding to physically crosslink sof aery he polymer, which significantly enhanced ped strength. The peel strength of 1 1 mol% H -containing copolymer is about 6 time as high as peel strength of a 3M Scotch* ^' tape. Figure 8 shows the Mylar backing alter the peel test. Strong peel force leads to plastic defbrmatlon of the Mylar backing during the peeling process. Peel force of polynBA was too weak to deform the backing, (Adhesive backings arc the curled portions in scotch tape and poly(HA~co~nBA) samples. Doubled hack tapes on the left side were used to connect adhesive backings with peel tester clamp).

[0040] In co clus on, hydrogen bonding of the imidazole groups in idstamme-eont&ining copolymer provides physical crosslinks and reversibility of adhesive material

Thermomeeh& caS analysis, thermal anal sis, peel test, and rheotogieal analysis proved histamine incorporation enhanced cohesive strength and mechanical property of polymers. The reversibility of hydrogen bonding also maintained process? biiity of adhesive materials.

0041| Although certain presently preferred embodiments of the invention have been specifically described, herein, it will be apparent to those skilled in the art to which the invention pertains that variations and modifications of the various embodiments shown and described here n may be made without departing from the spirit and scope of the invention. Accordingly, it is intended that the invention be limited only to the extent required by the appended claims ami the applicable ndes of law.