POLY( beta -HYDROXYORGANOATE) PRESSURE SENSITIVE ADHESIVE COMPOSITIONS

Abstract: The present invention provides pressure sensitive adhesives, compositions from which the pressure sensitive adhesives are formed, and articles having therein these pressure sensitive adhesives. The pressure sensitive adhesives, which have a Tg of less than about 20 DEG C, include a poly( beta -hydroxyorganoate) or mixture thereof. Preferably, these poly( beta -hydroxyorganoate)s include monomeric units of general formula (I), wherein a minor amount (preferably no greater than about 20 mole percent) of the monomeric units have an R group containing 1-3 carbon atoms; and a major amount (preferably at least about 80 mole percent) of the monomeric units have an R group containing 4-30 (preferably 4-20) carbon atoms.

Description: POLY(β-HYDROXYORGANOATE) PRESSURE SENSITIVE ADHESIVE COMPOSITIONS Field of the Invention The invention relates to pressure-sensitive adhesive compositions containing poly(β-hydroxyorganoate)s. Background of the Invention Tacky pressure-sensitive adhesive ("PSA") compositions suitable for use in adhesive tapes, for example, must have a requisite four-fold balance of adhesion, cohesion, stretchiness, and elasticity, an open time tack (i.e., period of time during which the adhesive is tacky at room temperature) on the order of days and often months or years, and a glass transition temperature (Tg) of less than about 20°C. PSA-coated tapes have been produced for at least 50 years, however, early PSA-coated tapes did not have very desirable characteristics. Early PSA tapes were merely expected to temporarily adhere to a surface upon which they were adhered. Adhesive failure, discoloration, and cohesive failure were tolerated. Today, PSAs are expected to possess this extremely delicate balance of properties known in the trade as the "four-fold" balance of adhesion, cohesion, stretchiness, and elasticity. Some PSA compositions also have desirable transparency and resistance to aging, even upon exposure to severe weathering conditions. Pressure sensitive adhesives have historically been based on petroleum-derived polymers such as poly(ethylene), poly(propylene), ethylene-vinyl acetate copolymers, and styrene block copolymers, for example. These compositions are typically further tackified, plasticized, and reinforced with a variety of resins, oils, and waxes, which are derived from both petroleum and naturally occurring feedstocks such as wood, gum, terpenes, etc. For example, early PSA compositions consisted of natural crude rubber tackified by esterfied wood rosin. However, these PSAs had poor aging properties, e.g., poor oxidative stability. These compositions were improved by the introduction of synthetic acrylic ester polymers, which were inherently tacky and possessed the elasticity and compliance required for the four- fold balance of properties. As the need arose, improvements were made in the basic acrylic ester PSA to meet the needs in the marketplace. Transparency and resistance to oxidation inherent in acrylic ester PSAs made them outstanding candidates for the most demanding PSA tape applications. Environmental factors are becoming increasingly important in products marketed to consumers such as PSA containing diaper tapes, packaging tapes, medical tapes, surgical drapes, and the like. Two very important environmental factors are the mode of production and the mode of disposal of such products. For example, during manufacture, it is important to use solvent-free processing. Additionally, with the trend toward environmentally degradable materials, a PSA that could be disposed in an environmentally sound manner (e.g., in a municipal solid waste compost site) would be an important feature. The classic composition of PSAs are generally resistant to degradation upon disposal in such an environment. In addition to resisting degradation themselves, classic PSA materials can inhibit the degradation of the substrates on which they are coated. Thus, what is needed are PSAs, i.e., adhesives having the four-fold balance of properties described above, composed of biodegradable polymers. Although hot melt adhesives, and even "pressure sensitive hot melt adhesives" (which are to be adhesives having a finite open time and lacking the four- fold balance of PSAs) composed of biodegradable polymers have been reported, little has been done in the area of biodegradable pressure sensitive adhesives. See, for example, U.S. Patent Nos. 5,169,889 (Kauffman et al.) and 5,252,646 (Iovine et al.), which describe hot melt adhesives, varying from pressure sensitive to nonpressure sensitive in character, containing either poly(lactide) homo- or copolymers or a linear polyester of 3-hydroxybutyric (HB) and 3-hydroxyvaleric acids (HV). The copolyesters, P(HB-cø-HV), are statistically random and of high crystallinity ( > 60%) throughout a range of compositions varying from 0 to 47 mol- % HV. See, for example, R.A. Gross et al., Macromolecules, 22, 1106-1115 (1989). Summary of the Invention The present invention stems from the growing movement towards products that have demonstrated some level of biodegradation. The present invention utilizes a class of naturally occurring, thermoplastic, biodegradable polymers. These biodegradable polymers are generally compostable, i.e. , capable of undergoing substantial conversion by microorganisms under aerobic conditions to carbon dioxide, water, and biomass. It is believed that at least some of these polymers are also degradable under anaerobic conditions. This class of polymers encompasses poly(hydroxyorganoate)s, i.e., poly(β-hydroxyorganoate)s, which possess thermal and oxidative stability, and chemical resistance. They are generally nontoxic and safe in use and upon disposal. They also possess a wide range of adhesive properties, particularly when formulated with an appropriate tackifier. These properties make suitable for use in pressure sensitive adhesives for a wide range of applications where it is desirable to have independent control of peel and shear adhesion, and where the ultimate disposal of the adhesive will be into a biologically active environment where biodegradation will be allowed to occur. Compositions with improved PSA properties may be made by blending two or more such polymers or by crossl inking. The present invention provides pressure sensitive adhesives, compositions from which the pressure sensitive adhesives are formed, and articles having a substrate with at least one surface on which is coated these pressure sensitive adhesives. The pressure sensitive adhesives, which have a Tg of less than about 20°C, include a poly(β-hydroxyorganoate) or mixture thereof. Preferably, these poly(β-hydroxyorganoate)s include monomeric units of the general formula: wherein: a minor amount (preferably no greater than about 20 mole percent) of the monomeric units have an R group containing 1-3 carbon atoms; and a major amount (preferably at least about 80 mole percent) of the monomeric units have an R group, i.e., side chain, containing 4-30 (preferably 4-20) carbon atoms. Particularly preferred embodiments include a poly(β-hydroxyorganoate) having a major amount of at least two different monomeric units with R groups containing 4-30 carbon atoms. The adhesive compositions of the invention can be applied to a variety of substrates by a wide range of processes, i.e., solution coating, solution spraying, thermal extrusion, emulsion coating, etc., to make adhesive articles, e.g., tapes, adhesive transfer films, surgical drapes, and the like. As used in this invention: "polymer" means a homopolymer or a copolymer (i.e., a polymer containing two or more dissimilar, i.e., different, monomers), which includes a terpolymer, a tetrapolymer, and the like; copolymers derived from more than one type of monomer may be either random or block copolymers; "tackifier" means a low molecular weight (typically having a molecular weight of less than 2000 g/mol.), high glass transition temperature (Tg) resin (typically having a Tg of greater than 50°C) used to control the adhesive tack of a polymer; "crosslinking agent" means a compound that either initiates a crosslinking process or connects polymer chains and becomes incorporated therein; this increases the molecular weight of the adhesive and thus its cohesive strength without unduly affecting its compliance or other PSA properties; this encompasses thermally or radiation activated crosslinkers, photoinitiators, sensitizers, ect. "chemical crosslinker" means a compound which, under the influence of heat or light, connects polymer chains and becomes incorporated therein; "radiation crosslinker" or "radiation active (or activated) crosslinker" means a compound which, under the influence of radiation, connects polymer chains and becomes incorporated therein; "sensitizer" means a material that absorbs energy and transfers energy to a different material in an activation process; "photoinitiator" means a material that has the ability to produce radicals upon exposure to light; and "thermal initiator" means a material that has the ability to produce radicals upon exposure to heat. As these crosslinking agents are defined, it should be apparent that some of the categories overlap such that certain compounds can be classified in more than one category. Thus, a thermal initiator could also be a chemical crosslinker, for example. Brief Description of the Drawings Fig. 1 is a Scanning Electron Micrograph of the adhesive of Example 38 as cast from solution. Fig. 2 is a Scanning Electron Micrograph of the adhesive of Example 38 after exposure for 28 days to the Biodegradability Test, with replacing inoculum and nutrient solutions at day 14. Fig. 3 is a Scanning Electron Micrograph of the adhesive of Example 38 after exposure for 28 days to the Biodegradability Test, without replacing inoculum and nutrient solutions at day 14. Fig. 4 is a Scanning Electron Micrograph of the adhesive of Example 41 as cast from solution. Fig. 5 is a Scanning Electron Micrograph of the adhesive of Example 41 after exposure for 28 days to the Biodegradability Test with replacing inoculum and nutrient solutions at day 14. Fig. 6 is a Scanning Electron Micrograph of the adhesive of Example 41 after exposure for 28 days to the Biodegradability Test without replacing inoculum and nutrient solutions at day 14. Detailed Description The present invention provides tacky PSA compositions and adhesive coated materials having me requisite four-fold balance of adhesion, cohesion, stretchiness, and elasticity, open time on the order of days, and a Tg of less than about 20°C. The adhesive compositions also have good peel strength and tack properties plus excellent shear strength and creep resistance, as well as excellent processability, with or without solvent. Generally, the adhesive compositions of the present invention also have optical clarity. The compositions of the present invention are generally resistant to oxidative and photochemical degradation for the anticipated use life of the PSA, although they will undergo degradation upon exposure to biologically active environments. The PSA compositions of the present invention preferably have a peel adhesion of at least about 1.0 N/dm, preferably at least about 10 N/dm. Thus, the PSA compositions of the present invention can be repositionable pressure sensitive adhesives. More preferably, the PSA compositions of the present invention also have a static shear of at least about 1 minute (preferably at least about 10 minutes, and more preferably at least about 25 minutes). They also have an open time at room temperature (i.e., 20-30°C), i.e., period of time during which the adhesive remains tacky, of at least about 7 days, preferably at least about 20 days, more preferably at least about 30 days, most preferably at least about 6 months. Particularly preferred PSA compositions have an opent time of at least about 1 year. The PSA compositions of the present invention include a poly(β- hydroxyorganoate), i.e., poly(hydroxyorganoate) or poly(3-hydroxyorganoate), or a mixture of various types of such polymers. Poly(β-hydroxyorganoate)s are a class of β-monoalkyl-substituted-poly-β-esters that are naturally occurring in a wide variety of bacterial microorganisms. These polyesters function as intracellular carbon and energy storage materials. They are biodegradable polymers. Various bacteria, e.g., Pseudomonas oleovorans, Pseudomonas putida, Pseudomonas aeruginosa, Alcaligenes eutrophus, Rhodospirillum rubrum, Bacillus megaterium are capable of metabolizing alkanes, alkanols, alkanoic acids, alkenes, alkenols, alkenoic acids, and esters, for example, to poly(β- hydroxyorganoate)s when grown under nutrient-limiting conditions. For example, when P. oleovorans is grown under nitrogen-limiting conditions on the substrates hexane through dodecane, poly(β-hydroxyorganoate)s are formed which, depending on the growth substrate used, contain variable amounts of the monomer units. In fact, P. oleovorans is capable of producing very unusual poly(β-hydroxyorganoate)s, such as those containing relatively long π-alkyl pendant groups. By using combinations of feedstocks, e.g., a combination of octane and nonane or octanoic and nonanoic acids, copolymers can be obtained, e.g., copolymers of β- hydroxyoctanoates and β-hydroxynonanoates. Poly(β-hydroxyorganoate)s having unsaturated pendant groups have also been produced, for example, from P. oleovorans grown with 1-alkenes, 3-hydroxyalkenoic acids, or alkenoic acids. The PSA compositions of the present invention preferably include a poly(β-hydroxyorganoate) in an amount of at least about 20 weight percent (wt-%), more preferably in an amount of at least about 30 wt-% . Although the compositions of the present invention could include 100 wt-% of a poly(β-hydroxyorganoate), preferably there is no greater than about 97 wt-% of the a poly(β-hydroxyorganoate). Particularly preferred PSA compositions of the present invention include about 40- 70 wt-% poly(β-hydroxyorganoate). Suitable poly(β-hydroxyorganoate)s for use in the present invention are biodegradable, have a Tg of less than about 10°C, preferably less than about 0°C, and more preferably less than about -5°C, and are soluble in common organic solvents. The pressure sensitive adhesives incorporating these polymers have a Tg of less than about 20°C, preferably less than about 5°C, and more preferably less than about -5°C. Prior to any crosslinking, suitable poly(β-hydroxyorganoate)s have a molecular weight (weight average) of at least about 30,000, preferably at least about 50,000, and more preferably at least about 100,000. They typically have a molecular weight of less than about 2 million. These polymers include monomeric units of the general formula: wherein R is an organic group, i.e., aliphatic, alicyclic, or aromatic group, containing 1-30 carbon atoms (preferably 1-20 carbon atoms), which can be saturated or unsaturated, branched or straight chain group, substituted or unsubstituted. The R group can be substituted, i.e., functionalized, with Br, Cl, or COOH groups, for example. The polymers useful in the PSA compositions of the present invention can include more than one type of repeat unit, i.e., monomeric unit, wherein R can vary from monomer unit to monomer unit within any one polymer. Thus, any one polymer can include a mixture of monomeric units, wherein the side chain, i.e., R group, contains anywhere from one carbon to thirty carbons. Polymers with good pressure sensitive properties, e.g., little crystallization, can tolerate up to a total of about 20 mole-% of monomeric units having 1-3 carbon atoms in the side chain. The remainder of the monomeric units have 4-30 (preferably 4-20, and more preferably 4-15) carbon atoms in the side chain. Thus, typical polymers useful in the PSA compositions of the present invention can have a total of up to 20 mole-% monomeric units wherein R is a G, G, or G, group, or mixtures thereof, and at least about 80 mole-% monomeric units wherein R is a G, G, G, G . . . C27 group, or mixtures thereof. Polymers that contain more than about 20 mole-% monomeric units wherein R is a G 3 group are generally unacceptable pressure sensitive adhesives because such groups tend to crystallize with time. Thus, d e polymers of the present invention can be homopolymers, copolymers, terpolymers, tetrapolymers, etc. There is generally no limit to the number of different types of repeat units in any one polymer. Examples of poly(β-hydroxyorganoate)s produced by bacteria that are useful for the preparation of poly(β-hydroxyorganoate)s include: poly(3- hydoxyheptanoate) (R = butyl); poly(3-hydroxy-5-methylhexanoate) (R = -butyl); poly(3-hydroxyoctanoate) (R = pentyl); poly(3-hydroxynonanoate) (R = hexyl); poly(3-hydroxydecanoate) (R = heptyl); poly(3-hydroxyundecanoate) (R = octyl); poly(3-hydroxydodecanoate) (R = nonyl); poly(3-hydroxy-7-octenoate) (R = 4- pentenyl); poly(3-hydroxy-6-heptenoate) (R = 3-butenyl); poly(3-hydroxy-8- nonenoate) (R = 5-hexenyl); poly(3-hydroxyoctanoate-co-3-hydroxynonanoate) (R = pentyl and hexyl, respectively); poly(3-hydroxyoctanoate-co-hydroxyundecanoate) (R = pentyl and octyl, respectively); poly(3-hydroxy-8-bromooctanoate) (R = 5- bromopentyl); poly(3-hydroxy-ll-bromoundecanoate) (R = 8-bromooctyl); poly(3- hydroxy-6-bromoheptanoate) (R = 4-bromobutyl); poly(3-hydroxy-5- phenylvalerate) (R = 2-phenylethyl); poly(3-hydroxyoctanoate-co-3-hydroxy-10- undecenoate) (R = pentyl and 7-octenyl, respectively); poly(3-hydroxynonanoate-co- 3-hydroxyoctadecanoate) (R = hexyl and pentadecyl, respectively); poly(3- nonanoate-co-3-hydroxy-9-octadecenoate) (R = hexyl and 6-pentadecenyl, respectively); and poly(3-hydroxy-3-phenylbutanoate) (R = benzyl). Each of these polymers is identified by its major repeat unit. That is, although each of these polymers contains a number of different repeat units, such that they are copolymers, terpolymers, etc., they are identified by die repeat units having d e largest mole percent composition. The poly(β-hydroxyorganoate)s of die present invention can be possibly eidier random or block copolymers, depending on the relative reactivities of the various monomers. However, diey are generally random copolymers, particularly because they are generally prepared by bacteria. Typically, polymers having a large percentage of two different monomeric units are prepared by using two sources of feedstock for d e bacteria to convert to a polymer. A preferred class of polymers of the present invention include unsaturation in d e side chains (in an uncrosslinked system). Preferably, these uncrosslinked polymers have no greater than about 20 mole percent monomeric units having unsaturation tiierein, and more preferably, about 1-10 mole percent. These monomeric units can have one or more double bonds in the sidechains, i.e., R groups. Another preferred class of polymers of the present invention include Cl, Br, or COOH groups in die side chain. Preferably, these uncrosslinked polymers have no greater tiian about 20 mole percent Cl, Br, or COOH groups. The addition of one or more tackifiers to me compositions of me present invention can provide a PSA having improved tack, lower viscosity, improved coatability, and improved peel adhesion. Tackifiers can also improve die open time of an adhesive. Compatible tackifiers useful in me adhesive compositions of die invention include polar or nonpolar tackifiers. Preferably, tiiey include rosin and rosin derivatives, resins derived by polymerization of CM unsaturated hydrocarbon monomers, such as polyterpenes and synthetic polyterpenes, and phenol-containing resins such as terpene phenolics and pure phenolic resins, and the like. As used herein, a "compatible" tackifier is one that is soluble at die molecular level in die PSA compositions with no phase separation. Hydrocarbon tackifying resins can be prepared by polymerization of monomers consisting primarily of olefins and diolefins and include, for example, residual by-product monomers of me isoprene manufacturing process. These hydrocarbon tackifying resins typically exhibit Ball and Ring Softening Points of about 60°C to about 145°G Examples of commercially available hydrocarbon tackifying resins include, but are not limited to terpene polymers, such as polymeric resinous materials obtained by polymerization and/or copolymerization of terpene hydrocarbons such as the alicyclic, mono, and bicyclic monoterpenes and their mixtures, including carene, isomerized pinene, terpinene, terpentene, and various other terpenes. Commercially available resins of the terpene type include me ZONAREZ terpene B-series and 7000 series available from the Arizona Chemical Corp., Wayne, NJ. Typical properties reported for the ZONAREZ terpene resins include Ball and Ring Softening Points of about 55°C to 125°C (ASTM E28-67), Acid Numbers of less than one (ASTM D465-59), and Saponification Numbers of less tiian one (ASTM D464-59). The terpene resin used in the examples below is a poly(β-pinene) resin, PICCOLYTE A135 available from Hercules Chemical Co. Inc. , which has a Ball and Ring Softening Point of 135°C, as well as POLYPALE polyterpene from Hercules. Commercially available aromatic resins include WINGTACK+, an aromatic C5 resin, available from Goodyear, Akron, OH, and INCOPOL HIOO, a hydrogenated indene, available from Amoco, Chicago, IL. Phenolic modified terpene resins and hydrogenated derivatives thereof are also useful tackifiers for the PSA compositions of the present invention. For example, the resin product resulting from the condensation, in an acidic medium, of a bicyclic terpene and a phenol, as well as pure phenolic alkyl resins, are useful tackifiers. Phenolic terpene resins are commercially available under the tradename PICOTEX from Hercules Corporation, Wilmington, DE. Phenolic resins are commercially available from Georgia Pacific, Decatur, GA, under the designation GP 2103. Suitable natural and modified rosins include gum rosin, wood rosin, tall oil rosin, distilled rosin, hydrogenated rosin, dimerized rosin, and polymerized rosin. Rosin esters are particularly useful tackifiers because they have generally higher softening points and higher molecular weights ti an unmodified rosins. Ed ylene glycol, glycerol, and pentaerythritol are the most common alcohols used for modification, e.g., esterification. Rosin esters are also quite stable and resistant to hydrolysis. Such stability typically increases with d e extent of hydrogenation. Rosin ester tackifying agents useful in the compositions of the present invention have softening temperatures of about 65°C to about 110°C. Preferred rosin ester tackifiers are glycerol rosin esters commercially available from a variety of sources. For example, glycerol rosin esters are available under the tradename FORAL 65, FORAL 85, FORAL 105, and FORAL AX from Hercules Corp., Wilmington, DE. Any combination of tackifiers can be used to improve tack. Preferably, a tackifier, or combination of tackifiers, is chosen such that the level of tack of die poly(β-hydroxyorganoate)s can be adjusted, depending on the application. More preferably, the tackifier is a biodegradable tackifier, such as glycerol rosin esters. An amount of a tackifier is used effective to adjust the tack of the adhesive for the application desired. Preferably, e total amount of tackifier(s) in the compositions of the present invention is less man about 400 parts, more preferably 3- 250 parts, and most preferably 11-150 parts, by weight per 100 parts of polymer. In corresponding weight percentages, me total amount of tackifier(s) in die compositions of the present invention is preferably less man about 80 wt-% , more preferably in a range of about 3-71 wt-%, and most preferably 10-60 wt-%. The PSA films of die present invention can be crosslinked to improve the internal strength of the adhesive. For example, the shear adhesion of a tackified composition can be enhanced by crosslinking with no loss of peel adhesion. They can be crosslinked by radiation, e.g., e-beam, widi or without a crosslinking agent. For example, wid out die presence of a crosslinking agent, e.g., crosslinker, sensitizer, or photoinitiator, radicals can be generated in the polymer tiiat can then crosslink. Alternatively, a crosslinking agent can be added to assist in crosslinking and/or become incorporated into the crosslinked polymer. Crosslinking agents tiiat do not require radiation activation can also be used, such as certain chemical crosslinkers. Thus, suitable crosslinking agents can be chemical crosslinkers, either organic or inorganic crosslinkers, or radiation active crosslinkers. Other crosslinking agents include thermal initiators, photoinitiators, and sensitizers. If desired, a crosslinking agent is used in an amount effective to cause crosslinking and improve the internal strength of d e adhesive. It should be understood that a mixture of crosslinking agents can be used to advantage, such as a photoinitiator and a sensitizer. Suitable thermal initiators include, but are not limited to, peroxides such as benzoyl peroxide, dibenzoyl peroxide, cumyl peroxide, di-t-butyl peroxide, meti yl ethyl keto peroxide, and nitriles such as azobisisobutyronitrile. Certain of these thermal initiators are also chemical crosslinkers. Preferably, a thermal initiator, or mixture of thermal initiators, (or chemical crosslinker) can be present in the PSA compositions in an amount of about 0.05-11 parts, more preferably about 0.1-5.3 parts, and most preferably about 0.1-3.1 parts, by weight of 100 parts of the polymer. In corresponding weight percentages (based on the total weight of die composition), the total amount of thermal initiator(s) in the compositions of the present invention is preferably in a range of about 0.05-10 wt-%, more preferably about 0.1-5.0 wt-% , and most preferably about 0.1-3.0 wt-% . Suitable photoinitiators include, but are not limited to: aldehydes, such as benzaldehyde, acetaldehyde, and their substituted derivatives; ketones such as acetophenone, bεnzophenone, bisbenzophenone, polybenzophenone, and their substituted derivatives such as SANDORAY 1000 (Sandoz Chemicals, Inc., Charlotte, NC); quinones photoinitiator such as the benzoquinones, anthraquinone and their substituted derivatives; thioxanthones such as 2-isopropylthioxanthone and 2-dodecyld ioxanthone; and certain chromophore-substituted vinyl halomethyl-sym- triazines such as 2,4-bis(trichloromethyl)-6-(3',4'-dimemoxyphenyl)-sym-triazine. Certain of these photoinitiators are also radiation crosslinkers, such as bisbenzophenone and triazines. Preferably, a photoinitiator, or mixture of photoinitiators, (or alternatively, radiation active crosslinker(s)) can be present in the PSA compositions in an amount of about 0.05-11 parts, more preferably about 0.1- 5.3 parts, and most preferably about 0.1-3.1 parts, by weight of 100 parts of the polymer. In corresponding weight percentages (based on the total weight of the composition), the total amount of photoinitiator(s) in the compositions of die present invention is preferably in a range of about 0.05-10 wt-% , more preferably about 0.1- 5.0 wt-% , and most preferably about 0.1-3.0 wt-% . Suitable sensitizers include, but are not limited to, xanthone, acetophenone, benzaldehyde, o-dibenzoylbenzenc, benzophenone, 2-acetylfluorenone anthraquinone, flavone, Micheler's ketone, 4-acetylbiphenyl, β-naphthyl phenyl ketone, β-naphd aldehyde, β-acetonaphthone, α-acetonaphmone, α-naphdτaldehyde, biacetyle, benzil, flurorenone, and duroquinone. Preferably, a sensitizer, or mixture of sensitizers, can be present in die PSA compositions in an amount of about 0.05-11 parts, more preferably about 0.1-5.3 parts, and most preferably about 0.1-3.1 parts, by weight of 100 parts of the polymer. In corresponding weight percentages (based on die total weight of d e composition), the total amount of sensitizer(s) in the compositions of the present invention is preferably in a range of about 0.05-10 wt-% , more preferably about 0.1-5.0 wt-% , and most preferably about 0.1-3.0 wt-% . The adhesive compositions containing radiation crosslinkers, photoinitiators, and sensitizers, can be cured using a source of radiation of sufficient energy (i.e., wavelengtii range) to generate free radicals when incident upon me particular crosslinking agent selected for use in the composition. The preferable wavelength range for the crosslinking agents disclosed above is about 400-250 nm. The radiant energy in this preferred range of wavelengths required to crosslink the adhesive film of die invention is about 50-5000 millLJoules/cm 2 and more preferably about 100-1000 mill Joules/cm 2 . Crosslinked adhesive films prepared from the PSA compositions of d e present invention preferably have a percent gel in the range of about 2-95 weight percent, more preferably about 30-80 weight percent, and most preferably about 50- 70 weight percent. As used herein, me percent gel is corrected for soluble tackifying resins and otiier additives as hereinafter described. Minor amounts, i.e. , less dian about 50 wt-% , of additives can also be included in the composition to provide adhesives for particular advantage and for special end uses. Such additives may include pigments, dyes, fillers, stabilizers, ultraviolet absorbers, antioxidants, processing oils, and the like. Antioxidants can be used to stabilize static shear, for example. Plasticizers can also be used, however, they are not particularly desirable because they tend to reduce me internal strength of me adhesive. Preferred additives are those that are degradable. Preferably, the amount of additives used can vary from 0.1 to 50 weight percent depending on the end use desired. The adhesive compositions of d e present invention are easily coated on suitable flexible or inflexible backing materials, preferably flexible backing materials, by conventional coating techniques to produce coated adhesive sheet materials in accord witii die present invention. The flexible backing material can be any material conventionally utilized as a tape backing, as well as other flexible materials. Examples of substrate materials, i.e., backing materials, include, but are not limited to: polymer films such as polyester (e.g., polyethylene terephdialate), polypropylene (e.g., biaxially oriented polypropylene), polyediylene, polyvinyl chloride, polyurethane, cellulose acetate, and ethyl cellulose; woven and nonwoven fabrics formed of tiireads or fibers of synd etic or natural materials such as cotton, nylon, rayon, glass, or ceramic material; metals and metal foils such as aluminum, copper, lead, gold and the like; paper; glass; ceramics; and composite materials comprised of laminates of one or more of these materials. Preferably, the adhesive composition can be coated on degradable substrates such as degradable plastic films, paper, and woven or nonwoven fabrics made of degradable threads or fibers. The PSA compositions of the present invention can be coated from solution by any of the coating processes well known in the art, such as knife coating, roll coating, gravure coating, curtain coating, spray coating, etc. Furthermore, die PSA compositions of the invention can be applied by extrusion coating, coextrusion coating, diermal coating, and me like, with no solvent present, thereby eliminating environmental and toxicity problems associated wi solution coating processes. Useful coating thicknesses for the present invention are in die range of about 12-2500 μm, preferably in die range of about 25-250 μm, and more preferably, in the range of about 25-125 μm. Another embodiment of me invention comprises a laminated structure of at least a first and a second substrate, die substrates being joined by a layer of d e adhesive composition of the invention. At least one of the substrates is capable of transmitting radiation so that the adhesive film can be crosslinked. Objects and advantages of mis invention are further illustrated by the following examples. The particular materials and amounts thereof recited in these examples as well as other conditions and details, should not be construed to unduly limit mis invention. All materials are commercially available except where stated or od erwise made apparent. Examples The following nonlimiting examples include exemplary preparations of the adhesives of die invention. All parts, percentages, ratios, etc., herein and in die rest of me specification are by weight unless odierwise specified. Preparation and Characterization of Poly(B-Hydroxyorganoate)s The polymers used in die PSA compositions of die present invention can be prepared according to die procedures described in K. Fritzsche et al., Int. J. Biol. Macromol., 12 85-91 (1990); H. Brand! et al., Applied Environ. Microbiol., 54 1977-1982 (1988); R.W. Lenz et al. , FEMS Microbiology Reviews, 103, 207- 214 (1992); R.A. Gross et al., Macromolecules, 22, 1106-1115 (1989); B. Hazer et al., Macromolecules, 27, 45-49 (1994); R. Peres et al., Polymer, 35, 1059-1067 (1994); K. Fritzsche et al., Makromol. Chem., 191, 1957-1965 (1990); and U.S. Application Serial No. 07/939,248, filed on September 2, 1992, entitled "Production of Polyhydroxyalkanoates from Pseudomonas. " Bacterial strain The organism used was Pseudomonas oleovorans (ATCC 29347). Stock cultures were stored on agar plates at 4°C. Medium composition, stock culture, and inoculum preparation are described in detail in T.L. Bluhm et al., Macromolecules, 19, 2871-2876 (1986). Growth Conditions The experiments were carried out wid a growdi medium containing the following materials: (N^∑HPCM, 45mM; K2HPO4, 33 mM; KH2PO4, 27 mM; and MgSO4, 2.5 mM. A microelement solution was added (0.1% v/v) which contained the following (per liter of 1 N HCl): 2.78 g FeS *7H2θ; 1.98 g MnCh*4H2θ; 2.81 g CoSα*7H 2 O; 1.67 g CaCl2*2H 2 O; 0.17 g CuCh-2H2O; 0.29 g ZnSCM 7H2θ. The medium was supplemented witii 25 mM sodium octanoate for the preparation of poly(β-hydroxyoctanoate) ("PHO"); 40 mM sodium nonanoate for the preparation of poly(β-hydroxynonanonoate) ("PHN"); 25 mM total mixture of a 9:1 molar ratio of sodium octanoate and sodium undecanoate for me preparation of poly(β-hydroxyoctanoate-co-β-hydroxy-ll-undecenoate) ("PHO/U"), 15 mM each of sodium octanoate and sodium nonanoate for the preparation of poly(β- hydroxyoctanoate-co-β-hydroxynonanoate) ("PHO/N"). The pH was adjusted to 7.0. These sodium salt feedstocks were prepared in situ from NaOH and e corresponding acid. Shake flask cultures were cultivated in 500 mL Erlenmeyer flasks, containing 200 mL of medium at 30°C and 150 rp (revolutions per minute). Modified flasks were indented to improve d e aeration of d e culture during shaking. Fermentor cultures were cultivated in a 2-liter Biostat E bioreactor (B. Braun Biotech Inc., Allentown, PA) The culture volume was 1.0 L; the temperature was maintained at 30°C and pH at 7.0; stirring was carried out at 250 rpm; and me aeration rate was 2.0 L of air per minute. Larger fed batch cultures were grown in Microferm 114 fermentors (New Brunswick Scientific, Edison, NJ) using culture volumes of 12 L; aeration was at 5 L/minute; stirring was carried out at 250-300 rpm; and temperature and pH were maintained at 30°C and 7.0, respectively. Feedstock (120 mL), consisting of 1.0 M sodium octanoate (or other sodium salt of an organic acid), and 125 mM mM NH growdi media (final culture concentration of 10 mM and 2.5 mM NH4 + respectively) were added after 10 hours growdi, and at 2 hour intervals tiiereafter. For other salts of organic acid feedstocks, the addition was such as to maintain growth. Cultures were harvested after 18 hours. Harvest times for other polymers were: 72 hours for PHN; 22 hours for PHO N; 24 hours for PHO/U. Dissolved oxygen was measured using a polarographic electrode (obtained from Ingold Inc., Wilmington, MA). Oxygen consumption of die culture was determined by analyzing d e oxygen concentration in d e air inlet and oudet of d e bioreactor using an OM-14 oxygen analyzer (Beckman Inc., Wakefield, MA). These parameters yielded a maximum oxygen transfer rate of 250 mL L'h "1 . In continuous cultures, growdi rates were established by increasing the cell density, and adjusting the dilution rate to maintain a given cell density. Aeration was constant at 2.0 liter of air per minute. All continuous culture experiments were done using die Biostat E bioreactor. Cell growth was determined photometrically by measuring me optical density (O.D.) of die culture at 660 nm, gravimetrically by weighing the amount of dry cells after washing and lyophilization and also by plate counting methods. Cells were harvested by centrifugation (4°C, 12000 x g, 15 minutes) resuspended in distilled water, and repelleted. Plate counting was done using stock culture media wid 2% agar added, incubated overnight at 30°C and counted. Only diose plates witii between 20 and 100 colonies were counted. Poly(β-hydroxyorganoate) Quantification and Analysis To determine the polymer content and composition of lyophilized whole cells die intracellular poly(β-hydroxyorganoate) was degraded to its constituent hydroxycarboxylic acid methyl esters by methanolysis. The mediyl esters were men assayed by gas chromotography according to d e method described in H. Brandl et al., Appl. Environ. Microbiol., 54, 1977-1982 (1988). Extraction of d e Polymer Poly(β-hydroxyorganoate) was extracted from lyophilized cells into chloroform using a soxhlet extractor, precipitated in 10 volumes of medianol, centrifuged, and allowed to dry to constant weight according to die procedure oudined in H. Brandl et al., Appl. Environ. Microbiol., 54, 1977-1982 (1988). Molecular Weight Determination The molecular weight of die extracted polymer was determined by gel permeation chromatography. Chloroform was used as die eluent at a flow rate of l.O mL minute. Polymer samples were dissolved in chloroform (20 mg/mL) and 100 microliters of this solution was analyzed. Calibration curves were generated using polystyrene standards. The Mw (weight average molecular weight), Mn (number average molecular weight), and PDI (polydispersity index) are reported. PHO Analysis Molecular weight determination was done by Gel Permeation Chromatography in chloroform solvent using polystyrene standards. Repeat unit analysis was done using Gas Chromatography. The poly(β-hydroxyorganoate) undergoes methanolysis, and me 3-hydroxy methyl esters of the hydrolyzed acid repeat units were analyzed. Gas Chromatography SIDE CHAIN REPEAT UNIT MOLE % LENGTH C-3 C-6 12 C-5 C-8 88 Thermal Analysis Molecular Weight Determination PDI _= 2.2 PHN Analysis Molecular weight determination was done by Gel Permeation Chromatography in chloroform solvent using polystyrene standards. Repeat unit analysis was done using Gas Chromatography. The poly(β-hydroxyorganoate) undergoes metiianolysis, and the 3-hydroxy methyl esters of the hydrolyzed acid repeat units are analyzed. Gas Chromatography SIDE CHAIN REPEAT UNIT MOLE % LENGTH C-2 C-5 4.6 C-4 C-7 42.6 C-6 C-9 52.9 Thermal Analysis T g = -34°C Molecular Weight Determination PDI = 2.5 PHO/N Analysis The PHO/N polymer was analyzed using GC, DSC, and GPC mediodology. Analyses were done to determine die repeat unit composition, melting and glass transition temperatures, and the molecular weight of die samples. Molecular weight was determined by GPC using polystyrene standards. The results of these analyses are tabulated below. Gas Chromatography SIDE CHAIN REPEAT UNIT MOLE % LENGTH C-3 C-6 3.6 C-4 C-7 12.7 C-5 C-8 37.4 C-6 C-9 21.6 C-7 C-10 0.7 C-8 C-l l 12.9 C-9 C-12 11.0 Thermal Analysis T, = -32.2°C Molecular Weight Determination PDI -= 3.03 PHO/Um Analysis The PHO/U[l] polymer was analyzed using GPC, NMR, and DSC methodology. Analyses were done to determine, melting and glass transition temperatures and die molecular weight of the samples. Molecular weight was determined by GPC using polystyrene standards. The results of these analyses are tabulated below. Thermal Analysis Molecular Weight Determination PDI = 2.7 Proton NMR Analysis Analysis of me proton NMR of the sample indicated tiiat diere is 7-9% unsaturated repeat units in die polymer. PHO/U[2] Analysis The PHO U[2] polymer was analyzed using GPC, NMR, and DSC methodology. Molecular weight was determined by GPC using polystyrene standards. The results of these analyses are tabulated below. Thermal Analysis Molecular Weight Determination PDI = 2.60 Proton NMR Analysis Analysis of the proton NMR of d e sample indicated tiiatthere is 12-16% unsaturated repeat units in the polymer. Test Methods The test procedures used in the examples to evaluate and compare the properties of the PSA compositions and tapes made from them are industry standard tests. These tests are described in detail in various publications of die American Society for Testing Materials (ASTM), Philadelphia, PA and me Pressure Sensitive Tape Council (PSTC), Glenview IL. References to these standards are also given. Shear Strength (ASTM D-3654-78) The shear strength is a measure of die cohesiveness or internal strengdi of an adhesive. It is based upon d e amount of force required to pull an adhesive strip from a standard flat surface in a direction parallel to die surface to which it has been affixed with a definite pressure. It is measured in units of time (minutes) required to pull a standard area of PSA coated sheet material from a stainless steel test panel under stress of a constant, standard load. The tests were conducted on adhesive coated strips applied to a stainless steel panel such that a 12.7 mm by 12.7 mm portion of each strip was in firm contact wid d e panel, with one end portion of the tape being free. The panel widi coated strip attached was held in a rack such tiiat die coated surface of me panel formed an angle of 182° widi die vertical tape free end, which was d en tensioned by application of a force of one kilogram applied as a hanging weight from the free end of d e coated strip. The 2° greater tiian 180° was used to negate peel adhesions, tiius insuring mat only me shear forces were measured in order to more accurately determine die holding power of die tape being tested. The time elapsed for each test specimen to separate from the steel panel was recorded as me shear strengdi. Mode of Failure (MOF) The time at which me mass falls is called "Shear Test" and is reported as "10,000+" if die tape has not failed after 10,000 minutes. Widi each Shear is indicated d e mode of failure as follows: PO = pop-off, i.e., 75-100% adhesive failure from steel plate; CF = adhesive split: bom surfaces completely covered by adhesive; NTR= residue failure: adhesive covering 100% of backing widi a small residue transferred to panel; The pop-off failure mode is preferred because it is indicative of adhesive failure of die adhesive/steel interfacial bond as opposed to cohesive failure of d e adhesive. Adhesives of various shear adhesions, all widiin me range of the present invention (1-10,000+ minutes), are preferred depending on end-use applications. Two specimens of each tape were tested and the shear tests were averaged to obtain the shear value. Peel Adhesion (ASTM D 3330-76) The peel adhesion is the force required to remove a PSA coated test specimen from a test panel measured at a specific angle and rate of removal. In the examples, this force was expressed in Newtons per decimeter (N/dm) widdi of coated sheet. The procedure followed was: 1) A test specimen 12.7 mm wide was applied to a horizontally positioned clean glass test plate. A 2.2 kg rubber roller was used to press a 12.7 cm lengtii of specimen into firm contact with die glass surface. 2) The free end of me specimen was doubled back nearly touching itself so the angle of removal was 180°. The free end was attached to die adhesion tester scale. 3) The glass test plate was clamped in d e jaws of tensile testing machine, which was capable of moving the plate away from the scale at a constant rate of 2.3 meters per minute. 4) The scale reading in Newtons was recorded as die tape was peeled from the glass surface. Percent Gel Test (ASTM D 3616-82) The percent gel is used as an indication of cure level. The percent gel is 100 times the gelled mass divided by die total mass of material that is capable of forming a gelled network. Crosslinking improves the creep and shear resistance of pressure- sensitive adhesives. The transition from a cohesive to an adhesive failure during peeling advances to a lower peel rate and higher temperature wid an increase in crosslink density. Many important properties of crosslinked pressure-sensitive adhesives vary with d e gel content. Hence, determination of the gel content provides a means for controlling the process and thereby raising die quality of die tape. Extraction tests permit verification of me proper gel content of polymers in the PSAs and tiiey also permit comparison between different crosslinked adhesives and their specific end uses. Gel Content Determination: A square test specimen (3.81 cm x 3.81 cm) containing approximately 0.15 g of PSA was cut from die tape and placed in a 120-mesh stainless steel basket measuring approximately 4 x 8 cm. The contents were weighed to die nearest 0.1 mg and then immersed in a capped beaker containing sufficient toluene to cover me specimen. After extraction for 48 hours, die basket (containing the specimen) was removed, drained, and placed in an oven at 93°C. The basket and specimen were dried to a constant weight and me gel content was determined as follows: weight lost during extraction Extract % = x 100 weight of original specimen Gel content = 100 - percent extract Two specimens of each tape were tested and d e results were averaged to obtain die gel content value. Biodegradability Test for Poly(hydroxyorganoate) Adhesives in die Presence of Ps. Maculicola Ps. Maculicola (previously ATCC 11781) was obtained from the Department of Microbiology, University of Massachusetts Amherst, Amherst, MA. The organism was cultured on E* media agar plates with the addition of 20 mM glucose at 37°C for 48 hours. E* media agar plates were prepared from the following recipe: 5.94 g of (NH HPO,; 5.8 g of K3PO4; and 3.7 g of KH2PO4. The above dry mix was added to 1.0 L of water containing 15.0 g of granular agar. The media was supplemented widi the following trace elements: 20 mL of 100 mM MgSO ; and 1.0 mL of die micro-elements solution (1.0 L of 1.0 M HCl containing: 2.78 g FeSCM-7H2θ; 1.98 g of MnCh*4H2O; 2.81 g of C0SO47H2O; 1.67 g of CaCh*2H2θ; 0.17 g of CuCh*2H 2 O; and 0.29 g of ZΠSCM 7H 2 O. An inoculum suspension was prepared in E* media brod using a 48 hour culture of die Ps. Maculicola to a density of a 0.5 McFarland Turbidity Standard #1 (approximately 10 s organisms per mL). The adhesive samples were cut into 1.25 x 1.25 or 1.25 x 0.7 cm pieces and were attached to me bottom of sterile polystyrene dishes (100 x 25 mm) with epoxy (eitiier a DEV-TUBE 5-minute epoxy from Devcon, Illinois Tool Works, Danvers, MA, or an extra fast setting epoxy from Hardman, Inc., Belleville, NJ) with d e test adhesive exposed. The epoxy was allowed to cure for at least 2 weeks at room temperature. To each petri dish was added 50 mL of E* media broth containing 10 mM glucose. The inoculum (50 μl) was added to each petri dish and the samples were incubated at 28°C for various time periods. Two sets of samples were prepared. In d e first set, the inoculum and nutrient brod solutions were replaced at 14 days. In die second set, the same suspension was used for the duration of the test. At 7, 14, 21, and 28 days, sample sets were removed from the incubator, rinsed widi deionized water, and allowed to dry. The adhesive samples were then visualized using scanning electron microscopy to determine if bacterial attachment to the surface had occurred and if etching or erosion of the surface had occurred. Example 1 An Adhesive Containing PoIy(hydroxynonanoate) [PHN] A laboratory scale coating was prepared by allowing 4 g of poly(β- hydroxynonanoate) (prepared as described above) to dissolve in 8 g of chloroform. This solution was knife-coated onto a 2 mil (50 μm) PET backing (Minnesota Mining and Manufacturing, St. Paul, MN) using a handspread coater. The handspread was dried at room temperature for 12 hours to remove the chloroform and die dry coating ti ickness was 23 μm. The sample was cut for use in the test procedures de¬ scribed for peel adhesion and shear strengd and die results are shown in Table 1. Example 2 An Adhesive Containing a UV-cured PHN The laboratory scale coating of Example 2 was prepared in the same manner as tiiat in Example 1, except that to the chloroform solution was added 12 mg of IRGACURE 184 (Ciba Geigy, Chicago, IL). The coating thickness was 20 μm. The handspread was subjected to UV (15W black lights, 1 hour at a distance of 10 cm) radiation after drying to effect a degree of crosslinking. The peel and shear test results for this material are shown in Table 1. Example 3 A Tackified Adhesive Containing PHN The laboratory scale coating of Example 3 was prepared in die same manner as that in Example 1, except that 2.67 g of polymer was used, and to d e chloroform solution was added 1.33 g of FORAL 85 hydrogenated rosin ester (Hercules Chemical, Wilmington, DE). The coating diickness was 20 μm. The peel and shear test results for this material are shown in Table 1. Example 4 A Tackified UV-cured Adhesive Containing PHN The laboratory scale coating of Example 4 was prepared in die same manner as tiiat described in Example 2, except that 2.67 g of polymer was used, and to the chloroform solution was added 1.33 g of FORAL 85 hydrogenated rosin ester. The coating diickness was 28 μm. The peel and shear test results are shown in Table 1. Example 5 A UV-cured PHN Adhesive with Tackifier Resin The laboratory scale coating of Example 5 was prepared in the same manner as that described in Example 4, except mat to 0.40 g of poly(β- hydroxynonanoate), 0.20 g of FORAL 85 and 6 mg of benzophenone (Aldrich Chemical Co., Milwaukee, WI) were added 1.33 g of chloroform. The dry coating diickness was 25 μm. The peel and shear tests for this UV-cured tape are shown in Table 1. Examples 6-31 Examples 6-31 were prepared as described in Example 5, except that the ratio PHN:tackifier:photoinitiator ratio was varied for different types and concentrations of tackifying resins and different types and concentrations of crosslinking agent. The compositional information and d e coating diickness are shown in Table 1. The results of d e peel and shear tests for tiiese UV-cured tapes are shown in Table 1. Examples 32-37 An Adhesive Containing Poly(β-hydroxyoctanoate) [PHO] Examples 32-37 were prepared as described in Example 5, except that the polymer used was poly(β-hydroxyoctanoate) (prepared as described above) and different types and concentrations of tackifying resins and crosslinking agents were used. The data describing die peel and shear test results are shown in Table 2. Example 38 An Adhesive Containing Poly(β-hydroxyoctanoate-co-β-hydroxynonanoate) [PHO/N] A laboratory scale coating was prepared by allowing 0.4 g of poly(β- hydroxyoctanoate-co-β-hydroxynonanoate) (prepared as described above) to dissolve in 0.8 g of chloroform. This solution was knife-coated onto a 2 mil (50 μm) PET backing (Minnesota Mining and Manufacturing, St. Paul, MN) using a handspread coater. The handspread was dried at room temperature for 12 hours to remove the chloroform. The dry coating diickness was 25 μm. The sample was cut for use in die test procedures described for peel adhesion and shear strengtii. The results are shown in Table 3. The material of Example 38 was subjected to me Biodegradability Test described above. The results of d e test are shown in Figures 2 and 3, which are Scanning Electron Micrographs of d e sample after 28 days exposure, widi and widiout replacing die inoculum and nutrient brotii solutions at 14 days, respectively. For reference, a micrograph of the initial sample is included as Figure 1. Figure 1 shows a smooth surface of the sample as coated from solution. The surface shown in Figure 2 has been eroded by d e action of the microorganisms, i.e., biodegradation. The extent of biodegradation was greater when die inoculum and nutrient broth solutions were replaced at 14 days as shown in comparing Figure 2 (replaced) and Figure 3 (not replaced). Examples 39-65 Adhesive tapes containing PHO/N were prepared as described in Example 38, except to 0.4 g of PHO/N was added 0.20 g of a tackifier resin and an amount of crosslinking agent as described in Table 3. Different types and concentrations of tackifying resins and crosslinking agents. The data describing d e peel and shear test results are shown in Table 3. A larger quantity sample of Example 41 was prepared in die same manner in order to provide samples for die Biodegradability Test. The results in die biodegradability test on Example 41 are shown in Figures 5 and 6, which are Scanning Electron Micrographs of die sample at 28 days exposure, widi and widiout replacing d e inoculum and nutrient brotii solutions at 14 days, respectively. For reference, a micrograph of the initial sample is included as Figure 4. Figure 4 shows die surface of Example 41 as coated from solution. The surface shown in Figure 5 has been eroded by die action of d e microorganisms, i.e., biodegradation, after 28 days in die Biodegradability Test. The extent of biodegradation was greater when me inoculum and me nutrient brotii solutions were replaced at 14 days, as can be seen in comparing Figure 5 (replaced) and Figure 6 (not replaced). Example 66 An Adhesive Containing Poly(β-hydroxyoctanoate- co-B-hydroxy-10-undecenoate) [PHO/U] A laboratory scale coating was prepared by allowing 0.4 g of poly(β- hydroxyoctanoate-co-β-hydroxyundecenoate) (prepared as described above) to dissolve in 0.8 g of chloroform. This solution was knife-coated onto a 2 mil (50 μm) PET backing (Minnesota Mining and Manufacturing, St. Paul, MN) using a handspread coater. The handspread was dried at room temperature for 12 hours to remove the chloroform. The dry coating thickness was 20 μm. The sample was cut for use in the test procedures described for peel adhesion and shear strength. The results are shown in Table 4. Examples 67-90 Adhesive tapes containing PHO/U were prepared as described in Example 66, except to 0.4 g of PHO/U was added 0.20 g of a tackifier resin and an amount of crosslinking agent as described in Table 3. PHO/U of two different compositions was used in die preparation of the adhesives. The difference is noted in Table 4. PHO/Ufl] contains 7-9 mole-% unsaturated side chains and PHO/U[2] contains 12-16 mole-% unsaturated side chains. Different types and concentrations of tackifying resins and crosslinking agents were used. The data describing die peel and shear test results are shown in Table 4. Examples 91-96 Preparation of UV cured Adhesives for use in the % Gel Test Examples 91-96 were prepared as described in Example 2, except tiiat either PHN or PHO/U was used as die polymer and various amounts of the photoinitiator, benzophenone (Aldrich Chemical Co., Milwaukee, WI), was used. The compositional information and me results of the % Gel Test are described in Table 5. TABLE 1 Ex # Composition Coating wt 180° peel (glass) Static MOF in thickness (N/dm) shear shear (μm) (min) 1 PHN 23 1 13 PO 2 PHN, 0.3% IRGACURE 184 20 1 14 PO 3 PHN, 35% FORAL 85 20 81 [AT] 1 CF 4 PHN, 35% FORAL 85, 0.3% IRGACURE 23 82 [AT] 1 CF 184 5 PHN, 35% FORAL 85, 1 % Bzophn 28 79 [CF] 2 CF ω t 6 PHN, 35% FORAL 85, 9% Bzophn 20 28 s 2 CF 7 PHN, 35% FORAL AX, 1 % Bzophn 28 66 [CF] 1 CF 8 PHN, 30% FORAL AX, 10% Bzophn 28 85 [CF] 2 CF 9 PHN, 35% FORAL AX, 0.15% MPBT 25 50 [CF] 1 CF 10 PHN, 35% PICCOLYTE A135, 1 % Bzophn 20 29 s 167 CF 11 PHN, 30% PICCOLYTE A135, 10% Bzophn 25 106 [CF] 1128 CF 12 PHN, 32% PICCOLYTE A 135, 5% Bzophn 25 33 s,[CF] 1133 CF 13 PHN, 35% PICCOLYTE A 135, 0.15% 25 74 36 CF Ex # Composition Coating wt 180° peel (glass) Static MOF in thickness (N/dm) shear shear (μm) (min) MPBT 14 PHN, 35% REGALRITE 355, 1 % Bzophn 25 69 2 CF 15 PHN, 30% REGALRITE 355, 10% Bzophn 25 87 [PO] 6 CF 16 PHN, 35% REGALRITE 355, 0.15% MPBT 23 i 19 3 CF 17 PHN, 35% GP 2103, 1 % Bzophn 23 136 s,[CF] 11 CF 18 PHN, 30% GP 2103, 10% Bzophn 23 93 [CF] 1 CF 19 PHN, 35% GP 2013, 0.15% MPBT 23 92 20 CF 20 PHN, 30% POLYPALE, 10% Bzophn 25 83 [PO/CF] 2 CF 21 PHN, 35% POLYPALE, 0.15% MPBT 25 si 59 5 CF 22 PHN, 30% EASTOTAC H100R, 10% 25 i 4 [PO] 10,000+ Bzophn 23 PHN, 30% INDOPOL H100, 10% Bzophn 28 si 13 [PO/NTR] 1 PO 24 PHN, 30% PICOTEX LC, 10% Bzophn 33 68 s,[CF] 2754 PO 25 PHN, 32% PICOTEX LC, 5% Bzophn 25 97 [CF] 1171 PO 26 PHN, 33% PICOTEX LC, 1 % Bzophn 25 76 [CF] 2 CF 27 PHN, 30% WINGTAC +, 10% Bzophn 25 si 23 [PO] 765 PO Ex ff Composition Coating wt 180° peel (glass) Static MOF in thickness (N/dm) shear shear (μm) (min) 28 PHN, 32% WINGTACK+, 5% Bzophn 25 i 12 [PO] — 29 PHN, 33% WINGTACK+, 1 % Bzophn 23 i 18 [PO] — 30 PHN, 32% PICCOLYTE A135, 5% Bzophn 25 51 s,[CF] 5257 CF 31 PHN, 32% PICOTEX LC, Bzophn 25 111 [CF] 475 CF Abbreviations: s = raspy peel, si = slightly immiscible, i = immiscible, PO = pop off, AT = adhesive transfer, CF = cohesive failure, NTR = nontacky residue, Bzophn = benzophenone, MPBT = 2,4-bis(trichlorometiiyl)-6-(3 , -med.oxyphenyl)- sym-triazine (manufactured by Minnesota Mining and Manufacturing Co., St. Paul, MN). EASTOTAC H100R is available from Eastman Chemical Co., Kingsport, TN. REGALRITE 355 is available from Hercules Corp., Wilmington, DE. fc The data of Table 1 demonstrate the ability of a poly(β-hydroxyorganoate) such as PHN to perform as a pressure sensitive adhesive. The polymer alone exhibited minimal PSA properties in die peel adhesion and static shear tests. The polymer can be tackified to increase d e peel adhesion and can be crosslinked to increase die time under which a load will be held in shear. The crosslinking experiments, which are described in this table, were done in static air. The most effective adhesives were formed when the polymer was crosslinked and tackified. The peel and shear values can be fine- tuned depending on the type of tackifier and degree of crosslinking that is required for a new PSA tape. The tackifier resins found to be the most effective were those of the general class of rosin esters or aromatic materials such as the FORAL 85, GP 2103, and PICOTEX resins. A variety of crosslinking agents that are able to initiate free radicals are effective at crosslinking the polymers of the invention. CO TABLE 2 Ex # Composition Coating 180° peel from glass Static MOF in diickness (N/dm) shear shear (μm) (min) 32 PHO, 35% FORAL 85, 9% Bzophn 23 59 s 766 CF 33 PHO, 30% PICCOLYTE A135, 9% Bzophn 25 13 s 34 PHO, 32% PICCOLYTE A135, 5% Bzophn 25 si 2 [PO] 35 PHO, 35% PICCOLYTE A 135, 0.15% 23 si 18 s 1925 CF MPBT 36 PHO, 32% WINGTACK+, 5% Bzophn 25 i 19 [NTR] LO 37 PHO, 35% WINGTACK+, 0.15% MPBT 28 i 14 [NTR] Abbreviations: s = raspy peel, si = slightly immiscible, i = immiscible, PO = pop off, CF = cohesive failure, NTR = nontacky residue, Bzophn = benzophenone, MPBT = 2,4-bis(trichloromethyl)-6-(3'-med oxyphenyl)-sym-triazine (manufactured by Minnesota Mining and Manufacturing Co., St. Paul, MN). The data of Table 2 are for PHO as a pressure sensitive adhesive. This polymer was found to exhibit the properties of a PSA to a lesser degree than for PHN. TABLE 3 Ex # Composition Coating 180° Peel from glass Static shear MOF in thickness (N/dm) (min) Shear (μm) 38 PHO/N 25 1 10,000+ 39 PHO/N, 32% GP 2103, 5% Bzophn 25 80 s,[CF] 6 CF 40 PHO/N, 32% FORAL 85, 5% Bzophn 25 112 s,[CF] 10,000+ 41 PHO/N, 32% PICOTEX LC, 5% 30 97 s,[CF] 8595 PO Bzophn CO 42 PHO/N, 10% FORAL 85, 5% Bzophn 25 32 756 CF 43 PHO/N, 20% FORAL 85, 5% Bzophn 25 72 [CF] 1285 PO 44 PHO/N, 30% FORAL 85, 5% Bzophn 28 102 [CF] 3319 PO 45 PHO/N, 30% FORAL 85, 5% Bzophn 25 73 — 46 PHO/N, 40% FORAL 85, 5% Bzophn 25 99 s,[CF] > 10,000 47 PHO/N, 40% FORAL 85, 5% Bzophn 23 117 [CF] — 48 PHO/N, 50% FORAL 85, 5% Bzophn 25 97 s,[CF] 123.5 CF 49 PHO/N, 60% FORAL 85, 5% Bzophn 33 8 [CF] 853 CF Ex # Composition Coating 180° Peel from glass Static shear MOF in thickness (N/dm) (min) Shear (μm) 50 PHO/N, 80% FORAL 85, 5% Bzophn 28 1 [NTR] 1 51 PHO/N, 55% FORAL 85, 5% Bzophn 30 72 [CF] — — 52 PHO/N, 20% PICOTEX LC, 5% Bzophn 25 81 53.5 PO 53 PHO/N, 30% PICOTEX LC, 5% Bzophn 28 112 [CF] 2844 PO 54 PHO/N, 40% PICOTEX LC, 5% Bzophn 25 147 [CF] 10,000+ 55 PHO/N, 60% PICOTEX LC, 5% Bzophn 28 16 s,[CF] 457 CF 56 PHO/N, 80% PICOTEX LC, 5% Bzophn 30 1 [NTR] 1 57 PHO/N, 50% PICOTEX LC, 5% Bzophn 25 74 s,[CF] 2 ωω 58 PHO/N, 45% PICOTEX LC, 5% Bzophn 23 72 s,[CF] 10,000+ 59 PHO/N, 55% PICOTEX LC, 5% Bzophn 30 16 s,[CF] 224 CF 60 PHO/N, 35% FORAL 85, 9% Bzophn 28 66 s 2075 PO/NTR 61 PHO/N, 30% PICCOLYTE A 135, 9% 28 11 s 10,000+ Bzophn 62 PHO/N, 32% PICCOLYTE A 135, 5% 20 54 s,[CF] 2620 CF Bzophn 63 PHO/N, 35% PICCOLYTE Al 35, 0.15% 18 79 s 10,000+ Ex # Composition Coating 180° Peel from glass Static shear MOF in thickness (N/dm) (min) Shear (μm) MPBT 64 PHO/N, 32% WINGTAC +, 5% 20 i 3 [PO] Bzophn 65 PHO/N, 32% PICOTEX LC, 5% 20 89 [CF] 6060 CF Bzophn Abbreviations: s = raspy peel, si = slightly immiscible, i = immiscible, PO = pop off, CF = cohesive failure, NTR = nontacky residue, Bzophn = benzophenone. LO The data of Table 3 show the utility of PHO/N as a PSA. High performance PSAs were obtained when the tackified polymer was crosslinked, although PHO/N alone showed properties of a PSA. The tackifiers which provided a range of peels and remained compatible with die polymer were of the general classes of rosin acid esters and aromatic resins. A range of compositions using two tackifiers was developed, using PICOTEX LC and FORAL 85. The examples showed a change in peel values with change in tackifier concentration. In general, PHO/N performed extremely well as a PSA. The crosslinking experiments which are described in this table were done in static air. TABLE 4 Ex # Composition Coating 180° peel from Glass Static shear MOF in thickness (N/dm) (min) shear μm 66 PHO/U 13 1 10,000+ 67 PHO/U[l], 35% FORAL 85, 9% Bzophn 23 63 s 2184 PO/NTR 68 PHO/U[l], 32% FORAL 85, 5% Bzophn 18 65 s 10,000+ 69 PHO/U[l], 35% FORAL 85, 1 % Bzophn 20 86 s 10,000+ 70 PHO/U[l], 35% PICCOLYTE A 135, 1 % 25 26 s 10,000+ S Bzophn 71 PHO/U[l], 35% PICCOLYTE A 135 , 0.15 % 23 si 4 s 10,000+ MPBT 72 PHO/U[l], 35% FORAL AX, 1 % Bzophn 23 74 [CF] 7 CF 73 PHO/U[l], 35% FORAL AX, 0.15 % MPBT 23 si 62 [CF] 16 CF 74 PHO/U[l], 32% PICOTEX, 5% Bzophn 23 71 273 CF/NTR 75 PHO/U[l], 30% PICOTEX LC, 5% Bzophn 25 89 76 PHO/U[l], 35% PICOTEX LC, 1 % Bzophn 25 si 82 10,000+ Ex It Composition Coating 180° peel from Glass Static shear MOF in thickness (N/dm) (min) shear J_™ 89 PHO/U[2], 30% PICOTEX LC, 5% Bzophn 23 4 s 431 PO 90 PHO/U[2], 40% PICOTEX LC, 5% Bzophn 23 2 s 2400+ Abbreviations: s = raspy peel, si = slightly immiscible, i = immiscible, PO = pop off, CF = cohesive failure, NTR = nontacky residue, Bzophn = benzophenone, MPBT = 2,4-bis(trichloromethyl)-6-(3 , -meuioxyphenyl)-sym-triazine (manufactured by Minnesota Mining and Manufacturing Co., St. Paul, MN). The data of Table 3 show the utility of PHO/U as a PSA. High performance PSAs were obtained when the tackified polymer was M crosslinked, although PHO/U alone showed properties of a PSA. The tackifiers which provided a range of peels and remained compatible wid die polymer were of the general classes of rosin acid esters and aromatic resins. A range of compositions using two tackifiers was developed, using PICOTEX LC and FORAL 85. The examples showed a change in peel values wid change in tackifier concentration. The tackified, crosslinked polymer PHO/U[l], containing side chains having 7-9 mole-% unsaturation performed well as a PSA; however, PHO/U [2] which contained 12-16 mole-% unsaturation in the side chains and provided only adhesives having lower peel adhesion. The crosslinking experiments which are described in this table were done in static air. TABLE 5 Example # Composition Coating wt. % Gel thickness (μm) 91 PHO/U, 10 % 24 80.88 Bzophn 92 PHO/U, 5% Bzophn 23 81.40 93 PHO/U, 1 % Bzophn 28 41.90 94 PHN, 10 % Bzophn 26 72.11 95 PHN, 5% Bzophn 25 73.06 96 PHN, 1 % Bzophn 26 48.71 Abbreviations: Bzophn = benzophenone. A set of examples of polymer and photoinitiator was prepared to carry out gel content experiments. A perusal of the data in Table 5 showed that an increase in concentration of initiator content increased the gel content. TABLE 6 Example # 180 ° Peel (glass) Aging Time (days) 25 °C 40 104 25 41 90 25 78 49s 25 79 97 25 31 102 25 30 48 25 74 27s 150 62 32s [CF] 150 10 120 [CF] 180 14 68 [CF] 180 19 98 [NTR] 180 13 118 [CF] 180 18 83 [CF] 195 15 63 [CF] 195 67 55 245 32 89s, [CF] 245 60 26s [CF] 245 Abbreviations: CF = cohesive failure The peel adhesion values after aging at room temperature for a specified period of time of some of the Examples from Tables 1-4 are listed here. As can be seen in the data, the peel adhesion of the PSAs were maintained with time, a vital characteristic of a PSA. This data also indicates that the adhesives remain tacky for the aging time shown. Consequently, an open time greater than the aging time was maintained. While this invention has been described in connection with specific embodiments, it should be understood that it is capable of further modification. The claims herein are intended to cover those variations which one skilled in the art would recognize as the chemical equivalent of what has been described herein. Thus, various omissions, modifications, and changes to the principles described herein may be made by one skilled in the art without departing from the true scope and spirit of the invention which is indicated by the following claims.

Claims: CLAIMS: 1. A pressure sensitive adhesive comprising a poly(β-hydroxyorganoate) and a tackifier, wherein the pressure sensitive adhesive has a Tg of less than about 20°C. 2. The pressure sensitive adhesive of claim 1 wherein the poly(β- hydroxyorganoate) is crosslinked. 3. The pressure sensitive adhesive of claim 1 wherein the poly(β- hydroxyorganoate) comprises monomeric units of the general formula: wherein: (i) a minor amount of the monomeric units have an R group containing 1-3 carbon atoms; and (ii) a major amount of the monomeric units have an R group containing 4-30 carbon atoms. 4. The pressure sensitive adhesive of claim 3 wherein the poly(β- hydroxyorganoate) comprises no greater than about 20 mole percent of the monomeric units having an R group containing 1-3 carbon atoms, and at least about 80 mole percent of the monomeric units having an R group containing 4-30 carbon atoms. 5. The pressure sensitive adhesive of claim 3 comprising a mixture of different poly(β-hydroxyorganoate)s. 6. The pressure sensitive adhesive of claim 3 wherein the poly(β- hydroxyorganoate) comprises a major amount of at least two different monomeric units having R groups containing 4-30 carbon atoms. 7. A pressure sensitive adhesive composition comprising: (a) a poly(β-hydroxyorganoate) comprising monomeric units of the general formula: wherein: (i) a minor amount of the monomeric units have an R group containing 1-3 carbon atoms; and (ii) a major amount of the monomeric units have an R group containing 4-30 carbon atoms; (b) a tackifier; and (c) a crosslinking agent. 8. The pressure sensitive adhesive composition of claim 7 wherein the poly(β- hydroxyorganoate) comprises no greater than about 20 mole percent of the monomeric units having an R group containing 1-3 carbon atoms, and at least about 80 mole percent of the monomeric units having an R group containing 4-30 carbon atoms. 9. The pressure sensitive adhesive composition of claim 7 wherein the poly(β- hydroxyorganoate) has unsaturated R groups. 10. The pressure sensitive adhesive composition of claim 9 wherein the poly(β- hydroxyorganoate) has no greater than about 20 mole percent monomeric units having unsaturation therein. 11. The pressure sensitive adhesive composition of claim 7 wherein the poly(β- hydroxyorganoate) has R groups containing Cl atoms, Br atoms, or COOH groups. 12. The pressure sensitive adhesive composition of claim 7 wherein the poly(β- hydroxyorganoate) comprises a major amount of at least two different monomeric units having R groups containing 4-30 carbon atoms 13. The pressure sensitive adhesive composition of claim 12 wherein the poly(β- hydroxyorganoate) comprises a major amount of 3-hydroxyoctanoate and 3- hydroxynonanoate monomeric units. 14. The pressure sensitive adhesive composition of claim 12 wherein the poly(β- hydroxyorganoate) comprises a major amount of 3-hydroxyoctanoate and 3- hydroxy-10-undecenoate monomeric units. 15. The pressure sensitive adhesive composition of claim 7 wherein the poly(β- hydroxyorganoate) comprises a major amount of 3-hydroxyoctanoate. 16. The pressure sensitive adhesive composition of claim 7 wherein the poly(β- hydroxyorganoate) comprises a major amount of 3-hydroxynonanoate. 17. The pressure sensitive adhesive composition of claim 7 wherein the tackifier is selected from the group consisting of a rosin or rosin derivative, a resin derived by polymerization of C5-9 unsaturated hydrocarbon monomers, and a phenol-containing resin. 18. An article comprising a substrate having at least one surface on which is coated a pressure sensitive adhesive comprising a poly(β-hydroxyorganoate), wherein the pressure sensitive adhesive has a Tg of less than about 20°C. 19. The article of claim 18 wherein the pressure sensitive adhesive further indues a tackifier. 20. The article of claim 18 wherein the poly(β-hydroxyorganoate) is crosslinked. 21. The article of claim 20 wherein the poly(β-hydroxyorganoate) is crosslinked using radiation without a crosslinking agent. 22. The article of claim 18 wherein the poly(β-hydroxyorganoate) comprises monomeric units of the general formula: wherein: (i) a minor amount of the monomeric units have an R group containing 1-3 carbon atoms; and (ii) a major amount of the monomeric units have an R group containing 4-30 carbon atoms. 23. The article of claim 22 wherein the poly(β-hydroxyorganoate) comprises no greater than about 20 mole percent of the monomeric units having an R group containing 1-3 carbon atoms, and at least about 80 mole percent of the monomeric units having an R group containing 4-30 carbon atoms. 24. The article of claim 22 wherein the pressure sensitive adhesive comprises a mixture of different poly(β-hydroxyorganoate)s. 25. The article of claim 22 wherein the poly(β-hydroxyorganoate) comprises a major amount of at least two different monomeric units having R groups containing 4-30 carbon atoms. 26. A method of adhering two substrates comprising: (a) applying to a substrate a pressure sensitive adhesive comprising a poly(β-hydroxyorganoate), wherein the pressure sensitive adhesive has a T g of less than about 20°C; and (b) applying a second substrate to the pressure sensitive adhesive. 27. The method of claim 26 whrein the poly(β-hydroxyorganoate) has monomeric units of the general formula: wherein: (a) a minor amount of the monomeric units have an R group containing 1-3 carbon atoms; and (b) a major amount of the monomeric units have an R group containing 4-30 carbon atoms. 28. The method of claim 26 wherein the poly(β-hydroxyorganoate) is crosslinked. 29. The article of claim 28 wherein the poly(β-hydroxyorganoate) is crosslinked using radiation without a crosslinking agent. 30. The method of claim 26 wherein the poly(β-hydroxyorganoate) contains a tackifier.

Inventors: GADDAM BABU N, HAMMAR W JAMES, RUTHERFORD DENISE R, BABU, GADDAM, M., HAMMAR, W., JAMES, RUTHERFORD, DENISE, R.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1995
Main classification: C09J167
IPC codes: C08L101, C09J167, C09J187, C09J193