Acrylic Pressure-sensitive Adhesives Research Articles

Polymeric surfactants with high acid values for emulsion type pressure-sensitive adhesives

Low molecular weight polymers with hydrophobic-carboxyl groups have been usually used as anionic surfactants in emulsion polymerization for coatings. However, such polymeric surfactants usually have low acid values below 200, because it is difficult to make high acid-value polymeric surfactants using a normal batch reactor. In this work, we polymerized high acid value polymeric surfactant having high acid values successfully up to 380 using CSTR (continuous stirring tank reactor). The synthesized polymeric surfactant was a random copolymer of P(BA-AA) and we applied them as anionic surfactants in making emulsion-type acrylic PSAs (Pressure-Sensitive Adhesives) to investigate the effects of high acid value on the adhesive properties. This CSTR enabled effective control of the polymerization reaction because it could control the composition and molecular weight of polymeric surfactants through varying monomer ratios, retention time, and initiator concentration. The surface tension analysis and emulsion stability test indicated that the polymeric surfactants exhibited a similar level of critical micelle concentration (CMC) and emulsion stability with other conventional anionic surfactants. Also, the adhesion property analysis showed that the PSA used a high acid value polymeric surfactant resulting in superior adhesive properties and heat resistance than the PSA used both low acid value polymeric surfactant and conventional low molecular weight surfactant. It was very notable that polymeric surfactants having unusually high acid values above 300 because of their high contents of carboxylic acid groups could result in superior adhesive properties and heat resistance.

Fabrication of core-shell polyacrylate latex pressure sensitive adhesives modified by fluorinated monomer and film properties

In this work, a series of fluorinated core-shell polyacrylate latex pressure sensitive adhesives (PSAs) were successfully synthesized through monomer-starved seeded semi-continuous emulsion polymerization. Specifically, (meth)acrylate monomers were employed as the main materials, with dodecafluoroheptyl methacrylate (DFMA) were used as modified monomer. The impact of fluorine monomer DFMA on the resulting core-shell latex and PSA properties was thoroughly examined. FTIR analysis confirmed the successful incorporation of DFMA into the latex copolymer through emulsion polymerization. TEM images illustrated that the morphology of latex particles exhibit a distinct core-shell structure. The results also showed that with the addition of DFMA, the water absorption and water whitening of the latex films decreased, while the water contact angle and thermal stability are improved. Interestingly, the latex films with DFMA added to the shell phase exhibit a larger WCA value when compared to those with DFMA in the core phase, further confirmed by XPS results. Finally, the adhesive properties of the fluorinated core-shell acrylate PSA were evaluated. The results of shear strength and gel content demonstrate that the prepared PSA exhibits excellent cohesive properties. Thus, this work could present a feasible strategy for optimizing the comprehensive properties of acrylate latex PSAs.

Crosslinkable latex-based acrylic adhesives containing functionalized cellulose nanocrystals (fCNCs)

In this study, crosslinkable acrylic adhesives with functionalized cellulose nanocrystal (fCNCs) were prepared via in situ emulsion polymerization at 80 °C for 3h. The neat acrylic pressure sensitive adhesives (PSAs) without any nanoparticles were prepared using butyl acrylate (BA), 65 wt%, and methyl methacrylate (MMA), 35 wt%, and various amounts of 2-hydroxyethyl methacrylate (HEMA), 1, 3, 5, 7 wt% based on total BA and MMA monomers. For preparing fCNCs reinforced adhesives, the cellulose nanocrystals (CNCs) were functionalized using various concentrations of 3-methacryloxypropyl trimethoxy silane (MPS), 5, 20, 40 mM. The cellulose nanocrystals (CNCs), functionalized cellulose nanocrystals (fCNCs), and the prepared adhesives were characterized by Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). The Adhesion performance of the adhesives was evaluated by lap shear and 180° peel tests. The results showed that increasing the HEMA content as crosslinking agent in the adhesive structure, enhanced its gel content, glass transition temperature (Tg), thermal stability, and adhesive performance, i.e. lap shear and peel strength. Finally, the adhesive containing 5 wt% HEMA was selected as the appropriate sample. Thereafter, the adhesives containing 5 wt% HEMA were synthesized in the presence of various amounts of fCNCs, i.e. 0.5, 1, 1.5 wt%. The Adhesion performance of the neat and reinforced adhesives indicated that increasing the fCNCs to the adhesive enhanced thermal stability, gel content, lap shear and peel strength. Additionally, the fCNCs prepared using higher concentration of MPS (40 mM) was more effective on the adhesion performance than the fCNCs prepared with the lower MPS contents, 5, 20 mM. The results showed that the adhesives prepared using 1 wt% and 1.5 wt% of fCNC40 (containing 40 mM MPS) exhibited better adhesion performance.

Silanization as a strategy to design polyurethane-acrylic hybrid pressure-sensitive adhesives

Pressure-sensitive adhesives (PSAs) are a critical class of adhesives used in numerous applications. Acrylic copolymers and polyurethanes are two main categories of polymers that PSAs are made from. However, to take advantage of unique properties of both of them, polyurethane-acrylic hybrid PSAs have been proposed. To date, for synthesis of these hybrid PSAs, there should have been an acrylic comonomer containing a specific functional group to be able to react with the isocyanate group. This research was conducted to eliminate the need for such an acrylic comonomer with a specific functional group through silanization. For this purpose, firstly, a silanized polyurethane (SPU) was synthesized through silanization of a polyol. Subsequently, copolymerization of two acrylic comonomers was performed in the absence or presence of SPU. In the next step, prior to adding the acrylic comonomers to the SPU, silane was added to SPU to enable higher grafting. The PSA containing 0.04 wt % of silane showed a peel force, static shear strength, and tack of 1.6, 1.4, and 2.9 times those of the acrylic PSA on stainless steel, respectively. With this proposed silanization strategy, it is possible to design a wide variety of polyurethane-acrylic hybrid polymers.

Water-compatible cross-linked pyrrolidone acrylate pressure-sensitive adhesives with persistent adhesion for transdermal delivery: Synergistic effect of hydrogen bonding and electrostatic force

Poor skin adhesion and mechanical properties are common problems of pressure-sensitive adhesive (PSA) in transdermal drug delivery system (TDDS). Its poor water compatibility also causes the patch to fall off after sweating or soaking in the application site. To solve this problem, poly (2-Ethylhexyl acrylate-co-N-Vinyl-2-pyrrolidone-co-N-(2-Hydroxyethyl)acrylamide) (PENH), a cross-linked pyrrolidone polyacrylate PSA, was designed to improve the adhesion and water resistance of PSA through electrostatic force and hydrogen bonding system. The structure of PENH was characterized by 1H NMR, FTIR, DSC, and other methods. The mechanism was studied by FTIR, rheological test, and molecular simulation. The results showed that the PENH patch could adhere to human skin for more than 10 days without cold flow, and it could still adhere after sweating or water contact. In contrast, the commercial PSA Duro-Tak® 87-4098 and Duro-Tak® 87-2852 fell off completely on the 3rd and 6th day, respectively, and Duro-Tak® 87-2510 showed a significant dark ring on the second day. Mechanism studies have shown that the hydrogen bond formed by 2-ethylhexyl acrylate (2-EHA), N-vinyl-2-pyrrolidinone (NVP), and N-(2-Hydroxyethyl)acrylamide (HEAA) enhances cohesion, the interaction with skin improves skin adhesion, and the electrostatic interaction with water or drug molecules enhances the ability of water absorption and drug loading. Due to the synergistic effect of hydrogen bonds and electrostatic force, PENH can maintain high cohesion after drug loading or water absorption. PENH provides a choice for the development of water-compatible patches with long-lasting adhesion. Statement of significanceBased on the synergistic effect of hydrogen bonding and electrostatic force, a hydrogen-bonded, cross-linked pyrrolidone acrylate pressure-sensitive adhesive for transdermal drug delivery was designed and synthesized, which has high adhesion and cohesive strength and is non-irritating to the skin. The patch can be applied on the skin surface continuously for more than 10 days without the phenomenon of “dark ring”, and the patch can remain adherent after the patient sweats or bathes. This provides a good strategy for choosing a matrix for patches that require prolonged administration.

Adhesion and Contact Aging of Acrylic Pressure-Sensitive Adhesives to Swollen Elastomers.

Fluid-infused (or swollen) elastomers are known for their antiadhesive properties. The presence of excess fluid at their surface is the main contributor to limiting contact formation and minimizing adhesion. Despite their potential, the mechanisms for adhesion and contact aging to fluid-infused elastomers are poorly understood beyond contact with a few materials (ice, biofilms, glass). This study reports on adhesion to a model fluid-infused elastomer, poly(dimethylsiloxane) (PDMS), swollen with silicone oil. The effects of oil saturation, contact time, and the opposing surface are investigated. Specifically, adhesion to two different adherents with comparable surface energies but drastically different mechanical properties is investigated: a glass surface and a soft viscoelastic acrylic pressure-sensitive adhesive film (PSA, modulus ∼25 kPa). Adhesion between the PSA and swollen PDMS [with 23% (w/w) silicone oil] retains up to 60% of its value compared to contact with unswollen (dry) PDMS. In contrast, adhesion to glass nearly vanishes in contact with the same swollen elastomer. Adhesion to the PSA also displays stronger contact aging than adhesion to glass. Contact aging with the PSA is comparable for dry and unsaturated PDMS. Moreover, load relaxation when the PSA is in contact with the PDMS does not correlate with contact aging for contact with the dry or unsaturated elastomer, suggesting that contact aging is likely caused by chain interpenetration and polymer reorganization within the contact region. Closer to full saturation of the PDMS with oil, adhesion to the PSA decreases significantly and shows a delay in the onset of contact aging that is weakly correlated to the poroelastic relaxation of the elastomer. Additional confocal imaging suggests that the presence of a layer of fluid trapped at the interface between the two solids could explain the delayed (and limited) contact aging to the oil-saturated PDMS.

Design of a tulobuterol patch with improved mechanical properties: effect of transdermal permeation enhancers on the release process of metal ligand-based acrylic pressure-sensitive adhesives.

The aim of this study was to design a tulobuterol (TUL) patch with good penetration behavior and mechanical properties. Particular attention was paid to the effect of transdermal permeation enhancers on the release process of metal ligand-based acrylic pressure-sensitive adhesive (AA-NAT/Fe3+). The type and dosage of the enhancers were screened by in vitro transdermal penetration in rat skin. The optimized formulation was evaluated in a pharmacokinetic study in rats. Furthermore, the molecular mechanism by which Azone (AZ) improves the release rate of TUL from AA-NAT/Fe3+ was investigated by FT-IR, shear strength test, rheological study, and molecular simulation. As a result, the optimized formula using AA-NAT/Fe3+ showed better mechanical properties compared to commercial products. Meanwhile, the AUC0-t and Cmax of the optimized patch were 1045 ± 89ng/mL·h and 106.8 ± 28.5ng/mL, respectively, which were not significantly different from those of the commercial product. In addition, AZ increased the mobility of the pressure-sensitive adhesive (PSA) rather than decreasing the drug-PSA interaction, which was the main factor in enhancing TUL release from the patch. In conclusion, a TUL transdermal drug delivery patch was successfully developed using metal-coordinated PSA, and a reference was provided for the design of metal-coordinated acrylic PSA for transdermal patch delivery applications.

Realizing Cross-linking-free Acrylic Pressure-Sensitive Adhesives with Intensive Chain Entanglement through Visible-Light-Mediated Photoiniferter-Reversible Addition-Fragmentation Chain-Transfer Polymerization.

A versatile and simplified synthesis scheme for intensively entangled acrylic pressure-sensitive adhesives (PSAs) was developed in this study by leveraging visible-light-driven controlled radical polymerization (photoiniferter/reversible addition-fragmentation chain-transfer polymerization) of acrylic copolymers under a controlled manner; the approach was differentiated by a single factor; molecular weight (Mw up to 2.8 MDa) with identical compositions. By manipulating Mw up to ultra-high ranges, PSAs with diversified viscoelastic properties were prepared and then assessed with a focus on realizing PSAs with a maximized degree of entanglement per chain through domination of high Mw contents, to help achieve excellent cohesiveness without a reinforcing cross-linking network. Moreover, fully linear solvent-soluble poly(acrylate)s were synthesized to facilitate reprocessing and reuse, highlighting the sustainability of the devised method and, consequently, its potential to be applied for effectively reducing industrial or daily waste.

Synthesis and Characterization of Pressure-Sensitive Adhesives Based on a Naphthyl Curing Agent.

The incorporation of a naphthyl curing agent (NCA) can enhance the thermal stability of pressure-sensitive adhesives (PSAs). In this study, a PSA matrix was synthesized using a solution polymerization process and consisted of butyl acrylate, acrylic acid, and an ethyl acrylate within an acrylic copolymer. Benzoyl peroxide was used as an initiator during the synthesis. To facilitate the UV curing of the solvent-borne PSAs, glycidyl methacrylate was added to introduce unsaturated carbon double bonds. The resulting UV-curable acrylic PSA tapes exhibited longer holding times at high temperatures (150 °C) compared to uncross-linked PSA tapes, without leaving any residues on the substrate surface. The thermal stability of the PSA was further enhanced by adding more NCA and increasing the UV dosage. This may be attributed to the formation of cross-linking networks within the polymer matrix at higher doses. The researchers successfully balanced the adhesion performance and thermal stability by modifying the amount of NCA and UV radiation, despite the peel strength declining and the holding duration shortening. This research also investigated the effects of cross-linking density on gel content, molecular weight, glass transition temperature, and other properties of the PSAs.

The Impact of Liquid Components on Alteration of the Adhesion of Polyacrylate and Silicone Patches.

Polyacrylates and polysiloxanes are polymers used in pressure-sensitive adhesive (PSA) patches. Liquid additives are co-solvents of the active substances or permeation enhancers, and their compatibility with the polymeric matrix and the effect on adhesive properties should be considered. The patches were prepared from commercial polyacrylates (three types of Duro-Tak®) and siloxanes (Bio-PSA® and Soft Skin Adhesive®). Propylene glycol, polyoxyethylene glycol, isopropyl myristate, triacetin, triethyl citrate and silicone oil were added (10% w/w). Formulations were evaluated microscopically and with a texture analyzer in terms of in vitro adhesiveness and hardness. Only silicone oil was compatible with the silicone matrices. The best compatibility of acrylic PSA was observed with triethyl citrate; one out of three Duro-Tak matrices was incompatible with every additive. In all compositions, the adhesiveness was impaired by the liquid additives. A significant drop in adhesiveness was noted after immersion of the patches in buffer and drying. The probe tack test was considered as the most useful for evaluation of the effect of the liquid additive on adhesiveness, but the results obtained with a spherical and cylindrical probe were contradictory. The structural changes caused by the additives were also demonstrated by a 90° peel test, considered as complementary to the tack test.

Probing the mechanism of release process from metal coordination-based acrylic pressure-sensitive adhesives: Synergistic effect of coordination and hydrogen bonding for controlled drug release

Hydrogen bonding, ionic interactions, and dipole–dipole interactions have been extensively studied to control drug release from patches. However, metal coordination bonding has not been fully explored for the control of transdermal drug release. In this study, metal coordination-based acrylic pressure-sensitive adhesives (PSAs) were designed and synthesized in order to systemically elucidate the effect of metal coordination on drug release from acrylic PSAs. Ketoprofen (KET) and donepezil (DNP) were selected as model drugs. Results showed that the burst release rate of KET was controlled by N-[tris(hydroxymethyl)methyl]acrylamide (NAT) and Fe3+, while the DNP release rate had no significant changes. It was found that the PSA-drug interaction, rather than the molecular mobility of PSA, played a dominant role in the controlled release process of KET. The hydrogen bond interaction between NAT and KET controlled the release process, while the coordination bond interaction between Fe3+ and KET further slowed down the release of KET. In conclusion, it was found that the controlled release of KET was achieved by the synergistic effect of coordination bonding and hydrogen bonding, which opens up a facile but powerful avenue for the design of brand-new controlled release systems and new opportunities for their application in transdermal drug delivery.

Bonding and UV debonding behaviors of acrylate pressure-sensitive adhesives by rheological methods

Bonding and UV debonding behaviors of acrylate pressure-sensitive adhesives by rheological methods

Rheological and Mechanical Properties of an Acrylic PSA.

The adhesion of pressure-sensitive adhesives (PSAs) is a complex phenomenon that can be understood through the characterization of different properties, including viscoelastic, mechanical, and fracture properties. The aim of the present paper is to determine the viscoelastic behaviour of an acrylic PSA and place it in the viscoelastic window, as well as to determine the tensile strength of the material. Additionally, different numbers of stacked adhesive layers and two crosshead speeds were applied to characterize the tensile strength of the adhesive in the different conditions. Adding a new interface between layers showed a negative influence in the tensile strength, while a higher crosshead speed implied a considerable increase in the same value. Finally, double cantilever beam (DCB) fracture tests were performed, and the J-integral approach was used to evaluate the fracture energy throughout the tests. The substrate roughness, the number of stacked layers, and the thickness of the PSA proved to decrease the performance of the PSA in fracture tests. While tensile bulk tests in viscoelastic materials are not easily found in the literature, as well as DCB tests, for fracture characterization, the obtained results allowed for the characterization of those properties in an acrylic PSA.

Phosphorus-based flame retardant acrylic pressure sensitive adhesives with superior peel strength and transfer characteristics

Acrylic pressure sensitive adhesives (PSAs) are widely utilized in various fields due to their excellent thermal, weather, and oil resistance. However, due to their flammability, they are vulnerable to fire, which brings a critical challenge for their application in various industries. Here, new phosphorus-based acrylic PSAs which show excellent flame retardancy are demonstrated, without sacrificing adhesion properties. By controlling the monomer composition based on five different monomers, we synthesized seven acrylic copolymers for PSAs, and investigated the correlation between monomer composition and adhesion characteristics in terms of peel strength and transfer characteristics. Among seven polymers, A5H5 which exhibits the highest peel strength (1117 gf/in.) and superior transfer characteristics (transfer area 8.30 %) is selected for further investigation. The phosphorous-based acrylic PSAs are prepared through addition of different amounts of dimethyl methylphosphonate in A5H5 polymeric matrix, and thoroughly investigated in terms of flame retardancy and adhesion characteristics in terms of peel strength and transfer characteristics. The phosphorus-based PSA (A5H5-D30) exhibited superior flame retardancy of V-0 rating under the UL-94 characterization method. Furthermore, the A5H5-D30 present excellent film transfer characteristic showing a transfer area of 0 % and residue of 0 wt% in air without massive decrease in peel strength (991 gf/in.).

Quantitative analysis of acrylic acid in acrylic pressure-sensitive adhesives by reactive pyrolysis-GC/MS using N,O-bis(trimethylsilyl)trifluoroacetamide as a trimethylsilylation reagent with two-step heating

Acrylic pressure-sensitive adhesives (APSAs) have been used in a variety of fields and the composition of their monomers is a very important factor in determining their physical properties. Monomers containing polar functional groups, such as acrylic acid (AA), are often used as raw materials for APSAs, and the number of these monomer units in the polymer chain has a significant effect on the adhesive properties. However, due to its high reactivity and polarity, it is not easy to accurately quantify AA in APSAs by conventional reactive pyrolysis gas chromatography mass spectrometry (Py-GC/MS). In this study, quantitative analysis of AA in APSAs was examined by reactive Py-GC/MS using N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) as a trimethylsilylation (TMS) reagent (Py (BSTFA)-GC/MS). First, the APSA sample was mixed with BSTFA and heated at 60 ºC for 30 min to accelerate TMS derivatization of any unpolymerized AA monomers (AA-TMS). If unreacted BSTFA remains after derivatization, it will react with AAs produced by the pyrolysis of acrylic ester units. These additional AA monomers,will results in the over-estimation of the true amount of unpolymerized AA monomers. To prevent this undesirable effect by residual reagent, the TMS-derivatized sample was further heated at 100 ºC for 10 min before pyrolysis in order to remove residual BSTFA and solvent. The derivatized sample was measured by Py-GC/MS at 600 ºC and the relative standard deviation of the peak area ratio of AA-TMS derived from unpolymerized AA monomers to the internal standard (anthracene-d10) was less than 5% (n = 5). In the calibration curves made for four APSA samples with known compositions, good linearity was obtained for the raw materials of butyl acrylate and 2-ethylhexyl acrylate in addition to AA-TMS. Quantitative analysis of AA monomers in a commercial APSA sample showed fairly good agreement with the amount of AA determined by the official method of analysis using the acid-base titration (JIS K 5601–2–1). The results obtained in this study indicate that Py (BSTFA)-GC/MS is effective for the compositional analysis of APSAs.

Thermal debonding pressure-sensitive adhesive blended with liquid crystal polymers

With the development of the electronic information industry, semiconductor components and electronic devices are becoming smaller and thinner, which are easy to be damaged during processing and transportation. Pressure-sensitive adhesives (PSA) can temporarily fix and protect these electronic components. As PSA with adjustable peel strength can be easily removed after processing without damaging the electronic components, the research on debonding caused by external stimuli for PSA is a topic of great industrial value. Here, the thermal debonding PSAs have been prepared by incorporating liquid crystal polymers (LCP) into the acrylate PSA matrix. Firstly, the linear LCP (LLCP) blended PSA can lead to some degree of improvement in thermal debonding properties but the serious phase separation between LLCP and PSA matrix results in much lower 180o peel strength at room temperature even than the neat PSA. Secondly, to solve the problem of compatibility, we proposed a new strategy for that semi-IPN LCP PSA system. Through this strategy, the photocurable liquid crystal monomer (LCM) could perform photocuring with PSA matrix and in-situ form semi-IPN. The decreased ratio of the second system with 20 wt% and 50 wt% LCM content could reach 94.3 % and 95.9 % respectively upon heating from 20 °C to 80 °C, both of which are much higher than that of the neat PSA system (85.4 %). What's more, the 180o peel strength of PSA with 20 wt% LCM at room temperature is also 46.7 % higher than that of the neat PSA. Obviously, such an in-situ formed semi-IPN LCP PSA strategy has promising commercial application potential.

The Effect of Silane Acrylate Containing Ethylene Glycol Chains on the Adhesive Performance and Viscoelastic Behavior of Acrylic Pressure-Sensitive Adhesives for Flexible Displays.

In this study, novel silane acrylates, such as diethylene glycol diacrylate (DEGDA) and tetraethylene glycol diacrylate (TEGDA), containing ethylene glycol chains were synthesized and introduced into acrylic pressure-sensitive adhesives (PSAs) to regulate their peel strength and rheological properties. The synthesized silane acrylates effectively improved the cohesion and adhesive properties of the acrylic PSAs, even with only 1 wt% addition. In addition, the glass transition temperature and flexibility of acrylic PSAs were also affected by the increase in free volume induced by ethylene glycol chains. The silane acrylates also improved the viscoelasticity of the acrylic PSAs, which exhibited excellent recovery (62-96%) and stress relaxation (>90%) properties owing to the increased elasticity. Additionally, the acrylic PSAs prepared with the silane acrylates showed excellent optical properties (transmittance ≥ 90%, haze ≤ 1%) and exhibited behavior suitable for application in flexible displays from a comprehensive perspective.

Building Tunable Degradation into High-Performance Poly(acrylate) Pressure-Sensitive Adhesives.

Pressure-sensitive adhesives (PSAs) based on poly(acrylate) chemistry are common in a wide variety of applications, but the absence of backbone degradability causes issues with recycling and sustainability. Here, we report a strategy to create degradable poly(acrylate) PSAs using simple, scalable, and functional 1,2-dithiolanes as drop-in replacements for traditional acrylate comonomers. Our key building block is α-lipoic acid, a natural, biocompatible, and commercially available antioxidant found in various consumer supplements. α-Lipoic acid and its derivative ethyl lipoate efficiently copolymerize with n-butyl acrylate under conventional free-radical conditions leading to high-molecular-weight copolymers (Mn > 100 kg mol-1) containing a tunable concentration of degradable disulfide bonds along the backbone. The thermal and viscoelastic properties of these materials are practically indistinguishable from nondegradable poly(acrylate) analogues, but a significant reduction in molecular weight is realized upon exposure to reducing agents such as tris (2-carboxyethyl) phosphine (e.g., Mn = 198 kg mol-1 → 2.6 kg mol-1). By virtue of the thiol chain ends produced after disulfide cleavage, degraded oligomers can be further cycled between high and low molecular weights through oxidative repolymerization and reductive degradation. Transforming otherwise persistent poly(acrylates) into recyclable materials using simple and versatile chemistry could play a pivotal role in improving the sustainability of contemporary adhesives.

Mechanistic insights into the effect of drug content on adhesive properties of transdermal patch containing lidocaine

This study aims to shed light on the relationship between drug content and adhesive properties in drug-in-adhesive transdermal patch, and to elucidate molecular mechanisms from the perspective of polymer chain mobility. Lidocaine was selected as model drug. Two acrylate pressure sensitive adhesives (PSAs) with different polymer chain mobility were synthesized. Tack adhesion, shear adhesion and peel adhesion of PSAs with 0, 5%, 10%, 15% and 20% w/w lidocaine contents were tested. Polymer chain mobility was determined by rheology and modulated differential scanning calorimetry experiments. Drug-PSA interaction was analyzed by FT-IR. The effect of drug content on free volume of PSA were determined by positron annihilation lifetime spectroscopy and molecular dynamics simulation. It was found that the polymer chain mobility of PSA was increased with increasing drug content. Due to the variation of polymer chain mobility, tack adhesion increased, and shear adhesion decreased. It was proved that interactions between polymer chains were destroyed by drug-PSA interactions, free volume between polymer chains was expanded, resulting in the increase of polymer chain mobility. We can conclude that the effect of drug content on polymer chain mobility should be considered, when designing a transdermal drug delivery system with controlled and satisfactory adhesion.

UV-Curable Polyurethane Acrylate Pressure-Sensitive Adhesives with High Optical Clarity for Full Lamination of TFT-LCD

Optically clear pressure-sensitive adhesives (PSAs) face the challenges presented by a range of electronic and touch screen applications. Although many efforts have been made to manipulate the optical and adhesion properties of ultraviolet (UV)-curable acrylate-based PSAs, further application and large-scale production are still limited owing to the intrinsically poor processability that stems from the large content of the high-vinyl-equivalent and low-viscosity acrylic monomers. Introducing a low-vinyl-equivalent and high-viscosity polyurethane acrylate (PUA) prepolymer into the formulation is a facile method to solve this issue without sacrificing the transparency. In this study, a series of PUA prepolymers are prepared to construct the model of PUA-co-2-ethylhexyl acrylate (2EHA), denoted as poly(PUA-2EHA). The influence of PUA prepolymer architectures (average functionality and molecular features) on the optical and adhesion properties is elaborately discussed. The chemical cross-linking-induced enhancement of the haze values of PUA-based PSAs is investigated for the first time. Moreover, an improved and uniform bright image display without blemish, which is usually called the Mura defect-free image display in the industrial field, is obtained by using poly(PUA-2EHA) as the optically clear adhesive for full lamination of the thin-film transistor liquid crystal display (TFT-LCD) module. The laminated TFT-LCD module could be disassembled easily without leaving the residue on the screen. These results provide clear design guidelines to regulate the properties of PUA-based PSAs, which are especially valuable for the large-scale industrial production of UV-cured PSAs and facilitate the development of display technologies.