Silicone Pressure-sensitive Adhesive Research Articles

UV-curable silicone pressure-sensitive adhesive based on thiol-ene reaction

In order to improve the curing efficiency and reduce energy consumption of silicone pressure-sensitive adhesive (SiPSA), a kind of UV-curable SiPSA based on thiol-ene reaction was prepared with methyl vinyl MQ resin as hard segment, methyl vinyl silicone rubber (110-2S) as soft segment and mercaptyl silicone oil as cross-linker. The UV-cured SiPSA exhibited excellent thermal stability and water resistance. Its physical features such as chemical composition, cross-linking extent and dispersion of MQ resin in silicone rubber were directly related to the vinyl content in MQ resin, the thiol/ene ratio and the resin/rubber ratio, which further affected mechanical properties and adhesive properties of SiPSA. With the vinyl content in MQ resin of 56 mmol/100 g, the thiol/ene molar ratio of 0.8 and the resin/rubber mass ratio of 1.4, the UV-cured SiPSA-B1.4–0.8 had better mechanical properties, moreover it had higher tensile shear strength of >2.0 MPa and showed interface failure on the surface of substrates, indicating that it had great potential applications as PSA.

Synthesis of UV rapid curing silicone coatings via photoinitiated thiol-ene click polymerization for pressure-sensitive adhesive

UV-curable silicone pressure-sensitive adhesive (SPSA) is composed of silicone rubber and silicone resin. Generally, the CC double bond in acryloyloxy group provides a photocurable group for SPSA. However, oxygen inhibition of acryloyloxy group block the degree of cure and CC double bond conversion of SPSA during the photopolymerization. Therefore, efficient photocurable groups for UV curing SPSA is particularly important to be developed. Thiol-ene click polymerizations have been widely used in photocrosslinked polymers due to the rapid efficiency of reactions. In this study, sulfhydryl functionalized silicone resin (SFSR) and methacrylate functionalized amino silicone rubber (MFASR) were synthesized to prepare a SPSA via photoinitiated thiol-ene click polymerization. The double bond in MSASR and sulfhydryl in SFSR were characterized by FT-IR spectroscopy and 1H NMR spectroscopy. The double bond conversion of SPSA was calculated after polymerization. The cohesion of SPSA was improved by SFSR, while the crosslinking degree was improved by thiol-ene. The loop tack of SPSA with 50 wt% SFSR was 9.01 N, and the 180° peel strength was 11.37 N/25 mm. The SPSA maintained good bonding adhesion to steel at various temperature.

Aging of silicone pressure-sensitive adhesives

Silicone pressure-sensitive adhesives (Si-PSA) exhibit unique properties, such as high Si–O–Si backbone flexibility, low intermolecular interactions, low surface tension, excellent thermal stability, and high UV transparency, which often explains why silicone PSAs have an impressive performance at high- and low-temperature extremes, excellent electrical properties, chemical resistance, and outstanding weathering resistance turning them superior compared to organic PSAs. It is well known that due to their unique properties, silicone pressure-sensitive adhesives are materials for special applications. In the present study, we focus on changing the useful properties of the best compositions of silicone pressure-sensitive adhesives in time to verify the impact of aging on them. The influence of time on given silicone pressure-sensitive adhesive tapes and their useful properties is a very important factor for the description of the life-time of potential products based on such compositions. Aging of Si-PSA was carried out for 1 h, 24 h, 7 days, 31 days, and 92 days. The tests did include such properties like adhesion, cohesion (at 20 and 70 °C), tack, and yellowness.

“Cool-off” Function of a Silicone Pressure-sensitive Adhesive Containing a Side-chain Crystalline Polysiloxane

We have first developed a silicone pressure sensitive adhesive (PSA) containing a side-chain crystalline siloxane, whose adhesion can be controlled with a change in temperature. The silicone PSA sh...

Development of transdermal drug delivery system of selegiline

Selegiline transdermal drug delivery system (TDDS) of drug-in-adhesive matrix type was developed using acrylic-rubber hybrid pressure sensitive adhesive (PSA). The permeation rate of selegiline was the highest from silicone, followed by acrylic-rubber hybrid, acrylics. Although the permeation rate of silicone PSA was higher than that of acrylic-rubber hybrid PSA, the cold flow of silicone PSA was unacceptable. When the drug concentration was increased from 3.5 to 8 % w/w of polymer weight, the drug permeation rate also increased proportionally. The correlation coefficient (R2) between selegiline content in the TDDS and the average cumulative amount permeated was 0.999. When the stability study of the TDDS was carried out at the accelerated condition of 40 °C/75 % relative humidity for 12 weeks, no significant changes in both the physical appearance and the drug content were observed. The drug permeation rate from the TDDS was much higher than that from Emsam®. The average cumulative flux of selegiline from the TDDS was 2 times higher than that from Emsam®.

Characterization of silicone pressure-sensitive adhesive episcleral implant for drug delivery

The development of an effective sustained ocular drug delivery system remains a challenging task. The objective of the present study was to characterize a silicone pressure sensitive adhesive (PSA) episcleral implant system for transscleral drug delivery. Silicone PSA implants for dexamethasone, atenolol, and bovine serum albumin (BSA) were prepared at different polymer-to-drug mass ratios. Implant adhesion to human cadaver sclera was measured. Drug release experiments were conducted in well-stirred containers in vitro. The results were then analyzed using a pharmacokinetic model and in vitro–in vivo data comparison from previous studies. The silicone PSA episcleral implants in the present study had an average diameter of 3.5 mm and a thickness of 0.8 mm. Drug release from the silicone PSA implants was influenced by drug solubility, implant polymer content, and implant coating. Drug release from the implants was observed to follow the receding boundary release mechanism and was solubility dependent with the higher water solubility drug showing higher release rate than the low-solubility drug. Increasing polymer content in the implants led to a significant decrease in the drug release rate. Coated implants reduced the initial burst effect and provided lower release rates than the uncoated implants. These implants provided sustained drug release that could last up to several months in vitro and demonstrated the potential to offer drug delivery for chronic ocular diseases via the transscleral route.

Development of transdermal therapeutic formulation of CNS5161, a novel NMDA receptor antagonist, by utilizing pressure-sensitive adhesives II: Improved transdermal absorption and evaluation of efficacy and safety

The aim of this study was to prepare a transdermal therapeutic formulation of CNS5161, an NMDA receptor antagonist developed as a drug for neuropathic pain. Since a silicone pressure-sensitive adhesive (PSA) was found to be the best PSA for CNS5161 among six different PSAs examined in our previous study, the effects of the loading concentration of CNS5161 on release and rat skin permeability were investigated using silicone PSAs. The release of CNS5161 was elevated with an increase in the drug concentration from 1% to 14%. The transdermal flux at the steady state reached a plateau at 8% and over, while crystallization of CNS5161 was not observed for any formulation even at high drug concentrations. The drug concentration in rat skin at the steady state was also saturated at 8% and over, which correlated well with the transdermal flux at the steady state. Therefore, skin permeation clearance defined to the skin concentration at the steady state was almost constant at 0.21/h from 2% to 14% of CNS5161, which suggests that drug concentrations in the skin would be a driving force for transport of the drug to the receptor side. Since increasing the concentration of CNS5161 in the PSA patch was not able to elevate the transdermal flux, 12 formulations containing several permeation enhancers were examined to improve the transdermal transport of CNS5161. Among them, the formulation containing propylene glycol, diisopropyl adipate, and polyvinylpyrrolidone significantly increased the transdermal flux by approximately 1.8-fold by improving the diffusivity of CNS5161 in the skin, and also significantly enhanced the analgesic effect of CNS5161. This formulation caused only slight skin irritation, which indicated that it would be a promising transdermal therapeutic system for CNS5161.

Silicone Adhesive Matrix of Verapamil Hydrochloride to Provide pH-Independent Sustained Release

Providing pH-independent oral release of weakly basic drugs with conventional matrix tablets can be challenging because of the pH-dependent solubility characteristics of the drugs and the changing pH environment along the gastrointestinal tract. The aim of the present study was to use a hydrophobic polymer to overcome the issue of pH-dependent release of weakly basic model drug verapamil hydrochloride from matrix tablets without the use of organic buffers in the matrix formulations. Silicone pressure-sensitive adhesive (PSA) polymer was evaluated because of its unique properties of low surface energy, hydrophobicity, low glass transition temperature, high electrical resistance, and barrier to hydrogen ion diffusion. Drug release, hydrogen ion diffusion, tablet contact angle, and internal tablet microenvironment pH with matrix tablets prepared using PSA were compared with those using water-insoluble ethyl cellulose (EC). Silicone PSA films showed higher resistance to hydrogen ion diffusion compared with EC films. Verapamil hydrochloride tablets prepared using silicone PSA showed higher hydrophobicity and lower water uptake than EC tablets. Silicone PSA tablets also showed pH-independent release of verapamil and decreased in dimensions during drug dissolution. By contrast, verapamil hydrochloride tablets prepared using EC did not achieve pH-independent release.

Study of drug release and tablet characteristics of silicone adhesive matrix tablets

Matrix tablets of a model drug acetaminophen (APAP) were prepared using a highly compressible low glass transition temperature (Tg) polymer silicone pressure sensitive adhesive (PSA) at various binary mixtures of silicone PSA/APAP ratios. Matrix tablets of a rigid high Tg matrix forming polymer ethyl cellulose (EC) were the reference for comparison. Drug release study was carried out using USP Apparatus 1 (basket), and the relationship between the release kinetic parameters of APAP and polymer/APAP ratio was determined to estimate the excipient percolation threshold. The critical points attributed to both silicone PSA and EC tablet percolation thresholds were found to be between 2.5% and 5% w/w. For silicone PSA tablets, satisfactory mechanical properties were obtained above the polymer percolation threshold; no cracking or chipping of the tablet was observed above this threshold. Rigid EC APAP tablets showed low tensile strength and high friability. These results suggest that silicone PSA could eliminate issues related to drug compressibility in the formulation of directly compressed oral controlled release tablets of poorly compressible drug powder such as APAP. No routinely used excipients such as binders, granulating agents, glidants, or lubricants were required for making an acceptable tablet matrix of APAP using silicone PSA.

Application of the bulk properties of a silicone PSA to peeling

Finite element analysis of peeling of a pressure sensitive flexible adhesive requires a knowledge of the mechanical performance of the adhesive layer. The bulk tensile properties of a silicone pressure sensitive adhesive (PSA) can be related to its behaviour when used as a thin adhesive layer in a commercial PTFE tape. A finite element analysis for fixed arm peeling of this tape predicts the strain energy density of the adhesive and these values are consistent with the measured data using a mandrel peel test. The effect of local constraint, the extent of the deformation, and distribution of stresses while during the peel test are demonstrated.

Characterization of the crosslinking process of silicone pressure-sensitive adhesives

The process of thermal crosslinking of silicone pressure-sensitive adhesives, catalyzed with dichlorobenzoyl peroxide, was investigated using DSC method. Crosslinking temperature as well as energy evolved during crosslinking process were measured. Peel adhesion and shear strength of thermally crosslinked silicone pressure-sensitive adhesives dependently on crosslinking agent concentration were determined. IR investigations confirmed the course of crosslinking reaction via formation of chemical bonds between methyl groups of silicone pressure-sensitive adhesive.

New Application and Technology of a Silicone Pressure-Sensitive Adhesive

Silicone Pressure Sensitive Adhesives (PSAs) were made from trimethylchlorosilane, ethylorthosilicate and octamethyl cyclotetrasiloxane. The effect of composition, formulation, and reaction conditions on the performance of the silicone PSAs was discussed. The suitable reaction temperature and the reactant molar ratio of Me 3 SiCl to (EtO) 4 Si for the synthesis of a so-called MQ resin are 15 - 35 °C and 0.7:1, the formulation's resin-to-gum ratio being 1.2:1 - 1.5:1. This paper describes the preparation of a mica and glass cloth tape composite by using the silicone PSAs and its application in the manufacture of fireproof cables usable at above 750°C. It was proved that the properties are consistent with IEC331.

Effect of PGML excipient mixture in a transdermal system on the in vitro transport of estradiol across skin.

To measure the effect of a combination of excipients from a silicone based pressure sensitive adhesive (PSA) on drug transport across skin. Partitioning of propylene glycol monolaurate (PG-ML) from silicone PSA and a solution formulation into the stratum corneum (SC) was measured using radiolabeled PG-ML. Transport of a model drug, estradiol, as well as PG-ML across skin were measured in vitro using heat separated epidermis from human cadaver skin. The PG-ML partitioning into SC showed a saturation and was independent of the formulation. The local dielectric of the lipid bilayers of the SC showed an increase as a result of PG-ML uptake, as determined by the decrease in fluorescence lifetime of a lipophilic probe incorporated into the SC. However, there was no alteration of lipid packing in SC. The PG-ML and estradiol transport showed a good correlation over 3 days, suggesting that the two species are co-transported across the epidermis.

New silicone pressure-sensitive adhesive technology

Useful silicone pressure-sensitive adhesives (PSAs) have been prepared from a newly developed high solids silicone technology. The platinum-catalysed silicone compositions consist of siloxane resin and hydrosilylation-reactive silicone fluids containing silicon-bonded vinyl and hydride functionalities. These high solids silicone compositions exhibit a manageable viscosity profile and cure at a rate proportional to the platinum level at temperatures as low as 100°C. The effect of the SiH to Si-vinyl stoichiometry ratio, the molar ratio of M H to D H, hydride crosslinker type and structure, and the chain length of the silicone oligomer on the peel and tack adhesive properties as well as the chain extension and branching hydrosilylation reactions were investigated.