Robust and recoverable dual cross-linking networks in pressure-sensitive adhesives

Pressure-sensitive adhesives (PSAs) demand the ability to simultaneously improve toughness and adhesion. However, these requirements of PSAs have remained a great challenge because robust and recoverable characteristics are usually contradictory properties of PSAs. Dual cross-linking networks developed by incorporating dynamic noncovalent bonds into chemical cross-linking networks have the potential to mitigate these requirements in a wide variety of applications including adhesives, hydrogels, and elastomers. Herein, a facile approach to achieve dual cross-linking networks of acrylic PSAs with excellent mechanical properties and high-adhesive performance that integrate physically cross-linked networks into chemically cross-linked networks is proposed. Diurethane acrylic monomer-pentaerythritol ethoxylate (DAM-PEEL) groups were introduced into the acrylic PSA system through photopolymerization. The PSA/DAM-PEEL dual cross-linking networks led to the development of the chemically cross-linked networks for both PSA and DAM via covalent bonds and the physically cross-linked networks between the amide groups of DAM and the hydroxyl groups of PEEL via hydrogen bonds. Consequently, the PSA/DAM-PEEL dual cross-linking networks were able to simultaneously improve the modulus and stretchability. This design strategy for developing dual cross-linking networks of materials could offer potential applications for various adhesive-related applications.     

Effect of Glass Transition Temperature of Pressure Sensitive Adhesives on Light Leakage in LCD Panel

Pressure-sensitive adhesives (PSA), which mainly are made of acrylic polymers, have been used to fix optical films to liquid crystal display (LCD) cells to prevent contraction or expansion of the optical film under high temperature and high humidity conditions, while residual stress on the polarizing film is generated and light-leakage results from it in the peripheral area of an LCD panel. In this work, we prepared two different kinds of PSAs and tested light leakage with respect to T_g, verifying that T_g would have an effect on light leakage. We calculated their T_g values using the Fox equation and investigated them by DSC. Rheological properties of the PSAs were also acquired by a rotational rheometer which confirm the relation between T_g and dynamic moduli (G′ and G″). It was found that the higher the T_g, the less is an amount of light leaked.     

Study on affecting factors of curing rate in ultraviolet curing adhesives containing modified acrylic ester prepolymers

Abstract

Ultraviolet (UV) curing adhesives have been extensively utilized in fields of health care and electronic components due to low energy consumption and solvent pollution. The most used system is modified acrylic ester system whose merits are low cost, high reliability and tensile strength. However, higher UV curing rate is still pursued especially in field of quick dry adhesives as well as influencing factors of curing rate are very complex. For clarifying affecting factors of curing rate as well as achieving higher curing rate, in this work, several UV curing adhesives with acrylic photosensitive resin prepolymers modified by epoxy and polyurethane were prepared. The impacts of class and content of radical photo-initiators, prepolymers and reactive diluents on UV curing rate were deeply researched. Moreover, the influence of oxygen polymerization inhibition on curing rate was discussed as well. The significantly elevated curing rates were obtained in as-prepared adhesives, in comparison with commercial ones. This work might offer a facile and effective strategy to obtain the promising high-performance modified acrylic ester prepolymer bearing UV curing adhesives with a significantly elevated high curing rate by well controlling these investigated affecting factors.     

Towards Advances in Molecular Understanding of Boric Acid Biocatalyzed Ring-Opening (Co)Polymerization of δ-Valerolactone in the Presence of Ethylene Glycol as an Initiator

Following our previous studies on the molecular level structure of (co)oligoesters obtained via anionic homo- and co-polymerization of novel β-substituted β-lactones, prepared by the atmospheric pressure carbonylation reaction of respective epoxides, the boric acid biocatalyzed ring-opening (co)polymerization of δ-valerolactone has been studied. As a co-monomer the 6-methy-ε-caprolactone, prepared by the one-pot oxidation of respective alcohol, and ethylene glycol as polymerization initiator were used. The obtained copolymers were characterized by ¹H-NMR, GPC and ESI-MS, respectively in order to confirm their chemical structures and identity. Subsequently, tandem mass spectrometry (MS-MS studies) via collision-induced dissociation were utilized to characterize the fragmentation pattern. ESI-MS and NMR analyses confirmed the formation of random linear copolymer chains composed of different polyester repeat units. MS-MS experiments showed that fragmentation proceeds via ester bound cleavage along the (co)polyester chains. The innovative aspect of this contribution is related to the elaboration of the telechelic (co)polymers end-capped with hydroxyl end groups and well-defined molecular architectures, which could facilitate the development of new flexible macromolecular systems for potential biomedical applications.     

Modification of Adhesive and Latex Properties for Starch Nanoparticle‐Based Pressure Sensitive Adhesives

Starch nanoparticle (SNP)‐based pressure sensitive adhesives (PSAs) with core‐shell particle morphology (starch nanoparticle core/acrylic polymer shell) are produced via seeded, semi‐batch emulsion polymerization at 15 wt% SNP loading (relative to total polymer weight) and 40 wt% latex solids. Crosslinker and chain transfer agent (CTA) are introduced to the acrylic shell polymer formulation at a range of concentrations according to a 3² factorial design to tailor the latex and adhesive properties of SNP‐based latexes. The crosslinker and CTA show no significant effect on polymerization kinetics, particle size, and viscosity. Latex gel content is predicted using an empirical model, which is a function of crosslinker and CTA concentration. Both the gel content and glass transition temperature strongly affect the adhesive properties (tack, peel strength, and shear strength) of the SNP‐based latex films. 3D response surfaces for the adhesive properties are constructed to facilitate the design of SNP‐based PSAs with desired properties.     

Ultraviolet curing of acrylic systems: Real‐time Fourier transform infrared,mechanical, and fluorescence studies

The photopolymerization of acrylic‐based adhesives has been studied by Fourier transform infrared and fluorescence analysis in real time. Real‐time infrared spectroscopy reveals the influence of the nature of the photoinitiator on the kinetics of the reaction. Furthermore, the incident light intensity dependence of the polymerization rate shows that primary radical termination is the predominant mechanism during the initial stages of the curing of the acrylic system with bis(2,4,6‐trimethylbenzoyl) phenyl phosphine oxide (TMBAPO) as a photoinitiator. The fluorescence intensity of selected probes increases during the ultraviolet curing of the adhesive, sensing microenvironmental viscosity changes. Depending on the nature of the photoinitiator, different fluorescence–conversion curves are observed. For TMBAPO, the fluorescence increases more slowly during the initial stage because of the delay in the gel effect induced by primary radical termination. Mechanical tests have been carried out to determine the shear modulus over the course of the acrylic adhesive ultraviolet curing. In an attempt to extend the applications of the fluorescence probe method, we have undertaken comparisons between the fluorescence changes and shear modulus. Similar features in both curves confirm the feasibility of the fluorescence method for providing information about microstructural changes during network formation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4236–4244, 2002     

Development of solvent-free acrylic pressure-sensitive adhesives

The present publication describes a problem to develop solvent-free acrylic pressure-sensitive adhesives (PSA). Solvent-free PSA are established materials for the manufacturing of various self-adhesive products. Only by means of these acrylic PSA was it possible to succeed in drafting the present surprisingly efficient generation of double-sided pressure-sensitive adhesive tapes, medical products, protective masking films, films for the graphics market, and various specialty products. New applications and technical specifications stimulate the continuous development of new methods of polymerization of solvent-free acrylates. New syntheses of solvent-free acrylic PSA include polymerization in the reactor with removal of the solvent and polymerization on the carrier. The polymerization process is connected with UV-crosslinking.     

Waterborne polyurethane-acrylic hybrid nanoparticles by miniemulsion polymerization: applications in pressure-sensitive adhesives

Waterborne polyurethane-acrylic hybrid nanoparticles for application as pressure-sensitive adhesives (PSAs) were prepared by one-step miniemulsion polymerization. The addition of polyurethane to a standard waterborne acrylic formulation results in a large increase in the cohesive strength and hence a much higher shear holding time (greater than seven weeks at room temperature), which is a very desirable characteristic for PSAs. However, with the increase in cohesion, there is a decrease in the relative viscous component, and hence there is a decrease in the tack energy. The presence of a small concentration of methyl methacrylate (MMA) in the acrylic copolymer led to phase separation within the particles and created a hemispherical morphology. The tack energy was particularly low in the hybrid containing MMA because of the effects of lower energy dissipation and greater cross-linking. These results highlight the great sensitivity of the viscoelastic and adhesive properties to the details of the polymer network architecture and hence to the precise composition and synthesis conditions.     

β-Cyclodextrin Derivative Grafted on Silica Gel Represents a New Polymeric Sorbent for Extracting Nitisinone from Model Physiological Fluids

Nitisinone (NTBC) is used in the treatment of disorders affecting the tyrosine pathway, including hereditary tyrosinemia type I, alkaptonuria, and neuroblastoma. An inappropriate dosage of this therapeutic drug causes side effects; therefore, it is necessary to develop a rapid and sensitive method to monitor the content of NTBC in patients’ blood. This study aimed to develop anew polymeric sorbent containing β-cyclodextrin (β-CD) derivatives grafted on silica gel to effectively extract NTBC from model physiological fluids. The inclusion complex formed between β-CD and NTBC was examined by proton nuclear magnetic resonance spectroscopy. The novel sorbents with derivatives of β-CD were prepared on modified silica gel using styrene as a comonomer, ethylene glycol dimethacrylate as a crosslinking agent, and 2,2′-azo-bis-isobutyronitrile as a polymerization initiator. The obtained products were characterized via Fourier transform infrared spectroscopy and then used as sorbents as part of a solid phase extraction technique. High NTBC recovery (70%indicated that the developed polymeric sorbent may be suitable for extracting this compound from patients’ blood samples.     

Influence of Particle Nucleation in Pressure Sensitive Adhesive Properties: Miniemulsion versus Emulsion Polymerization

Miniemulsion polymerization is a promising approach to produce and tailor pressure sensitive adhesives (PSAs). In this paper, a systematic comparison of the adhesive properties of latexes produced by miniemulsion and conventional emulsion polymerization is presented. Specifically, the influence of the total surfactant concentration, chain transfer agent concentration and chemical composition on the final adhesive properties of the polymer 2-ethyl hexyl acrylate/methyl methacrylate/acrylic acid was discerned using a 2³ factorial design for each polymerization method. In addition to the adhesive properties (i.e., loop tack, peel strength and shear strength), molecular weight distribution, particle size distribution (PSD) and glass transition temperature were analyzed. The results show that under the conditions used in this work, it is possible to produce PSAs using miniemulsion polymerization, a process wherein monomer droplet nucleation is the dominant particle nucleation mechanism. The use of a miniemulsion polymerization process, as opposed to the conventional emulsion technique, produced several differences such as larger particles sizes and narrower molecular weight distributions. Focusing on the PSA films that exhibited adhesive rather than cohesive failure, the PSA films generated via miniemulsion polymerization displayed higher values of loop tack and peel strength compared to those produced via conventional emulsion polymerization. Shear strength results were strongly dependent on the amount of gel content and sol molecular weight for both cases.     

Synthesis and Evaluation of Adhesion Properties of Homogeneous and Core-Shell Pressure-Sensitive Adhesives

Summary: Pressure-Sensitive Adhesives (PSAs) are used for many applications (e.g. tapes and labels), and the market is still growing as new applications are regularly discovered. Emulsion polymerization is widely used to produce water-based PSAs. In this work, the influence of morphology, diameter and acrylic acid concentration in the particles on adhesion properties (peel, tack and shear) was studied. To do so, two series of homogeneous and core-shell latex particles of poly(butyl acrylate-2-ethyl-hexyl acrylate) with different concentrations of acrylic acid (0, 1, 3 and 5 wt%) and three different average diameters, were synthesized by means of emulsion polymerization techniques. The materials were characterized by dynamic light scattering, zeta potential and transmission electronic microscopy. The contents of acrylic acid in the polymer and dispersed medium were determined and the higher quantity of it was found within the particles. The best equilibrium between adhesion properties was found in the core-shell particles with 3 wt% of AA.     

Fabrication and optical characterization of imprinted broad‐band photonic films via multiple gradient UV photopolymerization

A structured broad‐band photonic film is fabricated by a novel method using multiple gradient UV‐induced polymerization in the presence of cholesteric liquid crystals (CLCs). Here, imprinting and broadening of the reflection band of chiral nematic mesophase cells are achieved via controlled UV polymerization. The intensity gradient of UV light is modified by the distance between UV lamp and sample cell, which affects the polymerization rate and leads to the formation of imprinted helical constructions with different pitches. In this study, a comparison of new design process with traditional UV polymerization process is carried out. After seven cycles of gradient UV polymerization, the imprinted photonic construction exhibited a broadened reflection band and Bragg reflection, even for isotropic materials. Because of this, the reflection bandwidth showed a 70% improvement. Additionally, two stacked imprinted cells with different pitches can reflect incident light with a bandwidth over the visible wavelength range of 480–680 nm. A broad‐band photonic polymer film can be imprinted using multiple gradient UV photopolymerization in the presence of CLCs. Forming a UV intensity gradient and controlling the rate of photopolymerization are key factors in broadening the reflection band. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1427–1434     

Properties of single-component acrylic pressure-sensitive adhesives synthesized using <Emphasis Type="Italic">tert</Emphasis>-butyl peroxypivalate initiator

In this work, tert-butyl peroxypivalate initiator was newly used in the solution polymerization of acrylic copolymers with 2-ethylhexyl acrylate, butyl acrylate, methyl methacrylate and acrylic acid monomers for application of pressure-sensitive adhesives (PSAs). Its proper dosage was determined to vary from 0.6 to 1.2 wt % when a high monomer conversion (>99%) was ensured. In this amount range, polymer properties and adhesive performance of the PSAs were investigated. The results indicated that with the amount of tert-butyl peroxypivalate increased, the molecular weights of the polymer decreased and the molecular weight distribution became wider. It was also observed that the synthesized PSAs had high interfacial adhesion and low cohesion strength, and thus exhibited cohesive failure during the peel test. So cross-linking agent was employed to improve the shear strength of the PSAs and to eliminate the adhesive residue while at the sacrifice of loop tack and peel strength. As a whole, the optimal performance was obtained by using 1.2 wt % amount of initiator and 0.5 wt % concentration of cross-linker. In this case, the peel and shear strength have achieved the best balance. In addition, for the cross-linked PSA tapes, the peel strength slightly decreased with the dwell time.     

Transition Metal–(μ-Cl)–Aluminum Bonding in α-Olefin and Diene Chemistry

Olefin and diene transformations, catalyzed by organoaluminum-activated metal complexes, are widely used in synthetic organic chemistry and form the basis of major petrochemical processes. However, the role of M–(μ-Cl)–Al bonding, being proven for certain >C=C< functionalization reactions, remains unclear and debated for essentially more important industrial processes such as oligomerization and polymerization of α-olefins and conjugated dienes. Numerous publications indirectly point at the significance of M–(μ-Cl)–Al bonding in Ziegler–Natta and related transformations, but only a few studies contain experimental or at least theoretical evidence of the involvement of M–(μ-Cl)–Al species into catalytic cycles. In the present review, we have compiled data on the formation of M–(μ-Cl)–Al complexes (M = Ti, Zr, V, Cr, Ni), their molecular structure, and reactivity towards olefins and dienes. The possible role of similar complexes in the functionalization, oligomerization and polymerization of α-olefins and dienes is discussed in the present review through the prism of the further development of Ziegler–Natta processes and beyond.     

Efficient photopolymerization of thick pigmented systems using upconversion nanoparticles‐assisted photochemistry

Photopolymerization of thick pigmented systems still remains challenging due to the light screening effect of the pigments. Here, we present a facile method based on upconversion nanoparticles (UCNPs)‐assisted photochemistry to achieve efficient photopolymerization and improved curing depth of pigmented systems. Under a 980‐nm laser irradiation, UCNPs are able to convert NIR light into UV and visible light to activate photoinitiators for the initiation of polymerization. Influencing factors on photopolymerization were systematically investigated. With optimal parameters, 25.5 mm of photopolymerization depth combined with 70% of maximal double bond conversion was obtained. The peak temperature of 120.4 °C during UCNPs‐assisted photopolymerization is comparable with or lower than that of some reported frontal photopolymerization applied to prepare functional composite polymeric materials. Both indentation hardness and reduced modulus of the photocured materials using UCNPs as internal lamps were higher than those of the reference cured under traditional blue LED light. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 994–1002     

Photoinitiators for UV and visible curing of coatings: Mechanisms and properties

The radiation curing industry is one of the most rapidly developing fields in the entire coatings industry. The low toxicity, cheapness, speed, control and ease of formulation and operation are some of the main advantages of this growing technology. UV and/or visible light radiation is used to induce photochemical polymerization or crosslinking of a monomer, oligomer or prepolymer formulation containing a certain type of unsaturation, such as an acrylic group, and an appropriate initiator. The latter is used to absorb the light energy and transform it into active species, such as radicals or ions, capable of inducing such reactions. Applications extend to general coatings for paper, board, wood, tapes, compact discs and holograms, inks, photoresists for imaging processes and adhesives for welding and sealing in electronic circuit boards. The photoinitiator is the key to the control of these processes and, in recent years, has seen many new developments. These include the need for water-soluble, co-reactive and polymeric structures with low migration rates, as well as cheaper UV/ visible sensitizers with enhanced speed. New and effective cationic systems are also on the scene and, although expensive, are attracting significant academic and commercial interest.     

The Role of Components in Waterbased Microsphere Acrylic Psa Adhesive Properties

In this paper the batch suspension copolymerization of ethyl acrylate/2 ethyl hexylacrylate (EA/2-EHA) for production of suspension-based microsphere acrylic pressure sensitive adhesives (PSA) is presented. The effects on the adhesion properties of PSA different process (reaction temperature and stirrer speed) as well as chemical parameters (amount of EA, initiator concentration) are discussed. The conversion was monitored in-line using Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and the results were compared with the standard gravimetrical method. The glass transition temperatures (T_g) of the PSAs were measured using differential scanning calorimetry (DSC) technique, while molecular weight distribution (MWD) was determined by gel permeation chromatography (GPC). The adhesion properties of PSAs were characterized via the measurements of tack, peel adhesion and peel strength. The results of the experiments have shown that the kinetics of the suspension polymerization for production of PSAs is significantly affected by temperature of polymerization and the initiator concentration, but are shown to be relatively independent of the EA amount and the stirrer speed. The tack, peel and shear strength depend on the mean particle size and particle size (PS) distribution (PSD) and T_g. The mean particle size and PSD depend primarily on the stirrer speed during the PSA synthesis process, while the T_g is most affected by amount of EA used for the synthesis. The results have also shown a rather unexpected relationship between MWD of the PSAs and the applicative properties: tack, peel and shear are seen to be increasing to the decreasing values of weight average MWD, which is the exact opposite of the previously published research. The most likely explanation for this relationship is the formation of a gel during the synthesis of PSA.     

Photoreactive UV-crosslinkable acrylic pressure-sensitive adhesives containing type-II photoinitiators

UV-crosslinking is an established technology used in many industrial manufacturing processes. New applications and technical specifications of UV technologies stimulate the continuous development of photoinitiators that can efficiently meet specific requirements. A typical class of radical-reactive type-II photoinitiators has been used for the UV-initiated crosslinking of acrylic pressure-sensitive adhesives (PSAs).The activity of type-II photoinitiators such as: benzophenone derivatives, thioxanthone derivative, antraquinone derivative and fluorenone (without tertiary amine as a co-initiator) in the photoreactive UV-crosslinkable acrylic pressure-sensitive adhesives was described. The effect of the type-II photoinitiators on the acrylic PSA properties (tack, peel, and shear strength) was summarized.     

Crosslinkable propyleneimine pressure‐sensitive adhesive acrylates and their pot life

In this article a new generation of crosslinkers based on multifunctional propyleneimine derivatives involving crosslinking reactions of acrylic pressure‐sensitive adhesives (PSAs) were investigated. Their tack, peel adhesion, and shear strength after crosslinking, as well as their viscosity and pot life were also measured. Crosslinking of PSAs is an established technology used in many industrial manufacturing processes. Their novel applications and technical specifications stimulate continuous research and development into new crosslinkers with very interesting characteristics. Copyright © 2004 John Wiley & Sons, Ltd.     

Cyclodextrins Initiated Ring-Opening Polymerization of Lactide Using 4-Dimethylaminopyridine (DMAP) as Catalyst: Study of DMAP/β-CD Inclusion Complex and Access to New Structures

Cyclodextrins (CDs) are cyclic oligosaccharides used in many fields. Grafting polymers onto CDs enables new structures and applications to be obtained. Polylactide (PLA) is a biobased, biocompatible aliphatic polyester that can be grafted onto CDs by -OH-initiated ring-opening polymerization. Using 4-dimethylaminopyridine (DMAP) as an organocatalyst, a quantitative functionalization is reached on native α-, β-, γ- and 2,3-dimethyl- β-cyclodextrins. Narrow molecular weight distributions are obtained with the native CDs (dispersity < 1.1). The DMAP/β-CD combination is used as a case study, and the formation of an inclusion complex (1/1) is shown for the first time in the literature, which is fully characterized by NMR. The inclusion of DMAP into the cavity occurs via the secondary rim of the β-CD and the association constant (K_a) is estimated to be 88.2 M⁻¹. Its use as an initiator for ring-opening polymerization leads to a partial functionalization efficiency, and thus a more hydrophilic β-CD-PLA conjugate than that obtained starting from native β-CD. Polymerization results including also the use of the adamantane/β-CD inclusion complex as an initiator suggest that inclusion of the DMAP catalyst into the CD may not occur during polymerization reactions. Rac-lactide does not form an inclusion complex with β-CD.