Viscoelastic and adhesive properties of single‐component thermo‐resistant acrylic pressure sensitive adhesives

Poly(butyl acrylate‐vinyl acetate‐acrylic acid) based acrylic pressure sensitive adhesives (PSAs) were synthesized by solution polymerization for the fabrication of high performance pressure sensitive adhesive tapes. The synthesized PSAs have high shear strength and can be peeled off substrate without residues on the substrate at temperature up to 150°C. The PSAs synthesized in the present work are single‐component crosslinked and they can be used directly once synthesized, which is convenient for real applications compared to commercial multi‐component adhesives. The results demonstrated that the viscosity of the PSAs remained stable during prolonged storage. The effects of the preparation conditions such as initiator concentration, cross‐linker amount, organosiloxane monomer amount and tackifier resin on the polymer properties, such as glass transition temperature (T_g), molecular weight (M_w), surface energy and shear modulus, were studied, and the dependence of the adhesive properties on the polymer properties were also investigated. Crosslinking reactions showed a great improvement in the shear strength at high temperature. The addition of tackifier resin made peel strength increase compared to original PSAs because of the improvement of the adhesion strength. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40086.     

Molecular parameters and their relation to the adhesive performance of acrylic pressure‐sensitive adhesives

Model acrylic pressure‐sensitive adhesives (PSAs) based on poly(2‐ethyl‐hexyl acrylate‐stat‐acrylic acid) and poly(n‐butyl acrylate‐stat‐acrylic acid) at 97.5/2.5 wt % were synthesized using semicontinuous emulsion and solution polymerizations. Microgels formed in the lattices retained their discrete network morphology in the film. In contrast, acrylic solution was essentially gel free and crosslinking in the film was provided by the reaction of acrylic acid and post added Al Acetyl Acetonate after solvent evaporation, which led to continuous network morphology. The difference in film network morphology caused significantly lower shear holding power for the film from emulsion PSA compared with that of solvent‐borne film. Unlike shear holding power, loop tack and peel of acrylic PSAs were mainly controlled by the same sol/gel molecular parameters, regardless of emulsion or solution PSAs. The important molecular parameters are sol‐to‐gel ratio, entanglement molecular weight, weight average molecular weight, and to a lesser extent, glass transition temperature. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2230–2244, 2001     

The effect of varied monomer composition on adhesive performance and peeling master curves for acrylic pressure‐sensitive adhesives

A group of pressure‐sensitive adhesives were prepared with constant glass transition temperature, using emulsion polymerization. The monomers chosen were butyl acrylate, 2‐ethylhexyl acrylate, and methyl methacrylate, along with a small amount of acrylic acid. The proportion of acrylic acid monomer was held constant for each polymer preparation but acrylic ester monomer levels were varied. The glass transition temperatures of the acrylate copolymers were measured by using differential scanning calorimetry. Drying and weighing the tetrahydrofuran‐insoluble polymer fractions were used to determine the polymer gel fractions. Films of constant coating thickness were applied to poly(ethylene terephthalate) film and adhesive properties (tack and shear) were examined. Peel was examined through the construction of master curves derived from peel tests conducted over a range of temperatures and peel rates. As the 2‐ethylhexyl acrylate content increased, the latex gel fractions were found to increase. With increasing EHA and gel fraction, peel shear was found to increase. When peel force master curves were compared, divergence in peel master curves occurred as peel rates increased where polymers with higher butyl acrylate contents reached greater peel stress values. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2909–2917, 2004     

Modification research on the peel strength of the acrylate emulsion pressure‐sensitive adhesives

Pressure‐sensitive adhesives (PSAs) were produced with latexes synthesized via starved semibatch emulsion polymerization processes with butyl acrylate, three different kinds of hard monomers [styrene (St), methyl methacrylate, and 2‐phenoxy ethyl methacrylate (SR340)], acrylic acid, and 2‐hydroxy ethyl acrylate. The management of both the copolymer composition and the polymerization process allowed us to control the behavior of the PSAs. For the acrylate latexes, the types of hard monomers and their contents, the concentration of buffer [bicarbonate (NaHCO₃)], and three kinds of semibatch processes were manipulated to modify the polymer properties. The performance of the PSA films cast from these latexes was evaluated by the peel strength. The results show that the PSA prepared with St exhibited the highest peel strength among the three hard monomers, and the latex synthesized by SR340 showed the largest gel content compared with the other two hard monomers. With increasing buffer, the latex particle size increased, and the peel strength initially increased to a maximum and then decreased. Nevertheless, the stability of the latexes decreased with increasing buffer concentration. In addition, the effects of the three kinds of semibatch processes on the peel strength of the PSA were also evaluated. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40095.     

Synthesis of high‐solid‐content,acrylic pressure‐sensitive adhesives by solvent polymerization

In this study, we prepared high solid content (SC), solvent‐based, acrylic pressure‐sensitive adhesives (PSAs) with n‐dodecyl mercaptan as a chain‐transfer agent (CTA) and studied the crosslinking reactions between the crosslinker and the acrylic PSAs. Acrylic PSAs were prepared from 2‐ethyl hexyl acrylate, acrylic acid (AA), and 2‐azobisisobutyronitrile with a solution polymerization process. The results show AA resulted in an effective molecular weight in the acrylic PSAs, as it improved the hydrophilicity with increasing peel strength of the acrylic PSAs. As for the high SC, the molecular weight and system viscosity decreased through the addition of CTA. At a constant AA amount, the addition of CTA decreased the molecular weight and increased the hydrophobicity of the acrylic PSAs; this decreased the peel strength of the acrylic PSAs on the glass. Furthermore, the addition of CTA decreased the molecular weight and improved the acrylic PSAs' surface morphologies and optical properties. The acrylic PSAs produced in this study could meet production needs. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46257.     

Ab initio reversible addition–fragmentation chain transfer emulsion polymerization of styrene/butyl acrylate mediated by poly(acrylic acid)‐block‐polystyrene trithiocarbonate

Ab initio reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization of styrene/butyl acrylate was investigated with the trithiocarbonate macro‐RAFT agent poly(acrylic acid)‐block‐polystyrene (PAA‐b‐PS) as a stabilizer and a RAFT agent. Influences of the amount of ammonium persulfate (APS), the amount of PAA‐b‐PS and the mass ratio of monomers on emulsion polymerization and film properties are discussed. The particle morphology exhibited spherical‐like structure with particles of about 90 nm in diameter and relatively narrow particle size distribution characterized using transmission electron microscopy and dynamic laser scattering. Fourier transform infrared and ¹H NMR spectra showed that the styrene/butyl acrylate emulsion was successfully synthesized. The monomer conversion increased initially with increasing amount of APS, from 0.4 up to 0.8 wt%, and then decreased. The particle size increased and its distribution decreased gradually with increasing amount of APS. The monomer conversion increased from 76.83 to 94.21% as the amount of PAA‐b‐PS increased from 3 to 4 wt%, and then decreased with further increase of PAA‐b‐PS. The particle size decreased and its distribution increased with increasing amount of PAA‐b‐PS. The water resistance and solvent resistance of the polymer films initially increased and then decreased with decreasing mass ratio of butyl acrylate to styrene. © 2014 Society of Chemical Industry     

Preparation of acrylic/acrylate copolymeric surfactants by emulsion polymerization used in pesticide oil‐in‐water emulsions

In this work, acrylic/acrylate copolymeric surfactants, which can be used in the preparation of pesticide oil‐in‐water emulsions (EW), were synthesized by emulsion polymerization, using potassium persulfate (K₂S₂O₈) as an initiator, dodecyl mercaptan (DDM) as a chain transfer agent at the temperature range of 82–85°C. When the weight ratio of monomers was m(butyl acrylate) : m(methyl methacrylate) : m(acrylic acid) = 4 : 4 : 1.6 and the dosage of DDM was 2% (percentage of monomer mass), the prepared acrylic/acrylate copolymeric surfactants had a number‐average molecular weight of 2.5 × 10⁴ and exhibited good stability for pesticide EW. The carboxylic group distribution studies show that only the surface carboxylic groups make dispersed pesticide oil droplets more stable. The acrylic/acrylate copolymeric surfactants prepared by shot‐monomer had the most surface carboxylic group distribution (46.6%). To obtain greater surface carboxylic group distribution, maleic anhydride (MA) was used to modify the polymer system. Adding 2% MA (percentage of monomer mass) to the polymerization system, the surface carboxylic groups were increased 12% over unmodified acrylic/acrylate copolymeric surfactants. Compared with traditional pesticide EW, the avermectin EW prepared with acrylic/acrylate polymeric surfactant had much better stability. Meanwhile, its pesticide effect was similar to that of a control (1.8% abamectin emulsifiable solution). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of trifunctional cross-linker triallyl isocyanurate (TAIC) on the surface morphology and viscoelasticity of the acrylic emulsion pressure-sensitive adhesives

Acrylic pressure sensitive adhesive (PSA) latexes were synthesized via a starved monomer-seeded semi-continuous emulsion polymerization process with butyl acrylate (BA), methyl methacrylate, acrylic acid (AA), 2-hydroxyethyl acrylate and trifunctional cross-linker, triallyl isocyanurate (TAIC). Influences of TAIC on the resultant latex and PSA properties were comprehensively investigated. The results indicated that latex particle size was independent of the amount of TAIC in the pre-emulsion feed, while the viscosity of the latex increased remarkably with TAIC content increased. Thermal gravimetric analysis result showed that the thermal stability of the polymers was improved significantly with the addition of TAIC. Besides, with the increase in TAIC content, gel content of the polymer increased significantly, while molecular weight between cross link points (M_c) and sol molecular weight (M_w, M_n) of the polymer decreased remarkably. Moreover, for the cross-linked adhesive film, the shear strength was improved greatly while at the sacrifice of loop tack and peel strength, when compared with the uncrosslinked counterparts. Finally, dynamic mechanical analysis and atomic force microscopy were also used to evaluate the viscoelastic properties and surface morphology of the acrylic emulsion PSA film, respectively.     

Poly(methyl acrylate) and copolymer of acrylic acid and butyl acrylate prepared by γ‐irradiation in the presence of 1,1‐diphenylethene: Synthesis and application in emulsion polymerization

Poly(methyl acrylate) and amphiphilic copolymer of butyl acrylate and acrylic acid were prepared in the presence of 1,1‐diphenylethene (DPE) by γ‐irradiation‐induced polymerization. The influences of polymerization time, amounts of DPE in system on conversion, molecular weight (MW), and its distribution (M_w/M_n) were studied. The results indicate that the polymerization in the presence of DPE and initiated by γ‐irradiation shows the character of controlled radical reaction. The prepared copolymer was used as the polymeric emulsifier in the emulsion polymerizations of butyl acrylate (BA) and styrene (St), respectively, to assess the possibility of making monodisperse latices of relatively high solids content (～ 35–45%) in an one‐step batch process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of the MMA content on the emulsion polymerization process and adhesive properties of poly(BA‐co‐MMA‐co‐AA) latexes

In the past work, the shear resistance of pure poly(n‐butyl acrylate) was low, even incorporation of inorganic filler, silica in the composition. It is well‐known that the copolymerization of n‐butyl acrylate (BA) with methyl methacrylate (MMA) will increase the glass transition temperature, and enhance the shear resistance of acrylic polymers. In the current work, the preparation of a series of acrylic water‐borne pressure‐sensitive adhesives (PSAs) with the controlled composition and structure for the copolymerization of BA and acrylic acid (AA) with different MMA contents, poly(BA‐co‐MMA‐co‐AA) was reported and its effects on adhesive properties of the latices were investigated. The latices of poly(BA‐co‐MMA‐co‐AA) were prepared at a solid content of 50% by two‐stage sequential emulsion polymerization, and this process consisted of a batch seed stage giving a particle diameter of 111 nm, which was then grown by the semicontinuous addition of monomers to final diameter of 303 nm. Dynamic light scattering (DLS) was used to monitor the particle diameters and proved that no new nucleation occurred during the growth stage. Copolymerization of BA with MMA raised the glass transition temperature (T_g) of the soft acrylic polymers, and had the effect of improving shear resistance, while the loop tack and peel adhesion kept relatively high. The relationship between pressure‐sensitive properties and molecular parameters, such as gel content and molecular weight, was evaluated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Rheological and adhesion properties of acrylic pressure‐sensitive adhesives

Different pressure‐sensitive adhesives (PSAs) based on acrylic monomers were synthesized under different reaction conditions. The synthesized PSAs have good adhesive properties and without leaving any residue can be easily peeled off from the surface of a substrate. The relationship between PSAs rheological behavior and its adhesion properties (e.g., peel, tack, and shear resistance) has been studied at constant adhesive thickness. The samples were examined for their surface energy and viscoelastic characteristics. It was observed that increase in reaction temperature and reaction time results in decreased storage modulus due to lowered molecular weight, which finally leads to lower elasticity of the PSA. While the storage (G′) and loss (G″) modulus of samples increase with increased initiator concentration, the elasticity of PSA is increased as well. High G″ at high frequency (100 Hz) represents high peel strength because of higher dissipation of viscoelastic energy during debonding. The tack values increase by lowering storage modulus at 1 Hz due to higher M_e. Shear values are increased by higher storage modulus at low frequency (0.1 Hz) due to hydrogen bonding of the different components. Some parallel investigations on the surface energy of the samples showed that they have different properties because of the nature of different monomeric units with their corresponding orientations. Our results reveal that the peel strength is not affected by surface energy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of propyleneimine external cross-linker on the properties of acrylate latex pressure sensitive adhesives

Acrylate pressure sensitive adhesive (PSA) latexes were synthesized via a starved monomer seeded semi-batch emulsion polymerization process with butyl acrylate (BA), methyl methacrylate (MMA), acrylic acid (AA) and 2-hydroxyethyl acrylate (HEA). These PSA polymers were then cross-linked with trifunctional propyleneimine external cross-linker (SAC-100) to study the cross-linking reaction between carboxylic group of the polymer chain and cross-linking agent. It was found that cross-linking provided a significant influence on the film formation process based on the result of SEM analysis. In addition, with the increase of SAC-100 content, the gel content of the polymer increased significantly, while molecular weight between cross-link points (M_c) and the sol molecular weight (M_w, M_n) of the polymer decreased remarkably. The TGA result showed that the addition of the external cross-linker can enhance the thermal stability of the latex film. Moreover, for the cross-linked adhesive film, the shear strength was improved greatly while at the sacrifice of loop tack and peel strength, when compared with the uncross-linked counterparts. Besides, dynamic mechanical analysis (DMA) was also used to evaluate the viscoelastic properties of the acrylate emulsion PSA film.     

Crosslinking of pressure sensitive adhesive based on water‐borne acrylate

This publication shows how the kind of crosslinking agents and their contents influence important properties of acrylic based pressure‐sensitive adhesive (PSA) dispersions such as tack, adhesion and cohesion. Synthesized PSAs based on acrylic polymers, containing 2‐ethylhexyl acrylate, butyl acrylate, vinyl acetate, styrene and acrylic acid are used in the preparation of self‐adhesive dispersions used as coating of polyethylene foams and poly(vinyl chloride) and polyester foils. © 2003 Society of Chemical Industry     

Influence of polymer microstructure on the performance of post‐treated latex‐based pressure sensitive adhesives

Latex‐based butyl acrylate (BA)/acrylic acid (AA)/2‐hydroxyethyl methacrylate (HEMA) pressure sensitive adhesive (PSA) films with various microstructures were heated to improve their performance. The treated PSA films showed significantly better performance than original latex‐based PSA films with similar polymer microstructures. The effect of the heat treatment depended on the polymer microstructure of the untreated PSA films (or corresponding latices). Decreasing the amount of very small sol polymers (i.e., M_x < 2M_e) in gel‐free untreated PSA films, or both very small (i.e., M_x < 2M_e) and very large sol polymers (i.e., M_x > 20M_e) in gel‐containing untreated PSA films led to treated PSA films with significantly better performance. (Note: M_e is the molecular weight between two adjacent entanglement points in a polymer material.) In addition, simultaneously increasing the sol polymer molecular weight (M_w) as well as the size of the chain segments between two adjacent cross‐linking points (M_c) of the gel polymer in the original PSAs resulted in treated PSA films with better performance. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and properties of emulsifier/N‐methylpyrrolidone‐free crosslinkable waterborne polyurethane–acrylate emulsions for footwear adhesives. I. Effect of the acrylic monomer content

Stable emulsions of emulsifier/N‐methylpyrrolidone‐free crosslinkable waterborne polyurethane–acrylates (C‐WBPUAs) with various acrylic monomer contents (0, 10, 20, and 30 wt %) for footwear adhesive materials were successfully prepared in this study. The effects of the acrylic monomer content on the shelf stability, mean particle size, and viscosity of the C‐WBPUA emulsions; the tensile properties and dynamic mechanical thermal properties of the C‐WBPUA film samples; and the adhesive strengths between the upper (synthetic leather) and the sole (ethylene vinyl acetate rubber) in both the dry and wet states of the formulated adhesives (C‐WBPUA emulsion–thickener–hardener) were examined. The adhesive strengths of the formulated adhesives for footwear (leather–sole) in both the dry and wet states increased with increasing acrylic monomer content up to 20 wt %; after this, they almost levelled off. Thus, C‐WBPUA20 and C‐WBPUA30, where the number indicates the acrylic monomer content, can be recommended as high‐performance adhesive materials for footwear. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43758.     

Dismantlable adhesion properties of reactive acrylic copolymers resulting from cross-linking and gas evolution

ABSTRACT

The acrylic copolymers involving 2-hydroxyethyl acrylate (HEA) and tert-butyl acrylate (tBA) units as reactive units behave as pressure-sensitive adhesive type dismantlable adhesive materials. In order to clarify the individual role of HEA and tBA units on dismantlability, the 180° peel behavior after the dismantling treatment, i.e., heating in the presence of given amount of acid catalysts, was systematically investigated using the acrylic copolymers involving different amounts of the reactive units. It was revealed that transesterification of HEA units resulted in an increase in the cohesive force and modulus due to an increase in the molecular weight and cross-linking. Deprotection of tBA units, i.e., transformation of tBA to acrylic acid (AA) unit with isobutene evolution, promoted cross-linking by the esterification of AA units and tended to reduce a cohesive force by forming voids in the adhesive layer due to the evolution of isobutene gas. Interfacial failure in the peel tests corresponded with a high degree of cross-linking and increased modulus of the adhesive. Conversely, cohesive failure was associated with reduced cohesive strength of the adhesive layer and a low peel strength.     

2-Ethylhexyl acrylate/4-acryloyloxy benzophenone copolymers as UV-crosslinkable pressure-sensitive adhesives

Summary It has been previously shown that copolymer of 2-ethylhexyl acrylate with an 4-acryloyloxy benzophenone can be used as PSA. This paper presents synthesis and application of solvent-based polymer system for the preparation of acrylic pressure-sensitive adhesives (PSA). 2-Ethylhexyl acrylate benzophenone copolymers, having molecular mass in the range of 120 000 to 380 000 Dalton were prepared by free-radical solution polymerization. These copolymers were tacky but possessed insufficient cohesive strength after UV-crosslinking to be useful as PSAs. These copolymers resulted in materials having a balance of cohesive and adhesive characteristics required of a good PSA. Some of the parameters affecting the pressure-sensitive adhesive properties of the copolymer are: amount of the 4-acryloyloxy, molecular mass of the polymeric components, UV-reactivity and such properties like tack, peel adhesion and cohesion.     

Effect of 2‐ethylhexyl acrylate and N‐acryloylmorpholine on the properties of polyurethane/acrylic hybrid materials

A hybrid synthesis technology was used to prepare waterborne polyurethane/acrylic hybrid emulsions by polymerization of methyl methacrylate, butyl acrylate, 2‐ethylhexyl acrylate(EHA), and N‐acryloylmorpholine (AMCO) in presence of acrylic‐terminated PU dispersion. Various characterization methods were used to investigate the effect of EHA and ACMO content on the properties of the hybrid emulsions and their resultant films. The research results show that the introduction of EHA can enhance the elasticity of their films, meanwhile, ACMO endows the film with high gloss, adhesion on substrate, toughness, and hardness. Mixing the two monomers leads to yield the hybrid materials with moderate properties. While increasing the weight ratio of ACMO/EHA, the average particle size of the hybrid emulsions increases and their viscosity decreases. For the resultant films, their surface water contact angle, adhesion on substrates, tensile strength, and hardness increase, but the water resistance and elasticity decrease. It has been found that EHA and ACMO have a synergistic effect on gloss of the hybrid films and the hydrogen bond interaction increases with an increase in the ACMO content. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41463.     

Synthesis and photopolymerization of acrylic acrylate copolymers

Acrylate‐functionalized copolymers were synthesized by the modification of poly(butyl acrylate‐co‐glycidyl methacrylate) (BA/GMA) and poly(butyl acrylate‐co‐methyl methacrylate‐co‐glycidyl methacrylate). ¹³C‐NMR analyses showed that no glycidyl methacrylate block longer than three monomer units was formed in the BA/GMA copolymer if the glycidyl methacrylate concentration was kept below 20 mol %. We chemically modified the copolymers by reacting the epoxy group with acrylic acid to yield polymers with various glass‐transition temperatures and functionalities. We studied the crosslinking reactions of these copolymers by differential scanning calorimetry to point out the effect of chain functionality on double‐bond reactivity. Films formed from acrylic acrylate copolymer precursors were finally cured under ultraviolet radiation. Network heterogeneities such as pendant chains and highly crosslinked microgel‐like regions greatly influenced the network structure and, therefore, its viscoelastic properties. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 753–763, 2002     

Atom transfer radical polymerization grafting of highly functionalized polystyrene and poly(4‐methylstyrene) macroinitiators with tert‐butyl acrylate

Two monodisperse graft copolymers, poly(4‐methylstyrene)‐graft‐poly(tert‐butyl acrylate) [number‐average molecular weight (M_n) = 37,500, weight‐average molecular weight/number‐average molecular weight (M_w/M_n) = 1.12] and polystyrene‐graft‐poly(tert‐butyl acrylate) (M_n = 72,800, M_w/M_n = 1.12), were prepared by the atom transfer radical polymerization of tert‐butyl acrylate catalyzed with Cu(I) halides. As macroinitiators, poly{(4‐methylstyrene)‐co‐[(4‐bromomethyl)styrene]} and poly{styrene‐co‐[4‐(1‐(2‐bromopropionyloxy)ethyl)styrene]}, carrying 40% of the bromoalkyl functionalities along the chain, were used. The dependencies of molecular parameters on monomer conversion fulfilled the criteria for controlled polymerizations. In contrast, the dependencies of monomer conversion versus time were nonideal; possible causes were examined. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2930–2936, 2002