Acetyl-protected cytosine and guanine containing acrylics as supramolecular adhesives

Hydrogen bonding among nucleobase pairs serves as an efficient noncovalent interaction for designing supramolecular polymers with desired properties for pressure sensitive adhesives. Michael addition yielded acetyl-protected cytosine/guanine containing acrylic monomers with flexible spacers between the hydrogen bonding units and the acrylic backbone. Free radical polymerization of nucleobase-containing monomers afforded acetyl-protected cytosine/guanine homopolymers and random copolymers with n-butyl acrylate. Nucleobase incorporation significantly affected thermal, thermomechanical, rheological, morphological properties, and adhesive performance of polyacrylates. Guanine/cytosine-containing copolymers each exhibited a single glass transition (T_g) that increased with increasing nucleobase content. Self-association of acetyl cytosine and acetyl guanine units converted low T_g polyacrylates to physically crosslinked networks with mechanical integrity. Solution casting acetyl guanine-containing copolymers with 8 mol% or higher guanine content yielded free-standing films with microphase-separated morphologies. Acetyl cytosine-containing copolymers with 15 mol% or more cytosine formed free-standing films with less microphase-separation compared to the guanine copolymers. ¹H NMR titration experiments established a 1:1 binding stoichiometry between acetyl cytosine and acetyl guanine monomers in CDCl_3, similar to guanine-cytosine association. However, the acetyl protecting group hindered the formation of triple hydrogen bonding, resulting in double hydrogen bonding between acetyl cytosine and acetyl guanine with an intermediate binding strength comparable to their self-associations. Acetyl guanine-containing copolymers with 3 mol% acetyl guanine exhibited higher peel strength on stainless steel and higher extended service frequency range compared to cytosine-containing copolymers and various pressure sensitive adhesive controls.     

Preparation and characterization of high initial bonding strength reactive hot melt polyurethane adhesive derived from phthalate polyester polyols

A series of phthalate polyester polyols (PEs) were synthesized via a polycondensation reaction with phthalic anhydride (PA) and different glycols, such as neopentyl glycol (NPG), ethylene glycol (EG), diethylene glycol (DEG), 2-methy-1,3-propanediol (MPO), 1,4-butylene glycol (1,4-BDO) and trimethylolpropane (TMP). Reactive hot melt polyurethane adhesive (HMPUR) with high initial bonding strength was then prepared by poly(propylene glycol) 2000 (PPG-2000), Dynacoll 7360 with these resultant PEs. Effects of different glycols on the glass transition temperature (T_g) and viscosity of the PEs were investigated. Besides, influences of these resultant PEs on the water resistance, bonding strength, thermal stability and surface morphology of the HMPUR were further discussed. The experimental results showed that T_g and viscosity of the PEs decreased with the increase of the chain flexibility of diols. The initial bonding strength of the HMPUR increased with the increase of T_g of the PEs. The hydrogen bonds and cross-linking structure of the HMPUR will also lead to the increase of the bonding strength. In addition, the water resistance of HMPUR was improved by the cross-linking structure and lateral methyl groups of the PEs, while the thermal stability changed little. The surface morphology of the HMPUR showed that all samples have two phase structures and the HMPUR based on DEG and 1,4-BDO exhibited weak phase separation.     

A novel mucoadhesive polymer prepared by template polymerization of acrylic acid in the presence of poloxamer

A new mucoadhesive polymer was prepared by template polymerization of acrylic acid using poloxamer as a template polymer. FTIR results showed that the interpolymer complex was formed by hydrogen bonding between the carboxyl group of poly(acrylic acid) (PAA) and the ether group of poloxamer. The extent of hydrogen bonding in the PAA/poloxamer interpolymer complex increased as the ratio of PAA/poloxamer decreased. The T_g of PAA/poloxamer interpolymer complexes was matched well with the T_g calculated by Gordon‐Taylor's equation than that of their blends. This result suggests that the PAA and poloxamer in the interpolymer complexes are more compatible than their blends. The dissolution rate of PAA/poloxamer interpolymer complexes was much slower than that of their blends, and was dependent on the pH of the medium and the ratio of PAA/poloxamer. The adhesive bond strength of PAA/poloxamer interpolymer complexes to a plastic (polypropylene) plate was greater than their blends or a commercial product, Carbopol 971P NF. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1525–1530, 2001     

Investigation of thermal degradation of polystyrene by differential scanning calorimetry

Thermal degradation of polystyrene was performed in a differential scanning calorimeter under nitrogen atmosphere, and the glass transition temperature was measured continuously. From random chain scission kinetics and T_g-molecular weight relationships, the rate constant for random scission was obtained. The rate constant was found to undergo a drastic change at a critical molecular weight (∽45,000), which corresponds to a similar observation in relaxation studies. A viscosity-dependent mechanism for radical chain end termination is thus suggested.     

A study on hygrothermal degradation and recovery of an epoxy adhesive using molecular dynamics simulation

For application of epoxy adhesive to joining similar or dissimilar materials in vehicle bodies, its hygrothermal degradation (HTD) caused by severe environmental conditions of service will always be an issue until the relevant mechanism is clearly addressed and the remedy is found. This study provides experimental observations of an epoxy adhesive in terms of HTD and recoverability of the mechanical performance, and in the meantime, molecular dynamics (MD) simulations are performed to analyse the underlying mechanism. Comparing experimental results of the adhesive among states of the initial, HTD and dried manifests that the glass transition temperature (T_g) and the uniaxial tensile properties both reduced after HTD but partially recovered when dried. In the MD simulations, both of the dominant HTD factors, plasticization and hydrolysis, are accounted for via characterizations of water inclusion and bond scission. The simulation results reveal that both of the HTD factors reduce T_g, while only hydrolysis weakens the tensile properties. A quantitative comparison between the influences of plasticization and hydrolysis implies that hydrolysis is reversible for this specific epoxy adhesive.     

Thermal stability and compatibility of epoxy/polycarbonate and epoxy/tetramethyl polycarbonate blends

A series of the blends of tetrafunctional epoxy resins with polycarbonate (PC) or tetramethyl polycarbonate (TMPC) was prepared to investigate thermal stability and compatibility. The T_g behavior as a function of isothermal curing time was observed. The thermal stability of epoxy and epoxy/thermoplastics blends was estimated using thermogravimetric analysis (TGA). Fourier transform infrared (FTIR) investigation demonstrated the occurrence of thermal degradation and hydrolysis in epoxy and epoxy/PC blends during the curing process. The thermal degradation of cured epoxy was induced with etherification, a sort of side reaction, and resulted in the chain scission of networks leading to the decrease of T_g. The variance of thermal stability with a combination of two components in these blends resulted from the difference of the compatibility due to chemical structure similarity. The compatibility was corroborated with the morphology by scanning electron microscopy (SEM). © 1996 John Wiley & Sons, Inc.     

Enhancing mechanical properties of aromatic polyamide fibers containing benzimidazole units via temporarily suppressing hydrogen bonding and crystallization

The copolymerization modified poly(p‐phenylene terephthalamide) containing 2‐(4‐aminophenyl)?5‐aminobenzimidazole (PABZ) units in the main chain was synthesized and the corresponding poly‐p‐phenylene‐benzimidazole‐terephthalamide (PBIA) fibers were prepared by wet spinning. The HCl, the by‐product released during polymerization, can complex with PABZ units to prevent the formation of hydrogen bonding between PABZ units, resulting in amorphous PBIA fibers and a lower glass transition temperature (T_g). Therefore, for the purpose of gaining strong hydrogen bonding and high orientation degree at the same time in PBIA fibers, two‐step drawing–annealing processing was adopted. The as‐spun PBIA/HCl complex fibers were drawn first at 280°C, higher than the T_g of the PBIA/HCl complex fibers and lower than the decomplexed temperature of HCl, which temporarily suppresses the formation of hydrogen bonding and crystallization. Subsequently, the fibers were annealed to reform hydrogen bonding between PABZ units and crystallization via decomplexation of HCl at 400°C. However, when the drawing is above the decomplexed temperature of HCl, the decomplexation of HCl begins to occur which leads to the reform of hydrogen bonding and crystallization, and the tensile strength of the drawn‐annealed PBIA/HCl complex fibers decreases with a decrease in the HCl content of fibers. The tensile strength of two‐step drawn‐annealed fibers increased by approximately 15% compared to that of one‐step drawn PBIA/HCl complex fibers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42482.     

Effects of molecular weight and grafted maleic anhydride of functionalized polylactic acid used in reactive compatibilized binary and ternary blends of polylactic acid and thermoplastic cassava starch

Polylactic acid (PLA) was reactively functionalized with maleic anhydride (MA) and 2,5‐bis(tert‐butylperoxy)?2,5‐dimethylhexane (Luperox 101 or L101) using a twin screw extruder (TSE). The effects of functionality (grafted MA level) and/or number average molecular weight of functionalized PLA (PLA‐g‐MA) as the reactive polymer pairs (binary blends) and reactive compatibilizer (ternary blends) were investigated. Due to the dominant side reaction during melt free radical grafting, polymer degradation or chain scission, PLA‐g‐MA having a higher grafted MA had lower molecular weights and intrinsic viscosity as well as broader molecular weight distribution values. The thermal, physical, mechanical, and morphological properties of binary blends produced by using the TSE and injection molding at a ratio of 70 wt % PLA‐g‐MA and 30 wt % thermoplastic cassava starch (TPCS) were analyzed. The reactive blends having grafted MA more than 0.4 wt % had poor tensile strength and elongation at break. Similar trends in morphology and tensile properties were observed in the reactive ternary blends. The use of PLA‐g‐MA strongly impacted the elongation at break but not the modulus or tensile strength. An increase of PLA‐g‐MA's number average molecular weight ( or M_n) improved the tensile properties of the blends. The reactive ternary blend having 0.1 wt % grafted MA on PLA and PLA‐g‐MA basis and PLA‐g‐MA's M_n of 45 kDa offered the highest elongation at break. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42230.     

Influence of wood extractives on two-component polyurethane adhesive for structural hardwood bonding

ABSTRACT

When bonding wood for structural applications, the wood–adhesive bond is influenced by a variety of factors. Besides the physical and mechanical properties of wood species, their chemical composition, e.g. wood extractives, can play a role in bonding wooden surfaces. A two-component polyurethane system (2C PUR) was chosen to better adapt to the current adhesion problem. The influence of extractives on crosslinking was determined by Attenuated Total Reflection-Fourier Transform Infrared Spectrometer (ATR-FTIR) and on the rheological behavior in terms of gel point and storage modulus. Therefore, 2C PUR was mixed with 10% of eight common wood extractives separately. Furthermore, the mechanical properties of beech wood (Fagus sylvatica L.) bonded with extractive enriched adhesive were tested by means of tensile shear strength tests and evaluation of wood failure. These results of ATR-FTIR clearly show that the majority of crosslinking was terminated after 12 hr. Acetic acid and linoleic acid expedited the isocyanate conversion during the first 2.5 hr. The curing in terms of gel point and storage modulus of 2C PUR was accelerated by starch, gallic acid, linoleic acid, and acetic acid. Heptanal, pentanal, 3-carene, and limonene decelerated the curing. All extractives lowered the storage modulus determined after 12 hr. The bonding of beech wood with extractive–adhesive blends showed a slight decrease of the mechanical properties, with the exception of a marginal increase in the case of linoleic acid and pentanal.

In summary, it can be said that 2C PUR is sensitive to the influence of wood extractives and can therefore be partly held responsible for adhesion problems occurring when extractives in surface-wide and higher contents are available.     

The effect of benzenesulfonamide plasticizers on the glass transition temperature of an amorphous aliphatic polyamide

The plasticizing effect of benzenesulfonamides (BSAs) on an amorphous aliphatic polyamide (AAPA) has been studied using dynamic mechanical analysis of copper‐supported spin‐coated mixtures. It follows that N‐(n‐butyl)BSA (BBSA), an amorphous liquid hydrogen bonding BSA, is fully miscible with AAPA because their mixtures are characterized by a single glass transition (T_g) throughout the compositional range. The T_g–composition dependence, however, is not linear because experimental results suggest a 20 K fall in T_g occurring around 0.65 BBSA units per amide unit, which coincides with the system shifting from a polymer‐like to a liquid‐like glass‐forming material. When considering a crystallizable hydrogen‐bonding plasticizer such as ethylBSA (EBSA), AAPA/EBSA mixtures become fully crystalline at a 1.3 EBSA unit per amide group. Nevertheless, melting point depression together with the single T_g observed throughout the compositional range on quenched (and therefore amorphous) samples confirms the miscibility of AAPA chains with the plasticizer. N,N‐DialkylBSAs, which lack the sulfonamide proton and therefore the possibility of hydrogen bonding with amide groups, quickly phase separate from AAPA, the glass transition of the latter staying mainly unaffected apart from a small (9 K) decrease at 10–15 mol% plasticizer. © 2001 Society of Chemical Industry     

Effect of Hydrothermic Ageing on Dielectric and Mechanical Properties of Rigid Poly(vinyl chloride)

An accelerated hydrothermic ageing (according to N.F.T. 54043 method) was performed on samples of rigid poly(vinyl chloride). The test consisted of sample immersion in boiling water at 100°C for different exposure periods up to 480 h. The samples were removed from the boiling water every two hours for mechanical and dielectric characterization and color test. The dielectric measurements carried out on aged samples, up to 40 h, showed that the permittivity remained almost constant and its value was found to be 2.3 in the range –100 to +62.8°C. However, as the temperature approaches the glass transition (T_g = 88.3°C), the permittivity was observed to increase rapidly. It was also found that the permittivity of aged samples was lower than that of the non‐aged samples. The dielectric loss factor (tan δ) measurements with respect to temperature have confirmed the presence of two relaxations: β at low temperature (around –35°C) and α near the T_g. The combined action of water and temperature reduced the intensity of the corresponding relaxation peaks. The sample color index was evaluated up to 480 h using the SYNMERO scale in order to estimate the degradation extent. Unexpectedly, elongation at break under uniaxial traction remained unaffected by the hydrothermic ageing, meaning that two competing processes were involved simultaneously (sample degradation via chain scission and sample plastification via water absorption).     

Relationships between surface wettability and glass temperatures of high polymers

The adhesion between a polymer and a solid substrate may be considered to be one type of complex liquid-solid interaction. Relationships between surface wettability and bulk properties of liquidlike polymers are discussed. A new and direct empirical relationship between the glass temperature (T_g) and critical surface tension of a polymer (γ_c) is established: where n = degree of freedom, defined by Hayes, V_m = molar volume, and Φ = interaction parameter, or the ratio between reversible work of adhesion and geometrical mean of the work of cohesion. The effect of polarity and hydrogen bonding on this relationship is also discussed. The calculated γ_c's are much closer to the observed values than those calculated on the basis of parachor. With this new wettability relationship the wettability of polymers, especially of those forming no hydrogen bonds, can be related to thermal, rheological, mechanical, and relaxational properties.     

Morphology,Thermal Stability,and Mechanical Behavior of [Poly(propylene)‐grafted Maleic Anhydride]‐Layered Expanded Graphite Oxide Composites

PP‐g‐MA‐layered EGO composites were prepared directly by solution blending. Two types of PP‐g‐MA/EGO composites were prepared using different mixing methods: distributive and dispersive. In this study, the effects of the mixing method of EGO on the crystalline structure and thermo‐mechanical properties of PP‐g‐MA/EGO composites are reported. WAXD exhibited a shift in 2θ of the monoclinic (α) phase of PP‐g‐MA and (002) EGO peaks for PP‐g‐MA/EGO layered composites, which indicated a modification of the crystalline structure of PP‐g‐MA in the layered composites. DSC exhibited a single characteristic melting peak of monoclinic (α) crystalline phase PP‐g‐MA. The incorporation of EGO increased T_c indicating that the EGO acted as a nucleating agent for PP‐g‐MA. The crystallinity of the PP‐g‐MA/EGO composites was found to be dependent on the mixing method. Thermogravimetry demonstrated that PP‐g‐MA in the presence of EGO has higher degradation temperature, suggesting that the graphite particles acted as a thermal barrier material for PP‐g‐MA. DMA indicated that incorporation of EGO into PP‐g‐MA increased the storage modulus, due to the hydrogen bonding between EGO and MA of PP‐g‐MA.

     

Thermal behavior of gamma‐irradiated amorphous poly (ethylene terephthalate) films

Poly (ethylene terephthalate) (PET) was irradiated in air by gamma rays at dose rate of 28 kGy/h for doses up to 3500 kGy. The influences of gamma irradiation on the glass transition and degree of crystallinity were investigated by differential scanning calorimetry. For amorphous PET, the observed glass transition temperature T_g and step of heat capacity ΔC_p decreased with absorbed dose. These decreases were attributed to a predominant chain scission process. The glass transition temperature may be useful as an indicator of radiation to the PET. The results also showed that such chain scission increases in mobility lead to a greater crystallizability. POLYM. ENG. SCI. 46:1374–1377, 2006. © 2006 Society of Plastics Engineers     

Degradation of poly(D,L‐lactic acid)‐b‐poly(ethylene glycol)‐b‐poly(D,L‐lactic acid) copolymer by electron beam radiation

This article investigates the effects of electron beam (EB) radiation on poly(D ,L ‐lactic acid)‐b‐poly (ethylene glycol) copolymer (PLA‐b‐PEG‐b‐PLA). The copolymer films were EB irradiated at doses from 0 to 100 kGy. The degradation of these films was studied by measuring the changes in their molecular weight, mechanical and thermal properties. The dominant effect of EB radiation on PLA‐b‐PEG‐b‐PLA is chain‐scission. With increasing irradiation dose, recombination reactions or partial crosslinking may occur in addition to chain scission. The degree of chain scission G_s and crosslinking G_x of sample are calculated to be 0.213 and 0.043, respectively. A linear relationship is also established between the decreases in molecular weight with increasing irradiation dose. Elongation at break of the irradiated sample decreases significantly, whereas its tensile strength decreases slightly. The glass transition temperature (T_g) is basically invariant as a function of irradiation dose. Thermogravimetric analysis shows that its thermal stability decreases with increasing dose. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of hydrogen bonding interaction on the damping properties of poly(n‐butyl methacrylate)/small molecule hybrids

The hydrogen bonding interactions between poly(n‐butyl methacrylate) and a series of low molecular weight phenols containing two to four hydroxyl groups with different steric effects were investigated by differential scanning calorimetry and Fourier‐transform infrared spectroscopy. Results showed that the hydrogen bonding strength between the two components varies greatly according to the steric effects of the phenolic hydroxyl group. As the size of the group beside the hydroxyl increases, the hydrogen bond strength weakens. The glass transition temperature of binary hybrid systems was put into relation with the corresponding hydrogen bonding interaction strength. Strong hydrogen bonding strength increased T_g to higher values than that predicted by the linear additivity rule; by contrast, T_g of hybrid systems with weak hydrogen bonds showed linear changes. All of the samples showed linear variations at low concentrations of small molecules. The damping properties of five systems were analyzed by dynamic mechanical analysis. Either the loss factor or area of tan δ peak of the five systems increased compared with that of the pure polymer, thereby showing great improvements in the damping properties of the poly(n‐butyl methacrylate)/small molecule hybrid material. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41954.     

Novel mucoadhesive polymer prepared by template polymerization of acrylic acid in the presence of silk sericin

A novel mucoadhesive polymer was prepared by template polymerization of acrylic acid in the presence of sericin for a transmucosal drug‐delivery (TMD) system. FTIR results indicated that a polymer complex was formed between poly(acrylic acid) (PAA) and sericin through hydrogen bonding. The glass transition temperatures (T_g's) of sericin and PAA in the PAA/sericin polymer complex were inner‐shifted compared with the T_g's of sericin and PAA themselves. This may be due to the increased miscibility of PAA with sericin through hydrogen bonding. The dissolution rate of the PAA/sericin interpolymer complex was dependent on the pH. The mucoadhesive force of the PAA/sericin polymer complex was similar to that of a commercial product, Carbopol 971P NF. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 274–280, 2001     

Crosslinkable deoxidizing hybrid adhesive of epoxy–diacid for electrical interconnections in semiconductor packaging

For electrical interconnections in semiconductor packaging, epoxy‐based pastes have recently attracted considerable interest due to their excellent adhesion to various substrates and their reasonable electrical and mechanical properties, especially when combined with deoxidizing agents (to remove metallic oxides). Here, epoxy–diacid‐based hybrid pastes were examined to achieve a deoxidizing capability for eliminating Sn‐based solder oxides and adhesion between microchip and substrate as a one‐step process. Onset, exothermic peak and end temperatures of the reaction between epoxy and diacids were systematically probed using DSC, rheometry and Fourier transform infrared (FTIR) spectroscopy. The last moment of the adhesive reaction during heating substantially enhanced the thermal and mechanical properties of the epoxy–diacid adhesive despite the absence of exothermic enthalpy detected by DSC. The glass transition temperature (T_g) and Young's modulus gradually decreased as a function of aliphatic chain length of diacids except when the length was extremely short and voids were produced. Soldering (wetting) and deoxidizing capabilities of the hybrid adhesive were observed via optical microscopy and FTIR. The correlation between the reaction, T_g, conversion and viscosity was also investigated. Lastly, complete wetting and electrical interconnection with good mechanical robustness were achieved for a commercial chip/substrate set by flip‐chip bonding. © 2018 Society of Chemical Industry     

Polyester hot-melt adhesives. I. Factors affecting adhesion to epoxy resin coatings

The peel strength and tensile shear strength of polyester hot-melt adhesives on metals coated with epoxy resins are affected by four characteristics of the polyester: (1) inherent viscosity, (2) glass transition temperature (T_g), (3) degree of crystallinity, and (4) melting point. The inherent viscosity affects the strength, toughness, and crystallinity of the adhesive. The T_g and degree of crystallinity affect the low-temperature adhesive properties; the peel strength is relatively low when the T_g is appreciably above the use temperature. The T_g, degree of crystallinity, and melting point affect the high-temperature adhesive properties. A hot-melt adhesive with high peel and tensile shear strengths from 0° to 120°C is the polyester of 1,4-butanediol and trans-1,4-cyclohexanedicarboxylic acid.     

Effect of hygrothermal aging history on sorption process,swelling, and glass transition temperature in a particle‐filled epoxy‐based adhesive

The effects of hygrothermal aging history and initial water content on sorption behavior and the physical properties of a commercial particle‐filled epoxy‐based adhesive were studied by the analysis of the water reabsorption process. ATR‐FTIR analysis was performed to characterize the hydrogen bond interactions among the water and either resin or fillers. Swelling behavior and the depression of the glass transition temperature (T_g) under different hygrothermal aging histories were related to the water in the apparent free volume of the adhesive. The results show that the water diffusion of the adhesive is a non‐Fickian process. It is also observed that swelling (which is reversible and consistent with hydrogen bond formation) and the rate of diffusion are not only dependent on the hygrothermal temperature but also the hygrothermal history. In addition, the swelling observed on the reabsorption process does not alter the apparent free volume of this adhesive system, and T_g depression is independent of the final equilibrium water content of the system. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1581–1591, 2002; DOI 10.1002/app.10447