Synthesis of Alkyl‐Functionalized Hyperbranched Polymers and Their Use as Additives in Cationic Photopolymerization of Epoxy Resins

Summary: An alkyl‐functionalized hyperbranched polymer, HBP(OH)–C16, was synthesized by partial modification with fatty acid of an aromatic‐aliphatic OH‐terminated hyperbranched polyester HBP? OH. This product was used as additive in the cationic photopolymerization of an epoxy resin. The alkyl‐modified polyester takes part in the photopolymerization process thanks to the residual OH groups by means of chain‐transfer reactions. An increase of the epoxy conversion is observed by increasing the amount of the HBP additive in the photocurable resin with a modification of the bulk properties of the final ultraviolet‐cured films. The presence of HBP(OH)–C16 induces an increase in glass transition temperature, thermal stability, and solvent resistance. Moreover the surface properties of the films are modified achieving highly hydrophobic surfaces in the presence of even very low amounts of HBP(OH)–C16.

Structure of HBP–C16.     

Phenolic Hyperbranched Polymers as Additives in Cationic Photopolymerization of Epoxy Systems

Summary: A phenolic group containing hyperbranched polyester (HBP) was synthesized and employed as chain transfer agent in cationic photopolymerization of a biscycloaliphatic epoxy monomer ( CE ). The epoxy group conversion increases by increasing the amount of HBP in the photocurable resin, due to a chain transfer reaction involving the phenolic‐OH groups. HBP acts as a plasticizer inducing decrease of the T_g values together with an increase of the toughness properties. Meanwhile gel content increases together with the E′ values. By increasing the amount of HBP in the photocurable resin an increase of the density is evident indicating a decrease of free volume. Therefore an improvement of the gas barrier properties might be expected; at the same time an increase of the thermal stability is evident.

     

Rheological characterization of UV‐curable epoxy systems: Effects of o‐Boehmite nanofillers and a hyperbranched polymeric modifier

An organo‐modified Boehmite (o‐Boehmite) was used to prepare nanocomposite UV‐curing coatings, based on a cycloaliphatic epoxy resin (3,4‐epoxycyclohexylmethyl‐3′,4′‐epoxycyclohexane carboxylate). A hyperbranched polymer (HBP) based on highly branched polyester, was also added to the resin, with the aim to modify its reactivity, such as a possible route to increase the toughness of the resin. Different amounts of the nanofiller and the HBP, ranging from 5 up to 20 wt % of resin, were dispersed into the resin in the presence of triarylsulfonium hexafluoroantimonate, as a photoinitiator for the UV curing of the resin. The rheological behavior of the formulations produced was studied as function of the shear rate and of the content of each filler using a cone and plate rheometer. A general increase in viscosity was observed with increasing the volume fraction of each filler and a moderate pseudoplastic behavior was observed when o‐Boehmite filler was added. A non‐Newtonian behavior was observed with the incorporation of the HBP. The viscosity of the epoxy/boehmite resin mixtures was analyzed as function of the nanofiller volume fraction. In the case of epoxy/hyperbranched resin mixtures, the Cross equation was used to predict the viscosity of each formulation as a function of the shear rate and an appropriate relationship to predict the viscosity of each formulation as a function of the filler volume fraction, was determined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal and mechanical properties of a hydroxyl‐functional dendritic hyperbranched polymer and trifunctional epoxy resin blends

Curing characteristics of blends of a hydroxyl‐functionalized dendritic hyperbranched polymer (HBP) and a triglycidyl p‐amino phenol (TGAP) epoxy resin have been studied. THe HBP strongly enhances the curing rate owing to the catalytic effect of the hydroxyl groups. THe thermal and dynamic viscoelastic behavior of the blends of various compositions (HBP content 0–20%) have been examined and compared to the neat TGAP matrix. THe glass transition temperature (T_g) gradually decreases with increase in HBP concentration. The blends show a higher impact strength compared to neat TGAP. Scanning electron microscopy analysis indicates a single‐phase morphology.     

Physical and mechanical properties of dental nanocomposites composed of aliphatic epoxy resin and epoxidized aromatic hyperbranched polymers

Aliphatic epoxy resin (UVR6105) and epoxidized aromatic hyperbranched polymers (HBP) were used as dental resin matrixes, siliane‐treated inorganic nanoparticles as inorganic fillers, ethyl 4‐dimethylaminobenzoate, camphorquinone, and 4‐[(2‐hydroxytetradecyl)oxy] phenyl‐phenyliodoniumhexafluoroantimonate (CD1012) as initiators to formulate new kinds of dental nanocomposites. Their physical and mechanical properties were tested and the inner structure was observed by using scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. The 7 series thermal analysis system was used to determine the glass transition temperature of dental resins. Compressive strengths of dental nanocomposites are lower, diametral tensile strengths are comparable with, flexural strengths are higher than those of commercial hybrid composite (Spectrum‐TPH). The addition of HBP decreased the glass transition temperature of aliphatic epoxy resin. SEM photo micrograph shows that the nanoparticles were well dispersed and inlayed in the resin matrixes. TEM photo micrograph shows that the inner structure of dental resins presents club‐shaped. Epoxidized aromatic hyperbranched polymer can strengthen and toughen aliphatic epoxy resin. These nanocomposites are potential for dental application. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Study on esterification of acrylic phenolic resin by maleic anhydride and photocrosslinking properties of the alkali‐soluble product

An alkali‐soluble, photocrosslinkable polymer was synthesized by esterification of OH groups of acrylic phenolic resin with maleic anhydride. The OH groups were formed by the ring‐opening reaction of epoxy groups of epoxy phenolic resin with acrylic acid. The esterification conditions were studied. The results showed that it is better to use tetramethyl ammonium bromide as catalyst than N,N‐dimethylbenzylamine. The conversion of maleic anhydride in acetone can reach about 80% at 56°C for 4 h. The purified product was characterized by IR, DSC, and TGA. The product containing acrylate and maleic acid monoester groups, above a certain content, can be dissolved in 1% Na₂CO₃ solution. The photocrosslinkable properties of the product were investigated through selection of photoinitiator, accelarator, crosslinkable diluent monomer, etc. The acrylate and maleic acid monoester group‐containing phenolic resin exhibited very good photocrosslinking behavior, since it contains double bonds from both acrylate groups and maleic acid monoester groups. The activity of photoinitiator decreases in the order: isopropylthioanthraquinone > benzoin ethyl ether (BE) > anthraquinone (AQ) > benzophenone > Michel ketone (MK) > 2,2‐diethoxyacetophenone. The combination of some photoinitiators showed synergistic effects. The order of increasing activity for the accelerator is as follows: MK > ethyl p‐(dimethylamino)benzoate > N,N‐dimethylaniline > triethanolamine. The optimum diluent monomer is trimethylolpropane trimethacrylate. The gel content of the mixture of the resin and trimethylolpropane trimethacrylate could reach 85% using the combined photoinitiators of BE and AQ under UV exposure for 120 s. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1607–1614, 2005     

New coating systems based on vinyl ether‐ and oxetane‐modified hyperbranched polyesters

A series of hyperbranched aliphatic‐aromatic polyesters has been synthesized which contain vinyl ether or oxetane functionalities as curable groups. We investigated the curing behavior of these multifunctional polymers in the presence of reactive diluents in order to analyze the possibility of their application in high solids coatings. The vinyl ether‐modified hyperbranched polyesters with a high degree of modification yield the best coatings. Furthermore, coating systems containing vinyl ether‐modified hyperbranched polyesters and triethyleneglycol divinyl ether (DVE‐3) as reactive diluent showed a better performance compared to those containing 4‐hydroxybutyl vinyl ether (HBVE). Real time FT‐IR studies revealed a high conversion of functional groups (76%) for the cationic curing with DVE‐3. On the other hand, the curing reaction of the functional hyperbranched polymers without the presence of any reactive diluent stopped at 32% conversion of functional groups due to the reduced mobility of the polymer. The vinyl ether‐modified hyperbranched polyester could be cured also radically in the presence of diethyl maleate (DEM) as reactive diluent, whereas the curing of the oxetane‐modified polyesters was very slow and incomplete in all attempts.     

Modification of carbon black through grafting multihydroxyl hyperbranched polyether onto its surface

The hydroxy methyl groups were introduced onto the pristine carbon black surface through the reaction between unsaturated hydrogen atoms of the polycondensed aromatic rings of carbon black and formaldehyde in alkali condition. Using the resultant hydroxy methyl groups on the carbon black surface as the growth point, multihydroxyl hyperbranched polyether was grafted onto the carbon black surface by cationic ring‐opening polymerization of 3‐ethyl‐3‐(hydroxymethyl)‐oxetane in the presence of BF₃·OEt₂ to improve its dispersion ability in solvents. It was found that the modified carbon black could be dispersed in polar solvents, such as ethanol, chloroform, and DMF. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2086–2092, 2007     

Hyperbranched polymers in cationic photopolymerization of epoxy systems

Mixtures of epoxy resins in the presence of epoxy hyperbranched polymers (HBP), in the range of 5–15 wt%, were investigated in the cationic photocuring process. No significant differences in rate of polymerization or final epoxy groups conversion were observed. At low concentration, HBP acts as plasticizer and causes a decrease of the glass transition temperature of the epoxy matrix and of the E′ value. At higher concentration (about 15 wt%), two T_g values are evident, indicating a biphasic structure of the system. The SEM analysis of the fracture surface of the samples confirms a particulate structure with separate HBP domains interconnected to the epoxy matrix. In all the samples investigated, a clear increase of the impact resistance was observed, resulting either from the plasticization effect or from the particulate structure induced by the presence of the HBP resin.     

Investigation on the effect of the presence of hyperbranched polymers on thermal and mechanical properties of an epoxy UV‐cured system

The use of hydroxyl‐functionalized hyperbranched polymers (HBPs) (Boltorn^® H20, H30 and H40) was investigated with respect to a UV‐cured epoxy system. Their presence induced an increase of the final epoxy conversion, which was interpreted on the basis of a chain‐transfer reaction. A decrease of the T_g values in the photocured films was observed when the amount of HBP additive in the photocurable formulation was increased. When the amount of HBP in the photocurable resin was increased, the density of photocured films increased, indicating a decrease on the free volume. Moreover, a clear increase in toughness was observed and attributed to the plasticization effect induced by the presence of HBP. This effect is particularly interesting for epoxy thermosets, which are characterized by good mechanical properties, although they are brittle and fragile. By increasing the toughness properties of these photocured resins it may be possible to broad their applications. Copyright © 2005 Society of Chemical Industry     

One‐pot synthesis of hyperbranched poly(aryl ether ketone)s for the modification of bismaleimide resins

Hyperbranched poly(aryl ether ketone)s with hydroxyl end groups (HBP‐OH) and high degree of branching value (83%) were synthesized via an A₂ + B₃ approach. The polymerization conditions (e.g., polymerization temperature and time, monomer concentration, stoichiometric ratio of functional groups) were explored to avoid the gelation. Allyl‐terminated hyperbranched PAEKs (HBP‐AL) with low molecular weight (M_n = 3.4 × 10³) and narrow polydispersity (PDI = 1.65) were obtained via the etherification of HBP‐OH and it has been used for the modification of bismaleimide (BMI) resins. The prepolymers showed good processibilities with a viscosity below 0.6 Pa s at 110°C, though the viscosities slightly increased as the increase of HBP‐AL contents. The cured BMI resins showed high glass transition temperatures (T_g > 320°C) and good thermal stabilities (T_d > 400°C, both in nitrogen and air). It is inspiring to note that the incorporation of HBP‐AL into BMI matrix results in a significant enhancement of toughness without any noticeable loss in modulus, processibility, and T_g. POLYM. ENG. SCI., 54:1675–1685, 2014. © 2013 Society of Plastics Engineers     

Reactions of phenolic ester alcohol with aliphatic isocyanates—transcarbamoylation of phenolic to aliphatic urethane: A 13C‐NMR study

Reactions of aliphatic isocyanates with a phenolic ester alcohol (PHEA) were investigated using ¹³C‐NMR spectroscopy. PHEA has two reactive sites: a phenolic  OH group and a secondary aliphatic  OH group. Both  OH groups react with the isocyanate groups. With an organotin catalyst, dibutyltin dilaurate (DBTDL), the aliphatic  OH group reacts first. With a tertiary amine catalyst, 1,4‐diazabicyclo[2.2.2]octane (DABCO), or triphenylphosphine (Ph₃P) or even in the absence of a catalyst at room temperature (RT) the phenolic  OH group reacts first. With the organotin catalyst, the reactions are generally complete in a day at RT. With DABCO or triphenylphosphine or DNNDSA catalysts, the reactions are almost complete only in 3–4 days at RT in ethyl acetate or acetonitrile. Uncatalyzed reactions are slower. With an acid catalyst such as dinonylnaphthalenedisulfonic acid (DNNDSA), both  OH groups react with the isocyanate. When equimolar quantities of PHEA and hexamethylenediisocyanate (HDI) polymerize at RT or reflux in the presence of a catalyst, both  OH groups react, with the phenol reacting slowly. Upon refluxing, the phenolic  OH‐based urethane slowly rearranges (transcarbamoylation) to the aliphatic  OH‐based urethane. DABCO and Ph₃P catalysts effect this rearrangement at a much slower rate than does the acid catalyst. In the presence of a catalytic amount of DBDTL in a refluxing solvent, this rearrangement is complete in 2 h. By refluxing the phenolic–OH‐based urethane in isopropanol, the mechanism of transcarbamoylation was found to be intermolecular. The mechanism is likely to involve deblocking of the phenolic urethane and subsequent reaction of the isocyanate generated, with the aliphatic  OH group. This conclusion was confirmed by differential scanning calorimetry (DSC) experiments. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2212–2228, 2000     

Synthesis and self‐assembly of hyperbranched polyethers peripherally modified with adenosine 5′‐monophosphate

The chloride functionalized hyperbranched poly(3‐ethyl‐3‐oxetanemethanol) (HBPO) was prepared via reaction of thionyl chloride with hydroxyl groups. Adenosine 5′‐monophosphate (AMP) groups were attached to HBPO in CH₂Cl₂ in the presence of triethylamine (TEA) as an acceptor of HCl. The self‐assembly of resultant hyperbranched molecules bearing self‐complementary hydrogen‐bonding patterns would allow the generation of a highly organized supramolecular architecture in a selected solvent. The morphologies of self‐assembly structures were depended on the level of AMP in polymer and the concentration in solvent. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1147–1152, 2006     

Synthesis of wood‐based epoxy resins and their mechanical and adhesive properties

Wood‐based epoxy resins were synthesized from resorcinol‐liquefied wood. Wood was first liquefied in the presence of resorcinol with or without a sulfuric acid catalyst at high temperature. Because of the hydroxyl groups, the resorcinol‐liquefied wood was considered as a precursor for synthesizing wood‐based epoxy resin. Namely, the phenolic OH groups of the liquefied wood reacted with epichlorohydrin under alkali condition. By the glycidyl etherification, epoxy functionality was introduced to the liquefied wood. The epoxy functionality of the resins was controlled by the concentration of phenolic OH groups in the liquefied wood, which would be a dominant factor for crosslink density and properties of the cured epoxy resins. The flexural strength (150–180 MPa) and the modulus of elasticity (3.2 GPa) of the highly crosslinked wood‐based epoxy resin were equivalent to those of the commercially available epoxy resin, diglycidyl ether of bisphenol A (DGEBA). Also, the shear adhesive strength of the wood‐based epoxy resin was higher than that of DGEBA when plywood was used as the adhesive substrates. The mechanical and adhesive properties suggested that the wood‐based epoxy resins would be well suited for matrix resins of natural plant‐fiber reinforced composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2285–2292, 2006     

Effect of tall oil fatty acids content on the properties of novel hyperbranched alkyd resins

Hyperbranched alkyd resins (HBRA) were synthesized by modification of hydroxylated hyperbranched polyester (HBP1‐4) with tall oil fatty acids (TOFA). The core is a hydroxylated hyperbranched polyester of fourth generation with OH groups in the periphery (18), which is endcapped with tall oil fatty acids. The occurrence of these reactions, HBP1‐4 and TOFA, was determined by making use of acid value, nuclear magnetic resonance, and hydroxyl values. The effects of TOFA and HBP1‐4 on properties of the HBRA resins were investigated by vapor pressure osmometry, differential scanning calorimetry, thermogravimetric analysis, friction resistance, and hardness. The resins with higher modification percentage (HBRA4) presented the best thermal and hydrolytic stability, but lower friction resistance and hardness. All HBRA resins presented amorphous characteristics, OH groups, and double bonds in the periphery. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Novel moisture-cured hyperbranched urethane alkyd resin for coating application

A hyperbranched polyol (HBP) was synthesized using dipentaerythritol as a core material and 2,2-bis(methylol) propionic acid as a chain extender. This was reacted with varying concentrations of soya fatty acid to make hyperbranched alkyd (HBA) resins. The HBA resins containing unreacted hydroxyl groups were reacted with isophorone diisocyanate at NCO/OH ratio of 1.6:1 to make high solid hyperbranched urethane alkyd (HBUA) resins. The excess NCO content in the HBUA resins was used to cure with atmospheric moisture, and thus moisture-cured HBUA coatings were formed. The resins were characterized by FTIR, and ¹³C NMR spectroscopic analysis. A series of such resins were made using different fatty acid/isocyanate ratios with respect to the hydroxyl groups present in the HBP. The effect of compositions on the mechanical and weathering properties of the cured resins was investigated. It was observed that there was an optimum fatty acid–isocyanate ratio in terms of the requirements of solvent, mechanical and weathering properties of the resin. The requirement of solvents for formulating HBUA coatings is much lower compared to linear alkyd-based coatings. The present study reveals that the moisture-cured HBUA resins can be used as a binder material in the field of low-pollution weather-resistance coatings.     

A new strategy for controlling shrinkage of DGEBA resins cured by cationic copolymerization with hydroxyl‐terminated hyperbranched polymers and ytterbium triflate as an initiator

We report a novel strategy for preparing epoxy thermosetting systems with low shrinkage and improved flexibility and degradability. Diglycidyl ether of bisphenol A (DGEBA) resin was cured with different proportions of hydroxyl‐terminated hyperbranched polymer (HBP), using ytterbium triflate as a cationic initiator. The curing process was studied using differential scanning calorimetry and thermomechanical analysis. Characterization of the resulting materials was evaluated using DSC, thermogravimetric analysis, and dynamic mechanical thermal analysis, and the fracture surface was studied using scanning electron microscopy (SEM). When DGEBA is modified with HBP, it shows a homogeneous morphology and the HBP is incorporated chemically into the network, because hydroxyl groups can react with epoxides under cationic conditions. Higher proportions of HBP reduce the glass transition temperature (T_g) and thermal stability and increase the flexibility. When the proportion of HBP in the curing mixture is increased, the degree of shrinkage is reduced significantly and expansion can be observed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Improved thermosets obtained from diglycidyl ether of bisphenol A/4,4′‐diaminodiphenylsulfone based on a new epoxy‐terminated hyperbranched polymer

A new hyperbranched polymer (HBP) with a flexible aromatic skeleton and terminal epoxy groups was synthesized to improve the toughness of diglycidyl ether of bisphenol A. The HBP was characterized using nuclear magnetic resonance, Fourier transfer infrared spectroscopy and gel permeation chromatography. The effect of HBP on the thermomechanical and mechanical properties of modified epoxy systems was studied. For evaluating the efficiency of the modified epoxy systems, composite samples using glass fiber cloth were molded and tested. Using dynamic mechanical analysis, a slight reduction in glass transition temperature (T_g) with increasing HBP content was observed. Analysis of fracture surfaces revealed a possible effect of HBP as a toughener and showed no phase separation in the modified resin systems. The results showed that the addition of 15 phr HBP maximized the toughness of the modified resin systems with 215 and 40% increases in impact and flexural strengths, respectively. T_g and heat resistance of cured modified resin systems decreased slightly with an increase in HBP content and, at 15 phr HBP, only a 2.6% decrease in thermomechanical properties was observed. Meanwhile, a molded composite with HBP showed improved mechanical properties and retention rate at 150 °C as compared to that made with neat resin. © 2015 Society of Chemical Industry     

Synthesis of Fluorinated Hyperbranched Polymers and Their Use as Additives in Cationic Photopolymerization

Summary: A fluorine containing hyperbranched polymer was synthesized by modifying an aromatic‐aliphatic hyperbranched polyester with a semifluorinated alcohol via a Mitsunobu reaction and was subsequently used as an additive in cationic photopolymerization of an epoxy resin. The remaining OH groups of the fluorinated hyperbranched polymer interact with the polymeric carbocation through a chain‐transfer mechanism inducing an increase in the final epoxy conversion. The fluorinated HBP induces modification of bulk and surface properties, with an increase in T_g and surface hydrophobicity already reached at very low concentration. The HBFP additive can, therefore, protect the coatings from aggressive solvents, increases hardness, and allows the preparation of a low energy surface coating.

Synthesis of fluorinated hyperbranched polyester.     

Synthesis of chloromethylstyrene‐tetraethyleneglycol dimethacrylate copolymer beads having various phenolic derivatives immobilized via amide bond and their antioxidation activity

Resins having phenolic derivatives were prepared by treating a resin (RAS‐4G), having benzylamino groups, with benzoic acids containing phenolic hydroxyl groups. The RAS‐4G was prepared by treating macroreticular chloromethylstyrene‐tetraethyleneglycol dimethacrylate (4G) copolymer beads with potassium phthalimide in N,N‐dimethylformamide, followed by reflux in an ethanol/hydrazine monohydrate mixture. 4‐Hydroxy benzoic acid, (2,4‐, 3,4‐, and 3,5‐)dihydroxy benzoic acids, 3,4,5‐trihydroxy benzoic acid, etc., were used as benzoic acids with phenolic hydroxyl groups. The antioxidation ability of the resins having phenolic derivatives was investigated against the generation of 1,4‐dioxane hydroperoxide. The resins showed high inhibition ability against the generation of hydroperoxide. In particular, the resin (RAS‐4G‐3,4‐DHBA) having two phenolic hydroxyl groups had the highest inhibition ability. The resins were found to act as radical scavengers during the generation of 1,4‐dioxane hydroperoxide by UV irradiation in the presence of oxygen. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2097–2104, 2005