Photopolymerization behavior and properties of highly branched polyester acrylate containing thioether linkage used for UV curing coatings

The highly branched polyester acrylate containing thioether linkage (HBAT) was synthesized using an “oligomeric A₂ + B₃” approach. The dithiol, 1,6-hexamethylene bis(3-mercaptopropionate) (HMBM), was prepared through the esterification between 1,6-hexanediol and 3-mercaptopropionic acid, and then underwent an amine-catalyzed thiol-Michael addition to the acrylic double bond of 1,6-hexamethylene diacrylate to obtain an oligomeric dithiol (oligomeric A₂), then further with trimethylolpropane triacrylate as a B₃ monomer. The molecular structure was characterized with FT-IR and ¹H NMR spectroscopy. A broader molecular weight distribution from 1.74 to 2.75 was obtained for different oligomeric dithiol chains by GPC measurements. The photopolymerization kinetics study by photo-DSC analysis showed that the HBAT greatly reduced the oxygen inhibition in radical photopolymerization of acrylates in air. The maximum polymerization rate decreased along with the addition of HBAT into the UV curable resin (EB605) containing bisphenol A epoxy diacrylate and tripropylene glycol diacrylate due to the reduced double bond density and increased viscosity, whereas the final unsaturation conversion in cured film increased because of the longer spacer chain in HBAT compared to that in EB605 and the reduced crosslinking density by HBAT addition. The dynamic mechanical thermal analysis results showed that both the elastic modulus in the rubbery plateau and glass transition temperature of cured film decreased along with the incorporation of HBAT into EB605. The water swelling test and thermogravimetric analysis indicated that the thioether linkage in HBAT can greatly improve the water absorption resistance and oxidative stability of cured film.     

Physical and thermal properties of UV curable waterborne polyurethane dispersions incorporating hyperbranched aliphatic polyester of varying generation number

Three series of novel waterborne hyperbranched polyurethane acrylates for UV curable aqueous dispersions (WHPUD) based on hydroxy-functionalized hyperbranched aliphatic polyesters Boltorn™ of varying generation number were investigated. The effects of the overall composition, including acidic and acrylate groups, and functionality of hyperbranched polyester were studied in terms of particle size, rheology, photopolymerization kinetics, dynamic mechanical thermal as well as thermal degradation behaviors of WHPUDs. The average particle sizes of aqueous dispersions, 43-134 nm, were determined by laser light scattering. The stability and particle size were dependent on the amount of carboxylic acid groups, degree of neutralization, and molecular structure. The rheological features have revealed that all dispersions belong to pseudoplastic fluids. The shear thinning behavior of WHPUDs is more pronounced for lower generation of hyperbranched polyester. The photopolymerization rates of the resins under UV irradiation in the presence of a photoinitiator showed an increasing trend with higher functionality of acrylate. The glass transition temperature (T_g) of UV cured films evaluated by dynamic mechanical thermal analysis (DMTA) showed that the influence of end capping by hard segment consisting of IPDI-HEA is remarkable due to the increase of crosslink density. The T_g, storage modulus and loss modulus increased with increasing generation number from the second to the fourth. The results of TGA for cured WHPUD films indicated good thermal stability with no appreciable weight loss until 200 °C, and that an increase in the hard segment content provoked the increases in thermal degradation temperature. This behavior is rationalized by relating crosslink density dependence of chain end concentration and the generation number of hyperbranched polyester.     

Photopolymerization behavior and properties of highly branched poly(thioether-urethane) acrylates used for UV-curing coatings

The highly branched poly(thioether-urethane) acrylate (BPTUA) was synthesized through an “oligomeric A₂ + B₃” approach. The thiol-endcapped difunctional oligomeric A₂ was obtained by the addition reactions of isophorone diisocyanate with 1,4-butanediol, and then further with 1,4-butanediol bis(thioglycolate). Trimethylolpropane triacrylate was used as a B₃ monomer. The addition conduct of 1,6-hexanediol diacrylate with 1,4-butanediol bis(thioglycolate) was introduced into the polymeric chain for preparing the modified BPTUA (m-BPTUA). The molecular structures were characterized with FT-IR and ¹H NMR spectroscopy, and GPC analysis. The number average molecular weights (M_ns) of BPTUA and m-BPTUA were experimentally measured to be 13,500 g mol⁻¹ and 17,900 g mol⁻¹ with the polydispersity indices of 1.86 and 1.94, respectively. A series of UV-curable resins were fabricated based on bisphenol-A epoxy diacrylate (EB600) and tripropylene glycol diacrylate with the addition of either BPTUA or m-BPTUA in different ratios, and exposed to a UV lamp for obtaining the cured films in the presence of 1-hydroxycyclohexylphenyl ketone as a photoinitiator. From the photo-DSC measurements, the polymerization rate at the peak maximum decreased, whereas the final unsaturation conversion in cured film increased, along with the increase of either BPTUA or m-BPTUA. The elastic modulus in the rubbery plateau and the glass transition temperature from DMTA, as well the tensile strength and Young's Modulus of UV-cured film decreased with increasing either BPTUA or m-BPTUA loading, whereas the elongation at break, flexibility and strike performance were greatly enhanced. Moreover, for the m-BPTUA series, the enhancive effects on the properties were much more obviously than the BPTUA series. The water swelling test and thermogravimetric analysis indicated that the water absorption resistance and the oxidative stability of cured films were improved by the incorporation of thioether linkage into the crosslink networks.     

Synthesis and properties of novel polyurethane acrylate containing 3-(2-hydroxyethyl) isocyanurate segment

Novel UV curable multi-functional polyurethane acrylate (PUA) containing 3-(2-hydroxyethyl) isocyanurate (THEIC) segment was synthesized through three step reactions, the ring-opened reaction of ?-caprolactone with THEIC under the catalysis of tetrabutyl titanate (TBT), the polyaddition reaction between formed hydroxyl compounds and isophorone diisocyanate (IPDI) and condensation reaction between the product of the second step and pentaerythritol triacrylate (PETA). The chemical structure of PUA oligomer and some influence factors in synthesis process were characterized with GPC, ¹H NMR and FTIR. And its photopolymerization process and properties of cured films were also investigated.     

Synthesis and properties of waterborne UV‐curable polydimethylsiloxane‐based polyurethane oligomers: UV‐cured film with excellent water resistance and thermostability

Abstract

This paper designed and synthesized a series of waterborne UV-curable polydimethylsiloxane‐based polyurethane oligomers which contain polydimethylsiloxane segment in the end of the main chain, a plurality of double bonds in the side chain and two kinds of hydrophilic groups including nonionic polyethylene glycol with low molecular weight and ionic quaternary ammonium salt groups. The unique structure endowed not only the oligomer with an excellent water solubility, but also the UV-cured film with hydrophobicity, thermostability and mechanical properties. The prepared oligomers could form a stable white emulsion and had excellent photopolymerization capability, and their conversions of double bonds were all over 92%. The UV-cured film containing long chain polydimethylsiloxane exhibited better hydrophobicity, heat resistance and tensile strength. The polydimethylsiloxane segment located in the end of the oligomer molecular chain was more conducive to its enrichment in the surface of the cured films and improving of the hydrophobicity of the cured films. The water absorption, surface water contact angle and the initial decomposition temperature (T_5%) of the obtained UV-cured films were 2.7%, 91 and 301?°C, respectively.     

Synthesis and properties of hyperbranched polyurethane acrylate used for UV curing coatings

The hyperbranched polyurethane acrylate (HPUA) was synthesized through the addition of hyperbranched polyurethane endcapped by hydroxyl groups (HPU-OH), with the semiadduct urethane monoacrylate (IPDI-HEA). The HPU-OH was prepared by the amidation reaction of diethanolamine with isophorone diisocyanate. The molecular structure of HPUA was characterized by FTIR and ¹H NMR analyses. The number average molecular weight and its polydispersity index were measured by GPC to be 7714 g mol⁻¹ and 1.24, respectively. The HPUA was blended with epoxy acrylate EB600 and difunctional monomer TPGDA in different ratios, and exposed to a UV lamp for photopolymerization in the presence of Runtecure 1104 as a photoinitiator at room temperature. The photopolymerization rate and final unsaturation conversion reached to the highest values with only 5 wt% HPUA addition, whereas decreased as further added. The tensile strength of UV-cured films was improved by adding less than 10 wt% HPUA without damaging the modulus, having the value of 62.56 MPa for EB₉₀HPUA₁₀ film. Besides, the elongation at break increased continuously with the addition of HPUA, reaching to 130% for EB₇₀HPUA₃₀ film. Moreover, the impact strength was greatly enhanced by the addition of HPUA, possessing nearly two times high for EB₇₀HPUA₃₀ film compared with pure EB600 film. However, the T_g decreased as HPUA was added from the DMTA measurements. According to the ratios of T_s/T_g the HPUA has good compatibility with EB600/TPGDA resin.     

Synthesis of UV crosslinkable waterborne siloxane–polyurethane dispersion PDMS-PEDA-PU and the properties of the films

A UV crosslinkable waterborne siloxane–polyurethane dispersion, PDMS-PEDA-PU, was synthesized by incorporating acrylate groups into the side chain of the polyurethane using pentaerythritol diacrylate (PEDA). Polysiloxane groups were introduced into the soft segment of the polyurethane using polydimethylsiloxane (PDMS). They formed a crosslinking structure after UV radiation. The structure of PDMS-PEDA-PU was confirmed by the use of Fourier transform infrared spectroscopy (FTIR). X-ray diffraction (XRD) analysis indicated that the formed PDMS-PEDA-PU was amorphous. The curing rule of PDMS-PEDA-PU was investigated on the basis of the change in C=C conversion during the UV curing process. The influence of the PDMS/PEDA ratio was studied with respect to the water resistance, the thermal property, and the mechanical property of the films.     

Using mixture experimental design to study the effect of multifunctional acrylate monomers on UV cured epoxy acrylate resins

An epoxy acrylate resin was synthesized and the resin was used along with different multifunctional acrylate monomers, i.e. trimethylol propane triacrylate (TMPTA), tripropylene glycol diacrylate (TPGDA), 1,6-hexanedioldiacrylate (HDDA). The effect of the chemical structure of the monomers on some of the physical–mechanical properties of the resins and their cured films, such as viscosity, T_g, hardness and scratch resistance was studied. To minimize the number of experiments, mixture method was used as an appropriate tool for experimental design.     

分子结构中碳碳双键对水性UV聚氨酯分散体的影响

采用异佛尔酮二异氰酸酯(IPDI)、聚酯二元醇(聚己二酸-1,4丁二醇酯)(PBA)为主要原料合成了环氧改性的、固体分约为50%的水性紫外光固化聚氨酯分散体(PUD)。通过预聚物中聚氨酯分子末端的—NCO基团与丙烯酸羟丙酯(HPA)和季戊四醇三丙烯酸酯(PETA)上的羟基发生反应,从而引入碳碳双键,使PUD具备紫外光固化的性能。研究了水性UV分散体的碳碳双键对水性聚氨酯的拉伸强度、硬度、粒径等性能方面的影响,同时对涂膜进行动态力学性能测试(DMA)和断面结构表征(SEM)。结果表明:双键含量增加,UV涂料的拉伸强度和硬度增大,分散体和涂料的其他性能基本不变;DMA测试表明随着双键含量的减小,软段的T_g(s)移向低温,硬段的T_g(h)移向高温,相分离趋于完全;SEM测试表明树脂的交联程度越大,抵抗断裂的程度也越大。     

Study on microstructure of UV-curable polyurethane acrylate films

UV-curable polyurethane acrylates (UVPUA) were prepared, and Fourier transform infrared (FTIR) was used to monitor the synthesis process and cured films. Effects of soft segment length, isocyanate type, reactive diluent type and level, quenching, annealing and different UV-cured degree on the microstructure of UVPUA films have also been studied. With soft segment length increasing, the degree of hydrogen bonding between soft segment and hard segments decreases, and microphase separation of UVPUA becomes better. Soft segment crystallization appears with its molecular weight exceeding 2000, when its value reaches 4000, an even more obvious melting peak in differential scanning calorimetry (DSC) curve was observed. Congregation of hard segment domains and the improvement of phase separation were due to symmetry and regularity of isocyanate, while rigid benzene ring was beneficial to crystallize and increase the glass transition temperature (T_g). The increased crosslink density with increasing the function degree of diluent resulted in better phase separation, on the contrary, increasing the reactive diluent content led to the opposite because of a phase reversion. Microphase separation lower during quenching and annealing due to post-curing of 1,6-hexa-nediol diacrylate (HDDA) at high temperature, and with the UV-cured degree increasing, the phase separation got better first and then became worse.     

Surface modification of polypropylene sheets by UV‐radiation grafting polymerization

1,6‐Hexanediol diacrylate (HDDA) was grafted onto polypropylene (PP) substrates in the presence of benzophenone (BP) and isopropylthioxanthone (ITX) photoinitiators, and then polyurethane acrylate formulations were coated onto the HDDA‐g‐PP substrates, using UV radiation. The amount grafted and the grafting efficiency of the polymerizations were determined gravimetrically. The effects of the photoinitiator concentration and the UV radiation intensity on the physicochemical surface properties and the grafting efficiency of the UV‐radiation grafting polymerizations were characterized in detail using contact‐angle measurements, Fourier transform infrared spectroscopy with attenuated total internal reflection, and scanning electron microscopy. The results showed that the amount grafted and the surface polarity of the HDDA‐g‐PP substrates both increased linearly with increasing BP photoinitiator concentration and UV radiation intensity, and that the addition of a small amount of ITX markedly enhanced both parameters, probably due to photosensitization. The adhesion of the UV‐cured coating onto the HDDA‐g‐PP substrates was evaluated using the crosshatch adhesion test. The results indicated that the amount of HDDA grafted onto the PP substrates should exceed about 1 mmol/cm² for satisfactory adhesion with the UV‐cured coating. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1446–1461, 2006     

Synthesis, photopolymerization kinetics, and thermal properties of UV-curable waterborne hyperbranched polyurethane acrylate dispersions

A series of UV-curable waterborne hyperbranched polyurethane acrylate dispersions (WHBPUADs) were prepared via a three-step procedure based on isophorone diisocyanate (IPDI), hyperbranched polyester (HBP), maleic anhydride (MA), and hydroxy-ethyl acrylate (HEA). The structure of WHBPUADs was characterized by Fourier transform infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance spectroscopy (¹H NMR). FTIR was also applied to research the effect of double bond concentration on the kinetics of photopolymerization. The heat resistance of the cured films was characterized by thermogravimetric analysis (TGA), and their mechanical properties were also measured. The results showed that the double bond conversion (τ) and photopolymerization rate (R _p) were affected by the concentration of double bond and viscosity of WHBPUADs. The UV-curable systems with higher double bond concentration and lower viscosity led to higher τ and R _p. The maximum τ and R _p reached 93% and 71 mmol g⁻¹ s⁻¹, respectively. The WHBPUADs films possessed better heat resistance and mechanical properties, and with the increase of crosslink density, the heat resistance and hardnesses were further improved.     

不同官能度水性聚氨酯丙烯酸酯的合成及性能

以丙烯酸羟乙酯与季戊四醇三丙烯酸酯作为封端剂,分别合成了二官能度水性聚氨酯丙烯酸酯(WPUA2)和六官能度的水性聚氨酯丙烯酸酯(WPUA6),并用红外光谱、粒径仪、热重分析对合成产物结构和性能进行表征。研究表明,相比于使用低官能度WPUA2紫外光固化所得聚氨酯丙烯酸酯(PUA)涂膜,加入单体或使用多官能度WPUA6,都可使PUA固化膜凝胶率提高20%以上,吸水率降低30%;质量损失10%,分解温度增大82℃。提高预聚物官能度可有效提高涂膜交联密度和耐热性能,并具有与加入活性单体相似的应用效果。     

光聚合型聚硅氧烷改性聚醚聚氨酯丙烯酸酯低聚物的合成、表征与性能

以羟烷基聚硅氧烷(Q4-3667)、聚丙二醇(PPG-2000)、异佛尔酮二异氰酸酯(IPDI)、二乙醇胺和丙烯酸β-羟乙酯(HEA)为原料合成了一种光聚合型有机硅改性聚醚聚氨酯丙烯酸酯低聚物(Si~5E~5PUA),并用傅里叶红外光谱(FTIR)、核磁共振氢谱(1HNMR)、核磁共振硅谱(29SiNMR)和凝胶渗透色谱(GPC)对其结构进行了表征。详细研究了Si~5E~5PUA与不同单体配比体系的黏度、光聚合性能、聚合过程的体积收缩及其固化膜的玻璃化转变温度。结果表明,Si~5E~5PUA与丙烯酸酯单体具有良好的相容性;其体系具有优异的光聚合性能,最终双键转化率达90%以上,单体官能度的增加可以提高固化膜的玻璃化转变温度,Si~5E~5PUA体系的体积收缩在3.3%~5.6%。     

Synthesis and characterization of UV-curable waterborne polyurethane–acrylate ionomers for coatings

A new kind of ultraviolet (UV)-curable waterborne polyurethane–acrylate (PUA) ionomer, prepared from toluene diisocyanate (TDI), polyethylene glycol (PEG), dimethylolpropionic acid (DMPA), triethylamine (TEA), and 2-hydroxyethyl methacrylate (HEMA), was synthesized by the modified prepolymer mixing process in which water serves as a chain-extender and dispersant. Fourier transform infrared (FTIR) spectra demonstrated the formation of the PUA ionomers both in dispersions and in their corresponding cured films. Surface tension of the PUA dispersions decreased as the DMPA-to-PEG mole ratio increased. The investigation of rheological behavior of the PUA dispersions suggested that all the dispersions belong to pseudoplastic fluid and display the characteristic of common polymer dispersions. Differential scanning calorimetry (DSC) analysis showed that the increasing DMPA-to-PEG mole ratio may result in a higher T_g and a broader transition zone for the hard segment. The results of TGA for the PUA-cured films indicated good thermal stability with no appreciable weight loss until well above 200°C. Measurement of physical properties showed that all the PUA-cured films exhibited excellent adhesion, gloss, flexibility, and impact strength, as well as pendulum hardness, depending upon hard segment content. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2869–2876, 1999     

Compatibilization and property characterization of polycarbonate/polyurethane polymeric alloys

Semi‐crystalline dendritic poly(ether‐amide)s were synthesized by modifying hydroxyl end‐groups of dendritic poly(ether‐amide) with aromatic urethane acrylate and octadetyl isocyanate. The ratio of these modifiers can adjust the final properties of products to fulfill the requirements of UV‐curable powder coatings. These UV‐curable semi‐crystalline dendritic poly(ether‐amide)s have a T_g in the range of 41–45°C and a T_m of around 120°C. Their thermal behavior and semi‐crystalline properties were studied by DSC and XRD. The photopolymerization kinetics was investigated by Photo‐DSC. The residual unsaturation, thermal stability, and hardness of the UV‐cured films were also studied. The obtained results show that these semi‐crystalline dentritic poly(ether‐amide)s may be used as prepolymers in UV‐curable powder coating systems. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 287–291, 2003     

Chain‐extended polyurethane–acrylate ionomer for UV‐curable waterborne coatings

Conventional and chain‐extended UV‐curable waterborne polyurethane–acrylate (PUA) ionomers were prepared from diisocyanate, polyethylene glycol (PEG), dimethylolpropionic acid, and hydroxyethyl methacrylate, and identified with FTIR spectra and 500‐MHz ¹H‐NMR spectra. The number‐average molecular weight (M_n) and polydispersity of chain‐extended PUA were determined by gel permeation chromatography. For the synthesis of chain‐extended PUA, water was employed as the chain extender. The two kinds of PUA prepolymer could be easily dispersed in water in the form of self‐emulsified latex after the carboxyl group attaching to the backbone of PUA was neutralized with tertiary amine. The effects of M_n of PEG, carboxyl content, and type of diisocyanate on the interfacial tension and rheological behavior of PUA dispersions were investigated. The chain‐extended PUA prepolymer could photopolymerize to a greater extent than the conventional PUA, as indicated by differential photocalorimetry. The photopolymerization kinetics of chain‐extended PUA, based on different substrates, were also investigated. The differential scanning calorimetry analysis for the photo‐cured films from PUA dispersions suggested that lower M_n of PEG tended to favor phase mixing between soft and hard segment phases, and higher M_n of PEG would provoke phase separation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1818–1831, 2002; DOI 10.1002/app.10384     

Bio-based hyperbranched polyurethanes for surface coating applications

High performance vegetable oil based hyperbranched polymers are not only interesting but also very useful with respect to current scenario of advanced coating materials. So in the present study hyperbranched polyurethanes have been synthesized from the monoglyceride of Mesua ferrea L. seed oil, poly(?-caprolactone)diol, 2,4-toluene diisocyanate and glycerol without using any catalyst by a two-step one pot A₂ + B₃ approach. The linear analog (neglecting little possible branching due to different components of monoglyceride) of the hyperbranched polyurethane has also been prepared by the same method without using glycerol, just to compare with hyperbranched polymer. The formation of polymers was confirmed by FTIR, ¹H NMR, UV and SEM studies and measurements of hydroxyl value, solubility and viscosity. TGA results indicated the high thermal stability of hyperbranched and linear polymers (210–220 °C). The properties like tensile strength, impact strength, hardness, adhesion, flexibility, gloss, elongation at break and chemical resistance were influenced by the hard segment content of the polymers. The hyperbranched polyurethane with 30% hard segment content showed the optimum properties. The values of hydrodynamic diameter of hyperbranched polymers compared to the linear analog support the hyperbranched formation. Thus it confirms the formation of mechanically strong and thermally stable hyperbranched polyurethane coating materials from a vegetable oil.     

超支化聚氨酯丙烯酸酯的性能与UV固化动力学研究

采用2-羟基-2-甲基-1-苯基-1-丙酮（Darocur 1173）作为超支化聚氨酯丙烯酸酯（HBUA）的紫外光（UV）固化引发剂,研究了Darocur 1173用量、活性单体种类及用量对HBUA固化膜机械性能的影响,并用光差扫描量热法（Photo—DSC）对HBUA的光固化动力学进行了表征。结果表明,随着Darocur 1173用量的增加,光固化膜的摆杆硬度及冲击强度增大,最大光固化反应速率Rp^max提高,到达Rp^max的时间缩短。己二醇二丙烯酸酯（HDDA）作活性单体更有利于提高光固化膜的机械性能,并有利于促进光固化反应的进行。Darocur 1173和HDDA的适宜用量分别为4％（wt）和20％（wt）。