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Synthesis and Performances of UV-Curable Polysiloxane−Polyether Block Polyurethane Acrylates for PVC Leather Finishing Agents Jiye Cheng,†,‡ Yue Cao,†,‡ Shengling Jiang,§ Yanjing Gao,‡ Jun Nie,†,‡ and Fang Sun*,†,‡ †

State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China ‡ College of Science, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China § College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China S Supporting Information *

ABSTRACT: A series of multifunctional UV-curable polysiloxane−polyether block polyurethane acrylates prepolymers (TSi1E9PUA, TSi3E7PUA, TSi5E5PUA, TSi7E3PUA, and TSi9E1PUA) used for polyvinyl chloride (PVC) leather finishing agents have been prepared and characterized by nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), and gel permeation chromatography (GPC). All five multifunctional prepolymers exhibited excellent photopolymerization efficiency and good yellowing resistance. And the content of polysiloxane in prepolymers obviously affected the viscosity, thermal stability, tensile strength, elongation at break, and surface hydrophobicity of the photopolymerization systems. The system with the prepolymer containing more polysiloxane segments presented a high viscosity, and UV-cured film had relatively good thermal stability, elongation at break, and surface hydrophobicity accordingly. The properties of the prepolymers well satisfied the application requirements for leather finishing agents. Furthermore, surface microstructures of UV-cured films were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). More importantly, the PVC leather finishing agents designed based on the multifunctional polysiloxane−polyether block polyurethane acrylates possessed excellent comprehensive performances.

1. INTRODUCTION Poly(vinyl chloride) (PVC) has been drawing growing attention for many practical applications including medical products, artificial leather, electronic devices, construction materials, food packaging, and so on, owing to its low combustibility and resistance properties, inexpensive price, low heat release profile, good electrical insulation properties, and good chemical resistance.1−3 In particular, artificial leathers based on flexible PVC have been applied widely and developed dramaticlly in contact with the human body.4,5 As necessary leather auxiliary used for leather surface coating, leather finishing agents not only can protect the leather from damage but also can beautify the leather surface, thereby covering the shortage of artificial leathers. Besides, the commercial value and the lifetime of the leather products can be also significantly improved.6,7 And the leather finishing agents cooperating with photopolymerization techniques exhibit unique advantages, such as fast-curing, low energy consumption, solvent-free formulations, and high efficiency, compared with traditional leather finishing agents with the problem of environmental pollution and poor efficiency.8,9 We have proposed a novel photopolymerizable polysiloxanemodified polyurethane acrylate prepolymer (Si-IPDI-HEA) that can be used for PU leather finishing agents.10 The performance of the leather finishing agent can be dramatically enhanced by introducing organosilicon on account of the unique properties of polysiloxane involving low surface energy and tension, good flexibility, good weatherability, chemical and physiological inertness endowed by the Si−O bond.11 However, the © XXXX American Chemical Society

photopolymerization efficiency of Si-IPDI-HEA is still unsatisfactory, and its high cost resulting from the expensive polysiloxane also limits its extensive application. Therefore, how to improve the photopolymerization efficiency and reduce cost without compromise to other excellent performances is of vital importance to facilitate practical applications of siliconecontaining polyurethane acrylate prepolymer. Generally, increasing degree of functionality of a prepolymer can improve its photopolymerization efficiency. In addition, polyether-modified polyurethane is also widely applied to many fields because of the advantages of the low viscosity, good flexibility, water vapor permeability, excellent compatibility, and low cost.12 It is well-known that block polymers can effectively combine excellent performance of different materials.13−15 This gives us the impetus to design and synthesize novel multifunctional photopolymerzable polysiloxane−polyether block polyurethane acrylates for PVC leather finishing agents. The polysiloxane−polyether block polyurethane acrylates would exhibit excellent photopolymerization efficiency and low cost, resulting from the high degree of functionality and the combination of advantages of polysiloxane segments and polypropylene glycol segments, without compromise to other excellent performances. Received: January 1, 2015 Revised: April 13, 2015 Accepted: May 11, 2015

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DOI: 10.1021/acs.iecr.5b00009 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research Scheme 1. Structure of Polysiloxane−Polyether Block Polyurethane Acrylate

In this work, we synthesized five novel multifunctional polysiloxane−polyether block polyurethane acrylates (TSi1E9 PUA, TSi3E7 PUA, TSi5E 5PUA, TSi7 E3PUA, and TSi9E1PUA) with the gradual increase of organosilicon content based on polysiloxane, polypropylene glycol, isophorone diisocyanate, and 2-hydroxyethyl acrylate. Viscosities and photopolymerization kinetics of five polysiloxane−polyether block polyurethane acrylates cooperating with TPGDA were investigated. The thermal properties, yellowing resistance, and physical and mechanical properties of UV-cured films that contain the five prepolymers and acrylate monomers were evaluated. Furthermore, the performance of leather finishing agents for PVC leather based on the multifunctional polysiloxane−polyether block polyurethane acrylates was also studied.

mechanical stirrer, a thermometer, and a cooler. Dibutyltin dilaurate (DBTDL, 0.12 g) was added to the stirred mixture as a catalyst. And then IPDI (4.44 g, 20 mmol) was dropwise added into the flask by a constant pressure funnel over 10 min at 45 °C. When the value of isocyanate reached half of the initial value by titration,16 diethanol amine (2.1 g, 0.02 mmol) was added into the flask as a chain extender. Subsequently, IPDI (8.88 g, 40 mmol), HEA (4.64 g, 40 mmol), and hydroquinone (0.08 g) were added to the stirred mixture, and the reaction was continued for 5 h until the absorption peak of the −NCO group in the infrared spectra completely disappeared. The product was purified by column chromatography. A similar procedure was adopted to synthesize TSi3E7PUA, TSi5E5PUA, TSi7E3PUA, and TSi9E1PUA through changing of the ratio of the polysiloxane to the ether (Table S1 in Supporting Information). The IR spectra, 1H NMR, and 29Si NMR spectra of TSi 1E 9 PUA, TSi 3 E7 PUA, TSi5 E 5PUA, TSi7E3PUA, and TSi9E1PUA display the following similar characteristics (Figures S1−S15). IR (KBr, cm−1): 3323, 1536 (N−H), 2957, 2868 (−CH3, −CH2), 1721 (CO), 1640 (CC), 1458 (O−CH3), 1374 (C−CH3), 1297 (Si-CH3), 1241 (C−O−C), 1108 (Si−O−Si), 799 (Si-CH3). 1H NMR (δ, CDCl3, ppm): 0.07 (SiCH3), 0.83−1.26 (CH3CH2, CH3 of IPDI), 1.68−1.80 (CH2 of IPDI), 2.90−2.97 (CONHCH2), 3.36−3.81 (CONHCH, SiCH2O, OCH2CH2O), 4.30−4.40 (OCH2CH2N, COOCH2CH2O), 6.11−6.18 (COCHCH2), 5.85−5.87, 6.42−6.46 (COCHCH2). 29Si NMR (δ, CDCl3, ppm): −21.98 (−Si(CH3)2-O−). GPC (multiple PS standards): TSi1E9PUA: Mn = 6324, Mw = 9777, polydispersity index (PDI) = 1.55. GPC results of TSi3E7PUA, TSi5E5PUA, TSi7E3PUA, and TSi9E1PUA are listed in Table S2. 2.3. Characterization of Polysiloxane−Polyether Block Polyurethane Acrylates. The Fourier transform infrared (FTIR) spectra were recorded by a spectrometer with wavenumbers from 400 to 4000 cm−1 (Nicolet 50XC, Nicolet, USA). The 1H NMR and 29Si NMR spectra were recorded by an AV400 unity spectrometer (Bruker, Germany) operated at 400 MHz. The solvent was CDCl3, and the internal standard was tetramethylsilane. The molecular weights of the polysiloxane−polyether block polyurethane acrylates were characterized by a Waters 515-2410 gel permeation chromatography (GPC, Waters, USA). Dynamical thermal mechanical analyses (DMTA-IV, Rheometric Scientific Co.) were carried out with a heating rate of 5 °C/min. Measurements were collected from −50 to 200 °C with a frequency of 1 Hz. The thermogravimertic analysis instrument (STA-449C, Netzsch Instrument Co., Germany) was employed to investigate the thermostability of samples under the nitrogen

2. EXPERIMENTAL SECTION 2.1. Materials. Hydroxyalkyl-terminated polysiloxane (trade name Q4-3667, 2400 g/mol) was purchased from Dow Corning Corp. The hydroxyl value was 1.41 mg of KOH/g. Polypropylene glycol (PPG-2000) was purchased by Hangzhou Maohang Chemical Co., Ltd. Dibutyltin dilaurate (DBTDL) was provided by Shanghai Chemical Reagents Co. Diethanol amine was supplied by Tianjin Chisheng Trade Co. Isophorone diisocyanate (IPDI) was provided from Qingdao Xinyutian Chemical Co. Hydroquinone (HQ) was obtained by Beijing Yili Fine Chemical Co. 2-Hydroxyethyl acrylate (HEA), tripropylene glycol diacrylate (TPGDA), and isobornyl acrylate (IBOA) were supplied from Eternal Specialty Chemical (Zhuhai) Co., Ltd. 2-Hydroxyl-2-methyl-1-phenylpropane-1one (Darocur 1173) was purchased from Ciba Geigy Co. A commercial PU type resin (720), a solvent-based leather finishing agent, was obtained from Shanghai Heying Chemical Co. The preparation of Si-IPDI-HEA was reported in our previous work.10 Five kinds of polysiloxane−polyether block polyurethane acrylates prepared by an analogous procedure are designated as TSi 1 E 9 PUA, TSi 3 E 7 PUA, TSi 5 E 5 PUA, TSi7E3PUA, TSi9E1PUA, respectively. Here, T, Si, E, and PUA represented tetrafunctionality, polysiloxane chains, ether chains, and polyurethane acrylates, respectively. The superscript number meant different molar ratio of the polysiloxane to the polyether. The structure of polysiloxane−polyether block polyurethane acrylate is shown in Scheme 1. 2.2. Synthesis of Polysiloxane−Polyether Block Polyurethane Acrylates. The synthetic procedure of polysiloxane−polyether block polyurethane acrylates (TSi1E9PUA) is as follows. PPG-2000 (18 g, 9 mmol) and Q4-3667 (2.4 g, 1 mmol) were added to a four-necked flask, which was equipped with a B


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Industrial & Engineering Chemistry Research atmosphere. The heating rate was 10 °C min−1, and the temperature range was 30−500 °C. The adhesion force was tested by ASTMD3359. A rotary viscometer (NDJ-5S, China) was used to measure the viscosity of the UV-cured systems consisting of polysiloxane−polyether block polyurethane acrylates with monomer at 25 °C. The contact angle microscope (OCA20, Data Physics Co., Germany) was employed to measure the water contact angles of the UV-cured film surface. The photopolymerization kinetics of prepolymers was investigated by real-time infrared spectroscopy equipped with an MCT/A detector and an extended range KBr beam splitter (Nicolet 5700, Thermo Electron, USA).17 Tensile properties of UV-cured films were tested by a material testing instrument (Instron-1211) at 25 °C. The rate of extension was 10 mm/min. The surface morphology of the UV-cured films was observed using scanning electron microscopy (SEM, S-4700 Hitachi) with an accelerating voltage of 20.0 kV. The surface element of UV-cured films was characterized by an energy dispersive spectrometer (EDS, S-4700 Hitachi). 2.4. Preparation Procedure of UV-Cured Film. The photopolymerization system that consists of prepolymer, monomer, and the photoinitiator 2-hydroxyl-2-methyl-1phenylpropane-1-one (1173) with a certain weight ratio (prepolymers/monomer/1173 = 50/50/0.1 (wt %)) was prepared. The photosensitive liquid was coated onto a glass mold. And a high pressure mercury lamp (500 W, main irradiation wavelength of 365 nm, irradiation intensity of 40 mW cm−2, distance between the lamp and the photosensitive liquid layer of 5 cm) was employed to irradiate the liquid layer for 60 s to obtain the UV-cured film (76 mm × 13.8 mm × 0.3 mm).

Figure 2. (a) Effect of the structure of the prepolymers on double bond conversion. (b) Effect of the structure of the prepolymers on rate of polymerization. System composition: prepolymer/TPGDA = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.

3. RESULTS AND DISCUSSION 3.1. Viscosity. One of the most important parameters of prepolymer is viscosity that determines the viscosity of a

Figure 1. Viscosities of the systems. System composition: prepolymer/ monomer = 50/50 (wt %).

formulation and directly affects the flow ability, the rate of air release, and the properties of cured film. In this work, TPGDA and IBOA were added respectively as an additive into prepolymers at a constant ratio in order to measure viscosities of the prepolymers. Figure 1 demonstrates that the viscosities of the prepolymers increased gradually with the increase of the polysiloxane segment in the prepolymers. Generally, polysiloxane segments and polyurethane segments are not completely miscible in thermodynamics. This immiscibility may result in a

Figure 3. (a) TG curves of cured films. (b) DTG curves of cured film. Cured film composition: prepolymer/TPGDA = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.

respective aggregation of polysiloxane segments and polyurethane segments,18−20 thereby increasing intermolecular forces, which contribute to the high viscosity of the prepolymers. C


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Industrial & Engineering Chemistry Research

Figure 5. Temperature spectrum of tan δ of cured films. Cured film composition: prepolymer/TPGDA = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.

Figure 4. (a) TG curves of cured films. (b) DTG curves of cured film. Cured film composition: prepolymer/IBOA = 50/50 (wt %); photoinitiator 1173, 0.1 wt %. Figure 6. Temperature spectrum of tan δ of cured films. Cured film composition: prepolymer/IBOA = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.

Table 1. Thermal Decomposition Parameters of Samples of Photopolymerizaion Systemsa system composition 1 9

TSi E PUA-TPGDA TSi3E7PUA-TPGDA TSi5E5PUA-TPGDA TSi7E3PUA-TPGDA TSi9E1PUA-TPGDA TSi1E9PUA-IBOA TSi3E7PUA-IBOA TSi5E5PUA-IBOA TSi7E3PUA-IBOA TSi9E1PUA-IBOA

T5% (°C)

Tmax1 (°C)

Tmax2 (°C)

287 296 307 315 326 265 282 287 290 295

377 377 377 377 377 318 318 318 318 318

425 422 423 420 425 420 425 425 423 425

Table 2. Tensile Properties of UV-Cured Film team 1 9

TSi E PUA-TPGDA TSi3E7PUA-TPGDA TSi5E5PUA-TPGDA TSi7E3PUA-TPGDA TSi9E1PUA-TPGDA

tensile strength (MPa)

elongation at break (%)

± ± ± ± ±

9.0 ± 1.2 10.1 ± 1.4 12.5 ± 1.7 13.2 ± 2.2 15.7 ± 1.9

18.9 16.5 15.8 14.2 12.1

1.9 2.1 1.6 1.6 1.5

prepolymers also were not obviously different (Figure 2b and Figure S16b). For a system with TPGDA, the maximum rates of double bond conversion that appeared at 15−17 s were all about 5.5−5.8 percentage per second, while for system with HEA, the maximum rates of double bond conversion that appeared at 13−16 s were 6.8−7.2 percentage per second. Compared to the bifunctional prepolymer (Si-IPDA-HEA),10 the multifunctional polysiloxane−polyether block polyurethane acrylates exhibited relatively excellent photopolymerization efficiency. Additionally, the change of chain segments of prepolymers did not affect dramatically the photopolymerization efficiency. 3.3. Thermogravimetric Analysis. Thermogravimetric analysis (TGA) is one of the most widely used techniques for rapid evaluation of the thermal stability of various polymers. The samples of UV cured films were studied with thermogravimetric analysis to characterize their thermal stability. TG and DTG curves recorded at 10 °C min−1 heating rate in nitrogen are presented in Figure 3 and Figure 4, while

a

T5% is the temperature of 5% weight loss. Tmax is the peak temperature at maximum weight loss rate.

3.2. Photopolymerization Kinetics. The photopolymerization kinetics of the prepolymers was investigated by real-time infrared spectroscopy (RT-IR). The final degree of double bond conversion (DBC) and the rate of polymerization (Rp) are the most significant parameters characterizing the photopolymerization of a resin. Figure 2a and Figure S16a show the plots of conversion vs irradiation time of prepolymer by incorporating monomers under UV irradiation (main irradiation wavelength of 365 (±10) nm, irradiation intensity of 40 mW cm−2). It was found that all systems had very high final double bond conversions which were more than 95%. Moreover, the final double bond conversions of the systems did not present an obvious difference with the variation of proportions of polysiloxane chain and polypropylene glycol chain. Similarly, Rp values of the systems containing different D


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Industrial & Engineering Chemistry Research Table 3. Contact Angles and Dispersion Surface Energies of Cured Films team 1 9

TSi E PUA-TPGDA TSi3E7PUA-TPGDA TSi5E5PUA-TPGDA TSi7E3PUA-TPGDA TSi9E1PUA-TPGDA

system composition (wt %) 1 9

TSi E PUA/TPGDA/1173 TSi3E7PUA/TPGDA/1173 TSi5E5PUA/TPGDA/1173 TSi7E3PUA/TPGDA/1173 TSi9E1PUA/TPGDA/1173

= = = = =

50:50:0.1 50:50:0.1 50:50:0.1 50:50:0.1 50:50:0.1

θ(H2O) (deg)

γdS(H2O) (mN/m)

69.80 71.77 74.02 77.10 79.34

100.05 95.28 89.91 82.72 77.63

Figure 7. SEM images of UV-cured film. Cured film composition: prepolymer/TPGDA = 50/50 (wt %); photoinitiator 1173, 0.1 wt %. (a) TSi1E9PUA-TPGDA, (b) TSi3E7PUA-TPGDA, (c) TSi5E5PUA-TPGDA, (d) TSi7E3PUA-TPGDA, (e) TSi9E1PUA-TPGDA (the inset in (d) showed the content of Si in different area by EDS).

which can be obtained by cooperating with multifunctional monomers, can dramatically improve its thermal stability. Hence, Tmax1 of the system with IBOA was lower than that with TPGDA, in spite of the rigid structure in IBOA molecule. Furthermore, UV-curable systems with TPGDA and IBOA had the same molecular main chains, leading to the fact that their Tmax2 occurred at the same temperature range (420−425 °C). 3.4. Dynamic Mechanical Thermal Analysis (DMTA). The glass transition temperature (Tg) is a useful index in evaluating the potential implementation and performance of the polymer network. In this work, dynamic mechanical thermal analysis (DMTA) that can provide a direct link between a material’s chemical makeup and its mechanical behavior was employed to investigate the glass transition temperature of the UV-cured films. The tan δ curve is sensitive to structural changes that occur at the molecular level during the relaxation process and associated with the movement of small groups and chains of molecules within the polymer structure, all of which are initially frozen in.22 Only one damping peak for each tan δ curve was presented as shown in Figure 5 and Figure 6, which suggests that the compatibility between the prepolymers and acrylic monomers was good. Moreover, the intensity of damping peaks with multifunctional monomer (TPGDA) is lower than that with monofunctional monomer (IBOA), but their Tg were approximately similar. In general, the degree of cross-linking can be increased by incorporating the multifunctional monomer, thereby restricting

detailed parameter values obtained from the TGA curves are listed in Table 1. The initial decomposition temperature (T5%) can be considered as the temperature at which the weight loss was approximately 5 wt %, and Tmax corresponds to the temperature of the maximum decomposition rate. From Table 1, it was easily found that T5% depended on the polysiloxane content in the prepolymer molecule. With the increase of polysiloxane contribution in the UV-curable system, T5% increased and attained the largest value of 326 °C for the system with TPGDA and 295 °C for the system with IBOA. Remarkably, the fact confirms the positive impact of polysiloxane on the thermal stability of the UV cured films because of the thermostable silicon−oxygen bond.21 The thermal degradation processes of the UV cured films with TPGDA underwent single-step degradations with two DTG peaks at 377 °C (Tmax1) and 420−425 °C (Tmax2). However, the thermal degradation processes of the UV cured films with IBOA principally consisted of two flat stages. The first stage spanned the temperature range from 260 to 340 °C and culminated in a strong DTG peak at 318 °C (Tmax1). The second stage spanned the temperature range from 350 to 465 °C and culminated in a weak DTG peak at 420−425 °C (Tmax2). Compared with the system with TPGDA, the Tmax1 of the system with IBOA was lower, but the Tmax2 was almost the same. Generally, high degrees of cross-linking for a system, E


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molecule. It is the poor compatibility that may cause the respective aggregation of soft segments and hard segments, thereby weakening molecular mobility, resulting in a high Tg. 3.5. Tensile Property of the UV-Cured Film. Tensile properties were investigated as a vital indicator for the practical applications of UV-cured films. From Table 2, it was found that the tensile strength of the cured film decreased from the system TSi1E9PUA-TPGDA to the system TSi9E1PUA-TPGDA, while elongation at break presented a contrary trend. It can be contributed to the increase of flexible polysiloxane segments in prepolymer molecule. 3.6. Contact Angle and Dispersion Surface Energy of the Cured Film. Water contact angle and the dispersion surface energy (γdS) were employed to characterized hydrophilicity or hydrophobicity of the cured films surface. Here, γLV, γSL, and γSV are the surface tension at the liquid−vapor interface, solid−liquid interface, and solid−vapor interface, respectively. γSL = γSV − γLV cos θ

(1)

According to Fowkes’ study, the interface tension could also be calculated by the following formulation: γSL = γS + γLV − 2(γLd γSd)1/2

(2)

Equations 2 and 3 give γSd =

Figure 8. Yellowing resistance of the cured films with different prepolymers (a) before being placed at 120 °C for 4 h and (b) after being placed at 120 °C for 4 h. Cured film composition: prepolymers/ TPGDA = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.

[γLV(1 + cos θ )]2 4γLd

(3)

γdL

The testing liquid was H2O (γLV = 72.7 mN/m, = 23.9 mN/ m). And eq 3 was employed to calculate the values of γdS from the measured water contact angles (θ). The contact angles increased from the system TSi1E9PUATPGDA to TSi9E1PUA-TPGDA, while the corresponding dispersion surface energy decreased (Table 3). The more polysiloxanes the prepolymer contained, the lower the dispersion surface energy and the greater the contact angle the UV-cured film exhibited. It was indicated that the increase of polysiloxane content enhanced the hydrophobicity of the UV-cured film because of the low surface tension and energy of polysiloxane. The hydrophobicity of the cured film can be tuned by controlling polysiloxane content in the prepolymer. 3.7. Surface Morphology Analysis of the Cured Film. Scanning electron microscopy (SEM) was employed to characterize the surface morphology of the UV-cured films. Light-colored irregular protuberances were observed on the

intermolecular movements and reducing internal friction. However, because of the rigid structure of IBOA, Tg of the cured film with IBOA was almost similar to that with bifunctional monomer TPGDA. The polysiloxane generally exhibits a very low Tg (−120 °C),11,23 due to its unique structure. Interestingly, Tg of the investigated UV-cured films increased with the increase of polysiloxane content in the prepolymers. Besides, it was found that the width of the peaks broadened with the increase of polysiloxane content in prepolymer molecule. Generally, a wide damping peak means a poor compatibility among the segments of molecule.24−26 Therefore, it could be attributed to the fact that the introduction of the polysiloxane segments reduced the compatibility in thermodynamics between the segments of Table 4. Performances of PVC Leather Finishing Agent item Irradiation energy Folding resistancea Adhesion forceb Hydrolysis resistancec Antistickyd Alcohol resistancee

formulation with TSi1E9PUA





formulation with Si-IPDI-HEA

600 mJ/cm2

600 mJ/cm2

600 mJ/cm2

600 mJ/cm2

600 mJ/cm2

850 mJ/cm2

crack

crack

no change

no change

no change

no change

no change

5B no change

5B no change

5B no change

5B no change

5B no change

5B no change

sticky

sticky

nonsticky

nonsticky

nonsticky

nonsticky

good

good

good

good

good

good

5B coating falloff sticky to death good

720

Appearance of samples after folding for 6 × 104 times. bASTM D3359. cAppearance of samples after boiling for 360 h at 80 °C. dFolded the appearance of samples after pressing with 4000 g force for 2 h at 80 °C. eScrubbing 2000 times with alcohol.

a

F



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surface of UV-cured films by SEM (Figure 7). EDS results showed that the percentage of silicon in the light-colored irregular protuberances was 7.01 wt %, while it was 1.56 wt % in the surrounding dark areas. The difference indicated that the irregular protuberances were formed by the aggregation of the polysiloxane segments. Besides, the number of irregular protuberances increased with the increase of polysiloxane segments in prepolymer molecules. The aggregation of the polysiloxane segments may result a low dispersion surface energy and a strong restriction of molecular mobility. This was consistent with the results of water contact angle and DMTA measurements. 3.8. Yellowing Resistance. The yellowing resistance of the cured films containing different prepolymers was investigated. As is shown in Figure 8, whether before or after having been placed at 120 °C in air for 4 h, the films containing different polysiloxane−polyether block polyurethane acrylates exhibited very high transmittances that were more than 80% in the range 400−800 nm. Moreover, after placement at 120 °C for 4 h, the transmittance of the UV-cured films was reduced by 2−5%, which proved that the UV-cured films with polysiloxane− polyether block polyurethane acrylates had good yellowing resistance. 3.9. Properties of Leather Finishing Agent. According to the above research results, the polysiloxane−polyether block polyurethane acrylates prepolymers exhibited relatively good comprehensive performance for the leather finishing agent. The formulations containing the prepolymers were designed for PVC leather finishing agent, and their performance was tested. And the performance of commercial leather finishing agent 720 was also tested as a reference. Table 4 depicted that the designed leather finishing agents have excellent comprehensive performance for PVC leather and satisfied application requirements for leather finishing agents.

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ASSOCIATED CONTENT

* Supporting Information S

Synthesis procedures, IR and NMR spectra, reaction equation, and molecular weight distribution of the TSi1 E9 PUA, TSi3E7PUA, TSi5E5PUA, TSi7E3PUA, and TSi9E1PUA. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.5b00009.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +86-10-64449336. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from the National Natural Science Foundation of China (Grant 51273014) and the Fundamental Research Funds for the Central Universities (Grant YS1406) are gratefully acknowledged.

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4. CONCLUSION In this paper, a series of multifunctional polysiloxane−polyether block polyurethane acrylates prepolymers (TSi1 E9PUA, TSi3E7PUA, TSi5E5PUA, TSi7E3PUA, and TSi9E1PUA) used for PVC leather finishing agents have been synthesized and their structures were confirmed by 1H NMR,, 29Si NMR, FTIR, and GPC analyses. The effect of the ratios of polysiloxane segments to polypropylene glycol segments on photopolymerization efficiency of the prepolymers and physical and mechanical properties of UV-cured films was investigated. The results showed that all five multifunctional prepolymers possessed excellent photopolymerization efficiency. The content of polysiloxane in prepolymers exhibited an obvious influence on the viscosity, thermal stability, tensile strength, elongation at break, and surface hydrophobicity of the photopolymerization systems. When the prepolymer contained more polysiloxane segments, the system with the prepolymer presented a high viscosity, and corresponding UV-cured film had relatively good thermal stability, elongation at break, and surface hydrophobicity. SEM images and EDS results showed that the polysiloxane segments gradually aggregated with the increase of polysiloxane segments in prepolymer molecules. More significantly, the PVC leather finishing agents designed based on the multifunctional polysiloxane−polyether block polyurethane acrylates possess excellent comprehensive performances and have tremendous application potential. G


Article

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