Next Article in Journal
A Novel Method for Deposition of Multi-Walled Carbon Nanotubes onto Poly(p-Phenylene Terephthalamide) Fibers to Enhance Interfacial Adhesion with Rubber Matrix
Next Article in Special Issue
Synthetic Routes to Silsesquioxane-Based Systems as Photoactive Materials and Their Precursors
Previous Article in Journal
Enhancement by Metallic Tube Filling of the Mechanical Properties of Electromagnetic Wave Absorbent Polymethacrylimide Foam
Previous Article in Special Issue
Composites of Rigid Polyurethane Foams Reinforced with POSS
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Polymers
Volume 11
Issue 2
10.3390/polym11020373
polymers-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Mechanically Robust Hybrid POSS Thermoplastic Polyurethanes with Enhanced Surface Hydrophobicity

by
Xiuhuan Song
1,
Xiaoxiao Zhang
1,
Tianduo Li
1,
Zibiao Li
2,* and
Hong Chi
1,*
1
Shandong Provincial Key Laboratory of Molecular Engineering, School of Chemistry and Pharmaceutical Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China
2
Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Innovis, #08-03, Singapore 138634, Singapore
*
Authors to whom correspondence should be addressed.
Polymers 2019, 11(2), 373; https://doi.org/10.3390/polym11020373
Submission received: 24 January 2019 / Revised: 18 February 2019 / Accepted: 18 February 2019 / Published: 20 February 2019
(This article belongs to the Special Issue POSS-Based Polymers)
Browse Figures
Versions Notes

Abstract

:
A series of hybrid thermoplastic polyurethanes (PUs) were synthesized from bi-functional polyhedral oligomeric silsesquioxane (B-POSS) and polycaprolactone (PCL) using 1,6-hexamethylene diisocyanate (HDI) as a coupling agent for the first time. The newly synthesized hybrid materials were fully characterized in terms of structure, morphology, thermal and mechanical performance, as well as their toughening effect toward polyesters. Thermal gravimeter analysis (TGA) and differential scanning calorimetry (DSC) showed enhanced thermal stability by 76 °C higher in decomposition temperature (Td) of the POSS PUs, and 22 °C higher glass transition temperature (Tg) when compared with control PU without POSS. Static contact angle results showed a significant increment of 49.8° and 53.4° for the respective surface hydrophobicity and lipophilicity measurements. More importantly, both storage modulus (G’) and loss modulus (G’’) are improved in the hybrid POSS PUs and these parameters can be further adjusted by varying POSS content in the copolymer. As a biodegradable hybrid filler, the as-synthesized POSS PUs also demonstrated a remarkable effect in toughening commercial polyesters, indicating a simple yet useful strategy in developing high-performance polyester for advanced biomedical applications.

Graphical Abstract

1. Introduction

Polyurethane (PU) is a kind of thermoplastic elastomeric polymer, consisting of both hard and soft segments. The soft segments are usually composed of flexible polyester or polyether and the hard segments are usually composed of diisocyanates with benzyl structure [1]. Such alternating structure endows PU with good shape recovery property as well as high resistance to abrasion, stretchability [2], high adhesiveness and eases of processability because the hard phase can form a force center which holds the soft phase and retains the original shape [3]. Therefore, PU is widely applied in many fields including coating, foaming, adhesive, tissue engineering and holds a unique importance in daily life [4]. Despite the advantages as mentioned above, PU does show several drawbacks including low mechanical strength and short shelf-life. PU exhibits hydroscopic tendencies due to the hydrophilic urethane group. The poor hydrophobicity of polyurethane products could shorten their shelf-life as they absorb water and gradually decompose and lose their performance. Efforts have been devoted to improve the mechanical strength and hydrophobicity of PU by introducing various components to obtain organic-inorganic hybrid materials. The fillers can be graphene [5,6] small molecules [7], inorganic nanoparticles [8,9] and carbon nanotubes etc. [10]. For example, H. Jerry Qi and co-workers prepared photo-curable PUs made of aliphatic urethane diacrylate. Nanoparticles, such as fumed silica (200–300 nm), were added as a rheology modifier that imparts a shear thinning effect to uncured ink. Such a composition of the ink allows good printability as well thermal stability after printing [11]. Rigoberto C Advincula and coworkers used graphene oxide (GO) to further tailor their properties of polyurethanes and found that the addition of GO could enhance the mechanical property and thermal stability of PUs [12].
In the past few decades, polyhedral oligomeric silsesquioxanes (POSS) were reported to be a rising star in hybrid materials [13,14]. POSS represents the smallest molecular silica with the dimension in the range of 1–3 nm [15], and the general chemical formula of (RSiO1.5)n (n= 6, 8, 12, etc.), where R could be a hydrogen atom/organic group, such as alkyl, aryl, vinyl, acrylate, epoxide group, to name a few [16]. The first merit to incorporate POSS into polymers chains is the super-hydrophobic tendency of POSS which mainly results from the surrounding R group [17,18,19,20]. The second merit is the biocompatibility and non-toxicity of POSSs [21,22,23,24]. Moreover, according to our previous results, not only could POSS enhance thermal stability [25,26], but it could also strengthen the mechanical properties [27] and retain the optical stability of the materials [28,29] due to its special composition and cage-liked nanostructure. In addition, POSS can be introduced into a polymer matrix by using covalently bonding as a pendent side group [30,31,32,33] or as end groups [34,35]. For example, Mya KY et al. [36] and Kun Wei et al. [37] reported star-shape POSS grafted PUs, which exhibited enhanced thermal stability and mechanical properties. Turri et al. [38,39] and Choudhury et al. [40] studied the surface properties of linear PUs which were modified with mono-functional POSS. It was found that the PU/POSS nanocomposites could significantly reduce the surface free energy and improve the surface hydrophobicity of the hybrids. In these ways, the properties of the polymer were less affected because the main chains of the polymers remain unchanged.
Herein, a series of hybrid PUs with POSS in the main chains were designed and synthesized. The obtained PUs showed enhanced thermal stability and mechanical property due to the existence of bi-functional POSS. Moreover, PCL was used as chain extender due to its excellent flexibility of the polymer chains [41]. Nuclear magnetic resonance (1H-NMR), fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) verified the successful synthesis of PUs. Static contact angle tests showed that the respective hydrophobicity and lipophilicity were remarkably increased by 49.8° and 53.4° compared with the results obtained on neat PU. Scanning electron microscopy (SEM) showed that there are microspores on the surface of PU films. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) indicated 76 °C higher decomposition temperature (Td) and 22 °C higher glass transition temperature (Tg) compared to neat PU. Rheology tests suggested that both storage modulus (G’) and loss modulus (G’’) are improved in the hybrid PUs with the increasing ratio of POSS.

2. Materials and Methods

2.1. Materials

Phenyltrimethoxysilane (98%), methyldichlorosilane (97%), allyloxytrimethylsilane (98%), ε-caprolactone (99%) (ε-CL), Karstedt catalyst tin (II) 2-ethythexanoate (Sn(Oct)2) (96%) were all obtained from Alfa Aesar (Shanghai, China). Isopropyl alcohol, sodium hydroxide, triethylamine, dichloromethane, hexamethylene diisocyanate (HDI), polyethylene glycol (PEG: Mw = 1500) were purchased from Aladdin Reagent (Shanghai, China). PLGA (Mw = 100,000) was purchased from Sigma-Aldrich (Shanghai, China). All other solvents were purchased from Sino-pharm Chemical Reagent Co. Ltd. (Shanghai, China). Toluene, tetrahydrofuran and methanol were distilled before use, while other chemicals were used without further purification.

2.2. Synthesis of 3,13-dihydrooctaphenyl B-POSS

3,13-dihydrooctaphenyl B-POSS was synthesized as per our previous report [29]. Phenyltrimethoxysilane (15 mL, 0.08 mol), isopropyl alcohol (80 mL), deionized water (1.7 g, 0.09 mol) and sodium hydroxide (2.13 g, 0.05 mol) were charged to a three-necked flask under N2 atmosphere to synthesize octaphenyldicycloocatasiloxane tetrasodium silanolate Na4O14Si8(C6H5)8. The reaction was allowed to reflux at 96 °C for 4 h. After cooling down to room temperature, the mixture was stirred for additional 15 h. Solvent was removed via rotary evaporation and white powder was obtained after drying at 60 °C for 12 h in a vacuum oven. 3,13-dihydrooctaphenyl B-POSS was then obtained through the reaction between Na4O14Si8(C6H5)8 and methyldichlorosilane. Typically, a mixture of Na4O14Si8(C6H5)8 (11.24 g, 9.7 mmol), triethylamine (2.92 mL, 28.8 mmol) and anhydrous tetrahydrofuran (100 mL) in a flask was cooled down in an ice-water bath before the addition of methyldichlorosilane (3.385 g, 28.8 mmol) in tetrahydrofuran (10 mL). The reaction was conducted at 0 °C for one hour and 70 °C for another 3 h under dry nitrogen. White powder was collected via rotary evaporation and washed with 100 mL methanol three times. Finally, 4.57 g product with yield of 41 wt % was obtained. 1H-NMR (δ ppm, CDCl3): 0.38 (d, 6H, CH3–Si), 4.98 (d, 2H, Si–H), 7.14–7.50 (m, 40H, protons of aromatic rings).

2.3. Synthesis of 3,13-di(trimethylsilyl)oxypropyloctaphenyl B-POSS

3,13-di(trimethylsilyl)oxypropyloctaphenyl B-POSS was synthesized as per Wei et al.’s study [37]. 3,13-di(trimethylsilyl)oxypropyloctaphenyl B-POSS was synthesized via the hydrosilylation reaction between 3,13-dihydrooctaphenyl B-POSS and allyloxytrimethylsilane. Typically, 3,13-dihydrooctaphenyl B-POSS (5.44 g, 4.7 mmol), anhydrous toluene (50 mL), allyloxytrimethylsilane (3.67 g, 28.2 mmol) and the Karstedt catalyst were charged to a flask and the reaction was carried out at 95 °C for 36 h with vigorous stirring. Then, 6.76 g product with a yield of 82 wt % was collected after removing the solvent via rotary evaporation. 1H-NMR (δ ppm, CDCl3): 0.00 [s, 9H, –CH2CH2CH2OSi(CH3)3], 0.30 [s, 3H, –OSiCH3CH2CH2CH2OSi(CH3)3], 0.71 [t, 2H, –OSiCH3CH2CH2CH2OSi(CH3)3], 1.62 [m, 2H, –OSiCH3CH2CH2– CH2OSi(CH3)3] and 3.44 [t, 2H, –OSiCH3CH2CH2CH2OSi(CH3)3].

2.4. Synthesis of 3,13-dihydroxypropyloctaphenyl B-POSS

3,13-dihydroxypropyloctaphenyl B-POSS (B-POSS) was synthesized as per Wei et al.’s study [37]. 3,13-dihydroxypropyloctaphenyl B-POSS (B-POSS) was obtained through the deprotection reaction of 3,13-di(trimethylsilyl)oxypropyloctaphenyl B-POSS. 3,13-di(trimethlylsilyl)oxypropyloctaphenyl B-POSS (3.0 g, 2.12 mmol), anhydrous methanol (90 mL) and anhydrous CH2Cl2 (90 mL) in a flask were stirred and purged with nitrogen. Methyltrichlorosilane (0.68 g, 6.26 mmol) in anhydrous methanol (10 mL) was added dropwise to the solution within 30 min. The reaction was carried out at room temperature for 5 h, and then solvents were removed by rotary evaporation. Finally, 2.25 g powder was collected with yield of 93 wt % through washing the product with a mixture of THF and hexane (50/50 vol/vol) and dried in a vacuum oven. 1H-NMR (δ ppm, CDCl3): 0.31 (s, 3H, –OSiCH3CH2CH2CH2OH), 0.74 [t, 2H, –OSiCH3CH2CH2CH2OH], 1.63 [m, 2H,–OSiCH3CH2CH2–CH2OH], 3.47 [t, 2H, OSiCH3CH2CH2CH2OH]; MALDI-TOFMASS (product + Na+): 1292.1 Da (calculated: 1292.36 Da).

2.5. Synthesis of O-4000, O-8000, O-10000, O-12000 and O-14000

The B-POSS incorporated oligomers of polycarprolactone (PCL) were synthesized with B-POSS and ε-CL by varying ε-CL content as shown in Figure 1. In a typical reaction, a three-necked round bottom flask charged with B-POSS (1.5 g, 1.18 mmol), ε-CL (8.07 g, 70.79 mmol), Sn(Oct)2 (375 μL) and anhydrous toluene (150 mL), vigorously stirred at room temperature for 5 min and then reacted at 110 °C for another 20 h under dry nitrogen. After that, the solvent was eliminated via rotary evaporation and the mixture was precipitated by adding an excessive amount of methanol. Then, the precipitate was obtained through centrifugation and washed with methanol three times. The product was dried in a vacuum oven at 40 °C for 24 h and then 8.13 g product of O-8000 was obtained with a yield of 85%. 1H-NMR (δ ppm, CDCl3): 1.4–1.6 (m, 6H –CH2CH2CH2–), 2.3 (t, 2H –COOCH2–), 4.1 (t, 2H –CH2OH–), 7.14–7.50 (m, 5H aromatic protons). FTIR (KBr, cm−1): 1536 (–NH–), 1730 (–COO–). GPC (PS standard, THF): Mw = 10,100, Mw/Mn = 1.35. O-4000, O-10000, O-12000 and O-14000 were prepared using the same manner, simply varying the ε-CL feed content.

2.6. Synthesis of PUs (PU, PU-4000, PU-8000, PU-10000, PU-12000 and PU-14000)

To synthesize the designed linear PUs, the POSS-PCL oligomers are further reacted with HDI through stoichiometric and temperature control to produce five types of PUs with various physical properties as shown in Figure 1. In a typical procedure, O-8000 (6.5 g, 0.81 mmol) was dissolved in toluene and refluxed at 110 °C for 4 h. After cooling to 70 °C, Sn(Oct)2 (0.5 wt %, relative to the reactant) was added into solution and HDI (0.27 g, 1.62 mmol) in anhydrous toluene (10 mL) was added dropwise to the solution. The reaction was allowed to proceed at 70 °C for another 3 h under nitrogen. After that, the solvent was removed by rotary evaporation and PU-8000 was collected by precipitation with a large amount of ethyl ether. Finally, the product was obtained after drying at 40 °C for 24 h in a vacuum oven, and 5.65 g product was obtained with a yield of 83%. PU-4000, PU-10000, PU-12000 and PU-14000 were prepared through the same synthetic route with yields of 84%, 81%, 85% and 86%, respectively. Neat PU was obtained using PCL and HDI in the same way.
All the polyurethanes with B-POSS in the main chains were subjected to gel permeation chromatography (GPC) to measure their molecular weights. In all cases, high-molecular-weight products were obtained. It is noted that the polydispersity index (Mw/Mn) for these hybrid polyurethanes was slightly higher than that of the control polyurethane. The increased values of the polydispersity index could be attributed to the high steric hindrance of B-POSS. It is possible that the nanoscale size of B-POSS restricted the motion of the POSS macromer during the polymerization and that this effect was increasingly pronounced while its concentration was sufficiently high.
The synthetic route of B-POSS-PUs is shown in Figure 2. To adjust the content ratio of B-POSS incorporated into the main chain of PU, different amounts of ε-CL were used as chain extender and grafted onto B-POSS, and the products were denoted as O-xxx to differentiate the molecular weight of polycaprolatone (PCL), i.e., O-4000 represents the PCL grafts with Mw of 4000 g/mol.

2.7. Fabrication of Poly(lactic-co-glycolic acid) (PLGA) Composite Films

The as synthesized B-POSS, oligomers and PUs can be used as filler and doped into PLGA matrix by film casting with chloroform as a solvent. PLGA and B-POSS were dissolved in 100 mL of chloroform at room temperature. The mixture of the polymer and nanoparticles was placed in a Teflon dish, and the solution was evaporated at room temperature for 24 h. The formed film was vacuum-dried at room temperature for 24 h. The PLGA/B-POSS film was removed from the Teflon dish using liquid nitrogen. The film thickness was measured using a micrometer. PLGA/O-14000 and PLGA/PU-14000 were prepared through the same synthetic route.

3. Characterization

1H-NMR spectra were carried out on a Bruker AVANCE II 400 spectrometer (Bruker, Karlsruhe, Germany) using tetramethylsilane (TMS; d = 0 ppm) as the internal standard. Chemical shifts were reported in parts per million (ppm) and CDCl3 was used as solvent for all the samples.
Matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF-MS) (ultrafleXtreme MALDI-TOF/TOF, Bruker, Karlsruhe, Germany) with gentisic acid (2,5-dihydroxybenzoic acid, DHB) as the matrix and THF as the solvent was used to measure the molecular weight of B-POSS.
FTIR spectra were tested at room temperature via an IR Prestige-21 spectrometer (Bruker, Karlsruhe, Germany) operated at a resolution of 4 cm−1 with scan number of 32.
Thermogravimetric analysis was carried out using a thermogravimetric analyzer (TGA, SDT Q 600, TA Instruments, New Castle, DE, USA) at room temperature to 800 ° C at 10 °C/min under an air atmosphere.
The thermal behavior test of the polymer was measured using a DSC (Q10) differential scanning calorimeter (TA Instruments, New Castle, DE, USA). The polymer was heated from room temperature to 150 °C at a heating rate of 15 °C/min under air atmosphere.
The molecular weight and molecular weight distribution of the polymer were determined using THF as the eluent and polystyrene as the standard gel permeation chromatography (GPC, Shimadzu, Kyoto, Japan).
Scanning electron microscopy was used to characterize the surface morphology using SEM (QUANTA 200, FEI, Eindhoven, the Netherlands).
The rheological measurements of the polymer were carried out using a TA DHR-2 rheometer (TA Instruments, New Castle, DE, USA) on parallel plates of 20 mm diameter.
The tensile test was carried out using a microcomputer-controlled electronic universal testing machine (Hensgrand, WDW-02, Jinan, China) at a crosshead speed of 10 mm/min−1 and 25 °C.

4. Results and Discussion

4.1. Characterization of B-POSS

In this work, B-POSS was synthesized (Figure S1) and introduced into the main chains of PUs. 1H-NMR spectra of 3,13-dihydroxypropyloctaphenyl B-POSS (B-POSS), 3,13-di(trimethylsilyl) oxypropyloctaphenyl B-POSS and 3,13-dihydrooctaphenyl B-POSS is shown in Figure 2. The peaks of 3,13-dihydrooctaphenyl B-POSS appeared at 0.38 ppm (b), 3.41 ppm (e) and 7–8 ppm (f) were assigned to the protons of –Si–CH3, –CH2–OH and phenyl groups, respectively. The integration area ratio between b, e and f is 3.01: 2.04: 20.03, which is close to the theoretical ratios calculated from the structural formula. In Figure 2, the signals of 3,13-di(trimethylsilyl)oxypropyloctaphenyl B-POSS appeared at 0.38 ppm (b), 0.71 ppm (c), 1.62 ppm (d), 3.44 ppm (e) and 7–8 ppm (f), assigned to the protons of –Si–CH3, –CH2, –CH2O and benzene rings, respectively. In addition, the peaks of Si–H protons at 4.98 ppm disappeared completely, indicating the successful hydrosilylation reaction. For B-POSS, the methyl protons peak of trimethylsilyloxypropyl at 0.02 ppm also completely disappeared after the deprotection reaction of 3,13-di(trimethylsilyl)oxypropyloctaphenyl B-POSS. Moreover, the successful synthesis of B-POSS was further confirmed by MALDI-TOF mass spectroscopy, where the molecular weight of B-POSS was determined to be 1292.1 (B-POSS + Na+), which is in good agreement with the calculated value (1269.1) from the molecular structure (Figure S2).

4.2. Characterization of the B-POSS-PUs

The typical 1H-NMR spectra of O-8000 and PU-8000 were presented as an example for the structure analysis of the as-synthesized PUs. As shown in Figure 3, the chemical shifts at 4.1 ppm (l), 2.3 ppm (h), 1.6 ppm (I, k), 1.4 ppm (j) were assigned to the proton of CH2 on PCL in O-8000, indicating that PCL was grafted onto B-POSS successfully. As for PU-8000, the chemical shifts at 3.5 (m), 1.2 ppm (o, p, q, r) was assigned to the protons of CH2 in the coupling regent HDI. The phenyl groups of B-POSS moieties were detected at 7.14–7.50 ppm in the spectrum, suggesting that B-POSS have been successfully incorporated into the main chain of PUs.
Through FTIR, the characteristic peak of –NCO in HDI at 2268 cm−1 disappeared after chain extension through urethane reaction (Figure S3, ESI). In addition, the appearance of strong bands at 1536 cm−1 and 1730 cm−1 assigned to –NH and –COO vibrations in the newly formed urethane linkage indicated the successful of reaction of POSS-PCL with HDI. 1H-NMR, FTIR together with GPC indicated the successful synthesis of organic–inorganic hybrid PU copolymers.

4.3. Thermal Stability

Thermal stability and transitions of polymers were characterized by TGA and DSC analyses. TGA curves of PU, PU-4000, PU-8000 and PU-12000 are shown in Figure 4. One can see that the degradation temperatures (Td) are determined as 207, 238, 246, 266, 280 and 283 °C for neat PU, PU-4000, PU-8000, PU-10000, PU-12000 and PU-14000, respectively (Table 1). According to the molecular structure shown in Figure 1, different amount of ε-CL were reacted with B-POSS to adjust the chain length of PCL as well as the ratio of B-POSS in hybrid PUs. Therefore, the number of B-POSS on each polymer chain could be estimated based on the feeding ratio of ε-CL and the Mw of hybrid PUs, which was in the order of PU-14000 > PU-12000 > PU-10000 > PU-8000 >PU-4000 > PU, indicating that the thermal stability could be improved by B-POSS. The addition of POSS was reported to have significant effect in retarding the random breakage of the polymer backbone as well [38]. Comparison of the length of PCL in the hybrids with similar ratio of B-POSS indicated that PCL may also help to enhance thermal stability of the PUs because Td also depends on the molecular weight (Mn) of the polymer drastically [36], and the long-chain oligomers with POSS could enhances the thermal stability of the polyurethane by better dispersion [25,26,27,29]. The copolymer and neat PU exhibited similar TGA profiles, indicating that the incorporation of B-POSS had no significant effect on the degradation mechanism of the PUs backbone. The oxidation and decomposition of organic segments in pure PU and hybrid PUs are two stages of degradation. The residues in hybrid PUs were higher than those of neat PU which is probably due to the inorganic components in POSS. The formation of silica from thermal degradation of POSS is responsible for the residues after TGA run as reported from the FTIR analysis by Blanco and co-workers [42]. The silica coated on the surface of the material would protect the inner material from further decomposing due to its low thermal conductivity. Moreover, the weight percentage of B-POSS was in the order of PU-4000 > PU-8000 > PU-12000 > PU according to the molecular structure. Therefore, the decomposition yield of the residues could further confirm the better stability of the PUs due to the role of the B-POSS.
DSC curves of PU, PU-4000, PU-8000 and PU-12000 displayed in Figure 4B indicated that the glass transition temperatures (Tg) are 47, 54, 60, 64, 67 and 69 °C for PU, PU-4000, PU-8000, PU-10000, PU-12000 and PU-14000 (Table 1), respectively. Compared with neat PU, hybrid PUs showed enhanced Tg. This is probably due to rigid structure of POSS cages which could restrict the movement of the chain, thereby reducing the free volume; hence, a higher temperatures is required to provide the thermal energy to induce a glass transition in the polymers [43].

4.4. Surface Properties

Surface hydrophobicity of the hybrid PUs was investigated by static contact angle test. It has been reported that the incorporation of POSS cages can be used to enhance the hydrophobicity of polymers [27]. The hybrid PU polymers we synthesized in this study also exhibited hydrophobic feature as well as low surface free energy (Table 2). Static contact angles were tested with both water and ethylene glycol as probe liquids. Compared with neat PU, the water contact angle and ethylene glycol contact angles of the hybrid PUs were obviously improved. For example, the water contact angle of PU-14000 was as high as 108.9° (Figure 5), suggesting that the hydrophobicity and lipophilicity of PUs could be adjusted effectively by varying the B-POSS content in the copolymers.
The surface free energies of the organic-inorganic hybrid PUs were calculated according to the geometric mean model [44]:
cosθ = 2/γL [(γdL × γds)1/2 + (γpL × γps)1/2]
γs = γds + γps
where θ is the contact angle and γL is the liquid surface tension; γdL and γpL are the dispersive and polar components of γL; γs is the solid surface tension, γds and γps are the dispersed and polar components of γs respectively. From this, the total surface free energies range of the organic-inorganic hybrid Pus are calculated to be in the range of 12.13 to 27.02 mN/m. The low surface energy endows the linear hybrids with potential application of highly hydrophobic coating materials. The presence of B-POSS cages could accumulate at the surface of the copolymers and thus minimize the polymer-air surface tension.
Surface morphology of the as-synthesized PUs were investigated by SEM. Figure S4 shows the SEM images of neat PU (A), PU-10000 (B), PU-12000 (C) and PU-14000 (D). Neat PU exhibited smooth surface morphology, whereas uniform pore distributions with the diameter of 1.08 μm were observed in PU-12000. Such an ordered self-assembly structure could be attributed to the phase separation between B-POSS and alkyl chains in PUs. This unique structural formation has been reported to be useful in lowering the dielectric constant value [45]. However, needle-like surface morphology was observed in PU-14000, which could be explained by the more effective separation of B-POSS from longer PCL chains. However, spindle-like surface morphology was observed in PU-14000, which could be explained by the longer chain of PCLs resulted packing.

4.5. Mechanical Properties

The effect of different ratio of B-POSS on the mechanical property of PUs was investigated by measurement. A viscoelastic region was obtained through dynamic strain sweep test. As shown in Figure 6, the investigated region of storage modulus was viscoelastic and independent of strain. As the B-POSS content increased, the viscoelastic linear region in each sample becomes shorter because of the higher rigidity and brittleness of the sample as evidenced by the Payne effect [46]. Due to the disentanglement of polymer macromolecules, storage modulus (G’) decreases as strain increases in the slope region [47,48]. The presence of B-POSS may restrict the chain mobility of the PLGA. Dynamic frequency sweep was further studied, and the viscoelastic linear region of the materials was analyzed.
Dynamic frequency sweep was conducted at a strain of 0.5% to ensure the sufficient liner viscoelasticity region and sensitivity (Figure S5). G’ is higher than G’’ for all samples, suggesting that the samples are solid-like. Compared with neat PU, the hybrid PUs exhibited higher G’ and G’’ values and the increment is proportional to the POSS content in the copolymer. Rheology results indicated that the incorporation of B-POSS could improve the mechanical property and the mechanical strength of PU.

4.6. Influence on Mechanical Property of Poly(lactic-co-glycolic acid) (PLGA)

Due to the hybrid nature, the synthesized B-POSS, oligomers and hybrid PUs can be used as filler and doped into other polymer matrix to modulate their mechanical performances. To demonstrate the toughening effect of hybrid PUs, poly(lactic-co-glycolic acid) (PLGA) was selected as target polymer. As it is well-known, PLGA is a biodegradable functional polymer with good biocompatibility, non-toxicity and film-forming properties. It has been widely used in pharmaceutical, medical engineering materials and modern industrial fields [48]. However, the poor mechanical performance of PLGA has limited its application in more advanced areas. Interestingly, we found that the mechanical performance of PLGA could be greatly improved by blending with hybrid PUs in this study. The mechanical properties were investigated by tensile tests. The typical stress-strain curves in Figure S6 showed that the strength of the PLAG/POSS blends increased significantly whereas its high extensibility of PLGA was retained. After doping with 6.5 wt% of PU-14000, the mechanical strength was increased by 41.6% with a marginal sacrifice of the elongation-at-break (Table 3). This may result from the combined effects of high molecular weight of hybrid PUs and the good distribution of B-POSS in the blends. In addition, the B-POSS exhibited lowest toughness towards PLGA, probably because the rigid POSS materials could restrict the motion of PLGA chains and thus cause an increase in tensile strength and low strain. Among the tested samples, PLGA/O-14000 shows the highest toughness towards PLGA, as well as an improved elongation at breakage. Considering the use of organotins and diisocyanates precursors on the safety for pharmaceutical applications, Caracciolo, P.C. et al. [49] prepared a polyurethane elastomer network for drug transportation with DBTDL (dibutyltin dilaurate) as catalyst and diisocyanates as monomers. Gorna, K. et al. [50] reported using dibutyltin dilaurate as a catalyst and aliphatic hexamethylene diisocyanate, PCL and isosorbide glycol as precursors in preparing a biodegradable polyurethane scaffold for tissue repair and regeneration. Bonzani, I. C. et al. [51] also prepared a two-component injectable polyurethane for bone tissue engineering using pentaerythritol and glycolic acid 2,6-diisocyanate (ELDI) as a starting material under the catalysis of stannous octoate. Thus, such a simple yet useful strategy in modulating the mechanical performance of PLGA by hybrid PUs is promising in developing PLGA-based materials for more advanced biomedical applications.

5. Conclusions

In summary, a series of hybrid thermoplastic polyurethanes (PUs) incorporated with bi-functional polyhedral oligomeric silsesquioxane in the polymer backbone were successfully synthesized and fully characterized. With the introduction of B-POSS into the main chain, the surface hydrophobicity and thermal and mechanical stability of the hybrid PUs were significantly increased. The structure-property correlations were instigated by comparing with neat PU. As a new kind of thermoplastic filler, the hybrid PUs can also be used to improve the mechanical strength of PLGA, exhibiting promising application in biomedical devices.

Supplementary Materials

The following are available online at https://www.mdpi.com/2073-4360/11/2/373/s1, Figures S1–S6: characterization of B-POSS, hybrid PUs.

Author Contributions

Funding acquisition, H.C.; Investigation, X.S.; Resources: T.L.; Supervision, H.C., Z.L. and T.L.; Writing—original draft, X.S. and X.Z.; Writing—review & editing, H.C. and Z.L.

Funding

This work was financially supported by the National Natural Science Foundation of China (Grant No. 51702178), International Cooperation Research Special Fund Project (QLUTGJHZ2018001), the Taishan Scholar Program of Shandong (Grant No. 0308150303) and the Program for Scientific Research Innovation Team in Colleges and Universities of Shandong Province. Z.L would like to thank A*STAR for financial support.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Delebecq, E.; Pascault, J.-P.; Boutevin, B.; Ganachaud, F. On the versatility of urethane/urea bonds: Reversibility, blocked isocyanate, and non-isocyanate polyurethane. Chem. Rev. 2012, 113, 80–118. [Google Scholar] [CrossRef]
  2. Fan, X.; Tan, B.H.; Li, Z.; Loh, X.J. Control of PLA Stereoisomers-Based Polyurethane Elastomers as Highly Efficient Shape Memory Materials. ACS Sustain. Chem. Eng. 2017, 5, 1217–1227. [Google Scholar] [CrossRef]
  3. Yao, H.B.; Ge, J.; Wang, C.F.; Wang, X.; Hu, W.; Zheng, Z.J.; Ni, Y.; Yu, S.H. A flexible and highly pressure-sensitive graphene–polyurethane sponge based on fractured microstructure design. Adv. Mater. 2013, 25, 6692–6698. [Google Scholar] [CrossRef] [PubMed]
  4. Janik, H.; Marzec, M. A review: Fabrication of porous polyurethane scaffolds. Mater. Sci. Eng. C 2015, 48, 586–591. [Google Scholar] [CrossRef] [PubMed]
  5. Wang, X.; Hu, Y.; Song, L.; Yang, H.; Xing, W.; Lu, H. In situ polymerization of graphene nanosheets and polyurethane with enhanced mechanical and thermal properties. J. Mater. Chem. 2011, 21, 4222–4227. [Google Scholar] [CrossRef]
  6. Liu, H.; Dong, M.; Huang, W.; Gao, J.; Dai, K.; Guo, J.; Zheng, G.; Liu, C.; Shen, C.; Guo, Z. Lightweight conductive graphene/thermoplastic polyurethane foams with ultrahigh compressibility for piezoresistive sensing. J. Mater. Chem. C 2017, 5, 73–83. [Google Scholar] [CrossRef] [Green Version]
  7. Zhang, X.; Gong, T.; Chi, H.; Li, T. Nanostructured polyurethane perylene bisimide ester assemblies with tuneable morphology and enhanced stability. Roy. Soc. Open Sci. 2018, 5, 171686. [Google Scholar] [CrossRef] [Green Version]
  8. Kong, L.; Li, Y.; Qiu, F.; Zhang, T.; Guo, Q.; Zhang, X.; Yang, D.; Xu, J.; Xue, M. Fabrication of hydrophobic and oleophilic polyurethane foam sponge modified with hydrophobic Al2O3 for oil/water separation. J. Ind. Eng. Chem. 2018, 58, 369–375. [Google Scholar] [CrossRef]
  9. Yang, G.; Song, J.; Hou, X. Fabrication of highly hydrophobic two-component thermosetting polyurethane surfaces with silica nanoparticles. Appl. Surf. Sci. 2018, 439, 772–779. [Google Scholar] [CrossRef]
  10. Wang, H.; Wang, E.; Liu, Z.; Gao, D.; Yuan, R.; Sun, L.; Zhu, Y. A novel carbon nanotubes reinforced superhydrophobic and superoleophilic polyurethane sponge for selective oil–water separation through a chemical fabrication. J. Mater. Chem. A 2015, 3, 266–273. [Google Scholar] [CrossRef]
  11. Kuang, X.; Chen, K.; Dunn, C.; Wu, J.; Li, V.; Qi, H.J. 3D Printing of Highly Stretchable, Shape-Memory, and Self-Healing Elastomer toward Novel 4D Printing. ACS Appl. Mater. Interfaces 2018, 10, 7381–7388. [Google Scholar] [CrossRef] [PubMed]
  12. Chen, Q.; Mangadlao, J.D.; Wallat, J.; De, L.A.; Pokorski, J.K.; Advincula, R.C. 3D printing biocompatible polyurethane/poly (lactic acid)/graphene oxide nanocomposites: Anisotropic properties. ACS Appl. Mater. Interfaces 2017, 9, 4015–4023. [Google Scholar] [CrossRef] [PubMed]
  13. Li, Z.; Tan, B.H.; Jin, G.; Li, K.; He, C. Design of polyhedral oligomeric silsesquioxane (POSS) based thermo-responsive amphiphilic hybrid copolymers for thermally denatured protein protection applications. Polym. Chem. 2014, 5, 6740–6753. [Google Scholar] [CrossRef]
  14. Li, Z.; Kong, J.; Wang, F.; He, C. Polyhedral oligomeric silsesquioxanes (POSSs): An important building block for organic optoelectronic materials. J. Mater. Chem. C 2017, 5, 5283–5298. [Google Scholar] [CrossRef]
  15. Fan, X.; Cao, M.; Zhang, X.; Li, Z. Synthesis of star-like hybrid POSS-(PDMAEMA-b-PDLA)8 copolymer and its stereocomplex properties with PLLA. Mater. Sci. Eng. C 2017, 76, 211–216. [Google Scholar] [CrossRef]
  16. Uner, A.; Doganci, E.; Tasdelen, M.A.; Yilmaz, F.; Gürek, A.G. Synthesis, characterization and surface properties of star-shaped polymeric surfactants with polyhedral oligomeric silsesquioxane core. Polym. Int. 2017, 66, 1610–1616. [Google Scholar] [CrossRef]
  17. Zhang, W.; Müller, A.H.E. Architecture, self-assembly and properties of well-defined hybrid polymers based on polyhedral oligomeric silsequioxane (POSS). Prog. Polym. Sci. 2013, 38, 1121–1162. [Google Scholar] [CrossRef]
  18. Hirai, T.; Leolukman, M.; Liu, C.C.; Han, E.; Kim, Y.J.; Ishida, Y.; Hayakawa, T.; Kakimoto, M.; Nealey, N.F.; Gopalan, P. One-Step Direct-Patterning Template Utilizing Self-Assembly of POSS-Containing Block Copolymers. Adv. Mater. 2009, 21, 4334–4338. [Google Scholar] [CrossRef]
  19. Zheng, L.; Hong, S.; Cardoen, G.; Burgaz, E.; Gido, S.P.; Coughlin, E.B. Polymer nanocomposites through controlled self-assembly of cubic silsesquioxane scaffolds. Macromolecules 2004, 37, 8606–8611. [Google Scholar] [CrossRef]
  20. Liu, Y.; Yu, C.; Jin, H.; Jiang, B.; Zhu, X.; Zhou, Y.; Lu, Z.; Yan, D. A supramolecular Janus hyperbranched polymer and its photoresponsive self-assembly of vesicles with narrow size distribution. J. Am. Chem. Soc. 2013, 135, 4765–4770. [Google Scholar] [CrossRef]
  21. Raghunath, J.; Zhang, H.; Edirisinghe, M.J.; Darbyshire, A.; Butler, P.E.; Seifalian, A.M. A new biodegradable nanocomposite based on polyhedral oligomeric silsesquioxane nanocages: Cytocompatibility and investigation into electrohydrodynamic jet fabrication techniques for tissue-engineered scaffolds. Biotechnol. Appl. Bioc. 2009, 52, 1–8. [Google Scholar] [CrossRef] [PubMed]
  22. Wang, B.; Lin, Q.; Shen, C.; Han, Y.; Tang, J.; Chen, H. Synthesis of MA POSS–PMMA as an intraocular lens material with high light transmittance and good cytocompatibility. RSC Adv. 2014, 4, 52959–52966. [Google Scholar] [CrossRef]
  23. Kannan, R.Y.; Salacinski, H.J.; De Groot, J.; Clatworthy, I.; Bozec, L.; Horton, M.; Butler, P.E.; Seifalian, A.M. The antithrombogenic potential of a polyhedral oligomeric silsesquioxane (POSS) nanocomposite. Biomacromolecules 2006, 7, 215–223. [Google Scholar] [CrossRef] [PubMed]
  24. Ata, S.; Banerjee, S.L.; Singha, N.K. Polymer nano-hybrid material based on graphene oxide/POSS via surface initiated atom transfer radical polymerization (SI-ATRP): Its application in specialty hydrogel system. Polymer 2016, 103, 46–56. [Google Scholar] [CrossRef]
  25. Zhang, X.; Chi, H.; Li, T.; Wang, F.; Chin, W.S.; Xu, J. Energy transfer along a sequence controlled hybrid polymer. J. Polym. Sci. A 2018, 56, 1225–1233. [Google Scholar] [CrossRef]
  26. Chi, H.; Mya, K.Y.; Lin, T.; He, C.; Wang, F.; Chin, W.S. Thermally stable azobenzene dyes through hybridization with POSS. New J. Chem. 2013, 37, 735–742. [Google Scholar] [CrossRef]
  27. Chi, H.; Wang, M.; Xiao, Y.; Wang, F.; Joshy, K.S. Self-Assembly and Applications of Amphiphilic Hybrid POSS Copolymers. Molecules 2018, 23, 2481. [Google Scholar] [CrossRef]
  28. Han, Y.; Wang, F.; Lim, C.Y.; Chi, H.; Chen, D.; Wang, F.; Jiao, X. High-Performance Nano-Photoinitiators with Improved Safety for 3D Printing. ACS Appl. Mater. Interfaces 2017, 9, 32418–32423. [Google Scholar] [CrossRef]
  29. Chi, H.; Lim, S.L.; Wang, F.; Wang, X.; He, C.; Chin, W.S. Pure Blue-Light Emissive Poly(oligofluorenes) with Bifunctional POSS in the Main Chain. Macromol. Rapid Commun. 2014, 35, 801–806. [Google Scholar] [CrossRef]
  30. Liu, X.; Fan, X.; Jiang, L.; Loh, X.J.; Wu, Y.-L.; Li, Z. Biodegradable Polyester Unimolecular System as Emerging Materials for Therapeutic Applications. J. Mater. Chem. B 2018, 6, 5488–5498. [Google Scholar] [CrossRef]
  31. Kyung, M.; Lee, P.T.; Knight, T.; Chung, T.P.; Mather, P.T. Polycaprolactone−POSS Chemical/Physical Double Networks. Macromolecules 2008, 41, 4730–4738. [Google Scholar] [CrossRef]
  32. Frank, K.L.; Exley, S.E.; Thornell, T.L.; Morgan, S.E.; Wiggins, J.S. Investigation of pre-reaction and cure temperature on multiscale dispersion in POSS–epoxy nanocomposites. Polymer 2012, 53, 4643–4651. [Google Scholar] [CrossRef]
  33. Tan, B.H.; Hussain, H.; Leong, Y.W.; Lin, T.T.; Tjiu, W.W.; He, C. Tuning self-assembly of hybrid PLA-P(MA-POSS) block copolymers in solution via stereocomplexation. Polym. Chem. 2013, 4, 1250–1259. [Google Scholar] [CrossRef]
  34. Wang, Z.; Leng, S.; Wang, Z.; Li, G.; Yu, H. Nanostructured Organic−Inorganic Copolymer Networks Based on Polymethacrylate-Functionalized Octaphenylsilsesquioxane and Methyl Methacrylate: Synthesis and Characterization. Macromolecules 2011, 44, 566–574. [Google Scholar] [CrossRef]
  35. Markovic, E.; Clarke, S.; Matisons, J.; Simon, G.P. Synthesis of POSS−Methyl Methacrylate-Based Cross-Linked Hybrid Materials. Macromolecules 2008, 41, 1685–1692. [Google Scholar] [CrossRef]
  36. Mya, K.Y.; Gose, H.B.; Pretsch, T.; Bothe, M.; He, C. Star-shaped POSS-polycaprolactone polyurethanes and their shape memory performance. J. Mater. Chem. 2011, 21, 4827–4836. [Google Scholar] [CrossRef]
  37. Wei, K.; Wang, L.; Zheng, S. Organic-inorganic polyurethanes with 3,13-dihydroxypropyloctaphenyl double-decker silsesquioxane chain extender. Polym. Chem. 2013, 4, 1491–1501. [Google Scholar] [CrossRef]
  38. Turri, S.; Levi, M. Structure, Dynamic Properties, and Surface Behavior of Nanostructured Ionomeric Polyurethanes from Reactive Polyhedral Oligomeric Silsesquioxanes. Macromolecules 2005, 38, 5569–5574. [Google Scholar] [CrossRef]
  39. Turri, S.; Levi, M. Wettability of Polyhedral Oligomeric Silsesquioxane Nanostructured Polymer Surfaces. Macromol. Rapid Commun. 2005, 26, 1233–1236. [Google Scholar] [CrossRef]
  40. Oaten, M.; Choudhury, N.R. Silsesquioxane−Urethane Hybrid for Thin Film Applications. Macromolecules 2005, 38, 6392–6401. [Google Scholar] [CrossRef]
  41. Li, Z.; Tan, B.H. Towards the development of polycaprolactone based amphiphilic block copolymers: Molecular design, self-assembly and biomedical applications. Mater. Sci. Eng. C 2014, 45, 620–634. [Google Scholar] [CrossRef] [PubMed]
  42. Blanco, I.; Bottino, F.A.; Abate, L. Influence of n-alkyl substituents on the thermal behaviour of Polyhedral Oligomeric Silsesquioxanes (POSSs) with different cage’s periphery. Thermochim. Acta 2016, 623, 50–57. [Google Scholar] [CrossRef]
  43. Wang, W.; Guo, Y.-L.; Otaigbe, J.U. The synthesis, characterization and biocompatibility of poly(ester urethane)/polyhedral oligomeric silesquioxane nanocomposites. Polymer 2009, 50, 5749–5757. [Google Scholar] [CrossRef]
  44. Waltman, R.J.; Deng, H.; Wang, G.J.; Zhu, H.; Tyndall, G.W. The Effect of PFPE Film Thickness and Molecular Polarity on the Pick-Up of Disk Lubricant by a Low-Flying Slider. J. Appl. Polym. Sci. 2010, 39, 211–219. [Google Scholar] [CrossRef]
  45. Sasi, K.R.; Muthukaruppan, A. Dielectric and thermal behaviors of POSS reinforced polyurethane based polybenzoxazine nanocomposites. RSC Adv. 2015, 5, 33008–33015. [Google Scholar] [CrossRef]
  46. Payne, A.R. The dynamic properties of carbon black-loaded natural rubber vulcanizates Part II. J. Appl. Polym. Sci. 1962, 6, 57–63. [Google Scholar] [CrossRef]
  47. Cassagnau, P. Melt rheology of organoclay and fumed silica nanocomposites. Polymer 2008, 49, 2183–2196. [Google Scholar] [CrossRef] [Green Version]
  48. Quinlan, E.; López-Noriega, A.; Thompson, E.; Kelly, H.M.; Cryan, S.A.; O’Brien, F.J. Development of collagen–hydroxyapatite scaffolds incorporating PLGA and alginate microparticles for the controlled delivery of rhBMP-2 for bone tissue engineering. J. Control. Release 2015, 198, 71–79. [Google Scholar] [CrossRef] [Green Version]
  49. Caracciolo, P.C.; Pita, C.S.; Abraham, G.A.; Me’ndez, J.A.; Molera, J.G. Synthesis, characterization and applications of amphiphilic elastomeric polyurethane networks in drug delivery. Polym. J. 2013, 45, 331–338. [Google Scholar] [CrossRef]
  50. Gorna, K.; Gogolewski, S. Biodegradable porous polyurethane scaffolds for tissue repair and regeneration. J. Biomed. Mater. Res. A 2006, 79, 128–138. [Google Scholar] [CrossRef]
  51. Bonzani, I.C.; Adhikari, R.; Houshyar, H.; Mayadunne, R.; Gunatillake, P.; Stevens, M.M. Synthesis of two-component injectable polyurethanes for bone tissue engineering. Biomaterials 2007, 28, 423–433. [Google Scholar] [CrossRef] [PubMed]
Polymers 11 00373 g001 550
Figure 1. Synthesis of organic–inorganic hybrid PUs with B-POSS in the main chains.
Figure 1. Synthesis of organic–inorganic hybrid PUs with B-POSS in the main chains.
Polymers 11 00373 g001
Polymers 11 00373 g002 550
Figure 2. 1H-NMR spectra of 3,13-dihydroxypropyloctaphenyl B-POSS (B-POSS), 3,13-di(trimethylsilyl) oxypropyloctaphenyl B-POSS and 3,13-dihydrooctaphenyl B-POSS from top to bottom.
Figure 2. 1H-NMR spectra of 3,13-dihydroxypropyloctaphenyl B-POSS (B-POSS), 3,13-di(trimethylsilyl) oxypropyloctaphenyl B-POSS and 3,13-dihydrooctaphenyl B-POSS from top to bottom.
Polymers 11 00373 g002
Polymers 11 00373 g003 550
Figure 3. 1H-NMR spectra of O-8000 and PU-8000 in CDCl3.
Figure 3. 1H-NMR spectra of O-8000 and PU-8000 in CDCl3.
Polymers 11 00373 g003
Polymers 11 00373 g004 550
Figure 4. TGA curves of PU, PU-4000, PU-8000 and PU-12000 (A); DSC thermograms of PU, PU-4000, PU-8000 and PU-12000 (B).
Figure 4. TGA curves of PU, PU-4000, PU-8000 and PU-12000 (A); DSC thermograms of PU, PU-4000, PU-8000 and PU-12000 (B).
Polymers 11 00373 g004
Polymers 11 00373 g005 550
Figure 5. Plot of surface water contact angles of the organic–inorganic hybrid PUs.
Figure 5. Plot of surface water contact angles of the organic–inorganic hybrid PUs.
Polymers 11 00373 g005
Polymers 11 00373 g006 550
Figure 6. Dynamic strain sweep of: Gʹ for neat PU, PU-8000, PU-10000, PU-12000 and PU-14000.
Figure 6. Dynamic strain sweep of: Gʹ for neat PU, PU-8000, PU-10000, PU-12000 and PU-14000.
Polymers 11 00373 g006
Table
Table 1. Characteristics of PU, PU-2000, PU-4000 and PU-10000.
Table 1. Characteristics of PU, PU-2000, PU-4000 and PU-10000.
PolyurethaneMw (g/mol)Mn (g/mol)Mw/MnTd (°C)Tg (°C)
PU22,60022,1001.0220747
PU-400011,10079301.3923854
PU-800023,10015,1001.5324660
PU-1000029,90019,2001.5626666
PU-1200036,40022,7001.6028067
PU-1400045,20027,1001.6728369
Table
Table 2. Static contact angles and surface free energy of PU and B-POSS.
Table 2. Static contact angles and surface free energy of PU and B-POSS.
Static Contact AngleSurface Free Energy (mN/m)
SampleӨH2OӨethylene glycolγpsγdsγs
PU59.1 ± 0.640.2 ± 0.629.4811.9041.38
PU-400080.2 ± 0.863.2 ± 0.812.9614.0627.02
PU-800096.8 ± 0.977.1 ± 0.63.3117.4720.78
PU-10000103.9 ± 0.686.8 ± 0.82.4313.1015.53
PU-12000105.7 ± 0.888.9 ± 0.72.1312.4514.58
PU-14000108.9 ± 0.993.6 ± 0.61.9610.1712.13
Table
Table 3. Tensile strength and elongation at break of PLGA, PLGA/B-POSS, PLGA/O-14000 and PLGA/PU-14000.
Table 3. Tensile strength and elongation at break of PLGA, PLGA/B-POSS, PLGA/O-14000 and PLGA/PU-14000.
SampleTensile Strength (MPa)Elongation at Break (%)Toughness (MJ/m3)
PLGA0.36 ± 0.03953.16 ± 22.3241.85 ± 0.67
PLGA/B-POSS0.44 ± 0.02707.03 ± 14.2229.10 ± 0.28
PLGA/O-140000.48 ± 0.01833.62 ± 16.8291.98 ± 0.17
PLGA/PU-140000.51 ± 0.03725.52 ± 24.7270.64 ± 0.74

Share and Cite

MDPI and ACS Style

Song, X.; Zhang, X.; Li, T.; Li, Z.; Chi, H. Mechanically Robust Hybrid POSS Thermoplastic Polyurethanes with Enhanced Surface Hydrophobicity. Polymers 2019, 11, 373. https://doi.org/10.3390/polym11020373

AMA Style

Song X, Zhang X, Li T, Li Z, Chi H. Mechanically Robust Hybrid POSS Thermoplastic Polyurethanes with Enhanced Surface Hydrophobicity. Polymers. 2019; 11(2):373. https://doi.org/10.3390/polym11020373

Chicago/Turabian Style

Song, Xiuhuan, Xiaoxiao Zhang, Tianduo Li, Zibiao Li, and Hong Chi. 2019. "Mechanically Robust Hybrid POSS Thermoplastic Polyurethanes with Enhanced Surface Hydrophobicity" Polymers 11, no. 2: 373. https://doi.org/10.3390/polym11020373

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop