Novel Multiblock Poly(Îµ-caprolactone) Copolyesters Containing D

Research Article pubs.acs.org/journal/ascecg

Novel Multiblock Poly(ε-caprolactone) Copolyesters Containing D‑Glucose Derivatives with Different Bicyclic Structures Di-Di Xing, Yun-Wan Jia, De-Fu Li, Xiu-Li Wang,* and Yu-Zhong Wang* Center for Degradable and Flame-Retardant Polymeric Materials (ERCPM-MoE), College of Chemistry, State Key Laboratory of Polymer Materials Engineering, National Engineering Laboratory of Eco-Friendly Polymeric Materials (Sichuan), Sichuan University, 29 Wangjiang Road, Chengdu 610064, China S Supporting Information *

ABSTRACT: For improving the thermal stability, glass transition temperature (Tg), stiffness, and hydrophilicity of poly(ε-caprolactone) (PCL), two glucose-based bicyclic rigid structures, namely 1,4:3,6-dianhydrohexitols-Dglucidol (isosorbide, Is) and dimethyl 2,4:3,5-di-O-methylene-D-glucarate (glu-diester) have been introduced into PCL via chain extension. The two series of multiblock copolyesters obtained, PCL-b-PIS and PCL-b-PBG, have high number-average molecular weights in the range of 9.6 × 104 to 12.4 × 104 g mol−1 and small PDI values. The thermal and crystallization behaviors, hydrophilicity, as well as the mechanical properties of PCL-b-PIS and PCL-bPBG have been well investigated. In comparison, the improved effect on thermal stability and Tg of PCL is more pronounced for PCL-b-PBG than for PCL-b-PIS. Both glucose-based units retard the crystallinity of PCL. However, the crystal structure and melting temperature of PCL remain unchanged. The rigidness of PCL is enhanced when glucose-based bicyclic units are introduced as reflected by the increasing storage modulus over all of the studied temperatures. The mechanical properties of PCL-b-PIS are better than those of PCL-b-PBG, especially for the samples containing 30 wt % sugar units. This can be due to the good compatibility of PIS with the PCL block. Although both Is and glu-diester enhance the hydrophilicity of PCL, the PCL-b-PBG copolyester always shows higher hydrophilicity than that of PCL-b-PIS in the whole composition. KEYWORDS: PCL, D-Glucose-based units, Multiblock copolyesters, Thermal stability, Crystallization, Mechanical property

■

PCL. Yao et al.20 introduced rosin-ester structured segments into the side-chain of PCL via ring-opening polymerization and click chemistry and found that the rosin structure increased the Tg of PCL by more than 100 °C, although the hydrophilicity of PCL decreased. For the copolyesters containing poly(ethylene vanillate) (PEV) and PCL units, their melting temperatures (Tms) and Tgs were enhanced with increasing PEV content. When the molar fraction of PEV and PCL units was 20:80, the Tm and Tg of pure PCL were increased from 55 to 104 °C and from −63 to −18 °C, respectively.21 Because of their low molecular weights, the obtained copolyesters are brittle. Among the various biobased sources, sugar-based monomers, especially those with cyclic stiff structures, occupy an important position in improving the properties of polymers in particular for enhancing the Tgs of polymers.22,23 Among these sugarbased monomers, 1,4:3,6-dianhydrohexitols-D-glucidol, known as isosorbide (Is) produced from D-glucose, is the only commercially available bicyclic dianhydro alditol to date, which has been widely investigated as a comonomer for the synthesis of aromatic polyesters or aliphatic polyesters.23−28 Recently,

INTRODUCTION Poly(ε-caprolactone) (PCL) is a semicrystalline aliphatic polyester that has been widely investigated as biomedical and packaging materials due to its biocompatibility, biodegradability, and nontoxicity.1−7 PCL plays a major role in biodegradable polymers because of its wide miscibility with a many polymers and solubility in many organic solvents.8−11 However, the low glass transition temperature (Tg), low tensile strength and modulus, as well as slow degradation rate limit PCL’s practical application.12−14 To overcome these drawbacks and preserve its biodegradability, researchers have introduced some aliphatic polyesters such as poly(butylene succinate), poly(ethylene succinate), and poly(propylene succinate) into the main chain of PCL to obtain their block or random copolyesters.15−17 Although the Tg and biodegradability of PCL have been improved, the mechanical properties are still low. Some aromatic units have been used as modified units to increase the mechanical properties of PCL;18,19 however, the biodegradability of PCL has been lowered. Long-term problems from mankind include environmental pollution and exhaustion of oil resources. One answer, but of course not the only one, is the production and application of materials from renewable resources. Nowadays, many researchers are using biobased resources to improve the properties of © XXXX American Chemical Society

Received: April 24, 2017 Revised: May 29, 2017

A

DOI: 10.1021/acssuschemeng.7b01263 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Research Article

ACS Sustainable Chemistry & Engineering Scheme 1. Synthesis Routes for PCL-b-PBG

were obtained from Sigma-Aldrich and Aladdin Industrial Corporation (Shanghai, China), respectively, both of which were used without any purification. ε-Caprolactone (ε-CL, 99%) was purchased from Aladdin Industrial Corporation (Shanghai, China), dried over calcium hydride, and purified by vacuum distillation prior to use. Dimethyl 2,4:3,5-di-Omethylene-D-glucarate (glu-diester) was synthesized according to the literature33−35 and its 1H and 13C NMR spectra as well as LC-MS results are provided in Figures S1 and S2. All of the other solvents and regents (AR grade) were provided by Kelong Chemical Corporation (Chengdu, China) and used without any further treatment. Synthesis of Hydroxyl-Terminated Poly(butylene glucarate) (HO-PBG-OH) and Poly(isosorbide succinate) (HO-PIS-OH). Two series of prepolyesters (HO-PBG-OH, HO-PIS-OH) were synthesized through two steps: transesterification or esterification and polycondensation. To obtain dihydroxyl-terminated prepolymers, an excess of diol with respect to the diacid or diester is needed. The structure of Glux-diol and glu-diester is similar, both of which contain two fused 1,3-dioxane rings. Because of the simple synthesis process of glu-diester, in this work we choose the glu-diester as the modified monomer. The detailed synthesis steps for HO-PBG-OH are shown as follows: a predetermined amount of glu-diester and BDO with a molar ratio of 1:2.2 as well as Zn(OAc)2 (0.05 wt % of the total reactants) were charged into a 100 mL three-necked round-bottomed flask equipped with a mechanical stirrer, a water separator, and a nitrogen inlet pipe and then heated to 160 °C and maintained until the theoretical amount of methanol was produced. After that, TBT (0.05 wt % of the total reactants) was added to the system, and the reaction was conducted at 170 °C for 3 h under a vacuum. When the polymerization was complete, the product was cooled to room temperature. HO-PIS-OH was synthesized via esterification and polycondensation. The detailed synthetic steps are as follows: predetermined amounts of Is, SA (1.5:1 molar ratio), and Zn(OAc)2 (0.1 wt % of the total reactants) were charged into a 100 mL three-necked roundbottomed flask equipped with a mechanical stirrer, a water separator, and a nitrogen inlet pipe and then heated to 230 °C and maintained until the theoretical amount of water was produced. Then, TBT (0.1 wt % of the total reactants) was added to the system, and the reaction was continued at 230 °C for 4 h under vacuum. When the polymerization was completed, the product was cooled to room temperature. The obtained HO-PBG-OH and HO-PIS-OH were purified by dissolving in chloroform, precipitating in methanol, and then drying at 60 °C under a vacuum until reaching constant weights before the next synthesis and characterization.

Muñoz-Guerra’s group has carried out extensive work on using acetalized diols or dimethyl ester with the monocyclic and bicyclic structure as the third monomer to improve the properties of the polyesters.29−32 The functional groups in these acetalized compounds are primary and more reactive than those of Is, which are secondary hydroxyl groups at the 2- and 5-positions. For example, 2,4:3,5-di-O-methylene-D-mannitol (Manx-diol), 2,4:3,5-di-O-methylene-D-glucitol (Glux-diol), or dimethyl 2,4:3,5-di-O-methylene-D-glucarate (glu-diester) have been used as comonomers to prepare biobased poly(butylene terephthalate) (PBT) or poly(ethylene terephthalate) (PET) via melt polymerization. In terms of the polycondensation reaction, a high polymerization temperature is needed. However, these sugar derivatives are sensitive to heat, leading to low molecular weight and unsatisfactory conversion for the modified polyesters. Moreover, because of the random structure of copolyesters, the Tms of these obtained polyesters decrease compared to those of their corresponding homopolymers. In this paper, two glucose-based bicyclic monomers, gludiester and Is, are chosen as block units to prepare PCL-based block copolymers via chain extension. Via this modification method, the Tm of PCL is expected to be maintained while improving the thermal stability, stiffness, modulus, and hydrophilicity of PCL. Furthermore, the biobased origin of the two compounds used for copolymerization adds plus sustainability to PCL. These two units have different structures: Is has two fused tetrahydrofuran structures, whereas glu-diester consists of two fused 1,3-dioxane ring structures. Therefore, the influence of the structure difference of the two units on the properties of PCL has also been investigated.

■

EXPERIMENTAL SECTION

Materials. Succinic acid (SA, AR grade), 1,4-butanediol (BDO, AR grade), and zinc acetate (Zn(OAc)2, AR grade) were purchased from Kelong Chemical Corporation (Chengdu, China) and used as received. Tetrabutyl titanate (TBT) was also obtained from Kelong Chemical Corporation and dissolved in anhydrous toluene to prepare 0.2 g mL−1 solution before use. Isosorbide (Is, 98+%) was purchased from Alfa Aesar Chemical Co. (Shanghai, China). Hexamethylene diisocyanate (HDI, ≥ 99%) and stannous (II) octoate (SnOct2, 95%) B


Research Article

ACS Sustainable Chemistry & Engineering Scheme 2. Synthesis Routes for PCL-b-PIS

1

(s, 1H, H11), 4.86 (s, 1H, H13), 5.31 (s, 1H, H13), 4.99−5.05 (dd, 2H, H12). 1 H NMR of PCL-b-PIS (400 MHz, CDCl3), δ (ppm): 1.25 (s, 2H, 22 H ), 1.37 (m, 2H, H1), 1.49 (s, 2H, H23), 1.65 (m, 2H, H2), 2.31 (t, 2H, H3), 2.66 (dd, 2H, H15), 3.16 (d, 2H, H24), 3.81 (d, 1H, H17), 3.96 (s, 2H, H20), 4.06 (t, 2H, H4), 4.47 (d, 1H, H19), 4.83 (s, 1H, H18), 5.16 (d, 1H, H16), 5.22 (s, 1H, H21). Nuclear Magnetic Resonance (NMR). 1H and 13C NMR were acquired on a Bruker AC-P 400 MHz spectrometer at room temperature using CDCl3 and tetramethylsilane as the solvent and internal reference, respectively. Gel Permeation Chromatography (GPC). The molecular weight and polydispersity index (PDI) of the multiblock copolyesters and prepolymers were measured by GPC as performed on a Waters instrument with a Model 1515 pump, Waters Model 717 autosampler, and Model 2414 refractive index detector. CHCl3 and monodisperse polystyrenes were used as the eluent and standards, respectively. The sample concentration and flow rate of the eluent were 2.5 mg mL−1 and 1.0 mL min−1, respectively. Thermogravimetric Analysis (TGA). The thermal stability of samples (weights of approximately 3−5 mg) was investigated by TGA (TGA-Q500, TA Instruments, USA). The thermograms were recorded under a N2 atmosphere at a heating rate of 10 °C min−1. Differential Scanning Calorimetry (DSC). DSC was carried out on a TA Instruments DSC-Q200 with Universal Analysis 2000. Samples (3−5 mg) in an aluminum pan were first heated to 140 °C and held for 5 min to erase any thermal history, and then quenched to −70 °C and held for 1 min. Then, they were reheated to 140 °C at a rate of 10 °C/min; after holding at this temperature for 5 min, they were then cooled to −70 °C at the same speed. Dynamic Mechanical Analysis (DMA). Dynamic mechanical properties of the multiblock copolyesters were measured with a dynamic mechanical analyzer (DMA Q800, TA Instruments, USA). The films were prepared by hot pressing, and they were then cut into rectangular bar specimens with dimensions of 10 × 4 × 0.5 mm (length × width × thickness). The measurements were carried out in the tension mold at a heating rate of 2 °C/min in the range of −80 to 40 °C with a frequency of 1 Hz, static force of 0.01 N, and amplitude of 15 μm. Wide-Angle X-ray Diffraction (WAXD). WAXD was measured on a Philips X’Pert X-ray diffractometer with Cu Kα radiation. The experiment was carried out at room temperature with a scan rate of 2° min−1 scanning from 5° to 40°. Polarized Optical Microscopy (POM). A polarized optical microscope (Nikon Eclipse LV100POL Nikon Instruments Inc., Melville, NY, USA) equipped with a temperature controller

H NMR of HO-PBG-OH (400 MHz, CDCl3, shown in Figure S3), δ (ppm): 5.30 (d, 2H, H13), 4.86 (d, 2H, H13), 5.04 (dd, 2H, H12), 4.60 (d, 1H, H11), 4.37 (s, 1H, H8), 4.12 (s, 1H, H10), 4.02 (s, 1H, H9), 4.27 (m, 2H, H6), 3.68 (m, 2H, H14), 1.79 (t, 2H, H7). 1 H NMR of HO-PIS-OH (400 MHz, CDCl3, shown in Figure S4), δ (ppm): 5.22 (s, 1H, H21), 5.16 (m, 1H, H16), 4.82 (s, 1H, H18), 4.48 (d, 1H, H19), 3.96 (s, 2H, H20), 3.92 (d, 1H, H17α), 3.88 (d, 1H, H17β), 3.57 (d, 1H, H19′), 2.69 (dd, 2H, H15). Synthesis of Hydroxyl-Terminated Poly(ε-caprolactone) (HO-PCL-OH). HO-PCL-OH was synthesized via ring-opening polymerization of ε-CL using 1,4-butanediol as an initiator and Sn(Oct)2 as a catalyst. In a dry two-necked flask that was evacuated and purged with nitrogen three times, ε-CL (0.53 mol), BDO (0.009 mol), and Sn(Oct)2 (0.0018 mol) were injected by a syringe under a nitrogen atmosphere. Then, the flask was placed into the silicon oil bath preheated at 130 °C and conducted for 12 h with magnetic stirring. When the polymerization was completed, the vial was immersed in ice water to quench the reaction. The product was purified by dissolving in chloroform, precipitating with excess methanol, and then drying at 50 °C under a vacuum until reaching a constant weight. 1 H NMR of HO-PCL-OH (400 MHz, CDCl3, shown in Figure S5), δ (ppm): 1.38 (m, 2H, H1), 1.64 (m, 2H, H2), 2.31 (t, 2H, H3), 3.65 (t, 2H, H5), 4.06 (t, 2H, H4). Synthesis of Multiblock Copolyesters. PCL-b-poly(butylene glucarate) copolyester (PCL-b-PBG) was synthesized by chainextension reaction of HO-PCL-OH and HO-PBG-OH using HDI as a chain-extender. Briefly, HO-PCL-OH and HO-PBG-OH were charged into a 100 mL two-necked flask, and then the flask was vacuumed and purged with nitrogen three times. Then, the flask was placed in an oil bath preheated at 130 °C. When the reactants were molten under mechanical stirring, the exact amount of HDI (1:1 OH:NCO molar ratio) was injected by a syringe. The chain-extension reaction was conducted in a nitrogen atmosphere for 1 h. PCL-b-poly(isosorbide succinate) copolyester (PCL-b-PIS) was synthesized in the same way, and their detailed synthesis routes are illustrated in Schemes 1 and 2. All of the multiblock copolyesters were purified by dissolving in chloroform and precipitating with excess methanol. Then, the purified products were dried in a vacuum oven at 50 °C to constant weights before further characterization. For comparison, neat PCL was also prepared by chain extension of HOPCL-OH with HDI. 1 H NMR of PCL-b-PBG (400 MHz, CDCl3), δ (ppm): 1.38 (m, 2H, H1), 1.49 (s, 2H, H23), 1.65 (m, 2H, H2), 1.77 (m, 2H, H7), 2.30 (t, 2H, H3), 3.16 (s, 2H, H24), 4.06 (t, 2H, H4), 4.27 (s, 2H, H6), 4.60 C


Research Article

ACS Sustainable Chemistry & Engineering (HSC621V) was employed to investigate the crystalline morphology of multiblock copolyesters. The films of the specimen were obtained by casting the solution (10 mg mL−1 in CHCl3) onto a sliding glass. The films were first melted at 100 °C for 3 min to erase any thermal history and subsequently quenched to 30 °C and remained until crystallization was finished. Atom Force Microscopy (AFM). AFM (Innova, Burker Corporation) was used to acquire phase images of the multiblock copolyesters in tapping mode. Thin films of the polyesters were prepared by spin coating. The polyesters were dissolved in chloroform (5 mg mL−1) and cast onto a glass slide at 3000 rpm for 60 s. Water Contact Angles. Static water contact angles of HO-PBGOH and HO-PIS-OH as well as the two series of multiblock copolyesters were characterized using a contact angle analyzer (Model JC2000). The samples were glued to a movable sample stage horizontally, and then 3 μL of probe water was instilled onto the surfaces of the samples by a microsyringe. Tensile Test. The mechanical properties of copolyesters were studied by a universal testing machine (CMT6503, Shenzhen SANS Test Machine Co., Ltd., China) with a crosshead speed of 50 mm/ min. The dumbbell-shaped specimens with size of 4 × 0.5 × 20 mm (width × thickness × length) were prepared by hot pressing. At least five measurements were carried out for each sample, and the averaged results were reported.

methine proton connected to the ether bond of the terminal Is. In the same way, the average number of repeating units (n) and Mn of HO-PIS-OH can be obtained by the integral areas ratio of 4.82 and 3.57 ppm. The detailed values are also listed in Table 1. Figure S5 shows the 1H NMR spectrum of HO-PCLOH, and its n value and Mn are also calculated based on the integral areas of H4 and H5, whose values are 33 and 3890 g mol−1, respectively. The molecular weights of the prepolymers are also measured by GPC, and the detailed data are listed in Table 1. From Table 1, it can be seen that the molecular weights of the prepolymers determined by GPC are higher than those obtained by 1H NMR. This is reasonable because the Mn,GPC value is obtained by comparing with standard polystyrene samples. Extensive work reported that when the molar ratio of hydroxyl to isocyanate was 1:1, multiblock copolyesters with a satisfactory molecular weight can be achieved,36,37and an excess of diisocyanate may lead to cross-linking. Thus, in this work, HDI was chosen as the extender, and the molar ratio of hydroxyl to isocyanate was kept at 1:1. A series of multiblock copolyesters containing PCL and PBG or PIS in weight ratios of 90:10, 80:20, and 70:30 were successfully prepared. These copolyesters are named PCL-b-PBGx or PCL-b-PISx, where x stands for the PBG or PIS weight percentage in the copolymers. Figure 1 shows the 1H NMR spectrum of PCL-b-PBG30. Besides the characteristic peaks of PCL and PBG, new peaks at 1.49 (δH23) and 3.16 (δH24) ppm belonging to HDI appear in the spectrum of PCL-b-PBG30. The chemical shift of the terminal methylene group next to the terminal hydroxyl group disappears, indicating chain extension is carried out successfully. The weight ratio of PCL and PBG segments in the copolyesters can be calculated according to the equation

■

RESULTS AND DISCUSSION Structure Characterization of Multiblock Copolyesters. The multiblock copolyesters were synthesized via chain extension using HDI as an extender, and the detailed synthesis routes are shown in Schemes 1 and 2. As we know, the molar ratio of hydroxyl groups determines the dosage of HDI; therefore, the number-averaged molecular weight (Mn) of the dihydroxyl-terminated prepolyesters is obtained by 1H NMR. The Mn value of the hydroxyl-terminated prepolyesters can be obtained from the integral areas of the methylene protons of the repeating units and terminal methylene group. Figure S3 shows the 1H NMR spectrum of HO-PBG-OH in which the shifts occurring at 4.27 (δH6) ppm are assigned to the methylene protons of BDO in the repeating units, and the signal at 3.68 (δH14) ppm belongs to the methylene of BDO connected to the terminal hydroxyl group. On the basis of their integral areas ratio, the average number of repeating unit (n)

PCL/PBG (wt/wt) = 114Aδ = 2.31/(288Aδ = 4.27)

where Aδ=2.31 and Aδ=4.27 represent the integral areas of methylene protons (δH3 and δH6) of PCL and PBG units, respectively. The numbers 114 and 288 refer to the molecular weights of PCL and PBG repeating units. Table 2 shows that the actual weight ratios of PCL to PBG are almost the same as the feed ratio, demonstrating that all of the prepolymers are involved in the chain extension. For comparison, PCL-b-PISx copolyesters with the same weight ratio of PCL to PIS were synthesized in the same way. Figure 2 shows the typical 1H NMR spectrum of PCL-b-PIS30. In the spectrum, the characteristic resonance peaks of PCL and PIS segments exist, and the signals of terminal methylene protons belonging to OH-PCL-OH, as well as the terminal methine protons of HO-PIS-OH, disappear. Meanwhile, the new chemical shifts at 1.49 and 3.16 ppm belonging to HDI can also be found in its spectrum. All these results prove that the PCL-b-PISx copolyesters are successfully synthesized. Similarly, the weight ratios of PCL to PIS are obtained by the integral areas of methylene protons in PCL and PIS, respectively, according to eq 3.

Table 1. Molecular Weights of Hydroxyl-Terminated Prepolymers

a

sample

Mn,NMRa

Mn,GPCb

PDIb

na

HO-PCL-OH HO-PBG-OH HO-PIS-OH

3890 3690 3631

8416 5136 4248

1.6 1.5 1.3

33 13 15

(2)

Determined by H NMR. bObtained by GPC.

can be obtained and shown in Table 1. On the basis of eq 1, the Mn of HO-PBG-OH can be calculated as 3690 g mol−1. A Mn (HO‐PBG‐OH) = 288 × δ = 4.27 + 90 Aδ = 3.68 (1)

PCL/PIS (wt/wt) = 114Aδ = 2.31/(288Aδ = 2.64 )

where Aδ=4.27 and Aδ=3.68 represent the integral areas of internal and terminal methylene groups, respectively, 288 is the mass of repeating units, and 90 is the gross mass of the end chains. Figure S4 shows the 1H NMR spectrum of the HO-PIS-OH prepolymer. The chemical shift occurring at 4.82 (δH18) ppm belongs to the methine proton attached to the ether bond of Is in the repeating units, and 3.57 (δH19′) ppm is the signal of the

(3)

where Aδ=2.31 and Aδ=2.64 represent the integral areas of methylene protons in PCL and PIS, respectively, and the numbers 114 and 228 refer to the molecular weights of the PCL and PIS repeating units. The obtained weight ratios of PCL to PIS in PCL-b-PISx are also presented in Table 2, which are very close to their feed ratios. D


Research Article

ACS Sustainable Chemistry & Engineering

Figure 1. 1H NMR spectrum of PCL-b-PBG30.

Table 2. All of the copolyesters show high molecular weights, and their Mn and Mw are higher than 9.6 × 104 and 24 × 104 g mol−1, respectively. Compared to the random copolyesters containing the sugar-based units synthesized by direct polycondensation,30,38−40 chain extension is more in favor of obtaining high molecular weight copolyesters. Their PDI values are in the range of 2.1−3.1, which are comparable to those of random copolyesters. Comparing these two series of multiblock copolyesters containing the same content of bicyclic sugar structures, the Mn values of PCL-b-PISx are lower than those of PCL-b-PBGx, which is due to the lower reactivity of the secondary hydroxyl of isosorbide. Thermal Stability of Multiblock Copolyesters. The thermal stabilities of these two series of multiblock copolyesters are studied by TGA in a nitrogen atmosphere from 40 to 700 °C, their TG and DTG curves are shown in Figure 3. The temperature at 5% weight loss (T5%) and the maximum decomposition temperature (Tmax) of PCL-b-PBGx and PCL-bPISx obtained from Figure 3 are listed in Table 3. Like PCL, PCL-b-PBGx and PCL-b-PISx present only one decomposition range in N2. Their T5% and Tmax are much higher than those of PCL, indicating that the thermal stability of PCL has been significantly enhanced. This is reasonable because the aliphatic chain is more vulnerable to thermal decomposition than the cyclic aliphatic chain.40,41 For the multiblock copolyester PCLb-PBG with a PBG content of 30 wt %, the values of T5% and Tmax are 308 and 362 °C, respectively, which increase by 11 and 20% compared to those of neat PCL. Whereas for PCL-bPIS30, the T5% and Tmax increase by 8 and 9%, respectively. Comparatively speaking, the copolyesters containing PBG units show higher thermal stability than those containing PIS segments. For example, the T5% of PCL-b-PBG10 is 303 °C, which is approximately 30 °C higher than that of neat PCL, whereas for PCL-b-PIS10, its T5% is only 10 °C higher than that of PCL. Although 30 wt % PIS is introduced into the copolyester, its T5% is 299 °C, which is still lower than that of PCL-b-PBG10. The thermal stabilities of HO-PIS-OH and HO-PBG-OH were also tested by TGA (shown in Figure S6). Their T5%s are almost the same (271 °C for HO-PBG-OH and 273 °C for HO-PIS-OH), but the Tmax of HO-PIS-OH (409

Table 2. Compositions and Molecular Weights of PCL-bPBGx and PCL-b-PISx sample neat PCL PCL-bPBG10 PCL-bPBG20 PCL-bPBG30 PCL-bPIS10 PCL-bPIS20 PCL-bPIS30

feed ratioa

actual ratiob

Mn (×10−4 g mol−1)

Mw (×10−4 g mol−1)

PDI

100/0 90/10

100/0 89/11

19.0 12.4

44.9 29.0

2.4 2.3

80/20

80/20

11.8

24.7

2.1

70/30

73/27

11.5

27.4

2.4

90/10

88/12

12.0

26.6

2.2

80/20

82/18

10.5

24.6

2.3

70/30

72/28

9.6

30.4

3.1

a Weight ratio of PCL to PBG/PIS segments in the feed. bActual weight ratio of PCL to PBG/PIS segments determined by 1H NMR.

Figure 2. 1 H NMR spectrum of PCL-b-PIS30.

GPC is also used to determine the molecular weights of all of the multiblock copolyesters, and the results are also listed in E


Research Article


Figure 3. TG (a, b) and DTG (c, d) curves of PCL-b-PBGx and PCL-b-PISx.

PCL-OH in their DSC curves (Figure 4 and Figure S7). The Tms of PCL and HO-PCL-OH are the same, but the ΔHm of HO-PCL-OH is higher than that of neat PCL. Moreover, the Tc and ΔHc of HO-PCL-OH are higher than those of neat PCL. These indicate that the crystallization ability of HO-PCL-OH is higher than that of neat PCL, which is due to the low molecular weight. The two series of multiblock copolyesters retain good crystallization ability even with 30 wt % PBG or PIS units. Their Tc and Tms are almost the same as those of PCL, which is the merit of multiblock copolymers. Owing to their regular sequential structure, each segment can still preserve its own crystallization behavior. It has been well-demonstrated when the third monomer is incorporated into the main chain of PCL to prepare random copolyesters that their Tms are reduced linearly with the increase in the third monomer content.15,16 Considering the low melting point of pure PCL, this modification method via chain extension is more suitable for its further application. Concerning ΔHm, the ΔHm values of these two multiblock copolyesters are lower than those of PCL, especially for PCL-bPISx. The degree of crystallinity (Xc) of the multiblock copolyesters can be calculated according to eq 4

Table 3. Thermal properties of PCL-b-PBGx and PCL-bPISx sample neat PCL PCL-bPBG10 PCL-bPBG20 PCL-bPBG30 PCL-bPIS10 PCL-bPIS20 PCL-bPIS30 a

T5% (°C)

Tmax (°C)

Tc (°C)

ΔHc (J g−1)

Tm (°C)

ΔHm (J g−1)

Tga (°C)

χcb (%)

277 303

302 347

22 20

62.6 51.9

53 52

60.4 47.2

−38 −29

45 39

304

356

19

39.4

52

35.4

−24

33

308

362

21

39.3

53

30.5

−26

32

289

320

21

42.2

53

40.2

−32

33

295

325

19

39.6

53

33.5

−31

29

299

331

18

31.8

51

26.6

−27

28

Determined by DMA. bXc was calculated by DSC.

°C) is even higher than that of HO-PBG-OH (333 °C). Combining these data, it can be concluded the differences of thermal stability between PCL-b-PBGx and PCL-b-PISx are not only caused by the bicyclic structure of these sugar-based segments, the different molecular weights may be the other reason. In all, the thermal stability of PCL is improved considerably when these two glucose-based bicyclic structures are introduced. Thermal Transition and Crystallization Behaviors of Multiblock Copolyesters. Thermal transition behaviors of the two series of multiblock copolymers and hydroxylterminated prepolymers are investigated by DSC. Figure 4 shows the cooling and second heating scans of PCL-b-PBGx and PCL-b-PISx. The detailed data including crystallization temperature (Tc) and crystalline enthalpy (ΔHc), melting temperature (Tm), and melting enthalpy (ΔHm) are listed in Table 3. Neat PCL is a semicrystalline polymer with strong ability to crystallize, even after quenching. We can clearly see the crystallization and melting peaks of neat PCL and HO-

Xc = [ΔHm/wΔHm 0] × 100%

(4)

where ΔHm0 is the melting enthalpy of completely crystalline PCL (135 J g−1),42 and w is the weight fraction of PCL segments. The Xc values of PCL-b-PBGx and PCL-b-PISx as well as PCL are presented in Table 3. It is clear that the Xc value of PCL-b-PBG decreases from 45 to 32% when the content of PBG increases from 0 to 30 wt %. The Xc value of PCL-b-PIS also decreases from 45 to 28% as the content of PIS increases from 0 to 30 wt %. These results illustrate that the incorporation of PBG or PIS into the main chain of PCL depresses the crystallization of PCL, which can be ascribed to their asymmetric structures.43−45 However, the depressing F


Research Article


Figure 4. DSC cooling scans (a, b) and second heating scans (c, d) of PCL-b-PBGx and PCL-b-PISx at a rate of 10 °C/min.

Figure 5. DMA curves of tan δ (left) and storage modulus (right) of (a) PCL-b-PBGx and (b) PCL-b-PISx.

effect of PBG is lower than that of PIS. This phenomenon is also found by other researchers,22,38 i.e., they have found that diacetalized hexitols derived from D-glucitol appear to be more favorable than Is or 2,4:3,5-di-O-methylene-D-mannitol to maintain crystallinity. It is deduced that the glu-diester has great capacity to accommodate in an ordered array of chains.46 However, this explanation still needs to be proven further. It is

well-known that relatively high crystallinity is one of the key factors that leads to the slow degradation rate of PCL. The decrease of the crystallinity of these multiblock copolyesters may enhance the degradation rate of PCL, which will be discussed in a later section. Because of the high crystallinity of PCL and its multiblock copolyesters, we cannot obtain their Tgs from their DSC curves. G


Research Article


Figure 6. (a) Tg value dependence of the content of glucose-based units; (b) WAXD patterns of PCL-b-PBGx and PCL-b-PISx.

Figure 7. Crystalline morphologies of PCL-b-PBGx and PCL-b-PISx.

Thus, DMA is used to investigate how PCL’s Tg varies when these bicyclic glucose-based segments are incorporated. Panels a and b in Figure 5 show the temperature dependence of tan δ and storage modulus for the multiblock copolyesters and neat PCL in which the maximum tan δ temperature stands for the Tg of polymers.47 The obtained Tgs for PCL, PCL-b-PBGx, and PCL-b-PISx are listed in Table 3, and a more intuitive comparison of Tg for the two series of multiblock copolyesters is shown in Figure 6a. As we expected, the incorporation of these rigid bicyclic structures into PCL enhances its Tg. From Table 3, it can be seen that when PBG is incorporated into PCL, the highest temperature of Tg is −24 °C, which is 14 °C higher than that of PCL (−38 °C). When PIS is introduced into PCL, the highest temperature of Tg is −27 °C, which is 11 °C higher than that of PCL. When the same amounts of bicyclic glucose-based segments are introduced, the enhancement effect of PBG is more evident than that of PIS, which is because the stiffness of glu-diester is higher than that of Is, which has a stronger effect on restricting the chain mobility. Moreover, it can be seen that the Tgs of PCL-b-PIS increase with increasing content of PIS, but the Tgs of PCL-b-PBGx first increase with the percentage of PBG increasing until it reaches the maximum value for PCL-bPBG20 and then decreases. For the multiblock copolyesters, the compatibility between each segment will be reflected in their Tgs. From Figure S7, we can see that the Tgs of PIS and PBG are close to 60 and 70 °C, respectively. According to the literature, the Tgs of the PIS and PBG with low molecular weights are 60 and 90 °C, respectively.48,49 The obtained Tg

value of PBG is lower than that reported, which can ascribed to the lower molecular weight of PBG prepolymer in this work. Because their Tgs are higher than the Tm of PCL, only one Tg is shown in the overall studied temperature ranges. Tg results suggest that PIS segments have better compatibility with the PCL segment than with PBG, resulting in a steady rise of their Tgs.50 This will be further demonstrated by their AFM images, which will be discussed in the next section. Concerning the storage modulus, the introduction of PBG and PIS increases the storage modulus of PCL over all of the studied temperature ranges. This means the rigidness of PCL is enhanced as we expected. For the effect of bicyclic glucose-based segments on the crystal structure of PCL to be investigated, WAXD is used along detailed patterns of the copolyesters together with neat PCL (Figure 6b). Neat PCL shows two diffraction peaks at 21.5° and 23.8° corresponding to the (110) and (200) planes.51,52 All of the multiblock copolyesters show the same diffraction peaks as those of neat PCL regardless of the type and amount of glucose-based units, which demonstrates that PBG and PIS are excluded from the crystal region of PCL do not change the crystal structure or lattice of neat PCL. However, their diffraction intensities decrease as the content of the glucose-based structures increases, illustrating that their crystallinity becomes lower. This result is in accordance with DSC results. POM is used to study the crystalline morphologies of PCL-bPBGx, PCL-b-PISx, and neat PCL at 30 °C. The POM images of the copolyesters and the PCL are presented in Figure 7 and H


Research Article


Figure 8. AFM phase (top) and height images (bottom) of the multiblock copolyesters.

Tensile Properties. The mechanical properties of polymers are important for their practical usage. Because of its relatively low stiffness, the application of PCL is limited. When these two bicyclic glucose-based units are introduced into the PCL main chain, they show different effects on the mechanical properties of PCL (Table 4; stress−strain curves shown in Figure S10).

Figure S8, respectively. All of the multiblock copolyesters clearly show the characteristic “Maltese Cross” extinction patterns of spherulites. As the content of the glucose-based units increases, the sizes of the spherulites increase gradually. The regularity of obtained copolyseters declines when more glucose-based units are introduced, resulting in the reduction of nucleation density.34,53 The lower nucleation density leads to larger spherulites. As far as PCL-b-PBGx and PCL-b-PISx are concerned, the spherulite size of PCL-b-PISx is always bigger than that of PCL-b-PBGx with the same glucose-based segments. This demonstrates again that PIS retards the crystallization of PCL more severely than that of PBG, which is consistent with the results of DSC and WAXD. Microphase Separation of the Multiblock Copolyesters. From the results of DMA, it is found that the Tgs of PCLb-PISx continuously increase as the content of PIS increases. However, the Tgs of PCL-b-PBGx show maximum values for PCL-b-PBG20 and then drop. Because the Tgs of pure PIS and PBG are higher than the Tg of PCL, this phenomenon indicates the compatibility of PBG with the PCL segment is poorer than that of PIS. For this to be demonstrated further, the microphase separation of each block in the multiblock copolyesters is investigated by AFM in tapping mode. The phase (top) and height images (bottom) of neat PCL, PCL-b-PBG30, as well as PCL-b-PIS30 are shown in Figure 8. The AFM images for the other copolyesters are shown in Figure S9. The phase image of neat PCL is uniform, whereas after the introduction of PBG and PIS, the phase images of the multiblock copolyesters have changed, and two phase structures can be clearly seen. These indicate that microphase separation happens in the multiblock copolyesters. The detailed surface roughness can be obtained from their height images. The surface roughnesses for PCL, PCL-b-PIS30, and PCL-b-PBG30 are 2.90, 6.29, and 7.03 nm, respectively. These suggest that the microphase separation in PCL-b-PBG30 is more severe than that in PCL-b-PIS30. In other words, the segment compatibility of PIS with PCL is better than that of PBG with PCL, which is consistent with the results of DMA.

Table 4. Mechanical Properties of PCL-b-PBGx and PCL-bPISx sample neat PCL PCL-bPBG10 PCL-bPBG20 PCL-bPBG30 PCL-bPIS10 PCL-bPIS20 PCL-bPIS30

yield stress (MPa)

ultimate stress (MPa)

elongation at break (%)

Young’s modulus (MPa)

19.9 ± 0.8 17.1 ± 0.8

27.9 ± 4.4 20.8 ± 1.1

869 ± 244 553 ± 60

380 ± 31 383 ± 71

23.2 ± 1.1

23.7 ± 0.2

269 ± 85

513 ± 7

20.0 ± 0.3

20.1 ± 0.3

233 ± 106

409 ± 96

19.2 ± 0.4

36.5 ± 1.0

1303 ± 39

386 ± 9

21.4 ± 0.9

29.7 ± 2.3

618 ± 81

516 ± 38

27.4 ± 7.4

32.1 ± 1.8

564 ± 35

492 ± 19

Although the stiffness of glu-diester is higher than that of Is, the yield stress of PCL-b-PBG20 is only slightly higher than that of neat PCL, which is only increased by 17%. Their ultimate stress is lower than that of PCL. However, the consequence of the incorporation of PIS is more positive, as both the yield stress and ultimate stress are improved. When the content of PIS is 30 wt %, the yield stress of PCL-b-PIS reaches the maximum (27.4 MPa), which increases by 38% compared to that of neat PCL. Because of the stiffnesses of the two bicyclic structures, the Young’s modulus of PCL is increased with the insertion of the two glucose-based units, especially when the content of the two glucose-based bicyclic units is 20 wt %. Their Young’s moduli increase by 35 and 36%, respectively, compared to that of neat PCL. The elongation at break of PCL-b-PBGx or PCL-b-PISx is I


Research Article


lization of PCL, and the depressing effect is more serious for PCL-b-PISx. The two series of multiblock copolyesters do not change the crystal structure and Tm of PCL over the entire composition. Because of the rigid nature of the two bicyclic glucose-based units, storage modulus and Young’s modulus of PCL are enhanced. As we know, many factors influence the mechanical properties of polymers; thus, in this work, the effect of improving the tensile strength of PCL by these two glucosebased units is not apparent. Comparatively speaking, the mechanical properties of PCL-b-PISx are better than those of PCL-b-PBGx, which can be due to the good compatibility of PIS with the PCL block. Moreover, PCL becomes more hydrophilic with the augmentation of glucose-based units in which PCL-b-PBGx show higher hydrophilicity than that of PCL-b-PISx. In brief, although Is and glu-diester are both glucose-based derivatives, they have different effects on improving the performances of PCL due to their different bicyclic structures.

lower than that of PCL, except for PCL-b-PIS10. Considering that all the values of the elongation at break are higher than 200%, it can be confirmed that these multiblock copolyesters retain excellent toughness. It is well-known that the mechanical properties of polymer materials are affected by many factors, such as chain structure, crystallinity, phase morphology, compatibility, and so forth. Although the introduction of the two glucose-based bicyclic structures increases the stiffness of the chains, the crystallinity of PCL decreases. This means the improving stiffness effect is not desirable as we expected. Comparatively speaking, the mechanical properties of PCL-bPISx are better than those of PCL-b-PBGx, which can be due to the good compatibility of PIS with the PCL block. Hydrophilicity of Multiblock Copolyesters. The hydrophilicity is one of the key factors deciding the biodegradability and biocompatibility of materials.54 As we know, PCL is hydrophobic and has a very low biodegradation rate. The hydroxyl-terminated prepolymers of PBG and PIS are both hydrophilic in which PBG is more hydrophilic than PIS (shown in Figure S11). Thus, these multiblock copolyesters will be more hydrophilic than PCL. The water contact angles of PCLb-PBGx and PCL-b-PISx are measured, and the results are shown in Figure 9. As we expected, the water contact angles of

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b01263. Synthetic procedures of glu-diester; 1H and 13C NMR spectra of glu-diester; 1H NMR spectra of HO-PBG-OH, HO-PIS-OH, and HO-PCL-OH; TG and DTG curves of HO-PBG-OH and HO-PIS-OH; DSC curves of HOPCL-OH, HO-PBG-OH, and HO-PIS-OH; crystalline morphologies of neat PCL; AFM phase and height images of PCL-b-PBG10, PCL-b-PBG20, PCL-b-PIS10, and PCL-b-PIS20; water contact angles of HO-PBG-OH and HO-PIS-OH; and hydrolytic degradation curves of PCL-b- PBGx and PCL-b-PISx (PDF)

■

AUTHOR INFORMATION

Corresponding Authors

Figure 9. Water contact angles of PCL-b-PBGx and PCL-b-PISx.

*Tel./fax: +86-28-85410755. E-mail: [email protected]. *E-mail: [email protected].

copolyesters continuously decrease with the increase in the bicyclic glucose-based unit content. The water contact angles of PCL-b-PBG30 and PCL-b-PIS30 decrease from 92° of neat PCL to 77° and 79°, respectively. The increasing hydrophilicity effect is more pronounced for PBG due to its higher hydrophilicity. The increased hydrophilicity and decreased crystallinity will have a positive impact on accelerating the hydrolytic degradation rate of PCL. The hydrolytic degradation test is only carried out for 6 weeks, and the weight loss for all copolyesters is not large. However, from their degradation curves, it can be seen clearly that the weight loss of copolyesters is faster than that of pure PCL (Figure S12).

ORCID

Xiu-Li Wang: 0000-0002-2732-9477 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was financially supported by the National Key R&D Program of China (2016YFB0302102), National Natural Science Foundation of China (51573104), and the Sichuan Province Youth Science and Technology Innovation Team (No. 2017TD0006).

■

■

CONCLUSIONS In summary, two kinds of glucose-based units with bicyclic structures have been successfully incorporated into PCL through chain extension with HDI as a chain extender. With the introduction of the two glucose-based bicyclic structures, the thermal stability and Tg of PCL have been improved, and this effect is more apparent for the copolyester containing gludiester. Because of the relatively regular structures of block copolymers, the Tm of PCL has been well maintained. The introduction of these sugar-based units retards the crystal-

REFERENCES

(1) Goonasekera, C. S.; Jack, K. S.; Cooper-White, J. J.; Grøndahl, L. Dispersion of hydroxyapatite nanoparticles in solution and in polycaprolactone composite scaffolds. J. Mater. Chem. B 2016, 4, 409−421. (2) Park, J. H.; Kang, H. J.; Kwon, D. Y.; Lee, B. K.; Lee, B.; Jang, J. W.; Chun, H. J.; Kim, J. H.; Kim, M. S. Biodegradable poly(lactide-coglycolide-co-ε-caprolactone) block copolymers-evaluation as drug carriers for a localized and sustained delivery system. J. Mater. Chem. B 2015, 3, 8143−8153.

J


Research Article

ACS Sustainable Chemistry & Engineering (3) Wang, X. L.; Huang, F. Y.; Zhou, Y.; Wang, Y. Z. Nonisothermal crystallization kinetics of poly(ε-caprolactone)/montmorillonite nanocomposites. J. Macromol. Sci., Part B: Phys. 2009, 48, 710−722. (4) Mondal, D.; Griffith, M.; Venkatraman, S. S. Polycaprolactonebased biomaterials for tissue engineering and drug delivery: Current scenario and challenges. Int. J. Polym. Mater. 2016, 65, 255−265. (5) Woodruff, M. A.; Hutmacher, D. W. The return of a forgotten polymer-Polycaprolactone in the 21st century. Prog. Polym. Sci. 2010, 35, 1217−1256. (6) Gao, X.; Wang, B. L.; Wei, X. W.; Rao, W.; Ai, F.; Zhao, F.; Men, K.; Yang, B. W.; Liu, X. Y.; Huang, M. J.; Gou, M. L.; Qian, Z. Y.; Huang, N.; Wei, Y. Q. Preparation, characterization and application of star-shaped PCL/PEG micelles for the delivery of doxorubicin in the treatment of colon cancer. Int. J. Nanomed. 2013, 8, 971−982. (7) Wang, Y. Z.; Hao, J. G.; Li, Y. J.; Zhang, Z. W.; Sha, X. Y.; Han, L. M.; Fang, X. L. Poly(caprolactone)-modified Pluronic P105 micelles for reversal of paclitaxcel-resistance in SKOV-3 tumors. Biomaterials 2012, 33, 4741−4751. (8) Labet, M.; Thielemans, W. Synthesis of polycaprolactone: a review. Chem. Soc. Rev. 2009, 38, 3484−3504. (9) Chen, J. X.; Lu, L. L.; Wu, D. F.; Yuan, L. J.; Zhang, M.; Hua, J. J. Green poly(ε-caprolactone) composites reinforced with electrospun polylactide/poly(ε-caprolactone) blend fiber mats. ACS Sustainable Chem. Eng. 2014, 2, 2102−2110. (10) Nair, L. S.; Laurencin, C. T. Biodegradable polymers as biomaterials. Prog. Polym. Sci. 2007, 32, 762−798. (11) Doppalapudi, S.; Jain, A.; Khan, W.; Domb, A. J. Biodegradable polymers-an overview. Polym. Adv. Technol. 2014, 25, 427−435. (12) Ludueña, L. N.; Stocchi, A.; Alvarez, V. A. Fracture behavior of polycaprolactone/ clay nanocomposites. J. Compos. Mater. 2016, 50 (27), 3863−3872. (13) Mallakpour, S.; Nouruzi, N. Modification of morphological, mechanical, optical and thermal properties in polycaprolactone-based nanocomposites by the incorporation of diacidmodified ZnO nanoparticles. J. Mater. Sci. 2016, 51, 6400−6410. (14) Machado, A. V.; Amorim, S.; Botelho, G.; Neves, I. C.; Fonseca, A. M. Nanocomposites of poly(ε-caprolactone) doped with titanium species. J. Mater. Sci. 2013, 48, 3578−3585. (15) Seretoudi, G.; Bikiaris, D.; Panayiotou, C. Synthesis, characterization and biodegradability of poly(ethylene succinate)/poly(εcaprolactone) block copolymers. Polymer 2002, 43, 5405−5415. (16) Papadimitriou, S.; Bikiaris, D. N.; Chrissafis, K.; Paraskevopoulos, K. M.; Mourtas, S. Synthesis, characterization, and thermal degradation mechanism of fast biodegradable PPSu/PCL copolymers. J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 5076−5090. (17) Cao, A.; Okamura, T.; Ishiguro, C.; Nakayama, K.; Inoue, Y.; Masuda, T. Studies on syntheses and physical characterization of biodegradable aliphatic poly(butylene succinate-co-ε-caprolactone)s. Polymer 2002, 43, 671−679. (18) Wang, C. H.; Tsai, P. H.; Kan, L. S.; Chen, C. W. Synthesis and Characterization of Copolymeric Aliphatic−Aromatic Esters Derived from Terephthalic Acid, 1,4-Butanediol, and ε-Caprolactone by Physical, Thermal, and Mechanical Properties, and NMR Measurements. J. Appl. Polym. Sci. 2013, 127, 4385−4394. (19) González-Vidal, N.; Martínez de Ilarduya, A.; Herrera, V.; Muñoz-Guerra, S. Poly(hexamethylene terephthalate-co-caprolactone) Copolyesters Obtained by Ring-Opening Polymerization. Macromolecules 2008, 41, 4136−4146. (20) Yao, K.; Wang, J.; Zhang, W.; Lee, J. S.; Wang, C.; Chu, F.; He, X.; Tang, C. Degradable Rosin-Ester-Caprolactone Graft Copolymers. Biomacromolecules 2011, 12, 2171−2177. (21) Gioia, C.; Banella, M. B.; Marchese, P.; Vannini, M.; Colonna, M.; Celli, A. Advances in the synthesis of bio-based aromatic polyesters: novel copolymers derived from vanillic acid and εcaprolactone. Polym. Chem. 2016, 7, 5396−5406. (22) Lavilla, C.; Gubbels, E.; Martínez de Ilarduya, A.; Noordover, B. A. J.; Koning, C. E.; Muñoz-Guerra, S. Solid-State Modification of PBT with Cyclic Acetalized Galactitol and D-Mannitol: influence of

composition and chemical microstructure on thermal properties. Macromolecules 2013, 46, 4335−4345. (23) Duan, R. T.; Dong, X.; Li, D. F.; Wang, X. L.; Wang, Y. Z. Preparation and properties of bio-based PBS multiblock copolyesters contanining isosorbide units. Acta polymerica sinica. 2016, 1, 70−77. (24) Zhang, Z. C.; Kricheldorf, H. R.; Friedrich, C. Thermorheological and Mechanical Properties of Copolymers of Lactide, Isosorbide, and Different Phthalic Acids. Macromol. Rapid Commun. 2015, 36, 262−268. (25) Wu, J.; Eduard, P.; Jasinska-Walc, L.; Rozanski, A.; Noordover, B. A. J.; van Es, D. S.; Koning, C. E. Fully Isohexide-Based Polyesters: Synthesis, Characterization, and Structure−Properties Relations. Macromolecules 2013, 46, 384−394. (26) Gioia, C.; Vannini, M.; Marchese, P.; Minesso, A.; Cavalieri, R.; Colonna, M.; Celli, A. Sustainable polyesters for powder coating applications from recycled PET, isosorbide and succinic acid. Green Chem. 2014, 16, 1807−1815. (27) Feng, L.; Zhu, W.; Li, C.; Guan, G.; Zhang, D.; Xiao, Y.; Zheng, L. A high-molecular-weight and high-Tg poly(ester carbonate) partially based on isosorbide: synthesis and structure−property relationships. Polym. Chem. 2015, 6, 633−642. (28) Garaleh, M.; Yashiro, T.; Kricheldorf, H. R.; Simon, P.; Chatti, S. Co-)Polyesters Derived from Isosorbide and 1,4-Cyclohexane Dicarboxylic Acid and Succinic Acid. Macromol. Chem. Phys. 2010, 211, 1206−1214. (29) Lavilla, C.; Martínez de Ilarduya, A.; Alla, A.; García-Martín, M. G.; Galbis, J. A.; Muñoz-Guerra, S. Bio-Based Aromatic Polyesters from a Novel Bicyclic Diol Derived from D-Mannitol. Macromolecules 2012, 45, 8257−8266. (30) Japu, C.; Martínez de Ilarduya, A.; Alla, A.; Jiang, Y.; Loos, K.; Muñoz-Guerra, S. Copolyesters Made from 1,4-Butanediol, Sebacic Acid, and D-Glucose by Melt and Enzymatic Polycondensation. Biomacromolecules 2015, 16, 868−879. (31) Lavilla, C.; Alla, A.; Martínez de Ilarduya, A.; Benito, E.; GarciaMartin, M. G.; Galbis, J. A.; Muñoz-Guerra, S. Carbohydrate-Based Polyesters Made from Bicyclic Acetalized Galactaric Acid. Biomacromolecules 2011, 12, 2642−2652. (32) Lavilla, C.; Gubbels, E.; Alla, A.; Martinez de Ilarduya, A.; Noordover, B. A. J.; Koning, C. E.; Muñoz-Guerra, S. Carbohydratebased PBT copolyesters from a cyclic diol derived from naturally occurring tartaric acid: a comparative study regarding melt polycondensation and solid-state modification. Green Chem. 2014, 16, 1789−1798. (33) Japu, C.; Alla, A.; Martinez de Ilarduya, A.; García-Martín, M. G.; Benito, E.; Galbis, J. A.; Muñoz-Guerra, S. Bio-based aromatic copolyesters made from 1,6-hexanediol and bicyclic diacetalized Dglucitol. Polym. Chem. 2012, 3, 2092−2101. (34) Mehltretter, C. L.; Mellies, R. L.; Rist, C. E.; Hilbert, G. E. Dimethylene-D-gluconic Acid. J. Am. Chem. Soc. 1947, 69, 2130−2131. (35) Mehltretter, C. L.; Mellies, R. L.; Rist, C. E. Methyl 2,4:5,6dimethylene-D-gluconate. J. Am. Chem. Soc. 1948, 70, 1064−1067. (36) Li, S. L.; Wu, F.; Wang, Y. Z.; Zeng, J. B. Biobased Thermoplastic poly(ester urethane) Elastomers Consisting of Poly(butylene succinate) and Poly(propylene succinate). Ind. Eng. Chem. Res. 2015, 54, 6258−6268. (37) Li, S. L.; Zeng, J. B.; Wu, F.; Yang, Y.; Wang, Y. Z. Succinic Acid Based Biodegradable Thermoplastic Poly(ester urethane) Elastomers: Effects of Segment Ratios and Lengths on Physical Properties. Ind. Eng. Chem. Res. 2014, 53, 1404−1414. (38) Lavilla, C.; Muñoz-Guerra, S. Sugar-based aromatic copolyesters: a comparative study regarding isosorbide and diacetalized alditols as sustainable comonomers. Green Chem. 2013, 15, 144−151. (39) Noordover, B. A. J.; van Staalduinen, V. G.; Duchateau, R.; Koning, C. E.; van Benthem, R. A. T. M.; Mak, M.; Heise, A.; Frissen, A. E.; van Haveren, J. Co- and Terpolyesters Based on Isosorbide and Succinic Acid for Coating Applications: Synthesis and Characterization. Biomacromolecules 2006, 7, 3406−3416. (40) Yoon, W. J.; Oh, K. S.; Koo, J. M.; Kim, J. R.; Lee, K. J.; Im, S. S. Synthesis and characteristics of a biobased high-Tg terpolyester of K


Research Article

ACS Sustainable Chemistry & Engineering isosorbide, ethylene glycol, and 1,4-cyclohexane dimethanol: effect of ethylene glycol as a chain linker on polymerization. Macromolecules 2013, 46, 2930−2940. (41) Liu, F.; Qiu, J.; Wang, J. G.; Zhang, J. W.; Na, H. N.; Zhu, J. Role of cis-1,4-cyclohexanedicarboxylic acid in the regulation of the structure and properties of a poly(butylene adipate-co-butylene 1,4cyclohexanedicarboxylate) copolymer. RSC Adv. 2016, 6, 65889− 65897. (42) Wang, S. F.; Lu, L. C.; Gruetzmacher, J. A.; Currier, B. L.; Yaszemski, M. J. A biodegradable and cross-linkable multiblock copolymer consisting of poly(propylene fumarate) and poly(εcaprolactone): synthesis, characterization, and physical properties. Macromolecules 2005, 38, 7358−7370. (43) Tan, L. C.; Chen, Y. W.; Zhou, W. H.; Wei, J. C.; Ye, S. W. Synthesis of Novel Biodegradable Poly(butylene succinate) Copolyesters Composing of Isosorbide and Poly(ethylene glycol). J. Appl. Polym. Sci. 2011, 121, 2291−2300. (44) Zakharova, E.; Alla, A.; Martínez de Ilarduya, A.; MuñozGuerra, S. Bio-based PBS copolyesters derived from a bicyclic Dglucitol. RSC Adv. 2015, 5, 46395−46404. (45) Duan, R. T.; He, Q. X.; Dong, X.; Li, D. F.; Wang, X. L.; Wang, Y. Z. Renewable sugar-based diols with different rigid structure: comparable investigation on improving poly(butylene succinate) performance. ACS Sustainable Chem. Eng. 2016, 4, 350−362. (46) Zakharova, E.; Martínez de Ilarduya, A.; León, S.; MuñozGuerra, S. Sugar-based bicyclic monomers for aliphatic polyesters: a comparative appraisal of acetalized alditols and isosorbide. Des. Monomers Polym. 2017, 20, 157−166. (47) Can, E.; Bucak, S.; KInaci, E.; Ç alikoğlu, A. C.; Köse, G. T.; Gamze, T. Polybutylene succinate (PBS)-polycaprolactone(PCL) blends compatibilized with poly(ethylene oxide)-block-poly(propylene oxide)-blockpoly(ethylene oxide) (PEO-PPO-PEO) copolymer for biomaterial applications. Polym.-Plast. Technol. Eng. 2014, 53, 1178− 1193. (48) Casarano, R.; Bentini, R.; Bueno, V. B.; Iacovella, T.; Monteiro, F. B. F.; Iha, F. A. S.; Campa, A.; Petri, D. F. S.; Jaffe, M.; Catalani, L. H. Enhanced fibroblast adhesion and proliferation on electrospun fibers obtained from poly(isosorbide succinate-b-L-lactide) block copolymers. Polymer 2009, 50, 6218−6227. (49) Japu, C.; Martínez de Ilarduya, A.; Alla, A.; García-Martín, M. A. G.; Galbis, J. A.; Muñoz-Guerra, S. Bio-based PBT copolyesters derived from D-glucose: influence of composition on properties. Polym. Chem. 2014, 5, 3190−3202. (50) Wu, C. S. Preparation and characterization of a polycaprolactone/C60 composite and its improved counterpart (PCL-NH2/C60OH). J. Appl. Polym. Sci. 2010, 115, 3489−3499. (51) Narayanan, G.; Aguda, R.; Hartman, M.; Chung, C. C.; Boy, R.; Gupta, B. S.; Tonelli, A. E. Fabrication and characterization of poly(εcaprolactone)/α-cyclodextrin pseudorotaxane nanofibers. Biomacromolecules 2016, 17, 271−279. (52) Li, K.; Huang, J. C.; Gao, H. C.; Zhong, Y.; Cao, X. D.; Chen, Y.; Zhang, L. N.; Cai, J. Reinforced mechanical properties and tunable biodegradability in nanoporous cellulose gels: poly(L-lactide-cocaprolactone) nanocomposites. Biomacromolecules 2016, 17, 1506− 1515. (53) Li, S. L.; Wu, F.; Yang, Y.; Wang, Y. Z.; Zeng, J. B. Synthesis, characterization and isothermal crystallization behavior of poly(butylene succinate)-b-poly(diethylene glycol succinate) multiblock copolymers. Polym. Adv. Technol. 2015, 26, 1003−1013. (54) Yilgör, E.; Isik, M.; Kosak Söz, C.; Yilgör, I. Synthesis and structure-property behavior of polycaprolactone-polydimethylsiloxane -polycaprolactone triblock copolymers. Polymer 2016, 83, 138−153.

L


Novel Multiblock Poly(Îµ-caprolactone) Copolyesters Containing D

Recommend Documents