Structural and property modulation of cyclohexanedimethanol-based polycarbonates by bio-based tetrahydrofuran dimethanol with cyclic ether structures
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摘要: 1, 4-环己烷二甲醇基聚碳酸酯具有优异的热力学性能,但因其降解性能的影响,商业应用受到极大的限制。向其分子链中引入脂肪族单元可以有效提高降解能力,但却以牺牲其热力学性能为代价。因此,为了维持热力学与降解性能间的平衡,本文以具有环醚刚性的生物基2, 5-四氢呋喃二甲醇(THFDM)为改性单元,采用熔融酯交换缩聚法成功制备了高分子量聚(碳酸1, 4-环己烷二甲醇酯-co-碳酸2, 5-四氢呋喃二甲醇酯) (PCThC)共聚物。通过NMR图谱探究共聚物的组成和微观结构,证实了共聚物组分间的无规分布;DSC和WAXD图谱结果表明,THFDM单元的引入破坏了PCThC分子链的规整排列,使其结晶能力降低,共聚物从半结晶型过渡到无定型。THFDM中的刚性环结构有效阻止了共聚物玻璃转化温度(Tg)的快速下降,保持其较好的热稳定性;THFDM分子中的环结构赋予了聚合物更高的刚度,提高了聚合物的力学性能;此外,THFDM中的醚键改善了PCThC共聚物的亲水性,加快了水解速率,不论是在酸性或碱性缓冲溶液中,共聚物均表现出一定的降解能力。Abstract: 1, 4-cyclohexanedimethanol-based polycarbonates have desired thermodynamic property yet poor degradation capability. Introducing aliphatic units into the molecular chains could effectively improve the degradability at the severe expense of thermodynamic properties. For this reason, biobased 2, 5-tetrahydrofurandimethanol (THFDM) with cyclic ether rigidity was selected as the modification unit and poly(1, 4-cyclohexyldimethylene-co-2,5-tetrahydrofurandimethanol carbonate) (PCThC) copolymers with higher molecular weights were synthesized via melt ester exchange polycondensation method. The composition and microstructure were investigated by NMR, which confirmed the random distribution among the copolymer components. DSC and WAXD results reveals that the introduction of THFDM units break the regular arrangement of the molecular chains in PCThCs, reduce the crystallisation ability, which promote the transition from the semi-crystalline to amorphous. Furthermore, the rigid ring structure in THFDM prevents the rapid declination of glass transition temperature (Tg) and keeps the good thermal stability. The ring structure in the THFDM endow higher stiffness and better mechanical performance for the polymer. The ether bonds in THFDM enhance the hydrophilicity of the PCThC copolymers, resulting in a gradual acceleration of the hydrolysis rate. The copolymers exhibit pleasant degradation ability either under acidic or alkaline environment.
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表 1 聚(碳酸1, 4-环己烷二甲醇酯) (PCC)、聚(碳酸2, 5-四氢呋喃二甲醇酯) (PThC)和PCThC共聚物的分子量和特性黏度
Table 1. Molecular weights and characteristic viscosities of poly(1, 4-cyclohexyldimethylene carbonate) (PCC), poly(2, 5-tetrahydrofurandimethanol carbonate) (PThC), and PCThC copolymers
Sample Mn/(g·mol−1) Mw/(g·mol−1) Ð [η]/(dL·g−1) PCC 33500 50000 1.49 0.94 PC95Th5C 42700 65400 1.53 1.10 PC90Th10C 50500 76100 1.51 1.49 PC85Th15C 47600 72400 1.52 1.30 PC70Th30C 41500 68500 1.65 1.19 PC55Th45C 41300 60200 1.46 1.03 PC40Th60C 40500 64300 1.59 1.09 PThC 7300 10700 1.46 0.64 Notes: Mn and Mw—Number average molecular weight and weight average molecular weight of the polymer; ЗMolecular weight distribution; [η]—Characteristic viscosity; PCyThxC—x and y represent the molar feed ratios of THFDM and CHDM to diols, respectively; CHDM—1, 4-cyclohexanedimethanol; THFDM—2,5-tetrahydrofurandimethanol. 表 2 PCC、PThC和PCThC共聚物的组成
Table 2. Composition of PCC, PThC, and PCThC copolymers
Sample ThC unit in feedsa ThC unit in polymersb LnCC LnThC R PCC 0 0 — — — PC95Th5C 0.05 0.03 27.70 1.05 0.99 PC90Th10C 0.10 0.09 8.36 1.07 1.05 PC85Th15C 0.15 0.13 5.91 1.14 1.05 PC70Th30C 0.30 0.22 5.16 1.22 1.01 PC55Th45C 0.45 0.33 3.97 1.28 1.03 PC40Th60C 0.60 0.52 2.71 1.42 1.07 PThC 1 1 — — — Notes: a—Molar fraction of THFDM in the diol (CHDM+THFDM) feed; b—Molar fraction of ThC units in PCThC copolymers calculated by 1H NMR spectroscopy; LnCC and LnThC —Average sequence lengths of CC and ThC units; R—Randomness. 表 3 PCC、PThC和PCThC共聚物的热性能参数
Table 3. Thermal property parameters of PCC, PThC, and PCThC copolymers
Sample Tg/℃ Tm/℃ ΔHm/(J·g−1) Td,5%/℃ Td,max/℃ Xc/% PCC 51.6 137.7 21.6 368 418 27.7 PC95Th5C 50.3 136.6 18.1 367 410 17.7 PC90Th10C 48.7 — — 369 414 — PC85Th15C 46.7 — — 363 414 — PC70Th30C 44.8 — — 361 412 — PC55Th45C 42.6 — — 328 408 — PC40Th60C 34.9 — — 321 409 — PThC 25.3 — — 320 401 — Notes: Tg and Tm—Glass transition temperature and melting temperature; ΔHm—Enthalpy of melting; Td,5% and Td,max —Decomposition temperature at 5wt% mass loss and the maximum decomposition rate; Xc—Degree of crystallinity. 表 4 PCC、PThC和PCThC共聚物的力学性能参数
Table 4. Mechanical property parameters of PCC, PThC, and PCThC copolymers
Sample E/MPa σb/MPa εb/% PCC 351±15 29.5±1.8 174±24 PC95Th5C 511±30 49.6±3.4 137±13 PC90Th10C 515±27 46.2±2.2 127±16 PC85Th15C 570±32 22.4±1.1 114±7 PC70Th30C 501±23 29.7±2.5 159±21 PC55Th45C 514±17 28.5±1.2 284±16 PC40Th60C 93±25 8.1±0.2 261±34 PThC 8±2 1.0±0.1 445±43 Notes: E—Young's modulus; σb—Tensile strength; εb—Elongation at break. -
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