Unveiling chain–chain interactions in CO2-based crystalline stereocomplexed polycarbonates by solid-state NMR spectroscopy and DFT calculations

CO2-based stereocomplexed polycarbonates derived from the intermolecularly interlocked interaction between the enantiopure polymers with the opposite configuration exhibit high crystallinity, excellent thermal and mechanical stabilities. Deep insights into the mechanism of stereocomplexation are of particular importance to the design and manufacture of new promising and sustainable polycarbonates with enhanced physicochemical properties. Our solid-state NMR experiments linking with DFT computations clearly reveal the specific chain-chain interactions in a typical stereocomplexed poly（4,4-dimethyl-3,5,8-trioxabicyclo[5.1.0] octane carbonate）（PCXC）.13C CP/MAS NMR,1H DUMBO MAS NMR and 13C/1H relaxation-time measurements indicate that the formation of stereocomplex reduces the local mobilities of carbonyl, methine and methylene groups in each chain of PCXC significantly. Through a combination of two-dimensional 1H-13C HETCOR NMR and DFT calculation analysis, the cis-/trans-conformations and packing models of PCXC chains in the amorphous, enantionpure isotactic and stereocomplexed polycarbonates are identified. The splitting of 13C and 1H NMR chemical shifts of methine groups in the backbone carbon region demonstrates the ordered interlock interactions between the R-and S-chain in the stereocomplexed PCXC.

Stereocomplex Formation of Atactic Poly(methyl mcthacrylate)

Stereocomplexes formed in atactic poly(methyl methacrylatc) (α-PMMA) films cast form different solvents were studied by means of Fourier transform infrared spectroscopy (FTIR). and differential scanning calorimetry (DSC). The growth of stereocomplex was a function of annealing temperature and annealing time. respectively.

A Facile Strategy to Enhance the Formation of Stereocomplex Crystallites in Poly(L-lactic acid)/Poly(D-lactic acid) Blend with High Molecular Weights

Blending of poly(levorotatory-lactic acid) (PLLA) and poly(dextrorotatory-lactic acid) (PDLA) produces the stereocomplex crystallites (PLA SC), which present higher melting temperature and mechanical properties than that of neat PLLA or PDLA. However, in the PLLA/PDLA blends with higher molecular weights, the phase separation occurs and the SC exhibits weak memory after melting, which lead to a small amount of SC together with a large amount of homochiral crystallites (HC) develop during crystallization from the melt. In this study, a small content of graphite oxide was blended with PLLA and PDLA to form ternary blends, and it was exciting to find that the formation of SC was enhanced gradually with the content of graphite oxide. The SC exclusively developed when 2 wt% graphite oxide was incorporated into the PLLA/PDLA, and the crystallinity with ∼50% was received even during fast cooling from the melt (−50 ℃/min). The acceleration formation of SC was speculated due to the interaction between PLA molecular chains and the hydroxyl groups on the surface of graphite oxide and the obstruction of proliferation of graphite oxide.

Significantly Improved Stereocomplexation Ability in Cyclic Block Copolymers

Stereocomplex crystallization in cyclic polymer blend and cyclic block copolymers was investigated by means of dynamic Monte Carlo simulations.Five polymer systems(linear polymer blend,linear diblock copolymer,cyclic polymer blend,cyclic diblock copolymer and tetrablock copolymer)were established.It was interestingly found that the cyclic polymer blend exhibited the weakest stereocomplexation ability,while the two cyclic block copolymers showed stronger stereocomplexation ability than the linear diblock copolymer.This abnormal improved stereocomplexation ability of the cyclic block copolymers can be attributed to the synergy between the ring chain topology and the block copolymer structure.Compared with the linear block copolymers,the ring chain topology confined segmental motions of cyclic polymer chains to smaller regions,and then the segments belonging to the different blocks in the cyclic block copolymers have more chance to contact with each other.In this way,the cyclic block copolymers had better miscibility between segments belonging to different types of blocks,leading to the stronger stereocomplexation ability.

立构复合聚乳酸的制备专利研究进展

立构复合聚乳酸是其对映异构体左旋聚乳酸(PLLA)链段和右旋聚乳酸(PDLA)链段形成的具有螺旋互补结构的络合物,具有可降解、熔点高、耐水解性强、力学性能优异等特点。对专利申请中涉及制备立构复合聚乳酸的方法进行分类总结,统计各制备立构复合聚乳酸的制备专利申请量随申请年的变化,阐述目前制备立构复合聚乳酸研究的重点及未来研发方向。

高取向立构复合化聚乳酸超细纳米纤维膜的制备及长效驻极与滤除PM_(0.3)性能

利用聚L-乳酸(PLLA)和聚D-乳酸(PDLA)链之间建立的立构复合产生强的分子间相互作用,并通过高压电场极化和高倍取向拉伸赋予聚乳酸(PLA)纳米纤维高的取向和细化,同时促进电活性相(β相、立构复合晶)的形成.得益于高取向的纤维形貌和优异的电活性,高取向立构复合化PLA(AS-PLA)纳米纤维膜的介电常数和表面电位分别高达1.68和5.4 kV.同时,AS-PLA纳米纤维膜表现出卓越的过滤性能和摩擦电性能,特别是PDLA添加量为40%时制备的PLLA/PDLA40纳米纤维膜,即使在85 L/min的高气流量下对超细空气颗粒物(PM_(0.3))的滤除效率仍达到90.51%,且空气阻力仅为240.6 Pa,明显优于纯PLA纤维膜(滤除效率80.34%,空气阻力251.4 Pa).此外,在高湿度(RH=70%)和高强度呼吸气流(85 L/min)条件下,由AS-PLA纳米纤维膜作为摩擦电活性层组装的摩擦纳米发电机(TENG)过滤器仍显示出优异的PM_(0.3)去除效率,达到95.02%,远远超过普通PLA过滤器(去除效率仅为89.50%),表现出强的电荷再生能力.电活性的提高显著改善了纳米纤维膜的初始极化能力和摩擦电性能,在保证纤维膜初始电荷充足的同时可依赖摩擦电效应实现电荷再生,在不牺牲空气阻力的前提下实现长效过滤.

立构复合化聚乳酸纳纤膜的制备及高效滤除PM_(2.5)性能

聚乳酸(PLA)纳米纤维在环境友好型纤维过滤材料领域有良好的应用前景,但受制于其本征螺旋分子链构象和低介电常数的不足,导致其驻极性能差、过滤性能(过滤效率及压降)易衰减以及有效服役周期短.本文将高旋光性的聚L-乳酸(PLLA)和聚D-乳酸(PDLA)溶液共混,并通过静电纺丝过程的高压静电场诱导C=O基团加速取向极化,形成高电活性的立构复合晶体(SCs),显著提高聚乳酸纳纤膜的表面电位、介电常数及驻极效果等电活性特征,增大纤维表面静电斥力,促进PLA纳纤膜(PLA NFMs)的纤维细化,从而使其压降大幅降低(85 L/min,209.2 Pa),过滤PM_(2.5)效率显著提高至96.32%(纯PLLA对比样为72.44%).更重要的是,立构复合化PLA纳纤膜(SC-PLA NFMs)的过滤性能受气体流量变化影响较小(10~85 L/min),当气流增大时,过滤效率的衰减远远低于纯PLLA,在高气流下的稳定性使其能更好地满足在空气过滤领域的实际应用需求.此外,提高PLA纳纤膜电活性可显著增强摩擦生电输出性能和呼吸振动激发电信号,为基于人体呼吸的生理特征监测奠定理论基础.本文研究结果为扩大PLA材料在高性能呼吸防护领域和智能健康监测领域的应用提供了新颖的结构设计策略和可借鉴的解决方案.

高结晶多孔聚乳酸粉末的制备及其压电催化性能

聚乳酸(PLA)是一种生物基生物可降解的压电高分子材料,在有机污水处理、组织修复再生等领域有望发挥重要作用,但电活性低、压电响应性差等性能缺点严重限制了其实际应用。基于此,本文以碳酸氢钠(NaHCO_(3))为发泡剂,基于左旋聚乳酸(PLLA)和右旋聚乳酸(PDLA)的低温熔融共混制备高结晶的多孔立构复合聚乳酸(SC-PLA)粉末,研究了NaHCO_(3)含量对粉末微观结构与压电催化性能的影响。结果发现,NaHCO_(3)的加入对SC-PLA粉末的结晶度(约40%)和形貌均没有明显影响,但可赋予粉末丰富的微孔结构,使其在外力作用下更容易形变,进而表现出优异的压电性能。添加质量分数30%的NaHCO_(3)即可使SC-PLA粉末的孔隙率由8.9%大幅增加到66.9%,开路电压从4.0 V显著提升至22.0 V。压电催化实验表明,这种高压电性的多孔SC-PLA粉末可在超声振动激发下介导大量活性氧化种(ROS)的生成,实现对有机染料的高效催化降解(靛蓝胭脂红的降解率高达93.2%)。

Poly(β-cyclodextrin)-mediated Polylactide-cholesterol Stereocomplex Micelles for Controlled Drug Delivery

A series of host-guest interaction-adjusted polylactide stereocomplex micelles was prepared via the self-assembly of 4-armed poly（ethylene glycol）-block-poly（L-lactide/D-lactide）-cholesterol （4-armed PEG-b-PLLA/PDLA-CHOL） and poly（β-cyclodextrin） （PCD） with the molar ratios of CHOL/β-CD at 1：0.5, 1 ：l, and 1：2 in an aqueous environment. The hydrodynamic diameters of the micelles ranged from 84.1 nm to 107 nm depending on the molar ratio of CHOL/β-CD. It was shown that the micelle with the largest proportion of PCD possessed excellent abilities in drug release, cell internalization as well as proliferation inhibitory effect toward human A549 lung cancer cells. The results demonstrated that the stereocomplex and host-guest interactions-mediated PLA micelles exhibited great potential in sustained drug delivery.

The Stereocomplex Formation and Phase Separation of PLLA/PDLA Blends with Different Optical Purities and Molecular Weights

In this study, the poly（L-lactide）/poly（D-lactide） （PLLA/PDLA） blends with different optical purities of PLLA and various molecular weights of PDLA are prepared by solution mixing, and the stereocomplex formation and phase separation behaviors of these blends are investigated. Results reveal that optical purity and molecular weight do not vary the crystal structure of PLA stereocomplex （sc） and homochiral crystallites （hc）. As the optical purity increasing in the blends, the melting temperature of sc （Tsc） and the content of sc （AHsc） increased, while the melting temperature of hc （Thin） hardly changes, although the content ofhc （AHhm） decreased gradually. The Tsc and AHsc are also enhanced as the molecular weight of PDLA reduces, and the AHhm reduces rapidly even though the Thin does not vary apparently. With lower optical purities of PLLA and higher molecular weights of PDLA, three types of crystals form in the blends, i.e., PLA sc, PLLA hc and PDLA hc. As molecular weight decreases and optical purity enhances, the crystal phase decreases to two （sc and PDLA hc）, and one （sc） finally. This investigation indicates that the phase separation behavior between PLLA and PDLA in the PLLA/PDLA blends not only depends on molecular weights, but also relies on the optical purities of polymers.

Sustainable Blends of Poly(propylene carbonate)and Stereocomplex Polylactide with Enhanced Rheological Properties and Heat Resistance

Sustainable blends of poly(propylene carbonate)(PPC)and stereocomplex polylactide(sc-PLA)were prepared by melt blending equimolar poly(L-lactic acid)(PLLA)and poly(D-lactide acid)(PDLA)with PPC to form sc-PLA crystals in situ in the melt blending process.Differential seanning calorimetry analysis revealed that only sc-PLA,no homo-crystallization of PLLA or PDLA,formed in the PPC matrix as the sc-PLA con tent was more than 10 wt%.Very in triguingly,scan ning electronic microscopy observati on showed that sc-PLA was evenly dispersed in the PPC phase as spherical particles and the sizes of sc-PLA particles did not obviously increase with in creasing sc-PLA con tent.As a con seque nee,the rheological properties of PPC were greatly improved by incorporation of sc-PLA.When the sc-PLA con tent was 20 wt%,a percolati on n etwork structure was formed,and the blends showed solid-like behavior.The sc-PLA particles could reinforce the PPC matrix,especially at a temperature above the glass transition temperature of PPC.Moreover,the Vicat softening temperature of PPC/sc-PLA blends could be increased compared with that of neat PPC.

Stereocomplexation and Mechanical Properties of Polylactide-bpoly(propylene glycol)-b-polylactide Blend Films: Effects of Polylactide Block Length and Blend Ratio

In the present work, poly（propylene glycol） （PPG） was block copolymerized to form polylactide-poly（propylene glycol）-polylactide （PL-PPG-PL） triblock copolymers for preparing flexible stereocomplex PL （scPL） blend films. The scPL blend films were prepared by solution blending of poly（L-lactide）-PPG-poly（L-lactide） （PLL-PPG-PLL） and poly（D-lactide）- PPG-poly（D-lactide） （PDL-PPG-PDL） triblock copolymers before film casting. The influences of PL end-block lengths （2 ×10^4 and 4×10^4 g/tool） and blend ratios （75/25, 50/50 and 25/75 W/W） on the stereocomplexation and mechanical properties of the blend films were evaluated. From DSC and WAXD results, the 50/50 blend films had complete stereocomplexation. Phase separation between the scPL and PPG phases was not observed from their SEM images. The tensile stress and elongation at break increased with the sterecomplex crystallinities and PL end-block lengths. The PPG middle-blocks enhanced elongation at break of the scPL films. The results showed that the PL-PPG-PL triblock structures did not affect stereocomplexation of the PLL/PDL block blending. In conclusion, the phase compatibility and flexibility of the scPL films were improved by PPG block copolymerization.

Effect of Plasticizer Poly(Ethylene Glycol)on the Crystallization Properties of Stereocomplex-Type Poly(Lactide Acid)

The effects of the plasticizer poly（ethylene glycol） （PEG） on crystallization properties of equimolar poly（L-lactide） （PLLA）/poly（D-lactide） （PDLA） blends were investigated. Forma- tion of the stereocomplex-type poly（lactide acid） （sc-PLA） crystallites was confirmed by Wide-angle X-ray diffraction （WAXD） and differential scanning calorimetry （DSC） analyses. Sc-PLA crystallites without any homochiral poly（lactide acid） （hc-PLA） formed, as the result of the incorporation of the plasticizer PEG （more than or equal to 10%（wt）） at a processing temperature （240 ℃）. More-over, when the Mw of PEG reached 1 000 g · mol^-1, the crystal- lizability of stereocomplex crystallites was the best. Isothermal crystallization kinetics further revealed that PEG could accelerate the crystallization rate of sc-PLA, with the optimum crystallization kinetic parameters being obtained at 10% （wt） PEG. Several crys- tallization kinetics equations were applied to describe the effect of PEG on the crystallization behavior of sc-PLA. The influence of PEG on the spherocrystal morphologies of sc-PLA was also inves- tigated using polarized optical microscopy.

Stereocomplex Crystallization in Asymmetric Diblock Copolymers Studied by Dynamic Monte Carlo Simulations

Stereocomplex crystallization in asymmetric diblock copolymers was studied using dynamic Monte Carlo simulations,and the key factor dominating the formation of stereocomplex crystallites(SCs)was uncovered.The asymmetric diblock copolymers with higher degree of asymmetry exhibit larger difference between volume fractions of beads of different blocks,and local miscibility between different kinds of beads is lower,leading to lower SC content.To minimize the interference from volume fraction of beads,the SC formation in blends of asymmetric diblock copolymers was also studied.For the cases where the volume fractions of beads of different blocks are the same,similar local miscibility between beads of different blocks and similar SC content was observed.These findings indicate that the volume fraction of beads of different blocks is a key factor controlling the SC formation in the asymmetric diblock copolymers.The SC content can be regulated by adjusting the difference between the contents of beads of different blocks in asymmetric diblock copolymers.

Can Classic Avrami Theory Describe the Isothermal Crystallization Kinetics for Stereocomplex Poly(lactic acid)?

Classic Avrami model and its modifications have found diverse applications in describing the thermal and phase behaviors of inorganic metals and organic polymers. The direct introduction of classic Avrami equation to offer quantitative analyses of crystallization kinetic parameters for enantiomeric poly（lactic acid） （PLA） blends may, however, lead to contradictory conclusions. As revealed by this study, during the characterization of isothermal melt and cold crystallization for stereocomplex PLA containing equal-weight poly（L-lactic acid） and poly（D-lactic acid）, the kinetic parameters yielded by Avrami equation are not in line with the classic crystallization hypotheses or the direct morphological observations. The underlying mechanisms, to some extent, lie in the generation of stereocomplex crystals （SCs） during the cooling/heating which affects the subsequent crystallization dynamics. The huge gap between the melting enthalpies of 100% crystalline SCs （142 J/g） and homo-crystals （HCs, 93 J/g） is most likely responsible for the confusing kinetic parameters acquired from the deduction of Avrami equation, which is based on the integration of enthalpies as a function of crystallization time. This prompts for great care that the classic Avrami equation is not applicable to accurately describe the crystallization kinetics of stereocomplex PLA, given the generation of SCs prior to crystallization and the coexistence of HCs and SCs during crystallization.

Mixing of Racemic Poly(L-lactide)/Poly(D-lactide) Blend with Miscible Poly(D,L-lactide):Toward All Stereocomplex-type Polylactide with Strikingly Enhanced SC Crystallizability

Stereocomplex-type polylactide(SC-PLA)consisting of alternatively arranged poly(L-lactide)(PLLA)and poly(D-lactide)(PDLA)chains has gained a good reputation as a sustainable engineering plastic with outstanding heat resistance and durability,however its practical applications have been considerably hindered by the weak SC crystallizability.Current methods used to enhance the SC crystallizability are generally achieved at the expense of the precious bio-renewability and/or bio-degradability of PLAs.Herein,we demonstrate a feasible method to address these challenges by incorporating small amounts of poly(D,L-lactide)(PDLLA)into linear high-molecular-weight PLLA/PDLA blends.The results show that the incorporation of the atactic PDLLA leads to a significant enhancement in the SC crystallizability because its good miscibility with the isotactic PLAs makes it possible to greatly improve the chain mixing between PLLA and PDLA as an effective compatibilizer.Meanwhile,the melt stability(i.e.,the stability of PLLA/PDLA chain assemblies upon melting)could also be improved substantially.Very intriguingly,SC crystallites are predominantly formed with increasing content and molecular weight of PDLLA.More notably,exclusive SC crystallization can be obtained in the racemic blends with 20 wt%PDLLA having weight-average molecular weight of above 1×10^(5)g/mol,where the chain mixing level and intermolecular interactions between the PLA enantiomers could be strikingly enhanced.Overall,our work could not only open a promising horizon for the development of all SC-PLA-based engineering plastic with exceptional SC crystallizability but also give a fundamental insight into the crucial role of PDLLA in improving the SC crystallizability of PLLA/PDLA blends.

Adjustable crystalline stereocomplexes from enantiopure gradient polycarbonates

Stereoselective interaction was observed in the mixture of enantiopure gradient polycarbonate(denoted as PCOPC-g-PCPC, originated from the enantioselective terpolymerization of CO2, 3,4-epoxytetrahydrofuran(COPO) and cyclopentene oxide(CPO)) and various isotactic polycarbonates with opposite configuration in chloroform solution. The resultant crystalline stereocomplexes exhibit enhanced thermal stability and new crystalline behaviors, significantly distinct from their parent polymers. It was found that the cocrystallization selectively occurred between(R)-PCOPC(CO_2/COPO copolymer) and(S)-PCOPC-enriched segment in the gradient terpolymer(S)-PCOPC-g-PCPC, while(R)-PCPC(CO_2/CPO copolymer) selectively complexed with(S)-PCPC-enriched segment. No stereocomplexation was observed between(S)-PCOPC-g-PCPC and(S)-PCOPC or(S)-PCPC. This study is beneficial to finding new routes to prepare various semicrystalline materials having a wide variety of physical properties and degradability.

界面立构复合化电活性聚乳酸纳纤膜的制备及高效过滤性能

聚乳酸纤维膜在可降解空气过滤材料领域具有巨大潜力,但低比例的电活性相导致纤维膜的介电性能较弱,难以满足高性能空气颗粒物(PMs)过滤材料的需要.本文利用聚L-乳酸(PLLA)和聚D-乳酸(PDLA)组成的立构复合物(SC)提供高比例电活性相,采用同轴静电纺丝策略构筑界面立构复合化的电活性聚乳酸纳纤膜.通过改变纺丝时的注射速度,调控纤维形貌以及羰基(C=O)偶极子、β晶相和界面立构复合晶(SCs)的形成,得到的核壳(CS)结构纳纤膜具有改善的表面电势(9.3kV)和介电常数(1.60F/m).界面立构复合化的纤维膜力学性能提升显著,核部PLLA和壳部PDLA的注射速度分别为1.0和0.5 mL/h时获得的CS1.5纳纤膜的拉伸强度和杨氏模量分别达到17.2和351.1MPa,明显优于纯聚乳酸纤维膜.更重要的是,提升的电活性显著增强了聚乳酸纳纤膜对PM_(0.3)和PM_(2.5)的过滤效率,界面立构复合化在应对高流速下捕尘时具有独特优势,CS1.5纳纤膜的过滤效率由10 L/min时的82.5%提升至85 L/min时的97.9%.本文提出了采用界面立构复合化激发聚乳酸电活性的策略,为解决聚乳酸纤维膜过滤材料的应用瓶颈提供了有益的参考.

立构复合聚乳酸材料研究进展

石油基材料的过度消耗及塑料垃圾的产生给周边环境和人类生活造成了不可逆转的伤害,大力发展可替代石油基材料的产品成为当今急需解决的问题。聚乳酸作为一种线性脂肪族热塑性塑料,因具有良好的机械性能及可加工性,成为目前开发最广泛的商业化聚合物之一。立构复合聚乳酸为研发具有优异物理化学性能且可降解的热塑性塑料提供了研究思路。介绍了近年来几种较为新颖的立构复合聚乳酸材料的制备方法,归纳了立构复合聚乳酸材料的结构与性能,并指出其未来的研究方向。

立构复合调控聚乳酸基材料性能及其应用研究进展

从外场环境、异相成核剂和分子结构等三个方面综述了影响左旋聚乳酸(PLLA)和右旋聚乳酸(PDLA)间立构复合的主要因素,并对立构复合调控聚乳酸基材料性能的主要途径(立构复合成核剂、立构复合交联点及其立构复合网络、立构复合界面、完全立构复合/高立构复合程度)进行了总结。综述了立构复合聚乳酸基材料在药物载体、组织工程、包装、环境、功能材料和其他等领域的应用,对其未来的发展方向进行了展望。