Degradation Process of Bioresorbable Copolyesters. Microstructure Investigation by NMR and ESI-MS

Summary: On the basis of NMR and ESI-MS spectra completely different ways of degradation process for random and block polyesters copolymers have been observed. PGA/PLA copolymers containing more than 50% of glycolidyl units release short lactidyl microblocks more rapidly than long glycolidyl microblocks. In case of PGA/PCL copolymers chain structure before degradation and mechanism of degradation of two chosen samples are distinctly various despite of low content of GG units in copolymer chain (ca.10%) and lack of differences in NMR spectra. ESI-MS technique can be useful tool, complementary to NMR method in studying the chain microstructure.     

Modeling of Coesterification Process for Biodegradable Poly(Butylene Succinate‐co‐Butylene Terephthalate) Copolyesters

Comprehensive mathematical model based on the kinetics and thermodynamic equations is developed to examine a coesterification concept of biodegradable aliphatic‐aromatic copolyesters, poly(butylene succinate‐co‐butylene terephthalate) (PBST). The simulation results for batch process are validated with pilot experimental data. The continuous process is further studied to figure out the coesterification performance of succinic acid (SA) and terephthalic acid (TPA) with different reaction activities and thermodynamic properties in terms of reaction efficiency, small molecular evaporation and product quality. There is a compromise between the operating conditions of the two systems of SA/1,4‐butanediol (BDO) and TPA/BDO. Proper pressure reduction is beneficial to reaction efficiency and product quality. The way to increase reaction efficiency by raising temperature is limited due to the serious evaporation of reactants. Influenced by the solid–liquid equilibrium and the slow reaction rate of TPA, the esterification of acid needs sufficient residence time to complete.     

A Thermosensitive and Biodegradable Physical Gel with Chemically Crosslinked Nanogels as the Building Block

A triblock copolymer, poly(ethylene glycol)–poly(propylene glycol)–poly(ethylene glycol) was end-capped by acryloyl groups using a biodegradable oligolactide as spacer, and such biodegradable amphiphilic macromers could form micelles in water. A nanogel was prepared via polymerizing macromers in a micelle, and a macroscopic physical gelation was found upon heating a concentrated aqueous nanogel suspension. Such a sol–gel transition with a chemically crosslinked nanogel as the building block was thermoreversible. While the hydrogel affords a promising injectable biomaterial; this research reveals new physics of the thermogelling mechanism of amphiphilic block copolymers.

     

Copolyesters of isosorbide,succinic acid,and isophthalic acid: Biodegradable,high Tg engineering plastics

Isosorbide, succinyl chloride and isophthaloyl chloride are polycondensed under various reaction conditions. The heating in bulk with or without catalysts as well in an aromatic solvent without catalyst, and polycondensation with the addition of pyridine only yield low molar mass copolyesters. However, heating in chlorobenzene with addition of SnCl₂ or ZnCl₂ produces satisfactory molar masses. The number average molecular weights (M_n) of most copolyesters fall into the range of 7000–15,000 Da with polydispersities (PD) in the range of 3–9. The MALDI‐TOF mass spectra almost exclusively displayed peaks of cyclics indicating that the chain growth was mainly limited by cyclization and not by side reactions, stoichiometric imbalance or incomplete conversion. The glass‐transition temperatures increased with the content of isophthalic acid from 75 to 180 °C and the thermo‐stabilities also followed this trend. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2464–2471     

Block copolyesters of poly(pentamethylene p,p′‐bibenzoate) and poly(tetramethylene adipate)

Hydroxy‐terminated poly(pentamethylene p,p′‐bibenzoate) oligomers with different molecular weights were prepared. The poly(pentamethylene p,p′‐bibenzoate) oligomers showed rather high crystallinity, and some of them exhibited a monotropic smectic phase. Block copolyesters with hard segments of poly(pentamethylene p,p′‐bibenzoate) and soft segments of poly(tetramethylene adipate) were prepared by coupling the poly(pentamethylene p,p′‐bibenzoate) oligomer and a poly(tetramethylene adipate)glycol with methylene‐4,4′‐diphenylene diisocyanate in solution. The block copolyesters were characterized by IR, ¹H NMR, differential scanning calorimetry, a polarized microscope, and X‐ray diffraction. The thermal transitions of the block copolyesters were dependent on the composition and the molecular weight of the poly(pentamethylene p,p′‐bibenzoate) oligomer used. The hard segments in the block copolyesters showed no liquid crystallinity and exhibited rather low crystallinity or were even amorphous. The molecular weight of the poly(pentamethylene p,p′‐bibenzoate) oligomer used influences the glass‐transition temperature and crystalline properties of the soft segments in the block copolyesters significantly. The effect on the glass‐transition temperature of the soft segments is described as the difference in miscibility between the hard and soft segments. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2626–2636, 2002     

Polylactide Block Copolymers using Trimethylene Carbonate with Methoxyethoxy Side Groups for Dual Modification of Hydrophilicity and Biodegradability

Novel block copolymers using the monomers 5‐(2‐methoxyethyoxymethyl)‐5‐methyl‐[1,3]‐dioxa‐2‐one (TMCM‐MOE1OM) as a hydrophilic segment and lactides as a hydrophobic segment were designed in order to prepare controllable degradation polymers by dynamic polymer rearrangement based on the hydrophilicity. When the copolymer film contacted water, the hydrophobic polylactide (PLA) segments tend to be buried under the TMCM‐MOE1OM segments due to the hydrophilicity of the methoxyethoxy groups. The copolymers were hardly degraded by both proteinase K and lipase, while both of their homopolymers, poly(trimethylene carbonate) and PLA, were degraded, which suggests that the rearrangement of the TMCM‐MOE1OM segments at the outermost surface significantly improved the degradation ratio.

     

Surface Hydrophilicities and Enzymatic Hydrolyzability of Biodegradable Polyesters, 2

Control of the surface hydrophilicities and enzymatic hydrolyzability of hydrophobic aliphatic polyesters such as poly(ε‐caprolactone) (PCL) and poly(L ‐lactide) [i.e. poly(L ‐lactic acid) (PLLA)] was attempted by coating with hydrophilic poly(vinyl alcohol) (PVA). The PVA coating was carried out by immersion of the PCL and PLLA films in PVA solutions. The effects of PVA coating on the hydrophilicities were monitored by dynamic contact angle measurements, while the enzymatic hydrolyzability of the PVA‐coated PCL and PLLA films was evaluated by the weight losses after Rhizopus arrhizus lipase‐ and proteinase K‐catalyzed hydrolysis, respectively. It was found that the PVA coating successfully enhanced the hydrophilicities of the aliphatic polyester films and significantly suppressed enzymatic hydrolyzability of the aliphatic polyester films, excluding the PCL film coated at a very low concentration such as 0.01 g · dL^?1 and the crystallized PLLA film coated at 1 g · dL^?1, for which slight enhancement and no significant enhancement, respectively, were observed in the enzymatic hydrolyzability. Moreover, the hydrophilicities and enzymatic hydrolyzability of the aliphatic polyester films were controllable to some extent by varying the PVA solution concentration and the film crystallinity.

Advancing contact angle (θ_a) of PCL, PLLA‐C, and PLLA‐A films before and after the PVA coating by immersion in 1 g · dL^?1 solution.     

Screening of metal catalysts influence on the synthesis,structure, properties,and biodegradation of PLA‐PBA triblock copolymers obtained in melt

The synthesis of ABA type triblock copolymers comprising poly(1,4‐butylene adipate) macroinitiator and polylactide segments is described in this article. Acetylacetonates of various low‐toxic metals: Li, Mg, Ca, Zn, Fe, and Zr are used as catalysts. The course of polymerization, microstructure, thermal properties, and biodegradation of the copolymers obtained are analyzed based on the electronegativity of the metal used. The macroinitiator is completely incorporated into the major products, however, linear and cyclic lactide homopolymers and copolymers are present because of moisture presence and transesterification processes. The efficiency of side reactions depends on the catalyst used. The highest molar mass of copolymer is obtained with a Zr‐based catalyst. The efficacy of polylactide racemization is higher for catalysts comprising the metal of lower electronegativity. Under thermal degradation conditions the polylactide segment degrades before the macroinitiator one. The copolymers studied undergo faster biodegradation than polylactide and they can decompose in compost within 16 weeks. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1444–1456     

New Results in Weak Segregation Limit Theory of Block Copolymers

Summary: Some theoretical results recently obtained in papers with participation of the author in the field of statistical thermodynamics of block copolymers are briefly discussed.     

Optically Triggered Dissociation of Kinetically Stabilized Block Copolymer Vesicles in Aqueous Solution

We demonstrate a strategy for using an optical stimulus to trigger the dissociation of block copolymer (BCP) vesicles in aqueous solution. The BCP, comprising hydrophilic poly(ethylene oxide) (PEO) and a block of poly(methacrylic acid) bearing a number of spiropyran methacrylate comonomer units (P(MAA‐co‐SPMA)), was allowed to firstly self‐assemble into large vesicles in aqueous solution at pH = 3 with protonated carboxylic acid groups, and then become kinetically stable at pH = 8 due to the glassy vesicle membrane of P(MAA‐co‐SPMA). Fast dissociation of the vesicles was achieved through a cascade of events triggered by UV‐induced isomerization from neutral spiropyran to charged merocyanine in the membrane.

     

From Precision Synthesis of Block Copolymers to Properties and Applications of Nanoparticles

Inorganic nanoparticles have become a research focus in numerous fields because of their unique properties that distinguish them from their bulk counterparts. Controlling the size and shape of nanoparticles is an essential aspect of nanoparticle synthesis. Preparing inorganic nanoparticles by using block copolymer templates is one of the most reliable routes for tuning the size and shape of nanoparticles with a high degree of precision. In this Review, we discuss recent progress in the design of block copolymer templates for crafting spherical inorganic nanoparticles including compact, hollow, and core–shell varieties. The templates are divided into two categories: micelles self‐assembled from linear block copolymers and unimolecular star‐shaped block copolymers. The precise control over the size and morphology of nanoparticles is highlighted as well as the useful properties and applications of such inorganic nanoparticles.     

Biodegradable Gold Nanovesicles with an Ultrastrong Plasmonic Coupling Effect for Photoacoustic Imaging and Photothermal Therapy

The hierarchical assembly of gold nanoparticles (GNPs) allows the localized surface plasmon resonance peaks to be engineered to the near‐infrared (NIR) region for enhanced photothermal therapy (PTT). Herein we report a novel theranostic platform based on biodegradable plasmonic gold nanovesicles for photoacoustic (PA) imaging and PTT. The disulfide bond at the terminus of a PEG‐b‐PCL block‐copolymer graft enables dense packing of GNPs during the assembly process and induces ultrastrong plasmonic coupling between adjacent GNPs. The strong NIR absorption induced by plasmon coupling and very high photothermal conversion efficiency (η=37 %) enable simultaneous thermal/PA imaging and enhanced PTT efficacy with improved clearance of the dissociated particles after the completion of PTT. The assembly of various nanocrystals with tailored optical, magnetic, and electronic properties into vesicle architectures opens new possibilities for the construction of multifunctional biodegradable platforms for biomedical applications.     

A novel and versatile potassium‐based catalyst for the ring opening polymerization of cyclic esters

Poly(lactide) (PLA), poly(ε‐caprolactone) (PCL) and poly(trimethylene carbonate) (PTMC) homopolymers of high molecular weight were prepared using potassium‐based catalyst. Polymerizations were carried out in toluene at room temperature. The chemical structure of the polymers was investigated by ¹H and ¹³C NMR. The physical properties investigated by GPC and DSC for the polymers obtained are similar to those prepared using tin octanoate based catalyst. Using a sequential polymerization procedure, PLA‐b‐PCL, PLA‐b‐PTMC, and PCL‐b‐PTMC diblock copolymers were synthesized and characterized in terms of their composition and physical properties. The formation of diblock copolymers was confirmed by NMR and DSC measurements. In vitro cytotoxicity tests have been carried out using MTS assay and the results show the biocompatibility of these polymers in the presence of the fibroblast cells. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5348–5362, 2008     

Colloid‐Electrospinning: Fabrication of Multicompartment Nanofibers by the Electrospinning of Organic or/and Inorganic Dispersions and Emulsions

Solution‐, melt‐, and co‐axial electrospinning are well‐known methods for producing nano‐ and microfibers. The electrospinning of colloids (or colloid‐electrospinning) is a new field that offers the possibility to elaborate multicompartment nanomaterials. However, the presence of colloids in the electrospinning feed further complicates theoretical predictions in a system that is dependent on chemical, physical, and process parameters. Herein, we give a summary of recent important results and discuss the perspectives of electrospinning of colloids for the synthesis and characterization of multicompartment fibers.     

不同嵌段比的PEG-b-PDMAEMA共聚物在水溶液中的自聚集行为

采用氢核磁共振(¹H-NMR)、动态光散射(DLS)及透射电子显微镜(TEM)对聚乙二醇-嵌段-聚甲基丙烯酸N,N-二甲氨基乙酯(PEG-b-PDMAEMA)三种具有不同PEG/PDMAEMA嵌段比的PEG-b-PDMAEMA共聚物在水溶液中的自聚集行为进行了研究. 研究表明, 两嵌段比例是影响聚合物胶束化过程的关键因素: 只有当其中聚乙二醇含量较低(质量分数低于33%)时, 聚合物才具有其pH/温度敏感胶束化特性. 此外, 共聚物溶液随温度胶束化过程与共聚物嵌段比大小密切相关. PEG-b-PDMAEMA这种不同于传统双亲性嵌段共聚物(DHBCs)在选择性溶剂中独特的胶束化行为, 是由聚合物溶液体系中各种基团之间的氢键作用决定的.     

酶响应性线形-树枝状嵌段共聚物的合成、性能及应用

酶响应性线形-树枝状嵌段共聚物(LDBCs)能对内源性酶产生特异性响应,与只能对外源性刺激信号(如温度、光等)产生响应的聚合物相比,酶响应性LDBCs具有高选择性和更好的生物相容性,作为生物医用材料更适合在人体内使用。通过变换LDBCs的酶响应基团、线形链和树枝化基元,可调控酶响应性两亲LDBCs的自组装和酶响应性解组装性能。由于其独特的酶响应性能和优良的生物相容性,在药物递送和生物医学影像等方面有广阔的应用前景。本文总结归纳了酶响应性LDBCs的合成方法、LDBCs的结构(如线形链长度和结构、树枝化基元的疏水性)对其自组装性能和酶响应性能的影响以及应用,并对酶响应性LDBCs的发展方向进行了展望。     

Conductive,Monodisperse Polyaniline Nanofibers of Controlled Length Using Well‐Defined Cylindrical Block Copolymer Micelles as Templates

Stable colloidal dispersions of polyaniline (PAni) nanofibers with controlled lengths from about 200 nm–1.1 μm and narrow length distributions (L_w/L_n<1.04; L_w=weight average micelle length, L_n=number average micelle length) were prepared through the template‐directed synthesis of PAni using monodisperse, solution‐self‐assembled, cylindrical, block copolymer micelles as nanoscale templates. These micelles were prepared through a crystallization‐driven living self‐assembly method from a poly(ferrocenyldimethylsilane)‐b‐poly(2‐vinylpyridine) block copolymer (PFS₂₅‐b‐P2VP₄₂₅). This material was initially self‐assembled in iPrOH to form cylindrical micelles with a crystalline PFS core and a P2VP corona and lengths of up to several micrometers. Sonication of this sample then yielded short cylinders with average lengths of 90 nm and a broad length distribution (L_w/L_n=1.32). Cylindrical micelles of PFS₂₅‐b‐P2VP₄₂₅ with controlled lengths and narrow length distributions (L_w/L_n<1.04) were subsequently prepared using thermal treatment at specific temperatures between 83.5 and 92.0 °C using a 1D self‐seeding process. These samples were then employed in the template‐directed synthesis of PAni nanofibers through a two‐step procedure, where the micellar template was initially stabilised by deposition of an oligoaniline coating followed by addition of a polymeric acid dopant, resulting in PAni nanofibers in the emeraldine salt (ES) state. The ES–PAni nanofibers were shown to be conductive by scanning conductance microscopy, whereas the precursor PFS₂₅‐b‐P2VP₄₂₅ micelle templates were found to be dielectric in character.     

Novel synthesis of biodegradable linear and star block copolymers based on ε‐caprolactone and lactides using potassium‐based catalyst

Biodegradable, triblock poly(lactide)‐block‐poly(ε‐caprolactone)‐block‐poly(lactide) (PLA‐b‐PCL‐b‐PLA) copolymers and 3‐star‐(PCL‐b‐PLA) block copolymers were synthesized by ring opening polymerization of lactides in the presence of poly(ε‐caprolactone) diol or 3‐star‐poly(ε‐caprolactone) triol as macroinitiator and potassium hexamethyldisilazide as a catalyst. Polymerizations were carried out in toluene at room temperature to yield monomodal polymers of controlled molecular weight. The chemical structure of the copolymers was investigated by ¹H and ¹³C‐NMR. The formation of block copolymers was confirmed by NMR and DSC investigations. The effects of copolymer composition and molecular structure on the physical properties were investigated by GPC and DSC. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5363–5370, 2008     

Aqueous Networks and Toroids of Amphiphilic Block Copolymer with Non‐ionic Surfactants

Network formation: Comicellization of polystyrene‐block‐polyethylene oxide (PS–PEO) with non‐ionic surfactants leads to the formation of networks and chains of spheres. The aqueous network solutions are responsive to dilution, undergoing morphological transformations to cylinders with Y junctions and both two‐ and three‐dimensional toroids (see figure).