Enzymatic degradation of hyperbranched polyesters

In this work, the enzyme‐catalyzed degradation of hyperbranched polyesters (HBPEs) was investigated. Enzymatic degradation experiments were performed in a phosphate buffer in the presence of the lipases Candida cylindracea, Pseudomonas cepacia, Novozym 388, Amano CE, Lipomod 34P, and Cal‐B, whereas control experiments were performed in the same system without lipases. The extent of polymer degradation was determined by quantification of the released free fatty acids by gas chromatography. The influence of the alkane chain length and the number of alkane chain end groups on the lipase‐catalyzed hydrolysis of esterified HBPEs was investigated systematically. It was found that the increase in the alkane chain length of the end groups diminished the enzymatic degradation of the polymer, whereas the number of end groups had no influence on the degradation rate. The effect of temperature on the rate of degradation was also described. Surface morphological changes that occurred during the degradation were assessed with reflected electron microscopy. The changes in the crystallinity of the polymers after they were subjected to degradation were qualitatively determined with differential scanning calorimetry through the quantification of the enthalpy of melting. The enthalpy of melting of one HBPE sample increased from 79 to 90 and 94 J/g with and without the action of Lipomod 34P, respectively, in 7 days, showing the changes in the crystallinity of the polymer. The results prove that modified HBPEs are an important new class of biodegradable materials with a predictable degradation mechanism, and the degradation can be adjusted on the basis of the molecular engineering. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Macroscopic self-assembly of hyperbranched polyesters

We utilized melt polycondensation of 2,2-bis(hydroxymethyl) propionic acid (bis-MPA) and 2-ethyl-2-hydroxymethyl-1,3-propanediol (TMP) to synthesize a hyperbranched polyester core and subsequent substitution by reaction of terminal hydroxyl with benzoyl chloride in DMF in the presence of TEA as the acceptors of HCl. It has been found that well-defined macroscopic structures can be formed via hydrogen bonding and π-π stacking interactions. Meanwhile, the molecular structures, the nature of the solvent, the molecular concentration, the volatilizing ratio of solvent, and self-assembly temperature also affected the self-assembly structures. The type of self-assembly method offers a synthetic route to well-defined one-dimensional organic macrostructures.     

Rheological characteristics of hyperbranched polyesters

Summary When the effects of physical aging below T _g are erased, the rheological response of a series of aliphatic hyperbranched polyesters is Newtonian and the melt viscosity scales roughly linearly with M _w at high M _w, indicating entanglement to be absent. The rheological behavior is also highly sensitive to the nature of the terminal groups, suggesting the overall behavior to be close to that of an assembly of compact coreshell "particles". There are therefore strong parallels between the physical behavior of the hyperbranched polyesters in question and that of their ideal dendrimer analogues. Received: 14 April 2002 /Revised: 1 July 2002 / Accepted: 1 July 2002     

Relaxation processes in hyperbranched polyesters

Summary Dielectric permittivity and loss have been measured over the frequency range 10^-2 Hz-10 kHz between 100 K and 350 K for samples of 50/50 mixtures of each of two hyperbranched polyesters, one five-generation hydroxy functional (5G-OH) and one threegeneration alkyl-terminated polymer (3G), with dielectrically inactive linear polyethylene. The thermal transitions of the hyperbranched polymers were studied with differential scanning calorimetry. Three relaxation transitions were found in 5G-OH: , the glass-rubber transition and two subglass processes denoted and showing Arrhenius temperature dependence both with an activation energy of 96±2kJ mol^-1. The low temperature process could be assigned to motions of the terminal hydroxyl groups whereas is due to reorientation of the ester groups. Sample 3G showed only a glass transition and one subglass process being assigned to reorientation of the ester groups. The high activation energy (202 kJ mol^-1) of this process indicates that the ester groups are highly constrained in this polymer.     

Rheology of concentrated sulfonated poly(ether ether ketone) solutions

Sulfonated polyether ether ketone (SPEEK), an ionic polymer, has been shown to be a potential candidate for fuel cell electrolyte as a proton exchange membrane. Rheological behavior of SPEEK solutions is of great interest to understand the molecular associations as well as due to implications in membrane processing. In this work, SPEEK of various degrees of sulfonation (58–80) was prepared and rheology of concentrated solutions of SPEEK was studied. The rheological properties were evaluated using steady and oscillatory shear. It was found that steady shear viscosity and storage modulus at any given concentration, is the highest for the lowest degree of sulfonation SPEEK solutions in N‐methyl‐2‐pyrrolidone. The low frequency plateau in storage modulus was observed at some combinations of degrees of sulfonation and concentrations, indicating gel‐like behavior in these SPEEK solutions. No significant change in rheological behavior was observed with different polar solvents. Increase of several orders of magnitude in viscosity, storage and loss moduli were observed with increasing concentrations. The role of hydrophobic aggregation and inter‐chain associations in determining rheology of SPEEK solutions is argued based on comparisons with other material systems. The rheological behavior of SPEEK solutions with 70 as the degree of sulfonation, suggests crossover from hydrophobic‐hydrophilic balance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40044.     

Characterization of commercial aliphatic hyperbranched polyesters

Commercially available Boltorn Hx (x=20, 30) hyperbranched (HB) polyesters of different theoretical core/monomer ratio (1/12 for H20 and 1/28 for H30) were characterized with respect to molar mass, composition, and structure. The results were compared to those obtained for the Boltorn H40 with a core/monomer ratio of 1/60 [?agar E, ?igon M. Macromolecules 2002;35:9913 [11]]. The main side reaction in the pseudo one-pot synthesis of Boltorn polymers is a self-condensation of bis-MPA leading to the formation of HB structures without a core molecule. These are actually branches containing an unreacted carboxyl group. The fraction of HB structures without a core molecule increases with decreasing core/monomer ratio due to the decreasing fraction of HB structures with a core molecule. Since HB structures without a core molecule are of lower molar masses than HB structures with a core molecule, they particularly decrease the number average molar masses of the samples compared to the theoretically calculated ones. The polydispersity of Boltorn Hx increases with decreasing core/monomer ratio. Some of the hydroxyl groups were found to react intramoleculary forming ether bonds. Boltorn Hx polyesters have low degrees of branching due to the limited carboxyl group conversions, low DP_n values, the presence of the core unit, and lower reactivity of hydroxyl groups in linear repeat units compared to those in terminal ones. The degree of branching according to Frey increases with decreasing core/monomer ratio.     

Melt rheology of aliphatic hyperbranched polyesters

Rheological behavior in melt of aliphatic hyperbranched polyesters (AHBP), synthesized using pseudo‐one‐step and one‐step procedure, was investigated in this work. Three commercially available AHBP were also examined. Because of the presence of relatively strong hydrogen bonds between numerous end hydroxyl groups, AHBP of lower generation number, as well as the sample of tenth pseudo generation, show non‐Newtonian behavior in the entire investigated frequency and temperature region. However, for other examined AHBP, the slope of the frequency dependence of complex viscosity (η* = f(ω)) becomes smaller with the temperature increase. Therefore, samples of fourth, fifth, and sixth pseudo generations show Newtonian behavior at temperatures higher than 70°C. Value of glass transition temperature, melt flow activation energy, fractional free volume, and thermal expansion coefficient were determined for the investigated AHBP. The influence of the type of end groups on rheological properties of AHBP was also examined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rheology of concentrated suspensions

The dependence of the viscosities of highly concentrated suspensions on solids concentrations and particle size distributions is investigated by using an orifice viscometer. Based on the extensive amount of data on pertinent systems, an empirical equation which correlates the relative viscosities of suspensions (or relative moduli of filled polymeric materials) as a function of solids concentrations and particle size distributions is proposed. The equation has a constant which characterizes size distributions of spherical particles and can be determined experimentally without measuring viscosities. For uniform-size spherical particles, it reduces to the well-known Einstein equation at dilute solids concentrations.     

Solution properties of selectively modified hyperbranched polyesters

Simultaneous characterization of the degree of branching and molar mass on a molecular level for hyperbranched polymers is still strongly limited. Therefore model hyperbranched polyesters for development of new chromatographic techniques on the basis of 2,2-bis(hydroxymethyl)propionic acid were synthesized. The two types of OH-functionalities (linear and terminal) of the hyperbranched polymer were selectively modified using different protection groups. The modification of the terminal end groups was carried out using their diol character with the formation of a ketal ring without changing the chemical structure of the linear OH groups. In order to obtain completely non-polar polymer, the linear OH-units were functionalized with an acetyl group. The last modification step was the deprotection of the terminal end groups by removing the ketal ring. Fractions with various molar masses for each modification stage were obtained by preparative fractionation. Extensive characterization by SEC-MALLS, NMR spectroscopy, and viscosity measurements elucidated the dependence of the molecular shape in solution on the polarity. These results were supported by molecular dynamic simulations.     

Synthesis and characterization of glycerol-adipic acid hyperbranched polyesters

The structure and molecular weight of the hyperbranched polyesterification of adipic acid and glycerol were characterized by ¹³C NMR spectroscopy and size-exclusion chromatography as a function of reaction time and reaction stoichiometry. The glycerol substitution patterns and the extent of reaction of both glycerol and adipic acid were determined by NMR. The glycerol species concentrations determined by NMR were used with a Macosko–Miller conditional probability model to predict the hyperbranched polyester weight-average molecular weight. The model accommodated the difference in primary and secondary –OH reactivity and any substituent effects to glycerol –OH reactivity. In all cases, the predicted weight-average molecular weights were in excellent agreement with the absolute molecular weights determined by size-exclusion chromatography with light scattering detection.     

Boltorn型超支化聚酯的合成与表征

以季戊四醇(PEL)、三羟甲基丙烷(TMP)和2,2-二羟甲基丙酸(DMPA)为原料,合成了3种端羟基超支化聚酯(HBPE),即分别是以PEL为核的HBPE、以TMP为核的HBPE和无核的HBPE。采用FTIR、13C NMR、GPC等方法对其结构进行了表征,3种HBPE的Fréchet支化度分别为41.86%,41.49%和39.77%,而Frey支化度分别为32.29%,31.37%和23.11%。研究了中心核分子对HBPE的溶解性、特性黏度的影响。结果表明,随着核分子官能度的增加,HBPE的溶解性变好,特性黏度增加,支化度(DB)增加,分子量多,分散系数(PD I)变小。     

超支化聚酯在聚丙烯染色中的应用研究

以双酚酸为单体,采用熔融缩聚得到了超支化聚酯,并用棕榈酰氯对所得到的超支化聚酯进行烷基化改性.用红外和 1H-NMR对上述产物进行了表征.TG分析表明,烷基化改性的超支化聚酯具有较好的热稳定性,可以满足聚丙烯纺丝的温度要求.将烷基化改性的超支化聚酯和聚丙烯共混纺丝,在添加量为3.2%时,得到了可纺性良好的聚丙烯纤维.在常压沸染的条件下,超支化聚酯改性的聚丙烯纤维能很大幅度的改善分散染料的上染率.     

Rheology and transesterification between polycarbonate and polyesters

Rheological behavior of polycarbonate (PC)–polyester blends is studied. The miscibility and rheological behavior are discussed. Effect of catalyst, tetra‐n‐butyl orthotitanate on the transesterification reactions for a [60 (PC):40 (PET or PBT)] blend is studied rheologically. The blends were mixed for different spans of time for rheological study. The blends are analyzed on the basis of the mechanism suggested by other researchers. As the mixing time is increased, the blends show decrease in viscosity. Random copolymers also are amorphous in nature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2039–2047, 2007     

Rheology and structure of liquid crystalline alkylenearomatic polyesters

The rheological, thermodynamic and structural properties of two liquid crystalline polyesters—poly(oxyfumaroyloxy- 1,4-phenylene carbonyloxyalkyleneoxycarbonyl- 1,4-phenylene)s with six and ten methylene groups (PES-6 and PES- 10, respectively) and a statistical copolyester (co-PES) have been investigated. It has been shown that they all form a smectic LC-phase. The change from homopolyesters to co-PE S expands the temperature range of the LC-state. The high sensitivity of the structure to the prehistory in the melt state is typical for such copolymers. Prolonged heating leads to rearrangement of the co-PES crystalline structure and a drastic increase in viscosity. The orientation of these polymers during flow was investigated. It was shown that a high level of molecular orientation of the smectic layers, perpendicular to the direction of flow, was realized at high shear stresses. In the melt region, the existence of a metastable network with junctions of crystalline nature hinders the flow of the homo- and copolyesters. The structure of the unit cell of the crystallites depends on the composition and thermal history.     

环氧树脂改性超支化聚酯的合成及性能

以偏苯三酸酐、环氧氯丙烷及甲基丙烯酸缩水甘油酯为原料合成了超支化聚酯(HBP),再通过超支化聚合物的羧基与环氧树脂环氧基的反应得到环氧改性超支化聚合物;用GPC1、H-NMR、DSC、TGA表征了环氧改性超支化聚合物的结构和热性能;比较了不同环氧树脂用量改性前后树脂的光反应活性以及光固化涂层的耐擦洗性和硬度,测定了凝胶率-曝光时间曲线;以环氧改性超支化聚合物配制了光刻胶,在混合光源以及接触曝光的条件下,分辨率达到2~3μm,且图像十分清晰,断面整齐。环氧树脂用量为HBP羧基物质量的70%左右时,改性的超支化聚酯的光固化活性有明显提高,力学性能得到明显改进。     

对叔丁基苯甲酸改性超支化聚酯的合成和性能

以三羟甲基丙烷(TMP)为核,二羟甲基丙酸(bis-MPA)为AB2型单体,合成超支化聚酯(HBPE)。采用对叔丁基苯甲酸(PTBA)对其进行改性,得到PTBA取代度为10%~75%的超支化聚酯(HBP-10M~HBP-75M,统称HBP-Ms)。通过傅里叶变换红外光谱(FTIR)、核磁共振氢谱(1HNMR)和凝胶渗透色谱(GPC)对产物结构和相对分子质量(简称分子量,下同)进行表征,并考察HBP-Ms的溶解性和涂膜性能。研究结果表明,合成了支化度为0.47的HBPE,改性后的HBP-Ms具有良好的溶解性,可溶解在丙酮、DMF、乙酸乙酯、乙醚、苯和二甲苯,不溶于正己烷。HBP-Ms涂膜具有较高的硬度、光泽度和柔韧性,其中HBP-10M和HBP-25M具有更优异的溶解性和涂膜性能。TGA分析表明,PTBA可提高改性树脂涂膜的热稳定性。     

Rheology of guar solutions

The rheology of aqueous solutions of guar is studied over a wide range of shear rates and concentrations. At sufficiently low and high shear rates guar solutions show regions of Newtonian behavior, while at intermediate shear rates they are pseudoplastic. Preliminary normal stress data, and the effects of salt concentration are discussed. Molecular size distribution profiles of hydrated guar, obtained by low pressure (20 psig) filtration through Nucleopore filter membranes, are discussed in terms of guar purity.     

Scratch resistant tough nanocomposite epoxy coatings based on hyperbranched polyesters

Advanced multifunctional coatings were prepared by UV curing of epoxy based formulations containing hyperbranched polymers (HBP) and an epoxy functionalized alkoxysilane additive. The addition of HBP to the UV curable epoxy resin induced an important flexibilization of the glassy epoxy network with an increase in toughness of the cured polymeric coatings. Adding the functionalized alkoxysilane into the UV curable formulations, as inorganic precursor of silica phase, an improvement on surface hardness was obtained without strongly affecting the flexibilization and the toughness achieved by the addition of the HBP additive. The increase on surface hardness was accompanied with an increase in scratch resistance and modulus. Advanced scratch resistant and tough nanocomposite epoxy coatings were obtained by properly selecting the components of the formulation.     

Modifications and applications of hyperbranched aliphatic polyesters based on dimethylolpropionic acid

Over the past 16 years, hyperbranched polyesters (HBPEs) based on dimethylolpropionic acid have received much attention due to their unique structural characters, their excellent physical and chemical properties as well as their potential applications in coatings, additives, drug delivery, composites, membrane science and supermolecular chemistry. HBPEs have recently become one of the types of commercialized hyperbranched polymers, and their modifications and applications are focuses of research. This paper reviews the developments in the modifications and applications of HBPEs. Copyright © 2010 Society of Chemical Industry     

Behavior of hyperbranched polymers in solutions

Hyperbranched polycarbosilanes are investigated by the methods of molecular hydrodynamics and optics. Dependences of the hydrodynamic and conformational properties of these polymers on their molecular mass, the length of linear chains between branching points, and the chemical structure of end groups are analyzed. The hydrodynamic behavior of hyperbranched polycarbosilanes is explained by the fact that the dimensions of their macromolecules are compact and their shape is close to spherical. The convolution of chains between branching points becomes more pronounced with an increase in their length and a decrease in the molecular mass of the polymer. When end fluorinated groups are incorporated into the hyperbranched polycarbosilane, in thermodynamically good solvents and θ solvents, hydrodynamic characteristics change apparently owing to a change in the density of macromolecules in solution. In a poor solvent, the compaction of fluorinated macromolecules and a reduction in their shape asymmetry are observed. At a fixed branching degree, the hydrodynamic properties of hyperbranched polymers depend on the structural regularity of their macromolecules: In terms of hydrodynamic properties, the hyperbranched polycarbosilane with a degree of branching of 1 and a random distribution of branching points within the volume of a macro-molecule is appreciably different from a dendrimer of the same chemical nature and is close to polycarbosilanes with a degree of branching of 0.5.