Polyester Core Research Articles

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.

Synthesis of multi‐arm star polystyrene with hyperbranched polyester initiators by atom transfer radical polymerization

AbstractMulti‐arm star polystyrenes with hyperbranched polyester (HP3) core were prepared by atom transfer radical polymerization (ATRP). The structures of the polymers were investigated with FTIR and 1H NMR. GPC results showed that the resultant polymers had relatively broad polydispersity indices that arouse from the macromolecular initiator (HP3‐Br). The thermal properties were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC analysis indicated that polystyrene star polymers had only the glass transition temperatures (Tg), which changes with the weight ratio of multi‐functional macroinitiator‐to‐monomer. In addition, these star polymers could form the spherical micelles in the selected solvent (THF/n‐hexane). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 728–733, 2006

Synthesis and self-assembly of hyperbranched polyester peripherally modified by touluene-4-sulfonyl groups

In this paper, hyperbranched polyesters (HPs) were synthesized in the molten state from 2,2-bis(hydroxymethyl) propionic acid (bis-MPA) and 2-ethyl-2-hydroxymethyl-1,3-propanediol (TMP) using acid catalysis. The modified hyperbranched polyesters were obtained through the chemical modification of the hyperbranched polyester cores by substituting a controlled fraction of the terminal hydroxyl groups with touluene-4-sulfonyl chloride using triethylamine (TEA) as an acceptor of HCl. The resultant polyesters were characterized by 1H NMR, 13C NMR, FT-IR, UV and GPC and their self-assembly behaviors were investigated. The results revealed that self-assembled structures could be formed in selected solvents (trichloromethane/acetone or trichloromethane/ n-hexane).

Repair of Zone II Flexor Digitorum Profundus Lacerations Using Varying Suture Sizes: A Comparative Biomechanical Study

To compare the maximum tensile load, change in work of flexion, and gapping at the repair site after zone II flexor digitorum profundus tendon repairs using 2-0, 3-0, and 4-0 braided polyester 4-strand locked cruciate repair technique in fresh-frozen cadaveric hands with standard 6-0 suture epitenon repairs, to determine which suture size is the best for a core repair. A randomized study was designed using 41 tendons from 15 fresh-frozen cadaveric hands. We included only the flexor digitorum profundus tendons from the index, middle, and ring fingers to minimize variation between digits. Core suture size was randomized for each finger. A sharp laceration through the flexor digitorum profundus in zone II was made and a 4-strand locked cruciate braided polyester core stitch was performed along with a locked epitenon stitch. Cyclic loading was performed for 1,000 cycles. For each tendon the mean work of flexion (before/after zone II repair) and maximum tensile load were measured using a custom-designed tensiometer, as was gapping before maximum tensile loading. Mean gaps after 1,000 load-unload cycles to 3.9 N of pulp pinch did not approach the clinically significant limit of 3 mm in each group. By using a regression model, we found that the prerepair and postrepair comparisons for mean work of flexion to a 3.9-N pulp pinch showed the greatest change in work of flexion for 2-0 braided polyester. Statistical significance was found between 2-0 braided polyester and 3-0 or 4-0 braided polyester; however, the work of flexion between the 3-0 and 4-0 polyester was not clinically significant. The highest maximum tensile load was obtained with suture size 2-0 braided polyester. The maximal tensile load statistically showed 2-0 braided polyester to be stronger than 4-0 braided polyester but we found no statistically significant difference between 3-0 and 2-0 braided polyester or between 3-0 and 4-0 braided polyester. In this cadaveric study we found that increasing locking cruciate suture caliber from 4-0 to 2-0 increased maximum tensile strength but also caused increased work of flexion. Gapping was not affected by suture caliber. There was no significant difference in strength or mean change in work of flexion between 3-0 or 4-0 braided polyester sutures.

Hand-Related Mechanical Behavior of Enzyme-Treated Yarns

In the second part of our two-part study, we attempt to understand the influence of enzyme treatment on the properties of bicomponent yarns that exhibit systematic differences in fiber arrangement within the yarn. Our results show that the treatment alters the properties of a ring spun, random blended, polyester-cotton yarn more than it alters the properties of a corresponding sheath-core yarn. Results also reveal that the treatment has a different influence on the properties of two friction spun cotton-polyester yarns, one made with a staple polyester core and the other with a multifilament polyester core. The weight losses suffered by the treated yarns are also influenced by the fiber arrangements within the yarn.

Preparation of hydrogel hollow particles for cell encapsulation by a method of polyester core degradation

Implantation of encapsulated cells in particles of less than 1 mm (micro-encapsulation) has been proposed as a cell synthesized bio-molecule delivery system. Encapsulation provides immuno-isolation, protecting foreign cells from host immune system while nutrients, oxygen and therapeutic products can diffuse freely across capsule walls. A new method is described for the synthesis of a new family of hollow microparticles for cell encapsulation. Unlike other micro-encapsulation methods, encapsulation in those devices will take place after capsule synthesis, by micro-injection. The microcapsules were prepared by a three-steps original procedure: first, synthesis of a core particle, followed by coating with a layer of epichlorohydrin cross-linked amylo-pectin gel and, finally, selective degradation of the core particle to create the cavity. Initial experiments make use of amylo-pectin cross-linked with trimetaphosphate as core particle material. However, selective degradation was difficult to achieve. In further essays, polyesters were used successfully for the preparation of core particles. Optimizations were carried out and the permeability and morphology of the hollow particles were investigated. The preliminary results show that the new method has the potential to become a standard procedure to obtain hydrogel hollow particles. Moreover, the permeability study seems to be in accordance with specifications for immuno-isolation.

Hyperbranched polymers as scaffolds for multifunctional reversible addition–fragmentation chain‐transfer agents: A route to polystyrene‐core‐polyesters and polystyrene‐block‐poly(butyl acrylate)‐core‐polyesters

AbstractPolydisperse hyperbranched polyesters were modified for use as novel multifunctional reversible addition–fragmentation chain‐transfer (RAFT) agents. The polyester‐core‐based RAFT agents were subsequently employed to synthesize star polymers of n‐butyl acrylate and styrene with low polydispersity (polydispersity index < 1.3) in a living free‐radical process. Although the polyester‐core‐based RAFT agent mediated polymerization of n‐butyl acrylate displayed a linear evolution of the number‐average molecular weight (Mn) up to high monomer conversions (>70%) and molecular weights [Mn > 140,000 g mol−1, linear poly(methyl methacrylate) equivalents)], the corresponding styrene‐based system reached a maximum molecular weight at low conversions (≈30%, Mn = 45,500 g mol−1, linear polystyrene equivalents). The resulting star polymers were subsequently used as platforms for the preparation of star block copolymers of styrene and n‐butyl acrylate with a polyester core with low polydispersities (polydispersity index < 1.25). The generated polystyrene‐based star polymers were successfully cast into highly regular honeycomb‐structured microarrays. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3847–3861, 2003

Influence of Core Suture Material and Peripheral Repair Technique on the Strength of Kessler Flexor Tendon Repair

The purpose of our study was to determine the most favourable combination of core suture material and peripheral repair technique for Kessler tendon repair. Thirty freshly thawed pig flexor tendons were repaired by a Kessler technique, either with braided polyester or monofilament nylon suture. A peripheral augmentation was done using one of the three techniques—running, cross-stitch and Halsted. All repairs were tested by cyclic loading, followed by load-to-failure. During cyclic loading six of the 15 tendons with a nylon core failed, but none with a braided polyester core. Irrespective of peripheral technique, the monofilament nylon core suture allowed early central cyclic gapping, resulting in failure of the repair. During load-to-failure testing, the running stitch proved weakest and the cross-stitch repair toughest.

Cellular polymer composites based on bi-component fibers

Traditionally, bi-component fibers are used as non-woven fabrics where stiffness is not a primary concern. In this work, we show that solvent activation of the polyethylene sheath leads to significant swelling that can induce and form entanglement gel structures between fibers. Fiber-reinforced cellular polymers are produced using bi-component fibers containing a polyester core and a HDPE sheath. Upon removal of the solvent from the gel, a polyethylene membrane structure forms between polyester cores, creating a cellular fiber composite. Swelling of the polyethylene sheath is analogous to a micro-scale “blowing” process. The reinforced cellular structure exhibits improved mechanical properties compared to hot-bonded systems based on similar bi-component fibers. Other possible variants of the micro-scale “blowing” process are discussed.

Synthesis and properties of UV curable waterborne hyperbranched aliphatic polyester

The UV curable waterborne hyperbranched polyester (WBHP) consisting of a multi-hydroxy functional aliphatic polyester core, which is endcapped with methacrylic and salt-like groups in different ratios was synthesized. The core is second generation of hyperbranched aliphatic polyester Boltorn™ H20 with approximately 16 hydroxyl groups. The effects of different ratios of chemical structure of end groups were studied by evaluating various properties of WBHP such as solubility in water, dynamic viscosity, UV curing rate and final unsaturation conversion. A natural good control over the solubility of the samples was possible by salt-like functionality and raising the temperature. The investigation of solubility characteristics of the modified hyperbranched polyester illustrated that those with higher concentration of salt-like moiety were more soluble while those of having lower salt-like moiety were less soluble. The viscosity of the resin WBHP was reduced rapidly by dilution with water and raising temperature. Water showed a favorable viscosity reduction effect as compared to monomer and its blend with water. The polymerization rate of the resins under UV irradiation in the presence of a photoinitiator showed an increasing trend with higher concentration of methacrylate functionality.

Biodegradable comb polyesters containing polyelectrolyte backbones facilitate the preparation of nanoparticles with defined surface structure and bioadhesive properties

AbstractA major challenge in oral peptide and protein delivery remains the search for suitable carrier systems. Therefore, a new concept was investigated combining a modified three‐dimensional architecture, increased hydrophilicity of poly(lactic‐co‐glycolic acid) (PLGA) and charged groups in a single polymer. Biodegradable comb PLGA were synthesized by grafting short PLGA chains onto different poly(vinyl alcohol) (PVA) based backbone polyols, poly(2‐sulfobutyl‐vinyl alcohol) and poly(diethylaminoethyl‐vinyl alcohol). The polyelectrolyte backbones were obtained by etherification of PVA with charge‐containing pendent groups. The comb polymer structure could be confirmed by nuclear magnetic resonance, infrared spectroscopy, differential scanning calorimetry, elemental analysis and measurement of intrinsic viscosity. Nanoparticles (NP), as potential mucosal carriers systems, were prepared by controlled precipitation and investigated as a function of polymer composition. The amphiphilic character and the three‐dimensional architecture of the novel polyesters allowed the preparation of small nanoparticles even without the use of surfactants. Surface NMR, surface charge and hydrophobicity determination indicate a core–corona‐like NP structure, especially in the case of negatively charged polyesters. A structural model is proposed for the NP with an inner polyester core and an outer charged‐groups‐containing surface, depending on polymer composition and backbone charge density. The higher the polymer backbone charge density, the more pronounced its influence on the nanoparticle surface properties. The possibility of preparing NP without the use of a surfactant, as well as of designing the NP surface characteristics by polymer backbone charge density and polymer hydrophilic–hydrophobic balance, will be a major advantage in protein adsorption, bioadhesion and organ distribution. This makes these biodegradable polymers promising candidates for colloidal protein and peptide delivery. Copyright © 2003 John Wiley & Sons, Ltd.

Rheological behaviour during UV-curing of a star-branched polyester

Using a rheometer coupled with an UV-light generator, the viscoelastic behaviour during the fast cure of star-branched polyester is investigated. The 32 arm star polymers consist of a hyperbranched polyester core, Boltorn™ and linear grafts of poly(ε-caprolactone) (degree of polymerisation: 20–52) with methacrylate end groups. The resins are crystalline and the melting points range from 34 to 50 °C; films can be formed and cured below 80 °C. The crossover of G′ and G″ was used as the gel point. The time to reach the gel point, a few seconds, increases linearly with molecular weight.

Development of copolymers of poly( d, l-lactide) and methoxypolyethylene glycol as micellar carriers of paclitaxel

Diblock copolymers containing one block of methoxypolyethylene glycol (MePEG) and one block of either poly( d, l-lactide) (PDLLA), copolymers of poly( d, l-lactide-co-caprolactone) (PDLLACL) or poly(glycolide-co-caprolactone) (PGACL) were synthesized by a ring opening bulk polymerization in the presence of stannous octoate. The copolymer molecular weight and composition were controlled by changing the monomer weight ratios. The copolymers dissolved in aqueous media to form polymeric micelles with a hydrophobic polyester core and a water soluble MePEG shell. Micellar solutions of paclitaxel in the PGACL-MePEG copolymers showed poor physical stability and were the least able to maintain paclitaxel in solution. Micellar paclitaxel solutions with the greatest physical stability were obtained using PDLLA–MePEG copolymers, probably due to the decreased fluidity of the micellar core environment of PDLLA–MePEG compared to PDLLACL-MePEG copolymer micelles. The PDLLA–MePEG diblock copolymer was considered to be the optimal copolymer for the solubilization of paclitaxel. The results of a range of in vitro and in vivo biocompatibility/toxicology tests in animals showed the PDLLA–MePEG micelles to be biocompatible and non-toxic. Biodistribution studies using radiolabelled paclitaxel loaded PDLLA–MePEG micelles in rats showed that paclitaxel rapidly dissociated from the micellar components in the blood and that greater than 95% of the administered micellar diblock copolymer dose was eliminated within 15 h. There was also evidence to suggest that the diblock copolymer was cleaved into its two polymer components in the blood.

Nanotechnology for biomaterials engineering: structural characterization of amphiphilic polymeric nanoparticles by 1H NMR spectroscopy

Nanoparticles composed of diblock poly( d,l-lactide-co-glycolide)-poly(ethylene glycol) (PLGA-PEG) or a branched, multiblock PLA-(PEG) 3 were prepared by the single emulsion technique. Results of previous studies of these nanoparticles suggested that their structure is of the core-corona type with a polyester core and an outer PEG coating. In the present study, 1H NMR spectroscopy was utilized to provide direct evidence of the structure of these nanoparticles suspended in an aqueous environment. The results confirm the existence of the core-corona structure under these conditions, and show that the PEG moieties extend out from the nanoparticle core into the aqueous environment, and exhibit chain mobility similar to that of PEG in solution.

Selected Properties of Predominantly Cotton Staple-Core Knitted Fabrics

This study of single-jersey knit fabrics is the first to examine the basic properties of staple-core knits. Prior studies revealed certain functional and aesthetic advantages of woven staple-core fabrics when compared to 100% cotton or intimate-blend fabrics of the same construction. In this study, nominal 20s count staple-core yams have been spun on a ring spinning frame that incorporates patented modifications. The staple-core yams contain a high tenacity polyester core and a cotton sheath comprising two-thirds of the yam. The fabrics are knitted on a single-feed jersey knitter with a 88.9 mm (3.5-inch) diameter, 20-gauge cylinder. Fabric properties are examined after five home-laundering cycles, in the greige state, after scouring, and after scouring and heat setting. The staple-core knits are stronger, less permeable, and significantly more abrasion resistant than the cotton controls. They also show less differential shrinkage and look consistently better than the controls after laundering. Greater spirality is evident in the greige staple-core knits than in the cotton knits, but the skewness of all fabrics decreases with additional processing. Skewness is substantially eliminated by substituting S- for Z-twist staple-core yam. Relaxed S-twist staple-core fabrics are also denser and greatly more abrasion resistant than comparable Z-twist knits. This suggests that a reduction of yam torque might further improve the superior properties and performance of staple-core knits. Additional study is required to optimize heat setting procedures and provide meaningful discussion of the dimensional stability of staple- core knit fabrics.

Effect of skin treatment and core material on the bending behaviour of sandwich beams

The bending behaviour of sandwich beams with a glass-fibre-reinforced polyester core has been investigated analytically and experimentally. Sandwich beams consist of upper and lower aluminium skins and a soft core. Specimens were loaded under three-point bending conditions. Four different skin treatments and three different core materials were applied in order to study the effect of these parameters on the overall bending behaviour. A great number of specimens were manufactured and theoretical predictions were correlated with respective experimental findings.

Comparison of Filament-Core Spun Yarns Produced by New and Conventional Methods

In recent years, we have been reporting our research on composite yarns of mostly cotton content produced on a modified ring spinning system. Recently, we reported an improved method of producing an all staple-core spun yarn, and we have applied the same method to filament-core spinning, obtaining a yarn of greatly improved quality. The new filament-core yarn has almost total core coverage, does not strip, and is about 10% stronger (probably due to its improved yarn structure) than a conventional filament-core yarn. This paper briefly describes the new and conventional core spinning methods and evaluates nylon filament-core/cotton-wrap yarns produced with them. There is also a comparison of the cover factor, strip resistance, and microscopic cross sections of a few other core yarns (with Kevlar, fiberglass, and polyester cores). A significant improvement in the cover factor of the new yarn suggests that it may be very useful for sewing threads; ropes; twines; cables; special military, industrial, and surgical fabrics; and other textiles in which the high strength, durability, and a 100% cotton surface (for ease of finishing or coating) are important.

Comparison of Cotton/Polyester Core and Staple Blend Yarns and Fabrics

Cotton wrapped polyester core yams produced on a modified ring spinning frame were compared with yams spun from staple fiber blends. The yams contained ap proximately 70% cotton and 30% polyester. Yarns and fabrics made from both regular and high tenaeity polyesters were evaluated. Fabrics produced from the core yams were stronger and more durable than those of the staple blends, and they maintained their superiority in these properties through wet processing and resin .finishing. Other advantages of the core-yam fabrics included better cover and abrasion resistance.

Cotton Blend Fabrics from Polyester Core Yarns

Core spun yarns with a filament core and a cotton wrap were prepared and made into fabrics. The properties of these yarns and fabrics in comparison with all-cotton and intimate staple blend controls were investigated. This study included the dyeing of these fabrics and finishing for smooth drying and flame retardancy.