Soft Segment Content Research Articles

Influences of fluorine on microphase separation in fluorinated polyurethanes

Abstract The microstructures of fluorinated polyurethanes (FPUs) possess separated soft and hard phases related to their unique mechanical and physiochemical properties. We studied the microstructures of FPUs and H-bond interactions focusing on the influences of fluorine (F) content on the separation between the soft and hard phases by combining experimental and computational approaches. FPUs featuring F in side chains were synthesized using fluorinated polyether glycol as soft segments, MDI as hard segments, and 1,4-butanldiol (BDO) as chain extenders with various molar ratio of hard/soft segments. Fourier transform infrared spectroscopy (FTIR) and molecular dynamics (MD) studies both show that increasing F content of soft segments enhances H-bond interactions between soft and hard segments, thus reducing the extent of microphase separation. The direct visual inspection of microstructures by SEM reveals that the soft and hard segments separate more significantly as the fraction of the hard segments increases, consistent with the increasing density fluctuation of F and N elements found in the MD simulations. The glass transition temperatures (Tg) measured by DMA indicate that the optimal working temperature window of FPUs separating soft and hard glass transitions becomes narrow with increasing F and weakened phase separation. Tg predicted by MD are in quantitative agreement with the DMA experiments. This work demonstrates that how experiments and computations can be combined to study composition-structure-property relationships of polymers to optimize the separated microphase structures of FPU for overall good balance among materials performance, synthesis costs, and environmental impacts.

Mechanical properties and biodegradability of porous polyurethanes reinforced with green nanofibers for applications in tissue engineering

New class of green nanostructured biocomposites was designed and synthesized for tissue engineering applications. These newly introduced non-cytotoxic and biodegradable polyurethanes are composed of linear aliphatic hexamethylene diisocyanate and polycaprolactone diol. Porosities of different synthesized biocomposite samples were 70–75 % for non-reinforced matrices, 64–70 % for reinforced with 5 wt% biocellulose nanofiber (BCNF), 59–69 % for 10 wt% of BCNF, and 56–69 % for 15 wt% of BCNF. Compressive strength results showed an increase of 84 % with BCNF reinforcement of 5 wt% and more than twofold increase (increase of 120 %) for 10 wt%. The tensile strength also increased up to almost twofold (115 %) for reinforcement with 5 wt% BCNF and to more than twofolds (143 %) for 10 wt% reinforcement. Higher degrees of reinforcement up to 15 wt% showed a detrimental effect on both properties. Results from biodegradation experiments showed that biocomposite scaffolds exhibited progressive mass loss over 5-week period, which varied according to the composition (ranged from 17 to 29 %), where the loss in mass was higher when soft segment content was higher.

Thermoplastic polyurethanes with isosorbide chain extender

ABSTRACTIsosorbide, a renewable diol derived from starch, was used alone or in combination with butane diol (BD) as the chain extender in two series of thermoplastic polyurethanes (TPU) with 50 and 70% polytetramethylene ether glycol (PTMEG) soft segment concentration (SSC), respectively. In the synthesized TPUs, the hard segment composition was systematically varied in both series following BD/isosorbide molar ratios of 100 : 0; 75 : 25; 50 : 50; 25 : 75, and 0 : 100 to examine in detail the effect of chain extenders on properties of segmented polyurethane elastomers with different morphologies. We found that polyurethanes with 50% SSC were hard elastomers with Shore D hardness of around 50, which is consistent with assumed co‐continuous morphology. Polymers with 70% SSC displayed lower Shore A hardness of 74–79 (Shore D around 25) as a result of globular hard domains dispersed in the soft matrix. Insertion of isosorbide increased rigidity, melting point and glass transition temperature of hard segments and tensile strength of elastomers with 50% SSC. These effects were weaker or non‐existent in 70% SSC series due to the short hard segments and low content of isosorbide. We also found that the thermal stability was lowered by increasing isosorbide content in both series. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42830.

Thermoplastic polyurethanes with controlled morphology based on methylenediphenyldiisocyanate/isosorbide/butanediol hard segments

Isosorbide, a cyclic, rigid and renewable diol, was used as a chain extender in two series of thermoplastic polyurethanes (PUs). Isosorbide was used alone or in combination with butanediol to examine the effects on the morphology of PU. Two series of materials were prepared – one with dispersed hard domains in a matrix of polytetramethylene ether glycol soft segments of molecular weight 1400 g mol−1 (at 70 wt% soft segment concentration, SSC) and the other with co-continuous soft and hard phases at 50 wt% SSC. We investigated the detailed morphology of these materials with optical and atomic force microscopy, as well as ultra-small-angle X-ray scattering. The atomic force microscopy measurements confirmed the different morphologies in PUs with 50 wt% SSC and with 70 wt% SSC. Small-angle X-ray scattering data showed that in PU with 70 wt% SSC, the hard domain size varied between 2.4 and 2.9 nm, and decreased with increasing isosorbide content. In PU with 70 wt% SSC, we found that the correlation length and average repeat distances became smaller with increasing isosorbide content. We estimated the thickness of the diffuse phase boundary for PU with 70 wt% SSC to be ca 0.5 nm, decreasing slightly with increasing isosorbide content. © 2015 Society of Chemical Industry

Segmented polyurethane elastomers by nonisocyanate route

ABSTRACTNovel segmented polyurethane elastomers were successfully synthesized by a nonisocyanate route using dicyclic carbonates as precursors for both soft and hard segments. The hard segment was prepared from the dicyclic carbonate of bisphenol A and m‐xylylenediamine as chain extender. The soft segment was poly(tetramethylene ether) glycol of molecular weight 1000. Three polyurethanes with different morphologies were made with soft segment concentration of 70, 50, and 30%. Method of synthesis consisted in preparation of dicyclic carbonate of bisphenol A from a commercial epoxy resin and carbon dioxide, while dicyclic carbonate of poly(tetramethylene ether) glycol (PTMEG) was made from previously prepared diglycidyl ether of PTMEG and carbon dioxide. Polymers were prepared by reacting dicyclic carbonates with m‐xylylenediamine by one‐pot process. The monomers and polymers were characterized by Fourier transform infrared spectroscopy, differential scanning chromatography, thermogravimetric analysis, 1H NMR, 13C NMR, scanning electron microscopy, and mechanical measurements. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42492.

Synthesis and characterization of adipic acid/polyethylene glycol/poly(ethylene terephthalate) copolyester fiber

A series of aliphatic/aromatic copolyesters that contained different amounts of aliphatic segments, constructed from adipic acid (AA, 0∼0.117 mole ratios), were synthesized. The structure of each copolymer was confirmed by 1H nuclear magnetic resonance. The molecular weight was determined directly by gel permeation chromatography and indirectly by the intrinsic viscosity. The results of thermal tests revealed that both melting temperature ( T m) and crystallization temperature ( T c) decreased as the aliphatic segment content increased. The glass transition temperatures ( T g) that were determined by dynamic mechanical analysis followed the same trend as did T m. Moreover, the thermal stability, determined from thermogravimetric analysis, declined as polyethylene glycol (PEG) and AA were incorporated into the poly(ethylene terephthalate) (PET) main chains. All of the polymers that were synthesized herein were spun into fibers and then physically characterized. The tenacity of the fibers decreased as the soft-segment content increased. The crystalline structures, revealed by wide-angle X-ray scattering, indicated that the crystallinity decreased with increasing AA content because of the reduction of regularity of the PET chains. Most importantly, the tests that were carried out on the knitted fabric demonstrated that the moisture regain and cool feeling ( qmax) of the copolymer fabrics were better than those of fabrics that comprised neat PET chains, owing to the incorporation of soft PEG segments. Finally, the copolymer fabric exhibited better hydrolysis and enzymatic degradation than did neat PET fabric.

New thermoplastic polyurethane elastomers based on aliphatic–aromatic chain extenders with different content of sulfur atoms

Three series of new thermoplastic polyurethane elastomers (TPUs) were synthesized by a one-step melt polyaddition from aliphatic–aromatic chain extenders with different content of sulfur atoms, i.e., 2,2′-[sulfanediylbis(benzene-1,4-diyloxy)]diethanol (OSOE), 2,2′-[oxybis(benzene-1,4-diylsulfanediyl)]diethanol (SOSE) or 2,2′-[sulfanediylbis(benzene-1,4-diylsulfanediyl)]diethanol (SSSE), 1,1′-methanediylbis(4-isocyanatobenzene) (MDI) and 40, 50 or 60 mol% poly(oxytetramethylene) diol (PTMO) of $$ \bar{M}_{n} $$ = 1,000 g mol−1 as a soft segment. The structures of all the TPUs were examined by FTIR and atomic force microscopy. Their thermal behavior was investigated by means of differential scanning calorimetry and thermogravimetry (TG). For the selected polymers, the gaseous products evolved during the decomposition process were analyzed by TG-FTIR. Moreover, their physicochemical, tensile and adhesive properties as well as Shore A/D hardness were determined. The resulting TPUs were high-molar-mass materials with structures, which were amorphous or had a low degree of ordering. TPUs based on OSOE and SOSE showed a higher degree of microphase separation and glass-transition temperatures almost independent of soft-segment content (at ~−38 and −31 °C) than those from SSSE (from −28 to 1 °C). All TPUs were stable up to 288–297 °C, as measured by the temperature of 1 % mass loss. Their decomposition occurred in a two-step process and began within the hard segments. The main volatile products were carbon dioxide, carbonyl sulfide, aromatic compounds as well as aliphatic ethers and aldehydes. The polymers with 40 and 50 mol% PTMO content showed good tensile strength (~27–46 MPa), in most cases better than their commercial PTMO/MDI/butane-1,4-diol analogs with similar hardness values.

Structure–property relationships of polycarbonate diol‐based polyurethanes as a function of soft segment content and molar mass

ABSTRACTSegmented thermoplastic polyurethanes (PUs) have been synthesized with polycarbonate diol as soft segment and 4,4′‐diphenylmethane diisocyanate and butanediol as hard segment. Two different series employing two different soft‐segment molar mass, 1000 and 2000 g/mol, and by changing the hard‐segment content from 32 to 67% have been investigated with the aim to elucidate the effect of the different content variations on the properties. Morphological, thermal, and mechanical properties have been studied by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), wide angle X‐ray diffraction, atomic force microscopy, tensile and tear strength, hardness, and specific gravity tests. Properties have been explained from the standpoint of miscibility between hard‐ and soft‐segment microdomains of the tailored segmented PUs through an exhaustive analysis. FTIR, DSC, and DMA measurements revealed that miscibility between hard and soft microdomains increases as the molar mass of the macrodiol decreases. An increase in hard‐segment content entailed the formation of larger hard domains with higher crystallinity what results in superior mechanical properties such as higher tensile stress and tear strength, and hardness. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41704.

자동차 내장재용 열가소성 폴리프로필렌에 적용되는 선처리제용 친환경 수분산 폴리우레탄-우레아의 제조 및 성질

The significance of thermoplastic polyolefin polypropylene (PP) lies in its potential to replace polyvinyl chloride (PVC), the most widely used material for automobile interiors (door trim, dash board), which discharges harmful compounds in certain conditions. Another benefit of PP (0.855 amorphous 0.946 crystalline g/cm) is its low density compared to that of PVC (1.1-1.45 g/cm), which reduces vehicle weight. Market demand for eco-friendly water-based adhesive/coating material is rising significantly as a substitute for solvent-based adhesive/coating material which emits VOC and causes harmful working conditions. 232 * To whom correspondence should be addressed. E-mail: kimhd@pusan.ac.kr http://cleantech.or.kr/ct/ doi: 10.7464/ksct.2014.20.3.232 pISSN 1598-9721 eISSN 2288-0690 This is an Open-Access article distributed under the therms of the Ceative Commens Attribution Non-Commercial License (http://creativecommons.org/licences/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is property cited.. 자동차 내장재용 열가소성 폴리프로필렌에 적용되는 선처리제용 친환경 수분산 폴리우레탄-우레아의 제조 및 성질 233 Under such context, in this study, a series of eco-friendly waterborne polyurethane-urea primer (a paint product that allows finishing paint to adhere much better than if it were used alone) for hydrophobic PP were prepared from different mix of DMPA content, NCO/OH molar ratio, various wt% of silicone diol and various soft segment content, among which DMPA of 21 mole %, NCO/OH molar ratio of 1.2, modified silicone diol of 5 wt% and soft segment content of 73 wt% led to good adhesion strength. Additionally, the incorporation of optimum content of additives (0.5 wt% dispersing agent, 0.5 wt% levelling agent, 1.5 wt% antifoaming agent, 3.0 wt% matting agent) into the optimum waterborne polyurethane-urea also enabled good stability, levelling, antifoaming and non-glossy.

Effect of soft segment and clay volume fraction on rate dependent damping of polyurethane and polyurethane-clay nanocomposites

Amorphous polymers have been extensively used for energy dissipative applications due to their relatively low density and controllable rate dependent damping. In general, molecular mobility depends on the rate of applied loading and the ambient temperature, and results in a wide variety of mechanical properties. The variation in the macromolecular chain dynamics can be obtained by altering the chemical architecture and morphology of the constituent monomers. The present study is focused on finding a correlation between the chemical structure of the constituent monomer and the rate dependent viscous damping of the macromolecules. Polyurethane (PU) made up of isophorone diisocyanate (IPDI) and polycaprolactone diol (PCL) is considered to estimate the effect of soft segments (diol content) on damping property of PU. A linear viscoelastic mathematical model (based on standard-linear solid (SLS) model) is used to extract the rate dependent relaxation time constants for the materials. It is found that increasing the soft segment content in the PU does not improve damping limitlessly. Beyond a critical percentage of soft segment content, characteristic relaxation times have a significant drop. Further, the analysis is extended for PU-clay nanocomposites and a correlation between the clay volume fraction and relaxation constants is established. The study will help to choose and design PU and volume percentage of clay nanoparticle for manufacturing PU-clay nanocomposites with desired damping property.

Poly(urethane-dimethylsiloxane) copolymers displaying a range of soft segment contents, noncytotoxic chemistry, and nonadherent properties toward endothelial cells.

Polyurethane copolymers based on α,ω-dihydroxypropyl poly(dimethylsiloxane) (PDMS) with a range of soft segment contents were prepared by two-stage polymerization, and their microstructures, thermal, thermomechanical, and surface properties, as well as in vitro hemo- and cytocompatibility were evaluated. All utilized characterization methods confirmed the existence of moderately microphase separated structures with the appearance of some microphase mixing between segments as the PDMS (i.e., soft segment) content increased. Copolymers showed higher crystallinity, storage moduli, surface roughness, and surface free energy, but less hydrophobicity with decreasing PDMS content. Biocompatibility of copolymers was evaluated using an endothelial EA.hy926 cell line by direct contact, an extraction method and after pretreatment of copolymers with multicomponent protein mixture, as well as by a competitive protein adsorption assay. Copolymers showed no toxic effect to endothelial cells and all copolymers, except that with the lowest PDMS content, exhibited resistance to endothelial cell adhesion, suggesting their unsuitability for long-term biomedical devices which particularly require re-endothelialization. All copolymers exhibited excellent resistance to fibrinogen adsorption and adsorbed more albumin than fibrinogen in the competitive adsorption assay, suggesting their good hemocompatibility. The noncytotoxic chemistry of these synthesized materials, combined with their nonadherent properties which are inhospitable to cell attachment and growth, underlie the need for further investigations to clarify their potential for use in short-term biomedical devices.

Thermoplastic polyurethane elastomers from modified oleic acid

AbstractTwo novel potentially biodegradable thermoplastic polyurethane elastomers with unique structure and morphology were prepared from modified oleic acid. The hardness and mechanical properties were controlled by adjusting the soft segment concentration (SSC). Epoxidized methyl oleate was converted to methyl‐9‐ or −10‐hydroxystearate (hydroxystearate) by catalytic hydrogenation. The formed hydroxystearate was transesterified with 1,6‐hexanediol to obtain polyesterpolyol with molar mass 2500. Segmented polyurethanes with 50% and 70% SSC were prepared using the prepolymer method by reacting polyesterpolyol with diphenylmethane diisocyanate and 1,4‐butanediol as chain extender. Thermal and mechanical properties of the polymers indicated good micro‐phase separation. Both soft and hard segments displayed a certain degree of crystallization. Tensile strengths were 18 and 2.4 MPa for samples with 50% and 70% SSC, respectively. Elongations of 130% (50% SSC) and 43% (70% SSC) were somewhat lower than in comparable materials, presumably due to lower molar mass. © 2014 Society of Chemical Industry

Synthesis and characterization of advance PA6‐b‐PDMS multiblock copolymers

ABSTRACTAdvance polyamide‐6‐b‐polydimethylsiloxane (PA6‐b‐PDMS) multiblock copolymers were first synthesized via the polymerization in bulk. Binary carboxyl terminated PA6 was served as the hard segment and PDMS modified with hexamethylene diisocyanate (PDMS‐NCO) was the soft segment. A series of PA6‐b‐PDMS copolymers based on different content and length of soft segments were obtained. Interestingly, Differential scanning calorimetry (DSC) studies revealed no obvious change in melting temperature after introducing PDMS segments to copolymers. The high melting temperatures indicated these copolymers possess potential applications in automotive industry that require high continuous use temperatures. DSC and transmission electron microscopy studies both demonstrated increasing the length and the content of the soft segment contributed to increasing of the degree of microphase separation. However, the improvement of thermal stability resulting from PDMS segments was also observed by thermo gravimetric analysis. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2014,131, 41114.

Isothermal and non-isothermal crystallization kinetics of a polyglycolide copolymer having a tricomponent middle soft segment

• Crystallization behavior of biodegradable segmented copolyesters. • Comparison between isothermal and non-isothermal crystallizations. • Influence of soft segments on equilibrium melting temperature. • Avrami exponents from non-isothermal calorimetric methods. • Secondary nucleation constant from isoconversional methods. Kinetics of isothermal and non-isothermal crystallization studies of a biodegradable monofilament suture constituted by polyglycolide hard blocks and soft segments derived from glycolide, ɛ-caprolactone and trimethylene carbonate have been undertaken by means of calorimetric methods. This segmented polymer was semicrystalline with melting and crystallization characteristics defined by the polyglycolide hard segments. The amorphous phase had a glass transition temperature highly influenced by thermal processing and the random microstructure of the soft segment. Melting process was complex due to the occurrence of lamellae with different degree of perfection. Equilibrium melting point, determined by the Hoffman–Weeks methodology, became slightly lower than reported for polyglycolide and segmented copolymers having a lower soft segment content. A heterogeneous nucleation and a three-dimensional crystal growth were characteristic for isothermal crystallizations performed from the melt state, being the Avrami exponent very close to 3 for all experiments. Secondary nucleation constant was evaluated from the overall crystallization rates and by assuming the validity of Lauritzen–Hofmann approach. Results point out a maximum rate for a crystallization temperature of 131 °C and probably an underestimated nucleation constant. Kinetic parameters for non-isothermal crystallization were deduced by Avrami, Ozawa and Cazé methods. A good agreement with isothermal parameters was only attained with the last methodology, although results from the other ones were appropriate to simulate the crystallization process. Isoconversional analysis was a good methodology to estimate the secondary nucleation constant from a non-isothermal crystallization.

Preparation of Waterborne Polyurethane‐OMt Nanocomposites and Effect of Clay on UV Degradation

SummaryWaterborne polyurethane polymers (WPU) have gained importance for some decades because of their environmentally friendly characteristics due to low or zero content of solvents. Polyurethane properties can be modified by changing segmental structure or incorporating inorganic fillers into the polymer matrix. Montmorillonite (Mt) clay which is a member of smectite family is widely used in polymer clay composites as a filler. In this work, linear WPU nanocomposites were synthesized using different polyols as soft segment via acetone process which has many advantages over the prepolymer mixing process in terms of reliable reproducibility and convenience for obtaining linear polyurethanes. Sodium modified montmorillonite (NaMt) clay was used without any chemical pretreatment. WPU nanocomposites were prepared via in‐situ polymerization method by modification of sodium modified montmorillonite (NaMt) clay in polyol and following polyurethane reaction. Finally, spectroscopic, thermal, morphological characterizations and UV weathering tests carried out. As a result, different thermal and mechanical properties were observed due to different soft and hard segment content. Furthermore, increasing clay content caused lowering of resistance against UV degradation.

Bio-based shape memory polyurethanes (Bio-SMPUs) with short side chains in the soft segment

One of the obvious shortcomings of bio-based shape memory polyurethanes (Bio-SMPUs), which usually use natural oil based polyols as the soft segment, is their low mechanical strength because the long dangling chains (six to eight carbons) in these polyols prevent the Bio-SMPUs from deep micro-phase separation, and consequently deteriorate their mechanical properties. In this work, we prepared a bio-based polyester diol for the soft segment, in which short side chains (CC) were used to tune the transition temperature and the morphology of the Bio-SMPUs. The moderate concentration of short branch chains barely affects the micro-phase separation, and the mechanical properties of the Bio-SMPUs are quite satisfactory. With the same 70 wt% soft segment content, the tensile strength in this work is 13.2 MPa, while the one using ricinoleate-based soft segments reported 2.8 MPa. Through proper shape memory programming, the synthesized Bio-SMPUs show good shape memory properties with a shape fixing rate of greater than 98% and a shape recovery rate of 85% in the first cycle and greater than 90% in the following cycles. This study provides a framework for developing bio-based SMPUs with high mechanical and good shape memory properties at the same time.

Structural, thermal and surface characterization of thermoplastic polyurethanes based on poly(dimethylsiloxane)

In this study, the synthesis, structure and physical properties of two series of thermoplastic polyurethanes based on hydroxypropyl terminated poly(dimethylsiloxane) (HP-PDMS) or hydroxyethoxy propyl terminated poly(dimethylsiloxane) (EO-PDMS) as a soft segment, and 4,4?-methylenediphenyl diisocyanate and 1,4-butanediol as a hard segment were investigated. Each series is composed of samples prepared with a different soft segment. The polyurethanes were synthesized by two-step polyaddition in solution. The effects of the type and content of PDMS segments on the structure, thermal and surface properties of copolymers were studied by 1H NMR, 13C NMR and two-dimensional NMR (HMBC and ROESY) spectroscopy, GPC, DSC, TGA, WAXS, SEM, water contact angle and water absorption measurements. Thermal properties investigated by DSC indicated that the presence of soft PDMS segments lowers the glass transition and melting temperatures of the hard phase as well as the degree of crystallinity. SEM analysis of copolymers with a lower soft segment content confirmed the presence of spherulite superstructures, which arise from the crystallization of the hard segments. When compared with polyurethanes prepared from HP-PDMS, copolymers synthesized from EO-PDMS with the same content of the soft segments have higher degree of crystallinity, better thermal stability and less hydrophobic surface. Our results show that the synthesized polyurethanes have good thermal and surface properties, which could be further modified by changing the type or content of the soft segments.

Structure and properties of thermoplastic polyurethanes based on poly(dimethylsiloxane): Assessment of biocompatibility

Properties and biocompatibility of a series of thermoplastic poly(urethane-siloxane)s (TPUSs) based on α,ω-dihydroxy ethoxy propyl poly(dimethylsiloxane) (PDMS) for potential biomedical application were studied. Thin films of TPUSs with a different PDMS soft segment content were characterized by (1) H NMR, quantitative (13) C NMR, Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), contact angle, and water absorption measurements. Different techniques (FTIR, AFM, and DMA) showed that decrease of PDMS content promotes microphase separation in TPUSs. Samples with a higher PDMS content have more hydrophobic surface and better waterproof performances, but lower degree of crystallinity. Biocompatibility of TPUSs was examined after attachment of endothelial cells to the untreated copolymer surface or surface pretreated with multicomponent protein mixture, and by using competitive protein adsorption assay. TPUSs did not exhibit any cytotoxicity toward endothelial cells, as measured by lactate dehydrogenase and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide assays. The untreated and proteins preadsorbed TPUS samples favored endothelial cells adhesion and growth, indicating good biocompatibility. All TPUSs adsorbed more albumin than fibrinogen in competitive protein adsorption experiment, which is feature regarded as beneficial for biocompatibility. The results indicate that TPUSs have good surface, thermo-mechanical, and biocompatible properties, which can be tailored for biomedical application requirements by adequate selection of the soft/hard segments ratio of the copolymers.

In situ formed crosslinked polyurethane toughened polylactide

Polylactide (PLA), a biobased polymer, has a short elongation at break and low impact strength, which restricted its broad application as a commodity polymer. In this paper, super-tough polylactide/crosslinked polyurethane (PLA/CPU) binary blends with CPU dispersed in the PLA matrix were prepared by reactive blending of PLA with poly(ethylene glycol) (PEG) and polymeric methylene diphenylene diisocyanate (PMDI). The in situ polymerization of PEG and PMDI in the PLA matrix formed CPU, and the interfacial compatibilization between PLA and CPU phases occurred by the reaction of NCO groups with terminal hydroxyl groups of PLA, which was confirmed by Fourier transform infrared spectroscopy. The results of a tensile test and a notched Izod impact test suggest that the elongation at break and impact strength were increased to more than 20 and 30 times those of neat PLA, respectively. The effects of PEG molecular weight (namely soft segment length of CPU) and CPU content on the phase morphology and impact strength of PLA/CPU blends were investigated systematically. The optimum CPU particle size for high impact toughness was identified to be 0.7–1.0 μm when the soft segment length and the content of CPU were in the ranges of 1000–2000 g mol−1 and 20–30 wt%, respectively. The compatibility between the dispersed CPU and PLA matrix was studied by dynamic mechanical analysis through the change in glass transition temperatures of PLA and CPU components. The results suggest that the compatibility increased with increasing soft segment length and content of CPU, which was mainly due to the increased plasticization effect. With improved toughness, the PLA/CPU blends could be used as substitutes for some traditional petroleum-based polymers.

Comparative analysis of in vitro oxidative degradation of poly(carbonate urethanes) for biostability screening

The resistance to oxidation and environmental stress cracking of poly(carbonate urethanes) (PCUs) has generated significant interest as potential replacements of poly(ether urethanes) in medical devices. Several in vitro models have been developed to screen segmented polyurethanes for oxidative stability. High concentrations of reactive oxygen intermediates produced by combining hydrogen peroxide and dissolved cobalt ions has frequently been used to predict long-term oxidative degradation with short-term testing. Alternatively, a 3% H₂O₂ concentration without metal ions is suggested within the ISO 10993-13 standard to simulate physiological degradation rates. A comparative analysis which evaluates the predictive capabilities of each test method has yet to be completed. To this end, we have utilized both systems to test three commercially available PCUs with low and high soft segment content: Bionate PCU and Bionate II PCUs, two materials with different soft segment chemistries, and CarboSil TSPCU, a thermoplastic silicone PCU. Bulk properties of all PCUs were retained with minor changes in molecular weight and tensile properties indicating surface oxidative degradation in the accelerated system after 36 days. Soft segment loss and surface damage were comparable to previous in vivo data. The 3% H₂O₂ method exhibited virtually no changes on the surface or in bulk properties after 12 months of treatment despite previous in vivo results. These results indicate the accelerated test method more effectively characterized the oxidative degradation profiles than the 3% H₂O₂ treatment system. The lack of bulk degradation in the 12-month study also supports the hydrolytic stability of these PCUs.