Hard‐block degradable thermoplastic urethane‐elastomers for electrospun vascular prostheses

Thermoplastic polyurethane (TPU) elastomers with biodegradable chain extenders were synthesized and tested for mechanical performance and biocompatibility. The design of the TPUs was based on structural modification of a mechanically appropriate aromatic isocyanate‐based TPU. As the aromatic isocyanate was substituted with a less toxic but also less “hard” aliphatic isocyanate, the chain extender plays an important role on the mechanical properties. Here, the terephthalate ester chain extender was found to work better than hydroxyl ethyl lactate in providing polymers with mechanical properties similar to commercial aromatic isocyanate‐based TPUs. The polymers were degraded in aqueous solutions at elevated temperatures and compared to polylactic acid (PLA) to partially simulate biodegradation. The lactate‐based TPUs degraded about twice as fast as PLA while the terephthalate‐based TPU degraded much more slowly. The latter material was processed by electrospinning to give a tubular graft approximately the size of a large rat blood vessel. Initial results from implantation of these TPUs into rats are promising and indicate that biodegradation occurs and is likely beneficial to cell proliferation. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Domain structure and interphase dimensions in poly(urethaneurea) elastomers using DSC and SAXS

Small‐angle X‐ray scattering (SAXS) and differential scattering calorimetry (DSC) were used to demonstrate distinct differences in domain size, phase separation, and hydrogen bonding in a series of segmented urethaneurea elastomers prepared from isocyanate‐terminated prepolymers and aromatic diamine chain extenders. Two types of prepolymers were studied. The first contained a broadly polydisperse high molecular mass oligomer with relatively high levels of free isocyanate monomer. The second type of prepolymer contained low levels of high molecular mass oligomers with mass fractions greater than 90% of the two‐to‐one adduct of toluene diisocyanate (TDI) to polytetramethylene glycol (PTMEG). The mass fraction of the residual unreacted diisocyanate was less than 0.1% in the second type. Two chain extenders, 4,4′‐methylene bis‐(2‐chloroaniline)(Mboca) and 4,4′‐methylene bis‐(3‐chloro‐2,6‐diethylaniline) (MCDEA), were used to convert the prepolymers to poly(urethaneurea) elastomers. Materials prepared from the prepolymers with low oligomer polydispersity exhibited smaller hard segment domains with more ordered morphology, greater phase separation, and more hydrogen bonding than those prepared from prepolymers with high oligomer polydispersity. These tendencies were enhanced in those elastomers prepared by chain extension with MCDEA compared to those made with Mboca. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2586–2600, 1999     

丁羟胶型聚氨酯弹性体的水解稳定性

丁羟胶型聚氨酯弹性体的水解稳定性;弹性体;扩链剂     

Synthesis,structural characterization,and properties of polyurethane elastomers containing various degrees of unsaturation in the chain extenders

We prepared polyurethane block copolymers with both 50 and 70% soft segment concentrations, using 4,4′‐diphenylmethane diisocyanate–poly(propylene glycol) prepolymer and 1,4‐butanediol, cis‐2‐butene‐1,4‐diol, and 2‐butyne‐1,4‐diol as chain extenders. The effects of the different chain extenders were observed during synthesis and in the final products. A comparison of spectroscopic, mechanical, and thermal data reveals that polymer properties can be significantly altered by differences in chemical bonding within the chain extender backbone. Although all data support the expected differences in phase morphology between the two series of samples, they also suggest that increasing chain extender unsaturation reduced reactivity with isocyanate, adversely affected hydrogen bonding, lowered the degree of crystallinity of the hard segments, and decreased phase separation. The tensile strength, elongation, modulus, and elastic recovery decreased and the electrical conductivity of iodine‐doped samples increased with increasing chain extender unsaturation. The thermal stability of the urethane group was also lower in samples with increased unsaturation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1316–1333, 2002     

基于己内酰胺和乙醇胺的聚酯酰胺合成及表征

以己内酰胺及乙醇胺进行开环聚合,合成了聚酰胺预聚物(PrePA),并采用N,N'-碳酰双己内酰胺(CBC)和1,4-双(2-噁唑啉)苯(PBOX)对其进行了扩链反应.进一步将PrePA与己二酸缩聚,制备了聚酯酰胺预聚体(PrePEA),以CBC和PBOX复合扩链剂扩链,获得了特性黏数达0.74 dL/g的聚酯酰胺.并采用红外、核磁及WAXS对聚合物的结构和晶型进行了表征,以DSC和TGA测定了聚合物的热性能,同时对聚合物的力学性能进行了测定.     

Polyisobutylene‐based segmented polyureas. I. Synthesis of hydrolytically and oxidatively stable polyureas

Novel segmented polyurea elastomers containing soft polyisobutylene (PIB) segments were synthesized and characterized. The key ingredient, primary amine‐telechelic PIB oligomers (NH₂‐PIB‐NH₂) with number average molecular weights of 2500 and 6200 g/mol were synthesized. PIB‐based polyureas were prepared by using various aliphatic diisocyanates and diamine chain extenders with hard segment contents between 9.5 and 46.5% by weight. All copolymers displayed microphase morphologies as determined by dynamic mechanical analysis. Tensile strengths of nonchain‐extended and chain‐extended polyureas showed a linear dependence on the urea hard segment content. PIB‐based polyureas prepared with NH₂‐PIB‐NH₂ of M_n = 2500 g/mol, 4,4′‐methylendbis(cyclohexylisocyantate), and 1,6‐diaminohexane containing 45% hard segment exhibited 19.5 MPa tensile strength which rose to 23 MPa upon annealing at 150 °C for 12 h. With increasing hard segment content, elongation at break decreased from ～ 450% to a plateau of 110%. The hydrolytic and oxidative stability of PIB‐based polyureas were unprecedented. Although commercial “oxidatively resistant” thermoplastic polyurethanes degraded severely upon exposure to boiling water or concentrated nitric acid, the experimental polyureas survived without much degradation in properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 38–48, 2009     

双噁唑啉扩链尼龙1010

对尼龙 10 10的加成型化学扩链做了系统的研究 ,并对 2 ,2′ 双 (2 唑啉 ) (BOZ)和 1,4 双 (2 唑啉基 )苯 (PBO)的偶联效果和扩链产物的性能做了详细的探讨 ,前者的扩链效果较好 .研究结果表明 ,尼龙10 10熔体的转矩随着反应时间的延长显著增加 .但转矩达到极大值后开始缓慢下降 ,表明扩链产物在高温条件下发生热降解 .扩链剂的用量存在最佳值 ,用量不足时偶联反应不充分 ,用量过量时封端反应加剧 .扩链以后尼龙 10 10的端羧基含量大大降低 ,反应温度对反应速率的影响符合阿累尼乌斯关系式 .扩链产物极限粘度大大高于尼龙原料 ,表明分子量显著提高     

Synthesis and thermo-mechanical characterization of high performance polyurethane elastomers based on heterocyclic and aromatic diamine chain extenders

Two series of 4,4′-diphenylmethane diisocyanate (MDI) and poly(ethylene glycol adipate) (PEGA)-based polyurethane and polyurethaneurea elastomers were synthesized via a one-shot polymerization method and characterized using FTIR, ¹H NMR and ¹³C NMR. The samples in the first series are extended by aliphatic diol chain extenders while in the second series mixtures of aliphatic diols and furanic or aromatic diamine chain extenders are used. TGA experiments revealed that with furanic or aromatic diamine chain extenders the polymer degradation temperature is shifted 90 °C upwards, irrespective of the annealing time at 100 °C according to ASTM 0573-99. The values of Young's modulus and of the tensile strength are higher and the strain at break is lower for the samples in series 2 compared to those in series 1. Increasing the annealing time at 100 °C lowers Young's modulus. Dynamic mechanical thermal analyses points to a progressive microphase separation with annealing time.     

Synthesis and characterization of hyperbranched polyurethane-benzyltetrazole

A series of hyperbranched polyurethane-benzyltetrazoles（H-PBTZs） with different linkage structures were synthesized via the polycondensation of hexamethylenediisocyanate as an A₂ type monomer with（4-（1H-tetrazol-5- yl）benzyl）-diethanolamine（TBDEA） as a BB’₂ type monomer in the absence of catalyst at different temperatures.The FTIR, and ¹³C and ¹H-NMR spectroscopy were used to characterize the molecular structures of TBDEA and H-PBTZs as well as the counterpart linear polyurethane-benzyltetrazole（L-PBTZ）.The molecular composition was determined by the reaction selectivity that the isocyanate group reacted with the hydroxyl group in diethanolamine segment or the active hydrogen atom on tetrazole ring.Raising reaction temperature was propitious to the reaction of isocyanate group with the active hydrogen atom on tetrazole ring.The degrees of branching（DB） for H-PBTZs obtained from the ¹H-NMR spectra increased with raising reaction temperature.The wider molecular weight distribution of 1.7-2.9 for H-PBTZs was obtained via GPC analysis.TGA results showed that H-PBTZs had high thermal stability compared with L-PBTZ.     

Effect of Chain Straightening on Plateau Modulus and Entanglement Molecular Weight of Ni‐diimine Poly(1‐hexene)s

Summary: In this communication, we report the first rheological study on the chain‐straightened Ni‐diimine poly(1‐hexene)s and investigate the unique effect of chain straightening on plateau modulus and entanglement molecular weight of this series of polymers. Two Ni‐diimine poly(1‐hexene) samples having different levels of chain straightening were prepared with a chain‐walking Ni‐diimine catalyst, (ArNC(An) C(An)NAr)NiBr₂ (An = acenaphthene, Ar = 2,6‐(i‐Pr)₂C₆H₃) at two different temperatures. Rheological analyses show that the chain‐straightened polymers exhibit significantly enhanced plateau modulus and reduced entanglement molecular weight compared to regular poly(1‐hexene)s by metallocene catalysis. Such an effect becomes more pronounced with an increase in the level of chain straightening.

Loss moduli G″(ω) versus reduced angular frequency in a linear, natural logarithm plot for the three polymers at the reference temperature of 100 °C.     

Well-defined polyisocyanates via organotitanium(IV) catalyzed living polymerizations of isocyanates

The development of living organotitanium(IV) catalyzed polymerizations is presented. A living polymerization of alkyl isocyanates was developed using TiCl₃OCH₂CF₃, I, as a catalyst, through which large quantities of well-defined (in terms of molecular weight and polydispersity) polyisocyanates are obtainable under ambient conditions. η⁵-CpTiCl₂OCH₂CF₃ (Cp = cyclopentadienyl), II, is also an excellent catalyst for the polymerization of isocyanates and, unlike I, will polymerize monomers containing Lewis basic functional groups in the side chain. Compound II was used to synthesize poly(allyl isocyanate) and poly(2-isocyanatoethyl methacrylate). Both polymers were found to be soluble, in contrast to previous reports, and spectroscopic characterization showed that no crosslinking of the side chains had occurred.     

Synthesis and degradation profile of cast films of PPG-DMPA-IPDI aqueous polyurethane dispersions based on selective catalysts

Waterborne polyurethane (WBU) dispersions synthesized from poly(propylene glycol) (PPG), dimethylolpropionic acid (DMPA), and isophorone diisocyanate (IPDI) with catalysts of different selectivity were prepared via by the conventional prepolymer isocyanate process. Two types of chain extenders were used, ethylene glycol (EG) and propylene glycol (PG), producing polyurethanes. The dispersions were neutralized by the addition of triethylamine. The thermal stability of the materials, obtained as cast films prepared from aqueous dispersions was evaluated by thermogravimetry (TG). It was observed that initial degradation temperatures were above 140 °C, with two-step degradation profiles. The use of a more selective catalyst in the formulations led to materials with higher thermal stability. DTG curves exhibited stages not perceptible in the curves of weight loss, which were mainly influenced by the differences in the formulations. Thermal decomposition of the obtained polyurethanes was followed by TG coupled with FTIR spectroscopy.     

Synthesis of poly(2‐vinyl pyridine)‐b‐poly(n‐hexyl isocyanate) amphiphilic coil‐rod block copolymer by anionic polymerization

A well‐defined amphiphilic coil‐rod block copolymer, poly(2‐vinyl pyridine)‐b‐poly(n‐hexyl isocyanate) (P2VP‐b‐PHIC), was synthesized with quantitative yields by anionic polymerization. A low reactive one‐directional initiator, potassium diphenyl methane (DPM‐K), was very effective in polymerizing 2‐vinyl pyridine (2VP) without side reactions, leading to perfect control over molecular weight and molecular weight distribution over a broad range of initiator and monomer concentration. Copolymerization of 2VP with n‐hexyl isocyanate (HIC) was carried out in the presence of sodium tetraphenyl borate (NaBPh₄) to prevent backbiting reactions during isocyanate polymerization. Terminating the living end with a suitable end‐capping agent resulted in a P2VP‐b‐PHIC coil‐rod block copolymer with controlled molecular weight and narrow molecular weight distribution. Cast film from a chloroform solution of P2VP‐b‐PHIC displayed microphase separation, characteristic of coil‐rod block copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 607–615, 2005     

Synthesis and characterization of chiral poly(alkyl isocyanates) by coordination polymerization using a chiral half‐titanocene complex

A new chiral half‐titanocene complex, [CpTiCl₂(O‐(S)?2‐Bu)], is synthesized and characterized by ¹H and ¹³C NMR spectroscopy. This complex is employed for the coordination polymerization of n‐butyl and n‐hexyl‐ isocyanate leading to chiral polymers, as revealed by their CD spectra. Only the left‐handed helix is produced, due to the chiral (S)?2‐butoxy group, which is bound to the polymer chain end. The polymerization of 3‐(triethoxysilyl)propyl isocyanate produces less soluble polymers. On the other hand, phenyl isocyanate reacts slowly with the complex leading quantitatively and selectively to triphenyl isocyanurate. 2‐Ethylhexyl isocyanate is slowly and selectively cyclotrimerized in the presence of the half‐titanocene complex. However, a statistical copolymer of 2‐ethylhexyl isocyanate and hexyl isocyanate is produced. The reaction of benzyl isocyanate with the complex leads to a mixture of low molecular weight polymer and cyclotrimer. The polymers are characterized using SEC, NMR, and CD spectroscopy and their thermal properties are investigated by TGA/DSC analysis. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2141–2151     

Triblock copolymers and pentablock terpolymers of n‐hexyl isocyanate with styrene and isoprene: Synthesis,characterization, and thermal properties

Triblock copolymers and pentablock terpolymers of n‐hexyl isocyanate (H), styrene (S), and isoprene (I) of the type HSH (six samples, M_n:49–163 K, weight % of H:5–59), HIH (two samples, M_n:75 and 83.4 K, weight % of H:16 and 40), HSISH (one sample, M_n:79.4 K, weight % of H:13), and HISIH (one sample, M_n:128 K, weight % of H:25) were synthesized by high‐vacuum techniques in tetrahydrofuran at ?98 °C with the sodium naphthalene/sodium tetraphenylborate initiating system. All materials were characterized by size exclusion chromatography, membrane osmometry, and ¹H NMR. The combined molecular characterization results revealed a high degree of molecular and compositional homogeneity. The thermal properties of the synthesized materials were examined by thermogravimetric analysis and differential scanning calorimetry. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3094–3102, 2003     

Off‐atomic site charges in some anions,metal cations,and complexes: Significance for electrostatic properties and binding

Electronic structures and properties of several anions, metal cations, and their complexes with neutral molecules were investigated at the HF/6‐31G** and B3LYP/6‐31G** levels of theory. Charges shifted from atomic sites due to atomic orbital hybridization called hybridization displacement charges (HDC) were investigated in detail. It has been found that many components of HDC are associated with each atom of ion that are shifted from the atomic sites, those associated with metal cations being shifted by large distances as found previously in electrically neutral systems. It is shown that atomic orbitals are appreciably rehybridized in going from neutral molecules to anions and cations. Molecular dipole moments and surface molecular electrostatic potentials (MEP) are obtained satisfactorily using HDC for the various types of species mentioned above. In the OH^?? H₂O complex, reversal of direction of shift of an HDC component associated with the hydrogen atom of H₂O involved in hydrogen bonding, indicates that the hydrogen bond between OH^? and H₂O would have some covalent character. Other atomic site‐based point charge models cannot provide such information about the nature of bonding. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem 2007     

Studies on degradation of PET in mechanical recycling

PET Poly(ethylene terephthalate) was processed repeatedly in a twin extruder. Effect of reprocessing on molecular structure of PET was evaluated in terms of reduction in molecular weight and mechanical properties. This study shows that weight-average molecular weight M_w drops more notably compared with mechanical properties. Mechanical blending of virgin polymer with recycled PET was studied. The results of mechanical testings indicate that there is only slight loss in mechanical properties. The results suggest that mechanical recycling is a suitable method for recycling of PET for economic and environmental purposes.     

Poly-β-amides

High molecular weight poly-β-amides with fiber-forming properties (repeating unit? NH? CR₂? CR₂? CO? ) differ from the polyamides of the nylon series in that the amide groups are much more closely spaced. These polymers are thus the nearest of the synthetic polyamides to natural silk. The production of poly-β-amides was made possible by a recent synthesis of β-lactams from olefins and chlorosulfonyl isocyanate. The anionic polymerization of the β-lactams gives poly-β-amides containing up to 10 000 monomer units in the chain. The molecular weight can be controlled as desired by means of initiators and chain terminators, and the properties can be varied within wide limits by the choice of the β-lactam or by copolymerization of several β-lactams. Remarkable differences are observed between polymers containing structural units in the threo form and those containing erythro structural units. The poly-β-amides can be spun into fibers having valuable textile properties.     

Metallo‐supramolecular Crosslinked Polyurethanes

The effects of incorporating metal‐binding ligands as chain extenders in polyurethane elastomers were investigated. Segmented polyurethanes based on 2 kDa poly(tetramethylene oxide) (PTMO) and 4,4‐methylenebis(cyclohexyl isocyanate) were polymerized using a two‐step process in which 2,6‐bis(1‐ethyl‐5‐(methoxymethyl)‐1H‐benzo[d]imidazol‐2‐yl)pyridine was added as a chain extender. The resulting polyurethanes were then metallated using stoichiometric amounts of Zn(II) metal salts with different counterions. The resulting metallopolymers have substantially improved Young's moduli, increased failure stress, and improved thermomechanical behavior. The materials were microphase‐separated into anisotropic hard domains within a PTMO matrix. Simultaneous small‐angle X‐ray scattering and tensile testing revealed the minority hard segment domains remain relatively intact during elongation, likely due to the strength of the metal–ligand complex. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1744–1757