Water vapor permeability of shape memory polyurethane with amorphous reversible phase

Shape memory thermoplastic polyurethanes (TPUs), based on amorphous soft segment from the reaction of hexamethylene diisocyanate and 1,2‐butane diol, and the crystalline hard segment from 4,4′‐methylenediphenyl diisocyanate and 1,6‐hexanediol, were modified by hydrophilic segments, diol‐terminated poly(ethylene oxide) or dimethylol propionic acid (DMPA). Differential scanning calorimetry, dynamic mechanical testing, tensile testing, and the measurement of shape memory effect, water swell, and water vapor permeability were carried out to examine these TPUs. The hydrophilic segment increased the hysterisis in shape memory effect by reducing the crystallinity of the hard segment. The neutralized DMPA unit enhanced the sensitivity of the thermoresponsive water vapor permeability (WVP) by amplifying the increase of WVP at the temperature range above the glass transition temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3009–3017, 2000     

Synthesis of nylon‐6 triblock copolymers with bifunctional polymeric activators

ABA‐type copolymers were synthesized by the anionic polymerization of hexanelactam with the sodium salt of hexanelactam as an initiator and amino‐terminated polytetrahydrofuran telechelic functionalized with diisocyanates. Two types of diisocyanates, hexamethylene diisocyanate (1,6‐diisocyanatohexane) and isophorone diisocyanate (IF; 5‐isocyanato‐1‐isocyanatomethyl‐1,3,3‐trimethylcyclohexane), were used as precursors for polymeric activators (PACs). IF was used for the first time. It was proven that the PACs were incorporated as soft, flexible midblocks in the chains of hard nylon‐6 segments. The polymers were isolated and characterized with various spectroscopic techniques. The effects of the central PAC block (according to the type, molecular weight, and content) and the polymerization conditions on the kinetics, activation energies, molecular weights, and structures of the triblock copolymers were investigated. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4154–4164, 2000     

Biodegradable aliphatic thermoplastic polyurethane based on poly(ε‐caprolactone) and L‐lysine diisocyanate

A biodegradable aliphatic thermoplastic polyurethane based on L ‐lysine diisocyanate and 1,4‐butanediol hard block segments, and 2000 g/mol poly(ε‐caprolactone) diol soft block segments was synthesized. The resulting polymer was a tough thermoplastic with ultimate tensile strength of 33 MPa and elongation of 1000%. The polymer displayed classic segmented thermoplastic elastomer morphology with distinct hard block and soft block phases. Thermal and dynamic mechanical analyses determined that the material has a useful service temperature range of around ?40 °C to +40 °C, making it an excellent candidate for low‐temperature elastomer and film applications, and potentially as a material for use in temporary orthopedic implant devices. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2990–3000, 2006     

Effect of the diisocyanate on the structure and properties of polyurethane acrylate prepolymers

In this study, we investigated the role of diisocyanate on the properties of polyurethane acrylate (PUA) prepolymers based on polypropylene oxide (M̄_n = 2000 g · mol⁻¹). The diisocyanates studied were isophorone diisocyanate, 4‐4′dicyclohexylmethane diisocyanate, and toluene diisocyanate (pure 2,4‐TDI, pure 2,6‐TDI, and a TDI mixture, TDI_tech). The molecular structure of the diisocyanate had a major role on the course of the polycondensation and, more precisely, on the sequence length distribution of the final prepolymer. Moreover, the structural organization of the prepolymer also strongly depended on the nature of the diisocyanate. Two types of behaviors were particularly emphasized. On the one hand, the PUA synthesized from 2,4‐TDI displayed an enhanced intermixing between soft polyether segments and hard urethane groups, as revealed by the analysis of hydrogen bonding in Fourier transform infrared. Consecutively, the glass transition shifted to higher temperatures for these polymers. On the other hand, strong hard–hard inter‐urethane associations were observed in 2,6‐TDI‐based prepolymers; these led to microphase segregation between polyether chains and urethane groups, as revealed by optical microscopy. This inhomogeneous structure was thought to be responsible for the unusual rheological behavior of these PUA prepolymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2750–2768, 2000     

New fluorinated thermoplastic elastomers. II. Synthesis and characterization of perfectly alternating fluorinated polyimide–fluorinated polyhybridsiloxane block copolymers via polyhydrosilylation

The synthesis of perfectly alternating fluorinated polyimide–fluorinated polyhybridsiloxane block copolymers (FPI‐FPHSX) was achieved through polyhydrosilylation of α,ω‐diallylfluorinated polyimides (AT‐FPI) and α,ω‐dihydrosilane fluorinated–polyhybridsiloxanes (HT‐FPHSX). A series of three FPI‐FPHSX containing 15, 38, and 56 wt % of polyimide was synthesized and characterized by tuning the number‐average molecular weight either of the hard polyimide segments or of the soft polyhybridsiloxane segments. The influence of the soft and hard segment lengths on the behavior of the thermoplastic elastomer material was studied (hardness, surface tension, thermal stability). The FPI‐FPHSX block copolymers thermomechanical properties are also reported. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 200–207, 2004     

Structure and properties of segmented poly(urethaneurea)s with relatively short hard‐segment chains

We report the structure and properties of segmented poly(urethaneurea) (SPUU) with relatively short hard‐segment chains. The SPUU samples comprised poly(tetramethylene glycol) prepolymer as a soft segment and 4,4′‐diphenylmethane diisocyanate (MDI) units as a hard segment that were extended with ethylenediamine. To discuss quantitatively the conformation of the soft‐segment chain in the microphase‐separated domain space, we used SPUU samples for which the molecular weights of the hard‐ and soft‐segment chains are well characterized. The effects of the cohesive force in the hard‐segment chains on the structure and properties of SPUU were also studied with samples of different chain lengths of the hard segment, although the window of x_H, the average number of MDI units in a hard‐segment chain, was narrow (2.38 ≤ x_H ≤ 2.77). There were urethane groups in the soft segments and urea groups in the hard segments. Because of a strong cohesive force between the urea groups, we could control the overall cohesive force in the hard‐segment chains by controlling the chain lengths of the hard segment. First of all, microphase separation was found to be better developed in the samples with longer hard‐segment chains because of an increase of the cohesive force. It was also found that the interfacial thickness became thinner. The long spacing for the one‐dimensionally repeating hard‐ and soft‐segment domains could be well correlated with the molecular characteristics when the assumption of Gaussian conformation was employed for the soft‐segment chains. This is unusual for strongly segregated block copolymers and might be characteristic of multiblock copolymers containing rod–coil chains. The tensile moduli and thermal stability temperature, T_H, increased with an increase of the cohesive force, whereas the glass‐transition temperature, the melting temperature, and the degree of crystallinity of the soft‐segment chains decreased. The increase in T_H especially was appreciable, although the variation in the chain length of the hard segment was not profound. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1716–1728, 2000     

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

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

Synthesis and thermal,optical, and mechanical properties of sequence‐controlled poly(1‐adamantyl acrylate)‐block‐poly(n‐butyl acrylate) containing polar side group

We prepared the sequence‐controlled block copolymers including poly(1‐adamantyl acrylate) (PAdA) and poly(n‐butyl acrylate) sequences as the hard and soft segments, respectively, by the organotellurium‐mediated living radical polymerization. The thermal, optical, and mechanical properties of the adamantane‐containing block copolymers with polar 2‐hydroxyethyl acrylate (HEA) and acrylic acid (AA) repeating units were investigated. The microphase‐separated structures of the block copolymers were confirmed by the differential scanning calorimetry and atomic force microscopy observations as well as dynamic mechanical measurements. The α‐ and β‐dispersions due to the main‐chain and side group molecular motions, respectively, of the hard and soft segments were observed. Their transition temperatures and activation energies increased due to the formation of intermolecular hydrogen bonding by the introduction of the HEA and AA repeating units. The effects of the hydrogen bonding on their tensile elasticity, strength, and strain were also evaluated. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2899–2910     

Polyisobutylene‐based polyurethanes. III. Polyurethanes containing PIB/PTMO soft co‐segments

The synthesis, characterization, and structure–property behavior of polyurethanes containing polyisobutylene (PIB)/poly(tetramethylene oxide) (PTMO) soft co‐segments and bis(4‐isocyanatocyclohexyl)methane (HMDI)/hexanediol (HDO) hard segments is presented. The mechanical (stress/strain, hardness, and hysteresis) properties of these novel polyurethanes were investigated over a broad composition range. PIB‐based polyurethanes with HMDI/HDO hard segments showed better mechanical properties than earlier polyurethanes containing highly crystalline hard segments. The addition of moderate amounts (20% by weight) of PTMO significantly increased both tensile strengths and elongation. In the presence of larger amounts of PIB, these polyurethanes are expected to possess oxidative/hydrolytic/enzymatic stabilities superior to commercially available polyurethanes. These polyurethanes are softer and exhibit hysteresis superior to or comparable with conventional polyurethanes. According to initial thermal studies, these materials show good melt processibility. Overall, the mechanical properties of PIB based hybrid polyurethanes are similar to commercially important polyurethane type biomaterials. Our results show that the incorporation of PTMO segments to PIB‐based polyurethanes significantly improves elastomeric properties. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5278–5290, 2009     

Parameters affecting transition temperatures of poly(lactic acid‐co‐polydiols) copolymer‐based polyester urethanes and their shape memory behavior

A series of polyester urethanes (PEUs) comprising poly(lactic acid‐co‐polydiol) copolymers as a soft segment, 4,4′‐diphenylmethane diisocyanate (MDI) and 1,4‐butanediol (BDO) as a hard segment were systematically synthesized. Soft segments, which were block copolymers of L ‐lactide (LA) and polydiols such as poly(ethylene glycol) and poly(trimethylene ether glycol), were prepared via ring opening polymerization. Glass transition temperatures (T_g) of the obtained PEUs were found strongly dependent on properties of copolymer soft segments. By simply changing composition ratio, type and molecular weight of polydiols in the soft segment preparation step, T_g of PEU can be varied in the broad range of 0–57°C. The synthesized PEUs exhibited shape memory behavior at their transition temperatures. PEUs with hard segment ratio higher than 65 mole percent showed good shape recovery. These findings suggested that it is important to manipulate molecular structure of the copolymer soft segment for a desirable transition temperature and design optimal soft to hard segment ratio in PEU for good shape recovery. Copyright © 2011 John Wiley & Sons, Ltd.     

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     

Rheological characterization and microphase‐separated structure of a poly(ether‐block‐amide) segmented block copolymer

Melt of a segmented block copolymer having poly(lauryl lactam) as the hard segment and poly(tetramethylene oxide) as the soft segment was investigated by rheological techniques. Storage modulus of the polymer melt exhibits the nonterminal behavior resembling those of diblock and triblock copolymer melts, indicating the existence of a microphase‐separated structure. Contrary to block copolymers, the melt of the segmented block copolymer changes from a weak structure to a stiff one upon raising temperature. The storage modulus of the weak structure at low temperatures is inert to large‐amplitude oscillatory shear, while the oscillatory shear destroys the stiff structure at high temperatures and reduces its storage modulus to a value that is same as that of the weak structure. The tapping‐mode data of atomic force microscopy reveal that at low temperatures the polymer melt exhibits a biphasic structure consisted of small spherical soft domains dispersed in a slightly harder matrix; and at high temperatures the spherical domain structure preserves, though the domain coarsens and the hardness difference between the domain and the matrix enlarges. Infrared spectrum analysis shows that the temperature‐induced structural change is related to the dissociation of hydrogen bonding between the hard and soft segments. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2557–2567, 2005     

The influence of hard‐segments on two‐phase structure and shape memory properties of PCL‐based segmented polyurethanes

Poly(ε‐caprolactone)‐based segmented polyurethanes (PCLUs) were prepared from poly(ε‐caprolactone) diol, diisocyanates (DI), and 1,4‐butanediol. The DIs used were 4,4′‐diphenylmethane diisocyanate (MDI), 2,4‐toluenediisocyanate (TDI), isophorone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI). Differential scanning calorimetry, small‐angle X‐ray scattering, and dynamic mechanical analysis were employed to characterize the two‐phase structures of all PCLUs. It was found that HDI‐ and MDI‐based PCLUs had higher degree of microphase separation than did IPDI‐ and TDI‐based PCLUs, which was primarily due to the crystallization of HDI‐ and MDI‐based hard‐segments. As a result, the HDI‐based PCLU exhibited the highest recovery force up to 6 MPa and slowest stress relaxation with increasing temperature. Besides, it was found that the partial damage in hard‐segment domains during the sample deformation was responsible for the incomplete shape‐recovery of PCLUs after the first deformation, but the damage did not develop during the subsequent deformation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 557–570, 2007     

Preparation and characterization of waterborne poly(urethane urea) with well‐defined hard segments

A series of polyester‐based poly(urethane urea) (PUU) aqueous dispersions with well‐defined hard segments were prepared from polyester polyol, 4,4′‐diphenylmethane diisocyanate, dimethylolpropionic acid, 1,4‐butanediol, isophorone diisocyanate, and ethylenediamine. These anionic‐type aqueous dispersions had good dispersity in water and were stable at the ambient temperature for more than 1 year. For these aqueous dispersions, the particle size decreased as the hard‐segment content increased, and the polydispersity index was very narrow (<1.10). Films prepared with the PUU aqueous dispersions exhibited excellent waterproof performance: the amount of water absorption was as low as 5.0 wt %, and the contact angle of water on the surface of this kind of film was as high as 103° (this led to a hydrophobic surface). The water‐resistant property of these waterborne PUU films could be well correlated with some crystallites and ordered structures of the well‐defined hard segments formed by hydrogen bonding between the urethane/urethane groups and urethane/ester groups, as well as the degree of microphase separation between the hard and soft segments in the PUU systems. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2606–2614, 2005     

Synthesis of ABA‐triblock and star‐diblock copolymers with poly(2‐adamantyl vinyl ether) and poly(n‐butyl vinyl ether) segments: New thermoplastic elastomers composed solely of poly(vinyl ether) backbones

ABA‐type triblock copolymers and AB‐type star diblock copolymers with poly(2‐adamantyl vinyl ether) [poly(2‐AdVE)] hard outer segments and poly(n‐butyl vinyl ether) [poly(NBVE)] soft inner segments were synthesized by sequential living cationic copolymerization. Although both the two polymer segments were composed solely of poly(vinyl ether) backbones and hydrocarbon side chains, they were segregated into microphase‐separated structure, so that the block copolymers formed thermoplastic elastomers. Both the ABA‐type triblock copolymers and the AB‐type star diblock copolymers exhibited rubber elasticity over wide temperature range. For example, the ABA‐type triblock copolymers showed rubber elasticity from about ?53 °C to about 165 °C and the AB‐type star diblock copolymer did from about ?47 °C to 183 °C with a similar composition of poly(2‐AdVE) and poly(NBVE) segments in the dynamic mechanical analysis. The AB‐type star diblock copolymers exhibited higher tensile strength and elongation at break than the ABA‐type triblock copolymers. The thermal decomposition temperatures of both the block copolymers were as high as 321–331 °C, indicating their high thermal stability. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Microphase separation in RIM polyureas as studied by solid-state NMR

The microphase separation (MPS) in polyureas based on methylene diphenyl diisocyanate (MDI) hard segment, diethyltoluenediamine chain extender, and amino-terminated polypropylene glycol soft segment prepared by reaction injection molding (RIM) was studied by advanced solid-state NMR spectroscopy. Incomplete microphase separation leads to the presence of mobilized hard segments dispersed in the soft segment domains as well as immobilized soft segments residing in the hard domains. This is detected by ¹H-NMR spectra recorded under spinning at the magic angle (MAS) as well as two-dimensional wide-line separation (WISE) NMR spectra. The sizes of the various domains as well as the interfaces between them are quantified by spin diffusion measurements. In this way the impact of annealing, method of polymerization, and hard segment content on MPS is studied. Whereas annealing at temperatures up to 170°C results in improving the MPS, major changes are observed after annealing at higher temperatures (190°C), where the system changes from “soft-in-hard” to “hard-in-soft” behavior. The MPS decreases with increasing hard segment content. The highest MPS is observed for solution polymerized samples. The various NMR experiments clearly reveal the nonequilibrium nature of RIM systems. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 693–703, 1998     

Segmented polyurethanes derived from novel siloxane–carbonate soft segments for biomedical applications

A novel macrodiol based on mixed silicone and carbonate chemistries was synthesized and used as a soft segment precursor in the synthesis of two series of segmented polyurethane (PU) copolymers varying in hard segment content and soft segment molecular weight. The hard segments in these copolymers were derived from 4,4‐methylene diphenyl diisocyanate and 1,4‐butane diol. The phase transitions, microphase separation behavior, and mechanical properties of the copolymers were investigated using a variety of experimental methods. When compared with segmented PU copolymers having predominately poly(dimethyl siloxane) soft segments, these siloxane–carbonate soft segment copolymers exhibit enhanced intersegment mixing, and consequently relatively low mechanical modulus. With relatively low modulus and siloxane units in the soft phase, the siloxane–carbonate PUs have potential for use in cardiac and orthopedic biomedical applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Morphological analysis of photocured polyurethane acrylate networks. Correlation with viscoelastic properties

In this paper, we investigate the final morphology of photocured polyurethane acrylates based on polypropylene oxide by means of Transmission Electron Microscopy (TEM), Small Angle X‐ray Scattering (SAXS), and dynamic mechanical measurements. Two interrelated structural features on two different size scales can occur in these systems. TEM analysis demonstrates the presence of inhomogeneities on the length scale of 10–200 manometers, mostly constituted by clusters of small hard units (diacrylated diisocyanate) connected by polyacrylate chains. The bimodal shape of the dynamic mechanical relaxation spectra corroborates this two‐phase structure. Besides, a suborganization of the reacted diisocyanate hard segments inside the polyurethane acrylate matrix is revealed by SAXS measurements, depending on the nature of the hydroxylacrylate used for the synthesis of the precursor. Finally, UV‐exposure time is found to induce modifications on the viscoelastic properties of the final network, even at high double‐bond conversion: this effect can be due to a postreaction and to an increase of the crosslinking density inside the hard segments domains. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 919–937, 1999     

Shape memory biomaterials prepared from polyurethane/ureas containing sulfated glucose

Covalently crosslinked polyurethane/urea polymers were synthesized using diamine monomers modified with pendant glucose groups and 2,4‐toluene diisocyanate, poly(ethylene glycol) (PEG), and 1,1,1‐tris(hydroxymethyl)ethane (triol) comonomers. The polymers showed shape memory behavior with a switching temperature dependent on the glass transition temperature. The glass transition temperature is tuned by varying the mole ratio between the glucose‐diamine and PEG used in the polymerization. Increasing PEG content resulted in decreasing glass transition temperature, and a glass transition temperature of 39 °C, close to physiological temperatures, was obtained. The fixed shape showed gradual shape recovery behavior, but a fixity of 70% was achieved when the material was stored at 25 °C. The polymer recovered to the permanent shape when heated to 50 °C. Finally, the surface of a film of the polymer can be sulfated to achieve increased blood‐compatibility without sacrificing the shape memory properties. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2252–2257     

Preparation and characterization of a new class of poly(ether‐block‐amide)s via solvent free reactive processing

Novel poly(ether‐co‐amide) block copolymers (PEA) with polyamide‐6 as hard segments and different polyether (polyoxytetramethylene glycol [PTMG]/polyethylene glycol [PEG]) as soft segments were prepared via reactive processing. The chemical structure, crystalline properties, mechanical properties, water resistance, and thermal stability of as‐prepared PEAs were extensively studied by Fourier transform infrared spectroscopy, X‐ray diffraction, differential scanning calorimetry, dynamic mechanical analysis, tensile testing, water contact angle, water absorption, and thermal gravity analysis. Fourier transform infrared spectroscopy confirmed the chemical structure and composition of PEAs. The X‐ray diffraction and differential scanning calorimetry showed that PEAs consist of obvious crystalline polyamide‐6 hard segments and that the crystalline structure of PEG will be significantly changed with the addition of PTMG. Dynamic mechanical analysis and tensile testing showed that the obtained PEAs exhibit classical elastomeric rubber plateau and tensile behavior. Meanwhile, the introduction of PTMG will improve the mechanical properties of PEAs. PEA with PEG as soft segments exhibited extremely surface hydrophilicity and high water absorption of 127%; the increasing of PTMG content in soft segments will reduce the surface hydrophilicity and improve the water resistance. In addition, the obtained PEAs exhibited good thermal stability, which will meet requirement of multiple processing.