Synthesis and characterization of poly(dimethylsiloxane‐urethane) elastomers: Effect of hard segments of polyurethane on morphological and mechanical properties

A series of poly(dimethylsiloxane‐urethane) elastomers based on hexamethylenediisocyanate, toluenediisocyanate, or 4,4′‐methylenediphenyldiisocyanate hard segment and polydimethylsiloxane (PDMS) soft segment were synthesized. In this study, a new type of soft‐segmented PDMS crosslinker was synthesized by hydrosilylation reaction of 2‐allyloxyethanol with polyhydromethylsiloxane, using Karstedt's catalyst. The synthesized soft‐segmented crosslinker was characterized by FT‐IR, ¹H, and ¹³C NMR spectroscopic techniques. The mechanical and thermal properties of elastomers were characterized using tensile testing, thermogravimetric analysis, differential scanning calorimetry (DSC), and dynamical mechanical analysis measurements. The molecular structure of poly(dimethylsiloxane‐urethane) membranes was characterized by ATR‐FTIR spectroscopic techniques. Infrared spectra indicated the formation of urethane/urea aggregates and hydrogen bonding between the hard and soft domains. Better mechanical and thermal properties of the elastomers were observed. The restriction of chain mobility has been shown by the formation of hydrogen bonding in the soft and hard segment domains, resulting in the increase in the glass‐transition temperature of soft segments. DSC analysis indicates the phase separation of the hard and soft domains. The storage modulus (E′) of the elastomers was increasing with increase in the number of urethane connections between the hard and soft segments. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2980–2989, 2006     

Calorimetric and Dielectric Study of the Segmented Biodegradable Poly(ester‐urethane)s Based on Bacterial Poly[(R)‐3‐hydroxybutyrate]

Two series of segmented poly(ester‐urethane)s were synthesized from bacterial poly[(R)‐3‐hydroxybutyrate]‐diol (PHB‐diol), as hard segments, and either poly(ε‐caprolactone)‐diol (PCL‐diol) or poly(butylene adipate)‐diol (PBA‐diol), as soft segments, using 1,6‐hexamethylene diisocyanate as a chain extender. The hard‐segment content varied from 0 to 50 wt.‐%. These materials were characterized using ¹H NMR spectroscopy and GPC. The polymers obtained were investigated calorimetrically and dielectrically. DSC showed that the T_g of either the PCL or PBA soft segments are shifted to higher temperatures with increasing PHB hard‐segment content, revealing that either the PCL or PBA are mixed with small amounts of PHB in the amorphous domains. The results also showed that the crystallization of soft or hard segments was physically constrained by the microstructure of the other crystalline phase, which results in a decrease in the degree of crystallinity of either the soft or hard segments upon increase of the other component. The dielectric spectra of poly(ester‐urethane)s, based on PCL and PHB, showed two primary relaxation processes, designated as α_S and α_H, which correspond to glass–rubber transitions of PCL soft and PHB hard segments, respectively. Whereas in the case of other poly(ester‐urethane)s, derived from PBA and PHB, only one relaxation process was observed, which broadens and shifts to higher temperature with increasing PHB hard‐segment content. It was concluded from these results that our investigated materials exhibit micro‐phase separation of the hard and soft segments in the amorphous domains.     

Poly(caprolactone) containing highly branched segmented poly(ester urethane)s via A2 with oligomeric B3 polymerization

Highly branched, poly(caprolactone) (PCL) containing segmented poly(ester urethane)s were synthesized via polymerization of A₂ and oligomeric B₃ type monomers. An isocyanate functional butanediol‐based A₂ hard segment was synthesized and immediately reacted with a poly(caprolactone)‐based trifunctional (B₃) soft segment. Characterization of thermal properties using DMA and DSC analysis demonstrated that the PCL segment remained amorphous in branched poly(ester urethane)s. Conversely, the crystallinity of PCL segment was retained to some extent in a linear analogue with equivalent soft segment molecular weight. Tensile testing revealed a slight decrease in Young's modulus and tensile strength for the highly branched polymers compared with a linear analogue. However, highly branched poly(ester urethane)s demonstrated lower hysteresis. In addition to synthesis of highly branched polymers, poly(ester urethane) networks were synthesized from a highly branched hydroxyl‐terminated precursor and a low molar mass diisocyanate as the crosslinking agent. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6285–6295, 2008     

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     

Polycaprolactone based biodegradable polyurethanes

Two series of segmented polyurethanes were prepared with systematic variation in soft and hard segment length. The soft segment was constituted by polycaprolactone (PCL) blocks of molecular masses 530 or 2000 and the hard segment (HS) by urethane blocks, in a concentration that varied from 12% to 44% in weight of the whole polyurethane. Morphological analyses indicated that the amount of crystallinity of copolymers was strongly dependent on the PCL molar mass and hard segment content. The copolymers with longer PCL soft segments (Mn=2000) were semicrystalline, but those with shorter PCL segment (Mn=530) were unable to crystallize. The primary factor affectingthe biodegradability of copolymers as evaluated by Sturm tests was the extent of the phase separation, and that the segmental blending of the less biodegradable polyurethane (HS) blocks with PCL in the amorphous phase had a critical unfavorable consequence, which may be attributed to the size of the accessible area by microorganisms.     

Crystallization and melting behavior of the soft and hard segments in poly(ester-ether)s. I. Ethylene oxide-ethylene terephthalate segmented copolymers

The crystallization and melting behavior of a series of ethylene oxide-ethylene terephthalate (EOET) segmented copolymers with different soft segment molecular weight and hard segment weight content were studied by differential scanning calorimeter (DSC) and polarized microscope. The crystallizability of both the hard and the soft segments became worse than that of the corresponding homopolymers due to the interactions of the different segments. The crystallizability of the soft segments is mainly determined by the soft segment molecular weight, but is affected greatly by the content and the crystallinity of the hard segments. Conversely, the soft segment length and content also have a great effect on the crystallization of the hard segments. However, the melting points of the hard segments are determined by the average hard segment length. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2918–2927, 1999     

PIB‐based polyurethanes. IV. The morphology of polyurethanes containing soft co‐segments*

Novel polyurethanes consisting of polyisobutylene (PIB)/poly(tetramethylene oxide) (PTMO) or PIB/poly(hexamethylene carbonate) (PC) soft co‐segments in combination with 4,4′‐methylene‐bis(cyclohexyl isocyanate)/1,6‐hexanediol, 1,4‐butanediol, or 1,6‐hexamethylene diamine hard segments exhibit excellent mechanical properties (upto 31 MPa tensile strength with 700% elongation) together with unprecedented oxidative/hydrolytic stability. A structural model of the morphology of these polyurethanes was developed that reflects this combination of properties. The key new elements of our model are H bridges between the PTMO and PC type soft and urethane hard segments, which compatibilize the soft and hard domains, and the presence of large quantities of chemically resistant PIB soft segments that protect the other oxidatively/hydrolytically vulnerable constituents. A variety of FTIR, DSC, SAXS, AFM, and DMTA experiments strongly support the proposed morphological model. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6180–6190, 2009     

Preparation and characterization of N‐methyl‐substituted polyurethane

We prepared N‐methyl‐substituted polyurethanes with different substitution degrees from sodium hydride, methyl p‐toluene sulfonate, and polyether–polyurethane containing poly(oxytetramethylene) glycol, 4,4′‐diphenylmethane diisocyanate, and 1,4‐butanediol. The chemical structures were characterized with Fourier transform infrared and ¹H NMR. To investigate the effects of the N‐substitution degree on the morphology, thermal stability, and mechanical properties, we used differential scanning calorimetry, thermogravimetric analysis, and a universal testing machine. As the substitution degree increased, the new free (1708 cm^?1) and bonded (1650 cm^?1) carbonyl peaks increased. There was no bonded carbonyl peak in fully substituted polyurethane because the urethane groups had no hydrogen. At a small substitution degree, we observed a slight increase in the glass‐transition temperature and decrease in the endotherms of soft‐segment and hard‐segment domains due to the decrease in the hard‐segment domain and the increase in the urethane groups in the soft‐segment domain. The hard‐segment domain decreased and then disappeared as the N‐methyl substitution degree increased. These changes in the morphology resulted (1) in decreased modulus and tensile strength for the films because of the decrease in physical crosslinking points and (2) improved thermal stability as the substitution degree increased. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4077–4083, 2002     

Crystallization behavior and spherulite morphology of hard and soft segments in butylene terephthalate–ϵ‐caprolactone copolyesters

The crystallization behaviors and spherulite morphology of a series of butylene terephthalate–ϵ‐caprolactone (BCL) copolyesters were explored with differential scanning calorimetry, polarized light microscopy, and wide‐angle X‐ray diffraction. The crystallization characteristics reflecting the segmented properties of BCL copolyesters are discussed. For BCL copolyesters with low or high hard‐segment contents, the ϵ‐caprolactone segments or butylene terephthalate segments are long enough to crystallize and even grow spherulites under appropriate conditions, and the crystallizability strengthens with increases in the corresponding segment sequence length. In BCL copolyesters, the crystallization of the soft segments requires a considerably long sequence length, whereas the hard segments even containing only one structural unit can still crystallize and even grow spherulites. The hard segments can grow the usual spherulites at a higher temperature like the poly(butylene terephthalate) homopolymer. The crystallizabilities of hard segments and soft segments for BCL and ethylene terephthalate–ϵ‐caprolactone copolyesters are compared and discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 634–644, 2001     

Crystallization and melting behavior of the soft and hard segments in poly(ester-ether)s. II. Ethylene oxide-butylene terephthalate segmented copolymers

The crystallization behavior of a series of ethylene oxide-butylene terephthalate (EOBT) segmented copolymers with different soft segment molecular weight and hard segment weight content were examined by differential scanning calorimeter (DSC) and polarized microscope. Combined with the comparison with the crystallization behavior of ethylene oxide-ethylene terephthalate (EOET) segmented copolymers, it can be concluded that the crystallizability of both the soft segments and the hard segments in poly(ester-ether) segmented copolymers is much worse than those of the corresponding homopolymers due to the interactions between the soft and the hard segments. The crystallizability of the soft segments is mainly determined by the soft segment molecular weight, but is weakened by the hard segments. On the other hand, the soft segments have complicated influences on the crystallization of the hard segments. The melting temperatures of the hard segments change monotonically with the average hard segment length, but the corresponding melting enthalpies will reach a maximum at an intermediate soft segment molecular weight. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2928–2940, 1999     

Synthesis and properties of polycyanoethylmethylsiloxane polyurea urethane elastomers: A study of segmental compatibility

A series of polyurea urethane block polymers based on either aminopropyl-terminated polycyanoethylmethylsiloxane (PCEMS) soft segments or soft segment blends of PCEMS and polytetramethylene oxide (PTMO) were synthesized. The hard segments consisted of 4,4′-methylenediphenylene diisocyanate (MDI) chain-extended with 1,4-butanediol. The hard segment content varied from 11 to 36%, whereas the PTMO weight fraction in the soft segment blends varied from 0.1 to 0.9. The cyanoethyl side group concentration was also varied during the synthesis of the PCEMS oligomer. The morphology and properties of these polymers were studied by differential scanning calorimetry, infrared spectroscopy, dynamic mechanical and tensile testing, and small-angle x-ray scattering. These materials exhibited microphase separation of the hard and soft segments; however, attaching polar cyanoethyl side groups along the apolar siloxane chains promoted phase mixing in comparison with polydimethylsiloxane-based polyurethanes. The increased phase mixing is postulated to lead to improved interfacial adhesion and thus can account for the observed improvement in ultimate tensile properties compared with polydimethylsiloxane-based polyurethanes. Both hard segment content and cyanoethyl concentration are important factors governing the morphological and tensile properties of these polymers.     

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     

Biobased polyurethanes from polyether polyols obtained by ionic‐coordinative polymerization of epoxidized methyl oleate

A series of poly(ether urethane) networks were synthesized from polyether polyols obtained by ionic‐coordinative polymerization of epoxidized methyl oleate (EMO) using 4,4′‐methylenebis(phenyl isocyanate) or l ‐lysine diisocyanate as coupling agents. Moreover, a variety of segmented poly(ether urethane) networks with different hard segment contents were obtained using 1,3‐propanediol as the chain extender. The materials were characterized by differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical thermal analysis, and tensile properties. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Hydrogen bonding and crystallization in biodegradable multiblock poly(ester urethane) copolymer

The hydrogen bonding and crystallization of a biodegradable poly(ester urethane) copolymer based on poly(L ‐lactide) (PLLA) as the soft segment were investigated by FTIR. On slow cooling from melt, the onset and the progress of the crystallization of the urethane hard segments were correlated to the position, width, and relative intensity of the hydrogen‐bonded N? H stretching band. The interconversion between the “free” and hydrogen‐bonded N? H and C?O groups in the urethane units in the process was also revealed by 2D correlation analysis of the FTIR data. The crystallization of the PLLA soft segments was monitored by the ester C?O stretching and the skeletal vibrations. It was revealed that the PLLA crystallization was restricted by the phase separation and the urethane crystallization, and at cooling rates of 10 °C/min or higher, the crystallization of the PLLA soft segments was prohibited. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 685–695, 2009     

New segmented poly(ester‐urethane)s from renewable resources

The physical and mechanical properties of aliphatic homopolyesters from monomers obtainable from renewable resources, namely, 1,3‐propanediol and succinic acid, were improved by their combination with aromatic urethane segments capable of establishing strong intermolecular hydrogen bonds. Segmented poly(ester‐urethane)s were synthesized from dihydroxy‐terminated oligo(propylene succinate)s chain‐extended with 4,4′‐diisophenylmethane diisocyanate. The newly synthesized materials were exhaustively characterized by ¹H NMR spectroscopy, size exclusion chromatography, differential scanning calorimetry, dynamic mechanical analysis, and with respect to their main static mechanical properties, an Instron apparatus was used. The average repeat number of the hard segments, evaluated by NMR, ranged from 4 to 9, whereas that of the flexible segments was about 14. The degree of crystallinity, glass‐transition temperature, melting point, tensile strength, elongation, and Young's modulus were influenced by the ratio between hard and soft segments of the segmented copolymer in a predictable way. The results demonstrated that poly(ester‐urethane)s from 1,3‐propanediol and succinic acid are promising thermoplastics. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 630–639, 2001     

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     

Chain orientation and distribution in ring‐banded spherulites formed in poly(ester urethane) multiblock copolymer

A poly(ester urethane) multiblock copolymer containing poly(ε‐caprolactone) glycol (PCL) soft segments gives ring‐banded spherulite as crystallized from its melted film. Analysis based on polarized light microscopy and atomic force microcopy revealed that the ring‐banded structures consist of alternate convex and concave bands as a consequence of rhythmic growth. These convex and concave bands, which are composed of flat‐on and edge‐on lamellae, show layered terrace‐like and fibrillar morphology, respectively. The chain orientation and composition distribution in the ring‐banded spherulites were further investigated using FTIR imaging. The convex bands are mainly PCL‐rich domains with perpendicular chain orientation to the substrate, and the concave bands are urethane‐rich domains, where the PCL chains are perpendicular to the radial growth directions of the spherulite but parallel to the film plane. The formation of different orientations in the convex and concave bands is attributed to the rhythmic growth behavior for the copolymers with composition distribution along the chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 541–547, 2010     

Effect of the crosslink density on the morphology and properties of reaction‐injection‐molding poly(urethane urea) elastomers

The effect of the crosslink density on the morphology and properties of reaction‐injection‐molding poly(urethane urea) (PUU) elastomers was investigated. Fourier transform infrared spectroscopy data showed that the linear and crosslinked PUU had entirely different hard‐domain sizes and hard‐segment ordering. A study of the morphology indicated that an increase in the crosslink density increased microphase mixing. Differential scanning calorimetry studies indicated that the hard‐segment initial glass‐transition temperature was independent of the crosslink density. The glass‐transition temperature of the soft segment was highest when the network was perfect. The tensile‐strength behavior showed that the mechanical properties of PUU reached a maximum when the network was perfect. The increase in the resilience of the crosslinked PUU elastomer was higher than that of the linear PUU elastomer with an increase in temperature, and the reduction of the hardness of the former was also higher than that of the latter. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1126–1131, 2004     

Specific essential work of fracture of polyurethane thin films with different molecular structures

A series of polyurethane (PU) thin films with different hard-to-soft segment ratios were synthesized in our laboratory. The molecular and morphological structures of the PU films were characterized with Fourier transform infrared (FTIR), small-angle X-ray scattering (SAXS), wide-angle x-ray diffraction, dynamic mechanical analysis, and differential scanning calorimetry. The PU films showed a single glass transition when the hard-to-soft segment ratio varied from 1:2 to 1:8, suggesting no significant phase separation between the hard and soft segments. FTIR and SAXS results disclosed that the PU films had a network structure with the physical crosslinks formed via the intermolecular hydrogen bonds established between the hard segments. The fracture toughness of the ductile PU films was characterized with the essential work of fracture method under different conditions. It was found that the specific essential work of fracture was a function of the chain length between crosslinks and independent of the test temperature when fracture occurred at a temperature below the glass transition temperature. The physical meaning of this fracture parameter was proposed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1418–1424, 2007     

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