Influence of soft segment molecular weight on the mechanical hysteresis and set behavior of silicone-urea copolymers with low hard segment contents

Effect of polydimethylsiloxane (PDMS) soft segment molecular weight (M_n = 3200, 10,800 and 31,500 g/mol) and urea hard segment content (2.0-11.4% by weight) on the hysteresis and permanent set behavior of segmented silicone-urea (TPSU) copolymers were investigated. In spite of very low hard segment contents, all copolymers formed self-supporting films and displayed good mechanical properties. When the mechanical hysteresis and set behavior of the silicone-urea copolymers with similar hard segment contents (around 7.5% by weight) but based on PDMS-3K, PDMS-11K and PDMS-32K were compared, it was very clear that as the PDMS molecular weight increased, hysteresis and instantaneous set values decreased significantly. Copolymers based on the same silicone soft segment (PDMS-11K or PDMS-32K) but with different hard segment contents showed a linear increase in hysteresis and a slight decrease in the instantaneous set as a function of hard segment content. Constant initial stress creep experiments also showed lower creep as the PDMS segment molecular weight increased for copolymers with similar urea contents. Since the critical entanglement molecular weight (M_e) of PDMS is stated to be 24,500 g/mol, our results tend to suggest important contribution of chain entanglements on the hysteresis and instantaneous set of these silicone-urea copolymers.     

Contribution of soft segment entanglement on the tensile properties of silicone–urea copolymers with low hard segment contents

Novel, segmented thermoplastic silicone–urea (TPSU) copolymers based on rather high molecular weight aminopropyl terminated polydimethylsiloxane (PDMS) soft segments (<M_n> 10,800 and 31,500 g/mol), a cycloaliphatic diisocyanate (HMDI) and various diamine chain extenders were synthesized. Copolymers with very low urea hard segment contents of 1.43–14.4% by weight were prepared. In spite of very low hard segment contents, solution cast films showed very good microphase separation and displayed reasonable mechanical properties. Tensile strengths of TPSU copolymers showed a linear dependence on their urea hard segment contents, regardless of the structure of the diamine chain extender used. The modulus of silicone–urea copolymers is dependent on the urea concentration, but not on the extender type or PDMS molecular weight. When silicone–urea copolymers with identical urea hard segment contents were compared, copolymers based on PDMS-31,500 showed higher elongation at break values and ultimate tensile strengths than those based on PDMS-10,800. Since the critical entanglement molecular weight (M_e) of PDMS is about 24,500 g/mol, these results suggest there is a significant contribution from soft segment chain entanglement effects in the PDMS-31,500 system regarding the tensile properties and failure mechanisms of the silicone–urea copolymers.     

Fumed silica filled poly(dimethylsiloxane-urea) segmented copolymers: Preparation and properties

Novel fumed silica filled thermoplastic poly(dimethylsiloxane-urea) (TPSU) segmented copolymers were synthesized and characterized. TPSU copolymers were prepared from a cycloaliphatic diisocyanate, aminopropyl terminated PDMS oligomers with number average molecular weights of 3,200, 10,800 and 31,500 g/mol and 2-methyl-1,5-diaminopentane chain extender. Two different types of fumed silica HDK H2000 (hydrophobic) and HDK N20 (hydrophilic) were utilized and incorporated into silicone-urea copolymers in amounts of 1-60% by weight. Influence of the silica type (hydrophilic versus hydrophobic), amount of silica loading and the PDMS soft segment molecular weight on the morphology, tensile properties and modulus-temperature behavior of the nanocomposites were determined. Major observations of this study were: (i) under the blending conditions used, incorporation of silica does not seem to interfere significantly with the hydrogen bonding between urea groups, (ii) incorporation of silica does not affect the glass transition temperature of PDMS, (iii) incorporation of silica influences the tensile and thermomechanical properties of silicone-urea segmented copolymers significantly, (iv) average molecular weight of the PDMS soft segment in the silicone-urea copolymer plays a critical role on the improvement of the tensile properties of the fumed silica/TPSU composites.     

Microstructural organization of polydimethylsiloxane soft segment polyurethanes derived from a single macrodiol

Segmented polyurethane (PU) block copolymers were synthesized using 4,4′-methylenediphenyl diisocyanate and 1,4-butanediol as hard segments and oligomeric ethoxypropyl polydimethylsiloxane (PDMS) as the soft segments, with hard segment contents ranging from 26 to 52 wt%. The microphase separated morphology, phase transitions, and degrees of phase separation of these novel copolymers were investigated using a variety of experimental methods. Like similar copolymers with mixed ethoxypropyl PDMS/poly(hexamethylene oxide) soft segments, PU copolymers containing only ethoxypropyl PDMS soft segments were found to consist of three microphases: a PDMS matrix phase, hard domains, and a mixed phase containing ethoxypropyl end group segments and dissolved short hard segments. Analysis of unlike segment demixing using small-angle X-ray scattering demonstrates that degrees of phase separation increase significantly as copolymer hard segment content increases, in keeping with findings from Fourier transform infrared spectroscopy measurements.     

Structure-property behavior of poly(dimethylsiloxane) based segmented polyurea copolymers modified with poly(propylene oxide)

Poly(propylene oxide) (PPO) was incorporated in a controlled manner between poly(dimethylsiloxane) (PDMS) and urea segments in segmented polyurea copolymers and their solid state structure-property behavior was investigated. The copolymers contained PDMS segments of MW 3200 or 7000 g/mol and an overall hard segment content of 10-35 wt%. PPO segments of MW 450 or 2000 g/mol were utilized. Equivalent polyurea copolymers based on only PDMS as the soft segment (SS) component were used as controls. The materials (with or without PPO) utilized in this study were able to develop microphase morphology as determined from dynamic mechanical analysis (DMA) and small angle X-ray scattering (SAXS). DMA and SAXS results suggested that the ability of the PPO segments to hydrogen bond with the urea segments results in a limited inter-segmental mixing which leads to the formation of a gradient interphase, especially in the PPO-2000 co-SS containing copolymers. DMA also demonstrated that the polyureas based on only PDMS as the SS possessed remarkably broad and nearly temperature insensitive rubbery plateaus that extended up to ca. 175 °C, the upper temperature limit depending upon the PDMS MW. However, the incorporation of PPO resulted in more temperature sensitive rubbery plateaus. A distinct improvement in the Young's modulus, tensile strength, and elongation at break in the PPO-2000 and PDMS-7000 containing copolymers was observed due to inter-segmental hydrogen bonding and the formation of a gradient interphase. However, when PPO was incorporated as the co-SS, the extent of stress relaxation and mechanical hysteresis of the copolymers increased relative to the segmented polyureas based on the utilization of only PDMS as the soft segment component.     

Phase Behavior and Mechanical Properties of Siloxane-Urethane Copolymer

Two series of siloxane-urethane copolymers were prepared from polydimethylsiloxane (PDMS) with a molecular weight of 1000 or 1800 which was used as a soft segment, 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (1,4-BD). Differential scanning calorimetry (DSC) demonstrated that the position (T_gs) and breadth (ΔB) of soft-segment glass transition of copolymers remained constant as the hard-segment content increased. Heat capacities at soft-segment glass transition of the copolymer (ΔCp) were 0.195∼0.411 J/g^○C and heat capacities of pure PDMS (ΔCp₀) were 0.571∼0.647 J/g^○C, leading to the various ΔCp/ΔCp₀ ratios. The ΔCp/ΔCp₀ ratios decreased as the increasing of hard-segment content, showing poor phase separation. The FTIR spectrum confirmed the occurrence of hydrogen bonding in ether end-group of pure PDMS. The ether group of the soft segment led to interfacial mixing between soft and hard segments. The tan δ of the soft segment determined by dynamic mechanical testing (DMA) also identified the mixing of soft and hard segments. The mechanical properties of the copolymer were directly related to either the soft and hard segment contents or the chain lengths of soft and hard segments. The hard segment that reinforced the soft segment and interfacial thickness between soft and hard segment dominated the mechanical properties.     

Effect of soft segment molecular weight on tensile properties of poly(propylene oxide) based polyurethaneureas

Influence of soft segment molecular weight and hard segment content on the morphology, thermomechanical and tensile properties of homologous polyurethaneurea copolymers based on narrow molecular weight poly(propylene oxide)glycol (PPG) oligomers were investigated. A series of polyurethaneureas with hard segment contents of 12–45% by weight and PPG number average molecular weights <M_n> of 2000 to 11,800 g/mol were synthesized and characterized structurally by SAXS and mechanically by DMA and stress strain analysis. Bis(4-isocyanatocyclohexyl)methane and 2-methyl-1,5-diaminopentane were used as the diisocyanate and the chain extender respectively. All copolymers displayed microphase separation by SAXS and DMA. The critical entanglement molecular weight (M_e) of PPG is reported to be around 7700 g/mol. Our mechanical results suggest that when copolymers possess similar hard segment contents and are compared to those based on soft segments with number average molecular weights (M_n) greater than M_e, they generally displayed higher tensile strengths and particularly lower hysteresis and creep than those having soft segment molecular weights below M_e. These results imply that soft segment entanglements in thermoplastic polyurethaneureas may provide a critical contribution to the tensile properties of these copolymers – particularly in the range where the soft segment content is dominant.     

Segmented organosiloxane copolymers: 2 Thermal and mechanical properties of siloxane—urea copolymers

The structure-property behaviour of new siloxane-urea containing segmented copolymers has been investigated. Amino-propyl terminated poly(dimethylsiloxane) oligomers of from 900–3660 M_n were reacted with various diisocynates to form segmented copolymers with urea linkages. The length of the hard segments in these copolymers corresponds approximately to the length of the diisocynate unit employed. A number of mechanical and thermal properties were investigated for these phase separated materials. It was found that the performance of these copolymers was effected by varying the hard segment type and/or content and that high strength necessitates a microphase texture. The two phase nature of these copolymers was verified by dynamic mechanical, thermal and SAXS studies. The phase separation was found to occur in these copolymers even with 6% hard segment by weight. In conclusion, these materials displayed a behaviour similar to the segmented polyurethanes and were found to be superior to the unfilled silicone elastomers.     

Influence of mixed soft segments on microphase separation of polyurea elastomers

This paper describes the influence of mixed poly(tetramethylene oxide) (PTMO) soft segments on microphase separation and morphology, hydrogen bonding, and polymer transitions for a series of alternating polyurea copolymers prepared from a single modified diphenylmethane diisocyanate. The fraction of two PTMO soft segments [with molecular weight = 1000 and 250 g/mol] was systematically varied and incorporated during bulk polymerization. ATR-FTIR spectroscopy confirmed that the intended polymers were synthesized and was used to determine the state of the local hydrogen bonding in these copolymers. Systematic changes in hard domain microstructure as a function of soft segment composition were clearly observed in AFM tapping mode phase images: the polyureas become progressively disordered with increasing content of the shorter PTMO. This was confirmed in a quantitative fashion using small-angle X-ray scattering. Results from dynamic mechanical analysis experiments reveal rather significant changes in dynamic segmental relaxations and storage moduli at 25 °C for this series of polyureas, which are in keeping with the findings from other experiments.     

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

Advance 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.     

Ionene segmented block copolymers containing imidazolium cations: Structure-property relationships as a function of hard segment content

Imidazolium ionene segmented block copolymers were synthesized from 1,1′-(1,4-butanediyl)bis(imidazole) and 1,12-dibromododecane hard segments and 2000 g/mol PTMO dibromide soft segments. The polymeric structures were confirmed using ¹H NMR spectroscopy, and resonances associated with methylene spacers from 1,12-dibromododecane became more apparent as the hard segment content increased. TGA revealed thermal stabilities ≥250 °C for all imidazolium ionene segmented block copolymers. These ionene segmented block copolymers containing imidazolium cations showed evidence of microphase separation when the hard segment was 6-38 wt%. The thermal transitions found by DSC and DMA analysis found that the T_g and T_m of the PTMO segments were comparable to PTMO polymers, namely approximately −80 °C and 22 °C, respectively. In the absence of PTMO soft segments the T_g increased to 27 °C The crystallinity of the PTMO segments was further evidence of microphase separation and was particularly evident at 6, 9 and 20 wt% hard segment, as indicated in X-ray scattering. The periodicity of the microphase separation was well-defined at 20 and 38 wt% hard segment and found to be approximately 10.5 and 13.0 nm, respectively, for these ionenes wherein the PTMO soft segment is 2000 g/mol. Finally, the 38 and 100 wt% hard segment ionenes exhibited scattering from correlations within the hard segment on a length scale of approximately 2-2.3 nm. These new materials present structure on a variety of length scales and thereby provide various routes to controlling mechanical and transport properties.     

The properties of polyurethanes with mixed chain extenders and mixed soft segments

Series of polyurethaneurea elastomers were prepared from 4,4′-diphenylmethane diisocyanate, poly(teuramethylene ether) glycol and poly(hexamethylene carbonate) glycol for mixed soft segments, and 1,4-butanediol and isophoronediamine for mixed chain extenders. Characteristics of the copolymers related with compositions were examined. FT-IR spectra showed that most of the urea carbonyl groups associated in hydrogen bonding, while urethane carbonyls only partially did so. Thermal and mechanical properties were investigated through differential scanning calorimetry and tensile testing. These thermal and mechanical properties are discussed from the viewpoint of microphase domain separation of hard and soft segments. © 1994 John Wiley & Sons, Inc.     

Influence of soft segment composition on phase-separated microstructure of polydimethylsiloxane-based segmented polyurethane copolymers

Segmented polyurethane block copolymers were synthesized using 4,4′-methylenediphenyl diisocyanate (MDI) and 1,4-butanediol (BDO) as hard segments and various soft segments derived from poly(hexamethylene oxide) (PHMO) and poly(dimethylsiloxane) (PDMS)-based macrodiols and mixtures thereof. The microstructure and degrees of phase separation were characterized using a variety of experimental methods. Copolymers synthesized with the PDMS macrodiol and from PDMS/PHMO macrodiol mixtures were found to consist of three phases: a PDMS phase; hard domains; and a mixed phase of PHMO, PDMS ether end group segments and some dissolved hard segments. Two models were used to characterize the small-angle X-ray scattering from these copolymers: pseudo two-phase and core-shell models. Analysis using both methods demonstrates that as the PDMS content in the soft segment mixture increases, the greater the fraction of hard segments involved in hard domains than are dissolved in the mixed phase. Findings from analysis of the carbonyl region of FTIR spectra are also in agreement with greater hard/soft segment demixing in copolymers containing higher PDMS contents.     

Influence of system variables on the morphological and dynamic mechanical behavior of polydimethylsiloxane based segmented polyurethane and polyurea copolymers: a comparative perspective

The effect of the variables of polydimethylsiloxane (PDMS) soft segment (SS) length, hard segment (HS) type and content as well as choice of chain extender (its MW and symmetry) on the morphology of segmented polyurethane and polyurea copolymers was investigated. The methods of dynamic mechanic analysis, small angle X-ray scattering, atomic force microscopy, and mechanical testing were used in this analysis. Average PDMS MW of 900, 2500 or 7000 g/mol were utilized and the hard segment content ranged from 16 to 50 wt%. HMDI was used as the diisocyanate. All copolymers were synthesized via the prepolymer method. The PDMS MW had a marked effect on the morphology of the materials. Copolymers with PDMS MW of 2500 and 7000 g/mol were clearly found to be well microphase separated relative to those containing the 900 g/mol PDMS SS. The polyurea sample with a PDMS MW of 7000 and HS content of 25 wt% exhibited a remarkable service temperature window (for rubber-like behavior) of ca. 230 °C (from −55 to 175 °C) whereas it was ca. 200 °C wide (from −55 to 145 °C) for the equivalent polyurethane sample. In general, the degree of microphase separation was found to be greater in the polyurea samples due to their more cohesive bidentate hydrogen bonding.     

乙烯脲改性水性聚氨酯脲的制备与性能

采用一种新型的扩链剂乙烯脲(EU),在聚氨酯硬段引入具有刚性环状二取代脲基团,通过控制脲含量、交联度以及软段相对分子质量来制备一系列的EU改性水性聚氨酯脲(PUU-EU),并利用透射电镜(TEM)、广角X射线衍射(WAXD)、动态力学机械分析(DMA)、热失重分析(TGA)等测试方法,系统地研究PUU-EU微观结构与氢键化程度、微相分离、耐热性、力学强度的关系,并与1,4-丁二醇(BDO)扩链制备的水性聚氨酯(WPU)进行对比。结果表明,在一定范围内,PUU-EU随脲含量增加,其氢键化程度愈发完善,微相分离程度随之增加,力学强度逐步提高。     

Synthesis and characterization of hexafluoroisopropylidene bisphenol poly(arylene ether sulfone) and polydimethylsiloxane segmented block copolymers

A series of hexafluoroisopropylidene bisphenol poly(arylene ether sulfone) (BAF PAES) segmented block copolymers with varying fractions of polydimethylsiloxane (PDMS) were synthesized by a condensation reaction of hydroxyl-terminated BAF PAES and dimethylamino endcapped PDMS. The segmented block copolymers have high thermal stability. The BAF PAES homopolymer exhibits a tensile modulus of 1700 MPa and an elongation at break of 16%. Copolymerizing BAF PAES with increasing molecular weight amounts of PDMS results in tensile properties ranging from plastic to elastomeric where the elongation is 417% for a segmented block copolymer with 64 wt% PDMS incorporated. The morphological properties of these segmented block copolymers were characterized by atomic force microscopy (AFM), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). AFM and TEM images show the segmented block copolymers were microphase separated, and comparison with bisphenol A (BA) PAES-b-PDMS segmented block copolymers revealed complex differences between the morphological behavior of the two systems. SAXS data of the segmented block copolymers supports AFM and TEM images, indicating microphase separation but little long-range order.     

Thermoplastic polyurethane elastomers based on polycarbonate diols with different soft segment molecular weight and chemical structure: Mechanical and thermal properties

A series of thermoplastic polyurethane elastomers based on polycarbonate diol, 4,4′‐diphenylmethane diisocyanate and 1,4‐butanediol was synthesized in bulk by two‐step polymerization varying polycarbonate diol soft segment molecular weight and chemical structure, and also hard segment content, and their effects on the thermal and mechanical properties were investigated. Dynamic mechanical analysis termogravimetric analysis, differential scanning calorimetry, Fourier transform infrared‐attenuated total reflection spectroscopy and mechanical tests were employed to characterize the polyurethanes. Thermal and mechanical properties are discussed from the viewpoint of microphase domain separation of hard and soft segments. On one hand, an increase in soft segment length, and on the other hand an increase in the hard segment content, i.e., hard segment molecular weight, was accompanied by an increase in the microphase separation degree, hard domain order and crystallinity, and stiffness. In phase separated systems more developed reinforcing hard domain structure is observed. These hard segment structures, in addition to the elastic nature of soft segment, provide enough physical crosslink sites to have elastomeric behavior. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

Antibacterial Silicone-Urea/Organoclay Nanocomposites

Montmorillonite modified with distearyldimethyl ammonium chloride (C18-QAC) (Nanofil-15) (NF15) was incorporated into polydimethylsiloxane-urea (silicone-urea, PSU) copolymers. PSU was obtained by the reaction of equimolar amounts of aminopropyl terminated polydimethylsiloxane (PDMS) oligomer (<M_n> = 3,200 g/mol) and bis(4-isocyanatohexyl)methane (HMDI). A series of PSU/NF15 nanocomposites were prepared by solution blending with organoclay loadings ranging from 0.80 to 9.60% by weight, corresponding to 0.30 to 3.60% C18-QAC. Colloidal dispersions of organophilic clay (NF15) in isopropanol were mixed with the PSU solution in isopropanol and were subjected to ultrasonic treatment. Composite films were obtained by solution casting. FTIR spectroscopy confirmed that the organoclay mainly interacted with the urea groups but not with PDMS. XRD analysis showed that nanocomposites containing up to 6.40% by weight of organoclay had fully exfoliated silicate layers in the polymer matrix, whereas 9.60% loading had an intercalated structure. Physicochemical properties of nanocomposites were determined. PSU/NF15 nanocomposites displayed excellent long-term antibacterial properties against E. coli.     

Isopropyl alcohol: an unusual, powerful, ‘green’ solvent for the preparation of silicone–urea copolymers with high urea contents

Isopropyl alcohol (IPA) is used as the reaction solvent for the preparation of silicone–urea copolymers. Reactivity of isopropanol with bis(4-isocyanatocyclohexyl)methane (HMDI) was investigated at 23 °C using infrared spectroscopy. Spectroscopic studies indicated very low reactivity of IPA towards HMDI at 23 °C. High molecular weight segmented silicone–urea copolymers were prepared through the reaction of HMDI with aminopropyl and N-methylaminopropyl terminated polydimethylsiloxane (PDMS) oligomers and three different chain extenders, ethylene diamine (ED), hexamethylene diamine (HMDA) and 2-methyl-1,5-diaminopentane (Dytek A). Number average molecular weights of PDMS oligomers varied between 900 and 7000 g/mol, respectively. Reactions were carried out at room temperature in IPA. Silicone–urea copolymers with urea hard segment content between 10 and 42% by weight were prepared. Thermal and mechanical characterization of the copolymers indicated the formation of microphase-separated systems with excellent tensile strengths. Interestingly, structure of the diamine chain extender did not show any influence on the mechanical properties of the homologous series of silicone–urea copolymers.     

Microphase separation behavior on the surfaces of poly(dimethylsiloxane)‐block‐poly(2,2,3,3,4,4,4‐heptafluorobutyl methacrylate) diblock copolymer coatings

Microphase separation behavior on the surfaces of poly(dimethylsiloxane)‐block‐poly(2,2,3,3,4,4,4‐heptafluorobutyl methacrylate) (PDMS‐b‐PHFBMA) diblock copolymer coatings was investigated. The PDMS‐b‐PHFBMA diblock copolymers were successfully synthesized via atom transfer radical polymerization (ATRP). The chemical structure of the copolymers was characterized by nuclear magnetic resonance and Fourier transform infrared spectroscopy. Surface composition was studied by X‐ray photoelectron spectroscopy. Copolymer microstructure was investigated by atomic force microscopy. The microstructure observations show that well‐organized phase‐separated surfaces consist of hydrophobic domain from PDMS segments and more hydrophobic domain from PHFBMA segments in the copolymers. The increase in the PHFBMA content can strengthen the microphase separation behavior in the PDMS‐b‐PHFBMA diblock copolymers. And the increase in the annealing temperature can also strengthen the microphase separation behavior in the PDMS‐b‐PHFBMA diblock copolymers. Moreover, Flory‐Huggins thermodynamic theory was preliminarily used to explain the microphase separation behavior in the PDMS‐b‐PHFBMA diblock copolymers.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009