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.     

Phase separation of diamine chain-extended poly(urethane) copolymers: FTIR spectroscopy and phase transitions

As part of our continuing effort to understand microphase separation of poly(urethane urea) block copolymers, FTIR spectroscopy and thermal techniques (DSC and DMA) were used to investigate the phase behavior of two series of MDI-polytetramethylene oxide soft segment copolymers, chain-extended with ethylene diamine or a diamine mixture. Due to the complex nature and multiple absorbances in the carbonyl and N-H regions of the FTIR spectra, quantitative analysis was not possible. However, qualitative trends could be discerned, and the spectral changes were found to be in excellent agreement with our previous quantitative analysis of the same copolymers using small-angle X-ray scattering. DSC and DMA experiments both indicate that the soft phase T_g decreases with increasing hard segment content. This is contrary to increased hard segment mixing in the soft phase, but can be rationalized by taking into consideration soft segment crystallinity and the concentration of ‘lone’ MDI units in the soft phase.     

Preparation and properties of transparent thermoplastic segmented polyurethanes derived from different polyols

Various segmented polyurethanes of different soft segment structure with hard segment content of about 50 wt% were prepared from 4,4′‐diphenylmethane diisocyanate (MDI), 1,4‐butanediol and different polyols with a M_n of 2000 by a one‐shot, hand‐cast bulk polymerization method. The polyols used were a poly(tetramethylene ether)glycol, a poly(tetramethylene adipate)glycol, a polycaprolactonediol and two polycarbonatediols. The segmented polyurethanes were characterized by gel permeation chromatography (GPC), UV‐visible spectrometry, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X‐ray diffraction, and their tensile properties and Shore A hardness were determined. The DSC and DMA data indicate that the miscibility between the soft segments and the hard segments of the segmented polyurethanes is dependent on the type of the soft segment, and follows the order: polycarbonate segments > polyester segments > polyether segments. The miscibility between the soft segments and the hard segments plays an important role in determining the transparency of the segmented polyurethanes. As the miscibility increases, the transparency of the segmented polyurethanes increases accordingly. The segmented polyurethanes exhibit high elongation and show ductile behavior. The tensile properties are also affected by the type of the soft segment to some extent. POLYM. ENG. SCI., 47:695–701, 2007. © 2007 Society of Plastics Engineers.     

Characteristics of polyurethanes incorporating starch granules

Polyurethanes containing different starch contents were synthesized in a one-step reaction by suspending starch granules in polycaprolactone diol, MDI and 1,4 butane diol in a bulk phase at 175 °C. The products were characterized by FTIR spectroscopy, SEM, DSC, and swelling behavior. Their mechanical properties, e.g. tensile strength and elongation, were measured for different starch contents. The starch dispersed well as a grafted state in the polyurethane phase. The grafted percentage of polyurethane to starch granules increased with the starch content to a maximum point (about 20 wt%) and then decreased due to gapping between the two phases and probably the homo-polymerization tendency of the polyurethane. The DSC indicated that T_g increased with the starch content due to the decreased average molecular weight of the homo-polyurethane. Three endothermic transitions at 60-70 °C (I), ∼150 °C (II), 190-210 °C (III) were observed. Transition I was not changed by the starch content, whereas transition II appeared only for the psb2m3 series (32-48 wt% hard segment) at the lower range of 26 wt% of starch content. The temperature of transition III, which is related to the melting point of the hard segments, increased with the starch content despite a decrease in the molecular weight of the homo-polyurethane. The tensile strength and the elongation of the polymers slightly increased or were constant up to about 20 wt% of starch, and then decreased rapidly because of phase separation (gapping) between the starch granules and the polyurethane phase and division of the starch granules.     

Phase separation in segmented polyurethanes derived from mixtures of polyether polyols with different functionality

A series of segmented polyurethanes containing 60 wt° of hard segments (HS) was prepared from MDI (4,4-diphenylmethane diisocyanate) ethylene glycol and mixtures of a polyoxyethylene end-capped polyoxypropylene triol and a polyoxyethylene end-capped polyoxypropylene diol. The effects of the content of polyether diol in polyether polyols on phase separation and properties was investigated by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and investigation of tensile properties. The DSC and DMA results indicate that the polyurethane derived from only polyether triol exhibits obvious phase separation and that the HS is immiscible with the SS, but that the HS is compatible with the HS for the polyurethane derived from polyether diol. As the content of polyether diol increases, the compatibility between HS and SS increases. As the content of polyether diol increases, the tensile strength. elongation. toughness and tear resistance of the polyurethanes increases. but their moduli decrease. The modulus-temperature dependence in the temperature region of –30 to 65 °C increases as the polyether diol content increases.     

Study on thermal transitions of toluene diisocyanate-based polyurethane elastomers with poly (tetramethylene oxide) as the soft segment by TSC/RMA, DSC and DMA thermal analyzers

Thermal transitions of TDI-based polyurethane elastomers with PTMO as the soft segment were characterized by the depolarization technique in TSC and by using with the thermal windowing technique on selected specimens in the RMA measurements. Results indicate that the broadened thermal transition in the glass transition region as observed in the DSC thermogram is related to the combined T_g transition and the T_global transition in the TSC spectrum. This T_global transition is associated with the macromolecular property as detected by tan δ in DMA measurement. The increase in the T_g with a high NCO content may be explained by the structural modification found on the urethanic chain with the additional linkage of the hard segment that affects the cooperative motion of the molecular chain. Data measured from DSC, TSC/RMA and DMA with simulated DEA and wide angle X-ray data are presented for the characterization of the polyurethanes. The RMA measurement leads to a compensation search on T_g transition and provides pertinent thermokinetic data that correlates the NCO content with changes in enthalpy and entropy on the relaxation behaviors in the T_g transition of polyurethane elastomers.     

Phase separation and mechanical responses of polyurethane nanocomposites

Nanocomposites of a diamine-cured polyurethane with nanofillers of different kinds, sizes, and surfaces were studied. Atomic force microscopy, scanning electron microscopy, X-ray diffraction, tensile tests, and dynamic mechanical thermal analysis were employed in the experiments. Experimental results suggest that mechanical properties are strongly correlated to polymer phase separation, which depends on the nature of the interface between the polymer and the nanoparticles. Two stages of phase separation were observed: the first stage involves the self-assembly of the hard segments into small hard phases of about 10 nm in width; the second stage involves the assembly of the 10 nm wide hard phases into larger domains of about 40-100 nm in width. In the case of polyurethane/ZnO nanocomposites with 5 wt% (less than 1 vol%) 33 nm ZnO nanoparticles, the covalent bonds that were formed between the polymer and ZnO surface hydroxyl groups constrain both stages of phase separation in polyurethane, resulting in approximately 40% decrease in the Young's modulus, 80% decrease in the strain at fracture, and 11 °C increase in the glass transition temperature of the soft segments. In the case of polyurethane/Al₂O₃ nanocomposites with 5 wt% 15 nm Al₂O₃ nanoparticles, hydrogen bonds between the particles and the polymer mainly constrain the second step of the phase separation, resulting in about 30% decrease in the Young's modulus and 12 °C increase in the glass transition temperature, but only a moderate decrease in the strain at fracture. The most striking results come from polyurethane/clay composites, where only van der Waals type interactions exist between polyurethane and the organically modified clay (Cloisite 20A). With the addition of 5 wt% surface modified clay (Cloisite 20A), both the Young's modulus and the strain at fracture decrease more than 80%, but the glass transition temperature increases by about 13 °C. Adding 10 wt% Cloisite 20A into polyurethane almost totally disrupts the phase separation, resulting in a very soft composite that resembles a “viscous liquid” rather than a solid.     

Exploring long-range connectivity of the hard segment phase in model tri-segment oligomeric polyurethanes via lithium chloride

The influence of the extent of hydrogen bonding in mediating the long-range connectivity and percolation of the hard segment phase in model tri-segment oligomeric polyurethanes (PU) was explored by using LiCl as a molecular probe. A 22 wt% hard segment containing model PU plaque based on a mono-functional oligomeric polyether, 80:20 2,4:2,6 isomeric mixture of toluene diisocyanate, and water as a chain extender was employed. Samples cast from 20 wt% solutions in dimethyl acetamide were utilized. The tapping-mode atomic force microscopy (AFM) phase image of the solution cast film sample (soft segment T_g −63 °C) without LiCl exhibited the presence of long interconnected ribbon-like hard domains. The long-range connectivity and percolation of the hard phase that arose during plaque formation gave rise to a brittle rigid solid. A systematic break-up of the hard domains was also observed by AFM when the concentration of LiCl was increased from 0.1 to 1.5 wt%. DSC analysis indicated that the samples were able, however, to maintain a microphase separated morphology even at the highest LiCl concentration utilized in the study. FT-IR data confirmed that LiCl interacts with the hard domains of the model PU samples by disrupting the hydrogen bonding capability of the urea hard segments. A systematic softening of the samples was observed with increasing LiCl content as confirmed by thermomechanical analysis. Thus, this study indicates that hydrogen bonding plays an important role in assisting the hard segments in PU to develop long-range connectivity and percolation of this phase through the soft matrix.     

Morphology of polyurethane–isocyanurate elastomers

The dynamic viscoelastic properties and thermal transition behavior of reaction injection molding (RIM) and cast polyurethane—isocyanurate elastomers have been studied as a function of various segments (soft and hard urethane, and hard isocyanurate) content. RIM and cast elastomers were prepared at different concentrations of soft and hard urethane, and hard isocyanurate segments. RIM elastomers with the higher isocyanate index (lower hard urethane and greater isocyanurate segment content) displayed an unchanged T_g (glass transition temperature of soft segment) and increasing T_gh (glass transition temperature of hard segment) related to the hard urethane and isocyanurate segments. This is due to the phase separation between the soft and the hard segments. Cast elastomers synthesized from the higher amount of 1,4-butanediol (greater hard urethane and less hard isocyanurate segment content) showed an increasing T_gs, decreasing T_gh of hard urethane segments, and an unchanged T_gh of isocyanurate segments. This is related to the phase mixing between the soft and the hard urethane segments and the phase separation of hard isocyanurate and hard urethane segments.     

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.     

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.     

Synthesis and characterization of biodegradable poly(ester‐urethanes) based on bacterial poly(R‐3‐hydroxybutyrate)

A series of poly(R‐3‐hydroxybutyrate)/poly(ε‐caprolactone)/1,6‐hexamethylene diisocyanate‐segmented poly(ester‐urethanes), having different compositions and different block lengths, were synthesized by one‐step solution polymerization. The molecular weight of poly(R‐3‐hydroxybutyrate)‐diol, PHB‐diol, hard segments was in the range of 2100–4400 and poly(ε‐caprolactone)‐diol, PCL‐diol, soft segments in the range of 1080–5800. The materials obtained were investigated by using differential scanning calorimetry, wide angle X‐ray diffraction and mechanical measurements. All poly(ester‐urethanes) investigated were semicrystalline with T_m varying within 126–148°C. DSC results showed that T_g are shifted to higher temperature with increasing content of PHB hard segments and decreasing molecular weight of PCL soft segments. This indicates partial compatibility of the two phases. In poly(ester‐urethanes) made from PCL soft segments of molecular weight (M_n ≥ 2200), a PCL crystalline phase, in addition to the PHB crystalline phase, was observed. As for the mechanical tensile properties of poly(ester‐urethane) cast films, it was found that the ultimate strength and the elongation at the breakpoint decrease with increasing PHB hard segment content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 703–718, 2002     

Phase behavior and hydrogen bonding in biomembrane mimicing polyurethanes with long side chain fluorinated alkyl phosphatidylcholine polar head groups attached to hard block

To achieve a good biocompatibility, two sets of novel segmented polyurethanes, namely, poly(ether urethane)s and poly(carbonate urethane)s, with long side chain fluorinated alkyl phosphatidylcholine polar head groups attached to hard block have been synthesized recently in our laboratory by using a new diol with a long side chain fluorinated alkyl phosphatidylcholine polar head group 2-[2-[2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluoro-10-ethoxy-decyloxy]-N-(2-hydroxy-1-hydroxymethyl-1-methyl-ethyl)-acetamide] phosphatidylcholine, HFDAPC as an extender. These novel polyurethanes have shown a potential to be used as bio-membrane mimicry. In this article we investigated the phase behavior of these materials by Instron, DSC, DMA, and AFM because the phase behavior has a great effect on the surface properties thus the biological-related perspective. T_g decreases first then increases for the poly(carbonate urethane)s, but increases first then decreases for the poly(ether urethane)s with an increasing in fluorinate phosphatidylcholine content. On the other hand, the tensile modulus was found decrease for the poly(carbonate urethane)s but increase for the poly(ether urethane)s with an increasing in fluorinate phosphatidylcholine content. It was found via AFM that the phase separation increases in poly(ether urethane)s but phase mixing increases in poly(carbonate urethane)s, with increasing content of fluorinated phosphatidylcholine side chain. The interaction between hard and soft segment, particularly, the hydrogen bonding was investigated by FTIR. The effect of fluorinated phosphatidylcholine side group on the phase separation of polyurethane was discussed and compared with that of fluorinated polyurethanes containing only fluorinated side chains. Our result demonstrated how the phase behavior of polyurethanes could be controlled by tailoring the interaction between hard and soft segment.     

Block copolyetheresters with poly(trimethylene 2,6-naphthalenedicarboxylate) segments: Effect of composition on thermal properties

Block copolyetheresters with hard segments of poly(trimethylene 2,6-naphthalenedicarboxylate) and soft segments of poly(tetramethylene oxide) were prepared by melt polycondensation of dimethyl 2,6-naphthalenedicarboxylate, 1,3-propanediol and poly(tetramethylene ether)glycol (PTMEG) of molecular weights of 650, 1000 and 2000. The block copolyetheresters were characterized by FTIR, ¹H NMR, DSC, X-ray diffraction, TSC (thermal stimulated current), DMA and TGA. It was found that the thermal transitions were dependent on the composition. As the charge molar ratio of PTMEG to dimethyl 2,6-naphthalenedicarboxylate, x, increased, the T_m and ΔH_m of the polyester segments decreased, which has been also confirmed by the X-ray diffraction data. The polyether segments of the block copolyetheresters derived from PTMEG2000 could crystallize after cooling, but those of the block copolyetheresters derived from PTMEG1000 and PTMEG650 could not crystallize. The DSC, TSC and DMA results show consistent T_g data of the polyether segments. Based on the shift in T_g of the polyether segments, the amorphous parts of the polyether segments and the amorphous parts of the polyester segments were immiscible for the block copolyetheresters derived from PTMEG2000, but became partially miscible for the block copolyetheresters derived from PTMEG1000 and PTMEG650. The TGA results indicated that composition had little effect on thermal degradation under nitrogen.     

Block copolyetheresters. V. Low-temperature properties of thermotropic block copolyetheresters

The low-temperature properties of block copolyetheresters with hard segments of poly(alkylene p,p′-bibenzoate) and soft segments of poly(tetramethylene ether) were investigated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). In the temperature range of −100 to 60°C, two transition temperatures, a glass transition temperature (T_g) and a melting temperature (T_m), were found by DSC and are attributed to the polyether segments. The T_g monitored by DSC of the polyether segments of the block copolyetheresters is around −68°C and independent of the composition and the type of polyester segment. Thus, the amorphous parts of the polyether segments should be immiscible with the amorphous parts of the polyester segments. The polyether segments of the block copolyetheresters exhibit a lower T_m and a lower crystallinity than those of the poly(tetramethylene ether)glycol due to the presence of the polyester segments. The crystallizability of the polyether segments is dependent on the composition to some extent. The DMA data show that the dynamic modulus drops more abruptly around −10 to 15°C, indicating that the mechanical properties may change significantly due to the melting of the polyether segments. © 1996 John Wiley & Sons, Inc.     

Influence of ionic charge placement on performance of poly(ethylene glycol)-based sulfonated polyurethanes

Poly(ethylene glycol) (PEG)-based sulfonated polyurethanes bearing either sulfonated soft segments (SSSPU) or sulfonated hard segments (SHSPU) were synthesized using sulfonated monomers. Differential scanning calorimetry (DSC) revealed that sulfonate anions either in the soft segments or hard segments both increased the glass transition temperatures (T_g’s) of the soft segments and suppressed their crystallization. Moreover, dynamic mechanical analysis (DMA) and tensile analysis demonstrated that SSSPU possessed a higher modulus and tensile strength relative to SHSPU. Fourier transform infrared (FTIR) spectroscopy revealed that hydrogen bonding interactions in SHSPU were suppressed compared to SSSPU and noncharged PU. This observation suggested a high level of phase-mixing for SHSPU. In addition, atomic force microscopy (AFM) phase images revealed that both SSSPU and noncharged PU formed well-defined microphase-separated morphologies, where the hard segments phase-separated into needle-like hard domains at the nanoscale. However, SHSPU showed a phase-mixed morphology, which was attributed to increased compatibility of polar PEG soft segments with sulfonated ionic hard segments and disruption of hydrogen bonds in the hard segment. The phase-mixed morphology of SHSPU was further demonstrated using small angle X-ray scattering (SAXS), which showed a featureless X-ray scattering profile. In contrast, SAXS profiles of SSSPU and noncharged PU demonstrated microphase-separated morphologies. Moreover, SSSPU also displayed a broad ionomer peak ranging in q = 1–2 nm^?1, which resulted from the sodium sulfonate ion pair association in the polar PEG soft phase. Morphologies of sulfonated polyurethanes correlated well with thermal and mechanical properties.     

Properties of segmented polyurethanes derived from different diisocyanates

Various segmented polyurethane materials with a polyurethane hard segment (HS) content of 40 wt % were prepared by bulk polymerization of a poly(tetramethylene ether) glycol with M_n of 2000, 1,4‐butanediol, and various diisocyanates. The diisocyanates used were pure 4,4′‐diphenylmethane diisocyanate (MDI), 2,4‐toluene diisocyanate (T100), toluene diisocyanate containing 80% 2,4‐isomer and 20% 2,6‐isomer (T80), isophorone diisocyanate (IPDI), hydrogenated 4,4′‐diphenylmethane diisocyanate (HMDI), and 1,6‐hexane diisocyanate (HDI). The segmented polyurethane materials were characterized by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile properties, tear strength, and Shore A hardness. The DSC and DMA data show that the thermal transitions are influenced significantly by the diisocyanate structure. In the segmented polyurethane materials with aliphatic HS, the polyether soft segment (SS) is immiscible with the HS. However, in the segmented polyurethane materials with aromatic HS, the SS is partially miscible with the HS. The diisocyanate structure also influences the mechanical properties significantly and is described as the effect of symmetry and chemical structure of the HS. Various solution polymerized polyurethane resins with solid content of 30 wt % were also prepared and their thickness retention, water resistance, and yellowing resistance were determined for the evaluation of their usage as wet process polyurethane leather. The polyurethane resin with aliphatic HS show poorer thickness retention but better yellowing resistance. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 167–174, 2000     

Effect of the degree of soft and hard segment ordering on the morphology and mechanical behavior of semicrystalline segmented polyurethanes

The hierarchical microstructure responsible for the unique energy-absorbing properties of natural materials, like native spider silk and wood, motivated the development of segmented polyurethanes with soft segments containing multiple levels of order. As a first step in correlating the effects of crystallinity in the soft segment phase to the hard segment phase, we chose to examine the morphology and mechanical behavior of polyurethanes containing polyether soft blocks with varying tendencies to crystallize and phase segregate and the evolution of the microstructure with deformation. A series of high molecular weight polyurethanes containing poly(ethylene oxide) (PEO) (1000 and 4600 g/mol) and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) (1900 g/mol) soft segments with varying hard segment content were synthesized using a two-step solution polymerization method. The presence of soft segment crystallinity (PEO 1000 g/mol) was shown to improve the storage modulus of the segmented polyurethanes below the T_m of the soft block and to enhance toughness compared to the PEO-PPO-PEO soft segment polyurethanes. We postulate that this enhancement in mechanical behavior is the result of crystalline soft regions that serve as an additional load-bearing component during deformation. Morphological characterization also revealed that the microstructure of the segmented polyurethanes shifts from soft segment continuous to interconnected and/or hard domain continuous with increasing hard segment size, resulting in diminished ultimate elongation, but enhanced initial moduli and tensile strengths. Tuning the soft segment phase crystallinity may ultimately lead to tougher polyurethane fibers.     

Study on microstructure of UV-curable polyurethane acrylate films

UV-curable polyurethane acrylates (UVPUA) were prepared, and Fourier transform infrared (FTIR) was used to monitor the synthesis process and cured films. Effects of soft segment length, isocyanate type, reactive diluent type and level, quenching, annealing and different UV-cured degree on the microstructure of UVPUA films have also been studied. With soft segment length increasing, the degree of hydrogen bonding between soft segment and hard segments decreases, and microphase separation of UVPUA becomes better. Soft segment crystallization appears with its molecular weight exceeding 2000, when its value reaches 4000, an even more obvious melting peak in differential scanning calorimetry (DSC) curve was observed. Congregation of hard segment domains and the improvement of phase separation were due to symmetry and regularity of isocyanate, while rigid benzene ring was beneficial to crystallize and increase the glass transition temperature (T_g). The increased crosslink density with increasing the function degree of diluent resulted in better phase separation, on the contrary, increasing the reactive diluent content led to the opposite because of a phase reversion. Microphase separation lower during quenching and annealing due to post-curing of 1,6-hexa-nediol diacrylate (HDDA) at high temperature, and with the UV-cured degree increasing, the phase separation got better first and then became worse.     

Nano- and bulk-tack adhesive properties of stimuli-responsive, fullerene-polymer blends, containing polystyrene-block-polybutadiene-block-polystyrene and polystyrene-block-polyisoprene-block-polystyrene rubber-based adhesives

Nano-tack (measured using AFM) and bulk-tack adhesive forces of blends of C₆₀ and either polystyrene-block-polybutadiene-block-polystyrene (SBS) or polystyrene-block-polyisoprene-block-polystyrene (SIS) triblock copolymer pressure sensitive adhesives were measured after exposure to white light irradiation. The nano-tack adhesive forces in C₆₀-SIS/SBS were found to decrease with increasing C₆₀ concentration and exposure time, approaching the value for 100% polystyrene, providing an indication that significant surface hardening and crosslinking of the soft isoprene and butadiene phases occurs in the presence of C₆₀. Films produced during the study were smooth, having low RMS surface roughness, and showed nanoscale phase separation between the soft (diene) and hard (styrene) segments. This phase separation disappeared after addition of C₆₀ sensitizer and white light irradiation. Bulk adhesive measurements (tack and peel strength) showed a similar trend with C₆₀ concentration and exposure time, and in irradiated systems containing as little as 0.2 wt% C₆₀, a significant decrease in adhesion was observed. Estimated T_g (measured using DMA, shear mode) of the soft-block shifts to higher temperatures (increasing by 30-40 °C), and high gel fractions were obtained, indicating the presence of chemically crosslinked networks.