Papers by Keyword: Microphase Separation

Abstract: The series of compositions containing thermodynamically incompatible flexible blocks of aliphatic polyesters and rigid blocks of aromatic bis (urethane) imides in the volume of polymers was obtained on the basis of multiblock (segmented) poly (urethane-imides) and related aromatic polyimides. The series includes segmented poly (urethane-imides) with different relative content of flexible and rigid blocks, non-segregating mixtures of poly (urethane-imides) and thermoplastic partially crystalline polyimide, statistical copolymers of poly (urethane-imide) with imide, and non-segregating mixtures of statistical copolymers with thermoplastic polyimide. The derived polymer systems were studied using thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. The deformation and strength properties of film samples are determined. It is shown that the properties of the studied polymers change as their content of imides blocks increases, and the transition from thermoplastic poly (urethane-imide) elastomers to thermoplastic polyimides is observed.

Abstract: A series of waterborne polyurethane (WPU) with different soft segment structures were sythesised, and the effects of the structure and molecular weight of the soft segment on the degree of PU microphase separation were evaluated by the infrared spectroscopy (FTIR) computer peak fitting. The experiment results indicated that phase separation between hard and soft segments of poly (ether–urethane) was more significant than poly (ester–urethane), based on the qualitative analysis on the N–H stretching region of the FTIR spectrum. And the qualitative analysis on the carbonyl stretching region showed that PU with lower soft segment molecular weight had a higher relative amount of hard segment, and possesses higher microphase separation degree. The addition of polyether soft segment PEG had an internal plasticization by actuating the PCD molecular chain. Therefore, it becomes easier for PU to conduct structure adjustment and increased the phase separation degree.

Abstract: In this study, a method to generate arrays of Fe₃O₄ nanoparticles (MNPs) via block copolymer (BC) self-assembly was developed. A composite film of polystyrene-block-poly (2-vinylpyridine) (PS-b-P2VP)/MNPs was first prepared by spin-coating the PS-b-P2VP/MNPs mixed solution on a carbon substrate. After the composite film was annealed at high temperature for 2 days, it was found that the modified MNPs could be selectively incorporated into P2VP cylinders in PS-b-P2VP diblock copolymers and the P2VP cylinders were oriented parallel to the substrate. For a long time annealing (10 days), the P2VP cylinders become normal to the substrate and MNPs are located at the interface of P2VP and PS phases.

Abstract: The present study described the effect of the different synthetic methods, hard segment types, chain extension coefficient and the starting NCO/OH molar ratio on the compression set and the other properties of castable polyurethanes based on polytetrahydrofuran glycol (PTMG).The result showed that the system of PTMG/TDI/MOCA prepared by a quasi-prepolymer method and with the starting molar ratio of TDI to PTMG of 6:1 exhibits lower compression set.

Abstract: The present study described the effect of the starting NCO/OH molar ratio on the structure and properties of castable polyurethanes based on polytetrahydrofuran glycol (PTMG) and 2,4- toluene diisocyanate (TDI). The structural was tested by SEM. The result showed that higher starting NCO/OH molar ratio can lead to higher degree of microphase separation, decrease the compression set and improve the dynamic mechanical properties.

Abstract: A set of polyether-urethane block copolymers were prepared that poly (tetramethylene oxide) PTMO was regarded as soft segment, 4,4'-methylenebis(phenyl isocyanate)(MDI) and m-diphenylamine (MDM) was regarded as hard segment in this article. The microphase separation of polyether-urethane block copolymer was investigated by using infrared spectroscopy(FTIR), differential scanning calorimetry(DSC), small-angle X-ray scattering(SAXS),there obtained that there are two phases structure in polyether-urethane block copolymers and degree of phase separation decrease with increasing hard segment weight content.

Abstract: Hydroxyl-terminated hyperbranched polyurethane elastomer (HBPU) was synthesized by graft copolymerization of hyperbranched poly (amine-ester) polyols(HPAE) and polyether-based aliphatic polyurethane prepolymer(PPU), and the PPU was synthesized by step polymerization of isophorone diisocyanate(IPDI) with polyethylene glycol(PEG) and dibutyltin dilaurate(DBTDL) as catalyst. The FT-IR spectroscopy, TGA and XRD were used to characterize the structure, thermal properties and crystallinity of HBPU. The mechanical properties of the elastomers were conducted on a testing machine. Microphase separation of HBPU film surface was studied by atomic force microscopy (AFM). The experimental results showed that the HBPU took on excellent hydrogen bonding and mechanical properties. The tensile strength of HBPU elastomer reached to 20.6MPa, which increased by 41.2 times than that of PPU elastomer. And the elongation at break was as high as 251.3%.

Abstract: In this paper the effect of curing temperature on the morphology and properties of PAE based polyureas were evaluated using FTIR, AFM and electrochemical impedance spectroscopy (EIS). The PAE based polyureas were prepared from synthesized PAE chain extenders and hexamethylene diisocyanate（HDI）trimer/polytetramethylene ether glycol (PTMG) prepolymer. The morphology and properties were investigated through FTIR, EIS and atomic force microscope(AFM). The results indicated that curing temperature has a great influence on morphology and properties of the polyureas. FTIR studies showed that hydrogen-bonded urea carbonyl are increased from 74.3% to 82.1%, and the length of hydrogen bonding were decreased from 0.307 nm to 0.303 nm while curing temperature were increased from 20°C to 80°C. FTIR experimental studies indicated that the degree of hydrogen-bonded –NH groups and urea carbonyl groups increased while curing temperature increased, as a consequence, intermolecular force enhanced. The AFM was applied to study the topography of PAE based polyureas for the first time,and the microphase separation phenomenon of the PAE based polyureas were observed directly through AFM topography studies. AFM studies confirmed that the compatibility of soft and hard segment decreased and microphase separation degree increased while the curing temperature increased. The EIS studies indicated that during 90 days immersion, the resistance of 20°C cured samples changed obviously higher than 80°C cured ones. The results showed that much corrosion medium permeated into the coatings, and the corrosion resistance of 80°C cured PAE based polyureas exhibited a higher EIS features and a better corrosion resistance than the 20°C cured ones. The effect of curing temperature on EIS properties of PAE based polyureas could be confirmed by FTIR and AFM morphology studies.

Abstract: Fiberglass continuous strand mat(CSM)/poly(urethane-isocyanurate) composites were formed by SRIM process, treated under different conditions and then characterized based on dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) ,transmission electron microscopy (TEM) and the mechanical property tests. The results show that the mechanical properties of the composites could be increased with improving the degree of microphase separation. At a given temperature (120°C), the degree of microphase separation is the highest for 4h and decreases gradually with prolonging treatment time. For a given time (4h), the well microphase-separated morphology is obtained and the degree of microphase mixing is increased at 120°C and 140°C treatments, respectively. The degree of microphase separation of the composites decreases with enhancing the temperature to 140°C.

Abstract: Polystyrene-polymethylmethacrylate (PS-PMMA) block copolymers are well known to exhibit microphase separation to form a series of regular structures with local periodic arrangements of the blocks. By developing films of PS-PMMA within topographically patterned silicon (100) substrates (with photolithographically defined rectangular channels of depth 60 nm and widths 166 – 433 nm) these irregular arrangements form highly periodic structures where the features are parallel to the side walls of the channels. However, the use of silicon substrates leads to problems in processing of these films. PS-PMMA does not wet the surface, and this results in island formation on flat substrates. On channel etched substrates this phenomena ensures that the thickness of the films is irregular and poorly defined alignment is seen. Detailed considerations of this polymer system suggest that feature sizes below 25 nm are not realisable. The results suggest other copolymer systems should be studied.