Soft Chain Research Articles

Seeded semibatch emulsion copolymerization of methyl methacrylate and butyl acrylate using polyurethane dispersion: effect of soft segment length on kinetics

Aqueous acrylic–polyurethane (AC–PU) hybrid emulsions were prepared by semibatch emulsion copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA) in the presence of two polyurethane (PU) dispersions. PU dispersions were synthesized using isophorone diisocyanate (IPDI), 1000 or 2000 molecular weight poly(neopentyl)adipate, and dimethylol propionic acid (DMPA). The monomer mixture was added in the monomer emulsion feed. We studied the effect of PU chain rigidity on the rate of polymerization, the particle size and distribution, the number of particles, and the average number of radicals per particle. The rigidity was controlled by varying the molecular weight (Mn) of the polyol, which represents the soft chain segment. The monomer feed rate was varied in order to study its influence on the process. It was observed that PU particles, prepared with higher molecular weight polyol, swelled to a greater extent with acrylic (AC) component. In the pseudo steady state the polymerization rate acquired a constant value, comparable to the value of monomer addition rate. The total particle number in the reactor in the pseudo steady state was constant and similar to the number of PU particles in the initial charge. The obtained results suggested that the MMA/BA copolymerization in the presence of PU seeds showed intermediate behavior between Smith-Ewart cases I and II.

Preparation of UV-curable long chain dibasic acid modified epoxydiacrylates and their coating properties

A number of saturated long chain dibasic acid modified epoxydiacrylates were synthesized. The UV-curable formulations were prepared with those as oligomers. The physical and mechanical characterizations of the UV-cured films were investigated: the addition of the soft long chain in oligomers caused the remarkable increase of the relative elongation at break.

Phase morphology and molecular dynamics of a polyurethane ionomer reinforced with a liquid crystalline filler

Solution-blended binary composites of ionic segmented polyurethane (SPU-I) and liquid crystalline oligomer (LCO) were characterized by wide-angle (WAXS) and small-angle (SAXS) X-ray scattering, differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC) and dielectric relaxation spectroscopy (DRS). Both components mutually influenced their states of aggregation in blends (most significantly, promoting smearing-out of interfaces between stiff and soft chain fragments of SPU-I into broad interfacial regions of intermediate composition). Apparently, the blend with w=0.10 happened to be most favorable for crystallization of the LCO, while the degree of microphase separation for SPU-I became lower and the distribution of stiff domains by sizes became broader, the higher the LCO content. The overall molecular mobility of SPU-I in blends was significantly reduced. This reduction included the intensity of the secondary and the primary relaxations, and of the interfacial Maxwell–Wagner–Sillars (MWS) relaxation, whereas the transition temperatures remained essentially composition-invariant. The Arrhenius-like behavior for the dc conductivity concomitant to the non-Arrhenius (i.e., Vogel–Tammann–Fulcher) frequency dependence for the α relaxation in blends suggested a decoupling of conductivity from the motion of the SPU-I soft chain segments.

Mechanical and thermal properties of rigid polyurethane foams derived from sodium lignosulfonate mixed with diethylene‐, triethylene‐ and polyethylene glycols

AbstractSodium salt of lignosulfonic acid (LS), which was obtained as by‐product of cooking process in sulfite pulping, was solved in diethylene, triethylene or polyethylene glycol. Three series of polyurethane foams (LSPU) were synthesized by varying the LS content from 0 to 33 wt%. Apparent density (ρ) of LSPU foams ranged from 0.08 to 0.18 g cm−3 and was affected by both LS content and oxyethylene chain length. Glass transition temperatures increased with increasing amount of LS and with decreasing oxyethylene chain length. Thermal gravimetry analysis indicated that the LS component decomposes first and that the thermal stability increases with decreasing oxyethylene chain length. Compression strength and compression modulus increased linearly with increasing apparent density. It is concluded that LS is successfully utilized as a hard segment of rigid PU foams, whose thermal and mechanical properties can be tuned by changing the amount of LS and the length of soft oxyethylene chains.

Physical Properties and Biodegradation of Lactide-based Poly(ethy1ene glycol) Polymer Networks for Tissue Engineering

New lactide-based poly(ethy1ene glycol) (PEG) polymer networks (GL-PEG) have been prepared by photopolymerization using two nontoxic niacromers, triacrylated lactic acid oligomer emanating from a glycerol center (GL) and monoacrylated PEG. These materials may use as polymer scaffolds in tissue engineering because they provide biodegradable, cell-adhesion resistant, and ligand-immobilizable characteristics. The thermal and mechanical properties of the resulting GL-PEG networks were evaluated and their biodegradability was investigated in phosphate buffered saline (PBS) at 80°C. The glass transition temperature (Tg) of all networks after degradation relatively decreased and the trend was similar to those before biodegradation, whereas thermal decomposition temperature (Td1/2) increased in all networks to a certain degree. The tensile strength decreased as PEG was incorporated and as the molecular weight and content of PEG increased due to the soft PEG chains. Degradation rate of GL-PEG networks was controlled by the ratio of GL to PEG, and generally the rate of GL-PEG networks was faster than that of GL homonetworks.

Effect of Soft Segment Length and Chain Extender Structure on Phase Separation and Morphology in Poly(urethane urea)s

AbstractThe phase separation and morphology in poly(urethane urea)s were investigated as soft segment length and chain extender structure were varied. Increases in soft segment length led to increased phase separation that resulted in greater mobility of the soft segment. This was shown by lower soft segment glass transition temperatures in differential scanning calorimetry (DSC) as well as a shift of Emax″ and tan δmax to lower temperatures. Also the structure of the chain extender affected the degree of phase separation and mixing of the soft and the hard blocks in an interphase. Atomic force microscopy (AFM) was used to visualize the structure of the phase‐separated domains. The hard domains were in the form of spheres 5–10 nm, or long needles 5 nm thick and 50–300 nm long. As the soft segment length increased, there were more pure soft segment phase areas between the hard domains. At high hard segment content, a larger scale structure was found, consisting of both hard and soft segments.DSC thermograms of poly(urethane urea)s containing different soft segment lengths.magnified imageDSC thermograms of poly(urethane urea)s containing different soft segment lengths.

Synthesis and electrochemical characterization of polyurethane with fixed redox‐active units in hard segments

AbstractElectrochemically active polyurethanes containing ferrocene units in hard segments (PU–H–Fc) have been synthesized and identified by 1H‐NMR spectra. Electrochemical properties of PU–H–Fc blending with lithium perchlorates were investigated by cyclic voltammetry (CV) and compared with that of polyurethane with ferrocene units in polyether soft segments (PU–S–Fc) and of ordinary polyurethane blending with ferrocene (PU–B–Fc). The apparent formal potentials were found to be similar. The results illustrated that the original redox property of ferrocene was maintained when it was covalently linked to the hard segment as well as to the soft polyether main chain. The peak separation in PU–S–Fc was much greater than in PU–H–Fc, demonstrating that the softness and flexibility of the PEO chain was maintained by fixing the redox units on the hard segments instead of on the soft segments, and the diffusion rate of redox units was increased because the migration of the active substance was enforced by the motion of the polymer chain. The peak position and peak separation of PU–H–Fc were similar to those of ordinary polyurethane blending with ferrocene. In the PU–H–Fc system the physical loss of admix redox molecules by migration can be avoided and the diffusion rate of redox units maintained. This is highly desirable in many electrochemical systems. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1555–1561, 2003

Microtribological properties of a novel C60-containing self-assembled film

Using the self-assembly technique, we have fabricated a novel, ternary-component ultra-thin film based on rigid C60 molecules and soft poly(acrylic acid) chains through electrostatic attractions with diazoresin. Under UV irradiation, the film is linked by covalent bonds, following the decomposition of diazonium, and shows good stability, contrasting with ionic bond linkages. Using AFM/FFM, the microtribological properties of the ternary film were investigated. Because of the inclusion of rigid molecules and soft polymer chains having a covalent linkage, the film shows not only good load-bearing, but also low friction, properties.

Molecular and topological structures in polyester block copolymers

The thermomechanical analysis (TMA) was used to investigate structures, molecular-weight distributions and relaxation transitions in polyester block copolymers possessing properties of thermoplastic elastomers. The copolymers were synthesized by polycondensation of polytetramethylene oxide (PTMO, molecular weight 1000), 1,4-butanediol and dimethyl terephthalate. The concentration of PTMO blocks was varied between 10 and 80 wt.%. The TMA shows changes in molecular and topological structures of the polyester copolymers when the composition is varied. The copolymers based on PTMO and polybutylene terephthalate (PBT) appeared to have a three-block (regions) topological structure at PTMO concentrations between 10 and 70 wt.%. They consist of (1) a low-temperature topological block ( T g between −27°C and −76°C), formed by most likely by PTMO enriched with the amorphous portion of PBT; (2) an intermediate ( T g varies within 94–18°C range), being postulated PBT amorphous portion enriched with amorphous PTMO; and (3) a high-temperature topological block formed by PBT chain segments, the regularity of which gets disturbed under the influence of PTMO soft chains ( T g between 197°C and 53°C). At 75 wt.% of PTMO, the three-block topological structure is transformed into a diblock one characterized by miscibility of the low-temperature and intermediate amorphous topological blocks. Complete mutual miscibility of all topological blocks and formation of a single-topological block polymer occur at 80 wt.% PTMO content.

Structural Characterization of Segmented Polyurethanes by Small Angle Neutron Scattering

ABSTRACTThe beneficial mechanical properties of segmented polyurethanes derive from microphase separation of immiscible hard and soft segment-rich domains at room temperature. We are interested in the structure of the domains, how these are affected by hydrolytic aging, and how the structure is modified by low molecular weight plasticizers. To assessed the distribution of the plasticizer in polyurethane, we did small-angle neutron scattering measurements on mixtures of 23% hard segment poly(esterurethane) with different amounts of either non-deuterated or deuterated plasticizer. We analyzed the results using a simple model in which the contrast, Δρ = ρH Š ρ, between the hard and soft segment-rich domains is varied by the amount of deuterated or hydrogenated plasticizer, using the fact that I(Q) ∼ Δρ2. The result demonstrated that the plasticizer is largely associated with the soft segment rich domains. The structure of PESU with the chain extender of the hard segment was assessed after aging under hydrolytic conditions. The results show that the microphase structure coarsens and segregates and that the hard and soft segments segregated as a result of the loss of constraints from hydrolytic soft segment chain scission. The results on plasticizer distribution and the effects of hydrolytic aging give insight on the loss of mechanical properties that occur in each case.

Physical and potentiometric properties of polyurethane-based cation-selective membranes

Lipophilic salts based on tetraphenylborate derivatives [e.g., potassium tetrakis(p-chlorophenyl)borate (KTpClPB), sodium tetraphenylborate (NaTPB), and cesium tetrakis(3-methylphenyl)borate are essential ingredients used in the preparation of solvent polymeric cation-selective membranes. The effects of such lipophilic salts on the physical properties of a polyurethane (PU) matrix comprising 4,4'-diphenylmethane diisocyanate, 1,4-butanediol, and poly(tetramethylene ether glycol) were examined. Differential scanning calorimetry measurements revealed that the sodium and potassium salts doped in PU increased the glass-transition temperatures (T g ) of the matrix, while the film containing cesium salt exhibited slightly decreased T g . The temperature dependence of the ionic conductivity for PU60 films doped with KT p ClPB is well described by the Arrhenius-type equation, and that doped with NaTPB is described by the Vogel-Tammann-Fulcher (VTF)-type equation. The temperature dependence of the ionic conductivity on the VTF-type equation suggests that the transport of sodium ions in the PU60 matrix is more strongly coupled to the soft segmental motion, and potassium ions are decoupled from the polymer host and transported by activated hopping. The effect of added salt on the internal structure of PU membranes was investigated by measuring the ratio between the free and hydrogen-bonded C=O bands at 1703 and 1730 cm 1 , respectively. The results showed that the ether oxygens in the soft segment chains are strongly coupled to the potassium or sodium, but much less to cesium. The potentiometric properties of these lipophilic additive doped PU membranes were characterized by incorporating valinomycin and 4-tert-butylcalix[4]arene-tetraacetic acid tetraethylester as potassium- and sodium-selective ionophores, respectively. Their response behavior could be explained by the observed physical characteristics.

Structural Characterization of Segmented Polyurethanes by Small Angle Neutron Scattering

ABSTRACTThe beneficial mechanical properties of segmented polyurethanes derive from microphase separation of immiscible hard and soft segment-rich domains at room temperature. We are interested in the structure of the domains, how these are affected by hydrolytic aging, and how the structure is modified by low molecular weight plasticizers. To assessed the distribution of the plasticizer in polyurethane, we did small-angle neutron scattering measurements on mixtures of 23% hard segment poly(esterurethane) with different amounts of either non-deuterated or deuterated plasticizer. We analyzed the results using a simple model in which the contrast, Δ=H-, between the hard and soft segment-rich domains is varied by the amount of deuterated or hydrogenated plasticizer, using the fact that I(Q) ∼ Δ2. The result demonstrated that the plasticizer is largely associated with the soft segment rich domains. The structure of PESU with the chain extender of the hard segment was assessed after aging under hydrolytic conditions. The results show that the microphase structure coarsens and segregates and that the hard and soft segments segregated as a result of the loss of constraints from hydrolytic soft segment chain scission. The results on plasticizer distribution and the effects of hydrolytic aging give insight on the loss of mechanical properties that occur in each case.

Infrared linear dichroism study of a hydrolytically degraded poly(ester urethane)

Static and dynamic infrared linear dichroism data have been used to supply additional insight into changes in tensile properties as a consequence of hydrolytic degradation of a segmented poly(ester urethane). Unaged material responds to tensile deformation with the soft (polyester) segments supplying the elasticity and the hard (polyurethane) segments supplying strength. Upon hydrolytic degradation, the static and dynamic data indicate altered orientational responses at the molecular-level, which are interpreted as resulting from cleavage of the soft segment chains and altered hydrogen-bonding interactions for both segments.

Mixed (ionic and electronic) conductive solid polymer matrix. Synthesis and characterization of homopolymers of 3-(2,5,8,11,14,17,20,23-octaoxyhexadodecyl)thiophene and copolymers with 3-methylthiophene

The macromonomer, 3-(2,5,8,11,14,17,20,23-octaoxyhexadodecyl)thiophene, abbreviated as (3-OHDT), was synthesized. The macromonomer has a glass transition temperature of –77°C, which corresponds to the soft oligooxyethylene side chain attached to the thiophene. The homopolymer, poly[3-(2,5,8,11,14,17,20,23-octaoxyhexadodecyl)thiophene], abbreviated to P[3-(OHDT)], has been synthesized via oxidative coupling of the macromonomer using FeCl3. Two distinct glass transition temperatures are observed for the homopolymer. The Tg at –47°C corresponds to the soft oligooxyethylene phase and the Tg value at 72°C corresponds to the hard thiophene backbone. The homopolymer P[3-(OHDT)] can be doped with LiClO4 and I2 to generate ionic and electronic conductive phases, respectively. For the P[3-(OHDT)]/LiClO4 system, with an ethylene oxide to lithium mole ratio of 8 : 1, an ionic conductivity value of 1.7×10–6 S cm–1 is observed at 25°C. The room temperature electronic conductivity of P[3-(OHDT)]/doped with I2 is 3.5x10–4 S cm–1. Several random copolymers of 3-methylthiophene and 3-(2,5,8,11,14,17,20,23-octaoxyhexadodecyl)thiophene were also synthesized. Depending on the copolymer composition, glass transition temperatures ranged from 67°C to 76°C, the higher glass transition temperature corresponding to higher 3-methylthiophene content. The copolymers may be appropriately doped to generate conductive matrices, with a maximum ionic conductivity (ethylene oxide/Li+ mole ratio of 8 : 1) of 1.0×10–7 S cm–1 and electronic conductivity around 6.7×10–1 S cm–1 at 25°C.

A NOVEL PACKING MATERIAL FOR RP-HPLC

A simple, practical, and economical procedure had been developed to prepare novel C18 ether-bond reversed phase packing. A soft and long C18 alkyl chain was coupled onto silica (Sinopak-S, particle size d = 5μm, pore diameter Dp=11nm, and surface area s=170m2/g) with γ-glycidoxypropyltrimethoxysilane as a coupling agent. Characterization of prepared packing was carried out with elemental analysis and solid-state [13]C NMR. Chromatographic evaluation indicates that its reversed phase behavior was similar to ordinary ODS.

Harvesting thermal fluctuations: Activation process induced by a nonlinear chain in thermal equilibrium

We present a model in which the immediate environment of a bistable system is a molecular chain which in turn is connected to a thermal environment of the Langevin form. The molecular chain consists of masses connected by harmonic or by anharmonic springs. The distribution, intensity, and mobility of thermal fluctuations in these chains is strongly dependent on the nature of the springs and leads to different transition dynamics for the activated process. Thus, all else (temperature, damping, coupling parameters between the chain and the bistable system) being the same, the hard chain may provide an environment described as diffusion-limited and more effective in the activation process, while the soft chain may provide an environment described as energy-limited and less effective. The importance of a detailed understanding of the thermal environment toward the understanding of the activation process itself is thus highlighted.

Formation of Surface Relief Grating upon Light Irradiation in Conducting Polymer and Photochromic Polymer Composite System

The formation of surface relief grating upon light irradiation on a composite film of conducting polymer with rigid main chain structure and acrylate polymer containing azo-substituent with soft main chain structure has been studied. The diffraction efficiency of the photo-induced grating decreases with increasing concentration of conducting polymer with respect to the polyacrylate in the concentration range higher than 3%. This implies that the height of surface relief on the film is lowered upon doping conducting polymer, which is confirmed by an atomic force microscope observation. It has been found, however, that the formation of surface relief grating is promoted by slight doping of conducting polymer (<3%) and progresses even after stopping light irradiation on the composite film. Anomalous angular dependence of photoluminescence from the composite film having relief grating on it has also been found.

Perturbative study of classical Ablowitz-Ladik type soliton dynamics in relation to energy transport in alpha-helical proteins.

Classical Ablowitz-Ladik type soliton dynamics from three closely related classical nonlinear equations is studied using a perturbative method. Model nonintegrable equations are derived by assuming nearest neighbor hopping of an exciton(vibron) in the presence of a full exciton(vibron)-phonon interaction in soft molecular chains in general and spines of alpha-helices in particular. In all cases, both trapped and moving solitons are found implying activation energy barrier for propagating solitons. Analysis further shows that staggered and nearly staggered trapped solitons will have a negative effective mass. In some models the exciton(vibron)-phonon coupling affects the hopping. For these models, when the conservation of probability is taken into account, only propagating solitons with a broad profile are found to be acceptable solutions. Of course, for the soliton to be a physically meaningful entity, total nonlinear coupling strength should exceed a critical value. On the basis of the result, a plausible modification in the mechanism for biological energy transport involving conformational change in alpha-helix is proposed. Future directions of the work are also mentioned.

Analytical calculus and Monte Carlo simulation of crosslinked polymer formation in the copolymerization of tetraethoxysilane and poly(dimethylsiloxane)

Full Paper: To understand the fundamental aspects of the polycondensation reaction of hydrolyzed tetraethoxysilane (TEOS) and silanol-terminated poly(dimethylsiloxane) (PDMS), we modeled the reaction system as a stepgrowth polymerization of A4 and polydisperse A2 , assuming the reactivities of all functional groups are equal. The analytical solution for the weight-average molecular weight is developed, and in addition, a Monte Carlo simulation is conducted to investigate the detailed structural development. It was found that as long as the molecular weight of PDMS is much larger than TEOS, the apparent behavior is significantly different from usual gelling systems. The gel point is relatively insensitive to the weight fraction of crosslinker (TEOS), the polydispersity index may decrease during polymerization before the rapid increase to infinity, and the molecular weight distribution profile may not show a significant broadening toward gelation. Even though the present model assumes a complete random reaction process among functional groups, formation of a heterogeneous structure in which a tight core consisting of TEOS-based molecules is surrounded by soft PDMS chains was observed in the Monte Carlo simulation.

Formation and characteristics of nitrifying biofilm on a membrane modified with positively-charged polymer chains

Nitrifying bacteria hardly adhered to the surface of supporting materials in a fluidized bed bioreactor containing only inorganic compounds. The adhesivity of nitrifying bacteria was compared, between an unmodified membrane and a membrane modified with diethylamino groups, using the grafting method. The result showed that the diethylamino-group-grafted membrane successfully increased the adhesivity of nitrifying bacteria, which might be due to particular properties of the grafted membrane surface, such as positive charge and soft polymer chains. Moreover, the thickness of the biofilm exceeded 100 μm after incubation for 150 days in a continuously fed fluidized bed bioreactor. The results of fluorescence in situ hybridization (FISH) confirmed that the biofilm consisted mostly of ammonia-oxidizing bacteria. Moreover, the biofilm exhibited a much higher nitrification rate per unit area than other biofilms, which was confirmed by the analysis of the concentration profile of ammonium-nitrogen inside the biofilm using a microelectrode that we originally fabricated.