Polyisobutylene‐based polyurethanes. IX. synthesis,characterization, and properties of polyisobutylene‐based poly(urethane‐ureas)

Polyisobutylene (PIB)‐based polyurethanes (PUs) exhibit unparalleled hydrolytic‐oxidative‐biologic stability and are melt processible, however, their mechanical (strength) properties are modest mainly due to insufficient H bonds. We posited and demonstrate that the ultimate properties of PIB‐PUs are enhanced, while their melt processibility is maintained, by the judicious introduction of urea linkages, i.e., strong bifurcated H bonds, in the chain. The incorporation of bifurcated H bonds in PIB‐PUs was achieved by using the conventional butane diol chain extender (CE) in combination with controlled amounts of amino alcohol as co‐chain extender (co‐CE). Polyurethanes containing both urethane and urea linkages are polyurethane‐ureas (PUU). Specifically, PIB‐PUUs prepared with PIB‐diol/MDI together with 80/20 mole % butane diol/amino butanol exhibited ～30 MPa tensile strength, ～550% elongation, ～80 Shore A hardness, and ～137 °C flow temperature. Other amino alcohols, i.e., amino ethanol, ‐propanol, and ‐hexanol, were less effective co‐CEs. ¹H‐NMR and FT‐IR spectroscopies indicate the presence of bifurcated H bonds in PIB‐PUUs prepared with CE/co‐CE combinations. Characterization by differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical thermal analysis, and creep experiments also suggest bifurcated H bonds in PIB‐PUU. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2361–2369     

Morphology and tensile properties of model thermoplastic polyurethanes with MDI/butanediol based monodisperse hard segments

Morphology and tensile properties of model thermoplastic polyurethanes (TPUs) containing polyisobutylene (PIB) or poly(tetramethylene oxide) (PTMO) based soft segment and 4,4‐methylene bis(phenyl isocyanate) (MDI) and 1,4‐butanediol (BDO) based monodisperse hard segments (HSs), consisting of exactly two to four MDI units extended by BDO, were investigated. Using FT‐IR spectroscopy, increased hydrogen bonded C?O fraction was observed in model TPUs as the HS size increased. The hydrogen bonded C?O fraction was higher in PIB based TPUs compared with PTMO based TPUs, indicating higher phase separation in PIB based TPUs. The morphology of TPUs was investigated using AFM phase imaging, which showed ribbon‐like or interconnected hard domains in PTMO based model TPUs and randomly dispersed hard domains in PIB based model TPUs. SAXS revealed that the degree of phase separation in the model TPUs was higher than in their polydisperse analogues. Domain spacing as well as interfacial thickness increased with the increasing HS size, and both values were higher in PTMO based TPUs. The tensile analysis indicated that model TPUs exhibited higher modulus and slightly higher elongation compared with their polydisperse analogues. Only in PTMO based model TPUs, strain induced crystallization was observed above 300% elongation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2485–2493     

Diaminobisbenzothiazole chain extended polyurethanes as a novel class of thermoplastic polyurethane elastomers with improved thermal stability and electrical insulation properties

This work was devoted to the development of a new class of modified polyurethane as an electrical insulating material. For this purpose, NCO‐terminated urethane prepolymers at different NCO contents were prepared and chain extended by 6,6′‐oxybis(2‐aminobenzothiazole) (ABT) to produce thermoplastic polyurethane elastomers. All of the polymers were characterized by FTIR and ¹HNMR spectroscopies and examined for their thermal, mechanical, and electrical properties. The dynamic mechanical measurements results showed two glass transitions indicating phase separation. A considerable improvement in the thermal and electrical properties in comparison to common polyurethanes was detected for these polymers. The level of enhancement in the measured properties was related to the polyol molecular weight, hard segment content, and consequently the amount of the introduced urea and benzothiazole moieties. These findings indicated the improved high service temperature performance of these materials as electrical insulator for metallic surfaces. Copyright © 2008 John Wiley & Sons, Ltd.     

Anisotropic mechanical properties of thermoplastic elastomers in situ reinforced with thermotropic liquid‐crystalline polymer fibers revealed by biaxial deformations

The anisotropic mechanical properties of the thermoplastic elastomer (TPE) in situ reinforced with thermotropic liquid‐crystalline polymer (TLCP) fibers were investigated by uniaxial, strip‐biaxial, and equibiaxial tensile measurements. The in situ composite sheets were prepared from an immiscible blend of a TLCP, Rodrun LC3000, and a TPE, styrene‐(ethylene butylene)‐styrene (SEBS) triblock copolymer, by a melt extrusion process. The uniaxial orientation of the TLCP fibers in the TPE matrix generated during processing yielded a significant mechanical anisotropy in the composites. The biaxial tensile measurements clearly demonstrated the anisotropic mechanical properties of the composites: The modulus in the direction parallel to the machine direction (MD) was considerably higher than that in the transverse direction (TD), even at large deformations; in equibiaxial stretching, the yield strain in the MD was smaller than that in the TD; the composite containing 10 wt % of TLCP exhibited the highest mechanical anisotropy among the composites, with 0–30 wt % TLCP. The latter result was in accord with the SEM observation that the composite with 10 wt % of TLCP possessed the best fibrillar morphology and the highest degree of uniaxial orientation of the TLCP fibers. The yield strains in uni‐ and biaxial elongation for the composite containing 10 wt % of TLCP were almost the same as those for the neat styrene‐ethylene butylene‐styrene. The TLCP phase with good fibrillation did not appreciably alter the original yielding characteristics of the elastomer matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 135–144, 2005     

Polyesters containing sulfur. VII. New aliphatic‐aromatic polyesters for synthesis of polyester‐sulfur compositions and polyurethanes

New linear polyesters containing sulfur in the main chain were obtained by melt polycondensation of diphenylmethane‐4,4′‐bis(methylthioacetic acid) (DBMTAA) or diphenylmethane‐4,4′‐bis(methythiopropionic acid) (DBMTPA) and diphenylmethane‐4,4′‐bis(methylthioethanol) (DBMTE) at equimolar ratio of reagents (polyesters E‐A and E‐P) as well as at 0.15 molar excess of diol (polyesters E‐A_OH and E‐P_OH). The kinetics of these reactions was studied at 150, 160, and 170°C. Reaction rate constants (k₂) and activation parameters (ΔG^≠, ΔH^≠, ΔS^≠) from carboxyl group loss were determined using classical kinetic methods. E‐A and E‐P (M̄_n = 4400, 4600) were used for synthesis of new rubber‐like polyester‐sulfur compositions, by heating with elemental sulfur, whereas oligoesterols E‐A_OH and E‐P_OH (M̄_n = 2500, 2900) were converted to thermoplastic polyurethane elastomers by reaction with hexamethylene diisocyanate (HDI) or methylene bis(4‐phenyl isocyanate) (MDI). The structure of the polymers was determined by elemental analysis, FT‐IR and liquid or solid‐state ¹H‐, ¹³C‐NMR spectroscopy, and X‐ray diffraction analysis. Thermal properties were measured by DTA, TGA, and DSC. Hardness and tensile properties of polyurethanes and polyester‐sulfur compositions were also determined. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 835–848, 1999     

Synthesis and thermal transition behavior of model thermoplastic polyurethanes containing MDI/butanediol‐based monodisperse hard segments

Amine‐terminated monodisperse hard segments (MDHSs) containing two to four 4,4′‐methylenebis (phenyl isocyanate) extended by 1,4‐butanediol have been synthesized using carboxybenzyl protecting‐deprotecting strategy. Pure MDHSs in large scale were obtained in good yield and their structures were confirmed by ¹H‐, ¹³C‐NMR spectroscopy and GPC‐MALLS. Differential scanning calorimetry (DSC) showed that as the hard segment (HS) size increased, the melting and glass transition temperature and the change of heat capacity at glass transition of ethyl capped MDHSs increased. Model thermoplastic polyurethanes (TPUs) were synthesized using the reaction of bischloroformate of poly (tetramethylene oxide) (PTMO) diol or polyisobutylene (PIB) diol with amine‐terminated MDHSs. X‐ray diffraction results indicated the amorphous structure of model TPUs. DSC revealed HS related endotherms, regardless of SS, which were attributed to the local ordering of the HSs. Additional endotherms in PTMO based model TPUs might arise from the dissociation of hydrogen bonding between PTMO and HSs. The lower T_g in model TPUs compared to the polydisperse analogues observed by dynamic mechanical analysis (DMA) indicated higher microphase separation of monodisperse HSs. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3171–3181     

Effect of prepolymer molecular weight on solid state polymerization of poly(bisphenol a carbonate) with nitrogen as a sweep fluid

The effect of prepolymer molecular weight on the solid‐state polymerization (SSP) of poly(bisphenol A carbonate) was investigated using nitrogen (N₂) as a sweep fluid. Prepolymers with different number–average molecular weights, 3800 and 2400 g/mol, were synthesized using melt transesterification. SSP of the two prepolymers then was carried out at reaction temperatures in the range 120–190 °C, with a prepolymer particle size in the range 20–45 μm and a N₂ flow rate of 1600 mL/min. The glass transition temperature (T_g), number–average molecular weight (M_n), and percent crystallinity were measured at various times during each SSP. The phenyl‐to‐phenolic end‐group ratio of the prepolymers and the solid‐state synthesized polymers was determined using 125.76 MHz ¹³C and 500.13 MHz ¹H nuclear magnetic resonance (NMR) spectroscopy. At each reaction temperature, SSP of the higher‐molecular‐weight prepolymer (M_n = 3800 g/mol) always resulted in higher‐molecular‐weight polymers, compared with the polymers synthesized using the lower molecular weight prepolymer (M_n = 2400 g/mol). Both the crystallinity and the lamellar thickness of the polymers synthesized from the lower‐molecular‐weight prepolymer were significantly higher than for those synthesized from the higher‐molecular‐weight prepolymer. Higher crystallinity and lamellar thickness may lower the reaction rate by reducing chain‐end mobility, effectively reducing the rate constant for the reaction of end groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4959–4969, 2008     

Studies on thermoplastic polyurethanes based on new diphenylethane-derivative diols. II. Synthesis and characterization of segmented polyurethanes from HDI and MDI

Various new thermoplastic segmented polyurethanes were synthesized by a one-step melt polymerization from aliphatic-aromatic α,ω-diols containing sulfur in the aliphatic chain, including 4,4′-(ethane-1,2-diyl)bis(benzenethioethanol), 4,4′-(ethane-1,2-diyl)bis(benzenethiopropanol) and 4,4′-(ethane-1,2-diyl)bis(benzenethiodecanol) as chain extenders, hexane-1,6-diyl diisocyanate (HDI) or 4,4′-diphenylmethane diisocyanate (MDI) and 20-80 mol% poly(oxytetramethylene)diol (PTMO) with molecular weight of 1000 g/mol as a soft segment. The reaction was conducted at the molar ratio of NCO/OH = 1 and 1.05, and in the case of the HDI-based polyurethanes in the presence of dibutyltin dilaurate as a catalyst. The effect of the diisocyanate used on the structure and some physicochemical, thermal and mechanical properties of the segmented polyurethanes were studied. The structures of these polyurethanes were examined by FTIR and X-ray diffraction analysis. The thermal properties were investigated by differential scanning calorimetry and thermogravimetric analysis. Shore hardness and tensile properties were also determined. All the synthesized polymers showed partially crystalline structures. The MDI-based polyurethanes were products with lower crystallinity, higher glass-transition temperature (T_g) and better thermal stability in comparison with the HDI-based ones. The MDI series polymers also exhibited higher tensile strength (up to ∼36 MPa vs. ∼23 MPa) and elongation at break (up to ∼3900% vs. ∼900%), but lower hardness than the analogous HDI series polyurethanes. In both series of the polymers an increase in PTMO soft-segment content was associated with decreased crystallinity, T_g, hardness and tensile strength. An increase in PTMO content also involved an increase in elongation at break.     

Synthesis and properties of fluorinated thermoplastic polyurethane elastomer

A series of fluorinated thermoplastic polyurethane elastomers (FTPU) based on self-synthesized fluorinate polyether diol (PFGE) were prepared by two-step polymerization. For the purpose of improving the molecular weight and mechanical property of FTPU, polybutylene adipate (PBA) was used to be compounded with PFGE as the soft-segment of FTPU. Effects of the mass ratio of PFGE/PBA and the mass fraction of hard-segment on the mechanical property of FTPU were investigated. The structure and morphology of FTPU were characterized by FTIR, GPC, DMA, surface tension and AFM analysis.     

Effect of the composition ratio of copolymerized poly(carbonate) glycol on the microphase‐separated structures and mechanical properties of polyurethane elastomers

Randomly copolymerized poly(carbonate) glycols were employed as starting materials for the synthesis of polyurethane elastomers (PUEs). The poly(carbonate) glycols had hexamethylene (C₆) and tetramethylene (C₄) units between carbonate groups in various composition ratios (C₄/C₆ = 0/100, 50/50, 70/30, and 90/10), and the number‐average molecular weights of these poly(carbonate) glycols were 1000 and 2000. The PUEs were synthesized with these poly(carbonate) glycols, 4,4′‐diphenylmethane diisocyanate, and 1,4‐butanediol by a prepolymer method. Differential scanning calorimetry measurements revealed that the difference between the glass‐transition temperature of the soft segment in the PUEs and the glass‐transition temperature of the original glycol polymer decreased and the melting point of the hard‐segment domain increased with an increasing C₄ composition ratio. The microphase separation of the poly(carbonate) glycol‐based PUEs likely became stronger with an increasing C₄ composition ratio. Young's modulus of these PUEs increased with an increasing C₄ composition ratio. This was due to increases in the degree of microphase separation and stiffness of the soft segment with an increase in the C₄ composition ratio. The molecular weight of poly(carbonate) glycol also influenced the microphase‐separated structure and mechanical properties of the PUEs. The addition of different methylene chain units to poly(carbonate) glycol was quite effective in controlling the microphase‐separated structure and mechanical properties of the PUEs. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4448–4458, 2004     

Syntheses and properties of ABA,CBA, and CBC triblock copolymers based thermoplastic elastomers with glassy (A), elastomeric (B), and crystalline (C) blocks

In this contribution, we describe the syntheses, characterization, and properties of ABA, CBA and CBC triblock copolymers with glassy (A), elastomeric (B), and crystalline (C) blocks. These three hard-soft-hard triblock copolymers were prepared via living ring-opening metathesis copolymerization by use of Grubbs third generation catalyst through one-pot sequential monomer addition and subsequent hydrogenation. These hard-soft-hard triblock copolymers based thermoplastic elastomers have been analyzed by proton NMR, differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), IR, and transmission electron microscopy (TEM). The mechanical properties of these triblock copolymers were also measured by monotonic and step cyclic tensile test. Compared with the ABA triblock copolymer, the CBC triblock copolymer containing highly crystalline hard end-blocks shows enhanced tensile strength and the best elastic recovery of 90.8%. The hybrid CBA triblock copolymer displays much improved elongation, which is almost twice as long as the other two TPEs, and excellent elastic recovery of 87.0%.     

Effect of SSL and HSC on morphology and properties of PHA based SMPU synthesized by bulk polymerization method

Searching new shape memory polymer and the associating synthesis technology are critical on the development of smart materials. In this paper, a comprehensive study on Poly(hexylene adipate) PHA being the soft segment of shape memory polyurethane (SMPU) was presented. Bulk polymerization method was employed to synthesize the SMPU with different soft segment length (SSL) and hard segment content (HSC). The influences of SSL and HSC on its morphology and thermomechanical property using DSC, DMA, POM, and shape memory behavior were presented here. The results indicate that the thermal properties, dynamic mechanic properties, and crystal morphology of SMPU are influenced significantly by SSL and HSC. And it is found that the shape fixity increases with SSL but decreases with HSC. On the other hand, the shape recovery decreases with both SSL and HSC, and the associated recovery temperature increases either with the increasing SSL or with decreasing HSC. Lastly, it is concluded that in the PHA‐based‐SMPU, the lower limiting value of SSL for polyurethane having shape memory effect is 2000; their response temperature varied with SSL and HSC, changing from 41.0 to 51.9 °C. Stable hard segment crystal are formed at above 30% HSC sample in bulk polymerization, but shape memory behavior can also be observed when its physical crosslink point are formed in the lower HSC PHA‐based‐SMPU. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 444–454, 2007     

Synthesis and properties of renewable nonisocyanate polyurethanes (NIPUs) from dimethylcarbonate

Novel fully renewable AA‐BB type nonisocyanate polyurethanes (NIPUs) were synthesized using the transurethanization approach. Dicarbamate monomers were prepared by the reaction of a diamine with an excess of dimethylcarbonate (DMC), in presence of 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) as catalyst. Then, the dicarbamate was reacted with a diol to afford the polymer, in presence of TBD or K₂CO₃ as catalyst. Several renewable diamines and diols were tested. The two steps were conducted under neat conditions. The obtained materials exhibited T_g values varying from ?38 to 42 ° C, T_m values varying from 42 to 204 °C , and thermal stabilities above 200 ° C. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1351–1359     

Synthesis and characterization of poly(methylmethacrylate)/silica nanocomposites: Study of the interphase by solid‐state NMR and structure/properties relationships

Organic/inorganic nanocomposites were synthesized from poly(methylmethacrylate) (PMMA) and properly modified silica nanoparticles by in situ polymerization. Methacryloylpropyltrimethoxysilane was selected as nanoparticle surface modifier because it is characterized by unsaturated end groups available to radical reactions, making possible to suppose their participation in the acrylic monomer polymerization. As a result of the above hypothesized reactions, a phase constituted by polyacrylic chains grafted onto modified silica surface was isolated. ²⁹Si and ¹³C solid‐state nuclear magnetic resonance experiments permitted to analyze this phase in terms of composition and chain mobility as well as to highlight interaction mechanisms occurring between growing PMMA oligoradicals and functional groups onto silica surface. It was demonstrated that this PMMA grafted onto silica surface acts as an effective coupling agent and assures a good dispersion of nanoparticles as well as a strong nanoparticle/matrix interfacial adhesion. As a result of strong interactions occurring between phases, a significant increase of the glass transition temperature was recorded. Finally, the abrasion resistance of PMMA in the hybrids was significantly improved as a result of a different abrasion propagation mechanism induced by silica particles thus overcoming one of the most serious PMMA drawback. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Mechanical properties of gradient copolymers of styrene and n‐butyl acrylate

The mechanical properties of linear and V‐shaped compositional gradient copolymer of styrene and n‐butyl acrylate with composition of around 55 wt % styrene were investigated by comparing with their block copolymer counterparts. Compared with their block copolymer counterparts, the gradient copolymers showed lower elastic modulus, much larger elongation at break, and similar ultimate tensile strength at room temperature. This performance could be ascribed to that the local moduli continuously change from the hardest nanodomains to the softest nanodomains in the gradient copolymer, which alleviates the stress concentration during tensile test. Compared with the V‐shaped gradient (VG) copolymer, the linear gradient copolymer showed much higher elastic modulus but lower elongation at break. The mechanical properties of the gradient copolymers were more sensitive to the change in temperature from 9 °C to 75 °C. With recovery temperature increased from 10 °C to 60 °C, the strain recovery of VG copolymer would change steadily from 40% to 99%. However, the elastic recovery of linear and triblock copolymer was poor even at 60 °C. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 860–868     

The synthesis and characterization of new thermoplastic poly(thiourethane‐urethane)s

New thermoplastic segmented poly(thiourethane‐urethane)s (SPTUUs) were prepared by a one‐step melt polymerization from 20 to 80 mol % poly(tetramethylene oxide) of = 1000 or poly(hexamethylene carbonate) diol (PHCD) of = 860 as soft segments, hexamethylene diisocyanate (HDI) and bis[4‐(mercaptomethyl)phenyl]methanone (BMMPM) as a new dithiol chain extender at the NCO/(OH + SH) molar ratio of 1 in the presence of dibutyltin dilaurate as a catalyst. The structures of the SPTUUs were examined by FTIR, X‐ray diffraction analysis, and scanning electron microscopy. The SPTUUs were also characterized by physicochemical, thermal, and tensile properties as well as Shore A/D hardness. The SPTUUs with the PHCD soft segments showed better tensile properties than those with the PTMO soft segments. A nonsegmented polythiourethane based on BMMPM and HDI is also described. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1770–1782, 2008     

Development of oriented structure and properties on drawing of poly(vinylidene fluoride) by solid‐state coextrusion

Gel films of poly(vinylidene fluoride) (PVDF) consisting of α‐form crystals were drawn uniaxially by solid‐state coextrusion to extrusion draw ratios (EDR) up to 9 at an optimum extrusion temperature of 160 °C, about 10°C below the melting temperature (T_m). The development of an oriented structure and mechanical and electrical properties on coextrusion drawing were studied as a function of EDR. Wide‐angle X‐ray diffraction patterns showed that the α crystals in the original gel films were progressively transformed into oriented β‐form crystals with increasing EDR. At the highest EDR of 9 achieved, the drawn product consisted of a highly oriented fibrous morphology with only β crystals even for the draw near the T_m. The dynamic Young's modulus along the draw direction also increased with EDR up to 10.5 GPa at the maximum EDR of 9. The electrical properties of ferroelectricity and piezoelectricity were also markedly enhanced on solid‐state coextrusion. The D–E square hysteresis loop became significantly sharper with EDR, and a remanent polarization P_r of 100 mC/m² and electromechanical coupling factor along the thickness direction k_t of 0.27 were achieved at the maximum EDR of 9. The crystallinity value of 73–80% for the EDR 9 film, estimated from these electrical properties, compares well with that calculated by the ratio of the crystallite size along the chain axis to the meridional small‐angle X‐ray scattering (SAXS) long period, showing the average thickness of the lamellae within the drawn β film. These results, as well as the appearance of a strong SAXS maximum, suggest that the oriented structure and properties of the β‐PVDF are better explained in terms of a crystal/amorphous series arrangement along the draw axis. Further, the mechanical and electrical properties obtained in this work are the highest among those ever reported for a β‐PVDF, and the latter approaches those observed for the vinylidene fluoride and trifluoroethylene copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1371–1380, 2001     

Effect of long fiber thermoplastic extrusion process on fiber dispersion and mechanical properties of viscose fiber/polypropylene composites

Viscose fiber reinforced polypropylene (PP/VF) composites were manufactured using long fiber thermoplastic (LFT) extrusion techniques with two different methods namely LFT‐l and LFT‐2. The compatibilizer [maleated polypropylene (MAPP)] and dispersing agent [stearic acid (SA)] were added to the PP/VF in order to improve the fiber dispersion and interfacial adhesion. The PP/VF composites manufactured using LFT‐2 showed better fiber dispersion with higher tensile and flexural properties compared to the composites manufactured using LFT‐1 method. Similarly, the impact strength and toughness of the LET‐2 composites showed an improvement of 36 and 20% than LFT‐1 whereas the average fiber length of composites was decreased from 6.9 mm to 4.4 mm because of the increase in shear energy as a result of residence time. Further, the addition of SA and MAPP to LFT‐2 process has significantly improved the fiber dispersion and mechanical performance. The fiber dispersion and fracture behavior of the LFT‐1 and LFT‐2 composites were studied using scanning electron microscopy analysis. The Fourier transformation infrared spectra were also studied to ascertain the existence of type of interfacial bonds. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of molecular weight of macro‐iniferter on electro‐optical properties of polymer dispersed liquid crystal films prepared by iniferter polymerization

Polymer dispersed liquid crystal (PDLC) films were prepared by a devised method, in which photo‐polymerization induced phase separation in a mixtures of a macro‐iniferter, methyl acrylater, and liquid crystal. The morphology of the obtained PDLC films was examined on a polarized optical microscopy, and the effect of molecular weight of MIs on the electro‐optical properties was deliberately investigated. Decreasing the molecular weight of MIs in the films led to formation of larger liquid crystal droplets and a lower V_th values. V_sat increased and the memory effect decreased because of the increased interface anchoring strength induced by the higher molecular weight of polymer matrices. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1530–1534, 2009     

Generation of radical species on polypropylene by alkylborane‐oxygen system and its application to graft polymerization

Graft polymerization of ethyl acrylate and n‐butyl acrylate onto surface of polypropylene (PP) beads (diameter: 3.2 mm) were carried out by using a redox system composed of triethylborane (Et₃B) and molecular oxygen in air. The amounts of the grafted polymers increased by prolonging a period of soaking PP beads in a solution of Et₃B in hexane, a less polar solvent of which affinity with PP would be higher than that of tetrahydrofuran, a highly polar solvent. These results implied that the present graft polymerization involved: (1) interpenetration of Et₃B into the surface area with the aid of hexane as a solvent, (2) its aerobic oxidation to generate a radical species, (3) abstraction of proton from PP by the radical species, and (4) initiation of polymerization from the resulting radical on the PP surface. Besides the acrylates, acrylic acid, and glycidyl methacrylate were also grafted onto the surface of PP to endow it with carboxyl and epoxy moieties, respectively. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6163–6167, 2009