Liquid-liquid phase separation and crystallization behavior of poly(ethylene terephthalate)/poly(ether imide) blend

The liquid-liquid (L-L) phase separation and crystallization behavior of poly(ethylene terephthalate) (PET)/poly(ether imide) (PEI) blend were investigated with optical microscopy, light scattering, and small angle X-ray scattering (SAXS). The thermal analysis showed that the concentration fluctuation between separated phases was controllable by changing the time spent for demixing before crystallization. The L-L phase-separated specimens at 130 °C for various time periods were subjected to a temperature-jump of 180 °C for the isothermal crystallization and then effects of L-L phase separation on crystallization were investigated. The crystal growth rate decreased with increasing L-L phase-separated time (t_s). The slow crystallization for a long t_s implied that the growth path of crystals was highly distorted by the rearrangement of the spinodal domains associated with coarsening. The characteristic morphological parameters at the lamellar level were determined by the correlation function analysis on the SAXS data. The blend had a larger amorphous layer thickness than the pure PET, indicating that PEI molecules in the PET-rich phase were incorporated into the interlamellar regions during crystallization.     

Crystallization, spherulite growth, and structure of blends of crystalline and amorphous poly(lactide)s

The effects of incorporated amorphous poly(dl-lactide) (PDLLA) on the isothermal crystallization and spherulite growth of crystalline poly(l-lactide) (PLLA) and the structure of the PLLA/PDLLA blends were investigated in the crystallization temperature (T_c) range of 90-150 °C. The differential scanning calorimetry results indicated that PLLA and PDLLA were phase-separated during crystallization. The small-angle X-ray scattering results revealed that for T_c of 130 °C, the long period associated with the lamellae stacks and the mean lamellar thickness values of pure PLLA and PLLA/PDLLA blend films did not depend on the PDLLA content. This finding is indicative of the fact that the coexisting PDLLA should have been excluded from the PLLA lamellae and inter-lamella regions during crystallization. The decrease in the spherulite growth rate and the increase in the disorder of spherulite morphology with an increase in PDLLA content strongly suggest that the presence of a very small amount of PDLLA chains in PLLA-rich phase disturbed the diffusion of PLLA chains to the growth sites of crystallites and the lamella orientation. However, the wide-angle X-ray scattering analysis indicated that the crystalline form of PLLA remained unvaried in the presence of PDLLA.     

Morphology of melt-quenched poly(ε-caprolactone)-block-polyethylene copolymers

The morphology of a melt-quenched crystalline-crystalline diblock copolymer, poly(ε-caprolactone)-block-polyethylene (PCL-b-PE), was studied by small-angle X-ray scattering and transmission electron microscopy. The melting behavior of PCL-b-PE was also investigated by differential scanning calorimetry. The melting temperature of PCL blocks, T_m,PCL, was ca. 55 °C and that of PE blocks was ca. 96 °C. Therefore, the PE block always crystallized first during quenching from the microphase-separated melt into various temperatures T_c below T_m,PCL to yield an alternating structure composed of PE lamellae and amorphous layers (PE lamellar morphology), and subsequently the crystallization of PCL blocks started at T_c after some induction period. The PE lamellar morphology was preserved after the crystallization of PCL blocks at low crystallization temperatures (T_c<30 °C), that is, the PCL block crystallized within the PE lamellar morphology. At high crystallization temperatures (45 °C>T_c>30 °C), on the other hand, the crystallization of PCL blocks destroyed the PE lamellar morphology to result in a new lamellar morphology mainly consisting of PCL lamellae and amorphous layers (PCL lamellar morphology). The PE crystals were fragmentarily dispersed in the PCL lamellar morphology.     

Morphology development and crystallization behavior of a poly(ethylene terephthalate)/polycarbonate blend

The morphology development and crystallization behavior of an extruded poly(ethylene terephthalate)/polycarbonate blend were studied with optical microscopy, light scattering, and differential scanning calorimetry (DSC). During annealing at 280°C, liquid–liquid phase separation via spinodal decomposition proceeded in a melt‐extruded specimen. After the formation of the domain structure, the blend slowly underwent phase homogenization by transesterification between the two polymers. The specimen, annealed for various times (t_s's) at 280°C, was subjected to a temperature drop to 180°C for the isothermal crystallization, and then the effects of liquid‐phase changes on crystallization were investigated. The crystal growth rate decreased with t_s. The slow crystallization with a large t_s value was associated with the composition change of the separated phases and the change of the sequence distribution in the polymer chains during annealing. The influence of t_s on the endothermic behavior of the samples was examined. As t_s increased, the recrystallization rate was retarded during the DSC scan, displaying multiendothermic behavior. The DSC data also suggested that the increased level of transesterification would give rise to a higher number of species being rejected from the primary crystals, leading to enhanced secondary crystallization. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Isothermal and non-isothermal crystallization behavior of poly(l-lactic acid): Effects of stereocomplex as nucleating agent

The effects of incorporated poly(d-lactic acid) (PDLA) as poly(lactic acid) (PLA) stereocomplex crystallites on the isothermal and non-isothermal crystallization behavior of poly(l-lactic acid) (PLLA) from the melt were investigated for a wide PDLA contents from 0.1 to 10 wt%. In isothermal crystallization from the melt, the radius growth rate of PLLA spherulites (crystallization temperature (T_c)≥125 °C), the induction period for PLLA spherulite formation (t_i) (T_c≥125 °C), the growth mechanism of PLLA crystallites (90 °C≤T_c≤150 °C), and the mechanical properties of the PLLA films were not affected by the incorporation of PDLA or the presence of stereocomplex crystallites as a nucleating agent. In contrast, the presence of stereocomplex crystallites significantly increased the number of PLLA spherulites per unit area or volume. In isothermal crystallization from the melt, at PDLA content of 10 wt%, the starting, half, and ending times for overall PLLA crystallization (t_c(S), t_c(1/2), and t_c(E), respectively) were much shorter than those at PDLA content of 0 wt%, due to the increased number of PLLA spherulites. Reversely, at PDLA content of 0.1 wt%, the t_c(S), t_c(1/2), and t_c(E) were longer than or similar to those at PDLA content of 0 wt%, probably due to the long t_i and the decreased number of spherulites. This seems to have been caused by free PDLA chains, which did not form stereocomplex crystallites. On the other hand, at PDLA contents of 0.3-3 wt%, the t_c(S), t_c(1/2), and t_c(E) were shorter than or similar to those at PDLA content of 0 wt% for the T_c range below 95 °C and above 125 °C, whereas this inclination was reversed for the T_c range of 100-120 °C. In the non-isothermal crystallization of as-cast or amorphous-made PLLA films during cooling from the melt, the addition of PDLA above 1 wt% was effective to accelerate overall PLLA crystallization. The X-ray diffractometry could trace the formation of stereocomplex crystallites in the melt-quenched PLLA films at PDLA contents above 1 wt%. This study revealed that the addition of small amounts of PDLA is effective to accelerate overall PLLA crystallization when the PDLA content and crystallization conditions are scrupulously selected.     

Crystallization behavior of nano-composite based on poly(vinylidene fluoride) and organically modified layered titanate

To understand the effect of the nano-filler particles on the crystallization kinetics and crystalline structure of poly(vinylidene fluoride) (PVDF) upon nano-composite formation, we have prepared PVDF/organically modified layered titanate nano-composite via melt intercalation technique. The layer titanate (HTO) is a new nano-filler having highly surface charge density compared with conventional layered silicates. The detailed crystallization behavior and its kinetics including the conformational changes of the PVDF chain segment during crystallization of neat PVDF and HTO-based nano-composite (PVDF/HTO) have been investigated by using differential scanning calorimetric, wide-angle X-ray diffraction, light scattering, and infrared spectroscopic analyses. The neat PVDF predominantly formed α-phase in the crystallization temperature range of 110-150 °C. On the other hand, PVDF/HTO exhibited mainly α-phase crystal coexisting with γ- and β-phases at low T_c range (110-135 °C). A major γ-phase crystal coexists with β- and α-phases appeared at high T_c (=140-150 °C), owing to the dispersed layer titanate particles as a nucleating agent. The overall crystallization rate and crystalline structure of pure PVDF were strongly influenced in the presence of layered titanate particles.     

Light scattering studies on the crystalline morphology of stretched poly(ethylene 2,6-naphthalate) film

The crystalline morphology of poly(ethylene 2,6-naphthalate) (PEN) film obtained by uniaxial stretching at 145 °C (T_g + 25 °C) was investigated by use of a light scattering photometer equipped with a CCD camera system. The Hv scattering showed a symmetric, circular pattern at a low stretch ratio of λ < 3. The intensity profile became sharper with an increase in λ, suggesting that anisotropic crystal rods are randomly assembled and that the length of the rods increases with λ. At a high stretch ratio of λ ≥ 3, a double-cross-type pattern consisting of a broad rod-like pattern and sharp cross streaks was observed. The rod-like pattern became smaller and the streaks became sharper with an increase in λ. By the model calculation of the scattering pattern, the double-cross-type pattern is explained by the stacking of anisotropic crystal rods oriented in the stretch direction. As λ increases, the thickness of the rods and the number per stack increase, and the stacks and rods are slightly oriented in the stretch direction. The change in the wide angle X-ray diffraction pattern suggested that the ordering of the molecular chain in the crystal rods increases with increasing λ.     

Miscibility and crystallization in crystalline/crystalline blends of poly(butylene succinate)/poly(ethylene oxide)

Miscibility and crystallization behavior have been investigated in blends of poly(butylene succinate) (PBSU) and poly(ethylene oxide) (PEO), both semicrystalline polymers, by differential scanning calorimetry and optical microscopy. Experimental results indicate that PBSU is miscible with PEO as shown by the existence of single composition dependent glass transition temperature over the entire composition range. In addition, the polymer-polymer interaction parameter, obtained from the melting depression of the high-T_m component PBSU using the Flory-Huggins equation, is composition dependent, and its value is always negative. This indicates that PBSU/PEO blends are thermodynamically miscible in the melt. The morphological study of the isothermal crystallization at 95 °C (where only PBSU crystallized) showed the similar crystallization behavior as in amorphous/crystalline blends. Much more attention has been paid to the crystallization and morphology of the low-T_m component PEO, which was studied through both one-step and two-step crystallization. It was found that the crystallization of PEO was affected clearly by the presence of the crystals of PBSU formed through different crystallization processes. The two components crystallized sequentially not simultaneously when the blends were quenched from the melt directly to 50 °C (one-step crystallization), and the PEO spherulites crystallized within the matrix of the crystals of the preexisted PBSU phase. Crystallization at 95 °C followed by quenching to 50 °C (two-step crystallization) also showed the similar crystallization behavior as in one-step crystallization. However, the radial growth rate of the PEO spherulites was reduced significantly in two-step crystallization than in one-step crystallization.     

Lamella reorientation in thin films of a symmetric poly(l-lactic acid)-block-polystyrene upon crystallization at different temperatures

The thin films of a symmetric crystalline-coil diblock copolymer of poly(l-lactic acid) and polystyrene (PLLA-b-PS) formed lamellae parallel to the substrate surface in melt. When annealed at temperatures well above the glass transition temperature of PLLA block (T_g^PLLA), the PLLA chains started to crystallize, leading to reorientation of lamellae. Such reorientation behavior exhibited dependence on the correlation between the crystallization temperature (T_c), the glass transition temperature of PS (T_g^PS), the peak melting point of PLLA crystals (T_m^PLLA), and the end melting point of PLLA crystals (T_m,end^PLLA). When annealed at (T_c=) 80 °C (T_c < T_g^PS < T_ODT, order-disorder transition temperature), 123 °C (T_g^PS < T_c < T_m^PLLA < T_ODT), 165 °C (T_g^PS < T_m^PLLA < T_c < T_m,end^PLLA < T_ODT), the parallel lamellae became perpendicular to the substrate surface, exclusively starting at the edge of surface relief patterns. Meanwhile, the corresponding lamellar spacing was significantly enhanced. The PLLA crystallization between PS layers was hypothesized to account for the lamella reorientation during annealing. The crystallization, chain conformation, and possible chain folding mechanisms were discussed, based on detailed analysis of the lamellar structure before and after crystallization.     

Crystallization kinetics and morphology of poly(butylene succinate)/poly(vinyl phenol) blend

Biodegradable crystalline poly(butylene succinate) (PBSU) can form miscible polymer blends with amorphous poly(vinyl phenol) (PVPh). The isothermal crystallization kinetics and morphology of neat and blended PBSU with PVPh were studied by differential scanning calorimetry (DSC), optical microscopy (OM), wide angle X-ray diffraction (WAXD), and small angle X-ray scattering (SAXS) in this work. The overall isothermal crystallization kinetics of neat and blended PBSU was studied with DSC in the crystallization temperature range of 80-88 °C and analyzed by applying the Avrami equation. It was found that blending with PVPh did not change the crystallization mechanism of PBSU, but reduced the crystallization rate compared with that of neat PBSU at the same crystallization temperature. The crystallization rate decreased with increasing crystallization temperature, while the crystallization mechanism did not change for both neat and blended PBSU irrespective of the crystallization temperature. The spherulitic morphology and growth were observed with hot stage OM in a wide crystallization temperature range of 75-100 °C. The spherulitic morphology of PBSU was influenced apparently by the crystallization temperature and the addition of PVPh. The linear spherulitic growth rate was measured and analyzed by the secondary nucleation theory. Through the Lauritzen-Hoffman equation, some parameters of neat and blended PBSU were derived and compared with each other including the nucleation parameter (K_g), the lateral surface free energy (σ), the end-surface free energy (σ_e), and the work of chain folding (q). Blending with PVPh decreased all the aforementioned parameters compared with those of neat PBSU; however, the decrease extent was limited. WAXD result showed that the crystal structure of PBSU was not modified after blending with PVPh. SAXS result showed that the long period of blended PBSU increased, possibly indicating that the amorphous PVPh might reside mainly in the interlamellar region of PBSU.     

Initial structure development in the CO2 laser-heated drawing of poly(trimethylene terephthalate) fiber

Because rapid and uniform laser heating can fix the neck-drawing point in continuous drawing of PTT fiber, we have successfully analyzed the fiber structure development in the continuous drawing process by in-situ measurement with a time resolution of less than 1 ms. In this study, we investigated fiber structure development for PTT around the neck point controlled with a CO₂ laser-heated apparatus during continuous drawing, through on-line measurements of WAXD, SAXS, and fiber temperature. Fiber temperature attained by laser radiation initiated a rise around −3 mm in relation to the neck point at 0 mm, and increased to about 90 °C, which is past the 45 °C T_g for PTT. The instantaneous increase in fiber temperature continued with a vertical ascent, with plastic deformation around the neck point. The crystalline diffraction pattern was revealed initially at the elapsed time of 0.415 ms immediately after necking, and remained fairly constant with elapsed time. The ultimate crystalline diffraction pattern for a completely drawn fiber showed little difference from that at the initial stage. In PET a two-dimensionally ordered structure in the form of a mesophase was detected immediately after the necking, whereas in PTT the phenomenon was not observed. With elapsed time, the d spacing of (002) plane decreased gradually due to transformation of the initial all-trans conformation into trans-gauche-gauche-trans conformation, and ultimately the PTT molecular chain could favorably adopt the trans-gauche-gauche-trans conformation. SAXS pattern immediately after the necking revealed an X-shape; the scattering intensity concentrated on meridian directions due to individual crystal development, and at 2 ms two-pointed scattering started to appear. Past 8 ms, the typical two-pointed scattering pattern was prominent and its intensity increased with elapsed time. Long period decreased with increasing elapsed time, but the crystallite size of meridian (002) plane hardly changed. The decrease in long period might be caused by chain relaxation in the amorphous region.     

Thermal, spectroscopy, and morphological studies on polymorphic crystals in poly(heptamethylene terephthalate)

Polymorphism and its influential factors in poly(heptamethylene terephthalate) (PHepT) were probed using differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy, and wide angle X-ray diffraction (WAXD). PHepT exhibits two crystal types (α and β) upon crystallization at various isothermal melt-crystallization temperatures (T_cs) by quenching from different T_maxs (maximum temperature above T_m for melting the original crystals). Melt-crystallized PHepT with either initial α- or β-crystal by quenching from T_max lower than 110 °C leads to higher fractions of α-crystal, but crystallization from T_max higher than 140 °C leads to higher fractions of β-crystal. In addition to T_max, polymorphism in PHepT is also influenced by crystallization temperature (T_c = 25-75 °C). When PHepT is melt-crystallized from a high T_max = 150 °C (completely isotropic melt), it shows solely β crystal for higher T_c, and solely the α-crystal for T_c < 25 °C; in-between T_c = 25 and 35 °C, mixed fractions of both α- and β-crystals. However, by contrast, when PHepT is melt-crystallized from a lower T_max = 110 °C, it shows α-crystal only at all T_cs, high or low.     

Preparation and properties of biodegradable network poly(ester-carbonate) elastomers

Biodegradable elastomeric network poly(ester-carbonate)s were prepared from multifunctional aliphatic carboxylic acids such as tricarballylic acid (Y_t) or trimesic acid (Y) and polycarbonate diols (PCD) with molecular weights of 1000 and 2000 g/mol. Prepolymers prepared by a melt polycondensation were cast from dimethylformamide solution and postpolymerized at 270 °C for 40-80 min to form a network. The resultant films were transparent, flexible and insoluble in organic solvents. WAXS exhibited the crystalline peaks due to polycarbonate segments for the network films from PCD₂₀₀₀, while those from PCD₁₀₀₀ were amorphous. The tensile properties were determined for these network films at the temperatures 22, 30, 40 and 50 °C. These films showed elastomeric properties at all temperatures measured. The elongation at break was much higher for the films from PCD₂₀₀₀ (208-434%) than those from PCD₁₀₀₀ (40-120%), and decreased with increasing temperatures. The weight losses of the network films degraded in the buffer solution of Rhizopus delemar lipase at 37 °C increased with time, suggesting that these network films are biodegradable. The degradation rate of the network films from Y_t is faster than that from Y. The GPC curves showed that the lipase hydrolyzed both the ester linkages between Y or Y_t and PCD as well as polycarbonate moiety in the network polymer.     

Characterization on mixed-crystal structure of poly(butylene terephthalate/succinate/adipate) biodegradable copolymer fibers

Biodegradable poly(butylene terephthalate/succinate/adipate) (PBTSA) pellet, an ideal random copolymer characterized by ¹H solution NMR, was melt-spun into fibers. The crystal structure and physical properties of the as-spun fibers were investigated by WAXD, solid-state ¹³C NMR, DSC and tensile test measurements. Only poly(butylene terephthalate) (PBT)-like diffraction pattern was observed in WAXD; however, two different ¹³C spin-lattice relaxation time (T_1C) components were observed for aliphatic units, in which the longer and the shorter T_1C components correspond to the crystalline and the amorphous domains, respectively. Therefore the crystal structure of PBTSA was concluded to be formed by mixed crystallization of its comonomers. Such crystallization behavior enabled the PBTSA fibers to have well developed PBT-like crystal structure despite of its ideal randomness. Furthermore, due to the introduction of soft segments (BA and BS) into BT crystal lattice, melting temperature of PBTSA fibers (115 °C) was over 100 °C lower than that of PBT.     

AFM study of crystallization and melting of a poly(ethylene oxide) diblock copolymer containing a tablet-like block of poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} in ultrathin films

Crystallization and melting of a poly(ethylene oxide) (PEO) diblock copolymer containing a tablet-like block of poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) in ultrathin films have been studied using atomic force microscopy (AFM) coupled with a hot stage. The PEO and PMPCS block possess the number-average molecular weights (M_n) of 5300 and 2100 g/mol, respectively. The ultrathin films on the mica and glow-discharged carbon surfaces were obtained by static dilute solution casting at room temperature. Isothermal melt crystallization from ultrathin films always leads to flat-on lamellae. Selective area electron diffraction (SAED) experiments have demonstrated that the PEO blocks crystallize with a monoclinic structure identical to that of homo-PEO and the chain direction is perpendicular to the substrate. At T_c<44 °C, the monolayer crystals are dendrites. At T_c>48 °C, square-shaped crystals are formed with the (100) and (020) planes as the crystal edges. At 44 °C≤T_c≤48 °C, an intermediate monolayer morphology is observed. The monolayer thickness increases monotonically with increasing T_c. At the same T_c, the monolayer lamellae with the top and bottom amorphous layers contacting with the atmosphere and the substrate possess a significantly larger overall thickness than the long period of the crystals in bulk. For the spiral terraces induced by screw dislocation, the thickness of each terrace is close to that of the monolayer formed at the same T_c, and their melting is mainly determined by the terrace thickness.     

Polycarbonate/liquid crystalline polymer blend: Crystallization of polycarbonate

The enhanced crystallization of polycarbonate in the blend of liquid crystalline polymer/polycarbonate/(ethylene-methyl acrylate-glycidyl methacrylate) copolymer (LCP/PC/E-MA-GMA) was studied by wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The LCP/PC/E-MA-GMA 5/95/5 blends annealed at 200 °C, for 2, 4, 6, and 10 h, present an obvious crystalline structure corresponding to PC crystallization. The PC crystal obtained shows two melting temperature, T_m1 of about 214 °C and T_m2 of about 231 °C, with a total heat of fusion of 29 J/g (annealing time = 10 h). The preliminary results indicate that amorphous PC can be induced to crystallization by the synergistic action of LCP dispersed phase and reactive compatibilizer.     

Spherulite morphology and crystallization behavior of poly(trimethylene terephthalate)/poly(ether imide) blends

The spherulite morphology and crystallization behavior of poly(trimethylene terephthalate) (PTT)/poly(ether imide) (PEI) blends were investigated with optical microscopy (OM), small-angle light scattering (SALS), and small-angle X-ray scattering (SAXS). Thermal analysis showed that PTT and PEI were miscible in the melt over the entire composition range. The addition of PEI depressed the overall crystallization rate of PTT and affected the texture of spherulites but did not alter the mechanism of crystal growth. When a 50/50 blend was melt-crystallized at 180 °C, the highly birefringent spherulite appeared at the early stage of crystallization (t < 20 min). After longer times, the spherulite of a second form was developed, which exhibited lower birefringence. The SALS results suggested that the observed birefringence change along the radial direction of the spherulite was mainly due to an increase in the orientation fluctuation of the growing crystals as the radius of spherulite increased. The lamellar morphological parameters were evaluated by a one-dimensional correlation function analysis. The amorphous layer thickness showed little dependence on the PEI concentration, indicating that the noncrystallizable PEI component resided primarily in the interfibrillar regions of the growing spherulites.     

Strain recovery of post-yield compressed semicrystalline poly(butylene terephthalate)

Cubic specimens of a semicrystalline poly(butylene terephthalate) (PBT) have been compressed up to post-yield deformation levels with a fast (3.0 × 10⁻² s⁻¹) and a slow (1.5 × 10⁻⁴ s⁻¹) strain rate at three different temperatures (25 °C, 45 °C, and 100 °C, i.e. below, close and above the glass transition temperature of the material, T_g, respectively). Differently from literature results reported for amorphous polymers, semicrystalline PBT shows that, after a post-yield deformation, recovery occurs also at temperatures higher than T_g, and that an irreversible deformation, ?_irr, is set in the material. The irreversible strain component has been evaluated as the residual deformation after a thermal treatment of 1 h at 180 °C.After unloading, isothermal strain recovery has been monitored for time periods of 1 h at various temperatures. From the obtained data, strain recovery master curves have been constructed by a time-temperature superposition scheme. The features of the recovery process for the various deformation conditions have been analysed. In particular, it appears that specimens deformed below T_g show a lower irreversible component, whereas, when deformed above T_g, they display a higher irreversible deformation and a slower recovery process. Moreover, the effect of deformation rate appears particularly marked for samples deformed above T_g.     

Dependence of shrinking kinetics of poly(N-isopropylacrylamide) gels on preparation temperature

Preparation temperature dependence of equilibrium swelling degree and shrinking kinetics of poly(N-isopropylacrylamide) gel has been investigated by optical microscopic measurements. The degree of swelling, d/d₀, at 20 °C was found to be strongly dependent on the preparation temperature, T_prep, where d and d₀ are the diameter of gel during observation and preparation, respectively. The value of d/d₀ was about 1.2 for T_prep=20 °C, but steeply increased by approaching the phase separation temperature ≈32.0 °C. Above 32.0 °C, d/d₀ decreases stepwise to 1.46. This upturn in d/d₀ was correlated with spatial inhomogeneities in gels. That is, the gel became opaque by increasing T_prep. Though the shrinking half-time, t_1/2, of gel was on the order of 500 min for T_prep≤20 °C, t_1/2 decreased to 2 min for T_prep≥26 °C. Hence, a rapid shrinking was attained by simply increasing T_prep. The physical implication of this rapid shrinking in gels was discussed in conjunction with the gel inhomogeneities and a thermodynamic theory of swelling equilibrium.     

The structure of a cyanobiphenyl side chain liquid crystalline poly(silylenemethylene)

The structure of a side chain liquid crystalline poly(silylenemethylene) (-(SiCH₃R-CH₂)-: R=O(CH₂)₁₁O-Ph-Ph-CN, Ph=phenyl) (CN-11) has been studied by X-ray diffraction and differential scanning calorimetry (DSC). The DSC results showed that CN-11 has transitions at ∼92 °C (T₂) and ∼147 °C (T₁) during both cooling and immediate heating. A third transition occurred at ∼50 °C (T₃) during heating after annealing at room temperature. The X-ray fiber pattern of the CN-11 annealed at room temperature showed several wide and small angle reflections which were indexed by a monoclinic unit cell with parameters a=16.8 Å, b=7.42 Å, c=43.6 Å and β=102.1° (b: fiber direction), representing a crystal structure with layer thickness of ∼43 Å. Upon heating at T₃, the crystal structure became less ordered (but somewhat more ordered than smectic A (S_A) and smectic C (S_C)). This was followed by S_A (or S_C) phase at T₂, and ultimately an isotropic state (I) at T₁. The observed layer thickness (∼43 Å) is about ∼1.5 times the most extended side chain length, indicating a double-layer structure with tilted or interdigitated side chains. The X-ray fiber pattern had a four-point pattern at d=4.52 Å, suggesting that the side chains in the crystal are likely to be tilted by 56° from the polymer fiber axis.