Poly(p‐phenylene sulfide) nonisothermal cold‐crystallization

The poly(p‐phenylene sulfide) (PPS) nonisothermal cold‐crystallization behavior was investigated in a wide heating rate range. The techniques employed were the usual Differential Scanning Calorimetry (DSC), and the less conventional FT‐IR spectroscopy and Energy Dispersive X‐ray Diffraction (EDXD). The low heating rates (Φ) explored by EDXD (0.1 K min^?1) and FT‐IR (0.5–10 K min^?1) are contiguous and complementary to the DSC ones (5–30 K min^?1). The crystallization temperature changes from 95 °C at Φ = 0.05 K min^?1 to 130 °C at Φ = 30 K min^?1. In such a wide temperature range the Kissinger model failed. The model is based on an Arrhenius temperature dependence of the crystallization rate and is widely employed to evaluate the activation energy of the crystallization process. The experimental results were satisfactorily fit by replacing in the Kissinger model the Arrhenius equation with the Vogel–Fulcher–Tamann function and fixing U* = 6.28 k J mol^?1, the activation energy needed for the chains movements, according to Hoffmann. The temperature at which the polymer chains are motionless (T_∞ = 42 °C) was found by fitting the experimental data. It appears to be reasonable in the light of our previously reported isothermal crystallization results, which indicated T_∞ = 48 °C. Moreover, at the lower heating rate, mostly explored by FT‐IR, a secondary stepwise crystallization process was well evidenced. In first approximation, it contributes to about 17% of the crystallinity reached by the sample. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2725–2736, 2005     

Crystallization study of Sn additive Se–Te chalcogenide alloys

Calorimetric study of Se_85−x Te₁₅Sn _x (x = 0, 2, 4 and 6) glassy alloys have been performed using Differential Scanning Calorimetry (DSC) under non-isothermal conditions at four different heating rates (5, 10, 15 and 20 °C/min). The glass transition temperature and peak crystallization temperature are found to increase with increasing heating rate. It is remarkable to note that a second glass transition region is associated with second crystallization peak for Sn additive Se–Te investigated samples. Three approaches have been employed to study the glass transition region. The kinetic analysis for the first crystallization peak has been taken by three different methods. The glass transition activation energy, the activation energy of crystallization, and Avrami exponent (n) are found to be composition dependent. The crystallization ability is found to increase with increasing Sn content. From the experimental data, the temperature difference (T _p − T _g) is found to be maximum for Se₈₃Te₁₅Sn₂ alloy, which indicates that this alloy is thermally more stable in the composition range under investigation.     

Investigations of the Sub-Ambient Transitions in Frozen Sucrose by Modulated Differential Scanning Calorimetry (MDSC®)

40% w/w sucrose/water solutions were analyzed by Modulated Differential Scanning Calorimetry [1] in the sub-ambient temperature region. At these temperatures, the solutions exhibit a complex, two-step thermal event. The lower-temperature event is believed to be the glass transition of the amorphous sucrose phase. The nature of the higher-temperature event is the subject of controversy. This event has been shown to have distinct second-order characteristics, and as such is believed to be a second T_g. Others feel that this event is the onset of melting. The temperature region between these events contains a devitrification exotherm. Through the use of MDSC, both in scanning and stepwise quasi-isothermal modes, improved sensitivity and resolution of MDSC provides new insight into the nature of these transitions.This revised version was published online in November 2005 with corrections to the Cover Date.     

Influence of graphene nanosheets on stereocomplex crystallization behaviors of star‐shaped poly (D(L)‐lactide) stereoblock copolymer

The nanocompsites of star‐shaped poly(D‐lactide)‐co‐poly(L‐lactide) stereoblock copolymers (s‐PDLA‐PLLA) with two‐dimensional graphene nanosheets (GNSs) were prepared by solution mixing method. Crystallization behaviors were investigated using differential scanning calorimetry, polarized optical microscopy, and wide angle X‐ray diffraction. The results of isothermal crystallization behaviors of the nanocompsites clearly indicated that the GNS could remarkably accelerate the overall crystallization rate of s‐PDLA‐PLLA copolymer. Unique stereocomplex crystallites with melting temperature about 207.0°C formed in isothermal crystallization for all samples. The crystallization temperatures of s‐PDLA‐PLLAs shifted to higher temperatures, and the crystallization peak shapes became sharper with increasing GNS contents. The maximum crystallization temperature of the sample with 3 wt% GNS was about 128.2°C, ie, 15°C higher than pure s‐PDLA‐PLLA. At isothermal crystallization processes, the halftime of crystallization (t_0.5) of the sample with 3 wt% GNS decreased to 6.4 minutes from 12.9 minutes of pure s‐PDLA‐PLLA at 160°C.The Avrami exponent n values for the nanocomposites samples were 2.6 to 3.0 indicating the crystallization mechanism with three‐dimensional heterogeneous nucleation and spherulites growth. The morphology and average diameter of spherulites of s‐PDLA‐PLLA with various GNS contents were observed in isothermal crystallization processes by polarized optical microscopy. Spherulite growth rates of samples were evaluated by using combined isothermal and nonisothermal procedures and analyzed by the secondary nucleation theory. The results evidenced that the GNS has acceleration effects on the crystallization of s‐PDLA‐PLLA with good nucleation ability in the s‐PDLA‐PLLA material.     

New insights into the multiple melting behaviors of the semicrystalline ethylene‐hexene copolymer: Origins of quintuple melting peaks

A semicrystalline ethylene‐hexene copolymer (PEH) was subjected to a simple thermal treatment procedure as follows: the sample was isothermally crystallized at a certain isothermal crystallization temperature from melt, and then was quenched in liquid nitrogen. Quintuple melting peaks could be observed in heating scan of the sample by using differential scanning calorimeter (DSC). Particularly, an intriguing endothermic peak (termed as Peak 0) was found to locate at about 45 °C. The multiple melting behaviors for this semicrystalline ethylene‐hexene copolymer were investigated in details by using DSC. Wide‐angle X‐ray diffraction (WAXD) technique was applied to examine the crystal forms to provide complementary information for interpreting the multiple melting behaviors. Convincing results indicated that Peak 0 was due to the melting of crystals formed at room temperature from the much highly branched ethylene sequences. Direct heating scans from isothermal crystallization temperature (T_c, 104–118 °C) were examined for comparison, which indicated that the multiple melting behaviors depended on isothermal crystallization temperature and time. A triple melting behavior could be observed after a relatively short isothermal crystallization time at a low T_c (104–112 °C), which could be attributed to a combination of melting of two coexistent lamellar stack populations with different lamellar thicknesses and the melting‐recrystallization‐remelting (mrr) event. A dual melting behavior could be observed for isothermal crystallization with both a long enough time at a low T_c and a short or long time at an intermediate T_c (114 °C), which was ascribed to two different crystal populations. At a high T_c (116–118 °C), crystallizable ethylene sequences were so few that only one single broad melting peak could be observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2100–2115, 2008     

Temperature dependences of solid structure and properties of biodegradable poly(butylene succinate-co-terephthalate) (PBST) copolyester

In this paper, studies of the temperature dependence for spherulitic growth of PBST copolyester bearing 70 mol% butylene terephthalate units (named as PBST-70) ranged from 70 to 170 °C were first reported based on the Lauritzen–Hoffman secondary nucleation theory. The results showed that maximum spherulitic growth rate of PBST-70 was obtained under crystallization temperature of 90 °C, and more perfect spherulites were formed via increasing isothermal crystallization temperature by POM measurement. The classical regime I → II and regime II → III transitions occurred at the temperatures of 150 and 110 °C, respectively, using the empirical universal values of U* = 6300 J mol^?1 and T _∞ = T _g ? 30 K. Moreover, the effects of isothermal crystallization temperature on crystal lamellar thickness, thermal and tensile properties of PBST-70 were systematically investigated by small angle X-ray scattering, differential scanning calorimeter, and strength tester. The results indicated that the crystal lamellar thickness increased by increasing isothermal crystallization temperature. The endothermic peak shifted to higher temperature and the tensile properties of PBST-70 were enhanced under higher isothermal crystallization temperature.     

Influence of microcrystalline cellulose fiber (MCCF) on the morphology of poly(3-hydroxybutyrate) (PHB)

Biopolymer composites were prepared from poly(3-hydroxybutyrate) (PHB)/microcrystalline cellulose fiber (MCCF)/plastiziers/poly(vinyl acetate) by melt extrusion. The morphology, crystal structure, and non-isothermal crystallization of these composites were investigated by polarized optical microscopy (POM), differential scanning calorimetry, Fourier transform infrared spectrometer, and wide-angle X-ray diffraction. The results of DSC indicate that the addition of small amount of MCCF improved the crystallization rate. Non-isothermal crystallization shows that the composites 1 and 2 have lower crystallization half time (t _{0 .5}) than that of pure PHB. Higher MCCF contents in PHB (composite 4) lead to a decrease in the crystallization rate. POM micrographs show that the MCCF were well dispersed in the PHB matrix and served as a nucleating agent with a strong change in PHB morphology. Increasing the isothermal crystallization temperature above 120 °C, leads to the formation of banded spherulites with large regular band spacing. Decreasing the isothermal crystallization temperature below 100 °C produces more and small spherulites.     

Incident investigation on thermal instability of an intermediate using adiabatic calorimeter

Thermal instability is a loss of thermal control which liberates high amount of energy and pressure. An incident took place during drying of an intermediate having amino alcohol functional group in agitated nutsche filter dryer at plant scale. During our investigation using advanced reactive system screening tool (ARSST), thermal decomposition was observed. Onset temperature of decomposition (T _o) is at 85 °C, adiabatic temperature rise due to decomposition (ΔT _ad) is 215 °C, maximum temperature attained due to decomposition (T _max) is 300 °C, maximum self-heat rate (dT/dt)_max is 6,215 °C min^?1, and maximum rate of pressure rise (dP/dt)_max is 1,442 psi min^?1 obtained from ARSST experiments. T _D24 value is 75 °C which was estimated experimentally. The correlations of these results were utilized to identify the root cause of this incident and necessary control measures were taken accordingly.     

In situ Polymerization of Nanocomposites by TpTiCl2(Et) System: UHMWPE Filled with Carbon Nanotubes

Summary: Nanocomposites of ultra-high molecular weight polyethylene (UHMWPE) filled with multi-walled carbon nanotubes (CNT) were obtained by in situ polymerization of ethylene by TpTiCl₂Et. This novel catalytic complex activated with polymethylaluminoxane (P-MAO) (Al:Ti = 200) allowed to incorporate the CNT at different compositions (0,1-1 w/w %) into the UHMWPE matrix. The filler addition produced an important enhancement of the catalytic activity when it was compared to that of homogeneous ethylene polymerization carried out under the same experimental conditions (30 min; 1bar; 25 °C). This fact was attributed to in situ support of TpTiCl₂Et onto the CNT surface, which not only could induce the stabilization of the catalytic system but also allowed the growing of polymeric chains around the CNT structures. The characterization of these nanocomposites was carried out by Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). Thermal analysis showed that the incorporation of CNT (at the tested concentrations) did not produce changes in the polymer thermal stability, as revealed by the initial degradation temperature values. However, the CNT produced a nucleating effect in the crystallization of UHMWPE as observed by DSC, independently of the filler content. The crystallization temperature of the obtained nanocomposites increased and the crystallinity degree slightly increased as well.     

Characterization,crystallization kinetics,and melting behavior of poly(ethylene succinate) copolyester containing 10 mol % butylene succinate

Copolyester was synthesized and characterized as having 89.9 mol % ethylene succinate units and 10.1 mol % butylene succinate units in a random sequence, as revealed by NMR. Isothermal crystallization kinetics was studied in the temperature range (T_c) from 30 to 73 °C using differential scanning calorimetry (DSC). The melting behavior after isothermal crystallization was investigated using DSC by varying the T_c, the heating rate and the crystallization time. DSC curves showed triple melting peaks. The melting behavior indicates that the upper melting peaks are associated primarily with the melting of lamellar crystals with various stabilities. As the T_c increases, the contribution of recrystallization slowly decreases and finally disappears. A Hoffman‐Weeks linear plot gives an equilibrium melting temperature of 107.0 °C. The spherulite growth of this copolyester from 80 to 20 °C at a cooling rate of 2 or 4 °C/min was monitored and recorded using an optical microscope equipped with a CCD camera. Continuous growth rates between melting and glass transition temperatures can be obtained after curve‐fitting procedures. These data fit well with those data points measured in the isothermal experiments. These data were analyzed with the Hoffman and Lauritzen theory. A regime II → III transition was detected at around 52 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2431–2442, 2008     

Fabrication of newly developed pectin –GeO2 nanocomposite using extreme biomimetics route and its antibacterial activities

The combination of pectins and germanium dioxide may generate novel materials with excellent and unique properties combining the advantages of macromolecules, derived from renewable resources and metal oxide nanoparticles. Pectin–GeO₂ nanocomposite was prepared by hydrothermal method at room temperature. Structural morphology and chemical interactions between GeO₂ and pectin were analyzed using Fourier Transform Infrared Spectroscopy Equipped with Attenuated Total Reflectance (FTIR-ATR), AC impedance spectroscopy, Scanning Electron Microscopy-Energy Dispersive X-ray Spectrophotometer (SEM-EDS) Thermo gravimetric analysis (TG) and Differential Scanning Calorimetry (DSC). According to the TEM observation, the average composite granules size was about 70 nm and the embedded GeO₂ nanoparticles were uniform with an average diameter of 20 nm. The pectin-germanium dioxide degradation was observed in one single DSC endoderm peak at 100°C (Area swept 276.4 mJ and enthalpy change 48.1 J/g) and three DTG peaks in the temperature range between 165 and 570°C. All the results suggest the pectin–GeO₂ nanocomposite as a promising candidate for biomedical and environmental applications.     

Glass transition measurements of asphalts by DSC

The glass transition temperature (T_g), measured by Modulated Differential Scanning Calorimetry (MDSC), is related to the flow characteristics of asphalt at low temperatures as is the rate of change of the creep stiffnessm. This study compared the glass transition temperature of different asphalts (neat, chemically modified, and crumb rubber modified asphalts) with the creep stiffness, the rate of change of creep stiffness, and the low specification temperature of the continuous PG grading of those asphalts.From the rheological data (BBR) and the thermal data (MDSC) for the virgin and the modified asphalts, the modified products had the same variations of values ofm, S, and T_g at lower temperatures as those of their corresponding virgin asphalts. A correlation between the T_g andm value was observed for both the modified and unmodified asphalts. Since DSC measurements for asphalt low temperature properties use less operator time, less sample, and have less measurement and operator error than rheological methods, T_g has promise to be considered as a fast and easy laboratory method to obtain the low temperature useful range of asphalts in pavements.The authors would like to acknowledge Susan P. Needham for her work in conducting rheological testing for the modified and unmodified asphalts.     

Thermal analysis and microscopical characterization of cholesterol in gallstones

Summary Cholesterol constitutes the major component of most gallstones. It was identified and determined in gallstones by thermal analysis technique (DSC and TG-DTA), mainly by the use of the melting temperature (T_onset=145°C and T_max=149°C) and by DTG peak decomposition (T_max=364°C). Cholesterol anhydrous (ChA), which showed endothermic polymorphic peak, T_max=40°C, without mass loss, was differentiated from cholesterol monohydrate (ChH), which showed a broad endothermic peak, T_max=59°C, attributed to loss of water of crystallization (theoretical 4.45%). Morphological studies of gallstones were performed by optical microscopy and scanning electron microscopy (SEM). The stones consisted of a pigmented core with a variably-sized irregular central cavity, surrounded by a radially arranged deposits of plate-like ChH. The outer part of the stones showed ChA crystal arborescences. X-ray microanalysis gave a typical spectrum rich in C and O, and in some instances the presence of P, which was attributed to the presence of phospholipids. CaCO₃ was easily characterized by TG with the use of DTG decomposition peak at 674°C.     

Crystallization kinetics and melting behavior of metallocene short‐chain branched polyethylene fractions

Metallocene polyethylene (mPE) fractions are recognized as being more homogeneous with respect to short‐chain branch (SCB) distribution as compared with unfractionated mPEs. Differential scanning calorimetry and polarized optical microscopy (POM) were used to study the influences of SCB content on the crystallization kinetics, melting behavior, and crystal morphology of four butyl‐branched mPE fractions. The parent mPE of the studied fractions was also investigated for comparative purposes. mPE fractions showed a much simpler crystallization behavior as compared with their parent mPE during the cooling experiments. The Ozawa equation was successfully used to analyze the nonisothermal crystallization kinetics of the fractions. The Ozawa exponent n decreased from about 3.5 to 2 as the temperature declined for each fraction, indicating the crystal‐growth geometry changed from three‐dimensional to two‐dimensional. For isothermal crystallization, the fraction with a lesser SCB content exhibited a higher crystallization temperature (T_c) window. The results from the Avrami equation analysis showed the exponent n values were around 3 (with minor variation), which implied that the crystal‐growth geometry is pseudo‐three‐dimensional. Both of the activation energies for nonisothermal and isothermal crystallization were determined for each fraction with Kissinger and Arrhenius‐type equations, respectively. Double melting peaks were observed for both nonisothermally or isothermally crystallized specimens. The high‐melting peak was confirmed induced via the annealing effect during heating scans. The Hoffman–Weeks plot was inapplicable in obtaining the equilibrium melting temperature (T_m°) for each fraction. The relationship between T_c and T_m for the fractions is approximately T_m = T_c (°C) + 8.3. The POM results indicated that the crystals of parent or fractions formed under cooling conditions did not exhibit the typical spherulitic morphology as a result of the high SCB content. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 325–337, 2002     

Quiescent crystallization of polypropylene: Experiments and modeling

The quiescent crystallization of several polypropylenes (PPs) was examined using Differential Scanning Calorimetry (DSC) and Polarized Optical Microscopy (POM). The half‐times of crystallization were obtained from the DSC thermographs employing the Avrami/Nakamura equation to fit and predict crystallization kinetics under isothermal and nonisothermal conditions. The induction times under nonisothermal conditions were estimated from isothermal crystallization data and used in conjunction with the Nakamura model in order to capture the crystallization behavior of the studied PPs. The Avrami/Nakamura model is found to fit and predict the nonisothermal crystallization data of the various PPs well over a range of cooling rates supporting its use in the simulation of polymer processes of industrial relevance. POM was used in line with parallel plate rheometry (Anton Paar, MCR 502) under no flow conditions to study the shape and growth rate of crystals of various PP resins at different temperatures or cooling rates. The growth rate of crystals is impeded exponentially with increase of temperature. The various PP resins of different molecular architecture have shown different nucleation and growth rate characteristics behavior under similar processing conditions. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1259–1275     

Thermal properties of poly(methyl methacrylate-co-butyl acrylate-co-acrylic acid) modified with divinyl benzene and vinyltrimethoxysilane

The effect of butyl acrylate (BA), divinyl benzene (DVB) and vinyltrimethoxysilane (TMVS) on the thermal properties of poly(methyl methacrylate-co-butyl acrylate-co-acrylic acid) was investigated. Glass transition temperature (T_g), melting temperature (T_m) and specific heat capacity of the copolymers were investigated using Differential Scanning Calorimetry. Thermal stability of the copolymers which is associated with the degradation temperature (T_d) was studied by Thermogravimetric Analysis. Polyacrylates with T_g ranges between -19°Cand 19°C were obtained. With the incorporation of >7 wt% of DVB, the T_g of the copolymer increases from about ?17°C to ?10°C even though they have not undergone UV irradiation. Gel content results prove that crosslinking has occurred in the copolymers. With increasing amount of TMVS from 0 wt% to 7 wt%, the T_m of the copolymers prepared at acidic pH is about 40-60°C higher than that at the alkaline pH. However, the addition of TMVS gives no significant effect to the T_g and T_d of the copolymer films. The thermal stability of the copolymer has improved with increasing amount of BA and DVB, with DVB being more effective. The highest T_d of 425°C with 8% of DVB has been obtained. Consequently, a polyacrylate copolymer with a T_g of about ?13°C, a T_m of 170 °C and a T_d of about 424°C has been successfully synthesized. Hence, the soft polyacrylate with its relatively high T_m and T_d could serve as a superb material especially to be applied in the areas that require high melting temperature and good thermal stability.     

Isothermal melt and cold crystallization kinetics of poly(aryl ether ketone ether ketone ketone)

The isothermal melt and cold crystallization kinetics of poly(aryl ether ketone ether ketone ketone) are investigated by differential scanning calorimetry over two temperature regions. The Avrami equation describes the primary stage of isothermal crystallization kinetics with the exponent n ≈ 2 for both melt and cold crystallization. With the Hoffman–Weeks method, the equilibrium melting point is estimated to be 406 °C. From the spherulitic growth equation proposed by Hoffman and Lauritzen, the nucleation parameter (K_g) of the isothermal melt and cold crystallization is estimated. In addition, the K_g value of the isothermal melt crystallization is compared to those of the other poly(aryl ether ketone)s. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1992–1997, 2000     

Explosion evaluation and safety storage analyses of cumene hydroperoxide using various calorimeters

Plenty of thermal explosions and runaway reactions of cumene hydroperoxide (CHP) were described from 1981 to 2010 in Taiwan. Therefore, a thermal explosion accident of CHP in oxidation tower in 2010 in Taiwan was investigated because of piping breakage. In general, high concentration of CHP for thermal analysis using the calorimeter is dangerous. Therefore, a simulation method and a kinetic parameter were used to simulate thermal hazard of high concentrations of CHP only by the researcher. This study was applied to evaluate thermal hazard and to analyze storage parameters of 80 and 88 mass% CHP using three calorimeters for the oxidation tower, transportation, and 50-gallon drum. Differential scanning calorimetry (DSC) (a non-isothermal calorimeter), thermal activity monitor III (TAM III) (an isothermal calorimeter), and vent sizing package 2 (VSP2) (an adiabatic calorimeter) were employed to detect the exothermic behavior and runaway reaction model of 80 and 88 mass% CHP. Exothermic onset temperature (T ₀), heat of decomposition (ΔH _d), maximum temperature (T _max), time to maximum rate under isothermal condition (TMR_iso) (as an emergency response time), maximum pressure (P _max), maximum of self-heating rate ((dT/dt)_max), maximum of pressure rise rate ((dP/dt)_max), half-life time (t _1/2), reaction order (n), activation energy (E _a), frequency factor (A), etc., of 80 and 88 mass% CHP were applied to prevent thermal explosion and runaway reaction accident and to calculate the critical temperature (T _c). Experimental results displayed that the n of 80 and 88 mass% CHP was determined to be 0.5 and the E _a of 80 and 88 mass% CHP were evaluated to be 132 and 134 kJ mol^?1, respectively.     

Untersuchung der isothermen Kristallisation von Äthylen-Vinylacetat-Copolymeren mit Hilfe der Differential-Scanning-Calorimetrie

Zusammenfassung Die isotherme Kristallisation von Äthylen-Vinylacetat-Copolymeren verschiedener Zusammensetzung und verschiedenen Molekulargewichts aus der Schmelze wird bei Unterkühlungen zwischen etwa 10 und 30 Grad differentialkalorimetrisch untersucht. Es zeigte sich, daß sowohl die Kristallisationskinetik als auch der erreichbare Kristallinitätsgrad von Zusammensetzung undSummary The isothermal crystallization from the melt of ethylene vinyl acetate copolymers with different compositions and different molecular weights is investigated at supercoolings between 10 and 30 degrees by means of Differential Scanning Calorimetry. It was observed that the crystallization kinetics as well as the maximum degree of crystallinity depend both on composition and on molecular weight. The crystallization kinetics does not followAvrami's equation. The deviations are discussed.

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Mit 7 Abbildungen in 8 Einzeldarstellungen und 1 Tabelle

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Herrn Professor Dr.K.-H. Hellwege zum 60. Geburtstag gewidment.     

The synthesis of poly(phenylacetylene)s with bulky chiral silyl groups and the thermal stability of their helical conformation

The polymerization of (−)‐p‐[(tert‐butylmethylphenyl)silyl]phenylacetylene (t‐BuMePhSi*PA) and (+)‐p‐[{methyl(α‐naphthyl)phenyl}silyl]phenylacetylene (MeNpPhSi*PA) with the [(nbd)RhCl]₂ Et₃N catalyst yielded polymers with very high molecular weights over 2 × 10⁶ in high yields. The optical rotations of the formed poly(t‐BuMePhSi*PA) and poly(MeNpPhSi*PA) were as high as −356 and −150° (c = 0.11 g/dL in CHCl₃), respectively. The circular dichroism (CD) spectrum of poly(t‐BuMePhSi*PA) in CHCl₃ exhibited very large molar ellipticities ([θ]) in the UV region: [θ]_max = 9.2 × 10⁴ ° · cm² · dmol⁻¹ at 330 nm and −8.0 × 10⁴ ° · cm² · dmol⁻¹ at 370 nm. The [θ]_max values of poly(MeNpPhSi*PA) were also fairly large: [θ]_max = 7.1 × 10⁴ ° · cm² · dmol⁻¹ at 330 nm and −5.3 × 10⁴ ° · cm² · dmol⁻¹ at 370 nm. The optical rotations of poly(t‐BuMePhSi*PA) and poly(MeNpPhSi*PA), measured in tetrahydrofuran, chloroform, and toluene solutions, were hardly dependent on temperature in the range 22–65 °C. The CD effects of these polymers hardly changed in the temperature range 28–80 °C, either. These results indicate that the helical structures of these polymers are thermally appreciably stable. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 71–77, 2001