A new technique for measuring retrograde vitrification in polymer–gas systems and for making ultramicrocellular foams from the retrograde phase

A stepwise temperature‐ and pressure‐scanning thermal analysis method was developed to measure glass‐transition temperature T_g in the two‐phase polymer–gas systems as a function of gas pressure p, and was used to confirm recent theoretical predictions that certain polymer–gas systems exhibit retrograde vitrification, that is, they undergo rubber‐to‐glass transition on heating. A complete T_g‐p profile delineating the glass–rubber phase envelope was established for the PMMA‐CO₂ system. The retrograde vitrification behavior observed, where at certain gas pressures the polymer exists in the rubbery state at low and high temperatures and in the glassy state at intermediate temperatures, was similar to that reported previously based on the creep‐compliance measurements. The existence of the rubbery state at low temperatures was used to generate foams by saturating the polymer with CO₂ at 34 atm and at temperatures in the range −0.2 to 24 °C followed by foaming at temperatures in the range 24 to 90 °C. Foams with very fine cell structure never reported before could be prepared by this technique. For example, PMMA foams with average cell size of 0.35 μm and cell density of 4.4 × 10¹³ cells/g were prepared by processing the low temperature rubbery phase. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 716–725, 2000     

Indentation of poly(methyl methacrylate) under high‐pressure gases

The variation of the indentation hardness of a high molecular weight poly(methyl methacrylate) (PMMA) subjected to CO₂ and Ar at high pressure was measured in situ. The samples were subjected to gas exposure for 3 h at 40 °C before a conical indenter of an included angle at 105 °, with a fixed load of 0.237 kg, was applied for a loading time of 60 s. The data show that both CO₂ and Ar reduce the hardness of PMMA to a comparable extent at low pressures. The hardness of PMMA subjected to Ar indicates a minimum at about 4 MPa and then increases. CO₂ produced a monotone decreasing trend in hardness in the pressure range studied, and the glass‐transition temperature (T_g) was achieved at about 6.0 MPa. The change in hardness is attributed to plasticization of the polymer matrix that is more extensive for CO₂. The relationship between the change in hardness for this PMMA subjected to high‐pressure CO₂, the corresponding change in the T_g, and the associated swelling of the polymer is discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3020–3028, 2001     

Compressed‐gas‐induced crystallization in tert‐butyl poly(ether ether ketone)

tert‐Butyl‐substituted poly(ether ether ketone) (tBuPEEK), which does not undergo crystallization with thermal annealing, crystallizes readily when treated with compressed CO₂. The dissolved CO₂ causes a reduction in the glass‐transition temperature of the polymer–gas system and enhances the chain mobility of the macromolecules, thereby bringing about crystallization. In the presence of CO₂, crystallization is increasingly favored with increasing CO₂ pressure and treatment temperature. The melting point of tBuPEEK crystals increases linearly with the CO₂ pressure applied in the treatment, indicating an increase in the order and/or size of the crystals. The extent of crystallinity increases when small amounts of methanol or dichloromethane are used as a cosolute with CO₂. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1505–1512, 2001     

Development of hydrogenated ring‐opening metathesis polymers

New hydrogenated ring‐opening metathesis polymers with excellent thermal and optical properties were developed. These polymers were prepared by the ring‐opening metathesis polymerization of ester‐substituted tetracyclododecene monomers followed by the hydrogenation of the main‐chain double bond. The degree of hydrogenation was an important factor for the thermal stability of the polymers, and as complete hydrogenation as possible was necessary to obtain a thermally stable polymer. The completely hydrogenated ring‐opening polymer derived from 8‐methyl‐8‐methoxycarbonyl‐substituted monomer has a glass‐transition temperature of 171 °C and a 5% weight‐loss temperature of 446 °C. This polymer has excellent thermal and optical properties because of its bulky and unsymmetrical polycyclic structure in the main chain and is an alternative to glass or other transparent polymers such as poly(methyl methacrylate) and polycarbonate resin. This polymer has also been used in a wide variety of applications, such as optical lenses, optical disks, optical films, and optical fiber. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4661–4668, 2000     

One‐pot synthesis of terpolymers with long l‐lactide rich sequence derived from propylene oxide,CO2, and l‐lactide catalyzed by zinc adipate

We report here an efficient one‐port synthesis of terpolymers from PO, CO₂, and l ‐lactide (LLA) with long LLA rich sequence using the cheapest zinc adipate as catalyst. The copolymerizations were carried out under various experimental conditions to find out the optimal conditions. The terpolymer yields increase significantly from 151 to 417 (g polymer per g zinc) by the introduction of LLA as a third monomer. The polycarbonate moiety selectivity increases by nearly 60% at relatively high polymerization temperature (80 °C). Moreover, the differences in reaction kinetic of polycarbonate and polyester moieties were observed by in situ infrared monitoring. As confirmed by XRD and DSC, the synthesized terpolymers are a kind of semicrystalline polymer in which the crystalline PLA segment function as strong noncovalent crosslinking domains. Consequently, it exhibits much better thermal properties as well as remarkable higher mechanical strength compared with amorphous polycarbonate PPC. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1734–1741     

Synthesis of bio‐based poly(ethylene 2,5‐furandicarboxylate) copolyesters: Higher glass transition temperature,better transparency,and good barrier properties

The bio‐based polyester, poly(ethylene 2,5‐furandicarboxylate) (PEF), was modified by 2,2,4,4‐tetramethyl‐1,3‐cyclobutanediol (CBDO) via copolymerization and a series of copolyesters poly(ethylene‐co‐2,2,4,4‐tetramethyl‐1,3‐cyclobutanediol 2,5‐furandicarboxylate)s (PETFs) were prepared. After their chemical structures and sequence distribution were confirmed by nuclear magnetic resonance (¹H‐NMR and ¹³C‐NMR), their thermal, mechanical, and gas barrier properties were investigated in detail. Results showed that when the content of CBDO unit in the copolyesters was increased up to 10 mol%, the completely amorphous copolyesters with good transparency could be obtained. In addition, with the increasing content of CBDO units in the copolyesters, the glass transition temperature was increased from 88.9 °C for PET to 94.3 °C for PETF‐23 and the tensile modulus was increased from 3000 MPa for PEF to 3500 MPa for PETF‐23. The barrier properties study demonstrated that although the introduction of CBDO units would increase the O₂ and CO₂ permeability of PEF slightly, PECF‐10 still showed better or similar barrier properties compared with those of PEN and PEI. In one word, the modified PEF copolyesters exhibited better mechanical properties, higher glass transition temperature, good barrier properties, and better clarity. They have great potential to be the bio‐based alternative to the popular petroleum‐based poly(ethylene terephthalate) (PET) when used as the beverage packaging materials. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3298–3307     

Polar,functionalized diene‐based material. III. Free‐radical polymerization of 2‐[(N,N‐dialkylamino)methyl]‐1,3‐butadienes

The bulk free‐radical polymerization of 2‐[(N,N‐dialkylamino)methyl]‐1,3‐butadiene with methyl, ethyl, and n‐propyl substituents was studied. The monomers were synthesized via substitution reactions of 2‐bromomethyl‐1,3‐butadiene with the corresponding dialkylamines. For each monomer the effects of the polymerization initiator, initiator concentration, and reaction temperature on the final polymer structure, molecular weight, and glass‐transition temperature (T_g) were examined. Using 2,2′‐azobisisobutyronitrile as the initiator at 75 °C, the resulting polymers displayed a majority of 1,4 microstructures. As the temperature was increased to 100 and 125 °C using t‐butylperacetate and t‐butylhydroperoxide, the percentage of the 3,4 microstructure increased. Differential scanning calorimetry indicated that all of the T_g values were lower than room temperature. The T_g values were higher when the majority of the polymer structure was 1,4 and decreased as the percentage of the 3,4 microstructure increased. The Diels–Alder side products found in the polymer samples were characterized using NMR and gas chromatography‐mass spectrometry methods. The polymerization temperature and initiator concentration were identified as the key factors that influenced the Diels–Alder dimer yield. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4070–4080, 2000     

Synthesis and properties of new aromatic polysquaramide by solid‐state thermal polycondensation of salt monomer composed of squaric acid and bis(4‐aminophenyl) ether

The 1:1 stoichiometric salt monomer composed of squaric acid and bis(4‐aminophenyl) ether was successfully prepared and subjected to solid‐state thermal polycondensation under ordinary or high pressure, giving quite readily the aromatic polysquaramide with moderately high molecular weight. The polysquaramide formed was actually the random copolymer consisting of two component polymers, one of the main component being the polymer with a quasi‐aromatic mesoionic structure. The aromatic polysquaramide was crystalline and had a glass‐transition temperature of 245 °C, with an initial weight‐loss temperature of 400 °C in nitrogen. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2648–2655, 2002     

Chromatographic investigation of the effect of dissolved carbon dioxide on the glass transition temperature of a polymer and the solubility of a third component (additive)

The effect of dissolved carbon dioxide on the glass transition temperature of a polymer, PMMA, has been investigated using molecular probe chromatography. The probe solute was iso-octane, and the specific retention volumes of this solute in pure PMMA and mixtures of PMMA with CO₂ were measured over a temperature range of 0 to 180°C and CO₂ pressures from 1 to 75 atm. The amount of CO₂ dissolved in the polymer was calculated from a model fit to previously published solubility data determined chromatographically. Classical van't Hoff-type plots were used to determine the glass transition temperature of CO₂-impregnated PMMA from low pressure up to 46 atm of CO₂. Solvent-induced plasticization was observed with the glass transition temperature decreasing by about 40°C. At some pressures, glass transitions at low temperatures could not be determined from the van't Hoff plots because of the proximity of the polymer glass transition temperature to the gas–liquid transition temperature for CO₂. For these pressures, a new method was developed to determine the glass transition composition. The glass transition pressure was then calculated from the measured composition and temperature using an isotherm model. In every case, the glass transition temperature decreased linearly with increasing concentration of CO₂ in the polymer. However, at higher compositions, the glass transition pressure decreased with increasing composition and decreasing temperature. The observed retention volume of iso-octane with PMMA in a glassy state was correlated with an adsorption model developed from a theory for liquid–solid chromatography derived by Martire. This model accurately described the observed decrease in retention of iso-octane by adsorption on the surface of glassy PMMA with increasing concentration of CO₂ dissolved in the polymer. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2537–2549, 1998     

Synthesis and properties of new aromatic polyimides based on 2,5‐bis(4‐amino‐2‐trifluoromethylphenoxy)‐tert‐butylbenzene and various aromatic dianhydrides

A novel, fluorinated diamine monomer, 2,5‐bis(4‐amino‐2‐ trifluoromethylphenoxy)‐tert‐butylbenzene ( II ) was synthesized through the nucleophilic substitution reaction of tert‐butylhydroquinone (t‐BHQ) and 2‐chloro‐5‐nitrobenzotrifluoride in the presence of potassium carbonate to yield the intermediate dinitro compound I , followed by catalytic reduction with hydrazine and Pd/C to afford diamine II . A series of fluorinated polyimides V were prepared from II with various aromatic dianhydrides ( III _a–f ) via the thermal imidization of poly(amic acid). Most of V _a–f could be soluble in amide‐type solvents and even in less polar solvents. These polyimide films showed tensile strengths up to 106 MPa, elongation at break up to 21%, and initial modulus up to 2.1 GPa. The glass‐transition temperature of V was recorded at 245–304 °C, the 10% weight loss temperatures were above 488 °C, and left more than 41% residue even at 800 °C in nitrogen. Low dielectric constants, low moisture absorptions, and higher and light‐colored transmittances were also observed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5424–5438, 2004     

TSC study of the dielectric relaxations of human‐bone collagen

Differential scanning calorimetry (DSC) and thermally stimulated current (TSC) were used to characterize human‐bone collagen. DSC glass‐transition and denaturation temperatures of the collagen in a dehydrated state were 90 and 215 °C, respectively. By TSC, the main relaxation mode, labeled α and located around 90 °C, could be attributed to the dielectric manifestation of the glass transition. The corresponding molecular movements are cooperative with a compensation temperature close to the denaturation temperature. At low temperatures and in a hydrated state, a second mode labeled β₂ was observed at −110 °C. Dehydration shifted this mode to higher temperatures, revealing a weak mode labeled γ at −150 °C. This γ mode was attributed to motions of aliphatic side chains. An analysis of low‐temperature elementary spectra allowed us to assign the β₂ mode to structural water movements and revealed an additional compensation phenomenon in the temperature range (−80 to −50 °C). Because the compensation temperature of this mode was close to the collagen glass‐transition temperature, the corresponding mode β₁ was attributed to polar side‐chain motions, precursors of a collagen glass transition. Finally, around ambient temperature, three sharp peaks were attributed to hydrogen bonds breaking. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 987–992, 2000     

Efficient solvent‐free alternating copolymerization of CO2 with 1, 2‐epoxydodecane and terpolymerization with styrene oxide via heterogeneous catalysis

The alternating copolymerization of CO₂ with the terminated epoxides anchoring long alkyl groups is rarely reported because of their low reactivity and polycarbonate selectivity. This work describes a well‐controlled solvent‐free copolymerization of CO₂ with 1, 2‐epoxydodecane (EDD) with a long electron‐donating alkyl group via the catalysis of Zn‐Co(III) double metal cyanide complex catalyst. The productivity of the catalyst was up to 2406 g polymer/g Zn, that is, EDD conversion was 99.2%. The alternating degree of CO₂‐EDD copolymers were more than 99% and had high number‐average molecular weights (M_ns) of >100 kg mol^?1, while only 1.0 wt % 4‐decyl‐1,3‐dioxolan‐2‐one (DC) were detected. Moreover, by introducing styrene oxide (SO) with electron‐withdrawing phenyl group into EDD‐CO₂ copolymerization system, a new random terpolymer with either electron‐withdrawing or electron‐donating side groups was produced with single glass transition temperatures (T_gs) in a wide range from 3 to 56 °C, which might be potentially used as biodegradable elastomers or plastics. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 737–744     

Electron paramagnetic resonance spin probe study of carbon dioxide‐induced polymer plasticization

Steady‐state electron paramagnetic resonance (EPR) spectroscopy using nitroxide spin probes has been used to investigate the plasticization of poly(vinyl acetate) and poly(ethyl methacrylate) by carbon dioxide. By varying the CO₂ pressure at constant ambient temperature, the glass transition for each polymer could be depressed to 25 °C. This effect has been quantified by a parameter P_50G, obtained by plotting the EPR spectral width as a function of CO₂ pressure. Certain spin probes showed free volume distribution effects, manifested in the EPR spectra as “double peaks.” Possible reasons for this phenomenon are presented and discussed, and the efficacy of CO₂ as a plasticizer is clearly demonstrated by direct comparison with di‐n‐butyl phthalate. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2097–2108, 2005     

Synthesis and characterization of new soluble poly(amide‐imide)s derived from 2,2‐bis[4‐(4‐trimellitimidophenoxy)phenyl]hexafluoropropane

A series of new soluble poly(amide‐imide)s were prepared from the diimide‐dicarboxylic acid 2,2‐bis[4‐(4‐trimellitimidophenoxy)phenyl]hexafluoropropane with various diamines by direct polycondensation in N‐methyl‐2‐pyrrolidinone containing CaCl₂ with triphenyl phosphite and pyridine as condensing agents. All the polymers were obtained in quantitative yields with inherent viscosities of 0.52–0.86 dL · g^?1. The poly(amide‐imide)s showed an amorphous nature and were readily soluble in various solvents, such as N‐methyl‐2‐pyrrolidinone, N,N‐dimethylacetamide (DMAc), N,N‐dimethylformamide, pyridine, and cyclohexanone. Tough and flexible films were obtained through casting from DMAc solutions. These polymer films had tensile strengths of 71–107 MPa and a tensile modulus range of 1.6–2.7 GPa. The glass‐transition temperatures of the polymers were determined by a differential scanning calorimetry method, and they ranged from 242 to 279 °C. These polymers were fairly stable up to a temperature around or above 400 °C, and they lost 10% of their weight from 480 to 536 °C and 486 to 537 °C in nitrogen and air, respectively. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3498–3504, 2001     

Evaluation of gas sorption parameters and prediction of sorption isotherms in glassy polymers

A model of continuous‐site distribution for gas sorption in glassy polymers is examined with sorption data of CO₂ and Ar in polycarbonate. A procedure is presented for determining from a measured isotherm the number of sorption sites in a polymer, an important parameter that previously had to be assumed. With this parameter value and solubility data obtained at zero pressure, the model can reasonably predict sorption isotherms of CO₂ in glassy polycarbonate for a wide temperature range. The number of sorption sites and the average site volume evaluated from CO₂ sorption isotherms are employed for the prediction of Ar sorption isotherms with zero‐pressure solubility data and the independently measured partial molar volume of Ar. A reasonable fit to the measured isotherms of Ar is achieved. With the proposed procedure, the continuous‐site model shows several advantages over the conventional dual‐mode sorption model. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 883–888, 2000     

High‐pressure rheology and viscoelastic scaling predictions of polymer melts containing liquid and supercritical carbon dioxide

High‐pressure rheological behavior of polymer melts containing dissolved carbon dioxide (CO₂) at concentrations up to 6 wt % were investigated using a high‐pressure extrusion slit die rheometer. In particular, the steady shear viscosity of poly(methyl methacrylate), polypropylene, low‐density polyethylene, and poly(vinylidene fluoride) with dissolved CO₂ were measured for shear rates ranging from 1 to 500 s^?1 and under pressure conditions up to 30 MPa. The viscosity of all samples revealed a reduction in the presence of CO₂ with its extent dependent on CO₂ concentration, pressure, and the polymer used. Two types of viscoelastic scaling models were developed to predict the effects of both CO₂ concentration and pressure on the viscosity of the polymer melts. The first approach utilized a set of equations analogous to the Williams–Landel–Ferry equation for melts between the glass‐transition temperature (T_g) and T_g + 100 °C, whereas the second approach used equations of the Arrhenius form for melts more than 100 °C above T_g. The combination of these traditional viscoelastic scaling models with predictions for T_g depression by a diluent (Chow model) were used to estimate the observed effects of dissolved CO₂ on polymer melt rheology. In this approach, the only parameters involved are physical properties of the pure polymer melt that are either available in the existing literature or can be measured under atmospheric conditions in the absence of CO₂. The ability of the proposed scaling models to accurately predict the viscosity of polymer melts with dissolved high‐pressure CO₂ were examined for each of the polymer systems. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3055–3066, 2001     

Fibrillar structure of resorbable microblock copolymers based on 1,5‐dioxepan‐2‐one and ε‐caprolactone

The copolymerization of 1,5‐dioxepan‐2‐one (DXO) and ε‐caprolactone, initiated by a five‐membered cyclic tin alkoxide initiator, was performed in chloroform at 60 °C. Copolymers with different molar ratios of DXO (25, 40, and 60%) were synthesized and characterized. ¹³C NMR spectroscopy of the carbonyl region revealed the formation of copolymers with a blocklike structure. Differential scanning calorimetry measurements showed that all the copolymers had a single glass transition between ?57 and ?49 °C and a melting temperature in the range of 30.1–47.7 °C, both of which were correlated with the amount of DXO. An increase in the amount of DXO led to an increase in the glass‐transition temperature and to a decrease in the melting temperature. Dynamic mechanical thermal analysis measurements confirmed the results of the calorimetric analysis, showing a single sharp drop in the storage modulus in the temperature region corresponding to the glass transition. Tensile testing demonstrated good mechanical properties with a tensile strength of 27–39 MPa and an elongation at break of up to 1400%. The morphology of the copolymers was examined with polarized optical microscopy and atomic force microscopy; the films that crystallized from the melt showed a short fibrillar structure (with a length of 0.05–0.4 μm) in contrast to the untreated solution‐cast films. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2412–2423, 2003     

Synthesis and characterization of a novel AlQ3‐containing polymer

In this article, the synthesis of a tris(8‐hydroxyquinoline)aluminum (AlQ₃)‐containing poly(arylene ether) (4) is reported. The presence of AlQ₃ pendants in polymer 4 is confirmed by NMR, ultraviolet–visible, photoluminescence, and gel permeation chromatography analyses. This is the first report of the attachment of AlQ₃ complexes as side chains to a polymer. Polymer 4 has a glass‐transition temperature of 217.8 °C and is thermally stable with a 5% weight‐loss temperature greater than 500 °C under nitrogen, as determined by differential scanning calorimetry and thermogravimetric analyses, respectively. Polymer 4 is quite soluble in common organic solvents, such as tetrahydrofuran, N,N‐dimethylacetamide, and CHCl₃. A composite that is 80 wt % polymer 4 and 20 wt % AlQ₃ forms a transparent and tough film when cast from its chloroform solution. The application of this AlQ₃‐containing polymer in light‐emitting diodes is under investigation. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2887–2892, 2000     

Polymer electrolyte membranes based on p‐toluenesulfonic acid doped poly(1‐vinyl‐1,2,4‐triazole): Synthesis,thermal and proton conductivity properties

Throughout this work, the synthesis, thermal as well as proton conducting properties of acid doped heterocyclic polymer were studied under anhydrous conditions. In this context, poly(1‐vinyl‐1,2,4‐triazole), PVTri was produced by free radical polymerization of 1‐vinyl‐1,2,4‐triazole with a high yield. The structure of the homopolymer was proved by FTIR and solid state ¹³C CP‐MAS NMR spectroscopy. The polymer was doped with p‐toluenesulfonic acid at various molar ratios, x = 0.5, 1, 1.5, 2, with respect to polymer repeating unit. The proton transfer from p‐toluenesulfonic acid to the triazole rings was proved with FTIR spectroscopy. Thermogravimetry analysis showed that the samples are thermally stable up to ～250 °C. Differential scanning calorimetry results illustrated that the materials are homogeneous and the dopant strongly affects the glass transition temperature of the host polymer. Cyclic voltammetry results showed that the electrochemical stability domain extends over 3 V. The proton conductivity of these materials increased with dopant concentration and the temperature. Charge transport relaxation times were derived via complex electrical modulus formalism (M*). The temperature dependence of conductivity relaxation times showed that the proton conductivity occurs via structure diffusion. In the anhydrous state, the proton conductivity of PVTri1PTSA and PVTri2PTSA was measured as 8 × 10^?4 S/cm at 150 °C and 0.012 S/cm at 110 °C, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1016–1021, 2010     

Characterization of annealed isotactic polypropylene in the solid state by 2D time‐domain 1H NMR

Two‐dimensional time‐domain ¹H NMR was used to investigate annealed isotactic polypropylene in the solid phase. The spin–lattice relaxation in the laboratory frame and in the rotating frame were correlated with the shape of the free induction decay to identify and characterize relaxation components over the temperature range −120 to 120 °C. Several phase transitions were observed, and three distinct solid phases, with different chain mobilities, were detected. Two of these phases were identified as regions with different mobilities within the crystalline phase. The third phase was characterized by a high degree of isotropy in molecular motion. This phase, identified as the amorphous phase, appeared as the polymer was heated above a low‐temperature (−45 °C) phase transition. All transitions observed at higher temperatures occurred exclusively in this phase. About one‐third of the polymer chains reside between crystalline lamellae, whereas the majority form amorphous regions outside fibrils of multilamellar structure. Furthermore, the glass‐to‐rubber transition, occurring above −15 °C, consists of three stages. During the first stage, between −15 °C and 15 °C, regions with an increased segment mobility (labeled intermediate phase) appear gradually within the amorphous phase. At 15 °C, the intermediate phase consists of ∼10% of the polymer units, or one‐third of the polymer units constituting the amorphous phase. Between 15 °C and 25 °C, the intermediate phase increases rapidly to 18%. This is associated with the appearance of semiliquid and liquid regions, likely within the intermediate phase. Polymer chain segments (and possibly entire chains) involved in the liquidlike phases exhibit heterogeneous molecular motion with a correlation frequency higher than 10⁶ Hz. These two stages of glass‐to‐rubber transition occur within amorphous regions outside multilamellar structures. The third stage of the glass transition, appearing above 70 °C, is associated with the upper glass transition and occurs within the interlamellar amorphous phase. Finally, on a timescale of 100 ms or less, spin diffusion does not couple the amorphous regions outside fibrils with crystalline and amorphous regions within multilamellar fibrils. However, on a timescale of hundreds of milliseconds to seconds, all different regions within isotactic polypropylene are partially coupled. It is proposed that the relative magnitude of the crystalline magnetization, as observed in the T_1ρ experiment, is a good measure of polymer crystallinity. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2487–2506, 2000