Semi‐interpenetrating polymer networks composed of poly(N‐isopropyl acrylamide) and polyacrylamide hydrogels

Three series of semi‐interpenetrating polymer networks, based on crosslinked poly(N‐isopropyl acrylamide) (PNIPA) and 1 wt % nonionic or ionic (cationic and anionic) linear polyacrylamide (PAAm), were synthesized to improve the mechanical properties of PNIPA gels. The effect of the incorporation of linear polymers into responsive networks on the temperature‐induced transition, swelling behavior, and mechanical properties was studied. Polymer networks with four different crosslinking densities were prepared with various molar ratios (25:1 to 100:1) of the monomer (N‐isopropyl acrylamide) to the crosslinker (methylenebisacrylamide). The hydrogels were characterized by the determination of the equilibrium degree of swelling at 25 °C, the compression modulus, and the effective crosslinking density, as well as the ultimate hydrogel properties, such as the tensile strength and elongation at break. The introduction of cationic and anionic linear hydrophilic PAAm into PNIPA networks increased the rate of swelling, whereas the presence of nonionic PAAm diminished it. Transition temperatures were significantly affected by both the crosslinking density and the presence of linear PAAm in the hydrogel networks. Although anionic PAAm had the greatest influence on increasing the transition temperature, the presence of nonionic PAAm caused the highest dimensional change. Semi‐interpenetrating polymer networks reinforced with cationic and nonionic PAAm exhibited higher tensile strengths and elongations at break than PNIPA hydrogels, whereas the presence of anionic PAAm caused a reduction in the mechanical properties. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3987–3999, 2004     

Semi‐interpenetrating polymer networks of methyl cellulose and polyacrylamide prepared by frontal polymerization

In this study, the feasibility of frontal polymerization (FP) as an alternative and convenient technique for the preparation of semi‐interpenetrating polymer networks made of methyl cellulose (MC) and cross‐linked polyacrylamide (PAAm) is demonstrated. FP was performed in water and glycerol, as largely available, nontoxic solvents. Although FP occurred in both media, differences were found by comparing the samples made in the two solvents. In particular, those prepared in water are characterized by larger inhomogeneity and less reproducibility, thus accounting for the boiling effects that influence propagating polymerization fronts when water was used. The effects of the ratio among MC and PAAm, the amount of cross‐linker and solvent medium were studied in terms of influence on temperature and velocity of FP fronts, glass transition temperature (dried samples), swelling behavior, dynamic‐mechanical properties (gels swollen in both water or glycerol), and tensile behavior. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1268–1274     

Organic–inorganic interpenetrating polymer networks and hybrid polymer materials prepared by frontal polymerization

Novel polyacrylamide‐based hydrogels containing 3‐(trimethoxysilyl)propyl methacrylate and/or tetraethoxy silane were synthesized by means of frontal polymerization, using ammonium persulfate as initiator, N,N′‐methylene bisacrylamide as crosslinking agent and dimethyl sulfoxide as solvent. The obtained samples were treated at pH of 2 or 5 to induce the sol–gel reaction and evaluate their swelling behavior in the conditions. The occurrence of this reaction was assessed by solid‐state NMR. Moreover, the thermal properties of the dry materials were studied by differential scanning calorimetry and thermal gravimetric analysis, and their water‐contact angles were measured. It was found that the amount of Si affects the extent of swelling and the hydrophilicity of the resulting materials. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4618–4625     

Preparation and properties of poly(N‐isopropylacrylamide)/poly(N‐isopropylacrylamide) interpenetrating polymer networks for drug delivery

A novel poly(N‐isopropylacrylamide) (PNIPA)/PNIPA interpenetrating polymer network (IPN) was synthesized and characterized. In comparison with conventional PNIPA hydrogels, the shrinking rate of the IPN hydrogel increased when gels, swollen at 20 °C, were immersed in 50 °C water. The phase‐transition temperature of the IPN gel remained unchangeable because of the same chemical constituent in the PNIPA gel. The reswelling kinetics were slower than those of the PNIPA hydrogel because of the higher crosslinking density of the IPN hydrogel. The IPN hydrogel had better mechanical strength because of its higher crosslinking density and polymer volume fraction. The release behavior of 5‐fluorouracil (5‐Fu) from the IPN hydrogel showed that, at a lower temperature, the release of 5‐Fu was controlled by the diffusion of water molecules in the gel network. At a higher temperature, 5‐Fu inside the gel could not diffuse into the medium after a burst release caused by the release of the drug on the surface of the gel. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1249–1254, 2004     

Dielectric properties of self‐catalytic interpenetrating polymer network based on modified bismaleimide and cyanate ester resins

Bismaleimide (BMI) resins with good thermal stability, fire resistance, low water absorption, and good retention of mechanical properties at elevated temperatures, especially in hot/wet environments, have attracted more attention in the electronic and aerospace industries. However, their relatively high dielectric constant limits their application in the aforementioned fields. In this work, a new promising approach is presented that consists of the formation of a self‐catalytic thermoset/thermoset interpenetrating polymer network. Interpenetrating polymer networks (IPNs) based on modified BMI resin (BMI/DBA) and cyanate ester (b10) were synthesized via prepolymerization followed by thermal curing. The self‐catalytic curing mechanism of BMI/DBA‐CE IPN resin systems was examined by differential scanning calorimetry. The dielectric properties of the cured BMI/DBA‐CE IPN resin systems were evaluated by a dielectric analyzer and shown in dielectric properties‐temperature‐log frequency three‐dimensional plots. The effect of temperature and frequency on the dielectric constant of the cured BMI/DBA‐CE IPN resin systems is discussed. The composition effect on the dielectric constant of the cured IPN resin systems was analyzed on the basis of Maxwell's equation and rule of mixture. The obtained BMI/DBA‐CE IPN resin systems have the combined advantages of low dielectric constant and loss, high‐temperature resistance, and good processability, which have many applications in the microelectronic and aerospace industries. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1123–1134, 2003     

Thermal transitions of benzene in copolymers and interpenetrating polymer networks based on hydrophilic and hydrophobic components: Experimental evidence of hydrophobic interaction

Thermal transitions of benzene in a hydrophobic polymer network have been explained by us in terms of the phase diagram of the polymer‐solvent system. In this work, we executed a similar study on copolymers and interpenetrating polymer networks (IPNs) with controllable hydrophilic/hydrophobic ratios. Copolymers and IPNs were swollen with different amounts of benzene and subjected to cooling and heating scans with differential scanning calorimetry (DSC). Synthesis of the IPNs was carried out in such a way that phase separation appeared, and three qualitatively different types of DSC thermograms were identified depending on the benzene content of IPN. Thermal transitions of benzene in the hydrophilic/hydrophobic copolymers can also be explained as a consequence of the phase diagram of the system, but an increase in the glass‐transition temperature of the system can be correlated with the interactions among the hydrophilic groups of the copolymer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1713–1721, 2003     

Heterogeneity of glass transition dynamics in polyurethane‐poly(2‐hydroxyethyl methacrylate) semi‐interpenetrating polymer networks

The peculiarities of segmental dynamics over the temperature range of ?140 to 180 °C were studied in polyurethane‐poly(2‐hydroxyethyl methacrylate) semi‐interpenetrating polymer networks (PU‐PHEMA semi‐IPNs) with two‐phase, nanoheterogeneous structure. The networks were synthesized by the sequential method when the PU network was obtained from poly(oxypropylene glycol) (PPG) and adduct of trimethylolpropane (TMP) and toluylene diisocyanate (TDI), and then swollen with 2‐hydroxyethyl methacrylate monomer with its subsequent photopolymerization. PHEMA content in the semi‐IPNs varied from 10 to 57 wt %. Laser‐interferometric creep rate spectroscopy (CRS), supplemented with differential scanning calorimetry (DSC), was used for discrete dynamic analysis of these IPNs. The effects of anomalous, large broadening of the PHEMA glass transition to higher temperatures in comparison with that of neat PHEMA, despite much lower T_g of the PU constituent, and the pronounced heterogeneity of glass transition dynamics were found in these networks. Up to 3 or 4 overlapping creep rate peaks, characterizing different segmental dynamics modes, have been registered within both PU and PHEMA glass transitions in these semi‐IPNs. On the whole, the united semi‐IPN glass transition ranged virtually from ?60 to 160 °C. As proved by IR spectra, some hybridization of the semi‐IPN constituents took place, and therefore the effects observed could be properly interpreted in the framework of the notion of “constrained dynamics.” The peculiar segmental dynamics in the semi‐IPNs studied may help in developing advanced biomedical, damping, and membrane materials based thereon. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 963–975, 2007     

Semi‐interpenetrating polymer networks composed of diisocyanate‐bridged 4‐arm star‐shaped l‐lactide oligomers and poly(ε‐caprolactone)

Semi‐interpenetrating polymer networks (semi‐IPNs) were prepared by reactions of 2,4‐tolylene diisocyanate (TDI) and hydroxy‐terminated 4‐arm star‐shaped l ‐lactide oligomers (H4LAO_n's) with the degrees of polymerization of lactate unit per one arm, n = 3, 5, and 10 in the presence of poly(ε‐caprolactone) (PCL). Morphologies, thermal, and mechanical properties of the TDI‐bridged H4LAO_n (TH4LAO_n)/PCL semi‐IPNs were evaluated by comparing with those of poly(l ‐lactide) (PLA)/PCL blends. Compatibility between the two components of the TH4LAO_n/PCL semi‐IPN with a PCL content not more than 50 wt % was much better than those of the PLA/PCL blends with the same PCL content. All the TH4LAO_n networks were substantially amorphous and their tan δ peak or glass transition temperatures increased with decreasing n value. Most of the semi‐IPNs did not show clear glass transition temperature related to both the components. Tensile toughness and elongation at break for all the TH4LAO_n/PCL semi‐IPNs were much higher than those for the PLA/PCL blends with the same PCL content. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1420–1428     

Dynamic mechanical behavior of acrylonitrile butadiene rubber/poly(ethylene‐co‐vinyl acetate) blends

The dynamic mechanical behavior of uncrosslinked (thermoplastic) and crosslinked (thermosetting) acrylonitrile butadiene rubber/poly(ethylene‐co‐vinyl acetate) (NBR/EVA) blends was studied with reference to the effect of blend ratio, crosslinking systems, frequency, and temperature. Different crosslinked systems were prepared using peroxide (DCP), sulfur, and mixed crosslink systems. The glass‐transition behavior of the blends was affected by the blend ratio, the nature of crosslinking, and frequency. sThe damping properties of the blends increased with NBR content. The variations in tan δ_max were in accordance with morphology changes in the blends. From tan δ values of peroxide‐cured NBR, EVA, and blends the crosslinking effect of DCP was more predominant in NBR. The morphology of the uncrosslinked blends was examined using scanning electron and optical microscopes. Cocontinuous morphology was observed between 40 and 60 wt % of NBR. The particle size distribution curve of the blends was also drawn. The Arrhenius relationship was used to calculate the activation energy for the glass transition of the blends, and it decreased with an increase in the NBR content. Various theoretical models were used to predict the modulus of the blends. From wide‐angle X‐ray scattering studies, the degree of crystallinity of the blends decreased with an increasing NBR content. The thermal behavior of the uncrosslinked and crosslinked systems of NBR/EVA blends was analyzed using a differential scanning calorimeter. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1556–1570, 2002     

Synthesis and characterization of interpenetrating polymer networks with nonlinear optical properties

We report the synthesis and characterization of interpenetrating polymer networks (IPNs) exhibiting nonlinear optical (NLO) properties. The network consists of aliphatic polycarbonate urethane (PCU) and poly(methyl methacrylate-co-N,N-disubstituted urea), with a nonlinear optical (NLO) chromophore incorporated into N,N-disubstituted urea. The full IPNs have only one T_g, as determined by differential scanning calorimetry (DSC), together with scanning electron microscopy (SEM) observations, suggest a single phase morphology. The thin films of IPNs are transparent and the unpoled samples produced second harmonic generation (SHG) signals at room temperature. This result indicates that the NLO chromophore is oriented noncentrosymmetrically during the IPN formation process and is tightly held between the permanent entanglements of the two component networks of the IPN. © 1996 John Wiley & Sons, Inc.     

Hydrogel‐like elastic membrane consisting of semi‐interpenetrating polymer networks based on a phosphorylcholine polymer and a segmented polyurethane

To obtain a hydrogel‐like elastic membrane, we prepared semi‐interpenetrating polymer networks (IPNs) by the radical polymerization of methacrylates such as 2‐methacryloyloxyethyl phosphorylcholine (MPC), 2‐hydroxyethylmethacrylate, and triethyleneglycol dimethacrylate diffused into segmented polyurethane (SPU) membranes swollen with a monomer mixture. The values of Young's modulus for the hydrated semi‐IPN membranes were less than that for an SPU membrane because of higher hydration, but they were much higher than that for a hydrated MPC polymer gel (non‐SPU). According to a thermal analysis, the MPC polymer influenced the segment association of SPU. The diffusion coefficient of 8‐anilino‐1‐naphthalenesulfonic acid sodium salt from the semi‐IPN membrane could be controlled with different MPC unit concentrations in the membrane, and it was about 7 × 10² times higher than that of the SPU membrane. Fibroblast cell adhesion on the semi‐IPN membrane was effectively reduced by the MPC units. We concluded that semi‐IPNs composed of the MPC polymer and SPU may be novel polymer materials possessing attractive mechanical, diffusive‐release, and nonbiofouling properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 68–75, 2003     

Lower critical solution temperature sensitivity to structural changes in poly(N‐isopropyl acrylamide) homopolymers

The effect of the molecular weight on the lower critical solution temperature (LCST) has been discussed extensively, where LCST increased with molar mass, decreased or kept constant, which leads to confusion. This work is focused on the preparation of poly(N‐isopropyl acrylamide) homopolymers, obtained in a wide molecular weights range. The LCST behavior is analyzed by calorimetry and rheology, and a deep study of molecular features is carried out for a better knowledge of the influence of various parameters involved on LCST. Finally, the molecular weight trend is observed, and its influence on LCST is compared with the effect of other parameters as polymer concentration in water, end‐group effect, and tacticity. It is observed that other parameters such tacticity and end‐group effect will affect the LCST behavior over molecular weight, if this one is not high enough. Furthermore, the study of the LCST ranges will be a useful tool for analyzing the molecular weight trends. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1386–1393     

New silicone hydrogels based on interpenetrating polymer networks comprising polysiloxane and poly(vinyl alcohol) networks

A method for the synthesis of a new silicone hydrogel as a biphase material for soft contact lenses is considered. The method is based on the synthesis of sequential interpenetrating polymer networks (IPN) and includes the following stages: (1) cross‐linked silicone synthesis by the reaction of vinyl‐ and hydride‐containing oligosiloxanes; (2) silicone network saturation with vinyl acetate and cross‐linking monomer followed by UV‐initiated polymerization to form an IPN comprising the silicone and cross‐linked poly(vinyl acetate) (PVAc) network; (3) PVAc network alcoholysis with methanol to obtain silicone hydrogels comprising the silicone and cross‐linked poly(vinyl alcohol) (PVAl). A study of hydrophilic, optical, mechanical, and structural features of the silicone hydrogels showed that optical transparency is achieved for materials with the highest density of silicone network cross‐linking where the size of IPN structural units does not exceed 100 nm. The water content in hydrophilic networks of silicone hydrogel is found to be below the values typical of cross‐linked PVAl, leading to non‐additivity of IPN mechanical properties. Indeed, the elasticity moduli (E) of the hydrophilic and silicone networks are 0.4–0.7 and 0.7–1.8 MPa, respectively, whereas for some IPN this value reaches 3.0 MPa. The optimal parameters of synthesis providing the reduction of E to 0.8–1.6 MPa without deterioration of the required performance characteristics (optical transparency 90–92%, water content 20–39 wt%) are determined. Copyright © 2009 John Wiley & Sons, Ltd.     

Sequential interpenetrating poly(ethylene glycol) hydrogels prepared by UV‐initiated thiol–ene coupling chemistry

Poly(ethylene glycol) (PEG)‐diallyls, ranging from 2 to 8 kDa, were successfully reacted with a trifunctional thiol crosslinker via thiol–ene coupling reaction to construct four different primary PEG hydrogels. These systems were used as scaffolds for the preparation of a library of sequential interpenetrating networks (SeqIPNs). The solid content of the secondary networks varied between 21 and 34% and was dependent on the length of the absorbing PEGs. The gel fractions for the IPNs were above 85%. Additionally, the lowest degree of swelling was found for the IPN based on 2‐kDa PEG (315%), whereas the 8‐kDa PEG IPN exhibited a value of 810%. The SeqIPN strategy facilitated hydrogel systems that cover a larger domain of tensile modulus (192–889 kPa) when compared with single hydrogel networks (175–555 kPa). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Novel poly(N‐isopropylacrylamide)/clay/poly(acrylamide) IPN hydrogels with the response rate and drug release controlled by clay content

Novel interpenetrating network (IPN) hydrogels (PNIPAAm/clay/PAAm hydrogels) based on poly(N‐isopropylacrylamide) (PNIPAAm) crosslinked by inorganic clay and poly(acrylamide) (PAAm) crosslinked by organic crosslinker were prepared in situ by ultraviolet (UV) irradiation polymerization. The effects of clay content on temperature dependence of equilibrium swelling ratio, deswelling behavior, thermal behavior, and the interior morphology of resultant IPN hydrogels were investigated with the help of Fourier transform infrared spectroscopy, differential scanning calorimeter (DSC), scanning electron microscope (SEM). Study on temperature dependence of equilibrium swelling ratio showed that all IPN hydrogels exhibited temperature‐sensitivity. DSC further revealed that the temperature‐sensitivity was weakened with increasing amount of clay. Study on deswelling behavior revealed that IPN hydrogels had much faster response rate when comparing with PNIPAAm/clay hydrogels, and the response rate of IPN hydrogels could be controlled by clay content. SEM revealed that there existed difference in the interior morphology of IPN hydrogels between 20 [below lower critical solution temperature (LCST)] and 50 °C (above LCST), and this difference would become obvious with a decrease in clay content. For the standpoint of applications, oscillating swelling/deswelling behavior was investigated to determine whether properties of IPN hydrogels would be stable for potential applications. Bovine serum albumin (BSA) was used as model drug for in vitro experiment, the release data suggested that the controlled drug release could be achieved by modulating clay content. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 96–106, 2009     

Vibration damping materials based on interpenetrating polymer networks of carboxylated nitrile rubber and poly(methyl methacrylate)

Interpenetrating polymer networks (IPNs) based on carboxylated nitrile rubber (XNBR) and poly(methyl methacrylate)s were synthesized. Crosslinked XNBR was swollen in methyl methacrylate containing benzoyl peroxide as initiator and tetraethylene glycol dimethacrylate as crosslinking agent. The compositions of the IPNs were varied by changing the swelling time of the rubber in the methacrylate monomer. The dynamic mechanical properties of the IPNs were studied. The dynamic mechanical properties in the range 1–10⁵ Hz were obtained by the time‐temperature superposition of the data under multifrequency mode, which indicated high tan δ with good storage modulus in the entire frequency range. This indicates the suitability of these IPNs as vibration and acoustic dampers. Copyright © 2002 John Wiley & Sons, Ltd.     

Preparation and characterization of poly(N-isopropylacrylamide)-modified poly(2-hydroxyethyl acrylate) hydrogels by interpenetrating polymer networks for sustained drug release

In order to investigate the influence of hydrophobic moieties formed by poly(N-isopropylacrylamide) (PNIPAm) in a hydrogel matrix on the release behavior of the hydrogel, a series of poly(N-isopropylacrylamide) (PNIPAm)-modified poly(2-hydroxyethyl acrylate-co-2-hydroxyethyl 2-hydroxyethyl methacrylate) (P(HEA-co-HEMA)) via interpenetrating polymer networks (IPNs) were prepared by a sequential UV solution polymerization. Interestingly, it was found that P(HEA-co-HEMA)/PNIPAm IPN indicated a single glass transition temperature (T(g)) and the T(g)s of the IPNs increased with an increase in the PNIPAm component. This phenomenon may be attributed to hydrogen bonding between the two polymer networks, but the hydrogen bonding exerts less influence on the swelling behavior of the IPNs, due to the fact that IPNs can respond to changes in temperature like PNIPAm. Using 2-[(diphenylmethyl)sulphiny]acetamide (modafinil, MOD) and p-hydroxybenzoic acid (HBA) as model drug compounds, the release behavior of the IPNs was studied at body temperature, and it was found that the presence of PNIPAm could retard drug release regardless of the solubility of the drugs. Release profiles of HBA from the IPNs and their component samples as a function of time at 37 degrees C.     

Simultaneous interpenetrating polymer networks based on epoxy–acrylate combinations

Simultaneous interpenetrating polymer networks (SINs) based on epoxy/poly(n-butyl acrylate) systems were synthesized at 120°C. The polymerization kinetics were studied both in situ by Fourier Transform Infrared Spectroscopy (FT–IR). Three key events occurred during the polymerization, namely the gelation of the network I, gelation of the network II, and phase separation of one polymer from the other. Thus, metastable phase diagrams describing the relations between the three events were constructed. Three-dimensional tetrahedrons characterizing the four-component system (the two monomers and the two polymers) allow the visualization of these three key events and also define some critical points, for example, the loci of the points where simultaneous gelation of the two networks occurs. The inside of the tetrahedron was also investigated using partially reacted model compounds. These tetrahedrons can be used as guidelines for setting up a synthesis strategy leading to desired morphologies. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1973–1984, 1997     

Thermodynamics of adsorption of uranyl ions onto amidoximated poly(acrylonitrile)/poly(N‐vinyl 2‐pyrrolidone) interpenetrating polymer networks

The interaction of uranyl ions (UO) with interpenetrating polymer networks (IPNs) based on amidoximated poly(acrylonitrile)/poly(N‐vinyl 2‐pyrrolidone) was examined. The adsorption capacity of IPN hydrogels as well as the adsorption kinetics and the effect of temperature on UO ion adsorption were investigated. Thermodynamic quantities and kinetic parameters were calculated with adsorption isotherm data. The initial adsorption‐rate values for each temperature were calculated, and the corresponding rate constants decreased with increasing temperature. The adsorption enthalpy, entropy, and free energy of the UO ion with amidoximated IPN hydrogels were calculated from basic thermodynamic relations. It was assessed that adsorption occurred by strong electrostatic interactions with an adsorption enthalpy of ?31.5 kJ/mol. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 986–993, 2004     

Free‐volume and crystallinity in low molecular weight poly(ethylene oxide)

Positron annihilation lifetime spectroscopy (PALS), differential scanning calorimetry, X‐ray diffraction, and polarized light optical microscopy were used to study six low molar mass poly(ethylene oxide) samples with average molar masses ranging from 1 × 10³ to 10 × 10³ g mol^?1. Dynamic light scattering was used to determine molar mass and polydispersity rigorously. Polymer samples with 70–95% crystallinity, which is an unusual range in PALS studies, were prepared by molten material quenching. The ortho‐positronium pick‐off lifetime (τ₃) and relative fractional free volume (f_v), determined by the free volume model, correlated well with the average molar mass and crystallinity of the polymers. X‐ray diffraction and polarized light optical data support the interpretation of positron annihilation results. PALS parameter, I₃, which is associated with high cavity content, remained approximately constant at 20–22% for all samples. The cavities are present as crystallite defects in the spherulitic open texture and the amorphous phase for the low crystallinity sample (e.g., for M_w = 1390) and at the interfaces and in interlamellar spherulite regions of the more crystalline materials. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2400–2409, 2007