A water‐soluble CO2‐triggered viscosity‐responsive copolymer of N,N‐dimethylaminoethyl methacrylate and acrylamide

A series of copolymers PDAMs were synthesized with varying monomer ratio of acrylamide (AM) and N,N‐dimethylaminoethyl methacrylate (DMAEMA). The resulting copolymer solution shows an interesting property of viscosity‐response which is CO₂‐triggered and N₂‐enabled. Tertiary amine groups of PDAMs experience a reversible transition between hydrophobic and hydrophilic state upon CO₂ addition and its removal, which induced different rheological behavior. A combination of zeta‐potential, laser particle‐size analysis, and electrical conductivity analysis indicated that, when the monomer mole ratio of DMAEMA and AM is less than or equal to 3 : 7, the hydrophobic association structure between the copolymer molecules was destroyed by the leading of CO₂ and caused a viscosity decrease in its solution. On the contrary, when the monomer mole ratio of DMAEMA and AM is more than 3 : 7, a more extended conformation due to the protonated tertiary amine groups is formed and the enhanced repulsive interactions among the copolymer molecule results in a rise of its solution viscosity. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40872.     

Use of a CO2‐switchable hydrophobic associating polymer to enhance viscosity–response

A series of copolymers, poly(acrylamide)‐co‐poly(N,N‐dimethylaminoethyl methacrylate)‐co‐poly(N‐cetyl DMAEMA) (abbreviation PDAMCn), was synthesized with different monomer ratios. The resulting copolymer solution shows pronounced viscosity–response property which is CO₂‐triggered and N₂‐enabled. Electrical conductivity experiment shows that tertiary amine group on DMAEMA experiences a protonate and deprotonate transition upon CO₂ addition and its removal. In addition, different incorporation rates of DMAEMA leads to two kinds of morphological change in the presence of CO₂ and thus induces different rheological behaviors. PDAMCn incorporating longer hydrophobic monomer (C₁₈DM) show more pronounced initial viscosity and higher critical stress required to cause network deformation, which consequently enhances the viscosity–response property of the solution. The addition of NaCl could also tune the viscosity of PDAMCn solution. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41468.     

Synthesis and self‐assembly of amphiphilic star‐block copolymers consisting of polyethylene and poly(ethylene glycol) segments

We report on the synthesis and self‐assembly in water of well‐defined amphiphilic star‐block copolymers with a linear crystalline polyethylene (PE) segment and two or three poly(ethylene glycol) (PEG) segments as the building blocks. Initially, alkynyl‐terminated PE (PE‐?) is synthesized via esterification of pentynoic acid with hydroxyl‐terminated PE, which is prepared using chain shuttling ethylene polymerization with 2,6‐bis[1‐(2,6‐dimethylphenyl) imino ethyl] pyridine iron (II) dichloride/methylaluminoxane/diethyl zinc and subsequent in situ oxidation with oxygen. Then diazido‐ and triazido‐terminated PE (PE‐(N₃)₂ and PE‐(N₃)₃) are obtained by the click reactions between PE‐? and coupling agents containing triazido or tetraazido, respectively. Finally, the three‐arm and four‐arm star‐block copolymers, PE‐b‐(PEG)₂ and PE‐b‐(PEG)₃, are prepared by click reactions between PE‐(N₃)₂ or PE‐(N₃)₃ and alkynyl‐terminated PEG. The self‐assembly of the resultant amphiphilic star‐block copolymers in water was investigated by dynamic light scattering, transmission electron microscopy, and atomic force microscopy. It is found that, in water, a solvent selectively good for PEG blocks; these star‐block copolymer chains could self‐assemble to form platelet‐like micelles with insoluble PE blocks as crystalline core and soluble PEG blocks as shell. The confined crystallization of PE blocks in self‐assembled structure formed in aqueous solution is investigated by differential scanning calorimetry. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of high nano‐SiO2 contents on properties of epoxy‐modified polybenzoxazine

High‐performance nanosilica composites based on epoxy‐modified polybenzoxazine matrices are developed. Chemorheological study of benzoxazine–epoxy resin mixtures reveals that processing window of the benzoxazine resin (BA‐a) is substantially broadened with an addition of the liquid epoxy. Glass transition temperature (T _g) of the BA‐a copolymerized with epoxy resin shows a synergistic behavior with a maximum T _g value (174°C) at the benzoxazine–epoxy mass ratio of 80:20. The copolymer at this composition is also used as a matrix for nano‐SiO₂ composites. A very low melt viscosity of the benzoxazine–epoxy mixtures promotes good processability with the maximum attainable nano‐SiO₂ loading up to 35 wt%. From scanning electron microscopy investigation, fracture surface of the 35 wt% nano‐SiO₂‐filled benzoxazine–epoxy composite reveals relatively homogeneous distribution of the nano‐SiO₂ in the copolymer with good particle wet‐out. In addition, very high reinforcing effect was also observed in such high content of the nano‐SiO₂, i.e., about 2.5 times in modulus improvement. This improvement is attributed to the strong bonding between the copolymer matrix and the nano‐SiO₂ through ether linkage as confirmed by Fourier‐transform infrared investigation. POLYM. COMPOS., 38:2261–2271, 2017. © 2015 Society of Plastics Engineers     

Preparation and characterization of poly(trimethylene terephthalate)‐poly(ethylene oxide terephthalate) segmented copolymer/multiwalled carbon nanotubes composites by in situ polymerization

Poly(trimethylene terephthalate)‐poly(ethylene oxide terephthalate) block copolymer (PTG)/multiwalled carbon nanotubes (MWCNTs) composites were prepared via in situ polymerization. To improve the dispersion of MWCNTs in the PTG matrix, the poly(ethylene glycol)‐grafted multiwalled carbon nanotubes (MWCNT‐PEG) were produced by the “graft to” method. The transmission electron microscopy observation demonstrated that a homogeneous dispersion of MWCNT‐PEG was obtained. As a consequence, the percolation threshold for the rheology was around 0.5 wt% and the conductivity was ～1 wt%, respectively. Differential scanning calorimetry and polarized optical microscopy results confirmed that MWCNT‐PEG can act as an effective heterogeneous nucleating agent. Interestingly, the effects of MWCNT‐PEG on crystallization and melting of the poly(ethylene oxide terephthalate) blocks were more pronounced than on those of the PTT blocks. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Comb‐shaped copolymer as filtrate loss reducer for water‐based drilling fluid

A new comb‐shaped copolymer was synthesized by free radical copolymerization of 2‐acrylamide‐2‐methyl propane sulfonic acid, acrylamide, N‐vinyl‐2‐pyrrolidone, and allyl polyoxyethylene ether (APEG) monomers. The copolymer was evaluated as a filtrate loss reducer in water‐based drilling fluid at 180 °C environment, and found to work well without causing high viscosity effect. Composition of the copolymer was determined by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy, and gel permeation chromatography. FTIR, X‐ray diffraction,, and environmental scanning electron microscopy characterizations were used to probe the filtrate loss mechanism of the comb‐shaped copolymer. Thermogravimetry and differential scanning calorimetry results showed that thermal degradation of the copolymer is not obvious before 293.6 °C. The copolymer is found to be superior to its commercially available counterparts for controlling filtrate loss volume and maintaining a steady viscosity after 180 °C aging. Higher content of APEG in the copolymer helps maintain rheological properties of the drilling fluid after aging and reduces filtrate loss volume. The morphology of the copolymer in aqueous solution displays a comb‐shaped 3D structure and shows clear adsorption onto clay particles. The working mechanism for copolymer is that anchoring groups bind the copolymer onto clay particles through different binding mechanisms, while colloidal suspension stability is achieved by steric hindrance and electrostatic repulsion, as well as through PEG segment intercalation into clay lamellae. The copolymer is able to cover and seal the micro‐holes in the mud cake even at high temperature to reduce permeability. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45989.     

PEG 400/Paraffin oil non‐aqueous emulsions stabilized by PBut‐Block‐P2VP block copolymers

For the preparation of PEG 400 in paraffin oil non‐aqueous biocompatible emulsions, the stabilization efficiency was compared for two well‐defined poly(butadiene)‐block‐poly(2‐vinylpyridine) (PBut‐block‐P2VP) block copolymers, with similar molecular weights but different compositions. The PBut₁₂₈‐block‐P2VP₅₀ and PBut₁₈₉‐block‐P2VP₃₇ samples, designated as copolymer A and B, respectively, are self‐organized in paraffin oil as micelles with a P2VP core and a PBut corona. The PEG 400/paraffin oil emulsion characteristics were determined as a function of the copolymers concentrations and phase ratios. Higher static and shear stabilities were obtained for emulsions stabilized by copolymer B than for those obtained in the presence of copolymer A . A further difference concerns the droplet size, relative viscosity, and loss modulus values obtained at a given dispersed phase volume fraction. At constant copolymer concentrations, it appeared that copolymer B , with a longer PBut sequence, is a more efficient emulsifier and stabilizer than copolymer A . © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41390.     

Electrochemical preparation of poly(2‐bromoaniline) and poly(aniline‐co‐2‐bromoaniline) in acetonitrile

Electrochemical preparation of poly(2‐bromoaniline) (PBrANI) and poly(aniline‐co‐2‐bromoaniline) [P(An‐co‐2‐BrAn)] was carried out in an acetonitrile solution containing tetrabutylammonium perchlorate (TBAP) and perchloric acid (HClO₄). The cyclic voltammograms during the copolymerization had many features similar to those for the usual polymerization of aniline. The copolymer exhibits a higher dry electrical conductivity value than that of PBrANI and a lower one than that of PANI. The observed decrease in the conductivity of the copolymer relative to PANI is attributed to the incorporation of bromine moieties into the polyaniline chain. The structure and properties of the polymer and copolymer were elucidated using cyclic voltammetry (CV), FTIR, and UV‐vis spectroscopy. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2460–2468, 2003     

Electrochemical synthesis of poly(2‐iodoaniline) and poly(aniline‐co‐2‐iodoaniline) in acetonitrile

Poly(2‐iodoaniline) (PIANI) and poly(aniline‐co‐2‐iodoaniline) [P(An‐co‐2‐IAn)] were synthesized by electrochemical methods in acetonitrile solution containing tetrabutylammonium perchlorate (TBAP) and perchloric acid (HClO₄). The voltametry of the copolymer shows characteristics similar to those of conventional polyaniline (PANI), and it exhibits higher dry electrical conductivity than PIANI and lower than PANI. The observed decrease in the conductivity of the copolymer relative to PANI is attributed to the incorporation of the iodine moieties into the PANI chain. The structure and properties of these conducting films were characterized by FTIR and UV‐Vis spectroscopy and by an electrochemical method (cyclic voltametry). Conductivity values, FTIR and UV‐Vis spectra of the PIANI and copolymer were compared with those of PANI and the relative solubility of the PIANI and the copolymer powders was determined in various organic solvents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1652–1658, 2003     

CO2‐responsive swelling behavior and metal‐ion adsorption properties in novel histamine‐conjugated polyaspartamide hydrogel

Novel polyaspartamide copolymers containing histamine pendants (PHEA‐HIS) were prepared from polysuccinimide, which is the thermal polycondensation product of aspartic acid, via a successive ring‐opening reaction using histamine (HIS) and ethanolamine (EA). The prepared water‐soluble copolymer was then crosslinked by reacting it with hexamethylene diisocyanate in order to provide a hydrogel with both good gel strength and reversible CO₂ absorption characteristics. PHEA‐HIS gel is also pH‐sensitive and eligible to coordinate to metal ions such as Pb²⁺, Cu²⁺, and Ni²⁺ due to the imidazole units in its structure. The CO₂‐responsive swelling behavior, metal‐ion adsorption, and morphology of the crosslinked gels were investigated. The approach described here results is a promising hydrogel with potential for a variety of industrial and biomedical applications including CO₂ capture, CO₂‐responsive and switchable sensors, and smart drug delivery systems. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43305.     

Carbon dioxide switchable polymer surfactant copolymerized with 2‐(dimethylamino)ethyl methacrylate and butyl methacrylate as a heavy‐oil emulsifier

A CO₂‐switchable polymer surfactant was synthesized with 2‐(dimethylamino)ethyl methacrylate and butyl methacrylate. The conductivity, ζ potential, and particle size change illustrated the switchability of the surfactant, and this change could be repeated. Its surface tension decreased sharply when the sample was bubbled with CO₂; this indicated the enhancement of the surface activity. In the heavy‐oil emulsion with a surfactant concentration of 8 g/L, the viscosity almost reached the highest stability. When CO₂ overflowed the emulsion, it became unstable when the temperature beyond 40°C. The emulsion had a nice resistance to inorganic salt, which was maintained stably even when the concentration of NaCl was as high as 90,000 ppm. The emulsion could later be broken by the removal of CO₂. Its hydration rate was over 22 times faster than that in the presence of CO₂. The amount of residual oil in water was only about 53.84 ppm; this showed a good demulsification ability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41307.     

Synthesis and characterization of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) triblock copolymers with dibutylmagnesium as catalyst

Two series of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) triblock copolymers were prepared by the ring opening polymerization of ε‐caprolactone in the presence of poly(ethylene glycol) and dibutylmagnesium in 1,4‐dioxane solution at 70°C. The triblock structure and molecular weight of the copolymers were analyzed and confirmed by ¹H NMR, ¹³C NMR, FTIR, and gel permeation chromatography. The crystallization and thermal properties of the copolymers were investigated by wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry (DSC). The results illustrated that the crystallization and melting behaviors of the copolymers were depended on the copolymer composition and the relative length of each block in copolymers. Crystallization exothermal peaks (T_c) and melting endothermic peaks (T_m) of PEG block were significantly influenced by the relative length of PCL blocks, due to the hindrance of the lateral PCL blocks. With increasing of the length of PCL blocks, the diffraction and the melting peak of PEG block disappeared gradually in the WAXD patterns and DSC curves, respectively. In contrast, the crystallization of PCL blocks was not suppressed by the middle PEG block. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of conducting copolymer of Trans‐1‐(4‐methyl‐3′‐thienyl)‐2‐(ferrocenyl)ethene with EDOT

Ferrocene‐substituted conducting polymer namely poly(trans‐1‐(4‐methyl‐3′‐thienyl)‐2‐(ferrocenyl)ethene‐co‐3,4‐ethylenedioxythiophene) [P(MTFE‐co‐EDOT)] was synthesized and its electrochromic properties were studied. Monomer, MTFE, was obtained using 2‐(ferrocenyl)ethene and 3‐methyl‐4‐bromothiophene. The structure of monomer was determined via Fourier transform infrared spectroscopy (FTIR), ¹H‐NMR, and ¹³C‐NMR techniques. The copolymer was synthesized using this monomer and EDOT. The resulting copolymer P(MTFE‐co‐EDOT) was characterized by cyclic voltammetry, FTIR, scanning electron microscopy, atomic force microscopy, and UV–vis spectroscopy. The conductivity measurements of copolymer and PEDOT were accomplished by the four‐probe technique. Although poly(trans‐1‐(4‐methyl‐3′‐thienyl)‐2‐(ferrocenyl)ethene) [P(MTFE)] reveals no electrochromic activity, its copolymer with EDOT has two different colors (violet and gray). Band gap (E_g) and λ_max of P(MTFE‐co‐EDOT) were determined. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Particle size and distribution of biodegradable poly‐D,L‐lactide‐co‐poly(ethylene glycol) block polymer nanoparticles prepared by nanoprecipitation

A biodegradable block copolymer, poly‐D ,L ‐lactide (PLA)‐co‐poly(ethylene glycol) (PEG), was prepared by the ring‐opening polymerization of lactide with stannous caprylate [Sn(Oct₂)] as a catalyst; then, the PLA–PEG copolymer was made into nanoparticles by nanoprecipitation under different conditions. The average molecular weight and structure of PLA–PEG were detected by ¹H‐NMR and gel permeation chromatography. The sizes and distributions of the nanoparticles were investigated with a laser particle‐size analyzer. The morphologies of the nanoparticles were examined by transmission electron microscopy. The effects of the solvent–nonsolvent system, operation conditions, and dosage of span‐80 on the sizes and distributions of the nanoparticles are discussed. The results show that acetone–water was a suitable solvent–nonsolvent system and the volume ratio of the nonsolvent phase to the solvent phase (O/W) (v/v), the concentration of PLA–PEG in the solvent phase, and the dosage of span‐80 had important effects on the particle sizes and distributions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1884–1890, 2005     

Synthesis,spectral analysis,and catalytic activity of poly(aniline‐co‐congored)–metal oxide nanocomposites

Electrically conducting, water‐soluble fluorescent copolymer nanocomposites were synthesized by a solution polymerization method under different experimental conditions in the presence of CuO and V₂O₅ nanoparticles. The prepared copolymer nanocomposites were characterized with analytical tools, including Fourier transform infrared spectroscopy, ultraviolet–visible (UV–vis) spectroscopy, and fluorescence emission spectroscopy. The order of copolymerization was determined on the basis of the UV–vis absorption spectra and fluorescence emission spectra. The copolymer–CuO nanocomposite system exhibited the highest electrical conductivity. The scanning electron microscopy image showed the presence of more CuO nanoparticles on the surface of the copolymer. Furthermore, the catalytic activity of the copolymer nanocomposites was tested for the reduction of p‐nitrophenol. All three types of polymer systems exhibited almost the same apparent rate constant values. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46469.     

Effect of inorganic salts on viscosity of acrylonitrile‐N‐vinylpyrrolidone copolymer solutions

Effects of inorganic salts on viscosities of dimethyl sulphoxide (DMSO) solutions of acrylonitrile(AN)/N‐vinylpyrrolidone(N‐VP) copolymer are discussed. Viscosity was determined by the rotary viscosimeter. It was shown that the solution viscosity decreases quickly with addition of KCl and NaCl and the effect of NaCl is more prominent than that of KCl. As concentration of KCl and NaCl went beyond 0.025 mol/L, the viscosity showed a trend of increase. The viscosity increased considerably with addition of FeCl₃ and CuCl₂. Changes in solution viscosity became less obvious with addition of ZnCl₂. As temperature increased, the viscosity of the copolymer solution containing NaCl decreased most quickly and the copolymer solution consisting of FeCl₃ showed the slowest decrease. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3492–3495, 2003     

Synthesis of novel thermo‐ and redox‐sensitive polypeptide hydrogels

Multi‐responsive hydrogels have recently received considerable attention for bioapplications. Here, novel temperature‐ and redox‐responsive polypetide hydrogels have been developed. Thermo‐sensitive hydrogels based on poly(ethyleneglycol)‐block ‐poly(γ‐propargyl‐l ‐glutamate) (PEG‐PPLG ) were first synthesized by the ring opening polymerization of γ‐propargyl‐l ‐glutamate N ‐carboxyanhydride (PLG‐NCA ) with amino group terminated PEG monomethyl ether (mPEG‐NH₂ ) as macroinitiator and were then functionalized via the ‘thiol‐yne’ click reaction between the propargyl pendents and the thiol‐containing 1‐propanethiol. The sol ? gel phase transition of the obtained copolymer aqueous solution in response to temperature change was studied. The mass loss of the hydrogel in vitro was accelerated in the presence of H₂O₂ , exhibiting a redox‐responsive property. Further, the methyl thiazolyl tetrazolium viability results revealed that this polypetide hydrogel has excellent biocompatibility, presenting potential applications in the biomedical field. © 2016 Society of Chemical Industry     

Ultrasonochemical‐assisted fabrication and evaporation‐ induced self‐assembly (EISA) of POSS‐SiO2@Ag core/ABA triblock copolymer nanocomposite film

Poly(ethylene glycol)‐octafunctionalized polyhedral oligomeric silsesquioxane (POSS) (M_n = 5576.6 g/mol) alloying agent stabilized amphiphilic silica@silver metalloid nanocomposite blended with a triblock copolymer poly(p‐dioxanone‐co‐caprolactone)‐block‐poly(ethylene oxide)‐block‐poly(p‐dioxanone‐co‐caprolactone) (POSS‐SiO₂@Ag/PPDO‐co‐PCL‐b‐PEG‐b‐PPDO‐co‐PCL) has been synthesized in both water and in organic medium utilizing ultrasonochemical reaction. The POSS stabilized pre‐made metalloid was successfully dispersed in amphiphilic PPDO‐co‐PCL‐b‐PEG‐b‐PPDO‐co‐PCL (ABA) triblock copolymer matrix of molecular weight 45.9 × 10⁴ g/mol. The mechanism of synthesis of high concentration of SiO₂@Ag nanocomposite from TEOS/AgNO₃ (in the presence of NH₄OH as catalyst/NaBH₄ as reductant) nonmetal/metal precursors and the successful EISA of POSS‐SiO₂@Ag/ABA nanocomposite into films has been discussed. The successful synthesis of metalloid nanocomposite was morphologically accessed by field emission‐scanning electron microscopy, transmission electron microscopy and atomic force microscopy. Surface plasmon resonance was ensured from UV–visible spectral analysis. Identity and the crystallinity of as prepared nanocomposite were studied by X‐ray diffractometer. Structural and luminescence properties of the nanocomposite were examined by Fourier transform infrared spectroscopy and photoluminescence. Thermogravimetric analysis was carried out to study the thermal stability of the resulting hybrid nanocomposite. The resultant inorganic–organic nanocomposite can be easily suspended in water and would be useful in variety of applications. POLYM. COMPOS., 31:1620–1627, 2010. © 2009 Society of Plastics Engineers     

Rheological study of poly(ethylene glycol)/poly(N‐isopropylacrylamide‐co‐2‐acrylamido‐2‐methylpropanesulphonic acid) semiinterpenetrating network formation

The formation of a series of semiinterpenetrating network (SIPN) hydrogels made by free‐radical copolymerization of N‐isopropylacrylamide (NIPA) and 2‐acrylamido‐2‐methylpropanesulphonic acid (AMPS) with varying comonomer mole ratios, crosslinked with N,N′‐methylene‐bisacrylamide (MBAA) in the presence of poly(ethylene glycol) (PEG) with average molecular weight 6,000 g mol^?1 was studied via determination of complex viscosity, η*, using plate–plate rheometry. The isothermal time dependence of η* at various temperatures or the variation of η* with temperature of pregel solutions was utilized to detect the onset of gelation. The SIPN systems were compared with the corresponding gels made under the same conditions in the absence of PEG. The copolymer mainchain composition has a major effect on the time or temperature for onset of gelation and in particular gelation appears to be inhibited to some extent by MBAA when the AMPS/NIPA mole ratio in the pregel solution exceeds 0.5. The presence or absence of PEG in pregel solutions has a lesser effect on gelation. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2083–2087, 2004     

Rheology and extrusion foaming of chain‐branched poly(lactic acid)

In this study, the effect of macromolecular chain‐branching on poly(lactic acid) (PLA) rheology, crystallization, and extrusion foaming was investigated. Two PLA grades, an amorphous and a semi‐crystalline one, were branched using a multifunctional styrene‐acrylic‐epoxy copolymer. The branching of PLA and its foaming were achieved in one‐step extrusion process. Carbon dioxide (CO₂), in concentration up to 9%, was used as expansion agent to obtain foams from the two PLA branched using chain‐extender contents up to 2%. The foams were investigated with respect to their shear and elongational behavior, crystallinity, morphology, and density. The addition of the chain‐extender led to an increase in complex viscosity, elasticity, elongational viscosity, and in the manifestation of the strain‐hardening phenomena. Low‐density foams were obtained at 5–9% CO₂ for semi‐crystalline PLA and only at 9% CO₂ in the case of the amorphous PLA. Differences in foaming behavior were attributed to crystallites formation during the foaming process. The rheological and structural changes associated with PLA chain‐extension lowered the achieved crystallinity but slightly improved the foamability at low CO₂ content. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers