Melt free‐radical grafting of maleimides with hindered phenol groups onto polyethylene

A monomeric antioxidant, bearing carbamate groups, was synthesized from the reaction of 3,5‐di‐tert‐butyl‐4‐hydroxybenzyl alcohol and azidomaleimide. Another antioxidant was prepared from the reaction of N‐(4‐hydroxyphenyl)maleimide and 3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl) propionic chloride in the presence of triethylamine. These fictional antioxidants were grafted onto polyethylene (PE) via melt processing with free‐radical initiators in a minimax molder. The IR spectra of the grafted PE showed that the monomeric antioxidants were added to PE. IR spectroscopy methods were used for the quantitative determination of the extent of grafting of the monomeric antioxidants. Also, the extent of crosslinking was determined from the gel content. To optimize the reaction conditions, we investigated the effects of the initiator concentration, monomeric antioxidant, reaction time, and temperature on the extent of grafting. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2117–2122, 2004     

Synthesis and performance of phenolic polybutadiene‐bound stabilizers

An antioxidant derivative, 6‐sulfanylhexyl 3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl)propanoate, was synthesized and examined. With a radical initiator, the addition of this compound to pending vinyls of OH‐telechelic, low molecular weight liquid polybutadiene (LBH) was performed to various degrees of conversion to form polymeric antioxidants (PAOs) in which the phenolic moiety was separated from the main chain by a spacer [? CH₂CH₂? S? (CH₂)₆? O? CO? ]. Pure, unstabilized LBH was mixed in several ratios with PAOs, Irganox 1520, and Irganox 1076, and the oxidation stabilities of these mixtures, determined by thermogravimetric analysis and differential scanning calorimetry, were compared. Probably because of their good compatibility with LBH, PAOs exhibited equal or better effectiveness than commercial antioxidants of the Irganox type. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 885–889, 2003     

Antioxidant and antibacterial effects of natural phenolic compounds on green composite materials

The aim of this study is to establish the thermal performance of a biocomposite (Arbofill kokos®), stabilized with different natural phenolic additives, to check the antioxidant capacity of the resulting compounds. Different phenolic compounds (thymol, carvacrol, α‐tocopherol, and tannic acid) were used as biobased additives and the concentrations ranged between 0.5 wt% and 2 wt%. The results obtained were compared with formulations containing a typical industrial petroleum‐based antioxidant agent (octadecyl‐3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl) propionate). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to characterize the antioxidant performance of the selected natural additives. The antimicrobial effect of these natural phenolic compounds was also studied by analyzing the growth of bacterial colonies. The comparison between the natural phenolic compounds and the petroleum‐based antioxidant compound showed good antioxidant action for natural phenolic compounds; in all the mixtures of biocomposite and antioxidant agent the oxidation onset temperature (OOT) increased in a remarkable way, but the highest stabilization effect was achieved with α‐tocopherol with provides a % increase on OOT of about 45%. With regard to antibacterial activity of the different natural phenolic compounds, thymol, and carvacrol showed interesting antibacterial properties against Staphylococcus aureus. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Effect of antiaging agents on the outdoor natural weathering of bamboo powder/polypropylene foamed composites

The effect of outdoor natural weathering on the properties of injection molded 33 wt% bamboo powder (BP)/polypropylene (PP) foamed composites with and without the antioxidant and hindered amine light stabilizers (HALS) were investigated. The composites containing the antiaging agents had higher color stability, slightly greater retentions of flexural modulus, tensile and notched impact strengths, higher creep resistance, and better rheological stability than the reference composite. The antiaging agents of pentaerythritol tetrakis(3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl)propionate) and poly‐(n‐hydroxyethyl‐2,2,6,6‐tetramethyl‐4‐hydroxy‐piperidyl succinate) had more beneficial effect than n‐octadecyl‐β‐(4‐hydroxy‐3,5‐di‐tert‐butyl‐phenyl)‐propionate and bis(2,2,6,6‐tetramethyl‐4‐piperidinyl)sebacate. After 12 months of exposure, △E^* decreased from 22.8 of the reference composite to 9.9 of the composite with the antiaging agents. Rheological behavior results indicated that the storage modulus, complex viscosity, and non‐Newtonian fluid index of composites containing the antiaging agents were slightly increased. Natural weathering caused less decreases in the storage and loss moduli, crossover modulus, relaxation time, and average molecular weight for composites containing the antiaging agents than those for the reference composite. Environmental scanning electron microscopy (ESEM) observation confirmed the improved surface durability for composites containing the antiaging agents. J. VINYL ADDIT. TECHNOL., 22:311–319, 2016. © 2014 Society of Plastics Engineers     

Novel stabilization system for polypropylene via the Ziegler–Natta catalyzed polymerization in the presence of aluminum aryloxide

The aluminum aryloxide was prepared via the reaction of phenolic antioxidant, 3‐(3,5‐di‐t‐butyl‐4‐hydroxyphenyl)‐N‐octadecylpropionamide, with triethyl aluminum. Propylene polymerization using supported Ziegler–Natta catalyst systems was carried out in the presence of the antioxidant or its aluminum aryloxide. Although the antioxidant gave rise to decrease in catalyst yield and change in hydrogen response, the aluminum aryloxide had no influence on the catalytic polymerization behavior, and thus the obtained polymer characteristics such as molecular weight, polydispersity, and meso pentad as a stereoregularity were comparable to that polymerized without the antioxidant and the aluminum aryloxide. Polypropylene obtained in the presence of the aluminum aryloxide was well stabilized for oxidation and its stability was over 1000 h at 100°C (estimated to be over 30 years at room temperature). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1350–1358, 2006     

Synthesis and Characterisation of Anhydride‐Cured Epoxy Nanocomposites Containing Layered Silicates Modified with Phenolic Alkylimidazolineamide Cations

Summary: Phenolic alkylimidazolineamides were prepared and applied as modifiers in order to render layered silicates organophilic and to prepare polymeric nanocomposites. The imidazolineamine, 2‐{2‐[heptadec‐8‐enyl]‐4,5‐dihydro‐1‐imidazol‐1‐yl}‐1‐ethaneamine (IA), was reacted in bulk with one of the two phenolic compounds, ethyl 4‐hydroxybenzoate (P) or methyl 3‐[3,5‐di(tert‐butyl)‐4‐hydroxyphenyl]propionate (HP), which is an intermediate for antioxidants, to prepare the two phenolic imidazolineamides, PIA and HPIA. During protonation in water, both phenolic imadazolineamides were used successfully to exchange interlayer sodium cations of sodium bentonite and fluorohectorite, thus producing organophilic layered silicates with an increased interlayer distance of around 3.3 nm. The new phenolic organophilic layered silicates represent a novel class of phenolic organic/inorganic hybrid materials. They were applied as fillers in hexahydrophthalic anhydride‐cured bisphenol‐A diglycidyl ether (BADGE). Thermal analysis (DSC), transmission electron microscopy (TEM), wide angle X‐ray scattering (WAXS), and mechanical tests were used to evaluate the thermal, mechanical, and morphological properties. Although fracture toughness, measured as the stress intensity factor, K_Ic, and the energy release rate, G_Ic, increased by around 50% with increasing silicate content without sacrificing glass temperature, both tensile strength and Young's modulus increased only marginally. Low matrix reinforcement was attributed to inadequate compatibility matching, as evidenced by the slightly lower interlayer distances of the layered silicates encapsulated in the epoxy matrix.

Representative TEM micrographs of the sample ER‐bent‐PIA/10.     

Melt free‐radical grafting of hindered phenol antioxidant onto polyethylene

A monomeric antioxidant (3) was prepared by reacting 3,5‐di‐tert‐butyl‐4‐hydroxybenzyl alcohol (1) with N‐[4‐(chlorocarbonyl) phenyl] maleimide (2). This reactive antioxidant was grafted onto polyethylene (PE) by melt processing with free‐radical initiators in a mini‐max molder. The IR spectra of the grafted PE showed that the monomeric antioxidant was introduced onto the PE. IR spectroscopic methods and titration were used for the quantitative determination of the extent of grafting of the monomeric antioxidant. Also, the extent of crosslinking was indicated by the gel content. Grafting occurred in the following order: dicumyl peroxide (DCP) > benzoyl peroxide > 2,2′‐azobisisobutyronitrile. The influences of the DCP concentration and monomeric antioxidant on the extent of grafting were studied. The effects of the reaction time and temperature were also determined. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2968–2973, 2000     

Polyolefin elastomer grafted unsaturated hindered phenol esters: synthesis and antioxidant behavior

Monomeric antioxidants are synthesized from esterification of 3,5-di-tert-butyl-4-hydroxybenzoic acid and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid with unsaturated fatty alcohols. The antioxidant activity is evaluated both in blending and radical grafting processes. The effect of chain length and phenolic group is investigated on efficiency of antioxidants. It is demonstrated that the esters of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid exhibit significantly longer induction time. The results of radical grafting reaction shows synthesized antioxidants can be successfully grafted onto polymer chains and the phenolic moiety is functional after extraction process, while pure and commercially stabilized samples are degraded instantaneously. Also, different initiator systems are utilized to enhance the extent of grafting. Among MEK, DCP, and DHBP peroxides, DHBP can be more effective in increasing the antioxidant grafted onto polymer. In addition, possibility of rising in graft content is investigated in presence of redox initiator. Using this approach, polymer-bound antioxidant with prolonged thermal stability can be achieved.     

Alternating copolymerization and terpolymerization of vinyl‐substituted phenolic antioxidants with propene and carbon monoxide by a palladium(II)‐based catalyst: polyketones containing intramolecular stabilizers

The copolymerization and terpolymerization reactions of the vinyl‐substituted phenolic stabilizers, 6‐tert‐butyl‐2‐(1,1‐dimethylhept‐6‐enyl)‐4‐methylphenol, o‐allylphenol, 4‐methylstyrene‐2,6‐di‐tert‐butylphenol and 2,6‐di‐tert‐butyl‐4‐allylphenol, with propene and carbon monoxide, by using the solvent‐stabilized palladium(II ) phosphine complex [Pd(dppp)(NCCH₃)₂](BF₄)₂ (dppp, 1,3‐bis(diphenylphosphino)propane) as a catalyst precursor and methanol as a co‐catalyst, is described. The influence of functional α‐olefins/CO units, distributed statistically along the propene/carbon monoxide (P/CO) copolymer backbone, on the molecular weight, glass transition temperature (T_g), elastic behavior and stability of the high‐molecular‐weight P/CO copolymer has been investigated. Loss of both elasticity and transparency were observed upon incorporating o‐allylphenol as a termonomer. The terpolymers, which contain phenolic stabilizers, were shown to be more stable when compared to the stabilizer‐free polyketones. In contrast to the propene/carbon monoxide copolymer, no degradation was observed for the 2,6‐di‐tert‐butyl‐4‐allylphenol/P/CO terpolymer; instead, the molar masses increased. Copyright © 2004 Society of Chemical Industry     

Synthesis and antioxidant activities in polyolefin of dendritic antioxidants with hindered phenolic groups and tertiary amine

Two novel primary antioxidants with dendritic structure and hindered phenolic groups were synthesized using 3‐(3,5‐diter‐butyl‐4‐hydroxyphenyl) propionic acid as raw material and dendritic poly(amidoamine) (PAMAM) as linker in chloroform. The antioxidant activities of the dendritic antioxidants were evaluated in polyolefin by melt flow index (MFI), yellowness index (Y.I.), and oxidation induction time (OIT). The dendritic antioxidants had excellent processing property and oxidation resistance behavior in polyolefin. At the same weighed amount of antioxidant, the MFI and Y.I. values of mulitiple‐extruded polyethylene (PE) stabilized with the dendritic antioxidants were smaller than those of the commercial antioxidants, as well as the OIT values of polyethylene (PE) stabilized with the dendritic antioxidants were larger. Applying to polypropylene, the antioxidant ability of the second‐generation dendritic antioxidant (G2.0 dendritic antioxidant) with larger molecular weight was superior to the commercial antioxidants and that of the first‐generation dendritic antioxidant (G1.0 dendritic antioxidant) was equal to the commercial antioxidants. The dendritic antioxidants can prevent polyolefin from breaking of macromolecular chain in processing and had stabilizing effect in polyolefin in service life by donating H‐atoms and electron to free radicals. The dendritic antioxidants combined with Irgafos 168 had improvement of antioxidant activities of the dendritic antioxidants in polyolefin. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Relationship between bridged groups and antioxidant activity for aliphatic diamine bridged hindered phenol in polyolefins

Four aliphatic diamine bridged hindered phenols were successfully synthesized with aliphatic diamine as the bridged group and 3‐(3,5‐di‐tert‐butyl‐4‐hydroxy‐phenyl)‐propionyl chloride as the material, and their structures were clarified by NMR, Fourier transform infrared spectroscopy, and mass spectrometry. Their performance as antioxidant for polypropylene (PP) and linear low‐density polyethylene (LLDPE) were investigated through the melt flow rate and the oxidation induction time. The thermooxidative stabilities of PP and LLDPE with different aliphatic diamine bridged hindered phenols were assessed by the measurement of the oxidation induction temperature and with long‐term aging testing. The results showed that aliphatic diamine bridged hindered phenols could protect two kinds of polyolefins from thermal oxidative degradation, and the mechanical properties and antioxidant activities of polyolefins stabilized with aliphatic diamine bridged hindered phenols were increased with increasing length of the bridged group for aliphatic diamine bridged hindered phenols at the same concentration of phenolic hydroxyl group. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45095.     

Poly(silyl ester)s: A new route of synthesis via the condensation of Di‐tert‐butyl ester of dicarboxylic acid with dichlorosilane

Poly(silyl ester)s were synthesized by a new route via the condensation of di‐tert‐butyl ester of dicarboxylic acid with dichlorosilane by the elimination of tert‐butyl chloride as a driving force. Three new poly(silyl ester)s with molecular weights typically ranging from 2000 to 5000 amu were produced by the condensation of di‐tert‐butyl adipate with 1,5‐dichloro‐1,1,5,5‐tetramethyl‐3,3‐diphenyl trisiloxane and di‐tert‐butyl fumarate with 1,5‐dichloro‐1,1,5,5‐tetramethyl‐3,3‐diphenyl trisiloxane or 1,3‐dichlorotetramethyl disiloxane. Each polymer was characterized with infrared, ¹H‐NMR, and ¹³C‐NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis. This new approach showed several advantages. First, it did not require a catalyst or solvent. Second, the tert‐butyl chloride byproduct was volatile and was easily eliminated. Third, there was no reaction between the growing poly(silyl ester)s and the condensation byproduct, tert‐butyl chloride. Fourth, the monomers could be readily purified. Finally, the polymerization could be performed at relatively low temperatures and in a short time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1378–1384, 2006     

Synthesis of (3‐tert‐butyl‐4‐hydroxy‐5‐methylphenyl) propionate derivatives and their thermal antioxidation behavior for POM

Polyoxymethylene (POM) has been widely utilized in industry due to its light weight properties in engineering plastics. At present, POM applications are expanding into the car industry, especially in fuel tanks. Hindered alkyl phenol derivatives have been used as antioxidants for POM; however, these compounds are easily extracted by solvents. Two antioxidants with new structures (N,N′‐triethylenedioxy‐bis(3‐tert‐butyl‐4‐hydroxy‐5‐methylhydrocinnamamide) and N,N′,N′‐tris[(3‐tert‐butyl‐4‐hydroxy‐5‐methylphenyl)propionyl‐3‐oxapentyl]melamine) were synthesized and characterized, and their performance as antioxidants for POM was investigated in the present study. The results revealed that N,N′‐triethylenedioxy‐bis(3‐tert‐butyl‐4‐hydroxy‐5‐methylhydrocinnamamide) has good heat aging resistance compared to existing antioxidants for POM, and N,N′,N′‐tris[(3‐tert‐butyl‐4‐hydroxy‐5‐methylphenyl)propionyl‐3‐oxa‐pentyl]melamine has good extraction resistance against solvents. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Antioxidation and mechanism of phosphites including the free phenolic hydroxyl group in polypropylene

Inhibiting the degradation of polypropylene (PP) in melt processing and usage is an important issue in the plastic industry. It is becoming more and more urgent to increase the antioxidation of phosphites alone while maintaining the water resistance. In this study, one phosphite antioxidant, named bis‐2,2′‐methyl‐4,6‐di‐tert‐butylphenyl phosphite (BM46TBPP), which contains a water‐resistant inner ring and a free phenolic hydroxyl group together, was synthesized. Then, antioxidation in PP was characterized with multiple extrusions and oxidation induction times (OITs). Finally, the hydrogen‐donating ability of this antioxidant was tested with 2,2‐diphenyl‐1‐picrylhydrazyl radical colorimetry to explain the antioxidation mechanism. The results show that the phosphite BM46TBPP displays better antioxidation than tris(2,4‐di‐tert‐butylphenyl) phosphite (Irgafos 168) in melt processing and OIT testing. Furthermore, the priority of this antioxidant was more obvious when it was used in the presence of oxygen, so the antioxidant even made the PP stabilized by it alone show a longer OIT value than the PP stabilized by the complex system including Irgafos 168 and 2,4‐di‐tert‐butylphenol because there was a free phenolic hydroxyl group in the BM46TBPP antioxidant molecule and the hydroxyl group made the antioxidant show intermolecular synergistic antioxidation through hydrogen donation to radicals. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44696.     

Preparation and evaluation of some novel organo‐phosphorus compounds as antioxidants and antifatigue agents in rubber

Six organo‐phosphorus compounds were synthesized and incorporated in NR and SBR mixes. The rheometric characteristics of the green rubber mixes were determined using the oscillating disc rheometer. The prepared compounds were evaluated as antioxidants and antifatigue agents in NR and SBR vulcanizates. It was found that the prepared compounds are good antioxidant and antifatigue agents and their efficiency was better than that obtained by 4‐methyl‐2,6‐di‐tert‐butyl phenol, which is used in the rubber industry. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2984–2992, 2002; DOI 10.1002/app.2327     

Synthesis and reactivity of antioxidants based on vernolic acid and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid

The reactivity of sterically hindered phenols toward free radicals of the hydrocarbon cumene was studied. New compounds, i. e. methyl cis-13(12)-{3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy}-12(13)-hydroxyoleate and cis-13(12)-{3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy}-12(13)-hydroxyoleic acid were synthesized starting from vernolic acid and its methyl ester, respectively, and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid. Both new compounds possess antioxidant activities similar to those of commercially available antioxidants.     

Synthesis of two modified carotenoids and their behavior during light exposure

Two modified carotenoids, β‐6‐hydroxy‐2, 5, 7, 8‐tetramethyl‐chromane carboxylic acid β‐apo‐8'‐carotenoate (Caro‐Trolox) and 3, 5‐di‐tert‐butyl‐4‐hydroxy benzoic acid β‐apo‐8'‐carotenoate (Caro‐BHT) were synthesized by esterification of β‐apo‐8'‐carotenol with Trolox and with 3, 5‐di‐tert‐butyl‐4‐hydroxy benzoic acid, respectively. Their activity under light exposure was examined comparatively to that of Trolox, α‐tocopherol, β‐carotene, β‐apo‐8'‐carotenoic acid (CA} and ethyl β‐apo‐8'‐carotenoate. The substrate used was purified sunflower oil. In the absence of a photosensitizer (240 W/m² , 25 °C) Caro‐Trolox (200 mg/kg) behaved as an antioxidant and was quite stable (1/5 of the initial amount remained after 2‐wk storage). Caro‐BHT (200 mg/kg) showed no antioxidant activity and was quite unstable (it was destroyed within 7 d). In the presence of 5 mg/kg chlorophyll α (12000 lx, 25 °C) similar observations were made. The activity of Caro‐Trolox was concentration‐dependent. At a 100‐mg/kg level of addition its activity was similar to that of the mixture of α‐t_copherol (100 mg/kg) and β‐carotene (10 mg/kg). Its performance at the 10‐mg/kg level was slightly better than that of the other carotenoids. The antioxidant behavior of the modified carotenoids was attributed to the presence of the phenolic moiety as supported by the results of the 1, 1‐diphenyl‐2‐picrylhydrazyl test (e.g. EC₅₀ after 15 min: 26.2, Caro‐Trolox; 35.8, Caro‐BHT; 122, CA; 22.3, Trolox).     

Stabilization of high-density polyethylene

Several types of antioxidants are evaluated in high-density polyethylene for color and physical property stabilization during processing and thermal aging. A wide variety of evaluation tests are used and discussed. Heat- and light-induced oxidation mechanisms are reviewed. Antioxidants such as octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and tetrakis[methylene 3-(3′,5′-di-tert-butyl-4′-hydroxy phenyl) propionate] methane were found to provide very high retention of physical properties, excellent initial color and color retention. Combinations of antioxidant- and ultraviolet light absorbers were evaluated for stabilizing high density polyethylene exposed to artificial light and outdoor weathering. The combination of octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and 2-(2′-5′-di-tert-butyl-2′-hydroxy-phenyl)-5-chlorobenzotriazole was found to be a very efficient stabilizer system. Polymer containing this stabilizer combination had excellent color stability and minimum crosslinking and embrittlement after Arizona weathering.     

Preparation,structural characterization,and antioxidative behavior in natural rubber of antioxidant GM functionalized nanosilica

To restrain the migration and extractability of the antioxidants and improve the dispersion of nanosilica in natural rubber (NR), antioxidant 2‐tert‐butyl‐6‐(3‐tert‐butyl‐2‐hydroxy‐5‐methylbenzyl)‐4‐methyphenyl acrylate (GM) functionalized nanosilica was prepared using antioxidant coupling agent (KH590‐GM) as functional modifier, which was first synthesized through thiol‐ene reaction between the mercapto group of γ‐mercaptopropyl trimethoxysilane (KH590) and the CC double bonds of antioxidant GM. Fourier transform infrared spectroscopy and ¹H nuclear magnetic resonance confirmed the structure of KH590‐GM and GM functionalized nanosilica. Thermogravimetry analysis indicated that the grafting rate of GM functionalized nanosilica reached 13.4%, and the antioxidant had good thermal stability. Scanning electron microscope and mechanical properties measurement showed GM functionalized nanosilica was dispersed uniformly in NR vulcanizates, and helpful for the increase of the tensile strength and tensile stress of NR vulcanizates. Based on the study of the antioxidative behavior and extraction resistance of the NR vulcanizates, it was found that in contrast to NR vulcanizates with GM, the ageing coefficient and oxidation induction time of that with GM functionalized nanosilica increased to 0.66 and 39 min from 0.58 and 30 min, respectively. Furthermore, the NR vulcanizates with GM functionalized nanosilica also exhibited excellent extraction resistance. POLYM. COMPOS., 38:1241–1247, 2017. © 2015 Society of Plastics Engineers     

Controlled and stereospecific polymerization of rac‐lactide with a single‐site ethyl aluminum and alcohol initiating system

A single‐site ethyl aluminum complex, [2,2‐ diethyl‐1,3‐propylenebis(3,5‐di‐tert‐butyl‐salicylideneiminato)] ethyl aluminum (2), with a geminal diethyl substitutent on the diamino bridge was synthesized by the reaction of AlEt₃ with 1 equiv of N,N′‐(2,2‐diethyl‐1,3‐propylene)bis(3,5‐di‐tert‐butylsalicylideneimine). X‐ray diffraction showed that complex 2 contained a five‐coordinate aluminum atom with a distorted trigonal bipyramidal geometry in the solid state. ¹H‐NMR and ¹³C‐NMR spectra indicated that the two conformational enantiomers of 2 tautomerized quickly on the NMR timescale in solution. In the presence of isopropyl alcohol, the ring‐opening polymerization (ROP) of rac‐lactide with complex 2 produced a crystalline stereoblock polylactide (PLA). The stereoblocks contained an average of 12 units (L? = 12) of enantiomerically pure lactic acid. There was a linear relationship between the monomer conversion and number‐average molecular weights of the polymer. An induction period was observed for the polymerization. The induction period increased with decreasing concentration of catalyst 2 and isopropyl alcohol. In the presence of poly(ethylene glycol) (PEG), a PLA/PEG/PLA stereocomplex was prepared directly by the ROP of rac‐lactide with complex 2, which was confirmed by NMR, gel permeation chromatography, wide‐angle X‐ray diffraction, and differential scanning calorimetry. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 102–108, 2005