Activation Mechanisms of Trialkylaluminum in Alkali Metal Alkoxides or Tetraalkylammonium Salts / Propylene Oxide Controlled Anionic Polymerization

The anionic polymerization of propylene oxide (PO) initiated by alkali metal alkoxides is in non polar solvents a very slow and non controlled reaction process. Transfer reaction to monomer is predominant, allowing only the preparation of low molar masses PPO. The influence of the addition of trialkylaluminium to either an alkali metal alkoxide or a tetraalkylammonium salt used as initiator for PO polymerization in hydrocarbon media was investigated. A strong enhancement of the polymerization rate accompanied by a drastic decrease of the transfer reactions is observed, allowing the synthesis of PPO with well controlled molar masses. At constant monomer and alkali metal alkoxide concentrations, the polymerization rate increases with increasing trialkylaluminium concentration. Results indicate that the trialkylaluminium derivative is involved in the formation of two distinct complexes, one with the alkali metal alkoxide or the tetraalkylammonium salt and another one with the PO monomer which is strongly activated towards nucleophilic active species. Significant differences between the alkali metal and tetraalkylammonium based initiators are observed. In particular much less trialkylaluminum activator is needed with the ammonium salt to get the same rate of propagation and controlled polymerization.     

Synthesis of end‐functionalized polyethers by phosphazene base‐catalyzed ring‐opening polymerization of 1,2‐butylene oxide and glycidyl ether

For the living ring‐opening polymerization (ROP) of epoxy monomers, the catalytic activity of organic superbases, tert‐butylimino‐tris(dimethylamino)phosphorane, 1‐tert‐butyl‐2,2,4,4,4‐pentakis(dimethylamino)‐2Λ⁵,4Λ⁵‐catenadi(phosphazene), 2,8,9‐triisobutyl‐2,5,8,9‐tetraaza‐1‐phosphabicyclo[3.3.3]undecane, and 1‐tert‐butyl‐4,4,4‐tris(dimethylamino)‐2,2‐bis[tris(dimethylamino)phosphoranylidenamino]‐2Λ⁵,4Λ⁵‐catenadi(phosphazene) (t‐Bu‐P₄), was confirmed. Among these superbases, only t‐Bu‐P₄ showed catalytic activity for the ROP of 1,2‐butylene oxide (BO) to afford poly(1,2‐butylene oxide) (PBO) with predicted molecular weight and narrow molecular weight distribution. The results of the kinetic, post‐polymerization experiments, and MALDI‐TOF MS measurement revealed that the t‐Bu‐P₄‐catalyzed ROP of BO proceeded in a living manner in which the alcohol acted as the initiator. This alcohol/t‐Bu‐P₄ system was applicable to the glycidol derivatives, such as benzyl glycidyl ether (BnGE) and t‐butyl glycidyl ether, to afford well‐defined protected polyglycidols. The α‐functionalized polyethers could be obtained using different functionalized initiators, such as 4‐vinylbenzyl alcohol, 5‐hexen‐1‐ol, and 6‐azide‐1‐hexanol. In addition, the well‐defined cyclic‐PBO and PBnGE were successfully synthesized using the combination of t‐Bu‐P₄‐catalyzed ROP and click cyclization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of poly(n‐hexyl isocyanate‐b‐N‐vinylpyrrolidone) block copolymers by the combination of anionic and nitroxide‐mediated radical polymerizations: Micellization properties in aqueous solutions

A combination of anionic and nitroxide‐mediated radical polymerizations (dual initiator) was employed for the synthesis of poly(n‐hexyl isocyanate‐b‐N‐vinylpyrrolidone) (PHIC‐b‐PNVP) block copolymers. The samples were characterized with a size exclusion chromatograph equipped with refractive‐index and light scattering detectors as well as ¹H NMR spectroscopy. Relatively good control over the molecular weights was achieved. However, rather broad molecular weight distributions were obtained. The micellar properties of the PHIC‐b‐PNVP block copolymers were studied in water, which is a selective solvent for the poly(N‐vinylpyrrolidone) blocks. Static and dynamic light scattering revealed the presence of equilibrium between the micelles and clusters. The clusters partially deaggregated with increasing temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5719–5728, 2006     

Modification of proline‐based 2,5‐diketopiperazines by anionic ring‐opening polymerization

2,5‐Diketopiperazines (DKPs) are the smallest cyclic dipeptides found in nature with various attractive properties. In this study, we have demonstrated the successful modification of proline‐based DKPs using anionic ring‐opening polymerization (AROP) as a direct approach. Four different proline‐based DKPs with various side chains and increasing steric hindrance were used as initiating species for the polymerization of 1,2‐epoxybutane or ethoxyethyl glycidyl ether in the presence of t‐BuP₄ phosphazene base. The addition of a Lewis acid, tri‐isobutyl aluminum, to the reaction mixture strongly decreased the occurrence of side reactions. Impact of the DKP side‐chain functionalities on molar mass control and dispersity was successfully evidenced. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1008–1016     

Cationic copolymerization behavior of cyclic ether monomers with norbornene‐containing cyclic carbonate or spiro–orthoether structure

Cationic ring‐opening copolymerizations of various cyclic ether compounds with volume expanding monomers bearing norbornene backbones [norbornene‐spiro orthocarbonate (N‐SOC) and norbornene‐cyclic carbonate (N‐CC)] were carried out in the presence of a thermally latent initiator 1 . The 10% weight loss decomposition temperatures (T_d10) and the volume changes on the copolymerizations were measured for these resultant products. In the comparison between copolymerizations of bifunctional epoxide 2 with N‐SOC and with N‐CC, it was found that N‐CC served as a more useful volume controllable comonomer than N‐SOC. The copolymerizations with N‐CC yielded the products with a decrease in the volume change (volume shrinkage) and with an increase in the monomer feed ratio of N‐CC; T_d10 was relatively similar to the homopolymer of epoxide 2 and was observed except when the proportion of N‐CC was more than 20% in the monomer feed ratio of N‐CC. In contrast, similar copolymerizations with N‐SOC did not exhibit such tendencies, probably because of the low efficiency of the copolymerization derived from the low miscibility of N‐SOC for the epoxide. The other copolymerization systems of other bi‐ and monocyclic ether compounds ( 3 – 6 and phenyl glycidyl ether) with N‐CC also indicated an almost similar tendency toward that of the copolymerization with epoxide 2 . © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5113–5120, 2004     

Anionic ring‐opening polymerization of a five‐membered cyclic carbonate having a glucopyranoside structure

Anionic ring‐opening polymerizations of methyl 4,6‐O‐benzylidene‐2,3‐O‐carbonyl‐α‐D ‐glucopyranoside (MBCG) were investigated using various anionic polymerization initiators. Polymerizations of the cyclic carbonate readily proceeded by using highly active initiators such as n‐butyllithium, lithium tert‐butoxide, sodium tert‐butoxide, potassium tert‐butoxide, and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene, whereas it did not proceed by using N,N‐dimethyl‐4‐aminopyridine and pyridine as initiators. In a polymerization of MBCG (1.0 M), 99% of MBCG was converted within 30 s to give the corresponding polymer with number‐averaged molecular weight (M_n) of 16,000. However, the M_n of the polymer decreased to 7500 when the polymerization time was prolonged to 24 h. It is because a backbiting reaction might occur under the polymerization conditions. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Gas‐free initiators for high‐temperature free‐radical polymerization

Quaternary ammonium persulfates as free‐radical initiators for high‐temperature polymerization are synthesized and their shelf‐life stability investigated. These initiators do not have gaseous byproducts and are therefore ideal for frontal polymerization, a process in which polymeric materials are produced via a thermal front that propagates through the unreacted monomer/initiator solution. Quaternary ammonium persulfate initiators offer additional qualities such as high solubility in organic media and low volatility, which are desirable for frontal polymerization. The initiators are synthesized using two procedures, and the initiating efficacy of the respective products is compared to a peroxide initiator in the frontal polymerization of 1,6‐hexanediol diacrylate. Of all the quartenary ammonium persulfates synthesized, tricaprylmethylammonium (Aliquat) persulfate (APSO) is the best initiator for frontal polymerization because it is soluble in organic media, is very reactive, and does not produce volatile byproducts under decomposition. A study of the decomposition kinetics of APSO is performed, and frontal polymerization is proposed as a quicker analytical technique to assay the purity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3984–3990, 2000     

Synthesis of poly(isopropenylphenoxy propylene carbonate) and its facile side‐chain functionalization into hydroxy‐polyurethanes

4‐Isopropenyl phenol ( 4‐IPP ) is a versatile dual functional intermediate that can be prepared readily from bisphenol‐A ( BPA ). Through etherification with epichlorohydrin to the phenolic group of 4‐IPP , it can be converted into 4‐isopropenyl phenyl glycidyl ether ( IPGE ). On further reaction with carbon dioxide in the presence of tetra‐n‐butyl ammonium bromide ( TBAB ) as the catalyst, IPGE was transformed into 4‐isopropenylphenoxy propylene carbonate ( IPPC ) in 90% yield. Cationic polymerization of IPPC with strong acid such as trifluoromethanesulfonic acid or boron trifluoride diethyl etherate as the catalyst at ?40 °C gave a linear poly(isopropenylphenoxy propylene carbonate), poly( IPPC ), with multicyclic carbonate groups substituted uniformly at the side‐chains of the polymer. The cyclic carbonate groups of poly( IPPC ) were further reacted with different aliphatic amines and diamines resulting in formation of polymers with hydroxy‐polyurethane on side‐chains. Syntheses, characterizations of poly( IPPC ) and its conversion into hydroxy‐polyurethane crosslinked polymers were presented. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 802–808     

Synthesis of poly(2‐furyloxirane) with high molecular weight and improved regioregularity using macrocyclic ether as a cocatalyst to potassium tert‐butoxide

2‐Furyloxirane (FO), a monomer usually obtained from a nonpetroleum route, was prepared from the epoxidation reaction of furfural and trimethylsulfonium chloride. About 200–300 g FO can be obtained in each preparation process. Although anionic polymerization of FO generally gives low‐ molecular‐weight polymers even after long periods of polymerization, the reaction was greatly improved when macrocyclic ether was used as a cocatalyst to potassium tert‐butoxide. When 18‐crown‐6 was used as a cocatalyst, poly(2‐furyloxirane) (PFO) with a number‐average molecular weight (M_n) of 41.5 kg/mol and a polydispersity index of 1.3 was obtained at 94% yield after polymerization at 40 °C for 72 h. The PFO obtained contained a 61.7% head‐to‐tail (H‐T) structure in the absence of the macrocyclic ether, and it reached 70.6% when cryptand[2,2,2] was used as a cocatalyst. PFO with higher regioregular structures showed improved thermal properties. For PFO with M_n of around 20.0 kg/mol, its glass transition temperature (T_g) increased from ?3 to 6 °C when the H‐T content was increased from 61.7 to 70.6%. Raising the M_n of PFO also raised T_g. For PFO with 68.9% H‐T structure, its T_g could reach 7 °C when M_n was increased to 40 kg/mol. This study shows two effective ways to improve the thermal and mechanical performances of the polymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Well‐defined polycaprolactone precursors for low surface‐energy polyurethane films

For the purpose of developing model coating systems, it is important to use well‐defined coating precursors. In this work, polyester oligomers were synthesized by controlled ring‐opening polymerization of ε‐caprolactone and 4‐tert‐butyl‐ε‐caprolactone via an activated monomer mechanism. These well‐defined oligomers, including 3‐armed hydroxyl‐functionalized polyesters and perfluoroalkyl‐end‐capped linear polyesters, have been obtained with controlled functionality and low‐molecular weight polydispersity and without the formation of cyclic structures, as demonstrated by MALDI‐ToF MS analyses. The polymer architecture and functionality can be tuned by using different initiating alcohols. These oligomers have been used as precursors to prepare model low surface‐energy polyurethane coatings. Upon the addition of about 1 wt % of fluorine in the polyurethane films, the advancing contact angles for water and hexadecane have been increased to 105° and 78°, respectively; the surface enrichment of fluorinated species has been confirmed by X‐ray photoelectron spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 218–227, 2008     

Hydroxyfunctional oxetane‐inimers with varied polarity for the synthesis of hyperbranched polyether polyols via cationic ROP

Synthesis and characterization of novel hydroxyl‐functionalized oxetane‐inimers with varied alkyl chain length—3‐hydroxymethyl‐3‐methoxymethyloxetane, 3‐hydroxymethyl‐3‐propoxymethyloxetane, and 3‐hexoxymethyl‐3‐hydroxymethyloxetane—is reported. Cationic ring‐opening polymerization of these latent, cyclic AB₂‐monomers leads to hyperbranched (hb) polyether polyols with degrees of branching between 34 and 69%, confirmed by inverse‐gated (IG) ¹³C NMR spectroscopy. The hyperbranching polymerization yielded apparent molecular weights (M_n) ranging from 500 to 2500 g mol^?1 (size exclusion chromatography). Remarkably, by copolymerization of 1,1,1‐tris(4‐hydroxyphenyl)ethane as a “focal” unit, polymerization under slow monomer addition conditions lead to higher apparent molecular weights up to 11,220 g mol^?1. The end groups of the hb polymers were studied via matrix‐assisted laser desorption/ionization time of flight mass and NMR spectrometry. By varying the alkyl chain length, tailoring of the solubility and glass transition temperatures of the materials is possible. Potential applications range from macroinitiators with defined polarity to tailoring of surface properties of antifouling materials. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2850–2859     

Polyaddition of bis(seven‐membered cyclic carbonate) with diamines: A novel and efficient synthetic method for polyhydroxyurethanes

This article deals with the polyaddition of a novel bis(seven‐membered cyclic carbonate), 1,2‐bis[3‐(1,3‐dioxepan‐2‐one‐5‐yl)‐propylthio]ethane, with the diamines 4,9‐dioxa‐1,12‐dodecanediamine and p‐xylylenediamine. The polyaddition was carried out at 30–70 °C for 6–24 h in dimethyl sulfoxide to obtain the corresponding polyhydroxyurethanes with number‐average molecular weights of 10,900–35,700 in good yields. The reaction of a monofunctional seven‐membered cyclic carbonate, 5‐allyl‐1,3‐dioxepan‐2‐one (7CC), with monoamines was also carried out to examine the reactivity in comparison with that of six‐ and five‐membered cyclic carbonates. The reaction rate constants of 7CC with n‐hexylamine and benzylamine were estimated to be 48.5 and 11.0 L/mol · h, respectively, in dimethyl sulfoxide‐d₆ (initial reagent concentration = 1 M) at 30 °C. The seven‐membered cyclic carbonate ring was 2.98 and 5.82 kcal/mol more strained than those of the six‐ and five‐membered cyclic carbonates, respectively, according to a semiempirical molecular orbital calculation with the PM3 Hamiltonian. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4091–4100, 2001     

Non‐isocyanate synthesis and application of telechelic polyurethanes via polycondensation of diurethanes obtained from ethylene carbonate and diamines

Aliphatic polyurethanes could be obtained in high yield via a non‐isocyanate method based on the self‐polycondensation of dihydroxyurethanes obtained by the reaction of diamines and ethylene carbonate. The polycondensation under a N₂ atmosphere yielded [6,2]polyurethane with a M_n value of 5300 in 87% yield. Two‐step polycondensation, consisting of the polycondensation under a N₂ atmosphere followed by that under reduced pressure, was effective to improve the yield and the molecular weight up to 90% and 10,000, respectively. Although the second polycondensation step at 180 °C was accompanied by formation of urea groups, this side reaction was relatively suppressed at 150 °C. The resulting polyurethane having hydroxyl groups at both of the end groups was converted to polyurethane methacrylate via a reaction with glycidyl methacrylate, and the polyurethane methacrylate served as a crosslinker for radical polymerization of methyl acrylate. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Crosslinking polymerization leading to interpenetrating polymer network formation. I. Polyaddition crosslinking reactions of poly(methyl methacrylate‐co‐2‐methacryloyloxyethyl isocyanate)s with ethylene glycol resulting in polyurethane networks

At the start of our research program concerned with the elucidation of the crosslinking polymerization mechanism leading to interpenetrating polymer network (IPN) formation, in which IPNs consist of both polymethacrylates and polyurethane (PU) networks, this article deals with the polyaddition crosslinking reaction leading to PU network formation. Therefore, 2‐methacryloyloxyethyl isocyanate (MOI) was radically copolymerized with methyl methacrylate (MMA) in the presence of CBr₄ as a chain‐transfer agent. The resulting poly(MMA‐co‐MOI)s, having pendant isocyanate (NCO) groups as novel multifunctional polyisocyanates, were used for polyaddition crosslinking reactions with ethylene glycol as a typical diol. The second‐order rate constants depended on both the functionality of poly(MMA‐co‐MOI) and the NCO group concentration. The actual gel points were compared with the theoretical ones calculated according to Macosko's equation; the deviation of the actual gel point from the theoretical value became more remarkable for a greater functionality of poly(MMA‐co‐MOI) and at a lower NCO group concentration or at a lower poly(MMA‐co‐MOI) concentration. These are discussed mechanistically, with consideration given to the significance of intramolecular cyclization and intramolecular crosslinking reactions leading to the shrinkage of the molecular size of the prepolymer, along with the data of the intrinsic viscosities of resulting prepolymers and the swelling ratios of resulting gels. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 606–615, 2003     

N‐glycosylation approach to glucose‐functionalized diamine and its use for protection‐free synthesis of polyurea bearing glucoside pendant

A glucose‐functionalized diamine was prepared and used as a new monomer for polyurea synthesis. The diamine was prepared by N‐glycosylation of 1,6‐hexamethylenediamine with D ‐glucose. Upon adding diisocyanates to the diamine, isocyanate reacted selectively with the amino groups, not with the hydroxyl groups of the glucose‐derived structure, to give the corresponding polyureas. The polyureas exhibited highly hydrophilic nature due to the presence of the glucose‐derived side chain. A ternary system consisting of the glucose‐functionalized diamine, piperazine, and diisocyanate gave the corresponding polyureas, where content of the glucose‐derived moiety was tunable by feed ratio between the diamine and piperazine. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis of novel asymmetric dendritic‐linear‐dendritic block copolymers via “living” anionic polymerization of ethylene oxide initiated by dendritic macroinitiators

The first synthesis of asymmetric dendritic‐linear‐dendritic ABC block copolymers, that contain a linear B block and dissimilar A and C dendritic fragments is reported. Third generation poly(benzyl ether) monodendrons having benzyl alcohol moiety at their “focal” point were activated by quantitative titration with organometallic anions and the resulting alkoxides were used as initiators in the “living” ring‐opening polymerization of ethylene oxide. The reaction proceeded in controlled fashion at 40–50 °C affording linear‐dendritic AB block copolymers with predictable molecular weights (M_w = 6000–13,000) and narrow molecular weight distributions (M_w/M_n = 1.02–1.04). The propagation process was monitored by size‐exclusion chromatography with multiple detection. The resulting “living” copolymers were terminated by reaction either with HCl/tetrahydrofuran or with a reactive monodendron that differed from the initiating dendron not only in size, but also in chemical composition. The asymmetric triblock copolymers follow a peculiar structure‐induced self‐assembly pattern in block‐selective solvents as evidenced by size‐exclusion chromatography in combination with multi‐angle light scattering. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5136–5148, 2007     

Multi‐walled carbon nanotubes encapsulated with polyurethane and its nanocomposites

Poly(acryloyl chloride) (PACl) was employed to enhance the surface of multi‐walled carbon nanotubes (MWCNTs). MWCNTs were first acid treated to generate hydroxyl groups on the surface, which was reacted with PACl to obtain an encapsulation. The numerous acryloyl chloride groups on the out layer were esterified with a proper amount of ethylene glycol (EG). Subsequently, 4,4′‐methylenebis (phenylisocyanate) (MDI) and 1,4‐butanediol (BDO) were introduced into the system, and a polyurethane (PU) layer was formed in situ. The formation of PU layers on MWCNTs was confirmed by Fourier transform infrared spectrometer (FTIR) and X‐ray photoelectron spectroscope (XPS). The morphology of encapsulated MWCNTs was observed by transmission electron microscope (TEM) and scanning electron microscope (SEM). Thermo gravimetric analysis (TGA) showed the grafted polymer fraction was up to 90%. On introducing the modified MWCNTs into a PU matrix, an increase in tensile strength by 60.6% and improvement in modulus by 6.3% over neat PU was observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4857–4865, 2008