Heterotactic poly(N-isopropylacrylamide) prepared via radical polymerization in the presence of fluorinated alcohols

Radical polymerization of N-isopropylacrylamide in toluene at −40 °C in the presence of fourfold amounts of fluorinated alcohols was investigated. The ¹³C NMR analysis of the obtained polymers suggested that the addition of fluorinated alcohols induced heterotactic specificity in radical polymerization of NIPAAm, although syndiotactic poly(NIPAAm)s were obtained by adding alkyl alcohols as we have previously reported. To the best of our knowledge, this is the first synthesis of heterotactic poly(NIPAAm).     

Direct synthesis of syndiotactic-rich poly(N-isopropylacrylamide) via radical polymerization of hydrogen-bond-complexed monomer

Radical polymerization of N-isopropylacrylamide (NIPAAm) in toluene was investigated in the presence of hexamethylphosphoramide (HMPA). We succeeded in directly preparing syndiotactic-rich poly(NIPAAm), the syndiotacticity of which (r=70%) is the highest among those of radically-prepared poly(NIPAAm)s so far reported, by lowering polymerization temperature to −60 °C in the presence of a two-fold amount of HMPA. The NMR analysis revealed that the induced syndiotactic-specificity was ascribed to 1:1 complex formation between NIPAAm and HMPA. Furthermore, thermodynamic analysis described that the induced syndiotactic-specificity was enthalpically achieved.     

Hydrogen-bond-assisted isotactic-specific radical polymerization of N-isopropylacrylamide with pyridine N-oxide

Radical polymerization of N-isopropylacrylamide (NIPAAm) in CHCl₃ at low temperatures in the presence of pyridine N-oxide (PNO) was investigated. An isotactic poly(NIPAAm) with meso diad content of 61% was successfully prepared at −60 °C in the presence of a two-fold amount of PNO. Thermodynamic analysis suggested that the isotactic-specificity was entropically induced, probably due to conformational fixation near the propagating chain-end through coordination by PNO.     

A study of hydrogel thermal-dynamics using Fourier transform infrared spectrometer

A rapid and reliable method was presented for studying hydrogel dynamics/kinetics. Two temperature-sensitive hydrogels, poly-N-isopropylacrylamide (poly(NIPAAm)) and the copolymer of N,N-diethylacrylamide and sodium methacrylate (molar ratio=97:3, poly(NDEAAm-co-MAA)) were synthesized. The thermal-behaviors of the gels were studied through the absorbance intensities of both swollen water and gel frame components, and the peak positions of amide band along heating/cooling pathways under dynamic Fourier transform infrared (FTIR) probing. The results showed that the lower critical solution temperature (LCST) of poly(NIPAAm) is about 33-35 °C, which is consistent with reported value of ∼34 °C. Compared to poly(NIPAAm), poly(NDEAAm-co-MAA) has relatively continuous volume phase transition, starting at ∼35 °C and a better thermal-reversibility with similar swelling and deswelling profiles over a larger temperature range (10-80 °C for poly(NDEAAm-co-MAA) vs. 10-33 °C for poly(NIPAAm)). The H-bonding water along phase transition was also studied, showing a less reversibility of poly(NIPAAm) compared to poly(NDEAAm-co-MAA). In addition, FTIR spectrometer was also used to study the volume changes of poly(NDEAAm-co-MAA) under variations in environmental salinity.     

Effect of polymerization conditions on the syndiotactic-specificity in radical polymerization of N-isopropylacrylamide and fractionation of the obtained polymer according to the stereoregularity

Radical polymerization of N-isopropylacrylamide (NIPAAm) was examined in the presence of hexamethylphosphoramide (HMPA). The addition of an excess amount of HMPA induced syndiotactic-specificity that gradually enhanced as the feed monomer was consumed. The syndiotacticity of the obtained poly(NIPAAm)s was improved by increasing the [HMPA]₀/[NIPAAm]₀ ratio to five and prolonging the polymerization time to 96 h (racemo=72%). It was also revealed that more stereoregulated poly(NIPAAm) could be fractionated by reprecipitating the resulting polymers from hexane-THF mixture. This result suggested that more stereoregulated poly(NIPAAm) showed a lower solubility than less stereoregulated poly(NIPAAm)s. Furthermore, unusual hysteresis was observed in transmittance analysis of an aqueous solution of the fractionated syndiotactic poly(NIPAAm).     

Effect of a combination of hexamethylphosphoramide and alkyl alcohol on the stereospecificity of radical polymerization of N-isopropylacrylamide

Radical polymerization of N-isopropylacrylamide (NIPAAm) was investigated at low temperatures in the presence of both hexamethylphosphoramide (HMPA) and alkyl alcohols. Although HMPA and alkyl alcohols separately induced syndiotactic specificity in NIPAAm polymerization in toluene at low temperatures, a combination of HMPA and less bulky alkyl alcohols, such as methanol and ethanol, was found to induce isotactic specificity at −80 °C. NMR analysis of mixtures of NIPAAm, ethanol and HMPA suggested the formation of a 1:1:1 complex through O-H•••O=C and N-H•••O=P hydrogen bonding. It is believed that the steric effect of HMPA enhanced by cooperative hydrogen bonding was responsible for the combined effect of HMPA and alkyl alcohols in inducing isotactic specificity.     

‘Living’ radical polymerization of styrene mediated by spiro ring-substituted piperidinyl-N-oxyl radicals. The effect of the spiro rings on the control of polymerization

The bulk radical polymerizations of styrene (St) at 80-120 °C in the presence of 6-aza-7,7-dimethyl-9-hydroxyspiro[4.5]decane-6-yloxyl (1) and 1-aza-2,2-dimethyl-4-hydroxy[5.5]undecane-1-yloxyl (2) were studied. At 100 and 120 °C, the polymerizations were well controlled by those nitroxides to give poly(St)s with narrow polydispersities. On the other hand, the polymerization mediated by 2 at 80 °C showed a good ‘livingness’ of polymerization, but 1 had a poor ability to control the polymerization to give poly(St) with a broad polydispersity of 1.52. The rate constants (k_act) for the homolysis of the NO-C bond of the alkoxyamines prepared from 1 and 2 were measured at 333-373 K, and the A_acts and E_acts values were determined to be 2.8×10¹³ s⁻¹ and 128 kJ mol⁻¹ (1) and 4.0×10¹³ s⁻¹ and 125 kJ mol⁻¹ (2), respectively, from the Arrhenius plots. These results are compared with those for the structurally related piperidinyl-N-yloxyl radicals including TEMPO.     

Living radical polymerization of styrene mediated by a piperidinyl-N-oxyl radical having very bulky substituents

A new cyclic nitroxide 1 and the corresponding alkoxyamines 9 and 10 were synthesized and the polymerization of styrene (St) initiated with 10 was investigated. The NO-C bond of 9 is very weak, cleaving at room temperature. On the other hand, alkoxyamine 10 is stable at room temperature and the A_act and E_act for the NO-C bond homolysis were determined to be 1.4 × 10¹⁵ s⁻¹ and 124.5 kJ mol⁻¹, respectively. When the polymerization of St was carried out at 70 °C, the resultant poly(St) showed narrow polydispersities below 1.25. In the polymerization at 90 °C, the resulting poly(St) showed narrow polydispersity until 60% conversion, but M_w/M_n was rapidly increased above 60% conversion. On the other hand, the polymerization at 120 °C gave poly(St) with broad polydispersities. The unusual polymerization behavior was discussed on the basis of the SEC and ESR results.     

Effect of nitrobenzene on initiator-fragment incorporation radical polymerization of divinylbenzene with dimethyl 2,2′-azobisisobutyrate

The polymerization of divinylbenzene (DVB) with dimethyl 2,2′-azobisisobutyrate (MAIB) was conducted at 70 and 80 °C in benzene in the presence of nitrobenzene (NB) as a retarder. When the concentrations of DVB, MAIB, and NB were 0.45, 0.50, and 0.50 mol/l, respectively, the polymerization proceeded without any gelation to yield soluble polymers. The polymer yield (up to 65%) and the molecular weight (M_n=1.5-4.2×l0⁴ at 70 °C and 1.3-3.9×l0⁴ at 80 °C) increased with time. The polymer formed in the polymerization at 80 °C for 4 h consisted of the DVB units with (4 mol%) and without double bond (41 mol%), methoxycarbonylpropyl group as MAIB-fragment (48 mol%), and NB unit (7 mol%). Incorporation of such a large number of the initiator-fragments as terminal groups in a polymer molecule indicates that the polymer is of a hyperbranched structure. The polymer showed an upper critical solution temperature (40 °C on cooling) in an acetone-water [14:1 (v/v)] mixture. The results of MALLS and viscometric measurements and TEM observation supported that the polymers formed in the present polymerization have a hyperbranched structure. The polymerization system at 70 °C involved an ESR-observable nitroxide radical formed by the addition of polymer radical to the nitro group of NB. The polymerization was kinetically investigated in dioxane. The initial polymerization rate (R_p) at 70 °C was expressed by R_p=k[MAIB]^0.5[DVB]^0.9[NB]^−0.4. The kinetic results were explained on the basis of the reversible addition of polymer radical to NB and the termination between the polymer radical and the nitroxide radical. The overall activation energy of the polymerization was 27.8 kcal/mol.     

Synthesis, characterization and optical properties of fluorinated poly(aryl ether)s containing phthalazinone moieties

A series of novel fluorinated poly(aryl ether)s containing phthalazinone moieties (FPPEs) have been prepared by a modified synthetic procedure for optical waveguide applications. The obtained random copolymers exhibited excellent solubility in polar organic solvents, high glass transition temperatures (T_gs: 185-269 °C), good thermal stabilities (the temperatures of 1% weight loss: 487-510 °C) and good optical properties. By adjusting the feed ratio of the reactants, the refractive indices of TE and TM modes (at 1550 nm) could be well controlled in the range of 1.575-1.498 and 1.552-1.484, respectively. The optical losses of the FPPEs exhibited relatively low values (less than 0.27 dB/cm at 1310 nm). Additionally, the thermo-optic coefficient (dn/dT) values of the FPPEs at 1310 nm and 1550 nm (TE mode) ranged from −0.97 × 10⁻⁴ °C to −1.33 × 10⁻⁴ °C and from −0.96 × 10⁻⁴ °C to −1.29 × 10⁻⁴ °C, respectively.     

Polymerization of lactams, 95 Preparation of polyesteramides by the anionic polymerization of ε-caprolactam in the presence of poly(ε-caprolactone)

Preparation of polyesteramides-poly[(ε-caprolactam)-co-(ε-caprolactone)]s by anionic polymerization of ε-caprolactam in the presence of poly(ε-caprolactone) at 150 °C was studied in this paper. ε-Caprolactam magnesium bromide was used as an initiator of polymerization and polymeric materials containing 5-25 wt% ε-caprolactone units were obtained. Thermal methods (DSC and DMA) were employed for characterization of poly[(ε-caprolactam)-co-(ε-caprolactone)]s and their mechanical properties were also evaluated. By introducing the activator with N-acyllactam structure, the polymerization rate increased and it was possible to carry out the polymerization at 110 °C. Mechanical properties of polyesteramides were influenced by both the content of ε-caprolactone units incorporated into copolymer and polymerization temperature. The mechanism of incorporation of poly(ε-caprolactone) is discussed. The results show that it is not possible to restrict exchange transacylation reactions, progressing in the course of polymerization, by kinetic tools.     

Anionic polymerization of acrylates. XIV. Synthesis of MMA/acrylate block copolymers initiated with ester-enolate/tert-alkoxide complex

Diblock copolymers of methyl methacrylate (MMA) with 2-ethylhexyl, butyl, ethyl or tert-butyl acrylate (EtHA, BuA, EtA, t-BuA) have been prepared by the ligated anionic polymerization initiated with methyl 2-lithioisobutyrate (MIB-Li) in the presence of an excess of Li tert-butoxide (t-BuOLi) in toluene/THF mixture at −60 or −78 °C. The copolymers, prepared at −60 °C, show MWD with a hint of bimodality, indicating partial deactivation of the living PMMA upon addition of acrylic monomer. At −78 °C, the extent of this deactivation is distinctly lower, the formed block copolymers, in particular, poly(MMA-b-EtHA), have unimodal MWD and exhibit tails only in the lower-molecular-weight region. Poly(MMA-b-EtHA)s were extracted with acetonitrile dissolving PMMA; very small parts of the crude products dissolved, whereas prevailing parts remained as solids documenting thus formation of block copolymer in a high yield. Surprisingly, the highest amount of self terminated PMMA was found in block copolymerization of MMA with t-BuA at both the temperatures, the products of which had clearly bimodal MWDs. This finding is shortly discussed on the basis of relatively slow propagation of t-BuA in comparison with EtHA, BuA and EtA.     

Hyperbranched polymers from divinylbenzene and 1,3-diisopropenylbenzene through anionic self-condensing vinyl polymerization

Hyperbranched polymers were synthesized using anionic self-condensing vinyl polymerization (ASCVP) by forming ‘inimer’ (initiator within a monomer) in situ from divinylbenzene (DVB) and 1,3-diisopropenylbenzene (DIPB) using anionic initiators in THF at −40 °C. The reaction of equimolar amounts of DVB and nBuLi results in the formation of hyperbranched poly(divinylbenzene) through self-condensing vinyl polymerization (SCVP). The hyperbranched polymers were invariably contaminated with small amount of gel (<15%). No gelation was observed when using DIBP with anionic initiators. The presence of monomer-polymer equilibrium in the SCVP of DIPB restricts the growth of hyperbranched poly(DIPB). The inimer synthesized from DIPB at 35 °C undergoes intermolecular self-condensation to different extent depending on the nature of anionic initiator at −40 °C. The molecular weight of the hyperbranched polymers was higher when DPHLi was used as initiator. A small amount of styrene ([styrene]/[Li⁺]=1) was used to promote the chain growth by inducing cross-over reaction with styrene, and subsequent reaction of styryl anion with isopropenyl groups of inimer/hyperbranched oligomer. The hyperbranched polymers were soluble in organic solvents and exhibited broad molecular weight distribution (2<M_w/M_n<17).     

Synthesis of novel sulfonated polybenzimidazole and preparation of cross-linked membranes for fuel cell application

A novel sulfonated polybenzimidazole, sulfonated poly[2,2′-(p-oxydiphenylene)-5,5′-bibenzimidazole] (SOPBI), was successfully prepared by post-sulfonation reaction of the parent polymer, poly[2,2′-(p-oxydiphenylene)-5,5′-bibenzimidazole] (OPBI), using concentrated and fuming sulfuric acid as the sulfonating reagent at 80 °C, and the degree of sulfonation (DS) could be regulated by controlling the reaction conditions. No significant polymer degradation was observed in the post-sulfonation processes. Direct polymerization of 4,4′-dicarboxydiphenyl ether-2,2′-disulfonic acid disodium salt (DCDPEDS) and 3,3′-diaminobenzidine (DABz), however, resulted in insoluble gels either in polyphosphoric acid (PPA) or in phosphorus pentoxide/methanesulfonic acid (PPMA) in a ratio of 1:10 by weight reaction medium. The SOPBIs prepared by the post-sulfonation method showed good solubility in dimethyl sulfoxide (DMSO), high thermal stability, good film forming ability and excellent mechanical properties. Cross-linked SOPBI membranes were successfully prepared by thermal treatment of phosphoric acid-doped SOPBI membranes at 180 °C in vacuo for 20 h and the resulting cross-linked membranes showed much improved water stability and radical oxidative stability in comparison with the corresponding uncross-linked ones, while the proton conductivity did not change largely. Highly proton conductive (150 mS cm⁻¹, 120 °C in water) and water stable SOPBI membrane was developed.     

Super porous organic-inorganic poly(N-isopropylacrylamide)-based hydrogel with a very fast temperature response

Porous organic-inorganic (O-I) hydrogels showing a very fast temperature response, including very fast reswelling were prepared: only 6 s are needed for 72% deswelling (gel collapse) as well as for 72% reswelling. Both deswelling and reswelling are practically complete in 14 s. The gels were prepared from N-isopropylacrylamide (NIPA), N,N′-methylenebisacrylamide (BAA) and tetramethoxysilane (TMOS) by simultaneous radical polymerization and hydrolytic polycondensation of TMOS. The syntheses were carried out at temperatures below the lower critical solution temperature (LCST) of poly(NIPA) in two steps: during the first stage the temperature was held at T = +15 °C and during the second the temperature was lowered below the freezing point of the reaction mixture, T = −18 °C. The ice crystals, which grew during the second stage, served as the pore-forming agent. The best samples were obtained if the second stage was started shortly before the gel point of the reaction mixture. The introduction of the inorganic phase (silica) is necessary for the ability of fast reswelling and also results in a strong improvement of the hydrogels' mechanical properties, while the maximum swelling degree remains nearly unaffected.     

Living and block polymerization of α-olefins using a Ni(II)-α-diimine catalyst containing OSiPh2Bu groups

A new siloxy-substituted α-diimine compound and its corresponding Ni(II) complex, {bis[N,N′-(4-tert-butyl-diphenylsiloxy-2,6-dimethylphenyl)imino]acenaphthene}dibromonickel (6), were successfully synthesized and the molecular structure of 6 characterized by X-ray crystallography. The precatalyst 6 activated by methylaluminoxane (MAO) or diethylaluminum chloride (DEAC) was tested in the polymerization of ethylene, showed to be highly active (e.g. 2.2×10⁷ and 1.8×10⁷ g polymer (mol Ni.h.bar)⁻¹, respectively) and led to a branched polyethylene (ca. 35-55 branches/1000 C). The catalyst system 6/methylaluminoxane (MAO) catalyzes, at −11 °C, living polymerization of propylene, to a polypropylene showing a syndiotactic-rich microstructure (P_r=0.74). 1-Hexene was also successfully polymerized via a living process, both at −11 and +16 °C. The ¹³C NMR spectra of the poly(1-hexene)s obtained at room temperature show a microstructure almost exclusively composed by n-butyl and methyl branches, the latter being present in a much higher number. Diblock polypropylene-block-poly(1-hexene) and triblock poly(1-hexene)-block-poly(propylene-ran-1-hexene)-block-poly(1-hexene) copolymers have also been synthesized and characterized by GPC/SEC, DSC and NMR.     

Synthesis of nitrile and benzoyl substituted poly(biphenylene oxide)s via nitro displacement reaction

A series of substituted poly(biphenylene oxide)s (PBPOs) was synthesized via nucleophilic nitro displacement reactions. High molecular weight PBPO's with nitrile groups were effectively synthesized from the polymerization of A-B type monomers with K₂CO₃ as a base in N-methyl-2-pyrrolidinone (NMP) at 140 °C. The polymers are completely amorphous, soluble in polar aprotic solvents, and formed flexible films on solution casting. Para-linked PBPO with nitrile groups showed excellent thermal properties such as high 5% weight loss temperature above 530 °C and T_g at 241 °C which is higher than those of commercially available PPO™ (T_g=210 °C). The pendent nitrile groups of PBPO were easily transformed to carboxylic acid groups by acidic hydrolysis.     

Synthesis of sulfonated poly(arylene-co-naphthalimide)s as novel polymers for proton exchange membranes

A series of novel sulfonated poly(arylene-co-binaphthalimide)s (SPPIs) were successfully synthesized via Ni(0) catalytic coupling of sodium 3-(2,5-dichlorobenzoyl)benzenesulfonate and bis(chloronaphthalimide)s. Bis(chloronaphthalimide)s were conveniently prepared from 5-chloro-1,8-naphthalic anhydride and various diamines. Tough and transparent SPPI membranes were prepared and the electrolyte properties of the copolymers were intensively investigated as were the effects of different diamine structures on the copolymer characterisitics. The copolymer membrane Ia-80, with an ion exchange capacity (IEC) of 2.50 meq g⁻¹, displayed a higher proton conductivity, i.e. 0.135 S cm⁻¹ at 20 °C, as compared to Nafion 117 (0.09 S cm⁻¹, 20 °C). The copolymer membrane Id-70, containing 3,3′-dimethyl-4,4′-methylenedianiline (DMMDA) units, exhibited excellent stability toward water and oxidation due to the introduction of hydrophobic methyl groups on the ortho-position of the imido bond in the copolymer. The mechanical property of Id-70 remained virtually unchanged after immersing membrane in pressured water at 140 °C for 24 h. Furthermore, the introduction of aliphatic segment a hexane-1,6-diamine (HDA) in copolymer led to a significant increase in proton conductivity and water uptake with increasing temperature; the proton conductivity of the Ic-70 membrane reached 0.212 S cm⁻¹ at 80 °C, which was higher than Nafion 117 as well as of the membranes based on aromatic diamines at equivalent IEC values. Consequently, these materials proved to be promising as proton exchange membranes.     

Synthesis of polyether-based block copolymers based on poly(propylene oxide) and terephthalates

Poly(propylene oxide) (PPO) is a low reactive telechelic polyether and the synthesis of high molecular weight poly(propylene oxide)-based block copolymers was studied. The poly(propylene oxide) used was end capped with 20 wt % ethylene oxide and had a molecular weight of 2300 g/mol (ultra-low monol PEO-b-PPO-b-PEO). The type of terephthalic acid based precursors was varied: terephthalic acid, dimethyl terephthalate, diphenyl terephthalate, di(trifluoro ethyl) terephthalate, di(p-nitrophenyl) terephthalate) and terephthalic acid chloride. High molecular weight poly(propylene oxide) based segmented block copolymers were obtained with diphenyl terephthalate (inherent viscosity: 1.6 dl/g).The synthesis of polyether(ester-amide)s comprising PPO and isophthalamide-based segments was also studied by varying the polymerization temperature and time. High molecular weight poly(propylene oxide) block copolymers could be obtained if the reaction was carried out for 2 h at 250 °C under vacuum. Higher temperatures (280 °C) and longer times result in lower inherent viscosities, probably due to degradation of the polyether.     

Premium quality renewable diesel fuel by hydroprocessing of sunflower oil

Hydroprocessing of neat sunflower oil was carried out at 360-420 °C and 18 MPa over a commercial hydrocracking catalyst in a bench scale fixed bed reactor. In the studied experimental range, products consisted exclusively of hydrocarbons that differed significantly in composition. While the concentration of n-alkanes exceeded 67 wt.% in the reaction products collected at 360 °C, it decreased to just 20 wt.% in the product obtained at 420 °C. Consequently, the fuel properties of the latter product were very similar to those of standard (petroleum-derived) diesel fuel. Particularly, it exhibited excellent low-temperature properties (cloud point −11 °C; CFPP −14 °C). Reaction products obtained at 400 and 420 °C were blended into petroleum-derived diesel fuel in three concentration levels ranging from 10 to 50 wt.% and the fuel properties of these mixtures were evaluated. Diesel fuel mixtures containing the product of sunflower oil hydrocracking at 420 °C showed very good low-temperature properties including cloud point (−8 °C) and CFPP (−15 °C) that was further lowered to −25 °C due to addition of flow improvers.