Electrochemical polymerization of poly(o-anisidine) thin films: effect of synthesis temperature studied by cyclic voltammetry

The effect of temperature on the electrochemical synthesis of poly(o-anisidine) (POA) thin films has been investigated. The POA films were synthesized electrochemically under cyclic voltammetric conditions in aqueous solutions of H₂SO₄ at various temperatures between -6°C and 40°C. These films were characterized by cyclic voltammetry (CV), UV–visible spectroscopy and scanning electron microscopy (SEM). It has been found that the rate of polymer formation depends on the synthesis temperature and is highest at 15°C. The optical absorption spectra indicate a major peak at about 800nm and a shoulder at about 440nm independent of the synthesis temperature. The peak at about 800nm corresponds to the presence of the emeraldine salt phase of POA, while the latter may be attributed to the formation of radical cations. The absorbance and width of the peak at about 800nm is observed to increase at low synthesis temperatures. The POA film synthesized at 15°C shows predominant formation of the emeraldine salt phase of POA. The surface morphology as revealed by SEM, is observed to depend on the synthesis temperature, and is caused by different rates of polymer formation at different temperatures. © 1998 SCI.     

Studies of cyclic and linear poly(dimethylsiloxanes): 19. Glass transition temperatures and crystallization behaviour

Differential scanning calorimetry (d.s.c.) was used to investigate the thermal behaviour of cyclic and linear poly(dimethylsiloxanes) over the temperature range 103–298 K. Fractions of the polymers studied had number-average molar masses in the range 160 < M_n < 25 500 g mol^?1 and heterogeneity indices $\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{M}{}_{\mathrm{<mtext>n</mtext>}}\text{< 1.1}$ in most cases. D.s.c. was applied to measure the glass transition temperatures T_g cold crystallization temperatures T_c and polymer crystalline melting temperatures T_m of the oligomer and polymer fractions. Cyclic siloxanes [(CH₃)₂SiO]_x with number-average numbers of skeletal bonds n_n in the range 24 ≦ n_n ≦ 79 and linear siloxanes (CH₃)SiO[(CH₃)₂SiO]_ySi(CH₃)₃ with n_n in the range 10 ≦ n_n ≦ 40 were found not to crystallize. The T_g values of the linear siloxanes were found to be in agreement with values in the literature and they increased with increasing M_n. By contrast, the T_g values of the cyclics were found to decrease with increasing M_n.     

Synthesis and characterization of semi‐interpenetrating networks based on poly(dimethylsiloxane) and poly(vinyl alcohol)

Semi‐interpenetrating networks (Semi‐IPNs) with different compositions were prepared from poly(dimethylsiloxane) (PDMS), tetraethylorthosilicate (TEOS), and poly(vinyl alcohol) (PVA) by the sol‐gel process in this study. The characterization of the PDMS/PVA semi‐IPN was carried out using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and swelling measurements. The presence of PVA domains dispersed in the PDMS network disrupted the network and allowed PDMS to crystallize, as observed by the crystallization and melting peaks in the DSC analyses. Because of the presence of hydrophilic (? OH) and hydrophobic (Si? (CH₃)₂) domains, there was an appropriate hydrophylic/hydrophobic balance in the semi‐IPNs prepared, which led to a maximum equilibrium water content of ～ 14 wt % without a loss in the ability to swell less polar solvents. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Absolute online monitoring of acrylic acid polymerization and the effect of salt and pH on reaction kinetics

Using recently introduced Automatic Continuous Online Monitoring of Polymerization reactions (ACOMP), the kinetics of acrylic acid polymerization was studied. ACOMP yields the absolute weight‐averaged mass (M_w), monomer conversion, and other quantities. As the initiator concentration increased, it was shown that the rate increased and the M_w decreased as in regular free‐radical polymerization. The effect of salt on acrylic acid polymerization in an aqueous solution was investigated. The polymerization rate and M_w both decreased with an increasing salt concentration. ACOMP molecular weights were also compared with size‐exclusion chromatography on aliquots periodically withdrawn during the reaction, and good agreement was found. The effect of the pH on the rate and the molecular weight was also investigated, and when the medium pH was changed from 2 to 5 with sodium hydroxide, the rate and M_w both decreased as the pH increased. Light‐scattering results of reaction end products in the reference solvent showed that molecules synthesized at higher pH were in a more expanded form. When equimolar sodium hydroxide was added to the acrylic acid (pH ? 5) and sodium acrylate formed, adding salt did not effect the reaction kinetics of the poly(sodium acrylate); its effect on the products was a relatively minor decrease of M_w. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1352–1359, 2004     

Biodegradable blends of high molecular weight poly(ethylene oxide) with poly(3‐hydroxypropionic acid) and poly(3‐hydroxybutyric acid): a miscibility study by DSC,DMTA and NMR spectroscopy

The miscibility of high molecular weight poly(ethylene oxide) blends with poly(3‐hydroxypropionic acid) and poly(3‐hydroxybutyric acid) (P(3HB)) has been investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and high‐resolution solid state ¹³C nuclear magnetic resonance (NMR). The DSC thermal behaviour of the blends revealed that the binary blends of poly(ethylene oxide)/poly(3‐hydroxypropionic acid) (OP blends) were miscible over the whole composition range while the miscibility of poly(ethylene oxide)/poly(3‐hydroxybutyric acid) blends (OB blends) was dependent on the blend composition. OB blends were found to be partly miscible at the middle P(3HB) contents (25 %, 50 %) and miscible at other P(3HB) contents (10 %, 75 % and 90 %). Single‐phase behaviour for OP blends and phase separation behaviour for OB blends were observed from DMTA. The results from NMR spectroscopy revealed that the two components in the OP50 blend were intimately mixed on a scale of about 35 nm, while the domain sizes in the OB blend with a P(3HB) content of 50 % were larger than about 32 nm. © 2000 Society of Chemical Industry     

Interpenetrating polymer networks of poly(dimethylsiloxane): 1. Preparation and characterization

Model networks of ,ω-dihydroxy-poly(dimethylsiloxane) (PDMS) were prepared by tetrafunctional crosslinking agent tetraethyl orthosilicate (TEOS) and the catalyst stannous 2-ethylhexanoate. Hydroxylterminated chains of PDMS having molecular weights 15 × 10³ and 75 × 10³ g mol⁻¹ were used in the crosslinking reaction. Bimodal networks were obtained from a 50% (w/w) mixture of PDMS chains with M_n = 15 × 10³ and 75 × 10³ g mol⁻¹. A sequential interpenetrating network of these PDMS chains was also prepared. Physical properties of the elastomers were determined by stress-strain tests, swelling and extraction experiments, and differential scanning calorimetry measurements.     

Studies of cyclic and linear poly(dimethylsiloxanes): 18. Surface pressures of the monolayers in the plateau region

Measurements of the two-dimensional surface pressure π have been made as a function of average area per monomer A at areas too small to support a single monolayer, for films of cyclic and linear poly(dimethylsiloxane) (PDMS) spread on the surface of water at temperatures between 6°C and 31°C. The number-average numbers of monomer units were 10 to 196 for the rings and 10 to 1.2 × 10⁵ for the linear chains. The surface pressures were stable with time for films formed from molecules with more than 20 monomer units. For these films, two plateaux of surface pressure linked by a rounded step were observed for both rings and chains, and the step occurred at the same average area per monomer. However, although the levels of the plateaux were the same for films formed from all linear species, increases in levels of the plateaux with decreasing number of monomer units were observed for cyclic species. The temperature coefficient of the surface pressure was negative in all instances, suggesting that surface entropy is gained upon compression. The unstable films formed from the linear and cyclic decamers were also studied. The former displayed a step in the plateau region, the latter did not appear to. The present findings suggest that cyclic and linear PDMS with more than 20 monomer units collapse by a common mechanism. If the long-standing hypothesis that PDMS collapses by adopting a helical configuration is correct, this implies that rings with as few as 20 repeat units on the average coil into helices.     

Grafting of poly(acrylic acid) onto poly(amidoamine)-functionalized graphene oxide via surface-mediated reversible addition-fragmentation chain transfer polymerization

Graphene oxide was modified with third-generation poly(amidoamine) (PAMAM) to obtain dendrimer-grafted GO (DGO) with high content of functional groups. DGO's amine groups were conjugated with S-(thiobenzoyl)thioglycolic acid as proved by XPS and poly(acrylic acid) was grafted onto surface via RAFT polymerization (DGO@PAA). FT-IR results approved the synthesis of samples whereas TGA revealed 40.3% grafting of PAA. XRD patterns showed that with further modification, d-spacing increased. According to Raman spectra, modification resulted in more disordered structure whereas DGO@PAA showed a high value of I_D/I_G. Morphological studies were performed by SEM and TEM that showed a polymeric layer covered the surface of nanosheets.     

An experimental investigation of poly(vinyl chloride) emulsion polymerization: Effect of initiator and emulsifier concentrations on polymerization kinetics and product particle size

Effects of concentration changes in initiator species Na₂SO₃, (NH₄)₂S₂O₈ and CuSO₄, and emulsifier, ammonium stearate, on poly(vinyl chloride) (PVC) emulsion polymerization kinetics and on product particle size were experimentally investigated. It was observed that to obtain industrially significant rates and overall conversions, not only an optimum concentration ratio of Na₂SO₃/(NH₄)₂S₂O₈/CuSO ₄ must be used, but also the concentrations of these species must be above certain limits. Increasing the concentration of the emulsifier used did not influence the rate of polymerization, but led to increases in limiting conversions. Product particle size analyses indicate that average particle size is independent of initiator concentration and rate of initiation. An increase in the emulsifier concentration on the other hand appears to lead to an increase in number of particles in the system and thus promotes smaller particle sizes.     

A comprehensive single‐particle model for solid‐state polymerization of poly(L‐lactic acid)

We propose here, a comprehensive model for the solid‐state polymerization (SSP) of a low to moderate molecular weight (MW) prepolymer of lactic acid, to produce high MW poly(L ‐lactic acid) (PLLA). The reactions are rationally assumed to occur only in the amorphous region, and effective concentrations of end groups, vary with crystalinity, X_c, during SSP. We estimate byproduct diffusivities, D, using free volume theory. The effects of various parameters on the SSP of PLLA prepolymer have been examined with respect to the optimum MW, X_c and D. We introduce self‐consistently, scaling factors of ～ 0.27, in the experimental procedure, to determine via ¹⁹F‐NMR, concentrations of the end groups, after converting them to fluorinated ester groups. The relevant reaction rate constants are obtained by fitting to early time data from representative SSP experiments at 150°C, under high vacuum, on PLLA prepolymer powder (i.e., spherical geometry) of number average MW, M_n0 ～ 10,200 Da, which attains M_n ～ 150,000 Da, via SSP. The subsequent successful comparison of the model predictions with experimental data throughout the entire SSP duration indicates that the model is comprehensive and accounts for all the relevant phenomena occurring during the SSP to synthesize high MW PLLA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

溶液聚合法合成聚乳酸

研究了以L-乳酸为单体,以二苯醚和十氢萘为溶剂,用溶液聚合法合成聚乳酸。采用逐步减压、逐渐升温的工艺路线,二苯醚做溶剂,所得产物相对分子质量较高。探讨了反应过程中原料的干燥预处理、溶剂、反应时间、反应温度等因素对聚合产物相对分子质量的影响。结果表明,最佳的反应条件为:乳酸／二苯醚体积比2／3,氯化亚锡为催化剂,催化剂的质量分数0．5％(相对单体),在160℃下反应24 h。     

Polyurethane-polysiloxane interpenetrating polymer networks: 1. A polyether urethane-poly(dimethylsiloxane) system

The synthesis and properties of a polyether urethane network based on Adiprene L-100, of a poly(dimethylsiloxane) network and of nine interpenetrating polymer networks based on these polymers were investigated. To form the latter materials, the prepolymers were mixed and crosslinked simultaneously, but by separate mechanisms. Comparison of the network solubility parameters suggested marked incompatibility. Optical microscopy, dynamic mechanical analysis and the tensile testing indicated gross phase separation. From 90 to 50% of the polyether urethane component, this network was continuous and the poly(dimethylsiloxane) was present as dispersed phases. From 40 to 10% of the polyether urethane, the situation was reversed. Some degree of interchain mixing at phase boundaries was detected by ¹³C nuclear magnetic resonance spectroscopy.     

Preparation of poly(tert‐butyl acrylate)‐poly(acrylic acid) amphiphilic copolymers via radiation‐induced reversible addition–fragmentation chain transfer mediated polymerization of tert‐butyl acrylate

Poly(tert‐butyl acrylate) (PtBA) is a versatile hydrophobic macromolecule usually preferred in the development of new materials for a host of applications. PtBA homopolymers with well‐defined structure and controlled molecular weight in a wide range were successfully synthesized via radiation‐induced reversible addition–fragmentation chain transfer (RAFT) polymerization in the presence of a trithiocarbonate type RAFT agent. The polymerization of tBA was performed under ⁶⁰Co γ‐irradiation in the presence of 2‐(dodecylthiocarbonothioylthio)‐2‐methylpropionic acid (DDMAT) as the RAFT agent in toluene at room temperature with three [tBA]/[DDMAT] ratios (400, 600 and 1000) and different irradiation times. Radiation‐induced polymerization of tBA displayed controlled free radical polymerization characteristics: a narrow molecular weight distribution (M_w/M_n ~ 1.1), pseudo first order kinetics and controlled molecular weights. The system followed the RAFT polymerization mechanism even at very low amounts of RAFT agent ([tBA]/[DDMAT] = 1000), and molecular weights up to 113 900 with narrow dispersity (Ð =1.06) were obtained. PtBA was further hydrolysed into different amphiphilic PtBA‐co‐poly(acrylic acid) (PAA) copolymers by low (27.5%) and high (77.3%) degrees of hydrolysis. The pH sensitivity of the two copolymers was investigated by dynamic light scattering at pH 2 and pH 9 (above and below the pK_a value of PAA) and their hydrodynamic diameters and zeta potential values were determined. © 2020 Society of Chemical Industry     

Preparation of high‐molecular‐weight poly(L‐lactic acid)‐based polymers through direct condensation polymerization in bulk state

Poly(L ‐lactic acid‐co‐succinic acid‐co‐1,4‐butanediol) (PLASB) was synthesized by a direct condensation copolymerization of L ‐lactic acid, succinic acid (SA), and 1,4‐butanediol (BD) in bulk state using titanium(IV) butoxide (TNBT) as a catalyst. Weight average molecular weight (M_w) of PLASB increased from 3.5 × 10⁴ to 2.1 × 10⁵ as the content of SA and BD went up from 0.01 to 0.5 mol/100 mol of L ‐lactic acid (LA). PLASB having M_w in the range from 1.8 × 10⁵ to 2.1 × 10⁵ showed tensile properties comparable to those of commercially available poly(L ‐lactic acid) (PLLA). In sharp contrast, homopolymerization of LA in bulk state produced PLLA with M_w as low as 4.1 × 10⁴, and it was too brittle to prepare specimens for the tensile tests. M_w of PLASB synthesized by using titanium(IV)‐2‐ethyl(hexoxide), indium acetate, indium hydroxide, antimony acetate, antimony trioxide, dibutyl tin oxide, and stannous‐2‐ethyl 1‐hexanoate was compared with that of PLASB obtained by TNBT. Ethylene glycol oligomers with different chain length were added to LA/SA in place of BD to investigate effect of chain length of ethylene glycol oligomers on the M_w of the resulting copolymers. Biodegradability of PLASB was analyzed by using the modified Sturm test. Toxicity of PLASB was evaluated by counting viable cell number of mouse fibroblast cells that had been in contact with PLASB discs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 466–472, 2006     

Solution and solid state nuclear magnetic resonance investigation of poly(methylmethacrylate)/ poly(ethylene oxide) blends

It is well known that nuclear magnetic resonance spectroscopy (NMR) is a powerful method to characterize blends compatibility at the molecular level. In this work binary blends formed by poly(methylmethacrylate)/poly(ethylene oxide), PMMA/PEO, were investigated by different solution and solid state NMR techniques to obtain information on blends homogeneity and compatibility. It was characterized that the values of T₁^Hρ obtained by variable contact time and delayed contact time experiments, for each composition, were distinct and this fact suggests that regions with different molecular mobilities exist, as a consequence of blending interaction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2955–2958, 2003     

Study on the kinetics of transesterification reaction between poly(ethylene terephthalate) and its copolyesters

Polyethylene terephthalate (PET) was blended with two kinds of co[poly(ethylene terephthalate-p-oxybenzoate)] (POB–PET) copolyester, designated as P46 and P64, respectively. The PET and POB–PET copolyester were combined in the ratios of 85/15, 70/30, and 50/50. The blends were melt mixed in a Brabender Plasticorder at 275, 285, and 293°C for different amounts of time. The transesterification reactions during the melt mixing processes of PET with POB–PET copolyester blends were detected by proton nuclear magnetic resonance analysis. The values of the rate constants are a function of temperature and the composition of blends. The transesterification reactions that may occur during the melt mixing processes have been discussed also. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2727–2732, 1999     

Effect of temperature,solvent, Lewis acid and additives on the polymerization of tert‐butyl vinyl ether using Lewis acid‐induced N‐methyleneamines as cationic initiators

N‐Methyleneamines, formed by treating 1,3,5‐trimethylhexahydro‐1,3,5‐triazines with Lewis acids, have been shown to be capable initiators in the cationic polymerization of tert‐butyl vinyl ether, yielding polymers with amine functionality at the chain ends. Previous work was limited to titanium(IV) chloride (TiCl₄) as the Lewis acid in dichloromethane solvent at 0 °C (with resulting polymers possessing relatively broad polydispersity index (PDI) values near 2), while this contribution details the effect of reaction parameters on the polymeric products; specifically, the role of temperature, solvent, Lewis acid and additives. Ultimately, performing the polymerization at ?78 °C in dichloromethane with TiCl₄ as the Lewis acid and tetra‐n‐butylammonium chloride (nBu₄NCl) as the additive afforded the best control over the system, with polymers formed possessing low PDI values (<1.2). Dramatic changes in number‐average molecular weight and PDI were observed in polymers formed by initiating systems of Lewis acid‐induced N‐methyleneamines, with temperature, solvent, Lewis acid and additives all playing a role. By varying single parameters, optimization of the system was achieved. Copyright © 2009 Society of Chemical Industry     

Zwitterionic ring opening polymerization of lactide by metal free catalysts: Production of cyclic polymers

Tailor made N‐heterocyclic carbene (NHC) catalyst precursors namely (+) and (?) 1‐methyl‐3‐menthoxymethyl imidazolium chloride have been synthesized in high yield with a literature modified procedure. A reaction of catalyst precursor with potassium tert butoxide in situ generates the NHC catalyst. The zwitterionic ring opening polymerization of lactide (LA) mediated by a catalytic system composed of NHC catalyst at 25°C under argon atmosphere led to a cyclic poly(lactide) of a high molecular weight with a narrow molecular weight distribution. The cyclic poly(lactide) was characterized by NMR spectroscopy, Gel Permeation Chromatography (GPC) and Matrix‐assisted laser desorption ionization‐time of flight mass spectrometry (MALDI‐TOF MS). The NHC catalysts are active for lactide polymerization in the presence of air and elevated temperatures at 55°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and thermal properties of poly(methyl methacrylate)‐poly(L‐lactic acid)‐poly(methyl methacrylate) tri‐block copolymer

Poly(methyl methacrylate)‐poly(L ‐lactic acid)‐poly(methyl methacrylate) tri‐block copolymer was prepared using atom transfer radical polymerization (ATRP). The structure and properties of the copolymer were analyzed using infrared spectroscopy, gel permeation chromatography, nuclear magnetic resonance (¹H‐NMR, ¹³C‐NMR), thermogravimetry, and differential scanning calorimetry. The kinetic plot for the ATRP of methyl methacrylate using poly(L ‐lactic acid) (PLLA) as the initiator shows that the reaction time increases linearly with ln[M]₀/[M]. The results indicate that it is possible to achieve grafted chains with well‐defined molecular weights, and block copolymers with narrowed molecular weight distributions. The thermal stability of PLLA is improved by copolymerization. A new wash‐extraction method for removing copper from the ATRP has also exhibits satisfactory results. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Syntheses and thermal properties of poly(hydroxy)urethanes by polyaddition reaction of bis(cyclic carbonate) and diamines

In this study, we synthesized poly(hydroxy)urethanes by the polyaddition reaction of bis(cyclic carbonate) and diamine. Bis(cyclic carbonate) was prepared from diglycidyl ether based on bisphenol S and carbon dioxide. Thermal properties and solubilities of the poly(hydroxy)urethanes of five different diamines were compared. The thermal properties of the poly(hydroxy)urethanes depended on the structure of the diamine as well as the structure of the monomer. These poly(hydroxy)urethanes were soluble only in aprotic solvents because of the hydrophilic character of the hydroxy group. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2735–2743, 2001