Synthesis and characterization of biodegradable linear–hyperbranched barbell‐like poly(ethylene glycol)‐supported poly(lactic‐ran‐glycolic acid) copolymers through direct polycondensation

A series of biodegradable linear–hyperbranched barbell‐like poly(ethylene glycol) (PEG)‐supported poly(lactic‐ran‐glycolic acid) (PLGA) copolymers were synthesized with PEG, d ,l ‐lactic acid aqueous solution, glycolic acid and gluconic acid (Glu) under bulk conditions. The branching density of the hyperbranched section was varied by controlling the molar ratio of Glu to hydroxyl‐terminal groups of PEG ([Glu]/[OH] = 1, 3.5, 6.0, 8.5). Chemical structures of these copolymers were confirmed using NMR spectroscopy. The molecular weights were determined using ¹H NMR group analysis and gel permeation chromatography, both results being consistent with one another. The results of hydrolytic degradation indicate that these copolymers can degrade completely in no more than three weeks. The thermal properties were evaluated using differential scanning calorimetry and thermogravimetric analysis. The results indicate that the glass transition temperatures and melt temperatures of these copolymers are not above 50 °C. The self‐assembly behavior of the copolymers on hydrophilic surfaces was also investigated. The morphology of self‐assembly films made of the copolymers was observed using atomic force microscopy, and the results indicate that these copolymers exhibit more inhomogeneous and rough structural orientated films on a silicon wafer substrate with increasing branching densities. Due to the favorable biodegradability and biocompatibility of the PLGA and PEG, the results suggest new possibilities for these novel structural amphiphilic linear–hyperbranched barbell‐like copolymers as potential biomaterials. © 2013 Society of Chemical Industry     

The preparation and properties of segmented‐chain liquid crystalline polyesters based on 4,4′‐dihydroxybiphenyl by interfacial polycondensation

Thermotropic homopolyesters were prepared through interfacial polycondensation of 4,4′‐dihydroxybiphenyl with sebacoyl chloride. The optimal conditions of the process, in terms of the best yield, were studied through investigating the type of organic phase, amount of phase transfer agent, time and temperature of reaction, and volume ratio of aqueous to organic phase. The structure of the sample that had the best yield (53.235% ± 5%) was determined by means of elemental analysis, infrared spectra, and X‐ray. The effect of the molar ratio of the monomers on the yield and inherent viscosity was investigated. The inherent viscosity of the samples varied between 0.095 and 0.25 dL/g. The mesophase formed at elevated temperatures was studied by differential scanning calorimetry, polarized light microscopy, and depolarizing transmittance measurements. Our observations revealed that poly(4, 4′‐diphenyl sebacate), in contrast to previous reports that suggest this polymer is smectgenic, could produce nematic phase. It could be concluded that the chemical structure ordering of the poly(4, 4′‐diphenyl sebacate) plays a significant role in its liquid crystalline behavior. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1594–1606, 2005     

Improving lactic acid melt polycondensation: The role of co‐catalyst

A study on lactic acid polycondensation under melt conditions was carried out and a preliminary assessment revealed tin powder as a very good catalyst for poly(lactic acid) (PLA) synthesis by melt polycondensation while confirming previous information on SnCl₂ good performance. However, these catalysts also promoted side reactions leading to racemization and yellowing of the final polymer. The use of p‐toluenesulphonic acid (p‐TSA) or triphenylphosphine (PPh₃) as co‐catalysts proved to be very effective hindering colour formation and allowing synthesizing PLA samples with enhanced properties. The addition of these compounds to neat tin powder increased the PLA optical purity, whereas their addition to SnCl₂ speeded up the polymerization. A significant increase in molecular weight, from 32,500 to 52,000 g mol^?1, was recorded, with the new catalytic system SnCl₂/PPh₃ showing catalytic activity comparable with the one reported in the literature for SnCl₂/p‐TSA. Several characterization techniques were used for assessing polymer samples: the molecular weights were determined by SEC, thermal behavior measured by DSC, and racemization extent calculated from specific rotation measurements. UV/vis spectroscopy was confirmed as a powerful technique for evaluating yellowing of final polymers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Curing theory on the Aai–Bbj type polycondensation (III). The gelation range

By means of the gelation equation containing both inter- and intramolecular reaction parameters obtained by the authors, this paper deduces the gelation range of A_ai–B_bj type polycondensation. The experimental data are essentially in agreement with our theoretical results.     

Curing theory of the Aai–Bbj type polycondensation. (II) sol-gel distribution

An alternative way is proposed to approach the sol-gel distribution of A_ai–B_bj type polycondensation by taking into consideration intramolecular reaction. The equations deduced basically from the definition of the sol fraction and the chemical equilibrium of reactants in this paper can be reduced to those of Tang Au-chin's and Miller's expressions. Comparing experimental with theoretical values, we found that the results of this paper are closer to the real cases than those of other authors.     

Preparation and properties of flame-retardant polyphosphate esters: Low-temperature solution polycondensation of 3,3,′5,5′-tetrabromobisphenol AF and aryl phosphorodichloridates

This article describes the syntheses of aromatic polyphosphates from the reaction of various aryl phosphorodichloridates with 3,3′,5,5′-tetrabromobisphenol AF (TBPAF) in a chlorinated hydrocarbon solvent under low-temperature conditions. The new polyphosphates obtained were characterized by infrared, ¹³C and ³¹P nuclear magnetic resonance spectra, elemental analysis, inherent viscosity, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, limiting oxygen index, contact angle, and molar mass measurement. All of the polyphosphates obtained had high yields, and the inherent viscosities were in the range 0.12 - 0.15 dL g⁻¹. All of the polymers start degrading between 210 and 267°C and had 14 - 26% residual mass at 700°C in nitrogen. Polymer E, having a methoxy group in the side chain phenyl ring, showed better thermal stability than the other polymers. The X-ray diffraction patterns revealed that all of the polyphosphates were amorphous. These polyphosphates had glass transition temperatures between 140 and 154°C. Polymers obtained from TBPAF had excellent flame retardency, as indicated by high limiting oxygen index values in the range of 63 - 68. The water contact angles (θ_w) of all of the polyphosphates were in the range of 74 - 87°. The contact angles of polymers A and B were larger than those of other polyphosphates that contain more oxygen (polymers C and E) or bromine atoms (polymer D). © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 59–65, 1997     

Design,synthesis, and characterization of a potential flame retardant poly(lactic acid‐co‐pyrimidine‐2,4,5,6‐tetramine) via direct melt polycondensation

Directly starting from d ,l ‐lactic acid (LA) and pyrimidine‐2,4,5,6‐tetramine (PTA), the copolymer P(LA‐co‐PTA) as a novel potential solid compatible polymeric flame retardant is synthesized as designed via melt polycondensation. When the molar feed ratio LA/PTA is 60/1, the optimal synthetic conditions are discussed. After the prepolymerization at 140°C for 8 h, using 0.5 wt % stannous oxide as the catalyst, the melt copolymerization at 160°C for 4 h gives the copolymer with the biggest intrinsic viscosity 0.88 dL g^?1. The structures and properties of P(LA‐co‐PTA)s at different molar feed ratios are characterized by FT‐IR, ¹H‐NMR, ¹³C‐NMR, GPC, XRD, DSC, and TGA. The decomposition temperatures of P(LA‐co‐PTA)s are higher than these of homopolymer poly(d,l ‐lactic acid) (PDLLA). All copolymers have higher char yield than PDLLA, and the more PTA in the feed content, the higher char yield. What's more, there are some residues at 700–800°C, indicating that P(LA‐co‐PTA)s have good charring ability. When the monomer PTA is introduced into polylactic acid by chemical bonding as purine (PU) unit formed during the condensation, both the PTA's relatively higher nitrogen content and the PU's similar structure with flame retardant benzimidazole are beneficial to improve the thermal stability and charring ability, especially the latter. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40275.     

Catalyst free synthesis of poly(l‐lactic acid)–poly(propylene glycol) multiblock copolymers and their properties

A simple, green, and economical method for the synthesis of poly(l ‐lactic acid)–poly(propylene glycol) (PLLA–PPG) copolymers is put forward and a series of multiblock PLLA–PPG are synthesized with 1,6‐hexamethylene diisocyanate as chain extender of the melt polymerization. The effect of PPG content on the properties of PLLA–PPG copolymers is also investigated. The elongation at break of the resulting copolymer film with only 5% weight content PPG is 280%, and the tensile strength is 20 MPa. Dynamic mechanical analysis results demonstrated the existence of the shape memory effect for all the copolymers films and the shape recovery ratio of 101% is achieved for PLLA–PPG copolymer film with 5% weight PPG. The process for the synthesis of PLLA–PPG copolymers in the total absence of potentially toxic solvents and catalysts is analyzed, and the films of PLLA–PPG exhibit toughness and shape memory effect. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45299.     

Synthesis and characterization of new aromatic poly(amide–imide)s based on 4‐aryl‐2,6‐bis(4‐trimellitimidophenyl) pyridines

New diimide–dicarboxylic acids, ie 4‐phenyl‐2,6‐bis(4‐trimellitimidophenyl)pyridine and 4‐p‐biphenyl‐2,6‐bis‐(4‐trimellitimidophenyl)pyridine, were synthesized by the condensation reaction of 4‐phenyl‐2,6‐bis(4‐aminophenyl)pyridine and 4‐p‐biphenyl‐2,6‐bis(4‐aminophenyl)pyridine with trimellitic anhydride in glacial acetic acid or dimethylformamide. The monomers were fully characterized by FT‐IR and NMR spectroscopies, and elemental analyses. A series of novel poly(amide–imide)s with inherent viscosities of 0.68–0.87 dl g^?1 was prepared from the two diimide–diacids with various aromatic diamines by direct polycondensation. The poly(amide–imide)s were characterized by FT‐IR and NMR spectroscopies. The λ_max data for the resulting poly(amide–imide)s were in the range of 260–292 nm. These polymers exhibited good solubilities in polar aprotic solvents. The 10 % weight loss temperatures are above 485 °C under a nitrogen atmosphere. Copyright © 2004 Society of Chemical Industry     

Synthesis and characterization of biodegradable crosslinked polymers from 5‐hydroxylevulinic acid and α,ω‐diols

Novel biodegradable chemically crosslinked polymers, poly(5‐hydroxylevulinic acid‐co‐α,ω‐diol)s (PHLA‐diols), were synthesized from 5‐hydroxylevulinic acid and α,ω‐diols and characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis. The gel content, swelling ratio, tensile properties, and hydrolytic degradation behaviors were also measured and assessed. The glass‐transition temperature of the PHLA‐diols could be adjusted within a wide range (?50 to 30°C) by the type and feed ratio of the diol. Because of the low glass‐transition temperature and crosslink structure, they exhibited certain elastic properties. The tensile modulus, strength, and elongation at break measured at 37°C were 1.4–6.3 MPa, 0.8–1.6 MPa, and 10–25%, respectively. These polymers could be hydrolytically degraded. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of polysiloxane–polyester copolymer by lipase‐catalyzed polycondensation

Polysiloxane–polyester copolymers have been synthesized for the first time by direct polycondensation of a series of diacids (butanedioic, hexanedioic, and octanedioic acid) and α,ω‐bis(3‐hydroxypropyl) polydimethylsiloxanes catalyzed with Novozyme‐435 in high yields (>90%) without the cleavage of Si? O bonds. The effects of monomer chain length, reaction temperature, and water removal method on the number–average molecular weight (M_n) of the resulted copolymers were investigated. Thermogravimetric and differential scanning calorimetry analyses indicated that the produced copolymer was more thermally stable than poly(1,8‐octyladipate) and the T_g was lowered to ?111°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Surface Properties of CaO (or BaO)–La2O3–MgO Catalysts and Their Performance in Oxidative Coupling of Methane

CaO–La₂O₃–MgO and BaO–La₂O₃–MgO catalysts with different compositions have been studied for their bulk and surface properties (viz. crystal phases, surface area, acidity/acid strength distribution, basicity/base strength distribution, etc.) and catalytic activity/selectivity in the oxidative coupling of methane (OCM) at different processing conditions (reaction temperature, 700–850°C; CH₄/O₂ ratio in feed, 3·0, 4·0 and 8·0 and GHSV, 102000 and 204000 cm³ g⁻¹ h⁻¹). The surface acidity and strong basicity of La₂O₃–MgO are found to be increased due to the addition of a third component (CaO or BaO), depending upon its concentration in the catalyst. The addition of CaO or BaO to La₂O₃–MgO OCM catalyst causes a significant improvement in its performance. Both the CaO- and BaO-containing catalysts show a high activity and selectivity at 800°C, whereas, the activity and selectivity of BaO-containing catalysts at 700°C is lower than that of CaO-containing catalysts. © 1997 SCI.     

Linear polymers with sulfur in the main chain III. Synthesis of polythioesters by polycondensation of bis(4,4′‐mercaptophenyl)sulfide with various acid dichlorides and their properties

Synthesis and properties of sulfur‐containing linear polythioesters derived from bis(4,4′‐mercaptophenyl)sulfide (MPS) and various acid dichlorides (AC) have been studied to evaluate the effect of the thioester group in comparison with corresponding linear polyesters. Polycondensations between MPS and azelaoyl chloride (AZC) chosen as a model reaction system were investigated under various conditions by solution polycondensation, to find optimal conditions to get high molecular weight and quantitative yield. The obtained polymer using chloroform as a solvent indicated the highest molecular weight, determined by gel permeation chromatography (GPC). Thus the polythioesters from MPS and AC were synthesized under the above‐mentioned conditions. The thermal properties of polythioesters including the MPS moiety were evaluated by thermogravimetry/differential thermal analysis (TG/DTA), and differential scanning calorimetry (DSC). Those indicated that the polythioesters including the MPS moiety were crystalline polymers with relatively high heat resistance. These polythioesters were found to show an odd–even effect with the glass transition temperature, melting point, and oxygen permeability based on the methylene numbers. The tensile strength and storage modulus decreased with the number of methylene units. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 508–515, 2005     

Synthesis of high molecular weight poly(L‐lactic acid) via melt/solid polycondensation: Intensification of dehydration and oligomerization during melt polycondensation

Melt/solid state polycondensation (MP/SSP) is a cost‐effective route for synthesis of high molecular weight poly(L ‐lactic acid) (PLLA). However, the reaction rates in its four stages need to be enhanced greatly and the reaction times to be shortened largely before the MP/SSP technology can be industrialized. In this study, a new catalyst addition policy, i.e., adding TSA at the dehydration stage and SnCl₂·2H₂O at the MP stage, and more appropriate temperature and pressure programs were presented and applied in the MP process of LLA. The presence of TSA from dehydration appeared very effective for speeding up the dehydration and oligomerization stages as well as depressing racemization in the whole MP process. The polymerization degree (X_n) of oligomer was clearly increased, and the reaction time was shortened to a great extent. Direct using reduced pressure was also very helpful for intensifying the dehydration stage, only leading to LLA loss as little as 2%. A PLLA with M_w of 44,000 and optical purity of 96.8% suitable for subsequent SSP was produced after dehydration for 2 h, oligomerization for 2 h and MP for 4 h under appropriate conditions. And an interesting strong dependence of the M_w of final PLLA product on the X_n of the oligomer was observed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Study of biodegradability of poly(δ-valerolactone-co-L-lactide)s

The biodegradability of poly(δ-valerolactone-co-L -lactide)s was studied both with enzymatic (lipase from Rhizopus arrhizus) and nonenzymatic hydrolyses. The hydrolyzability was evaluated by recording the amount of the hydrolyzed water-soluble products. The enzymatic hydrolysis was considerably affected by copolymer composition. The copolyester, the most susceptible to enzymatic hydrolysis, was the one containing a 90 mol % δ-valerolactone unit. The copolymers were also nonenzymatically hydrolyzed at 70°C. The results were similar to those of enzymatic hydrolysis, confirming the influence of copolymer composition on the hydrolyzability. However, the L -lactide rich copolymers were more susceptible to hydrolysis. These results suggest that poly(δ-valerolactone) is easily degraded by lipase, whereas poly(L -lactide) is degraded through simple hydrolysis. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 741–748, 1997     

Synthesis and characterization of novel biodegradable polymeric prodrugs containing 5‐fluorouracil and 4‐amino‐N‐(2‐pyrimidinyl) benzene sulfonamide terminal groups

To develop novel biodegradable polymeric prodrugs with target‐directing and drug‐active functional groups, a series of polymeric antitumor prodrugs containing sulfadiazine and 5‐fluorouracil terminal groups were prepared via the two‐step reaction of chlorinated poly(lactic acid) or chlorinated poly(lactic acid‐co‐glycolic acid) with potassium sulfadiazine (SF‐K) and 1,3‐dihydroxymethyl‐5‐fluorouracil. The synthesized polymers were characterized by means of infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, gel permeation chromatography, viscosity measurements, differential scanning calorimetry, and ultraviolet (UV) spectroscopy. The GA/LA value was varied, so that the effects of the comonomer content on the solubility, thermal properties, and degradable behaviors were examined respectively. It was found that introducing the GA units could increase the melting temperature (T_m), the hydrolytic degradation, and the hydrophilicity, while it decreased the glass transition temperature (T_g). The drug content of 5‐FU measured by UV spectra is 56.3 in maximum. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Hydroxymethylation and polycondensation reactions in urea–formaldehyde resin synthesis

Formaldehyde–urea (F/U) reaction products with molar ratios of 1.8, 2.1, and 2.4 were synthesized at pH 8.3, and the last one also at pH 4.5 using 45% formaldehyde aqueous solution. For obtaining the resin, the synthesis of F/U 2.1 was continued by acid‐catalyzed condensation at pH 4.5 and posttreatment with second part of U (F/U 1.05/1) at 70°C and pH 8.3. The products were analyzed using ¹³C‐NMR spectrometry. Higher excess of F increases the dihydroxymethyl content on account of smaller dimethylene ether content. Certain ¹³C chemical shifts in carbonyl and methylene region of spectra were assigned to trishydroxymethylurea, being the main trisubstituted urea compound in hydroxymethylated product. Acid catalyst promotes the formation of methylene groups by polycondensation of hydroxymethyl groups, against the background of similar content of dimethylene ethers in both catalytic conditions. The ratio of linear/branched chains is emphasized in characterizing the resin structure. Higher hydroxymethyl content in acid‐catalyzed polycondensation is an advantage of three‐step synthesis technology. The amount of binding methylene and dimethylene ether groups linked only to secondary amino groups can be increased by transhydroxymethylation with subsequent polycondensation in posttreatment with U in suitable reaction conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1673–1680, 2006     

Poly(L‐lactic acid)/silicone dioxide nanocomposites prepared via in situ melt polycondensation of L‐lactic acid in the presence of acidic silica sol: Dispersion stability of nanoparticles during dehydration/oligomerization

In this work, the stability of nanoparticles during the dehydration/oligomerization (D/O) stage in situ melt polycondensation of L ‐lactic acid to prepare poly(L ‐lactic acid) (PLLA)/SiO₂ nanocomposite was studied. The change in the appearance of the reaction mixture was tracked, and the resultant oligo(L ‐lactic acid) (OLLA)/SiO₂ and PLLA/SiO₂ nanocomposites were characterized by transmission electron microscopy, ¹H‐NMR, and light transmittance. The electric double layer and the grafted OLLA chains provided static and steric stabilities during the early and late phases, respectively. However, there existed an intermediate transitional phase with weak stability when the static stability was weakened, but sufficient steric stability had not yet been established; this led to soft or hard aggregation, depending on the SiO₂ loading and agitation conditions. At low or moderate SiO₂ loading (<5–10%), the soft aggregation could be depressed with appropriate agitation conditions and redispersed with the aid of gradually established steric interaction energy. Consequently, well‐dispersed PLLA/SiO₂ nanocomposites with SiO₂ loadings of 5 and 10% were successfully prepared by in situ melt polycondensation with an arc stirrer at 400 and 600 rpm, respectively, during the D/O stage. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

High‐molecular‐weight aliphatic polycarbonates by melt polycondensation of dimethyl carbonate and aliphatic diols: synthesis and characterization

Aliphatic polycarbonates (APCs) synthesized by polycondensation of dialkyl carbonates and aliphatic diols have often been used as precursors for the preparation of novel polyurethanes. However, they could not be applied in plastics directly because of poor mechanical properties caused by low molecular weight. In the work reported in this paper, three kinds of fairly high molecular weight (M_w ≥ 166 000 g mol^?1) APCs with narrow dispersity ( ) were successfully synthesized via a successive two‐step polycondensation of dimethyl carbonate and diols, using a novel TiO₂/SiO₂‐based catalyst. This process gave a high yield of above 85%. ¹H NMR spectra indicated that there was no detectable decarboxylation happening during polycondensation at high temperature. The effects of molecular weight on the mechanical properties of the APCs are discussed. APCs with M_w greater than 70 000 g mol^?1 showed useful mechanical properties. Especially, poly(butylene carbonate) and poly(hexamethylene carbonate) exhibited excellent tensile strengths of 34.1 and 40.0 MPa, respectively, when their M_w was ca 170 000 g mol^?1. All the APCs showed appreciable biodegradability under enzymatic degradation. Copyright © 2011 Society of Chemical Industry     

Enantioselective Aza‐Morita–Baylis–Hillman Reaction Using Aliphatic α‐Amidosulfones as Imine Surrogates

The bifunctional catalyst 6′‐deoxy‐6′‐acylamino‐β‐isocupreidine ( 1 ) served both as a base to trigger the in situ generation of N‐sulfonylimine from readily available α‐amidosulfones and as a chiral nucleophile to initiate the enantioselective aza‐Morita–Baylis–Hillman (aza‐MBH) reaction. α‐Methylene‐β‐amino‐β‐alkyl carbonyl compounds, difficultly accessible previously, can now be synthesized in excellent yields and enantioselectivities.