Polyurethane elastomers based on amphiphilic poly(caprolactone)‐b‐poly(butadiene)‐b‐poly(caprolactone) triblockcopolyols

Hydroxyl‐terminated poly(butadiene) (HTPB; M_n = 2100 g mol⁻¹) was capped with 30 and 60 wt % of ɛ‐caprolactone to reach amphiphilic triblock copolymers in form of capped poly(butadiene) CPB. The former (CPB30; M_n = 3300 g/mol) is amorphous with a glass temperature of −56 °C. CPB60 (M_n = 4000 g mol⁻¹) is semi‐crystalline with a melting point of 50 °C and a glass transition at −47 °C. The CPBs, HTPB and polycaprolactone diol (M_n = 2000 g mol⁻¹) were used as soft segment components in the preparation of polyurethane elastomers (PUE), using a 1/1 mixture of an MDI prepolymer and uretonimine modified MDI, and hard phase components in form of 1,3‐propane diol, 1,4‐butane diol, and 1,5‐pentane diol. CPB‐based elastomers with 1,4 butane diol (8 wt %) show hard domains as fringed aggregates with a better connection to the continuous phase than the HTPB‐based PUE. The soft segment glass transition temperature (T_g) is at −28 °C for HTPB‐based PUE and at −43 °C for those of CPB. The tensile strength of the CPB30&60‐based PUE is found between 20 and 30 MPa at an elongation at break of 400% and 550%, respectively. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1162–1172     

A three parameter kinetic model of formation of linear polyurethane from 2,4‐toluenediisocyanate and butane‐1,4‐diol

A model of linear isothermal polymerization of two bi‐functional monomers, one of which has alike functional groups of different reactivities, is presented. The model has been applied to the polymerization of 2,4‐toluenediisocyanate (TDI)^a and butane‐1,4‐diol carried out in solution at 86 or 101°C. The rate constant K of the reaction between an isocyanate group in position 4 of TDI and a hydroxy group, the ratio κ of reactivities of groups in position 4 relative to that in position 2, and the ratio k_φ of reactivities of an isocyanate group in the monomer relative to that at the end of an oligomer chain, have been evaluated from experimental data to be 6.51·10^–4 dm³·mol^–1·s^–1, 1.47, and 1.55 at 86°C, and 17.2·10^–4 dm³·mol^–1·s^–1, 1.55, and 1.62 at 101°C, respectively.     

Preparation of silicone‐graft copolymers by homogeneous radical copolymerization in supercritical carbon dioxide

Copolymerizations of 1,1‐dihydroperfluorooctyl methacrylate (FOMA; M₁) and methacryloxypropyl‐terminated polydimethylsiloxane [M‐PDMS (M_n = 5.9 K); M₂] and homopolymerization of M‐PDMS in supercritical CO₂ are described. The homopolymerization of M‐PDMS proceeded homogeneously without difficulty to produce oligomers (M_n = 30 K). The copolymerizations of FOMA and M‐PDMS also proceeded homogeneously over a wide monomer feed ratio. The ratio of M‐PDMS incorporated into the copolymer obtained was almost equal to the monomer feed ratio even up to the high conversion. The reactivity ratio r₁ was determined to be 1.66. DSC examination of the copolymers indicated a microphase‐separated morphology consisting of poly‐FOMA (PFOMA) and PDMS domains for all copolymer compositions. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1139–1145, 2000     

Synthesis and thermal transition behavior of model thermoplastic polyurethanes containing MDI/butanediol‐based monodisperse hard segments

Amine‐terminated monodisperse hard segments (MDHSs) containing two to four 4,4′‐methylenebis (phenyl isocyanate) extended by 1,4‐butanediol have been synthesized using carboxybenzyl protecting‐deprotecting strategy. Pure MDHSs in large scale were obtained in good yield and their structures were confirmed by ¹H‐, ¹³C‐NMR spectroscopy and GPC‐MALLS. Differential scanning calorimetry (DSC) showed that as the hard segment (HS) size increased, the melting and glass transition temperature and the change of heat capacity at glass transition of ethyl capped MDHSs increased. Model thermoplastic polyurethanes (TPUs) were synthesized using the reaction of bischloroformate of poly (tetramethylene oxide) (PTMO) diol or polyisobutylene (PIB) diol with amine‐terminated MDHSs. X‐ray diffraction results indicated the amorphous structure of model TPUs. DSC revealed HS related endotherms, regardless of SS, which were attributed to the local ordering of the HSs. Additional endotherms in PTMO based model TPUs might arise from the dissociation of hydrogen bonding between PTMO and HSs. The lower T_g in model TPUs compared to the polydisperse analogues observed by dynamic mechanical analysis (DMA) indicated higher microphase separation of monodisperse HSs. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3171–3181     

Poly(N‐vinylpyrrolidone)–polydimethylsiloxane amphiphilic ABA triblock copolymers

Triblock copolymers of N‐vinylpyrrolidone (NVP) and polydimethylsiloxane (PDMS) were synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization using two different types of difunctional telechelic PDMS‐based dixanthate macroinitiators. The incorporation of PDMS into the triblock copolymers was evidenced by ¹H NMR spectroscopy and varied between 4 mol % and as high as 20 mol %, dependent on reaction time and monomer conversion. The copolymer homogeneity was characterized in terms of molecular weight distribution determined by GPC to estimate the level of control over the chain length. Monomodal molecular weight distributions were observed, and ¹H NMR spectroscopy indicated the copolymers had number average molecular weights (M_n) ranging between 28,000 and 160,000 g/mol. In addition, thin film phase separation and critical micelle concentrations for these copolymers were analyzed via transmission electron microscopy and surface tension measurements, respectively. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3387–3394     

Synthesis of a novel hybrid liquid‐crystalline rod–coil diblock copolymer

A series of novel rod–coil diblock copolymers on the basis of mesogen‐jacketed liquid‐crystalline polymer were successfully prepared by atom transfer radical polymerization from the flexible polydimethylsiloxane (PDMS) macroinitiator. The hybrid diblock copolymers, poly{2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene}‐block‐polydimethylsiloxane, had number‐average molecular weights (M_n's) ranging from 9500 to 30,900 and relatively narrow polydispersities (≤1.34). The polymerization proceeded with first‐order kinetics. Data from differential scanning calorimetry validated the microphase separation of the diblock copolymers. All block copolymers exhibited thermotropic liquid‐crystalline behavior except for the one with M_n being 9500. Four liquid‐crystalline diblock copolymers with PDMS weight fractions of more than 18% had two distinctive glass‐transition temperatures. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1799–1806, 2003     

Soft nanoparticles assembled from linear poly(ethylene glycol) and linear brush polydimethylsiloxane diblock copolymers

A series of novel amphiphilic diblock copolymers composed of hydrophilic linear poly(ethylene glycol) (PEG) and linear brush hydrophobic polydimethylsiloxane (PDMS) were synthesized. Three different molecular weights of monomethyl ether PEG were initially functionalized with 2‐bromoisobutyryl bromide to afford macroinitiators suitable for atom‐transfer radical polymerization. The macroinitiators were characterized by gel permeation chromatography, ¹H and ¹³C nuclear magnetic resonance spectroscopic analysis and matrix‐assisted laser desorption ionization time‐of‐flight mass spectroscopy. The three different molecular weight macroinitiators were then chain extended with monomethacryloxypropyl‐terminated PDMS and photoactive 2‐(methylacyloyloxy)ethyl anthracene‐9‐carboxylate in different molar ratios to afford a series of photoresponsive amphiphilic diblock copolymers with high conversions. Self‐assembly of these linear–linear brush diblock copolymers in N,N‐dimethylformamide afforded nanoparticles with hydrodynamic diameters (d_H) ranging from 41 to 268 nm, as determined by dynamic light scattering analysis. Crosslinking and stabilization of the nanoparticles was achieved via [4+4] photodimerization of the anthracene moieties upon exposure to UV radiation at 365 nm with the reverse reaction studied at a wavelength of 254 nm. Transmission electron microscopy revealed that the self‐assembled nanoparticles and their crosslinked derivatives had spherical morphologies. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1251–1262     

One pot synthesis and gelation studies of amphiphilic triblock polyurethanes

This article shows a generalized synthetic strategy to make amphiphilic ABA type triblock polyurethane (PU) in a SINGLE reaction pot. This is achieved by condensation polymerization between a hydrophobic diol and a di‐isocyanate in the presence of a polyethylene glycol monomethyl ether (M_w = 2000 or 5000 g mol^?1) as mono‐functional impurity. Using different ratios of the three reactants with a fixed parameter such that the total concentration of –OH = isocyanate, a series of PUs are produced with both the ends capped with PEG. These polymers show facile gelation ability in solvents like dimethyl formamide, dimethyl sulfoxide, and dimethyl acetamide by H‐bonding interaction among the urethane groups. A comprehensive structure–property relationship study reveals importance of the right balance between the weight fractions of the soft and hard segments in self‐assembly and efficient gelation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2502–2508     

Synthesis and characterization of model diblock copolymers of poly(dimethylsiloxane) with poly(1,4‐butadiene) or poly(ethylene)

Model diblock copolymers of poly(1,4‐butadiene) (PB) and poly(dimethylsiloxane) (PDMS), PB‐b‐PDMS, were synthesized by the sequential anionic polymerization (high vacuum techniques) of butadiene and hexamethylciclotrisiloxane (D₃) in the presence of sec‐BuLi. By homogeneous hydrogenation of PB‐b‐PDMS, the corresponding poly(ethylene) and poly(dimethylsiloxane) block copolymers, PE‐b‐PDMS, were obtained. The synthesized block copolymers were characterized by nuclear magnetic resonance (¹H and ¹³C NMR), size‐exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and rheology. SEC combined with ¹H NMR analysis indicates that the polydispersity index of the samples (M_w/M_n) is low, and that the chemical composition of the copolymers varies from low to medium PDMS content. According to DSC and TGA experiments, the thermal stability of these block copolymers depends on the PDMS content, whereas TEM analysis reveals ordered arrangements of the microphases. The morphologies observed vary from spherical and cylindrical to lamellar domains. This ordered state (even at high temperatures) was further confirmed by small‐amplitude oscillatory shear flow tests. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1579–1590, 2006     

Visible light‐induced thiol‐ene reaction: A new strategy to prepare Α,ω‐dithiol and Α,ω‐divinyl telechelic polythiolether oligomers

A new strategy is developed to prepare both α,ω‐dithiol and α,ω‐divinyl linear telechelic polythiolether oligomers by visible light induced thiol‐ene chemistry in the presence of a fac‐Ir(ppy)₃ photoredox catalyst. Polythiolether oligomers of well‐defined end groups and controlled molecular weights have been successfully synthesized at varying monomer molar ratios of 1,4‐benzenedimethanethiol (BDMT) to diethylene glycol divinyl ether (DEGVE). ¹H NMR and MALDI‐TOF MS analyses demonstrate that as‐prepared polythiolethers possess high end‐group fidelity, which is further supported by the successful polyaddition of polythiolethers bearing α,ω‐dithiol and α,ω‐divinyl groups. For example, with the α,ω‐dithiol‐ (M_n = 1900 g mol^?1, PDI = 1.25) and α,ω‐divinyl‐terminated (M_n = 2000 g mol^?1, PDI = 1.29) polythiolethers as macromonomers, the molecular weight of resulting polythiolether is up to 7700 g mol^?1 with PDI as 1.67. The reactivity of the terminal thiol group is further confirmed by the addition reaction with N‐(1‐pyrenyl)maleimide. UV‐vis spectra and fluorescene measurements suggest that fac‐Ir(ppy)₃ undergo a redox quenching process reacted with BDMT to generate thiyl free radicals. With these results, the mechanism of the thiol‐ene reaction catalyzed by photoredox catalyst is proposed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 740–749     

Synthesis,self‐assembly,and thermosensitivity of amphiphilic POEGMA‐PDMS‐POEGMA triblock copolymers

In this article, the synthesis and self‐assembly of a novel well‐defined biocompatible amphiphilic POEGMA‐PDMS‐POEGMA triblock copolymer were studied. The copolymer was synthesized by atom transfer radical polymerization of oligo(ethylene glycol) methyl ether methacrylate (OEGMA) using α,ω‐dibromo polydimethylsiloxane macroinitiator (Br‐PDMS‐Br). Br‐PDMS‐Br was synthesized through the esterification of α,ω‐hydroxypropyl polydimethylsiloxane and 2‐bromoisobutyryl bromide. The structures of the copolymers were confirmed by proton nuclear magnetic resonance spectroscopy, and gel permeation chromatography. The copolymers showed reversible aggregation in response to temperature cycles with a lower critical solution temperature (LCST) between 61 and 66 °C, as determined by ultraviolet‐visible spectrophotometry and dynamic light scattering. The LCST values increased in proportion to the length of the hydrophilic block and were lower than that of the POEGMA homopolymer. The self‐assembly behavior of the copolymers in aqueous solution was investigated by fluorescence spectroscopy and transmission electron microscopy. The critical micelle concentration value (1.08–0.26 10^?6 mol L^?1) decreased as the length of the POEGMA chain increased. The POEGMA‐PDMS‐POEGMA copolymers can easily self‐assemble into spherical micelles in aqueous solution. Such biocompatible block copolymers may be attractive candidates as ‘‘smart'' thermo‐responsive drug delivery systems. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2684‐2691     

Polyimide polydimethylsiloxane triblock copolymers for thin film composite gas separation membranes

This article demonstrates the successful fabrication of thin‐film‐composite (TFC) membranes containing well‐defined soft‐hard‐soft triblock copolymers. Based on “hard” polyimide (PI) and “soft” polydimethylsiloxane (PDMS), these triblock copolymers (PDMS‐b‐PI‐b‐PDMS), were prepared via condensation polymerization, and end‐group allylic functionalization to prepare the polyimide component and subsequent “click” coupling with the soft azido functionalized PDMS component. The selective layer consisted of pure PDMS‐b‐PI‐b‐PDMS copolymers which were cast onto a precast crosslinked‐PDMS gutter layer which in turn was cast onto a porous polyacrylonitrile coated substrate. The TFC membranes' gas transport properties, primarily for the separation of carbon dioxide (CO₂) from nitrogen (N₂), were determined at 35 °C and at a feed pressure of 2 atm. The TFC membranes showed improvements in gas permselectivity with increasing PDMS weight fraction. These results demonstrate the ability for glassy, hard polymer components to be coated onto otherwise incompatible surfaces of highly permeable soft TFC substrates through covalent coupling. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3372–3382     

Conformationally restricted linear polyurethanes from acetalized sugar‐based monomers

Linear polyurethanes based on sugar monomers having D ‐gluco, galacto, and D ‐manno configurations and their secondary hydroxyl groups protected as bicyclic acetals, have been prepared by polyaddition reaction of these diol monomers to hexamethylene diisocyanate ( HMDI ) and 4,4′‐methylene‐bis(phenyl isocyanate) ( MDI ). The new polyurethanes seem to be amorphous materials, except that obtained from 2,3:4,5‐di‐O‐methylene‐galactitol and HMDI. Weight‐average molecular weights, determined by GPC, were in the range 16,000–115,200. TGA analyses indicated that the thermal stability of these bicyclic polyurethanes is comparable to those based on the isosorbide; both the onset and the maximum rate decomposition temperatures increased significantly with respect to the polyurethanes based on acyclic sugar monomers. The presence of the acetalized alditol units in the polyurethanes also increased the T_gs as compared with their acyclic analogs. Deacetalization of the polyurethanes containing di‐O‐isopropylidene‐D ‐mannitol units yielded the polyhydroxylated polymers in good yields, without apparent degradation of the polymer chain. These hydroxylated polymers showed an enhanced hydrophilicity and degradability and lower T_gs and thermal stability than their parent acetalized polyurethanes. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Well‐defined PE‐b‐PDMS diblock copolymers via the combination of thiol‐ene click and esterification reactions: Facile synthesis and compatibilization for HDPE/silicone oil blends

Well‐defined diblock copolymers of linear polyethylene (PE) and poly(dimethylsiloxane) (PDMS) have been synthesized through a facile route combining the thiol‐ene click chemistry of vinyl‐terminated polyethylene (PE‐ene) and the sequential esterification reaction. The resulting diblock copolymers are characterized by ¹H NMR, FT‐IR, DSC, TGA, and TEM. In addition, the PE‐b‐PDMS diblock copolymers have been evaluated as compatibilizers in the blends of high‐density polyethylene (HDPE) and silicone oil. The morphological analysis and mechanical properties demonstrate that the compatibilized blends with low loading concentration of PE‐b‐PDMS display significant improvements in modulus of elasticity and elongation at break as compared to the uncompatibilized binary blends. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3205–3212     

Polymethylene‐block‐polystyrene copolymers: A new synthetic approach using a combination of polyhomologation and reversible addition‐fragmentation chain‐transfer polymerization and their microfibers and microspheres fabricated through electrospinning process

Well‐defined polymethylene‐block‐polystyrene (PM‐b‐PS) diblock copolymers were synthesized via a combination of polyhomologation of ylides and reversible addition‐fragmentation chain‐transfer (RAFT) polymerization of styrene. Trithiocarbonate‐terminated polymethylenes (PM‐TTCB) (M_n = 1400 g mol^?1; M_w/M_n = 1.09 and M_n = 2100 g mol^?1; M_w/M_n = 1.20) were obtained via an esterification of S?1‐dodecyl‐S′‐(α,α′‐dimethyl‐α″‐acetate) trithiocarbonate with hydroxyl‐terminated polymethylene synthesized via polyhomologation of ylides followed by oxidation. Then, a series of PM‐b‐PS (M_n = 5500–34,000 g mol^?1; M_w/M_n = 1.12–1.25) diblock copolymers were obtained by RAFT polymerization of styrene using PM‐TTCB as a macromolecular chain‐transfer agent. The chain structures of all the polymers were characterized by proton nuclear magnetic resonance (¹H NMR), gel permeation chromatography, and Fourier transform infrared spectroscopy. The thiocarbonylthio end‐group of PM‐b‐PS was transformed into thiol group by aminolysis and confirmed by UV–vis spectroscopy. In addition, microfibers and microspheres of such diblock copolymers were fabricated by electrospinning process and observed by scanning electron microscopy (SEM). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2892–2899     

Novel copolymer networks via the combination of polyaddition and anionic polymerization

A two‐step synthetic route to novel copolymer networks, consisting of polymethacrylate and polyacetal components, was developed by combining the polyaddition and anionic polymerization techniques. The functional polymethacrylates containing hydroxyl or vinyloxyl side groups were used as crosslinkers. They were anionically synthesized as follows: the copolymer of 2‐hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) was prepared by the anionic copolymerization of 2‐(trimethylsiloxy)ethyl methacrylate and MMA, followed by hydrolysis. The copolymer poly(HEMA‐co‐MMA) thus obtained possessed a hydroxyl group in each of its HEMA units. Another kind of vinyloxyl‐containing (co)polymer was prepared by the anionic homopolymerization of 2‐(vinyloxy)ethyl methacrylate (VEMA) or its copolymerization with MMA. The resulting (co)polymer possessed reactive vinyloxyl side groups. The copolymer networks were obtained by reacting each of the above‐mentioned (co)polymers with a polyacetal prepared via the polyaddition between a divinyl ether and a diol. Three divinyl ethers (ethylene glycol divinyl ether, 1,4‐butanediol divinyl ether, and 1,6‐hexanediol divinyl ether) and three diols (ethylene glycol, 1,4‐butanediol, and 1,6‐hexanediol) were employed as monomers in the polyaddition step, and their combinations generated nine kinds of polyacetals. When a polyaddition reaction was terminated with a divinyl ether monomer, a polyacetal with two vinyloxyl end groups was obtained, which could further react with the hydroxyl groups of poly(HEMA‐co‐MMA) to generate a copolymer network. On the other hand, when a diol was used as terminator in the polyaddition, the resulting polyacetal possessed two hydroxyl end groups, which could react with the vinyloxyl groups of poly(VEMA) or poly(VEMA‐co‐MMA), to generate a copolymer network. All the copolymer networks exhibited degradation in the presence of acids. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 117–126, 2001     

Synthesis of high‐molecular‐weight aliphatic–aromatic copolyesters from poly(ethylene‐co‐1,6‐hexene terephthalate) and poly(L‐lactic acid) by chain extension

A series of aliphatic–aromatic multiblock copolyesters consisting of poly(ethylene‐co‐1,6‐hexene terephthalate) (PEHT) and poly(L ‐lactic acid) (PLLA) were synthesized successfully by chain‐extension reaction of dihydroxyl terminated PEHT‐OH prepolymer and dihydroxyl terminated PLLA‐OH prepolymer using toluene‐2,4‐diisoyanate as a chain extender. PEHT‐OH prepolymers were prepared by two step reactions using dimethyl terephthalate, ethylene glycol, and 1,6‐hexanediol as raw materials. PLLA‐OH prepolymers were prepared by direct polycondensation of L ‐lactic acid in the presence of 1,4‐butanediol. The chemical structures, the molecular weights and the thermal properties of PEHT‐OH, PLLA‐OH prepolymers, and PEHT‐PLLA copolymers were characterized by FTIR, ¹H NMR, GPC, TG, and DSC. This synthetic method has been proved to be very efficient for the synthesis of high‐molecular‐weight copolyesters (say, higher than M_w = 3 × 10⁵ g/mol). Only one glass transition temperature was found in the DSC curves of PEHT‐PLLA copolymers, indicating that the PLLA and PEHT segments had good miscibility. TG curves showed that all the copolyesters had good thermal stabilities. The resulting novel aromatic–aliphatic copolyesters are expected to find a potential application in the area of biodegradable polymer materials. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5898–5907, 2009     

Copolymerization of propylene with 1,3‐butadiene using isospecific zirconocene catalysts

Poly(propylene‐ran‐1,3‐butadiene) was synthesized using isospecific zirconocene catalysts and converted to telechelic isotactic polypropylene by metathesis degradation with ethylene. The copolymers obtained with isospecific C₂‐symmetric zirconocene catalysts activated with modified methylaluminoxane (MMAO) had 1,4‐inserted butadiene units ( 1,4‐BD ) and 1,2‐inserted units ( 1,2‐BD ) in the isotactic polypropylene chain. The selectivity of butadiene towards 1,4‐BD incorporation was high up to 95% using rac‐dimethylsilylbis(1‐indenyl)zirconium dichloride (Cat‐A)/MMAO. The molar ratio of propylene to butadiene in the feed regulated the number‐average molecular weight (M_n) and the butadiene contents of the polymer produced. Metathesis degradations of the copolymer with ethylene were conducted with a WCI₆/SnMe₄/propyl acetate catalyst system. The ¹H NMR spectra before and after the degradation indicated that the polymers degraded by ethylene had vinyl groups at both chain ends in high selectivity. The analysis of the chain scission products clarified the chain end structures of the poly(propylene‐ran‐1,3‐butadiene). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5731–5740, 2007     

Synthesis and characterization of hyperbranched poly(urea‐urethane)s based on AA* and B2B* monomers

Hyperbranched aromatic and aliphatic poly(urea‐urethane)s were prepared by the one‐pot method using 2,4‐toluylene diisocyanate (TDI), isophorone diisocyanate, and 2(3‐isocyanatopropyl)cyclohexyl isocyanate as AA* monomers and diethanol amine and diisopropanol amine as B₂B* monomers. The characteristics of the resulting polymers were very sensitive to slight changes in the reaction conditions, such as temperature, concentration, and type of catalyst used, as can be seen from the results of gel permeation chromatography and differential scanning calorimetry. The structures were analyzed in detail using ¹H and ¹³C NMR spectroscopy. By using model compounds, the different isomeric structures of the TDI polymers were deduced, their percentages of their linear, terminal, and dendritic subunits were calculated, and their degree of branching (DB) was determined. DB values up to 70% were reached depending on the reaction conditions and stoichiometry of the monomers. The number of terminal groups decreased significantly when dibutylamine was used to stop the reaction instead of B₂B*, indicating the presence of a significant number of unreacted isocyanate groups in the hyperbranched product when the polyaddition reaction was stopped. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3062–3081, 2004     

Fluoropolyethers end‐capped by polar functional groups. I. Kinetic approach to the reaction of hydroxy‐terminated fluoropolyethers with cycloalyphatic and aromatic diisocyanates

Urethane reactions of cycloaliphatic and aromatic diisocyanates with hydroxy‐terminated fluoropolyethers (FPEs) of various molecular weights and structure, at NCO : OH = 2, have been studied by monitoring, by IR analysis, the rate of decrease in NCO absorbance at 2264–2268 cm⁻¹. Different diisocyanates have been tested, among them the following: 4,4′‐dicyclohexylmethane diisocyanate (H₁₂MDI); 5‐isocyanato‐1,3,3‐trimethylcyclohexylmethyl isocyanate or isophorone diisocyanate (IPDI); 2,4‐toluene diisocyanate (TDI). Ethyl acetate (EA), methyl isobutyl ketone (MIBK), and hexafluoroxylene (HFX) have been used as solvents in presence of dibutyltin dilaurate (DBTDL) or 1,4‐diazabicyclo[2.2.2]octane (DABCO) as catalysts. These reactions gave rise to NCO‐end‐capped FPE–oligourethanes. Preliminary solubility tests for HO‐terminated FPEs in various solvents made it possible to select proper candidates for carrying out reaction in homogeneous conditions at high concentrations of reagents (30–50% w/w). The second‐order kinetic mechanism was shown to be valid. Positive deviations from linearity for the second‐order kinetics around 40–80% conversion, found for most of the FPE diols, were attributed to the autocatalysis of the isocyanate–hydroxyl reaction by the arising urethane groups. Uncatalyzed reactions with cycloaliphatic diisocyanates are very slow at 40°C. The tertiary amine DABCO is a much less effective catalyst than DBTDL. FPEs having terminal OH groups separated from the perfluorinated main molecular chain by  (OCH₂CH₂)_n segments (n = 1–2) are generally more reactive than FPEs with end  CH₂OH groups. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 557–570, 1999