A comparative study of the structure-property behavior of highly branched segmented poly(urethane urea) copolymers and their linear analogs

The solid-state structure-property behavior of highly branched segmented poly(urethane urea) (PUU) copolymers and their linear analog was investigated. A limited study of their solution rheological behavior was also undertaken. The linear PUUs were synthesized by the two-step prepolymer method, whereas the oligomeric A₂+B₃ methodology was utilized to synthesize the highly branched materials. The soft segments (SS) were either poly(tetramethylene oxide) (PTMO) or poly(propylene oxide) (PPO). All copolymers utilized in this study, with one exception, contained 28 wt% hard segment (HS) content. DMA, SAXS, and AFM studies indicated that the linear as well as the highly branched PUUs were microphase separated. The SS T_g of the highly branched PUUs was nearly identical to that of their respective linear analogs. However, the linear copolymers exhibited broader and less temperature sensitive rubbery plateaus, both attributed to one or both of two reasons. The first is better hydrogen bonding organization of the HS phase as well as greater HS lengths than in the highly branched analogs. The second parameter is that of a potentially higher chain entanglement for the linear systems relative to the branched analogs. Tapping-mode AFM phase images confirmed the microphase morphology indicated by SAXS and DMA. Ambient temperature strain-induced crystallization was observed in the PUU based on PTMO 2040 g/mol at a uniaxial strain of ca. 400%, irrespective of the chain architecture. Stress-strain, stress relaxation, and mechanical hysteresis of the highly branched copolymers were in general slightly poorer than that of their linear analogs. Ambient temperature solution viscosity of the highly branched materials in dimethyl formamide was substantially lower that that of the linear samples of nearly equal molecular weight.     

Photopolymerization behavior and properties of highly branched polyester acrylate containing thioether linkage used for UV curing coatings

The highly branched polyester acrylate containing thioether linkage (HBAT) was synthesized using an “oligomeric A₂ + B₃” approach. The dithiol, 1,6-hexamethylene bis(3-mercaptopropionate) (HMBM), was prepared through the esterification between 1,6-hexanediol and 3-mercaptopropionic acid, and then underwent an amine-catalyzed thiol-Michael addition to the acrylic double bond of 1,6-hexamethylene diacrylate to obtain an oligomeric dithiol (oligomeric A₂), then further with trimethylolpropane triacrylate as a B₃ monomer. The molecular structure was characterized with FT-IR and ¹H NMR spectroscopy. A broader molecular weight distribution from 1.74 to 2.75 was obtained for different oligomeric dithiol chains by GPC measurements. The photopolymerization kinetics study by photo-DSC analysis showed that the HBAT greatly reduced the oxygen inhibition in radical photopolymerization of acrylates in air. The maximum polymerization rate decreased along with the addition of HBAT into the UV curable resin (EB605) containing bisphenol A epoxy diacrylate and tripropylene glycol diacrylate due to the reduced double bond density and increased viscosity, whereas the final unsaturation conversion in cured film increased because of the longer spacer chain in HBAT compared to that in EB605 and the reduced crosslinking density by HBAT addition. The dynamic mechanical thermal analysis results showed that both the elastic modulus in the rubbery plateau and glass transition temperature of cured film decreased along with the incorporation of HBAT into EB605. The water swelling test and thermogravimetric analysis indicated that the thioether linkage in HBAT can greatly improve the water absorption resistance and oxidative stability of cured film.     

Photopolymerization behavior and properties of highly branched poly(thioether-urethane) acrylates used for UV-curing coatings

The highly branched poly(thioether-urethane) acrylate (BPTUA) was synthesized through an “oligomeric A₂ + B₃” approach. The thiol-endcapped difunctional oligomeric A₂ was obtained by the addition reactions of isophorone diisocyanate with 1,4-butanediol, and then further with 1,4-butanediol bis(thioglycolate). Trimethylolpropane triacrylate was used as a B₃ monomer. The addition conduct of 1,6-hexanediol diacrylate with 1,4-butanediol bis(thioglycolate) was introduced into the polymeric chain for preparing the modified BPTUA (m-BPTUA). The molecular structures were characterized with FT-IR and ¹H NMR spectroscopy, and GPC analysis. The number average molecular weights (M_ns) of BPTUA and m-BPTUA were experimentally measured to be 13,500 g mol⁻¹ and 17,900 g mol⁻¹ with the polydispersity indices of 1.86 and 1.94, respectively. A series of UV-curable resins were fabricated based on bisphenol-A epoxy diacrylate (EB600) and tripropylene glycol diacrylate with the addition of either BPTUA or m-BPTUA in different ratios, and exposed to a UV lamp for obtaining the cured films in the presence of 1-hydroxycyclohexylphenyl ketone as a photoinitiator. From the photo-DSC measurements, the polymerization rate at the peak maximum decreased, whereas the final unsaturation conversion in cured film increased, along with the increase of either BPTUA or m-BPTUA. The elastic modulus in the rubbery plateau and the glass transition temperature from DMTA, as well the tensile strength and Young's Modulus of UV-cured film decreased with increasing either BPTUA or m-BPTUA loading, whereas the elongation at break, flexibility and strike performance were greatly enhanced. Moreover, for the m-BPTUA series, the enhancive effects on the properties were much more obviously than the BPTUA series. The water swelling test and thermogravimetric analysis indicated that the water absorption resistance and the oxidative stability of cured films were improved by the incorporation of thioether linkage into the crosslink networks.     

Vegetable oil based highly branched polyester/clay silver nanocomposites as antimicrobial surface coating materials

The unison of nanotechnology and polymer science enables the development of novel silver-based polyester nanocomposite as an antimicrobial coating material. Highly branched polyester/clay silver nanocomposites based on vegetable oil with different loadings of silver were prepared via reduction of silver salt by employing dimethylformamide as solvent as well as reducing agent at room temperature. Organically modified montmorillonite clay of 2.5 wt% was used as the nanofiller for the property improvement of the pristine polymer. The highly branched polyester resin was synthesized by condensation of 2,2-bis(hydroxymethyl) propionic acid with Mesua ferrea L. seed oil based carboxyl terminated pre-polymer, as reported earlier. FTIR, UV–vis, XRD, SEM and TEM studies substantiate the formation of well-dispersed silver nanoparticles within the clay gallery with an average size of 15 nm. The thermostability of the silver nanocomposites obtained by thermogravimetric analysis was enhanced by 20 °C. The mechanical properties such as tensile strength and scratch hardness were improved 4.5 and 2.6 units respectively and impact resistance improved a little by nanocomposites formation. The antimicrobial efficacy of the as-prepared silver nanocomposites was also premeditated and highly antibacterial activity against Gram negative bacteria (Escherichia coli and Psuedomonas aeruginosa) was observed. Excellent chemical resistance in various chemical media except in alkali has also been noticed. The study reveals that the polyester/clay silver nanocomposites based on vegetable oil show the potential to be applicable as antibacterial surface coating materials.     

Solid-state polycondensation of natural aldopentoses and 6-deoxyaldohexoses. Facile preparation of highly branched polysaccharide

Solid-state polycondensation of natural aldopentoses and 6-deoxyaldohexoses was found to take place in the presence of H₃PO₄ (5 mol%) at 100-110 °C under a N₂ flow, giving highly branched polysaccharide (Conv. 47-81%, M_w=2700-12?000, M_n=1400-2900); the reaction mixtures were powdery throughout the polymerization. The product polysaccharide was per-O-methylated and subjected to the structure analyses. The acid-hydrolysis, which gave a variety of the partially O-methylated monosaccharides, suggested that the product polysaccharides proved to have highly branched structures consisting of both furanose and pyranose units. MALDI-TOF mass analysis revealed that the 1,4-anhydride terminal unit was formed and participated to the polymerization.     

Comparison of surface mechanical properties among linear and star polystyrenes: Surface softening and stiffening at different temperatures

In a previous study, we reported both surface softening and stiffening for poly(α-methylstyrene) (PαMS) over a temperature range from room temperature to 21 °C above the glass transition temperature (T_g) using the spontaneous particle embedment technique. In the present study, we have explored the surface mechanical responses of a linear polystyrene (PS), a 3-arm star PS, and an 8-arm star PS emphasizing the range of temperature from T_g −10 °C to T_g +10 °C, similar to that in which the prior study had shown a transition from surface softening (increased mobility) to stiffening (decreased mobility). We used atomic force microscopy for particle embedment depth estimation and the isochronal form of the Lee and Radok (LR) model for surface compliance determination. We observed both surface softening and stiffening for the linear PS and 3-arm star PS for the studied temperature range. However, surface softening was observed at all temperatures in this study for the 8-arm star PS. The surface compliance results for the different PS molecular architectures are compared with those for the linear PαMS from the previous study.     

A highly branched polythiourethane acrylate used for UV-curable high antireflection coatings

A series of highly branched polythiourethane acrylates (BPTUAs) were prepared through the double thiol-ene click reaction of thiol-endcapped difunctional thiourethane as an oligomer A₂ (Oligo-TU) with trimethylolpropane tri(thioglycolate ethylene glycol acrylate) (TMPTTA) as a trifunctional monomer B₃ in different ratios. The Oligo-TU was synthesized via the addition reactions of 2,4-toulene diisocyanate with 1,4-butanediol, and further with 4,4′-thiobisbenzenethiol. The TMPTTA was synthesized by the thiol-ene click reaction of trimethylolpropane tri(thioglycolate) (TMPTT) with an excess of ethylene glycol diacrylate. For comparison, a tetrafunctional thiourethane acrylate (TUA) was also synthesized. Finally, the obtained BPTUA and TUA were further modified with 2-mercaptobenzothiazole, 2-mercaptothiazoline and mercapto-5-methyl-thiadiazole, respectively, to form highly branched polyfunctional thiazole-based acrylates BPTUA-TAs and TUA-TAs. The molecular structures were confirmed by FT-IR and ¹H NMR analyses. The number average molecular weights and their polydispersity were determined by GPC spectroscopy. The UV irradiation using a medium pressure mercury lamp was applied to prepare the optical films in the presence of a photoinitiator. The refractive indices of UV-cured films were measured using a He-Ne laser at 632.8 nm. The results showed that both BPTUA and TUA films possess the similar refractive indices in the range of 1.592–1.604. However, the higher refractive indices in the range of 1.603–1.620 with BPTUA-TA films than 1.601–1.609 of TUA-TA films were obtained. All samples showed the high pencil hardness and impact resistance, as well good flexibility.     

Novel synthesis of highly branched comb-like polymers by coupling reaction of polystyryllithium with 1,1-diphenylethenyl-functionalized polystyrene

Well-defined highly branched comb-like polystyrenes (PS) having one branch in each repeating unit have been successfully synthesized by the coupling reaction of living PS anions with 1,1-diphenylethenyl (DPE) groups along PS backbone prepared via atom transfer radical polymerization. When excess polystyryllithium (PSLi) was used, the quantitative grafting efficiency was achieved. The resulting polymers were characterized by NMR, IR, GPC, and SLS in detail.     

Influence of polymerization procedure on polymer topology and other structural properties in highly branched polymers obtained by A2 + B3 approach

Computational studies were carried out to investigate the influence of polymerization procedure on the topology and various macromolecular characteristics of the highly branched polymers formed by the reaction of A₂ and B₃ type monomers through step-growth polymerization reactions. The influence of three different polymerization procedures on the properties of the polymers formed was investigated, namely, (i) slow addition of A₂ over B₃, (ii) slow addition of B₃ over A₂, and (iii) mixed A₂ + B₃. Topology, degree of branching, number and weight average molecular weights, and polydispersity index of the polymers were determined using Monte Carlo simulations, assuming different levels of cyclization ratios during the reactions. Interestingly model polymers obtained by the slow addition of B₃ over A₂ produced much higher degree of branching or truly hyperbranched polymers, when compared with the other two methods, which mainly resulted in linear growth with slight branching.     

Surface segregation of branched polyethyleneimines in a thermoplastic polyurethane

Hyperbranched polyethyleneimines were modified with methacrylated fluorosurfactants and aliphatic epoxides to provide a library of macromolecules with controlled chain ends and residual amine functionality. These materials were co-dissolved with a thermoplastic polyurethane-ether and the blends were subsequently deposited as films cast from solution. The surface chemistry of the cast films was determined using angle resolved X-ray photoelectron spectroscopy (AR-XPS) and Rutherford backscattering spectroscopy (RBS). Experimental results indicate that the modified hyperbranched polymers (HBPs) concentrate at the air-polymer interface. Furthermore, HBPs that were complexed to polyoxometalates (POMs) using electrostatic interactions also exhibited surface segregation in cast polymer films, resulting in ca. 10-fold increase of metal at the film surface relative to the known bulk concentration. Results from XPS and RBS examination of the films are consistent with surface segregation of the HBP-POM hybrids, exhibiting increased metal, fluorine, and nitrogen content near the surface of the film, as well as significant changes in wetting behavior. This study indicates that modified HBPs may be used to selectively transport inorganic species such as polyoxometalates to polymer film surfaces.     

Synthesis and characterisation of star branched polyesters with dendritic cores and the effect of structural variations on zero shear rate viscosity

A series of branched polyesters consisting of poly(ε-caprolactone) (PCL) (degree of polymerisation: 5-200) initiated from hydroxy-functional cores and end-capped with methylmethacrylate have been prepared. The cores were third-generation hyperbranched polyester, Boltorn, with approximately 32 hydroxyl groups, a third-generation dendrimer with 24 hydroxyl groups and a third-generation dendron with eight hydroxyl groups. Finally, a linear PCL was synthesised as a reference material. All initiators were based on 2,2-bis(methylol) propionic acid (bis-MPA). ¹³C NMR spectra of the polymers showed that those with shorter arms contained unreacted hydroxyl groups on the core. Rheological measurements of zero shear rate viscosity, η₀, showed that the branched polyesters had a considerably lower η₀ than linear polyester with similar molecular weight. The low melt viscosity and the crystallity produced a rheological behaviour suitable for the film formation process for powder coatings. Measurements of mechanical properties of cured films showed that those with low arm molecular weight, M_a, were amorphous while those of high M_a were crystalline.     

Electrospinning of linear and highly branched segmented poly(urethane urea)s

Electrospun fibrous mats were formed from linear and highly branched poly(urethane urea)s. The highly branched poly(urethane urea)s were synthesized using an A₂+B₃ methodology, where the A₂ species is an oligomeric soft segment. Since the molecular weight of the A₂ oligomer is above the entanglement molecular weight, the highly branched polymers formed electrospun fibers unlike typical hyperbranched polymers that do not entangle. Stress-strain experiments revealed superior elongation for the electrospun fibrous mats. In particular, the highly branched fiber mats did not fail at 1300% elongation, making the electrospun mats promising for potential applications where enhanced tear strength resistance is required.     

Highly branched polyurethane acrylates and their waterborne UV curing coating

A series of UV curable highly branched waterborne polyurethane acrylates (BWPUAs) were synthesized using an “oligomeric A₂ + B₃” approach. The thiol-endcapped difunctional oligomeric A₂ was synthesized first by the addition reaction of isophorone diisocyanate, α,α-dimethylol propionic acid and 2-hydroxyethyl acrylate, then further underwent thiol-Michael reaction with 1,6-hexamethylene bis(thioglycolic acetate). Trimethylolpropane triacrylate was used as a B₃ monomer. The molecular structures were characterized with FT-IR and ¹H NMR spectroscopy. 1,6-Hexanediol diacrylate (HDDA) was incorporated into the polymeric chain for preparing the HDDA-modified BWPUAs (BWPUA-Hs). For the comparison, the linear waterborne polyurethane acrylate (LWPUA) was synthesized. The UV curing kinetics study results by using the photo-DSC approach showed that the BWPUAs possessed higher photopolymerization rate and final unsaturation conversion in the UV cured films compared with the LWPUA, which increased with the increase of unsaturation concentration in BWPUA. Moreover, the photopolymerization performance, and water and solvent resistance properties were greatly enhanced by the incorporation of HDDA segment into the BWPUA chain. The dynamic mechanical thermal analysis results showed that the elastic modulus in the rubbery plateau, and the glass transition temperature of UV cured film increased with increasing unsaturation concentration in BWPUA, whereas decreased with the introduction of HDDA flexible segment. The thermogravimetric analysis confirmed the high thermal stability of UV cured BWPUA films. All UV cured BWPUA and BWPUA-H films showed better flexibility and middle refractive indices due to the thioether linkage in the polymer network.     

Thermogelling of highly branched poly(N‐isopropylacrylamide)

Highly branched poly(N‐isopropylacrylamide) (PNIPAM) has been synthesized by a reversible addition‐fragmentation chain transfer (RAFT) copolymerization of NIPAM and a vinyl contained trithiocarbonate RAFT agent. ¹H‐NMR measurements revealed that the degrees of branch (DB) are in the range of 0.032–0.105. Laser light scattering (LLS) measurements gave the hydrodynamic radii (R_h) of the polymers to be 3.6–5.7 nm with molecular weight in the range of 1.3 × 10⁴ g/mol–2.3 × 10^?4 g/mol. Highly branched PNIPAM with terminal thiol groups were obtained by aminolysis the polymers, and the product can be oxidized by air to form disulfide bonds (? S? S? ) among chains and resulting in the formation of nanoparticle in aqueous solution. Interestingly, the nanoparticle in size of R_h ? 80 nm showed a thermogelling behavior to form bulk hydrogel when the temperature was increased up to 25°C due to the thermo‐induced association of the PNIPAM chains among the nanoparticles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Studies on the blends of polycarbonate and highly branched polystyrene

A highly branched polystyrene (HBPS) was synthesized via the copolymerization of 4‐(chloromethyl) styrene with styrene using the self‐condensing atom transfer radical polymerization method. The addition of this highly branched polystyrene as a melt modifier for polycarbonate (PC) was attempted. Indeed, the results show that the addition of highly branched polystyrene can decrease the melt viscosity of PC with little change in mechanical properties, although the blends do exhibit lower thermal stability compared with pure PC. Extrapolation shows that all of the blends have an initial weight loss temperature above 450°C with a statistic heat‐resistant index T_s above 225°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2425–2430, 2004     

Linear or branched structure? Probing molecular architectures of fullerene-styrene copolymers by size exclusion chromatographs with online right-angle laser-light scattering and differential viscometric detectors

The poly(C₆₀-co-styrene)s prepared by radical copolymerizations of C₆₀ and styrene in bulk were characterized by multiple-detector size-exclusion chromatographs consisting of a refractometer, a differential viscometer, and/or a right-angle laser-light scattering photometer. The multidetector systems enabled the determinations of reliable, absolute molecular weights of the copolymers. The plots of intrinsic viscosity vs. molecular weight and radius of gyration vs. molecular weight offered valuable information about the molecular architectures of the copolymers. The slopes of the plots reveal that the structure of the copolymer changes with its C₆₀ content: the copolymer with a low C₆₀ content of 0.58 wt% possesses a linear structure, whereas its conger with a high C₆₀ content of 1.14 wt% possesses a branched structure.     

Design and regulation of the surface and interfacial behavior of protein molecules

Surface and interfacial behavior of protein molecules are crucial for the protein function involved in many biochemical processes and biomedical products such as enzyme design, bio-separation, drug design and delivery. This article is devoted to an overview of design and regulation of the surface and interfacial behavior of protein molecules. The improvement of enzyme surface such as the directed evolution and the rational design of enzymes is introduced at first, followed by the rational design of protein interface for the protein assembly. Thereafter, the design of micro-environment and ligands are described as two examples for the design guided by protein surface. Then the design of protein surface and interface with the help of artificial intelligence will be discussed.     

支化聚合物的合成及表征

支化聚合物由于其独特的结构和性能以及可实现规模化生产的特点,已迅速成为一类重要的和具有广阔应用潜力的高分子材料。本文综述了近年来制备支化聚合物常用的合成方法：主链引发法、主链-支链偶联法以及单体-大分子单体共聚法;介绍了表征支化聚合物支化度的方法：红外光谱法、核磁共振法、差热分析法、GPC和自动粘度计联用法,并评价了各种方法的优缺点,目的在于加深人们对该领域的了解,从而促进该领域的快速发展。     

支化及超支化聚乙烯研究进展

综述了支化及超支化聚乙烯的制备方法及功能化改性研究进展,重点介绍了后过渡金属催化剂催化乙烯"链行走"制备超支化聚乙烯的研究进展,同时介绍了功能性超支化聚乙烯的应用,并展望了其发展前景。     

Preparation and properties of branched polybutylenesuccinate

To obtain long branched polybutylene succinate (PBS), modified PBSs were prepared by introducing a branching agent, trimethylol propane (TMP), to the polycondensation system of succinic acid and 1,4‐butanediol. Molecular parameters such as absolute molecular weight and root‐mean‐square (RMS) radius of the modified PBSs were measured by gel permeation chromatography (GPC) with a multiangle laser light‐scattering (MALLS) detector. The RMS radius of TMP05, PBS prepared by incorporating 0.5 wt % TMP during polycondensation, was the smallest of all PBSs tested at the same molecular weight. The notable shear thinning and much reduced loss tangent for TMP05 qualitatively supported the difference in their molecular structures predicted by GPC. The analytical results indicated that introducing 0.5 wt % TMP produced PBS with chain branches long enough to produce molecular entanglements. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1388–1394, 2001