Preparation and characterization of block and graft copolymers using macroazoinitiators having siloxane units

α,ω-Amine terminated organofunctional polydimethylsiloxane (PDMS) was condensed with 4,4′-azobis-4-cyanopentanoyl chloride (ACPC) to prepare macroazoinitiators containing siloxane units. Interfacial polycondensation reaction at room temperature was applied: ACPC was slightly dissolved in carbon tetrachloride and it was poured on aqueous NaOH solution of PDMS. Block copolymers containing PDMS as a block segment combined with polystyrene (PS) have been derived by the polymerization of styrene monomer initiated by these macroazoinitiators. PS-b-PDMS block copolymers were characterized by using nuclear magnetic resonance and infrared spectroscopy. Thermal and mechanical properties of the block copolymers were studied by using thermogravimetric analysis, differential scanning calorimetry, and a Tensilon stress-strain instrument. The morphology of block copolymers was investigated by scanning electron microscopy. PDMS-g-polybutadiene (PBd) graft copolymers were also prepared by reaction of PBd with the above macroazo-initiator. Increase in the amount of macroazoinitiator in the mixture of PBd (52% w/w) leads to the formation of crosslinked graft copolymers. Molecular weights of soluble graft copolymer samples were between 450 and 600 K with a polydispersity of 2.0–2.3. © 1996 John Wiley & Sons, Inc.     

Surface properties of block and graft polystyrene–polydimethylsiloxane copolymers

The surface compositions of a series of polystyrene‐b‐polydimethylsiloxane (PS‐b‐PDMS) and polystyrene‐g‐polydimethylsiloxane (PS‐g‐PDMS) copolymers were investigated using ATR‐FTIR and XPS technique. The results showed that enrichment of PDMS soft segments occurred on the surface of the block copolymers as well as on that of graft copolymers. And the magnitude order of the enrichment was as follows: PS‐b‐PDMS > PS‐g‐PDMS, which was attributed to the facilitating of the movement of the PDMS segments in PS‐b‐PDMS copolymer. Meanwhile, the solvent type and the contact medium had influence on the accumulation of PDMS on the surfaces. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Synthesis and characterization of poly(ether sulfone)‐graft‐polydimethylsiloxane copolymers

Novel poly(arylene ether sulfone) (PAES) polymers containing polydimethylsiloxane (PDMS) side chains were synthesized and characterized with NMR and Fourier transform infrared spectroscopy. The thermal properties of the copolymers were evaluated with differential scanning calorimetry and thermogravimetric analysis. The polymers showed perfect thermal stability, as the decomposition temperatures were all above 380°C, and exhibited glass‐transition temperatures in the range 130–188°C. Furthermore, the surface properties of the copolymers were evaluated by X‐ray photoelectron spectroscopy and contact angle analysis. The results show that the hydrophobic abilities of the graft copolymer surfaces were improved significantly compared to PAES through the introduction of the PDMS chains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis, characterization and properties of chitosan modified with poly(ethylene glycol)-polydimethylsiloxane amphiphilic block copolymers

Synthesis of poly(ethylene glycol)-polydimethylsiloxane amphiphilic block copolymers is discussed herein. Siloxane prepolymer was first prepared via acid-catalyzed ring-opening polymerization of octamethylcyclotetrasiloxane (D₄) to form polydimethylsiloxane (PDMS) prepolymers. It was subsequently functionalized with hydroxy functional groups at both terminals. The hydroxy-terminated PDMS can readily react with acid-terminated poly(ethylene glycol) (PEG diacid) to give PEG-PDMS block copolymers without using any solvent. The PEG diacid was prepared from hydroxy-terminated PEG through the ring-opening reaction of succinic anhydride. Their chemical structures and molecular weights were characterized using ¹H NMR, FTIR and GPC, and thermal properties were determined by DSC. The PEG-PDMS copolymer was incorporated into chitosan in order that PDMS provided surface modification and PEG provided good water swelling properties to chitosan. Critical surface energy and swelling behavior of the modified chitosan as a function of the copolymer compositions and contents were investigated.     

Synthesis and characterization of gelatin‐polydimethylsiloxane graft copolymers

Gelatin‐polydimethylsiloxane (PDMS) graft copolymers were prepared through the reaction between gelatin and α‐[3‐(2,3‐epoxypropoxy)propyl]‐ω‐butyl‐PDMSs. The copolymers were characterized by FTIR and ¹H‐NMR spectra. As proved by wide angle X‐ray analysis, a new characteristic crystalline peak appeared after the bonding of PDMS to gelatin chains. The microstructure and the elemental identification of gelatin and copolymers were followed through scanning electron microscope with energy dispersive spectrometer. The glass transition temperature of gelatin and copolymers were obtained by differential scanning calorimetry analysis. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Copolymerization of 4-cyanophenyl acrylate with methyl methacrylate: synthesis, characterization and determination of monomer reactivity ratios

A novel acrylic monomer, 4-cyanophenyl acrylate (CPA) was synthesized by reacting 4-cyanophenol dissolved in methyl ethyl ketone with acryloyl chloride in the presence of triethylamine as a catalyst. Copolymers of CPA with methyl methacrylate (MMA) at different composition was prepared by free radical solution polymerization at 70 ± 1 °C using benzoyl peroxide as an initiator. The copolymers were characterized by FT-IR, ¹H-NMR and ¹³C-NMR spectroscopic techniques. The solubility tests were checked in various polar and non polar solvents. The molecular weight and polydispersity indices of the copolymers were estimated by using gel permeation chromatography. The glass transition temperature of the copolymers increases with increases MMA content. The thermal stability of the copolymer increases with increases in mole fraction of CPA content in the copolymer. The copolymer composition was determined by using ¹H-NMR spectra. The monomer reactivity ratios determined by the application of linearization methods such Fineman–Ross (r ₁ = 0.535, r ₂ = 0. 0.632), Kelen–Tudos (r ₁ = 0.422, r ₂ = 0.665) and extended Kelen–Tudos methods (r ₁ = 0.506, r ₂ = 0. 0.695).     

Preparation of Monomer Casting Nylon-6-b-Polydimethylsiloxane Copolymers with Enhanced Mechanical and Surface Properties

Nylon-6-b-polydimethylsiloxane copolymer was synthesized with macroinitiator through in situ polymerization. The macroinitiator with two chain-growing centers per molecule is based on hydroxyl terminated polydimethylsiloxane (PDMS) functionalized with diisocyanate. The influence of PDMS contents on the properties of copolymers was studied. Differential scanning calorimetry and X-ray diffraction were used to investigate the melting temperature, crystallization temperature and crystal form of samples, and the results showed that the crystallinity of polymers decreased. The mechanical properties of samples were studied by notched-impact testing and tension test. The notched impact strength was improved by 200% with PDMS concentration up to 4?wt%. The form of scaly was seen by scanning electron microscope proved the improvements of the impact strength of the copolymer. The water contact angles test showed that the surface tension of copolymers decreased with the PDMS content increasing and the surface of copolymer changed from hydrophilic to hydrophobic.     

Liquid crystalline acrylic copolymers for high-solids enamel coatings

Carboxyl functional liquid crystalline (LC) acrylic copolymers were synthesized and were compared with carboxyl functional control copolymers of M?_n about 5000–15,000. Both types were crosslinked with a hexakismethoxymethyl melamine (HMMM) resin at 150°C, a temperature below the clearing points of the LC copolymers. Birefringent phases were visible in the crosslinked films made from LC polymers. FT-IR indicated the presence of unreacted COOH in all crosslinked materials. Unreacted COOH groups in crosslinked LC copolymers appeared only slightly higher than those in crosslinked amorphous copolymers. The potential utility of these LC copolymers as binders for thermosetting coatings was assessed. Variables studied were HMMM content, the length of PHBA grafts, T_g and M?_n of the acrylic copolymer backbone, and functionality. Optimum LC copolymers have low backbone T_g (<O°C) and low functionality (< 7.5 mol %). Cured films of such copolymers have both high hardness (> 35 KHN), high impact resistance (> 80 in. ib), excellent adhesion, and good solvent resistance.     

A comparison of composition and sequence distribution of p(AM-MADQUAT) prepared by solution and inverse microemulsion polymerization

Acrylamide (AM)/2-(methacryloyloxy)ethyltrimethylammonium chloride (MADQUAT) copolymers were prepared by solution and inverse microemulsion polymerization using ammonium persulfate ((NH₄)₂S₂O₈)/sodium hydrosulfite (NaHSO₃) as redox initiator at 30 °C. The comonomer reactivity ratios, determined using the Kelen–Tudos (KT) method, were r _A = 0.30, r _M = 1.31 in solution and r _A = 0.63, r _M = 1.13 in the inverse microemulsion, respectively. The copolymer microstructure was deduced from the run number and the heterogeneity, based on reactivity ratios. It was found that copolymerization in the inverse microemulsion resulted in close to ideal copolymerization, giving almost random copolymers; copolymerization in solution resulted in some alternating copolymers. The copolymer compositions indicated that high-conversion samples obtained from the inverse microemulsion are much more homogeneous in composition compared with those obtained in solution. It was found that the composition distribution of the copolymer prepared by inverse microemulsion polymerization remained at approximately the feed ratio. The sequence distribution of the copolymer was predicted by first-order Markov statistical and Bernoulli statistical models, respectively. The results showed that the sequence distribution of the copolymer prepared by inverse microemulsion polymerization was almost random, which led to a wider cationic charge distribution and a microstructure that was coincident with the feed ratio.     

Synthesis of syndiotactic polystyrene-graft-poly(ethylene glycol) copolymer by photochemical reaction

Syndiotactic polystyrene-graft-poly(ethylene glycol) (sPS-g-PEG) copolymer was prepared by photochemical attachment of poly(ethylene glycol) chains to the benzoylated syndiotactic polystyrene (BesPS) backbone. BesPS, a functional polymer bearing benzophenone moiety, was prepared in a heterogeneous process through Friedel-Crafts acylation reaction using benzoyl chloride as benzoylating agent. This substrate was then dispersed in o-dichlorobenzene at room temperature and mixed with poly(ethylene glycol) , which was reacted with the benzophenone moieties by illumination with UV light (λ > 340 nm). As a result of the photochemical reaction, the hydrophilic poly(ethylene glycol) was chemically attached to the hydrophobic syndiotactic polystyrene backbone. The resultant copolymer was characterized by FT-IR, NMR, and X-ray photoelectron spectroscopy. In addition, the thermal properties of graft copolymers were also studied by means of DSC.     

Poly(dimethylsiloxane)urethane‐co‐poly(methyl methacrylate) with 2,4‐toluene diisocyanate and m‐xylene diisocyanate. I. Compatibility and impact strength of copolymers

In this study, slightly crosslinked poly(dimethylsiloxane)urethane‐co‐poly(methyl methacrylate) (PDMS urethane‐co‐PMMA) graft copolymers based on two diisocyanates, 2,4‐toluene diisocyanate (2,4‐TDI) and m‐xylene diisocyanate (m‐XDI), were successfully synthesized. Glass‐transition behaviors of the copolymers were investigated. Results confirm that PDMS–urethane and PMMA are miscible in the 2,4‐TDI system, but are only partially miscible in the m‐XDI system. The methylene groups adjoining the isocyanate in the m‐XDI system show increased phase‐separation behavior over the 2,4‐TDI system, in which the benzene ring adjoins the isocyanate. The functional group of PDMS–urethane improves the impact strength of the copolymers. The toughness depends on the compatibility of PDMS–urethane and PMMA segments in the copolymers. In the m‐XDI system, the impact strength of the copolymer containing 3.75 phr macromonomer achieves a maximum value (from 13.02 to 22.21 J/m). The fracture behavior and impact strength of the copolymers in the 2,4‐TDI system are similar to that of PMMA homopolymer, although they are independent of the macromonomer content in the copolymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1875–1885, 2002     

Nanophase morphology and crystallization in poly(vinylidene fluoride)/polydimethylsiloxane‐block‐poly(methyl methacrylate)‐block‐polystyrene blends

An approach to achieve confined crystallization of ferroelectric semicrystalline poly(vinylidene fluoride) (PVDF) was investigated. A novel polydimethylsiloxane‐block‐poly(methyl methacrylate)‐block‐polystyrene (PDMS‐b‐PMMA‐b‐PS) triblock copolymer was synthesized by the atom‐transfer radical polymerization method and blended with PVDF. Miscibility, crystallization and morphology of the PVDF/PDMS‐b‐PMMA‐b‐PS blends were studied within the whole range of concentration. In this A‐b‐B‐b‐C/D type of triblock copolymer/homopolymer system, crystallizable PVDF (D) and PMMA (B) middle block are miscible because of specific intermolecular interactions while A block (PDMS) and C block (PS) are immiscible with PVDF. Nanostructured morphology is formed via self‐assembly, displaying a variety of phase structures and semicrystalline morphologies. Crystallization at 145 °C reveals that both α and β crystalline phases of PVDF are present in PVDF/PDMS‐b‐PMMA‐b‐PS blends. Incorporation of the triblock copolymer decreases the degree of crystallization and enhances the proportion of β to α phase of semicrystalline PVDF. Introduction of PDMS‐b‐PMMA‐b‐PS triblock copolymer to PVDF makes the crystalline structures compact and confines the crystal size. Moreover, small‐angle X‐ray scattering results indicate that the immiscible PDMS as a soft block and PS as a hard block are localized in PVDF crystalline structures. © 2019 Society of Chemical Industry     

Synthesis and properties of chitosan-modified poly(vinyl butyrate)

Modification of chitosan by grafting of vinyl butyrate was carried out in homogeneous phase using potassium persulfate as redox initator and 1.5% acetic acid as solvent. The percent grafting and grafting efficiency were analysed and the high grafting efficiency up to 94% was observed. The effects of reaction variables such as monomer concentration, initiator concentration, temperature and reaction time were investigated. It was observed that the solubility of chitosan was markedly reduced after grafting with vinyl butyrate. The grafted product is insoluble in common organic solvents as well in dilute organic and inorganic acids. Characterization of the graft copolymers were carried out by using Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM) technics. Characteristic signal of carbonyl group was observed at 1,731 cm⁻¹ which belongs to the poly vinyl butyrate segments in the graft copolymer. The melting transition of the chitosan main chain in the copolymer shifted to 124°C from its original value 101°C. In addition to these, we have also studied topology of the graft copolymer and the SEM micrograph showed continuous homogenous matrix which means there is no phase separation.     

Lipase Catalyzed Synthesis of Poly(ε-Caprolactone)−Poly(Dimethylsiloxane)−Poly(ε-Caprolactone) Triblock Copolymers

Immobilized lipase B from Candida antarctica was used to synthesize copolymers of poly(ε-caprolactone) (PCL) with α,ω-(dihydroxy alkyl) terminated poly(dimethylsiloxane) (PDMS). The reactions were carried out in toluene with a 1:2 w/v ratio of the monomers to solvent at 70 oC. The PCL−PDMS−PCL triblock copolymer composition was varied by changing the feed ratio of the reactants [CL]/[PDMS] (80:20; 60:40; 40:60; 20:80 w/w, respectively). The enzymatically synthesized copolymers were characterized by GPC, FTIR, TGA, DSC and XRD. The successful synthesis of the copolymers was confirmed by the appearance of a single peak in all of the respective GPC chromatograms. An increased feed ratio of [CL]/[PDMS] produced an increase in the number-average molecular weight (M_n) of the copolymers from 4,400 g mol⁻¹ (20:80 w/w of [CL]/[PDMS]) to 13,950 g mol⁻¹ (80:20 w/w of [CL]/[PDMS]). The copolymers were shown by DSC and XRD to be semi-crystalline and the degree of crystallinity increased with an increase in the [CL]/[PDMS] feed ratio. The crystal structure in the copolymers was analogous to that of the PCL homopolymer. In enzymatic polymerization the recovery and reuse of the enzyme is highly desirable. When the lipase was recovered and reused for the copolymerization, higher molecular weight copolymers were obtained upon a second use. This appears to be due to an increased activity of the immobilized lipase following an opening up of the acrylic resin matrix in the organic medium. This improvement was not maintained for subsequent recycling of the lipase principally due to the disintegration of the acrylic resin matrix.     

In situ compatibilization of low-density polyethylene and polydimethylsiloxane rubber blends using ethylene–methyl acrylate copolymer as a chemical compatibilizer

The effect of the ethylene–methylacrylate copolymer as a chemical compatibilizer in the 50:50 blend of low-density polyethylene (LDPE) and polydimethylsiloxane rubber (PDMS) has been studied in detail. Ethylene–methylacrylate (EMA) reacted with PDMS rubber during melt-mixing at 180°C to form EMA-grafted PDMS rubber (EMA-g-PDMS) in situ, which acted as a compatibilizer in the LDPE–PDMS rubber blend. An optimum proportion of the compatibilizer (EMA) was found to be 6 wt % based on results of dynamic mechanical analysis, adhesion studies, and phase morphology. Lap shear adhesion between the phases increased significantly on incorporation of 6 wt % of EMA. Dynamic mechanical analysis showed a single glass transition (T_g) peak at ?119°C. This was further supported by X-ray diffraction studies, which exhibited a remarkable increase in the degree of crystallinity and phase morphology and showed a drastic reduction in the size of the dispersed phase at the optimum concentration of EMA. © 1993 John Wiley & Sons, Inc.     

Multiscale Modeling of the Morphology and Properties of Segmented Silicone-Urea Copolymers

Abstract  

Molecular dynamics and mesoscale dynamics simulation techniques were used to investigate the effect of hydrogen bonding on the microphase separation, morphology and various physicochemical properties of segmented silicone-urea copolymers. Model silicone-urea copolymers investigated were based on the stoichiometric combinations of α,ω-aminopropyl terminated polydimethylsiloxane (PDMS) oligomers with number average molecular weights ranging from 700 to 15,000 g/mole and bis(4-isocyanatocyclohexyl)methane (HMDI). Urea hard segment contents of the copolymers, which were determined by the PDMS molecular weight, were in 1.7–34% by weight range. Since no chain extenders were used, urea hard segments in all copolymers were of uniform length. Simulation results clearly demonstrated the presence of very good microphase separation in all silicone-urea copolymers, even for the copolymer with 1.7% by weight hard segment content. Experimentally reported enhanced properties of these materials were shown to stem from strong hydrogen bond interactions which leads to the aggregation of urea hard segments and reinforcement of the PDMS.     

Transmission electron microscopic observations of the multilevel microstructure of crosslinked copolymers with methacrylates and siloxane macromers by a radically polymerizable tuning approach

We investigated by Transmission Electron Microscopy (TEM) the morphologies of crosslinked copolymers from methacrylate monomers from methylmethacrylate (MMA) and trifluoroethylmethacrylate (TFEMA), polydimethylsiloxane (PDMS) macromers with molecular weight (Mn) of 1,700 and 4,700 g/mol, and crosslinker. Depending on the PDMS content, we observed, spherical PMMA islands in which small PDMS domains were dispersed, PMMA continuous phase, closely packed PTFEMA islands, and homogeneously dispersed PDMS domains were observed with low or middle magnification. Fine observation at 100,000‐fold magnification revealed the “fundamental” common size domain, which was determined by the M_n value of the PDMS macromer. Thus we found two microstructure types: (1) a “fundamental domain” due to the M_n of the PDMS macromer, and (2) an aggregated domain. The former was constant under all conditions, but the latter was affected by the comonomer and its ratio. The present results are essential in understanding the chemical and physical characteristics of crosslinked copolymers from PDMS macromers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermo‐ and pH‐responsive behaviors of graft copolymer and blend based on chitosan and N‐isopropylacrylamide

Thermo‐ and pH‐sensitive polymers were prepared by graft polymerization or blending of chitosan and poly(N‐isopropylacrylamide) (PNIPAAm). The graft copolymer and blend were characterized by Fourier transform‐infrared, thermogravimetric analysis, X‐ray diffraction measurements, and solubility test. The maximum grafting (%) of chitosan‐g‐(N‐isopropylacrylamide) (NIPAAm) was obtained at the 0.5 M NIPAAm monomer concentration, 2 × 10⁻³ M of ceric ammonium nitrate initiator and 2 h of reaction time at 25°C. The percentage of grafting (%) and the efficiency of grafting (%) gradually increased with the concentration of NIPAAm up to 0.5 M, and then decreased at above 0.5 M NIPAAm concentration due to the increase in the homopolymerization of NIPAAm. Both crosslinked chitosan‐g‐NIPAAm and chitosan/PNIPAAm blend reached an equilibrium state within 30 min. The equilibrium water content of all IPN samples dropped sharply at pH > 6 and temperature > 30°C. In the buffer solutions of various pH and temperature, the chitosan/PNIPAAm blend IPN has a somewhat higher swelling than that of the chitosan‐g‐NIPAAm IPN. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1381–1391, 2000     

In situ cross‐linked‐PDMS/BPPO membrane for the recovery of butanol by pervaporation

In this study, an in situ crosslinked polydimethylsiloxane/brominated polyphenylene oxide (c‐PDMS/BPPO) membrane on ceramic tube has been prepared for the recovery of butanol by pervaporation. A series of BPPO with different bromide‐substituted ratio were firstly synthesized through Wohl–Ziegler reaction. BPPO and PDMS were sequentially assembled and in situ crosslinked to form the final c‐PDMS/BPPO membrane. The results of solid‐state NMR and Differential Scanning Calorimeter demonstrated that the c‐PDMS/BPPO copolymer has a crosslinking structure and the SEM result proved the coverage of ceramic tube by copolymer layer. The effects of preparation conditions including dipping time and bromide‐substituted ratio of BPPO on the membrane performance were studied. The pervaporation experiments of butanol–water mixture indicated that the c‐PDMS/BPPO membrane exhibited an acceptable flux of 220 g·m^?2·h^?1 and high separation factor of 35 towards butanol, when the bromide‐substituted ratio was 34 wt % and the dipping time was 1.33 h. Moreover, the c‐PDMS/BPPO membrane performed excellent stability in an about 200 h continuous butanol recovery, as compared to the PDMS membrane. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40004.     

Synthesis and characterization of graft copolymers of syndiotactic polystyrene with polybutadiene and 4‐methylstyrene

The basic method for synthesizing syndiotactic polystyrene‐g‐polybutadiene graft copolymers was investigated. First, the syndiotactic polystyrene copolymer, poly(styrene‐co‐4‐methylstyrene), was prepared by the copolymerization of styrene and 4‐methylstyrene monomer with a trichloro(pentamethyl cyclopentadienyl) titanium(IV)/modified methylaluminoxane system as a metallocene catalyst at 50°C. Then, the polymerization proceeded in an argon atmosphere at the ambient pressure, and after purification by extraction, the copolymer structure was confirmed with ¹H‐NMR. Lastly, the copolymer was grafted with polybutadiene (a ready‐made commercialized unsaturated elastomer) by anionic grafting reactions with a metallation reagent. In this step, poly(styrene‐co‐4‐methylstyrene) was deprotonated at the methyl group of 4‐methylstyrene by butyl lithium and further reacted with polybutadiene to graft polybutadiene onto the deprotonated methyl of the poly(styrene‐co‐4‐methylstyrene) backbone. After purification of the graft copolymer by Soxhlet extraction, the grafting reaction copolymer structure was confirmed with ¹H‐NMR. These graft copolymers showed high melting temperatures (240–250°C) and were different from normal anionic styrene–butadiene copolymers because of the presence of crystalline syndiotactic polystyrene segments. Usually, highly syndiotactic polystyrene has a glass‐transition temperature of 100°C and behaves like a glassy polymer (possessing brittle mechanical properties) at room temperature. Thus, the graft copolymer can be used as a compatibilizer in syndiotactic polystyrene blends to modify the mechanical properties to compensate for the glassy properties of pure syndiotactic polystyrene at room temperature. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009