Structural modifications of segmented poly(hydroxyether-siloxane) copolymers

Summary Hydroxyether linked copolymers were synthesized from ,-bis(aminopropyl)polydimethyl diphenylsiloxane oligomers and diglydicylether of bisphenol-A (DGEBA). The siloxane oligomers were synthesized by the bulk coequilibration of the various weight percents cyclic dimethylsiloxane tetramer (D₄) with cyclic diphenylsiloxane tetramer (D₄) using a basic catalyst. The molecular weight and functionality was controlled by the incorporation of 1,3-bis(aminopropyl)-tetramethyldisiloxane end blocker. The copolymers containing low diphenylsiloxane compositions have two T_g's suggesting a microphase separation. Networks containing higher diphenylsiloxane compositions show a single phase morphology. The mechanical behavior of these copolymers is influenced by the composition changes.     

Effects of morphology and surface characteristics of poly(imide siloxane)s and deep UV/O3 surface treatment on the interfacial adhesion of poly(imide siloxane)/alloy-42 leadframe joints

The effect of surface characteristics and morphology of poly(imide siloxane) (PIS) on the true interfacial adhesion between PIS films and alloy-42 substrates was studied. The effect of the viscosity of PIS films and the surface treatment of deep UV/O₃ (d-UV/O₃) on alloy-42 plates on the peel strength of PIS films/alloy-42 joints has also investigated. 3,3′,4,4′-benzophenone tetracarboxylic dianhydride/2,2′-bis[4-(3-aminophenoxy)phenyl]sulfone (BTDA/m-BAPS) based PIS films with α,ω-bis(3-aminopropyl)polydimethyl siloxane (APPS) molecular weight M_n = 996 g/mole (PIS9Siy) show two phases in all compositions and the linear dependence of the critical surface tension on the surface concentration of the silicon, [Si_surf], on the PIS films. The PIS films with the APPS M_n = 507 g/mole (PIS5Siy) or M_n = 715 g/mole (PIS7Siy) exhibit a morphology change from a homogeneous phase to an inhomogeneous phase starting at the mole ratio (y) of APPS/PIS = 2.7% and 1.1%, respectively. The curves of critical surface tension dependence on the [Si_surf] discontinue or deflect at these two compositions, respectively. The treatment of d-UV/O₃ on alloy-42 plates improves the wetting on the alloy surface and promotes the peel strength between the PIS films and alloy-42 plates by a magnitude of ≥ 20%. These results show that the flowability of the same PIS films bonding at different temperatures significantly affects the bonding strength of the joints, but the flowability of different PIS films bonding at the same temperature, e.g. 400 °C, is not the key factor governing the bonding strength of the joints. The true interfacial adhesion of the PIS5Si0.6/alloy-42 joint is 80% higher than that of the unmodified BTDA/m-BAPS based polyimide film/alloy-42 joint. However, zero true interfacial adhesion is obtained between the PIS9Siy films and alloy-42 plates. The wetting kinetics experiment shows that the higher the siloxane content in the PIS, the higher the activation energy for the adhesive bonding process. Moreover, the phase sepration significantly increases the activation energy. The scanning electron micrographs of the peeled-off PIS film surfaces from the PIS/alloy-42 joints reveal the rougher surface morphology from the sample with the higher interfacial adhesion.     

Lipase Catalyzed Synthesis and Thermal Properties of Poly(dimethylsiloxane)–Poly(ethylene glycol) Amphiphilic Block Copolymers

Resin immobilized lipase B from Candida antarctica (CALB) was used to catalyze the condensation polymerization of two difuctional siloxane and poly(ethylene glycol) systems. In the first system, 1,3-bis(3-carboxypropyl)tetramethyldisiloxane was reacted with poly(ethylene glycol) (PEG having a number-average molecular weight, M_n = 400, 1000 and 3400 g mol⁻¹, respectively). In the second system, α,ω-(dihydroxy alkyl) terminated poly(dimethylsiloxane) (HAT-PDMS, M_n = 2500 g mol⁻¹) was reacted with α,ω-(diacid) terminated poly(ethylene glycol) (PEG, M_n = 600 g mol⁻¹). All the reactions were carried out in the bulk (without use of solvent) at 80 °C and under reduced pressure (500 mmHg vacuum gauge). The progress of the polyesterification reactions was monitored by analyzing the samples collected at various time intervals using FTIR and GPC. The thermal properties of the copolymers were characterized by DSC and TGA. In particular, the effect of the chain length of the PEG block on the molar mass build up and on the thermal stability of the copolymers was also studied. The thermal stability of the enzymatically synthesized copolymers was found to increase with increased dimethylsiloxane content in the copolymers.     

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.     

Synthesis of polysulfone block copolymers containing polydimethylsiloxane

The synthesis of polysulfone-polydimethylsiloxane (PSU-PDMS)linear block copolymers has been carried out in solution by condensation of chloro-terminated bisphenol A, diphenylsulfone and , -di (hydrogensilyl)-polydimethylsiloxane with Si–C bond. ¹H-NMR spectra of the block copolymers allow the estimation of siloxane and polysulfone ratio. The molecular weight of the polysulfone and polysiloxane oligomers and the block copolymers was determined by GPC. Thermogravimetric analysis indicates a thermal stability of block copolymers up to 400°C and allows estimation of the process activation energy. Microphase separation of the block copolymers was observed by differential scanning calorimetry (DSC).     

Thermal stabilities of end groups in hydroxyalkyl terminated polydimethylsiloxane oligomers

Summary Thermal stabilities of α,ω-hydroxypropyl, α,ω-hydroxybutyl, α,ω-2-hydroxypentyl and α,ω-hydroxyhexyl terminated polydimethylsiloxane (PDMS) oligomers were studied. Hydroxypropyl and hydroxybutyl terminated polydimethylsiloxane oligomers showed degradation upon heating, through the loss of functional end groups as determined by FT-IR spectroscopy and gel permeation chromatography. α,ω-Hydroxyhexyl and α,ω-2-hydroxypentyl terminated polydimethylsiloxane oligomers were stable under similar conditions. Instability of the end groups is due to the back biting of the terminal silicon in the PDMS by the primary hydroxyl oxygen, leading to the formation of 5 and 6 membered, stable, heterocylic compounds. Loss of end groups also resulted in a dramatic increase in the molecular weights of the oligomers produced, as determined by gel permeation chromatography. Received: 19 January 1998/Revised version: 27 February 1998/Accepted: 5 March 1998     

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.     

Properties of aqueous solutions of several salts of α,ω-alkanediol disulfates

Several salts of α,ω-sulfates, MO₃SO(CH₂)_n OSO₃M(n=12, 14, 16, 18, and M=Li, Na, and K) were prepared from the corresponding α,ω-alkane diols. The Krafft points of these α,ω-sulfates with common counterion as estimated by electroconductivity measurements increased with the increase of the hydrocarbon chain length, and the effect of the counterions on the Krafft points of the α,ω-sulfates with the same hydrocarbon chain length was in the order : Li<Na<K. Solutions of the α,ω-sulfates, except disodium dodecanediol disulfate, showed two break points corresponding to the first and second critical micelle concentration in each plot of the electroconductivity as a function of the concentration. The existence of the second break point suggested that another aggregation of rearrangement of the existing aggregates occurs in α,ω-sulfate solutions in addition to the usual micelle formation. The first and second break points of α,ω-sulfates with sodium counterion decreased logarithmically with increasing total number of methylene groups. The relationships were given as follows: log(first break point)=−0.138Nc−0.095; log(second break point)=−0.104Nc−0.251. The effect of the counterions upon the break points of α,ω-sulfates with the same hydrocarbon chain length was in accordance with their positions in the lyotropic series.     

Synthesis and Characteristics of Novel Poly(Imide Siloxane) Segmented Copolymers

New poly(imide siloxane) copolymers for possible use as tough environmentally stable structural matrix resins and structure adhesives have been prepared. Thus, 3,3'-4,4'-benzophenone tertracarboxylic dianhydride was reacted with various Mn aminopropyl-terminated polydimethylsiloxane oligomers and a meta-substituted diamine “chain-extender” such as 3,3'-diaminodiphenyl sulfone or 3,3'-diaminobenzophenone to produce the siloxane-modified poly(amic acid). Thin films were cast from the reaction mixtures and subsequent thermal dehydration produced the poly(imide siloxane) block or segmented copolymers. Upper “cure” temperatures of 300°C were used to insure complete imidization. By varying the amount and molecular weight of the siloxane oligomer, a variety of novel copolymers of controlled composition have been synthesized. Tough, transparent, flexible soluble films were produced by this method. The thermal and bulk properties of films having low to moderate siloxane content closely resemble those of the unmodified polyimide controls. However, toughness and surface behavior can be enhanced.     

Imide—Dimethylsiloxane block copolymers: Design and synthesis of a permanent buried oxygen ion etch barrier

Imide—siloxane multiblock copolymers were investigated. A key feature of these copolymers is the preparation of bis(aminopropyl) oligomers via anionic ring-opening polymerization. The molecular weights of the oligomers ranged from 1000 to 5000 g/mol. The oligomers were coreacted with 4,4′-oxydianaline (ODA) and pyromellitic dianhydride (PMDA) diethyl ester chloride in a N-methyl-2-pyrrolidone/THF—solvent mixture in the presence of N-methylmorpholine. The resulting amic ethyl ester siloxane copolymers were isolated and washed to remove homopolymer contamination. Copolymer compositions, determined by ¹H-NMR, ranged from 20 to 65 wt % siloxane content and the measured compositions were close to those charged. Solutions of the copolymers were cast and cured (350°C) to effect imidization, producing clear films. The films showed tough ductile mechanical properties with moduli varying with siloxane content. The copolymers displayed good thermal stability with decomposition temperatures in the proximity of 450°C. Multiphase morphologies were observed irrespective of siloxane block lengths or compositions. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 199–208, 1997     

Studies on the reactions of ω-carbethoxy fatty acid sodioesters with brominated compounds

Several ω-carbethoxy fatty acid sodioesters (C₂H₅-O₂ CCHNa(CH₂)_n−1-CO₂C₂H₅ and C₂H₅-O₂CCHNa(CH₂)_n−2-CHNaCO₂ C₂H₅ where n/6, 7, or 8) were condensed with ω-bromoaliphatic esters (Br(CH₂)_zCO₂C₂H₅ where z-5, 8 or 10), α,ω-dibromoalkanes (Br(CH₂)_n′-Br where n′=4, 6 or 8) and α,α′ m- or p-xylene. Tri- and tetraesters and several carbethoxy cycloheptanones which arose mainly from Dieckmann type condensations were isolated. The infrared spectra of the tri- and tetraesters were compared with those of their parent ω-carbethoxy fatty acid ester and additional peaks in the regions ofV _C=O andV _C-O-C were observed. Reactions involving the formation of both the α-sodio and α,α′ salts are also discussed.     

Asymmetric polymerization of N-substituted maleimides with organolithium — bisoxazolines complex

Asymmetric anionic polymerizations of achiral N-substituted maleimide (RMI) (N-cyclohexyl (CHMI), N-phenyl (PhMI), N-tert-butyl (TBMI)) by n-butyllithium (n-BuLi) or fluorenyllithium (FlLi) complexes of chiral bisoxazoline derivatives in toluene gave optically active polymers ([α]²⁵ ₄₃₅− 2.9° to − 8.2°). The polymers prerared with initiator of n-BuLi – 2,2′-bis(4,4′-isopropyl-,3-oxazoline) showed negative specific rotations (poly(RMI), [α]²⁵ ₄₃₅− 5.8° to − 8.2°) which were greater than those ([α]²⁵ ₄₃₅− 2.9° to − 5.9°) with other chiral 2,2′-bis(4,4′-alkyl-1,3-oxazoline) (alkyl group = iso-butyl and benzyl). Received: 29 July 1997/Revised: 27 August 1997/Accepted: 1 September 1997     

Synthesis and characterization of polysulfone–poly(alkylene oxide) block copolymers containing poly(dimethylsiloxane)

Block copolymers of polysulfone–poly(alkylene oxide)–poly(dimethylsiloxane) have been prepared by the addition of preformed α,ω-bis(hydrogensilyl)poly(dimethylsiloxane) oligomers to allyl end-capped poly(alkylene oxide)–polysulfone. The hydrosilylation reaction, catalyzed by platinum, was employed for incorporation of the siloxane chain into the copolymers in a 1 : 1 or 1 : 2 molar ratio of Si–H-terminated polydimethylsiloxane to allyl end-capped polysulfone. The products were characterized by IR, ¹H-NMR, and gel permeation chromatography. The thermal stability was determined by thermogravimetric analysis. Differential scanning calorimetry was used to investigate microphase separation in the block copolymers. © 1996 John Wiley & Sons, Inc.     

New telechelic polymers and sequential copolymers by polyfunctional initiator-transfer agents (inifers)

Summary α, ω-Di (nitrile)polyisobutylenes (nitrile-telechelic polyisobutylenes) have been synthesized by reacting α, ω-di (hydroxy) polyisobutylenes (hydroxyl-telechelic polyisobutylenes) with acrylonitrile, p-cyanobenzoyl chloride, p-cyanobenzoic acid and p-cyanobenzyl chloride by the use of a variety of catalysts, e.g. N-benzyltrimethylannnonium hydroxide, 4-N,N′-dimethylaminopyridine, dicyclohexylcarbodiimide, tetrabutylammonium hydrogen sulfate and tricaprylymethylammonium chloride. IR and ¹H-NMR analyses of models and polymer products suggest quantitative functionalization, except with p-cyanobenzyl chloride where only ∼ 80% functionalization was achieved. Methanesulfonation of the polymer-diol with methanesulfonyl chloride followed by reaction with NaCN in the presence of tricaprylymethylammonium chloride phase transfer catalyst gave quantitatively α, ω-di (nitrile) polyisobutylene.     

Synthesis and characterization of amphiphilic triblock-graft PEG-(<Emphasis Type="Italic">b</Emphasis>-PαN<Subscript>3</Subscript>CL-<Emphasis Type="Italic">g</Emphasis>-Alkyne)<Subscript>2</Subscript> degradable copolymers

The study proposes a straightforward strategy for synthesizing novel, amphiphilic triblock-graft PEG-(b-PαN₃CL-g-Alkyne)₂ degradable copolymers. First, this investigation performs copolymerization of α-chloro-ε-caprolactone (αClCL) using α,ω-dihydroxyl-terminated macroinitiator poly(ethylene glycol) (PEG) and stannous octoate as the catalyst. In a second step, the current work converts pendent chlorides into azides by reacting with sodium azide. Finally, various kinds of terminal alkynes react with pendent azides by copper-catalyzed Huisgen’s 1,3-dipolar cycloaddition, thus a “click” reaction. These copolymers are characterized by differential scanning calorimetry (DSC), ¹H NMR, IR and gel permeation chromatography. The resulting triblock-graft copolymers exhibit lower crystallinity and melting temperature with respect to the original PEG. The triblock-graft copolymers form micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 1.58–8.62 mg L⁻¹, depending on polymer composition. The ¹H NMR spectrum of micelles in D₂O demonstrate only the PEG signal and thus confirm the PCL-g-Alkyne blocks constitute the micelle core, while the central PEG block constitutes the micelle shell. The hydrophilic segment lengths influence the micelle shape. The mean hydrodynamic diameters of micelles from DLS range from 90–200 nm. The work describes drug entrapment efficiency and drug loading content of micelles depending on the composition of triblock-graft polymers.      

Novel block copolymers containing poly(phenylmaleimide) segments: Block copolymerization ofN-phenylmaleimide onto poly(oxyethylene) and poly(butadiene)

Summary Novel block copolymers having poly(N-phenylmaleimide) segments onto poly(oxyethylene) or poly(butadiene) were synthesized. The block copolymerization of N-phenylmaleimide was carried out anionically with lithium alkoxides of poly(ethylene glycol) or α,ω-dihydroxypoly(butadiene). The block copolymers obtained were characterized by¹H NMR, GPC and TLC.     

Dynamic mechanical study of the transition from swollen particles to hydrogel caused by neutralization

Summary The copolymer of 2-(2-carboxybenzoyloxy)ethyl methacrylate (CEM) with butyl methacrylate (BMA) (BMA/CEM = 40/60 wt.) and terpolymers CEM/BMA/ 2-hydroxyethyl methacrylate (HEMA) ((BMA + HEMA)/CEM = 40/60 wt.; HEMA/BMA = 35/5, 30/10, 20/20 and 10/30) were prepared by emulsion radical copolymerization in water in the presence of sodium dodecyl sulfate and their dynamic mechanical behaviour was investigated as a function of the degree of neutralization α. Main attention was devoted to the transition from swollen particles to physical gel with increasing degree of neutralization and to the structure of formed hydrogels. From the results it followed: (a) the transition from swollen particles to the gel state occurs in a narrow neutralization interval at α∼ 0.45 for BMA/CEM copolymer; increasing the HEMA content shifts the transition to lower α values; (b) with increasing shear strain γ, the hydrogels passed from the gel to liquid state and this transition at the critical strain γ_c, was reversible; (c) junctions in the gel state are probably formed by the hydrophobic interactions of the ends of CEM units which form clusters and the junction concentration is independent of the HEMA content and degree of neutralization α; (d) increasing degree of neutralization α and the HEMA content (increasing polarity of the system) stabilizes the junctions and the critical γ_c values increase; (e) the values of the low-strain storage G′₀ and loss G″₀ moduli together with critical strains γ_c did not depend on angular frequnecy ω in the interval 10⁻¹− 10 rad/s. Received: 5 January 2000/Accepted: 23 May 2000     

Micellization Behavior of Cationic Gemini Surfactants in Aqueous-Ethylene Glycol Solution

The micellization behavior of gemini surfactants i.e. alkanediyl-α,ω-bis(cetyldimethylammonium bromide) (C₁₆-s-C₁₆,2Br⁻ where s = 3, 4, 10) in 10% (v/v) ethylene glycol solution was investigated by surface tension and conductometric measurements at 300 K. The critical micelle concentration, degree of micellar ionization, surface excess concentration, minimum surface area per molecule of surfactant, surface pressure at the CMC and Gibbs energy of adsorption of the dimeric surfactants have also been determined in the presence of different salts (NaCl, NaBr and NaI). The critical micelle concentration and degree of micellar ionization values decrease significantly in the presence of sodium halides and follows the sequence NaCl < NaBr < NaI. The free energy, enthalpy and entropy of micellization of dimeric surfactants in 10% (v/v) ethylene glycol solution were determined using the temperature dependence of the critical micelle concentration. The standard free energy of micellization was found to be negative in all the cases.     

Application of arrhenius kinetics to evaluate oxidative stability in vegetable oils by isothermal differential scanning calorimetry

In this study, 10 different vegetable oils were oxidized at four different isothermal temperatures (383, 393, 403, and 413 K) in a differential scanning calorimeter (DSC). The protocol involved oxidizing vegetable oils in a DSC cell with oxygen flow. A rapid increase in evolved heat was observed with an exothermic heat flow appearing during initiation of the oxidation reaction. From this resulting exotherm, the onset of oxidation time (T _o) was determined graphically by the DSC instrument. In our experimental data, linear relationships were determined by extrapolation of the log (T _o) against isothermal temperature. The rates of lipid oxidation were highly correlated with temperature. In addition, based on the Arrhenius equation and activated complex theory, reaction rate constants (k), activation energies (E _a), activation enthalpies (ΔH ^‡), and activation entropies (ΔS ^‡) for oxidative stability of vegetable oils were calculated. The E _a′, ΔH ^‡, and ΔS ^‡ for all vegetable oils ranged from 79 to −104 kJ mol⁻¹, from 76 to −101 kJ mol⁻¹, and from −99 to −20 J K⁻¹ mol⁻¹, respectively. Based on the results obtained, differential scanning calorimetry appears to be a useful new instrumental method for kinetic analysis of lipid oxidation in vegetable oil.     

Microphase separation in amorphous poly(imide siloxane) segmented copolymers

A series of amorphous poly(imide siloxane) (PIS) segmented copolymers with various segmental lengths and contents of poly(dimethyl siloxane) (PDMS) were synthesized by condensation polymerization. Extraction was utilized to obtain highly pure PISs for a study of phase separation. The PISs self-assemble from dilute solutions that are initially rod-like structures and then rapidly transform to vesicles. Moreover, the vesicles change to solid spheres as the PDMS content increases. A variety of morphologies of the PIS films, including unilamellar vesicle, multilamellar vesicle, sea-island and others, are found as a function of the content and the segmental length of PDMS. Small angle X-ray scattering demonstrates the coexistence of large-scale phase separations and nano-scale phase separations of approximately 20 nm. The DSC results reveal that the phase separation is induced and dominated by the aggregation of PDMS segments. Furthermore, the surfaces of the hard phases in the PDMS-900 PISs are found to be fractal.