Ideal tetrafunctional amphiphilic PEG/PDMS conetworks by a dual‐purpose extender/crosslinker. II. Characterization and properties of water‐swollen membranes

Select characteristics and properties of a series of ideal tetrafunctional amphiphilic conetworks consisting of random poly(ethylene glycol) (PEG) and polydimethylsiloxane (PDMS) segments crosslinked by a novel dual‐purpose crosslinker/extender were determined. The overall composition of the conetworks was varied in the 16–40% PEG range, and membranes were prepared by polymerizing/crosslinking charges in molds. Membranes were characterized by equilibrium swelling (both in water and n‐heptane) and by determining their oxygen permeabilities and select mechanical properties. Swelling in water increases, whereas in heptane it decreases with increasing PEG content. Significant swelling in both solvents indicates bicontinuous (bipercolating) PEG and PDMS phases. Bicontinuity is reached with ～13% PEG in the conetworks. The oxygen permeabilities of optically clear water‐swollen membranes containing 24, 32, and 40 wt % PEG are ～350, ～245 and ～185 barrers, respectively, i.e., oxygen permeability decreases by increasing the hydrophilic constituent. These oxygen permeabilities are far superior to those of contemporary soft contact lenses. The tensile strengths and moduli of water‐swollen membranes decrease, while elongations increase, with increasing PEG content. Dry membranes exhibit first order transitions at ?52 and ～46 °C indicating phase‐separated crystalline PDMS and PEG domains, respectively. Both dry and water‐swollen membranes are optically clear, indicating the presence of PEG and PDMS domains with dimensions well below the wavelength of visible light. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4965–4971, 2005     

Third‐generation amphiphilic conetworks. I. Synthesis and swelling behavior of poly(N,N‐dimethyl acrylamide)/polydimethylsiloxane conetworks

A strategy has been developed for the synthesis of novel amphiphilic conetworks (APCNs) of poly(N,N‐dimethyl acrylamide) (PDMAAm) and polydimethyl‐siloxane (PDMS) segments crosslinked with polyhydrosiloxanes. The synthesis proceeds in three steps in one pot (see Figure 2 for reactions and abbreviations): (1) the preparation of a charge containing three components (an asymmetric–telechelic macromonomer, MA‐PDMS‐V, plus two symmetric–telechelic crosslinkers, MA‐PDMS‐MA and V‐PDMS‐V), (2) the free‐radical terpolymerization of N,N‐dimethyl acrylamide, MA‐PDMS‐V, and MA‐PDMS‐MA into a slightly crosslinked and soluble graft of a PDMAAm backbone carrying‐PDMS‐V branches, and (3) the crosslinking of PDMS branches with polyhydrosiloxanes. The effects of key experimental parameters (e.g., composition, molecular weights, and initiator and crosslinker concentrations) on synthesis details and swelling behavior have been studied. The water uptake/permeability of APCNs is significantly increased by the addition of homo‐PDMAAm to graft charges, crosslinking of the graft, and, after the desirable morphology is stabilized, removing the homo‐PDMAAm by water extraction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 295–307, 2007     

Thermoplastic amphiphilic conetworks

Our main objective was the design, synthesis, characterization, and testing of a novel class of materials, thermoplastic amphiphilic conetworks (TP‐APCNs). A further objective was the evaluation of TP‐APCNs as biomaterials, for example, as immunoisolatory membranes in a bioartificial pancreas, or as extended‐wear soft contact lenses. The synthesis of the first TP‐APCNs was accomplished by blending an amphiphilic graft polymer, poly(dimethyl acryl amide)‐g‐polydimethylsiloxane (PDMAAm‐g‐PDMS), with a commercial PDMS‐containing polyurethane (PU). The common PDMS segments coalesce and form a single phase, whereas the hard/crystalline segments of the PU physically crosslink the blend. The properties of TP‐APCNs can be controlled by the graft/PU ratio and segment molecular weights. TP‐APCNs with cocontinuous hydrophilic and hydrophobic phases were prepared as demonstrated by swelling in water and n‐heptane. Depending on the blend ratio and molecular weights, optically clear water‐swollen TP‐APCNs with 0.5–4 MPa tensile strength, 70–280% elongation, together with 2–11 × 10^?7 cm²/s glucose permeability, and 1.2–8 × 10^?8 cm²/s insulin permeability were prepared. TP‐APCNs are processible by casting and molding. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 682–691, 2009     

Cyclosiloxane‐based networks: Synthesis,thermal characterization,and microstructure

This article mainly concerns the synthesis of novel PD₅/PDMS conetworks by the copolymerization of cyclic D₅H and linear HO? PDMS? OH units, and the characterization of the product by DMTA, DSC, and TGA. The ultimate properties of the conetworks may be controlled by varying the relative composition of D₅H and PDMS components. DMTA and DSC thermograms indicate compatibility between the PD₅ and PDMS domains. Understanding of the polymer chemical transformations involved in conetwork formation combined with an analysis of DMTA and DSC thermograms led to a proposition of the microarchitecture of PD₅/PDMS conetworks. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 630–637, 2005     

Amphiphilic conetworks. III. Poly(2,3‐dihydroxypropyl methacrylate)–polyisobutylene and poly(ethylene glycol) methacrylate–polyisobutylene based hydrogels prepared by two‐step polymer procedure

This article describes the synthesis and characterization of new amphiphilic polymer conetworks containing hydrophilic poly(2,3‐dihydroxypropyl methacrylate) or poly(ethylene glycol) methacrylate (PEGMA) and hydrophobic polyisobutylene chains. This conetworks were prepared by a two‐step polymer synthesis. In the first step, a cationic copolymer of isobutylene and 3‐isopropenyl‐α,α‐dimethylbenzyl isocyanate (IDI) was prepared. The isocyanate groups of the IB‐IDI random copolymer were subsequently transformed in situ to methacrylate (MA) groups in reaction with 2‐hydroxyethyl methacrylate (HEMA). In the second step, the resulting MA‐multifunctional PIB‐based crosslinker, PIB(MA)_n, with an average functionality of approximately four per chain, was copolymerized with 2,3‐dihydroxypropyl methacrylate or poly(ethylene glycol) methacrylate by radical mechanism in tetrahydrofuran giving rise to amphiphilic conetworks containing 11–60 mol % of DHPMA or 10–12 mol % of PEGMA. The synthesized conetworks were characterized with solid‐state ¹³C‐NMR spectroscopy and differential scanning calorimetry. The amphiphilic nature of the conetworks was proved by swelling in both water and n‐heptane. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4074–4081, 2007     

Chemical modification of poly(substituted-acetylene). I. Synthesis and gas permeability of poly(1-trimethylsilyl-1-propyne)/poly (dimethylsiloxane) graft copolymer

In order to improve the selectivity and the stability and the stability for gas permeation of poly (1-trimethylsilyl-1-propyne) (PTMSP) membrane, it was chemically modified by grafting polydimethylsiloxane (PDMS) chains. The graft copolymers were synthesized by four different methods via metallation of PTMSP with n-butyllithium. PDMS content of the graft co-polymers was controlled in the range of 4–92 mol %. Very tough, thin membranes could be prepared from these graft copolymers using a solvent casting method. Thermal property and gas permeability of the copolymer membranes thus obtained were evaluated. These membranes were relatively thermally stable, and the softening points were over about 150°C. Oxygen permeability coefficients Po₂ and selectivity Po₂/PN₂ of PTMSP/PDMS graft copolymers depended on the PDMS content, the former was in the range of 1 X 10^?8 to 2 × 10^?7 cm³ (STP)· cm/(cm²· s · cm. Hg) and the latter was 2.0–3.1. Minimum values of PO₂ and PN₂ occured at PDMS content of about 55 mol %. The introduction of more than 60 mol % of PDMS resulted in oxygen permeability coefficient which was maintained for more than one moth (PO₂ = 2 ? 6 × 10 ^?8 cm ³ (STP)· cm/(cm²·s·cm Hg), PO₂/PN₂ = 2.3–2.7).     

Hydrolyzable poly(ester-urethane) networks from L-lysine diisocyanate and D,L-lactide/ϵ-caprolactone homo- and copolyester triols

Bioabsorbable poly(ester-urethane) networks were synthesized from ethyl 2,6-diisocyanatohexanoate (L -lysine diisocyanate) (LDI) and a series of polyester triols. LDI was synthesized by refluxing L-lysine monohydrochloride with ethanol to form the ester, which was subsequently refluxed with 1,1,1,3,3,3-hexamethyldisilazane to yield a silazane-protected intermediate. This product was then phosgenated using triphosgene. Polyester triols were synthesized from D,L-lactide, ?-caprolactone, or comonomer mixtures thereof, using glycerol as initiator and stannous octoate as catalyst. Polyurethane networks were cured using [NCO]/[OH] = 1.05 and stannous octoate (0.05 wt %) for 24 h at room temperature and pressure and 24 h at 50°C and 0.1 mm Hg. LDI-based polyurethane networks were totally amorphous and possessed very low sol contents. Networks based on poly (D,L-lactide) triols were rigid (T_g ∽ 60°C) with ultimate tensile strengths of ～ 40–70 MPa, tensile moduli of ～ 1.2–2.0 GPa, and ultimate elongations of ～ 4–10%. Networks based on ?-caprolactone triols were low-modulus elastomers with tensile strengths and moduli of ～ 1–4 MPa and ～ 3–6 GPa, respectively, and ultimate elongations of ～ 50–300%. Networks based on copolymers displayed physical properties consistent with monomer composition and were tougher than the networks based on the homopolymers. Tensile strengths for the copolymers were ～ 3–25 MPa with ultimate elongations up to 600%. Hydrolytic degradation under simulated physiological conditions showed that D ,L -lactide homopolymer networks were the most resistant to degradation, undergoing virtually no change in mass or physical properties for 60 days. ?-Caprolactone-based networks were resistant to degradation for 40 days, and high-lactide copolymer-based networks suffered substantial losses in physical properties after only 3 days. © 1994 John Wiley & Sons, Inc.     

Synthesis,characterization, and crosslinking of methacrylate‐telechelic PDMAAm‐b‐PDMS‐b‐PDMAAm copolymers

The synthesis and molecular characterization of a new amphiphilic conetwork (APCN) designed for silicone hydrogel use is described. The synthesis strategy, outlined in Scheme 1 , calls for the preparation, by the RAFT technique, of a new methacrylate‐telechelic amphiphilic pentablock, MA‐PHEA‐b‐PDMAAM‐b‐PDMS‐b‐PDMAAm‐b‐PHEA‐MA, and its crosslinking to the target APCN. The sketch shows the architecture of the APCN (dotted lines, PDMAAm; solid lines, PDMS; clusters, MA‐based crosslinking sites; see Fig. 3 ). All six synthesis steps proceed smoothly and efficiently, and the products are optically clear, colorless membranes exhibiting properties appropriate for ophthalmic use. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4284–4290, 2007     

Specific properties of in situ ruthenium‐catalyzed polyamide 12/polydimethylsiloxane compatibilized blend

The main objective of this work focused on the chemical modification of polyamide 12 (PA12) properties through the reaction with a hydride‐terminated polydimethylsiloxane (PDMS‐SiH). The investigated PA12/PDMS‐SiH blend was compatibilized by ruthenium derivative catalyzed hydrosilylation reaction in molten state. This original route enhanced interfacial adhesion and avoid PDMS‐SiH leaching phenomenon between the two immiscible phases. More specifically, the size of PDMS‐SiH domains in the blend decreased from around 4 μm to 800 nm and from 30 to 1 μm after compatibilization with 10 and 20 wt % PDMS‐SiH, respectively. For the best compatibilized PA12/PDMS‐SiH blend, the introduction of PDMS lowered the surface free energy and the PA12‐based blend turned from hydrophilic to hydrophobic behavior, as evidenced by the water contact angle measurements. Gas permeability and CO₂/H₂ and CO₂/He gas selectivity were also improved with the increase in PDMS content. Besides, the mechanical properties were enhanced with 13% increase in Young's modulus after in situ compatibilization with 15 wt % PDMS‐SiH. Thermal stability was also improved after compatibilization as the initial degradation temperature of reactive blends obviously increased compared with nonreactive ones. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 978–988     

Amphiphilic conetworks. IV. Poly(methacrylic acid)‐l‐polyisobutylene and poly(acrylic acid)‐l‐polyisobutylene based hydrogels prepared by two‐step polymer procedure. New pH responsive conetworks

This article describes the synthesis and characterization of new amphiphilic polymer conetworks containing hydrophilic poly(methacrylic acid) (PMAA) or poly(acrylic acid) (PAA) and hydrophobic polyisobutylene (PIB) chains. These conetworks were prepared by a two‐step polymer synthesis. In the first step, a cationic copolymer of isobutylene (IB) and 3‐isopropenyl‐α,α‐dimethylbenzyl isocyanate (IDI) was prepared. The isocyanate groups of the IB–IDI random copolymer were subsequently transformed in situ to methacrylate (MA) groups in reaction with 2‐hydroxyethyl methacrylate (HEMA). In the second step, the resulting MA‐multifunctional PIB‐based crosslinker, PIB(MA)_n, with an average functionality of approximately four methacrylic groups per chain, was copolymerized with methacrylic acid (MAA) or acrylic acid (AA) by radical mechanism in tetrahydrofuran giving rise to amphiphilic conetworks containing 31–79 mol % of MAA or 26–36 mol % of AA. The synthesized conetworks were characterized with solid‐state ¹³C‐NMR spectroscopy and differential scanning calorimetry. The amphiphilic nature of the conetworks was proven by swelling in both aqueous media with low and high pH and n‐heptane. The effect of varying pH on the swelling behavior of the synthesized conetworks is presented. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1284–1291, 2009     

Novel amphiphilic triblocks fitted with photocrosslinkable termini,and their photocrosslinking to conetworks

Two new telechelic amphiphilic triblock copolymers, HE₃‐PEG‐b‐PDMS‐b‐PEG‐HE₃ and HE₃‐PEG‐b‐PDMS‐b‐PEG‐HE₃, i.e., sequence‐reversed triblocks of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic polydimethylsiloxane (PDMS) segments fitted with photocrosslinkable tri[2‐(3,4‐cyclohexane oxide)ethyl‐dimethylsiloxy]silane (HE₃) termini, were synthesized, characterized, photocrosslinked to amphiphilic conetworks (APCNs), and the properties of the APCNs were analyzed. APCNs in which the crosslinking sites are located in the hydrophobic domains exhibited significantly better mechanical properties than those in which the crosslinks were in the hydrophilic domains. The stiff domains formed of the UV‐crosslinkable HE₃ chain‐end substituents provide not only crosslinking but reinforcement as well. The crosslinking/reinforcement efficiency was greatly enhanced by the addition of excess HE₃. Water‐swollen APCNs were optically clear and exhibited mechanical properties appropriate for biomedical application. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 174–185, 2008     

Polymerizability,copolymerizability, and properties of cyanoacrylate‐telechelic polyisobutylenes II: copolymerization of three‐arm star cyanoacrylate‐ telechelic polyisobutylene with ethyl cyanoacrylate

This research concerned the synthesis and characterization of novel conetworks containing polyisobutylene (PIB) and polyethyl‐2‐cyanoacrylate [poly(Et‐CA)] sequences. The syntheses involved the copolymerization of CA‐telechelic three‐arm star PIB [Ø(PIB‐CA)₃] with ethyl‐2‐cyanoacrylate (Et‐CA) mediated by nucleophiles or by living tissue (fresh eggs). The conetworks were characterized by swelling in hexanes, tetrahydrofuran (THF), and acetone, and the results indicate co‐continuous PIB and poly(Et‐CA) domains. The conetworks exhibit two T_gs indicating phase‐separation between PIB and poly(Et‐CA). The outstanding oxidative resistance of the conetworks was demonstrated by exposure to concentrated nitric acid. The tensile strengths, moduli, and elongations of a series of conetworks with different overall compositions were investigated and the findings interpreted in terms of covalently linked rubbery and glassy domains. AFM also suggests the presence of phase‐separated rubbery and glassy domains. DMTA spectra of a Ø(PIB‐CA)₃ homonetwork, and Ø(PIB‐CA)₃/Et‐CA conetworks were analyzed and interpreted in terms of coexisting rubbery and glassy domains. Observations made during the exposure of Ø(PIB‐CA)₃/Et‐CA mixtures to proteinaceous tissue, in combination with characterization data, were used to propose a structural model for the conetworks. Copyright © 2007 John Wiley & Sons, Ltd.     

Modification of polyisoprene‐block‐poly(vinyl trimethylsilane) block copolymers via hydrosilylation and hydrogenation,and their gas transport properties

Polyisoprene‐block‐poly(vinyl trimethylsilane) (PI‐b‐PVTMS) block copolymers having different isoprene contents are successfully chemically modified and characterized by proton nuclear magnetic resonance spectroscopy (¹H‐NMR), Fourier transform infrared spectroscopy, gel permeation chromatography, and thermogravimetric analysis. Gas transport properties of the initial block copolymers and their derivatives modified via hydrosilylation and hydrogenation are measured. The modified block copolymers show higher permeabilities for O₂ and H₂ than the unmodified block copolymers while maintaining similar O₂/N₂ and H₂/N₂ selectivities. Hydrosilylation and hydrogenation of block copolymers with a low isoprene content result in a permeability increase for O₂ and H₂ of 15 to 40%, respectively. Similarly, for block copolymers with high isoprene contents, increases in permeabilities up to 125% are observed compared to initial PI‐b‐PVTMS. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym. Phys. 2013 , 51, 1252–1261     

Ideal tetrafunctional amphiphilic PEG/PDMS conetworks by a dual‐purpose extender/crosslinker. I. Synthesis

The synthesis of a new type of amphiphilic conetwork (APCN) consisting of well‐defined hydrophilic poly(ethylene glycol) (PEG) and hydrophobic polydimethylsiloxane (PDMS) segments is described. The conetwork is ideal (the lengths of each PEG and PDMS chain segments, respectively, are identical) and tetrafunctional (exactly four chains emanate from each crosslink site). The synthesis of the conetworks was achieved by the use of a novel dual‐purpose extender/crosslinker Y (bis [(dimethylsilyl)oxy]‐[(etoxydimethylsilyl)oxy]phenylsilane, (SiPh(SiH)₂OEt)), in two steps: (1) Synthesis of a new linear random multiblock copolymer (MBC) (AY)_n(BY)_m, where A is the hydrophilic PEG and B is the hydrophobic segment, and (2) Crosslinking the multiblocks by catalytic condensation of the SiOEt groups in the Y units. The extender/crosslinker fulfills two totally different functions: First, it extends two incompatible hydrophilic and hydrophobic prepolymers (PEG and PDMS) to a random MBC, and, subsequently, it cross‐links the multiblocks to the target APCN. The synthesis and characterization of the extender/crosslinker is also presented. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4953–4964, 2005     

Pure and mixed gas acetone/nitrogen permeation properties of polydimethylsiloxane [PDMS]

The permeability of polydimethylsiloxane [PDMS] to acetone, nitrogen, and acetone/nitrogen mixtures has been determined at 28°C. In pure gas experiments, the permeability of PDMS to nitrogen was 245 × 10⁻¹⁰ cm³(STP) · cm/cm² · s · cmHg and was independent of pressure. The permeability of PDMS to acetone vapor increased exponentially with increasing acetone pressure. PDMS is much more permeable to acetone than to nitrogen; acetone/nitrogen selectivity increases from 85 to 185 as acetone partial pressure in the feed increases from 0 to 67% of saturation. In mixed gas permeation experiments, the nitrogen permeability coefficient is independent of acetone relative pressure and is equal to the pure gas permeability coefficient. The acetone permeability coefficient has the same value in both mixed gas and pure acetone permeation experiments. Average acetone diffusivity in PDMS, determined as the ratio of permeability to solubility, decreases with increasing acetone concentration due to mild clustering of acetone in the polymer (because acetone is a poor solvent for PDMS) and changes in the polymer–penetrant thermodynamic interactions which influence diffusion coefficients. A Zimm–Lundberg analysis of the acetone sorption isotherm is also consistent with acetone clustering in PDMS. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 289–301, 1998     

Synthesis and characterization of novel biodegradable copolyesters by transreaction of poly(ethylene terephthalate) with copoly(succinic anhydride/ethylene oxide)

Poly(ethylene terephthalate)/copoly(succinic anhydride/ethylene oxide) copolymers, (PET/PES copolymers) were synthesized by the transreaction between PET and PES and characterized with GPC, ¹H NMR, and DSC. Most of the copolymers obtained were random copolymers. The films cast of these copolymers were transparent. The thermal, mechanical properties, and biodegradability of the copolymers obtained were studied with respect to the composition and lengths of aliphatic and aromatic units in the copolymers. In the copolymers having high PET content, the melting points, due to the PET segment, were observed by DSC measurement, although the fusion heats of the copolymers were small. The enzymatic hydrolyzability by a lipase from Rhizopus arrhizus and biodegradability by activated sludge of the copolymers decreased with an increase in PET content. When the length of succinic acid unit in the copolymer was below 2, the hydrolyzability of the copolymers decreased considerably. The tensile strengths of the cast films prepared from the copolymers synthesized by the transreaction increased with an increase in PET content, whereas, the elongations at break decreased. Their tensile strengths were half, and the elongations were double compared to those of PET homopolymer film. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4478–4489, 2000     

Cyclolinear polysiloxanes. II. Crosslinking and characterization

The synthesis and characterization of two groups of novel networks prepared from cyclolinear polysiloxanes are described. The first group of networks from cyclolinear polysiloxanes (N‐CLPSs) was synthesized by the hydrosilation of vinyl‐terminated cyclolinear polyorganosiloxanes [prepared from diacetoxydiethyltetramethylcyclotetrasiloxane (D₄Et₂OAc₂) or diacetoxytriethylpentamethylcyclopentasiloxane (D₅Et₃OAc₂)] with a copolymer of dimethylsiloxane and methylhydrosiloxane as the crosslinking agent. Hydrosilation was effected with a platinum carbonyl catalyst with a cyclovinylsiloxane moderator. The second group of networks (N‐eCLPSs) was prepared similarly with extended cyclolinear polysiloxanes. The mechanical properties of the novel networks were comparable to those of polydimethylsiloxane networks (N‐PDMS). The oxygen permeabilities were similar to or slightly higher than that of N‐PDMS. The glass‐transition temperatures of D₄Et₂OAc₂‐ and D₅Et₃OAc₂‐based N‐CLPSs were ?67.8 and ?90.8 °C, respectively, whereas the incorporation of polydimethylsiloxane spacers into similar N‐eCLPSs lowered their glass‐transition temperatures to ?109.7 and ?115.0 °C. Upon heating to 800 °C in air, N‐CLPSs yielded more residue than N‐eCLPSs, which in turn yielded more residue than N‐PDMS. These results may have been due to the presence of T units in the cyclic siloxane units, which may have inhibited chain degradation or the formation of volatile products. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4053–4062, 2006     

Amphiphilic Networks. I. Network Synthesis by Copolymerization of Methacryloyl-Capped Polyisobutylene with 2-(Dimethylamino) Ethyl Methacrylate and Characterization of The Networks

New amphiphilic networks have been synthesized by free-radical co-polymerization of hydrophobic methacryloyl-capped polyisobutylenes (MA-PIB-MA) with hydrophilic 2-(dimethylamino)ethyl methacrylate. Two MA-PIB-MAs have been prepared with M_n = 4920 and 10 200, and two series of networks were prepared with MA-PIB-MA contents between 48 and 71.5%. Variation of the molecular weight of MA-PIB-MA and its concentration in the network allows for a wide range of mechanical properties and swellability in hydrophilic and hydrophobic solvents. Differential scanning calorimetry shows the existence of two glass transitions in these networks and thus indicates a phase-separated domain structure. Tensile strengths and elongations were dependent on MA-PIB-MA contents varying from 57.7 to 39.8 kg/cm² and from 168 to 200%, respectively, with increasing MA-PIB-MA content. Solvent swelling of the networks ranged from 170 to 20% in water and from 40 to 170% in n-heptane with increasing MA-PIB-MA contents.     

Rendering polyureas melt processible

Because of the presence of extensive H‐bonding in the hard segments, polyureas are processed by solution techniques (e.g., dry spinning) by the use of relatively costly and environmentally unfriendly solvents. Thus, the objective of this research was to render polyureas melt processible, (i.e., to reduce their flow temperature, T_flow) without compromising their excellent mechanical properties. We hypothesized and herein demonstrate that by using conventional chain extenders (CEs) in combination with small amounts of H‐bond acceptor chain extenders (HACEs), the T_flow of polyureas can be significantly reduced from ～230 to ～180 °C, and thus melt processible products with excellent mechanical properties can be obtained. We document the synthesis of conventional polytetramethylene oxide‐based and novel polyisobutylene (PIB)‐based polyureas with T_flows ～ 180 °C and excellent mechanicals by the addition of few percents of commercially available HACEs. Products were characterized by various techniques, including Instron (tensile strengths, elongations), durometer (Shore A Hardness), dynamic mechanical thermal analysis (T_flow), and thermal gravimetric analysis (TGA) (thermal weight loss). According to TGA, a polyurea with T_flow of ～180 °C did not degrade up to ～234 °C in air. A micromorphology for melt processible polyureas is proposed that emphasizes flexibilized hard segments in the presence of HACEs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Anionic amphiphilic end‐linked conetworks by the combination of quasiliving carbocationic and group transfer polymerizations

A series of amphiphilic end‐linked conetworks was synthesized by the combination of two “quasiliving” polymerization techniques, quasiliving carbocationic (QLCCP) and group transfer polymerizations (GTP). The hydrophobic monomer was polyisobutylene methacrylate synthesized by the QLCCP of isobutylene and subsequent terminal modification reactions. The hydrophilic monomer was methacrylic acid (MAA) introduced via the polymerization of 2‐tetrahydropyranyl methacrylate followed by acid hydrolysis after (co)network formation. The conetwork syntheses were performed by sequential monomer/crosslinker additions under GTP conditions. All the precursors and the extractables from the conetworks were characterized by gel permeation chromatography and ¹H NMR. The resulting polymer conetworks were investigated in terms of their degree of swelling (DS) in aqueous media and in tetrahydrofuran (THF) over the whole range of ionization of the MAA units and in n‐hexane for uncharged conetworks. The DSs in water increased with the degree of ionization (DI) of the MAA units and the hydrophilic content in the conetwork, whereas the DSs in THF increased with the reduction of the DI of the MAA units. The effective pK of the MAA units in the conetworks increased from 8.4 to 10.5 with decreasing MAA content. These findings can facilitate the design of similar unique conetworks with adjustable swelling behavior and composition‐dependent pK values. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4289–4301, 2009