Bicomponent nanophase-separated poly(2-hydroxyethyl methacrylate)-linked-polyisobutylene (PHEMA-l-PIB) amphiphilic conetworks were synthesized by radical copolymerization of methacrylate−telechelic polyisobutylene (MA−PIB−MA) and different amounts of 2-(trimethylsilyloxy)ethyl methacrylate (SEMA) followed by quantitative hydrolysis of the trimethylsilyl protecting groups. The PIB content of the resulting conetworks, determined by elemental analysis and solid-state 1H NMR under fast magic-angle spinning (MAS), varied between 17 and 63% w/w. Phase separation and morphology of these conetworks were investigated by DSC, small-angle X-ray scattering (SAXS), and for the first time by 1H spin diffusion solid-state NMR. Two T g values were observed by DSC in all samples. The observed T g values were close to the literature values of both homopolymers (110 °C for PHEMA and −67 °C for PIB), indicating a strong phase-separated morphology in these conetworks. Parameters were optimized for the 1H spin diffusion NMR experiments, and the measurements were carried out with six filtering cycles and a 10 μs delay between pulses at 90 °C. The NMR and SAXS measurements prove strong phase-separated morphology. The sizes of the hydrophilic (PHEMA) and hydrophobic (PIB) nanodomains were determined to be in the 5−15 nm range. The spin diffusion experiments also indicate strongly separated phases without a detectable interface with mixed components. The long period of our system seems to depend weakly on the volume fraction whereas the morphology of the nanophases depends on the volume fraction.
Amphiphilic conetworks (APCN) are new materials composed of covalently bonded otherwise immiscible hydrophilic and hydrophobic polymer chains. The amphiphilic nature of these new crosslinked polymers is indicated by their swelling ability in both hydrophilic and hydrophobic solvents. Special synthetic techniques have been developed for the preparation of these new unique materials, such as poly(2‐hydroxyethyl methacrylate)‐l‐polyisobutylene (PHEMA‐l‐PIB), poly(methacrylic acid)‐l‐polyisobutylene (PMAA‐l‐PIB) and poly(N,N‐dimethylaminoethyl methacrylate)‐l‐polyisobutylene (PDMAEMA‐l‐PIB) (‐l‐ stands for linked by). Due to their unique architecture, macrophase separation of the immiscible components is prevented by the chemical bonding in the conetworks. As a results, phase separation leads to nanodomains with usually 2‐20 nm domain sizes as shown by AFM measurements. The nanophase separated morphology may also lead to smart temperature responsive gels with high mechanical stability, such as in the case of poly(N,N‐dimethylaminoethyl methacrylate)‐l‐polyisobutylene APCNs as discovered during these studies. In another approach, poly(2‐hydroxyethyl methacrylate)‐l‐polyisobutylene and poly(methacrylic acid)‐l‐polyisobutylene APCNs were prepared by a special two‐step process. The new PMAA‐l‐PIB polyelectrolyte APCNs possess smart (intelligent) reversible pH‐responsive properties in aqueous media. These unique conetwork structures and properties of these new emerging materials may lead to numerous new potential applications, such as smart materialk products, sustained drug release matrices, biomaterials, nanohybrids, nanotemplates etc.
While two of our earlier papers on poly(dimethyl acryl amide)/polymethylhydrosiloxane/polydimethylsiloxane (PDMAAm/PMHS/PDMS) amphiphilic conetworks concerned synthesis and biological properties, respectively, the present contribution focuses on oxygen and insulin permeabilities, and select mechanical properties. We show that by increasing the PDMAAm content from 20 to 60% (i.e., by decreasing the hydrophobic content from 80 to 40%), oxygen permeabilities decrease from ∼240 to ∼130 barrers. Evidently, oxygen permeability is a function of the sum of the oxyphilic components, PDMS + PMHS, in the conetworks. In contrast, insulin permeability is a function of the hydrophilic component, and reaches a desirable 1.5 × 10−7 cm2/s at 61% PDMAAm. We also studied the permeabilities of glucose, dextran, and albumin through a PDMAAm61/PMHS6/PDMS33 membrane and found, unsurprisingly, that the permeability of these molecules follows their hydrodynamic radii, and we project that the permeability of IgG is infinitesimally low. Tensile strengths and ultimate elongations of water‐swollen membranes are also a function of conetwork composition: by increasing the PDMAAm content from 30 to 60%, strengths decrease from 1.6 to 1.2 MPa, and elongations from ∼60 to ∼40%. Overall, the permeabilities and the mechanical properties of these membranes are appropriate for implantation and, specifically, for immunoisolation of living tissue. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4276–4283, 2007
A generally accepted method for the determination of high oxygen permeabilities (Dk >100 barrers) of water-immersed membranes is unavailable. We designed and developed a generally applicable method, together with simple equipment, to measure the oxygen permeability up to Dk $800 barrers of highly oxygen permeable membranes in contact with water. A theory of the methodology is also presented, giving particular attention to the boundary layer effect and the edge effect. The practical applicability of our technique is demonstrated by preparing and using highly oxygen permeable water-logged membranes, such as polydimethylsiloxane and polysiloxane copolymers important for medicine. According to our measurements, the Dk's of polydimethylsiloxane, poly(dimethylsiloxane 0.80 -co-diethylsiloxane 0.20 ), and poly(dimethylsiloxane 0.84 -co-diphenylsiloxane 0.16 ) are 792 6 26, 505 6 10, and 249 6 10 barrers, respectively. Evidently, the oxygen permeabilities of polysiloxanes are strongly reduced by substituting the À ÀOSiMe 2 À À repeat unit with the structurally similar À ÀOSiEt 2 À À and À ÀOSiPh 2 À À repeats. V V C 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3491-3501, 2005
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
Complex copolymers are heated to slowly increasing temperatures on a direct probe (DP) inside the plasma of the atmospheric pressure chemical ionization (APCI) source of a quadrupole ion trap. Slow heating allows for temporal separation of the thermal degradation products according to the stabilities of the bonds being cleaved. The products released from the DP are identified in situ by APCI mass spectrometry and tandem mass spectrometry. DP-APCI experiments on amphiphilic copolymers provide conclusive information about the nature of the hydrophobic and hydrophilic components present and can readily distinguish between copolymers with different comonomer compositions as well as between cross-linked copolymers and copolymer blends with similar physical properties. The dependence of DP-APCI mass spectra on temperature additionally reveals information about the thermal stability of the different domains within a copolymer.
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