Bahattin M. Baysal

Structure and Protein Separation Efficiency of Poly(N-isopropylacrylamide) Gels: Effect of Synthesis Conditions

Crosslinked poly(N-isopropylacrylamide) (PNIPA) gels with different crosslink densities in the form of rods and beads were prepared by free-radical crosslink- ing copolymerization. Solution and inverse suspension polymerization techniques were used for the gel synthesis. The gels were utilized to concentrate dilute aqueous solutions of penicillin G acylase (PGA), bovine serum albumin (BSA), and 6-aminopenicillanic acid (6-APA). The discontinuous volume transition at 347C observed in the gel swelling was used as the basis of concentrating dilute aqueous protein solutions. PNIPA gels formed below 187C were homogeneous, whereas those formed at higher temperatures exhibited heterogeneous structures. The water absorption capacity of PNIPA gels in the form of beads was much higher, and their rate of swelling was much faster than the rod-shaped PNIPA gels. It was also found that the polymerization techniques used significantly affect the properties of PNIPA gels. The separation efficiency decreased when the protein molecules PGA or BSA in the external solution were replaced with small-molecular-weight compounds, such as 6-APA. The protein separation efficiency by the gel beads increased to 100% after coating the bead surfaces with BSA. q 1998

Swelling of polyacrylamide gels in polyacrylamide solutions

Swelling behavior of polyacrylamide (PAAm) and polyacrylamide-co-poly- acrylic acid (PAAm-co-PAAc) gels was investigated in aqueous solutions of monodis- perse PAAms with molecular weights (M V w) ranging from 1.5 1 10 3 to 5 1 10 6 g/mol. The volume of the gels decreases as the PAAm concentration in the external solution increases. This decrease becomes more pronounced as the molecular weight of PAAm increases. The classical Flory-Huggins (FH) theory correctly predicts the swelling behavior of nonionic PAAm gels in PAAm solutions. The polymer-polymer interaction parameter x23 was found to decrease as the molecular weight of PAAm increases. The swelling behavior of PAAm-co-PAAc gels in PAAm solutions deviates from the predictions of the FH theory. This is probably due to the change of the ionization degree of AAc units depending on the polymer concentration in the external solution. q 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1313-1320, 1998

Poly(dl-lactic acid)/triblock PCL–PDMS–PCL copolymers: synthesis, characterization and demonstration of their cell growth effects in vitro

Abstract This paper describes the copolymerization of dl -lactic acid (DLLA) and triblock polycaprolactone–poly(dimethylsiloxane)–polycaprolactone (TEGOMER). The physical properties of poly( dl -lactic acid)/triblock PCL–PDMS–PCL (PDLLA/TEGOMER) copolymer were determined by IR, 1 H NMR and DSC. T g values of copolymer decreased with increasing TEGOMER unit content. Degradation of PDLLA/TEGOMER copolymer films was investigated in phosphate buffered saline at pH=7.4 and at 37°C. The copolymers degraded to half of their original molecular weight values in 40xa0days. The morphology of the films during degradation was examined by scanning electron microscopy (SEM). Cell growth experiments using Swiss 3T3 fibroblasts demonstrated that PDLLA/TEGOMER copolymer matrices allow the attachment and growth of cells.

Semi-interpenetrating hydrogel networks of poly(2-hydroxyethyl methacrylate) with poly[(D, L-lactic acid)-co-(ε-caprolactam)]

Semi-interpenetrating hydrogel networks (IPNs) composed of poly(2-hydroxyethyl methacrylate), PHEMA, and poly[(D,L-lactic acid)-co-(e-caprolactam)], copoly(D,L-LA/e-CLM), were synthesized. Linear copoly(D,L-LA/e-CLM) chains were interpenetrated into the crosslinked three-dimensional networks of PHEMA. Physical properties of IPN samples such as stress-strain behavior, swelling, extraction and glass transition (Tg) were examined. Glass transition temperature of the PHEMA was shifted to lower temperatures, indicating interpenetration of PHEMA and copoly(D,L-LA/e-CLM) chains. The extraction results showed that the entrapping level between two components of PHEMA/copoly(D,L-LA/e-CLM) in simultaneous semi-IPN is very high. These results confirm that the decrease in swelling ratios with increase in copoly(D,L-LA/e-CLM) contents is probably due to the entanglement effect. Semi-IPNs showed higher ultimate strength and modulus but lower elongation with respect to pure PHEMA hydrogel. The semi-IPN samples exhibited brittle fracture morphology which is consistent with tensile properties.

Coil–globule transition of poly(methyl methacrylate) by intrinsic viscosity

The coil–globule transition for poly(methyl methacrylate) has been studied in the mixed solvent tert-butyl alcohol+water system. Two polymeric samples having molecular weights Mw=2.55×106 and Mw=4.73×106 were used. The contraction and expansion of the molecular chains were determined by viscometric measurements. The results were compared with light scattering data obtained recently for the same system. A smooth and continuous contraction was observed below the θ temperature (41.5u2009°C). The temperature dependence of [η] can be represented by a master curve in αη3|τ|Mw1/2 vs |τ|Mw1/2 plot, where αη3=[η(T)]/[η(θ)] is a viscosity expansion factor and τ=(T−θ)/T is the reduced temperature. A comparison of the observed globular radius with a theory for contracted coil confirmed the coil–globule transition for this system.

Thermal, mechanical, and morphological characterization studies of poly(2,6‐dimethyl‐1,4‐phenylene oxide) blends with polystyrene and brominated polystyrene

The miscibility of the binary and ternary blends of poly(2,6-dimethyl-1,4-phenylene oxide), brominated polystyrene, and polystyrene was investigated using a differential scanning calorimeter. The morphology of these blends was characterized by scanning electron microscopy. These studies revealed a close relation between the blend structure and its mechanical properties. The compatibilizing effect of poly(2,6-dimethyl-1,4-phenylene oxide) on the miscibility of the polystyrene/brominated polystyrene blends was examined. It was found that poly(2,6-dimethyl-1,4-phenylene oxide), which was miscible with polystyrene and partially miscible with brominated polystyrene, compatibilizes these two immiscible polymers if its contention exceeds 33 wt %. Upon the addition of poly(2,6-dimethyl-1,4-phenylene oxide) to the immiscible blends of polystyrene/brominated polystyrene, we observed a change in the morphology of the mixtures. An improvement in the mechanical properties was noticed.

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.

Phase transition of polyacrylamide gels in PEG solutions

Abstract Non-ionic polyacrylamide gels immersed in aqueous solutions of poly(ethylene glycol) (PEG) exhibit a continuous volume change upon continuous increase of the PEG concentration in the external solution. The volume change becomes discontinuous when ionizable groups are incorporated into the network. As the proportion of ionizable groups increases, or, as the molecular weight of PEG decreases, the critical concentration of PEG required for a discontinuous volume collapse rises. The distribution of PEG inside and outside the gel phase changes with gel volume; it also exhibits a discontinuous change at the phase transition. Flory-Huggins theory gives a qualitative description of the phenomenon.

Coil to globule transition behaviour of poly(methyl methacrylate) in isoamyl acetate

Abstract The coil–globule transition behaviour of poly(methyl methacrylate) has been studied in isoamyl acetate by using the dynamic light scattering technique. The dimensions of the polymer show smooth and continuous contraction below θ temperature (61.0°C). The hydrodynamic size of PMMA in isoamyl acetate (Mw=3.3×106xa0gxa0mol−1) decreases to 41% in an unperturbed state at 18.4°C. The temperature dependence of a chain contraction can be represented by a master curve in αh3∣τ∣Mw1/2 vs ∣τ ∣Mw1/2 plot, where αh=Rh/Rh,θ and τ=(T−θ)/θ. A high-chain density value implies that the highly collapsed globule contains 56% isoamyl acetate in its hydrodynamic volume.

Swelling of polyacrylamide gels in aqueous solutions of ethylene glycol oligomers

Abstract Addition of a small amount of ethylene glycol oligomers (OEG), with the number of repeat units y = 2–4, in an aqueous solution leads to the contraction of both linear and cross-linked poly(acrylamide-co-acrylic acid) chains. The results present clear evidence for the screening effect of OEG on the ionic groups of the polymer chains. Measurements indicate that the pre-swollen poly (acrylamide-co-acrylic acid) gels immersed in aqueous OEG solutions are at equilibrium. However, as the molecular weight of OEG increases, these gels cannot attain their equilibrium swelling ratio due to the appearance of non-equilibrium structures. The stability of these structures increases as the initial swelling degree of the gels increases.