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Polyhydroxyalkanoate (PHA) synthase is an enzyme that polymerizes the acyl group of hydroxyacyl-coenzyme A (CoA) substrates. Aeromonas caviae PHA synthase (PhaCAc) is an important biocatalyst for the synthesis of a useful PHA copolymer, poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] [P(3HB-co-3HHx)]. Previously, a PhaCAc mutant with double mutations in asparagine 149 (replaced by serine [N149S]) and aspartate 171 (replaced by glycine [D171G]) was generated to synthesize a 3HHx-rich P(3HB-co-3HHx) and was named PhaCAc NSDG. In this study, to further increase the 3HHx fraction in biosynthesized PHA, PhaCAc was engineered based on the three-dimensional structural information of PHA synthases. First, a homology model of PhaCAc was built to target the residues for site-directed mutagenesis. Three residues, namely tyrosine 318 (Y318), serine 389 (S389), and leucine 436 (L436), were predicted to be involved in substrate recognition by PhaCAc. These PhaCAc NSDG residues were replaced with other amino acids, and the resulting triple mutants were expressed in the engineered strain of Ralstonia eutropha for application in PHA biosynthesis from palm kernel oil. The S389T mutation allowed the synthesis of P(3HB-co-3HHx) with an increased 3HHx fraction without a significant reduction in PHA yield. Thus, a new workhorse enzyme was successfully engineered for the biosynthesis of a higher 3HHx-fraction polymer.

This work concerns the preparation and characterization of poly (acrylonitrile-co-methyl methacrylate) Copolymer, P(AN-co-MMA), nano-particles using precipitation polymerization technique. Potassium per-sulfate redox initiation system was used to perform polymerization process in an alcoholic aqueous system. The impact of different polymerization conditions such as comonomer concentration and ratio, polymerization time, polymerization temperatures, initiator concentration and co-solvent composition on the polymerization yield and particle size was studied. Maximum polymerization yield, 70%, was obtained with MMA:AN (90%:10%) comonomer composition. Particle sizes ranging from 16 nm to 1483 nm were obtained and controlled by variation of polymerization conditions. The co-polymerization process was approved by FT-IR and TGA analysis. The copolymer composition was investigated by nitrogen content analysis. Copolymers with a progressive percentage of PAN show thermal stabilities close to PAN Homopolymer. SEM photographs prove spherical structure of the produced copolymers. The investigated system shows promising future in the preparation of nanoparticles from comonomers without using emulsifiers or dispersive agents.

Poly(N-isopropylacrylamide-co-N,N'-methylene-bisacrylamide) (P(NIPAAm-co-MBA)) hydrogels were prepared in water using redox initiator. The copolymer composition at high conversion (> 95%) was determined indirectly by HPLC (high performance liquid chromatography) analysis of the leaching water and directly by solid state 13C CP MAS NMR (cross polarization magic angle spinning nuclear magnetic resonance) spectroscopy of the dried gels, and was found to be close to that of the feed. The effect of cross-linker (MBA) content in the copolymer was investigated in the concentration range of 1.1–9.1 mol% (R:90–10; R = mol NIPAAm/mol MBA) on the rheological behaviour and mechanical strength of the hydrogels. Both storage and loss modulus decreased with decreasing cross-linker content as revealed by dynamic rheometry. Gels R70 and R90 with very low cross-linker content (1.2–1.5 mol% MBA) have a very loose network structure, which is significantly different from those with higher cross-linker content manifesting in higher difference in storage modulus. The temperature dependence of the damping factor served the most accurate determination of the volume phase transition temperature, which was not affected by the cross-link density in the investigated range of MBA concentration. Gel R10 with highest cross-linker content (9.1 mol% MBA) behaves anomalously due to heterogeneity and the hindered conformation of the side chains of PNIPAAm.

Relating polymer structure to its performance properties is a primary motivation for determining the structure of a polymer chain. If a polymer chain is completely characterized and the structural basis of its properties is known, one can optimize and control polymerization to produce the best possible properties from the chemical system. Infrared (IR) spectroscopy represents a powerful technique for characterization of the polymers. Several relative and absolute methods have been developed to determine the copolymer composition. Among these methods, IR technique as a relative method is a considerably faster and lower cost procedure than other methods like absolute nuclear magnetic resonance (NMR) analysis. In the present work, vinyl acetate/vinyl benzoate copolymers were synthesized by reverse iodine transfer polymerization (RITP) with different molar ratios of comonomers in the initial feed in the presence of iodine as in situ generator of the transfer agent and 2,2′-azobis(isobutyronitrile) as the initiator at 70˚C. Fourier transform infrared (FTIR) spectroscopy was used to determine the composition of the vinyl acetate/vinyl benzoate copolymers. Based on the five copolymers with known compositions determined by 1H NMR spectroscopy, a FTIR calibration curve was obtained. The composition of the synthesized vinyl acetate/vinyl benzoate copolymers with unknown compositions was then determined from the calibration curve and FTIR data. Feed composition and individual and overall molar conversions of the comonomers were calculated after determining the copolymer composition. The results obtained from the FTIR method were in good agreement with those obtained theoretically, indicating the accuracy of the method presented in the present research.