Synthesis and characterization of biodegradable poly(ester‐urethanes) based on bacterial poly(R‐3‐hydroxybutyrate)

A series of poly(R‐3‐hydroxybutyrate)/poly(ε‐caprolactone)/1,6‐hexamethylene diisocyanate‐segmented poly(ester‐urethanes), having different compositions and different block lengths, were synthesized by one‐step solution polymerization. The molecular weight of poly(R‐3‐hydroxybutyrate)‐diol, PHB‐diol, hard segments was in the range of 2100–4400 and poly(ε‐caprolactone)‐diol, PCL‐diol, soft segments in the range of 1080–5800. The materials obtained were investigated by using differential scanning calorimetry, wide angle X‐ray diffraction and mechanical measurements. All poly(ester‐urethanes) investigated were semicrystalline with T_m varying within 126–148°C. DSC results showed that T_g are shifted to higher temperature with increasing content of PHB hard segments and decreasing molecular weight of PCL soft segments. This indicates partial compatibility of the two phases. In poly(ester‐urethanes) made from PCL soft segments of molecular weight (M_n ≥ 2200), a PCL crystalline phase, in addition to the PHB crystalline phase, was observed. As for the mechanical tensile properties of poly(ester‐urethane) cast films, it was found that the ultimate strength and the elongation at the breakpoint decrease with increasing PHB hard segment content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 703–718, 2002     

Porous elastomeric beads from crosslinked emulsions

The production of porous polymeric particles is attractive for a large number of applications and can be achieved by various techniques. Although numerous production schemes exist for glassy polymers, difficulties arise for soft, rubbery materials that need a chemical crosslinking step, such as elastomers. This is particularly true for poly(dimethylsiloxane) (PDMS), which shows the lowest glass‐transition temperature among the polymers. Recent studies suggest in situ hydrogen bubble formation or vacuum drying of water droplets dispersed in the polymer matrix in order to generate porous PDMS structures. In this work we report early results based on the chemical crosslinking of water in PDMS emulsion droplets in a mechanically stirred thermostated water vessel. This approach is shown to lead to high porosity PDMS beads (ca. 10^?3 m particle diameter) with an open structure whose properties (diameter and porosity) are strongly influenced by the starting composition (solvent, surfactant, and polymer types and ratios), as well as the operating parameters (agitation and temperature). The possible uses of these derived beads are discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 967–971, 2002     

Synthesis and characterization of chitosan/poly(acrylic acid) polyelectrolyte complex

Polyelectrolyte complex based on chitosan and acrylic acid monomer by photoinitiated free‐radical polymerization in the absence of crosslinker showed a large transition in swelling in response to changes in pH of surrounding medium. Their ability to swell arises from polyelectrolyte interactions and molecular structure of the complex. The main properties of interest that related to the molecular structure, swelling volumes, glass transition temperature, and elastic modulus of the complex were investigated. The effect of water content, the only variable in the sample component, played an important role in molecular structure of the complex and as a consequence, the extent of intermolecular linkage, especially amide bonds which in turn governed the degree of swelling of the polyelectrolyte complex in this study. The decreased degree of swelling and higher temperature shift of glass transition temperature was found with increased water content, whereas increased modulus of elasticity of dry complex was found in lower water content of synthesis component. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1025–1035, 2002     

Study on pH‐sensitive and thermosensitive polymer networks containing polyacetal segments

A series of pH‐sensitive and thermosensitive polymer networks were first obtained by copolymerization of telechelic poly(1,3‐dioxolane) (PDXL) with acrylic acid (AA), acrylamide (AM), and N‐isopropylacrylamide (NIPAM), respectively. The copolymerization of PDXL diacrylate (PDXLDA) with AA, AM, or NIPAM is expected to lead to polymer networks in which homopolymeric segments of the monomer are connected by polyacetal segments. As a combination of these two parts, these polymer networks can have some interesting physical properties. For example, the copolymer networks of poly(AA‐b‐DXL) showed pH sensitivity, and both the copolymer networks of poly(AM‐b‐DXL) and poly(NIPAM‐b‐DXL) showed temperature sensitivity. Moreover, because of the low ceiling temperature of polyDXL, the networks containing polyacetal segments (PDXL) can degrade by treatment with a trace of appropriate cationic initiator. The polymer networks prepared were characterized by Fourier transform infrared, differential scanning calorimetry, and swelling data. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3002–3006, 2002; DOI 10.1002/app.2329     

Mechanical and thermal properties of poly(ethylene terephthalate) fibers crosslinked with disulfonyl azides

A novel method for the crosslinking of poly(ethylene terephthalate) fibers is described using 1,6‐hexanedisulfonyl azide, 1,3‐benzenedisulfonyl azide, and 2,6‐naphthalenedisulfonyl azide. The azides are diffused into poly(ethylene terephthalate) fibers (Dacron) from perchloroethylene solution, and the fibers are heat treated to bring about decomposition of the sulfonyl azide and give rise to crosslinking. A study is made of the mechanical and thermal properties of the resultant fibers, which are changed considerably in comparison to the untreated fiber. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1517–1527, 2002     

Synthesis and characterization of pH‐sensitive networks containing degradable poly(1,3‐dioxolane) segments

pH‐sensitive networks were obtained by radical copolymerization of telechelic poly(1,3‐dioxolane) (PDXLDA) with acrylic acid (AA). PDXLDA was synthesized by acrylation of the corresponding dihydroxylated polyacetal (polyDXL) with AA in pyridine. The copolymer networks of poly(AA‐b‐DXL) showed pH sensitivity due to —COOH groups, which are insoluble in any solvents, but can swell in water or good solvents. The swelling behavior is closely related to the solvents and is composition‐dependent. The networks containing polyDXL segments can be decrosslinked under acidic conditions due to the low ceiling temperature of polyDXL. After degradation, the linear segments of polyDXL became cycled molecules. The networks' structure, swelling behavior, and degradation were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, GC–MS analysis, and swelling data. This kind of material can be potentially used in biosystems, such as in intelligent drug‐delivery systems. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1678–1682, 2002     

Graft copolymerization studies. III. Methyl methacrylate onto polypropylene and polyethylene terephthalate

The tert‐butoxy radical‐facilitated grafting of methyl methacrylate (MMA) onto commercial polypropylene (PP) pellets and fiber was investigated in heterogeneous conditions similar to practical systems. Free‐radical grafting of several other monomers onto PP fiber was also investigated. Also, preliminary data from the grafting of MMA onto poly(ethylene terephthalate) pellets is presented. The PP‐graft‐PMMA residues were detected by solid‐state ¹³C‐NMR and photoacoustic IR spectroscopy. There was a good correlation between the degree of grafting (DG) determined from these spectroscopic techniques and the results from gravimetric methods. A maximum grafting efficiency of over 50% was found, whereas DG (20%) remained constant at various PP pellet, initiator, and monomer concentrations. However, at relatively low PP fiber concentrations, the DG was 27%; the increase was most likely due to the greater surface area of the fiber. There was also a reduction in DG (14%) at relatively low initiator concentrations. The reaction conditions were altered to favor grafting by the addition of more polymer substrate. When the ratio of tert‐butoxy radicals to PP was decreased, more of the substrate remained unmodified, and empirical calculations showed the formation of grafts with up to 40 monomer units. At high initiator concentrations, calculations showed that the graft residues were 1–2 units long. Therefore, variation of the polymer, initiator, and monomer concentrations was shown to have a significant effect on grafting. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 898–915, 2002     

Preparation of hyperbranched polymers by atom transfer radical polymerization

A cheap acrylic AB* monomer, 2‐(2‐chloroacetyloxy)‐isopropyl acrylate (CAIPA), was prepared from 2‐hydroxyisopropyl acrylate with chloroacetyl chloride in the presence of triethylamine. The self‐condensing vinyl polymerization by atom transfer radical polymerization (ATRP), a “living”/controlled radical polymerization, has yielded hyperbranched polymers. All the polymerization products were characterized by proton nuclear magnetic resonance spectroscopy (¹H NMR). CAIPA exhibited distinctive polymerization behavior that is similar to a classical step‐growth polymerization in the relationship of molecular weight to polymerization time, especially during the initial stage of the polymerization. However, a significant amount of monomer remained present throughout the polymerization, which is consistent with typical chain polymerization. Also, if a much longer polymerization time was used, the polymer became gel. As a result of the unequal reactivity of group A* and B*, the polymerization is different from an ideal self‐condensing vinyl polymerization: the branch structures of polymers prepared depend dramatically on the ratio of 2,2'‐bipyridyl to CAIPA. Hyperbranched polymers exhibit improved solubility in organic solvent, however, they have lower thermal stability than their linear analogs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2114–2123, 2002     

Sequencing of N‐vinyl‐2‐pyrrolidone/glycidyl methacrylate copolymers by one‐dimensional and two‐dimensional nuclear magnetic resonance spectroscopy

Copolymers of N‐vinyl‐2‐pyrrolidone (V) and glycidyl methacrylate (G) monomers of different compositions were prepared by free‐radical solution polymerization. The copolymer composition of these copolymers was determined with ¹H‐NMR spectra. The reactivity ratios calculated from the Kelen–Tudos and nonlinear least‐square error‐in‐variable methods were r_V = 0.03 ± 0.01 and r_G = 5.05 ± 0.84 and r_V = 0.02 and r_G = 4.72, respectively. The triad sequence distribution in terms of V and G centered triads was determined from ¹³C{¹H}‐NMR spectroscopy. The complete spectral assignment of ¹³C{¹H}‐ and ¹H‐NMR spectra was performed with the help of distortionless enhancement by polarization transfer and two‐dimensional ¹³C–¹H heteronuclear single quantum coherence. The ¹H–¹H couplings were explained with total correlation spectroscopy and nuclear Overhauser enhancement spectroscopy spectra. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 50–60, 2002; DOI 10.1002/app.10186     

Melting behavior of poly(trimethylene terephthalate)

In this study, the melting behavior of isothermally crystallized polytri‐ methylene terephthalate (PTT) was investigated. Multiple melting behaviors in DSC heating trace were found because two populations of lamellar stacks were formed during primary crystallization and the recrystallization at heating process, respectively. This fact could be also confirmed from the result of optical microscopy observation. The Hoffman–Weeks equation was applied to obtain equilibrium melting temperature (T). The T value of PTT is about 525 K, which is 10 K higher than that reported. Combining the enthalpy of fusion from the DSC result and the degree of crystallinity from WAXD result, the value of the equilibrium‐melting enthalpy ΔH was deduced to be approximately 28.8 kJ mol^?1. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2426–2433, 2002