High Molecular Weight Polyester Obtained by Polymerization of Dimethylketene Using Metallocene Initiators: A Step toward Ziegler-Natta Supporting Application in Non-Olefin Systems.

In this report, highly active metallocene initiators are used for the polymerization of a ketene monomer, dimethylketene, which typically contains two adjacent double bonds (R2 CCO). By using the methylzirconocene methyltriarylborate complex (Cp2 ZrMe+ MeB(C6 F5 )3 - ) as the activation system, associated with the possible cleavage of CC and CO bonds in ketene monomers, a structure-specific and high-molecular-weight polyester ( M n ¯ > 300 000 g mol-1 ) can be afforded. The resulting polyester structure, comprehensively characterized by NMR, indicates a significant reactive selectivity of the "bent-sandwich" cationic site Cp2 ZrMe+ . It reveals that the positively charged zirconium (Zr+ ) prefers to coordinate with a negatively charged oxygen (O- ) when it is already bonded to the carbon, while a negatively charged carbon (C- ) will be assigned in priority if the oxygen-zirconium bond exists. This report allows for broadening the application field of metallocene initiators in non-olefin reactions and deepening our insight into the mechanism of the living insertion/Ziegler-Natta polymerization.

Exploration of polyamide structure-property relationships by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

RATIONALE: Polyamides (PA) are among the most used classes of polymers because of their attractive properties. Depending on the nature and proportion of the co-monomers used for their synthesis, they can exhibit a very large range of melting temperatures (Tm ). This study aims at the correlation of data from mass spectrometry (MS) with differential scanning calorimetry (DSC) and X-ray diffraction analyses to relate molecular structure to physical properties such as melting temperature, enthalpy change and crystallinity rate. METHODS: Six different PA copolymers with molecular weights around 3500 g mol(-1) were synthesized with varying proportions of different co-monomers (amino-acid AB/di-amine AA/di-acid BB). Their melting temperature, enthalpy change and crystallinity rate were measured by DSC and X-ray diffraction. Their structural characterization was carried out by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Because of the poor solubility of PA, a solvent-free sample preparation strategy was used with 2,5-dihydroxybenzoic acid (2,5-DHB) as the matrix and sodium iodide as the cationizing agent. RESULTS: The different proportions of the repeating unit types led to the formation of PA with melting temperatures ranging from 115°C to 185°C. The structural characterization of these samples by MALDI-TOF-MS revealed a collection of different ion distributions with different sequences of repeating units (AA, BB; AB/AA, BB and AB) in different proportions according to the mixture of monomers used in the synthesis. The relative intensities of these ion distributions were related to sample complexity and structure. They were correlated to DSC and X-ray results, to explain the observed physical properties. CONCLUSIONS: The structural information obtained by MALDI-TOF-MS provided a better understanding of the variation of the PA melting temperature and established a structure-properties relationship. This work will allow future PA designs to be monitored.

Solvent-based and solvent-free characterization of low solubility and low molecular weight polyamides by mass spectrometry: a complementary approach.

RATIONALE: Polyamides (PA) belong to the most used classes of polymers because of their attractive chemical and mechanical properties. In order to monitor original PA design, it is essential to develop analytical methods for the characterization of these compounds that are mostly insoluble in usual solvents. METHODS: A low molecular weight polyamide (PA11), synthesized with a chain limiter, has been used as a model compound and characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). In the solvent-based approach, specific solvents for PA, i.e. trifluoroacetic acid (TFA) and hexafluoroisopropanol (HFIP), were tested. Solvent-based sample preparation methods, dried-droplet and thin layer, were optimized through the choice of matrix and salt. Solvent-based (thin layer) and solvent-free methods were then compared for this low solubility polymer. Ultra-high-performance liquid chromatography/electrospray ionization (UHPLC/ESI)-TOF-MS analyses were then used to confirm elemental compositions through accurate mass measurement. RESULTS: Sodium iodide (NaI) and 2,5-dihydroxybenzoic acid (2,5-DHB) are, respectively, the best cationizing agent and matrix. The dried-droplet sample preparation method led to inhomogeneous deposits, but the thin-layer method could overcome this problem. Moreover, the solvent-free approach was the easiest and safest sample preparation method giving equivalent results to solvent-based methods. Linear as well as cyclic oligomers were observed. Although the PA molecular weights obtained by MALDI-TOF-MS were lower than those obtained by (1)H NMR and acido-basic titration, this technique allowed us to determine the presence of cyclic and linear species, not differentiated by the other techniques. TFA was shown to induce modification of linear oligomers that permitted cyclic and linear oligomers to be clearly highlighted in spectra. CONCLUSIONS: Optimal sample preparation conditions were determined for the MALDI-TOF-MS analysis of PA11, a model of polyamide analogues. The advantages of the solvent-free and solvent-based approaches were shown. Molecular weight determination using MALDI was discussed.

Tandem mass spectrometry of low solubility polyamides.

The structural characterization of polyamides (PA) was achieved by tandem mass spectrometry (MS/MS) with a laser induced dissociation (LID) strategy. Because of interferences for precursor ions selection, two chemical modifications of the polymer end groups were proposed as derivatization strategies. The first approach, based on the addition of a trifluoroacetic acid (TFA) molecule, yields principally to complementary bn and yn product ions. This fragmentation types, analogous to those obtained with peptides or other PA, give only poor characterization of polymer end-groups [1]. A second approach, based on the addition of a basic diethylamine (DEA), permits to fix the charge and favorably direct the fragmentation. In this case, bn ions were not observed. The full characterization of ω end group structure was obtained, in addition to the expected yn and consecutive fragment ions.

Perioperative course and medium-term outcome of the transobturator and infracoccygeal hammock for posthysterectomy vaginal vault prolapse.

OBJECTIVE: To describe the perioperative course and medium-term anatomic and functional outcomes of the transobturator-infracoccygeal hammock for posthysterectomy vaginal vault prolapse repair. METHODS: A prospective consecutive series of 52 women with a stage 2 vaginal vault prolapse or higher that occurred after total hysterectomy who underwent surgery between 2003 and 2007. Principal outcome measures were anatomic cure (stage 1 or lower) and impact on quality of life measured using the pelvic floor distress inventory (PFDI) and pelvic floor impact self-reported questionnaire (PFIQ). Anatomical results were analyzed using chi(2) and Fisher exact tests, and PFDI and PFIQ scores were analyzed using the Wilcoxon test. RESULTS: With a median follow-up of 36months, the anatomic cure rate was 96%. Significant improvements were noted in POPQ-S scores after surgery (P<0.05). Stress urinary incontinence was cured in 73% of patients and improved in 15% of patients. The PFDI and PFIQ scores were improved (P<0.05). One mesh extrusion was observed. The rates of mesh contraction and new cases of dyspareunia were 31% and 13%, respectively. CONCLUSION: The transvaginal mesh hammock represents a useful treatment for recurrent and major vaginal vault prolapse, and has few complications.

Biomechanical analysis of polypropylene prosthetic implants for hernia repair: an experimental study.

BACKGROUND: Although polypropylene (PP) is the most common biomaterial used for ventral and inguinal hernia repairs, its mechanical properties remain obscure. METHODS: Retraction, solidity, and elasticity of 3 large pore-size monofilament PP prostheses, 1 heavy-weight PP (HWPP), a second low-weight PP, and a third coated with atelocollagen were evaluated in a rabbit incisional hernia model. A small pore-size multifilament PP implant (MPP) also was tested. RESULTS: Unlike pore size, the weight of the prosthesis was not an influencing factor for retraction. Atelocollagen coating reduced retraction (P < .05). HWPP and MPP were less likely to rupture (P < .05). HWPP had comparatively better elasticity (P < .05), whereas MPP supported the greatest elastic force (P < .05). Nevertheless, the amount of shrinkage of MPP (30% of the original size) made this prosthesis unusable. CONCLUSIONS: In this study, HWPP presented the most advantageous biomechanical compromise for hernia surgery.

Experimental biomechanical evaluation of polypropylene prostheses used in pelvic organ prolapse surgery.

INTRODUCTION AND HYPOTHESIS: Although polypropylene (PP) is the most common biomaterial used to repair genital prolapse via vaginal route, its mechanical properties however remain obscure. METHODS: An abdominal hernia rabbit model was used to evaluate retraction, solidity, and elasticity of the principal types of PP prostheses currently available, i.e., three large pore size monofilament prostheses, one heavy weight (HWPP), a second low weight (LWPP), and a third coated with atelocollagen (CPP). A small pore size multifilament PP (MPP) implant was also tested. RESULTS: In comparison with HWPP (12%), LWPP (15%), and MPP (30%), CPP had less retraction (8% of the original size). Unlike pore size, weight prosthesis is not an influencing factor for retraction. Atelocollagen coating reduced retraction. HWPP and MPP were the most solid prostheses. MPP supported the greatest elastic force. CONCLUSIONS: When the biomechanical parameters were comparatively assessed, HWPP was considered to have the most advantageous properties for prolapse surgery.

Mechanical evaluation of synthetic biomaterials used in the correction of pelvic floor disorders--experimental study in rabbits.

OBJECTIVE: To evaluate the biomechanical properties of the principal prosthetic materials currently used in genital prolapse surgery. STUDY DESIGN: Based on an animal model of incisional abdominal hernia, 40 adult rabbits were implanted. Four 2.5 cm x 2.5 cm parietal defects, were created in the abdominal fascia and muscles while respecting the peritoneum. For each rabbit, the defect was repaired by four different large pore size prostheses which varied according to the material used: two with monofilament of heavy (75 g/m(2)) or low (38 g/m(2)) weight polypropylene (PP), and two with multifilament of heavy (115 g/m(2)) or low (59 g/m(2)) weight polyethylene-terephthalate (PET). Animals were sacrificed in groups of 10 after 14, 30, 90 and 180 days to evaluate contraction, solidity and elasticity of the prostheses. RESULTS: PP and PET retracted, independently of their weight, in 81.25% and 20% respectively. Intensity of contraction was not predictable but median value of retracted surface was 14% with PP, none with PET. Contraction settled quickly after tissue integration and did not subsequently occur. Heavyweight PET was considered the most solid material (70 N cm(-1)), low-weight PP the most fragile (20 N cm(-1)). Heavy forms of PP or PET resisted better to the rupture than the light forms which were sometimes insufficient to resist the extreme values of the human abdominal pressure (16 N cm(-1)). PP was more flexible than PET, but PET was the only form which was able to support extreme values of the abdominal pressure and remain in the elastic range. Duration of implantation did not modify solidity or elasticity of the prostheses. CONCLUSION: In our abdominal rabbit model, as regards mechanical properties, heavyweight PET seems to be the optimal biomaterial.