Novel perfluoropolyalkylethers monomers: synthesis and photo-induced cationic polymerization

Several difunctional oligomers were synthesized by functionalizing perfluoropolyalkylether (PFPAE) chains with different vinyl ethers and epoxides end-groups. Due to their innate synthetic challenges and demanding purification protocols, the PFPAE derivatives were obtained in low yield and with an average functionality lower than 2. However, the functionalized PFPAE oligomers were successful in being used in photo-induced cationic polymerization processes, obtaining transparent and soft films. The influences of the fluorinated chains, and various end-groups on the photopolymerization process were investigated, as well their chemical stability, thermal degradation, and surface properties. Graphical abstract

Critical conversion in the processes of polymer formation

Relations between the critical conversion of gelation αc and the conditions of polymer formation by living and terminated polymerization were studied. It was shown that the weight average functionality of the initial system given by the formula,Φ22(0)=∑ i(i-1)mi where mi is the initial concentration of an i-functional monomer, is the parameter determining the value of αc. Formulas relating the critical conversion to the kinetic parameters of polymerization processes are presented. For polycondensation processes the kinetic equation based on the concept of bond blocks is proposed. It allows for estimating the gel point even for systems in which the substitution effect takes place for one of the components. The equation α ∑ i(i-1)ni=1 is , where α is the current conversion and ni are the values specifying the concentrations of i-functional blocks. The latter values are functions of α and may be calculated kinetically.

Percutaneous Minimal Osteosynthesis of Fractures of the Proximal Humerus in Elderly Patients

Introduction: The aim of this study was to evaluate the subjective and objective outcome of the percutaneous minimal osteosynthesis in elderly patients. Untreated, unstable and dislocated proximal humeral fractures show poor functional and subjective results. Reduction and fixation of the fragments is essential to achieve a good clinical outcome. Especially noted in elderly patients, the osteosynthesis is concurrent with the implantation of a prosthesis. Patients and methods: We examined 31 patients with a mean age of 72 years (51-87) after an average follow-up period of 15.8 months (9-31). To assess the functional and subjective results, we used the Constant Score as well as an adapted version of the Oxford Shoulder Score. Radiographs in two planes displayed the anatomical situation, the healing of the fracture, and the evidence or absence of avascular necrosis..Results: There were no local complications such as hematomas or wound infections. The results of the Constant Score showed an average of 63.5 Pts. (18-82 Points) and adapted to age and gender by 90.2% (28.1-118.8%). Compared with the uninjured arm with an average of 77.1 Points (20-89 Points) and 109.5% (29-129%) respectively, we achieved an average functionality of 82.6%, operated versus non-operated side. All but one fracture, that showed signs of avascular necrosis with disintegration of the humeral head, were fully consolidated. The subjective results were very good in 18 patients, good in 7, satisfying in 3 and poor in 3 patients..Conclusion: Our data indicate that the percutaneous minimal osteosynthesis is a valuable method for the fixation of proximal fractures of the humerus in elderly patients. The technique has a very low rate of complications and the time of convalescence is short. If closed reduction fails or a stable percutaneous fixation of the fracture by K-wires is not possible, the change to open reduction and internal fixation or the implantation of a prosthesis is required.

Synthetic oligopeptides as polymer precursors

By reacting N-carboxyanhydrides of L-phenylalanine, DL-phenylalanine, L-leucine or of a mixture of DL-phenylalanine and L-leucine with hexamethylenediamine (15-20 mol.% related to monomer) in absolute benzene at 25 °C, which was followed by an additional treatment with hexamethylenediamine (60 °C, 4 h), oligopeptides were prepared with the average functionality (Fn) 1.72-1.96 with respect to primary amino groups. The reaction between these oligopeptides and poly(oxyethylene) terminated with isocyanate groups (Fn 1.69-1.94) in anhydrous chloroform at 25 °C leads to copolymers of the type A-B and A-B-A with a minority content of copolymers (A-B)m for m ≥ 2. The low efficiency of the coupling reaction is attributed to the formation of an important amount of monofunctional oligopeptide in the preparation reaction.

Functionality Distribution of Hydroxyl-Terminated Polybutadienes by Gel Permeation Chromatography. II. Measurements for Commercial Polymers

The study of molecular weight and functionality parameters of telechelic hydrocarbon-based prepolymers has received much attention in recent years owing to the influence that these parameters exert on the vulcanization and product properties. An excellent review of these systems has been presented by French. Previous work has been limited to the determination of the average functionality of the whole polymer or of fractions obtained by some appropriate fractionation procedure. Muenker and Law, for instance, used extensive column elution techniques for separating the various species and then determined the average functionality of the fractions. In the previous paper, we described a dual-detector gel permeation chromatography (GPC) method for simultaneously determining the molecular weight averages, molecular weight distribution, hydroxyl equivalent weight, functionality averages, and functionality distributions of hydroxyl-terminated polybutadienes. The method is based on the simultaneous use of a differential refractive index and ultraviolet GPC detectors to analyze the polymers before and after derivatization of the hydroxyl groups with phenyl isocyanate. In this paper, the method will be utilized to determine these parameters for several commercial hydroxyl-terminated polybutadiene prepolymers and to compare the data with existing literature values.