The homopolymerization of 2,3-dimethyl-1,3-butadiene and the copolymerization of 1,3-butadiene/2,3-dimethyl-1,3-butadiene using the catalyst system AlEt2Cl-Co(acac)2. A structural investigation of the products

The homopolymerization of 2,3-dimethyl-1,3-butadiene with the catalyst system AlEt₂Cl-Co(acac)₂ affords polymers consisting of about 81% cis-1,4-units and 19% 1,2-units. The copolymerization of 1,3-butadiene/2,3-dimethyl-1,3-butadiene using the same system is of the ideal type and the composition of the copolymers is practically identical with that of the monomer mixture. The structure of the copolymers depends on their composition. The butadiene units, which are more than 95% cis-1,4 in the homopolymer, become partially 1,2 in the copolymers; their amount increases with increasing dimethylbutadiene content. Conversely, the fraction of dimethylbutadiene units with 1,2-structure decreases in the copolymers with increasing butadiene content. In the copolymers containing more than 50% of butadiene, the dimethylbutadiene units are practically all cis-1,4. The analysis of sequence distribution shows that the 1,2-butadiene units in the copolymers are not randomly distributed but are mostly adjacent to dimethylbutadiene units. The results obtained with dimethylbutadiene are compared with those reported for the homopolymerization of isoprene and the copolymerization of isoprene/butadiene using the same catalyst system.     

Polymerization of 4‐Methyl‐1,3‐pentadiene with Catalysts Based on Cyclopentadienyl Titanium Chlorides: Effect of anti/syn Isomerism of the Allylic Group on the Chemoselectivity and the Role of Backbiting Coordination in 1,3‐Diene Polymerization

Summary: Homopolymerization of 4‐methyl‐1,3‐pentadiene (MP) and copolymerization of 4‐methyl‐1,3‐pentadiene with alkenes (ethylene, 1‐pentene, 4‐methyl‐1‐pentene) were performed to investigate the effect of the so‐called backbiting coordination on the chemoselectivity of 1,3‐diene polymerization. Three homogeneous catalyst systems were used: CpTiCl₃‐MAO, Cp₂TiCl₂‐MAO and Cp₂TiCl‐MAO. Backbiting coordination is possible with the first catalyst, but not with the other two. The three catalysts gave similar results, which indicates that backbiting has no effect on the polymerization chemoselectivity, contrary to what has been reported in recent literature. An interpretation is presented for the formation of 1,4 units in MP/alkene copolymers. This interpretation is based on the fact that allyl groups have predominantly a syn configuration in MP homopolymerization, whereas allyl groups of anti configuration are formed in MP/alkene copolymerization. The role of backbiting in diene polymerization is discussed.

The effect of anti/syn isomerism on the chemoselectivity in the different polymerizations.     

Copolymerization of 1,3-dienes with CpTiCl3-MAO. Some cases in which the mode of monomer coordination affects the copolymer structure

The following pairs of monomers were copolymerized using the catalyst system CpTiCl₃/methylaluminoxane (MAO): 1,3-butadiene/(E)-1,3-pentadiene, 1,3-butadiene/4-methyl-1,3-pentadiene and 4-methyl-1,3-pentadiene/(Z)-1,3-pentadiene. The copolymers were characterized by NMR and infrared examination. 4-Methyl-1,3-pentadiene/(Z)-1,3-pentadiene and 1,3-butadiene/(E)-1,3-pentadiene gave copolymers having a composition intermediate between that of an ideal and that of an alternating copolymer. 1,3-Butadiene/4-methyl-1,3-pentadiene gave block copolymers only. These results have been interpreted on the basis of a different mode of coordination of the monomers. The cis-η⁴ coordination is by far the most stable for 1,3-butadiene and (E)-1,3-pentadiene, while for (Z)-1,3-pentadiene and 4-methyl-1,3-pentadiene there is probably an equilibrium between the cis-η⁴ and trans-η² form. Both these forms are reactive in the case of (Z)-1,3-pentadiene, while only the trans-η² form is so in the case of 4-methyl-1,3-pentadiene.     

Mediterranean Diet and Lifestyle Habits during Pregnancy: Is There an Association with Small for Gestational Age Infants? An Italian Single Centre Experience

Background. The small-for-gestational-age (SGA) in infants is related to an increased risk of developing Non-Communicable Diseases later in life. The Mediterranean diet (MD) is related to lower odds of being SGA. The study explored retrospectively the association between SGA, maternal MD adherence, lifestyle habits and other SGA risk factors during pregnancy. Methods. One hundred women (16–44 years) with a pregnancy at term were enrolled. Demographic data, parity, pre-gestational BMI, gestational weight gain, pregnancy-related diseases, and type of delivery were collected. The MD adherence (MEDI-LITE score ≥ 9), physical activity level, and smoking/alcohol consumption were registered. SGA neonates were diagnosed according to the neonatal growth curves. Results. Women were divided into “SGA group” vs. “non-SGA group”. The MD was adopted by 71% of women and its adherence was higher in the “non-SGA group” (p = 0.02). The prevalence of pregnancy-related diseases (gestational diabetes/pregnancy-induced hypertension) was higher in the “SGA group” (p = 0.01). The logistic regression showed that pregnancy-related diseases were the only independent risk factor for SGA. Conclusions. MD may indirectly reduce the risk of SGA since it prevents and exerts a positive effect on pregnancy-related diseases (e.g., gestational diabetes and hypertension). The small sample size of women in the SGA group of the study imposes a major limitation to the results and conclusions of this research, suggesting however that it is worthy of further investigation.     

Prevalence of muscle relaxant sensitivity in a general population: implications for a preoperative screening.

BACKGROUND: Muscle relaxants (MR) are responsible for 59% of peroperative anaphylactic reactions. A major issue would be to determine whether a systematic preoperative screening in the general population should be recommended. OBJECTIVE: The purpose of the study was to evaluate the prevalence of muscle relaxant sensitivity in a sample of the general population and to assess the role of possible risk factors. METHODS: Two hundred and fifty-eight subjects, aged 20-40 years, visiting a health care centre for a check-up were evaluated. Protocol included a questionnaire (occupation, symptoms of atopy, previous surgery, history of drug allergy), skin-prick tests to four commercial muscle relaxants and measurement of specific IgE against quaternary ammonium ions. Atopy was evaluated by skin-prick tests to common inhalant allergens and by a Phadiatop test. RESULTS: Of the study group, 9.3% had either a positive skin test to one or more muscle relaxant or a presence of specific IgE to quaternary ammonium ions. No risk factor was identified in the studied group. CONCLUSION: Since the rate of MR sensitivity is much higher than the anticipated rate of peroperative reactions due to allergy, a systematic preoperative screening for MR allergy should not be recommended for adults in a general population.     

Predictive factors of renal involvement or relapsing disease in children with Henoch-Schönlein purpura

Predictive factors of renal involvement or relapsing disease in children with Henoch-Schönlein purpura (HSP) are poorly known. We examined clinical and laboratory variables concerning HSP evolution in children hospitalized in the last decade to predict the possibility of renal complications or relapse occurrence. Periodic clinical evaluations with urinalysis were performed for 6±3.6 years. Simple logistic regression showed that persistent rash and severe abdominal pain at the onset of HSP are significantly related to renal involvement, while persistent rash is significantly related to relapsing disease. Multiple logistic regression showed that persistent rash remains related to renal involvement when adjusted for sex, age, and severe abdominal pain and conversely that severe abdominal pain is not related to renal involvement when adjusted for sex, age, and persistent rash. In conclusion, persistent rash over a period longer than 1 month seems to represent a significant predictor of renal sequelae and disease relapse in children with HSP.     

Is systematic preoperative screening for muscle relaxant and latex allergy advisable?

We investigated a female population prior to general anaesthesia, using skin prick tests with latex and muscle relaxants to appraise the validity and feasibility of a systematic preoperative screening for these substances. Anaesthetists performed skin tests, and positive and doubtful tests were checked in our allergy department. Of 114 patients, 42 had uninterpretable tests because of dermographism (28 patients) or suppression of skin reactivity (14 patients). Among the other 72, nine had a positive or doubtful test to latex, and seven a positive or doubtful test to one or more muscle relaxants. After checking, only four sensitizations to latex and one to muscle relaxant were confirmed. In conclusion, a systematic screening for latex and muscle relaxant allergy is not advisable. In contrast, screening for latex allergy in selected high-risk groups (spina bifida, health-care workers) is necessary.