Distributive polymerization

Highly c/s-selectivity and low molecular weight distribution polymerization of l -butadiene with cobalt(II) pyridyl bis(imine) complexes in the presence of ethylaluminum sesquischloride effect of methyl position in the ligand... 

Table II. Effect of Lewis acid Nd compound molar ratio on molecular-weight distribution. Polymerization conditions butadiene concentration, 10 wt % in cyclohexane catalyst concentration, 7.5 X 10 5 mol/1 molar ratio Nd(vers)3, Et3AI2Cl3, AlEt3 is 1 X 30 polymerization time 2 h, and 60°C.

Table 1 Molecular weight, molecular weight distribution, polymerization temperature...

Fig. 4 Effect of inlet monomer concentration on molecular distributions. Polymerization conditions are 75 °C,4000 psig, r=20-22 min, [l]o=2.8-3.3 mmol/L [52]...

Mw/M = 2, highly linear Copolymerization random distribution, LLDPE co-monomers propene, 1-butene, 1-octene Elastomers, Terpolymers of Ethene, Propene and Diene low transition metal concentration in the polymer, narrow molecular weight distribution Polymerization to ... 

Also water may serve as a liquid medium, in which the finely distributed polymeres are floating . These adhesives are commercially available as dispersions (Latin dispergere = finely distribute) (Section 5.4). 

Table IV shows the reactivity ratios rG and r, derived from the probabilities in Table III in accord with a first-order Markov model (2), where it is assumed that the more likely propagating terminal radical structure is 1 (—CHF-) and not 0 (—CH2). This assumption is consistent with gas phase reactions of VF with mono-, di-, and trifluoromethyl radicals, which add more frequently to the CH2 carbon than to the CHF carbon (20). The reactivity ratio product is unity if Bernoullian statistics apply, and we see this is not the case for either PVF sample, although the urea PVF is more nearly Bernoullian in its regiosequence distribution. Polymerization of VF in urea at low temperature also reduces the frequency of head-to-head and tail-to-tail addition, which can be derived from the reactivity ratios according to %defect — 100(1 + ro)/(2 + r0 + r,). Our analysis of the fluorine-19 NMR spectrum shows that commercial PVF has 10.7% of these defects, which compares very well with the value of 10.6% obtained from carbon-13 NMR (13). Therefore the values of 26 to 32% reported by Wilson and Santee (21) are in error.

Enzyme-catalyzed biosynthesis of a biopolymer may proceed by either distributive polymerization or processive polymerization. In biosynthetic polymerizations, the enzyme that has added a monomeric unit to the growing chain can either dissociate or recombine randomly with other growing termini or it can remain bound to the same chain and increases the chain length by additional units. Enzymes that dissociate between each addition and distribute themselves among all the termini are called distributive. Enzymes that process along the same chain without dissociation are called processive. 

RAFT polymerizations of W-isopropylacrylamide (NIPAM) as monomer and a trithiocarbonate as chain transfer agent have been carried out using a flow microreactor under homogeneous conditions (Fig. 26) [210]. In a flow process, an increase in the inner diameter of the tube results in slightly lower conversions and wider molecular weight distributions. Polymerization rates in a flow microreactor are considerably higher than those of batch polymerization because of uniform heating (Table 6). 

Dialysis provides an easy and efficient way for the preparation of small, finely distributed polymeric nanoparticles [73,74]. In this process, polymer is dissolved in an organic solvent and placed inside a dialysis tube with proper molecular weight cutoff and dialysis performed against a non-solvent that is miscible with the solvent. The displacement of the solvent inside the dialysis membrane causes the progressive aggregation of polymer due to a loss of solubility and the construction of a homogeneous suspension of nanoparticles. The mechanism of the dialysis process is based on similar phenomena to that of nanoprecipitation [65]. 

BF3 Et20 catalyst. Bimodal molecular weight distribution. Polymerization in DMF solution. 

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