POLYMERISATION TIME

The performance of the molecularly imprinted monolith in terms of molecular recognition and flow-through properties depends on several factors, especially the density and the porosity of the polymer. In order to obtain a monolith with high selectivity and high permeability, some preparation conditions must be optimised, in particular the composition of the prepolymerisation mixture including the amount of template, the type and amount of functional monomer, crosslinker, porogenic solvent and the initiator, and the polymerisation conditions such as initiation process and polymerisation time. 

The extent of LCB and its distribution depends mainly on the catalyst system and the conditions used in the polymerisation. Polymerisation conditions (monomer and comonomer concentration, type of catalyst, temperature and concentration of transfer agents) are important variables to be taken into account when one is looking at the rheological behaviour of the polymers. By decreasing the ethene concentration and increasing the polymerisation time in the reactor the LCB frequency can be enhanced [59, 81]. The polymers made with these catalysts have a complex branching structure composed of comb and tree structures of different lengths. 

Poly [4-[2-(hydroxyphenyl)propyl-2]-phenyl]phenyl siloxanc is a solid dark brown mass (the volatile content is not more than 7-8%, the polymerisation time at 250 °C not more than 6 minutes). The polymer dissolves well in a mixture of toluene and tetraethoxysilane. It is used as a binding agent for plastic laminates and other composites. 

After supplying silanol, the heating of apparatus 17 is switched on and the solvent is distilled, sending air through the bubble at the speed of 3 m3/h at 150 °C. The solvent vapours are condensed in cooler 11 and collected in receptacle 18. The distillation of the solvent occurs simultaneously with the condensation of silanol. During the distillation the temperature in apparatus 17 is increased to 170-200 °C, and the speed of air supply is raised to 30 m3/h. The mixture is periodically sampled to determine the viscosity and polymerisation time of the polymer. After the distillation air supply is stopped, the reactor receives a necessaiy amount of the solvent from batch box 10 and the mixture is cooled to 60 °C. The solution (var-... 

The slurry process is the oldest and still widely used method for manufacturing polymers of ethylene, propylene and higher a-olefins. In this process, the monomer dissolves in the polymerisation medium (hydrocarbon diluent) and forms a solid polymer as a suspension containing ca 40 wt-% of the polymer the polymerisation occurs below the melting point of the polymer. In slurry polymerisation, the temperature ranges from 70 to 90 °C, with the ethylene pressure varying between 7 and 30 atm. The polymerisation time is 1-4 h and the polymer yield is 95-98 %. The polymer is obtained in the form of fine particles in the diluent and can be separated by filtration. Removal of the catalyst residues from the polymer can be achieved by the addition of alcohol (isopropanol, methanol), followed by recovery and extraction of the catalyst residues. The polymer is freed from diluent by centrifuging and then dried. In the case of polypropylene manufacture, the atactic fraction remains in the diluent [28,37]. 

One of the best catalysts for the syndiospecific polymerisation of styrene appeared to be that derived from CpTiCl3 and methylaluminoxane. The polymerisation rate for this system decreases with increasing polymerisation time such behaviour is very similar to that of other Ziegler Natta catalysts. A maximum polymerisation rate is achieved at 50 °C [6]. Other catalysts such as CpTi(OBu)3 [Al/Me/O] are also reported to exhibit a very high activity and syndiospecificity in the polymerisation of styrene [50,51]. 

A possible explanation of the induction period is the substitution of the soft ligands from the crystalline structure with PO that are in excess. After the induction period, the PO polymerisation rate is so high that in one to three hours it is possible to add all the PO that is needed for the reaction. As a comparison, the polymerisation time, in the presence of KOH, is around 7-11 hours. 

Figure 8.12 Dependence of transformation degree on (co)polymerisation time for monomeric systems 1 MMA 2 4FMA-MMA (50 50) ...

Near-IR spectroscopy (10000-4000/cm) was successfully used to monitor conversion dining conventional, anionic solution polymerisation of styrene and isoprene to homopolymers and block copolymers. The conversion of the vinyl protons in the monomer to methylene protons in the polymer was easily monitored under conventional (10-20% solids) solution polymerisation conditions. In addition to the need for an inert probe, high sampling frequencies were required since polymerisation times ranged from 5s in tetrahydrofuran to 20 minutes in cyclohexane. Preliminary data indicate that near IR is capable of detecting sequence distribution for tapered block copolymers, geometric isomer content, and reactivity ratios for free-radical copolymerisation. 20 refs. USA... 

Figure 3.17 The dependence of on isoprene polymerisation time in the presence of TiCl4-Al(i-C4H9)3 (1, 3) and TiCl4-Al(i-C4H9)3-piperylene (2, 4) catalytic systems. The traditional method (1, 2) and hydrodynamic impact on a catalytic system in the turbulent mode (3,4)...

Peak analysis of the active centre kinetic inhomogeneity distribution curves reveals that Type I AC (responsible for the polybutadiene fraction with a MW in the range of 2400) only exist in traditional polymerisation processes disappearing by polymerisation time = 20 min. Type II AC are also deactivated by this time. Type V AC (which are responsible for the high MW fraction of a polymer) become active by the polymerisation time of 60 min ( 15% conversion). The pattern of the polybutadiene MWD curves is evidently influenced by the wide range of different types of AC, which affect the polymerisation process at all stages. 

Immobilization by entrapment of P. laminosum When P. laminosum cells were entr ped in PU foams according to Brouers et al. (3), complete loss of viability was observed after 2-3 days of immobilization. Consequently, in an attempt to overcome the toxicity problems, different parameters were modified (temperature of polymerisation, prepolymer culture medium ratio, polymerisation time, light intensity, temperature of incubation, concentration of initial cell suspension, etc.) without any success. In all cases, high toxicity was observed which lead to a rapid death of the immobilized cells. It seems that this toxicity originates in the polymerisation reaction due to a possible release of toxic compounds and local increase of temperature and pressure. 

The polymerisation of styrene in miniemnlsions stabilised with anionic sodium dodecyl sulphate or nonionic Lntensol AT50 results in stable polymer dispersions with particle diameters between 30 and 480 nm and narrow particle size distributions. Steady-state mini-emulsification results in a system with critical stability , i.e. the droplet size is the prodnct of a rate equation of fission by ultrasound and fusion by collisions, and the mini-droplets are as small as possible for the timescales involved. The droplet growth by monomer exchange, or the T1 mechanism, is effectively suppressed by addition of a very hydrophobic material, whereas droplet growth by collisions, or the T2 mechanism, is subject to the critical conditions. The growth of the critically stabilised miniemulsion droplets is usually slower than the polymerisation time therefore, in ideal cases, a 1 1 copy of droplets to particles is obtained, and the critically stabilised state is frozen. 6 refs. 

Using an electrohydrodynamic processing method, a polyurethane-based core was coated with a polyanihne shell to produce stable aqueous emulsions. Using a chiral dopant, (lS)-(H-)-10-camphor sulphonic acid (HCSA) induced a high degree of optical activity in the particles. Dispersions of highly optically active colloids could be prepared both with and without polystyrenesulphonate. In both cases, the optical activity increased on standing after polymerisation. Particle size increased with polymerisation time. 16 refs. 

Biodegradable fumarate-based polyHIPEs synthesised from propylene fumarate dimethaciylate have been investigated as injectable scaffolds for the repair of critical sized bone defects. Culture of NIH/3T3 fibroblasts on such polyHIPEs yielded 95% viability after 24 h. Switching from a thermally initiated curing system to redox initiation resulted in a reduction of the polymerisation time. HIPEs with either a reductant or an oxidant could be... 

Short polymerisation times may also result in lower degrees of crosslinking, which limits the formation of well-defined rebinding cavities, which in turn can reduce selectivity due to decreased polymer rigidity. This could also serve as an explanation of the increased swelling and template uptake, as a more flexible polymer will facilitate mass transfer through the polymer and allow for more binding to take place. The associated cavity deformation has a substantial impact on the reproducibility of results and on selectivity for the template (Spivak, 2005). 

NMP makes possible the synthesis of a range of complex polymer architectures with high control over the PDI and molecular weight [46]. However, the polymerisation of methacrylate monomers, the long polymerisation time and the complexity of preparing functional initiators for further polymer modification limit the application of this technique in the routine laboratory. 

In another new method for a known polymer it was shown that 2VP will polymerise under /Bz/PILi/6 °C/LiCl// conditions provided that the excess of LiCl is at least 4-fold and that the polymerisation time is kept very short... 

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