Monomer-polymeric phase

Up to a monomer concentration [MJ ], corresponding to conversion PJ = ([Mq] -[M J/IMq], where [Mq] is an initial concentration of monomer in the block, the polymerising system is a monophase. This is represented by a solution of the polymer in the monomer and is named as the monomer-polymeric phase (MPPh). 

Equations (6.61 >-(6.70) describe the kinetics of the linear photoinitiated polymerization of methacrylates in optically thin layers up to high degrees of conversion in the three reactive zones, namely the liquid monomer-polymeric phase, in the kolid polymer-monomeric phase and at the boundary of the above-mentioned phase division, according to the conception about the microheterogeneity of system. 

The types of postpolymerization kinetic curves shown can be qualitatively explained using the conception of the three reactive zones proposed earlier. Up to the moment when the polymerizing system is in the liquid monomer-polymeric phase (MPPh), namely up to the moment of conversion = 0 5, only a weak post-effect is observed. MPPh is characterized by low concentration of free radicals with a short life time. A visible post-effect is observed in the autoacceleration stage Po > Py , that is, at the beginning of polymer-monomeric phase elimination and formation of the interface layer at the phase division boundary between MPPh and the polymer-monomeric phase PMPh, which are new reactive zones. In such reactive zones the translational and segmental mobilities of the macroradicals are sharply decreased and the life times are sharply increased. This explains the essential post-effect. 

Microemulsion and miniemulsion polymerization differ from emulsion polymerization in that the particle sizes are smaller (10-30 and 30-100 nm respectively vs 50-300 inn)4" and there is no monomer droplet phase. All monomer is in solution or in the particle phase. Initiation takes place by the same process as conventional emulsion polymerization. 

Microemulsion and miniemulsion polymerization processes differ from emulsion polymerization in that the particle sizes are smaller (10-30 and 30-100 nm respectively vs 50-300 ran)77 and there is no discrete monomer droplet phase. All monomer is in solution or in the particle phase. Initiation usually takes place by the same process as conventional emulsion polymerization. As particle sizes reduce, the probability of particle entry is lowered and so is the probability of radical-radical termination. This knowledge has been used to advantage in designing living polymerizations based on reversible chain transfer (e.g. RAFT, Section 9.5.2)." 2... 

Successful NMP in emulsion requires use of conditions where there is no discrete monomer droplet phase and a mechanism to remove any excess nitroxide formed in the particle phase as a consequence of the persistent radical effect. Szkurhan and Georges"18 precipitated an acetone solution of a low molecular weight TEMPO-tcrminated PS into an aqueous solution of PVA to form emulsion particles. These were swollen with monomer and polymerized at 135 °C to yield very low dispersity PS and a stable latex. Nicolas et at.219 performed emulsion NMP of BA at 90 °C making use of the water-soluble alkoxyamine 110 or the corresponding sodium salt both of which are based on the open-chain nitroxide 89. They obtained PBA with narrow molecular weight distribution as a stable latex at a relatively high solids level (26%). A low dispersity PBA-WocA-PS was also prepared,... 

Emulsion polymerization has proved more difficult. N " Many of the issues discussed under NMP (Section 9.3.6.6) also apply to ATRP in emulsion. The system is made more complex by both activation and deactivation steps being bimolecular. There is both an activator (Mtn) and a deactivator (ML 1) that may partition into the aqueous phase, although the deactivator is generally more water-soluble than the activator because of its higher oxidation state. Like NMP, successful emulsion ATRP requires conditions where there is no discrete monomer droplet phase and a mechanism to remove excess deactivator built up in the particle phase as a consequence of the persistent radical effect.210 214 Reverse ATRP (Section 9.4,1,2) with water soluble dialky 1 diazcncs is the preferred initiation method/87,28 ... 

As suggested by Barrett (2), it is assumed that following the particle nucleation stage, the polymerization proceeds in the particle (monomer/polymer) phase with no mass transfer limitation. Therefore, the dispersion polymerization is similar to a mass or suspension polymerization, and kj can not be assumed to be constant even at isothermal conditions, since kp and even kp are dependent on the degree of polymerization because of a gel effect. (2., ,D However, since the application of the model is for a finishing step, with polymer molecular weight and viscosity fairly well established, further changes in kp and kp should be minimal. 

The rat constant k,, is a function of reaction temperature, functionality and environmental factors which include molecular diffusion. Steric hindrance may be significant with these chemically complex monomers. These functions likely are separable. To address functionality, consider the number average molecular weight of the polymeric phase... 

Two vinyl chloride polymerization reactors were being operated by the same team of operators. Reactor 3 was in the cool down and dump phase of the process, and reactor 4 was nearly full of monomer and in the polymerization phase. The foreman and three employees set to work... 

Fig. 8 Powder X-ray diffraction patterns (CuK ) of Zn2Al/PSS nanocomposites obtained via a in situ polymerization (1). The patterns of the monomer-exchanged phase (2), and of the pristine material at room temperature (3) and at 150 °C (4) are also reported for comparison, b polymer direct exchange (1), reconstruction (2) or restacking of the layers over the polymer (3) or the monomer (4). Patterns are offset for clarity...

As shown in Figure 6.4, the water-insoluble monomer (M) is attracted to the lyophilic ends in the micelles, causing the micelles to swell. The number of swollen micelles per milliliter of water is on the order of 10. However, at the initial stages of polymerization (phase I) most of the monomer is present as globules that resemble those observed in suspension polymerization. 

The chemical structure on the left shows one half of the (symmetrical) monomer in the top half and a possible curing structure with piperidine (bottom half) in the aromatic region. In the amorphous phase much of this detail is smoothed out, presumably by the distribution of molecular environments leading to a distribution of isotropic chemical shifts. The spectra of amorphous and polymerized phases are quite similar in the aromatic region 691... 

When the polymerization begins, the monomers are simultaneously copolymerized alone and also as a graft on the rubber backbone. As the monomers polymerize, two phases appear (8) ... 

Heterogeneous Copolymerization. When copolymer is prepared in a homogeneous solution, kineiic expressions can be used to predict copolymer composition Bulk and dispersion polymerization are somewhat different since the reaction medium is heterogeneous and polymeri/aiion occurs simultaneously in separate loci. In bulk polymerization, for example, the monomer swollen polymer particles support polymerization within the particle core us well as on the particle surface, lit aqueous dispersion or emulsion polymeri/aiion the monomer is actually dispersed in two or three distinct phases a continuous aqueous phase, a monomer droplet phase, and a phase consisting of polymer particles swollen at Ihe surface with monomer. This affect the ultimate polymer composition because llie monomers are partitioned such that the monomer mixture in the aqueous phase is richer in the more water-soluble monomers than the two organic phases. 

Moles monomer polymerized per liter aqueous phase 6 Unseeded polymerizations c Seeded polymerizations 10.3 420... 

An example of this case is a vinyl (A2 ) - divinyl (A4) polymerization. The assumption of an ideal polymerization means that we consider equal initial reactivities, absence of substitution effects, no intramolecular cycles in finite species, and no phase separation in polymer- and monomer-rich phases. These restrictions are so strong that it is almost impossible to give an actual example of a system exhibiting an ideal behavior. An A2 + A4 copolymerization with a very low concentration of A4 may exhibit a behavior that is close to the ideal one. But, in any case, the example developed in this section will show some of the characteristic features of network formation by a chainwise polymerization. 

Methods The polymer beads were synthesized by suspension polymerization in concentrated aqueous NaCl solution using 0.1% (of monomers) AIBN as initiator, a monomer/aqueous phase ratio of 2/5 and freshly precipitated Mg(0H)2 as suspending agent (9). The beads were Soxhlet extracted with ethanol for 24 hours and after drying classified into mesh sizes. The 30 mesh (0.59-0.70 mm ) and 18 mesh (1.00-1.19 mm 4>) fractions were used for release experiments (30 mesh for DC1 18 mesh for OX). 

These assumptions will be adopted in the present study. The main conclusion is that monomer consumption and the development of polymer species may be considered as taking place independently for each phase, but with different rates. If II, is the specific polymerization rate in the monomer-rich phase and Rc in the polymer-rich phase one can write ... 

Nanoparticles/Nanocapsules Obtained by Inter facial Polymerization Nanoparticles/ nanocapsules can be obtained by fast polymerization of a monomer at the interface between the organic and the aqueous phase of an emulsion. Alkylcyanoacrylates have been proposed for the preparation of both oil- and water-containing nanocapsules [59], These monomers polymerize within a few seconds, initiated by hydroxyl ions from equilibrium dissociation of water or by nucleophilic groups of any compound of the polymerization medium. 

Ionic and coordination polymerizations are inhibited by the presence of a certain amount of water. In this case, the amount of water means tens to hundreds parts per million (ppm). Therefore the emulsion and suspension processes in water are limited to monomer polymerizing by the radical mechanism. The most frequently used methods of liquid-phase polymerization of the more conventional monomers are summarized in Table 2. 

Monomer solubility in polymer at 323 K and saturated vapour pressure is 6 mol dm Assuming additivity of polymeric phase volume, i. e. PV = Mq/MQ + fqlfQ, it holds... 

---