Heptane dispersion polymerization

PVA Particles. Dispersions were prepared in order to examine stabilization for a core polymer having a glass transition temperature below the dispersion polymerization temperature. PVA particles prepared with a block copolymer having M PS) x 10000 showed a tendency to flocculate at ambient temperature during redispersion cycles to remove excess block copolymer, particularly if the dispersion polymerization had not proceeded to 100 conversion of monomer. It is well documented that on mixing solutions of polystyrene and poly(vinyl acetate) homopolymers phase separation tends to occur (10,11), and solubility studies (12) of PS in n-heptane suggest that PS blocks with Mn(PS) 10000 will be close to dissolution when dispersion polymerizations are performed at 3 +3 K. Consequently, we may postulate that for soft polymer particles the block copolymer is rejected from the particle because of an incompatibility effect and is adsorbed at the particle surface. If the block copolymer desorbs from the particle surface, then particle agglomeration will occur unless rapid adsorption of other copolymer molecules occurs from a reservoir of excess block copolymer. 

Fig. 51. Schematic illustration of the mechanism of microgel formation in the anionic dispersion polymerization of 1,4-DVB initiated by living PBS chains in heptane. [Reprinted with permission from Ref. 247, Copyright 1995, American Chemical Society].

Here we discuss dispersion polymerizations that are not related to vinyl monomers and radical polymerization. The first one is the ring-opening polymerization of e-caprolactone in dioxane-heptane (30). A graft copolymer, poly(dodecyl acrylate)-g-poly(e-caprolactone), is used as a stabilizer. The polymerization proceeds via anionic or pseudoanionic mechanism initiated by diethylaluminum ethoxide or other catalysts. The size of poly(caprolactone) particles depends on the composition of stabilizer, ranging from 0.5 to 5 i,m. Lactide was also polymerized in a similar way. Poly(caprolactone) and poly(lactide) particles with a narrow size distribution are expected to be applied as degradable carriers of drugs and bioactive compounds. 

The polymerizations are generally carried out in bulk or in solution (THF, di-oxane, toluene, etc.). The dispersion polymerization of e-CL using a mixture of 1,4-dioxane and heptane and surface-active agents yields a polymer in the form of microspheres with a narrow molecular weight distribution [63]. 

Sosnowski et al. [124,125] have reported that uniform biodegradable polymeric particles with diameters of less than 5 pm can be prepared by ringopening dispersion polymerization of L,L-lactide in heptane-dioxane mixed solvent in the presence of poly(dodecyl acrylate)-g-poly( -caprolactone), which were synthesized by copolymerization of dodecyl acrylate with poly(e-caprolactone) macromonomers, 46. It is noted that the polymer particles consist of well-defined poly(L,L-lactide) polymers with Mn lxl04 and Mw/Mn 1.06. 

Dispersion polymerization has also been applied to the ring opening polymerization of e-caprolactone and lactide in heptane-dioxane (4/1 v/v) with poly(dodecyl methacrylate)-g-poly(e-caprolactone) as stabilizer [97]. Diethyl-aluminium ethoxide and tin(II) 2-ethylhexanoate were used as initiators in these two systems, respectively, to obtain functional microspheres with a narrow particle size distribution and a narrow molecular weight distribution [98]. Table 2 provides an overview of microspheres obtained by living dispersion polymerization. 

Figure 13 GPC trace of the anionic dispersion polymerization of s-caprolactone In 1,4-dioxane heptane (1 9 v/v) mixture. Polymerization conditions [s-caprolactone]o = 4.0 x 10 mol initiator [(CH3)3SiONa]o = 5.1 x 10" moM room temperature. From calibration on PCL samples with narrow molecular weight distribution Mn = 106 600, MJMn = 5. Reproduced with permission from Slomkowski, S. Sosnowski, S. Gadzinowski, M. Colloids Surf. A Physicochem. Eng. Aspects 1999, 153,111. ...

Polymerization and copolymerization proceed in organic liquids, which act as precipitants for the PA being formed. For this, nonpolar solvents such as xylene, ethylbenzene [82], n-heptane [83], various gasoline fractions [83] and oils are generally applied. In most cases, the processes used resemble dispersion polymerization (when the monomer is soluble in the medium), although suspension polymerization (when the lactam is only incompletely soluble in the given medium) may also be used. 

Suspension (co)polymerization is carried out in aqueous solutions of monomers dispersed in the form of 0.1-5 mm diameter droplets by stirring in nonmixed water-organic liquids in the presence of initiators. The organic liquids that are not dissolving monomers and (co)polymers are represented by solvents that either form azeotropic water mixtures (toluene, heptane, cy-... 

Fig. 20. Photographs taken through a transparent barrel section in a twin-screw extruder showing the presence of bubbles at an extraction pressure of 8 Torr (MacKenzie, 1979). The polymeric solution is heptane-poly(dimethyl siloxane). (a) Screw rotational speed is 15 min . Note how bubbles are dispersed on pushing side of flight. Flow is from right to left, (b) Stationary screw. Note how the bubbles shown in (a) coalesce when the screw is stopped. 

We have found a rare reaction where two topochemical processes occur competitively in a single crystal, that is, a competitive photocyclo-dimerization and -polymerization in the crystal of 1,4-dicinnamoylbenzene 3 (15). On photoirradiation with a mercury lamp (100W) at 20°C for 9 h, the crystals of 3 (2.00g), dispersed in heptane (400 ml), are transformed into amorphous substances consisting of a tricyclic dimer, 21,22,23,24-tetraphenyl-1,4,11,14-tetraoxo-2 (3), 12 (13) -diethano(4,4Jparacyclophane, 4 (isolated yield 57%) (16), a mixture of oligomers (ca. 30%) and unreacted 3 (7%). 

Acetal, (Polyacetal) Poly-oxymethylene (POM) Acetal is a polymer obtained through an addition reaction of formaldehyde — (CH2—0) . It excels in mechanical performance and is regarded as a prominent engineering polymer. It appeared in 1959 with the commercial name Delrin . A short time later a useful copolymer was also developed with a cyclic ether like ethylene oxide. The monomer formaldehyde is a gas produced mostly by oxidizing methanol, and it is very useful in thermoset polymers like phenol, urea and melamine-formaldehydes. For high purity it is initially converted to trioxane or paraformaldehyde. The polymerization is carried out by ionic mechanism, wherein the monomer is dispersed in an inert liquid (heptane). The molecular weights reach 20,000 to 110,000. 

Catalyst was prepared by ball milling MgCl2 with TiCU, dispersed in n-heptane with A1(C4H9>3 at r = 75 C. C2 and H2 were introduced and for 2 h the polymerization was carried out at 1 MPa PE yield ranged from 50 to 590 kg/1 g of Ti... 

On the other hand, by free radical suspension polymerization of MMA in n-heptane solution in the presence of poly(styrene)-Wocfc-poly(ethene-aZt-propene) (SEP) as a dispersing agent, PMMA samples were prepared with similar molecular weights and polydispersity under both conventional and microwave conditions [37]. The reactions were run for 1 h at 70 °C with different monomer (9.0-28.3vol.%), SEP (21.7-5.4 wt%), and AIBN (1.0-0.27 wt%) concentrations (Table 1). In a typical experiment, 30 ml of the reaction mixture was fed into a 50-... 

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