Solution copolymerizations

Utilization of another function of the macroinitiator was tried in emulsion polymerization [30]. An MAI composed of PEG (molecular weight of a segment is 1000) linked with AGP units was confirmed to be usable as a surface active initiator (Inisurf) for preparing PSt-b-PEG [30]. A higher molecular weight block copolymer was obtained in comparison with the case of solution copolymerization. 

Barrett and Thomas (10)proposed that these effects of differential monomer adsorption could be modeled by correcting homogeneous solution copolymerization reactivity ratios with the monomer s partition coefficient between the particles and the diluent. The partition coefficient is measured by static equilibrium experiments. Barrett s suggested equations are ... 

Data taken from Preparation of O-Type Polymer (III) Solution Copolymerization of Glycidyl Methacrylate, Tech. Bull. 6J12 1000A. Nippon Oil Fats Co., Ltd., Tokyo, Japan 1974. 

Another interesting example belonging to the same general principle was described by Graham (56). On one hand he prepared an amine terminated polystyrene (sodium amide initiation in liquid ammonia) and showed that it contained only one terminal primary amine group per polymer chain. On the other hand copolymers were prepared by free-radical initiated solution copolymerization of small amounts of /S-iso-cyanatoethyl methacrylate with several other monomers as methyl, butyl and lauryl methacrylates, acrylonitrile and styrene. 

The molecular weights of polymer products of the DBP runs are relatively low and very similar to those in the solution copolymerization [69]. These results in-... 

In this paper we would like to describe a new design, based on gas chromatographic analysis of the monomer mixture, for production of constant composition copolymers and its application to emulsion copolymerization. This design was already shortly described and applied to solution copolymerization (3) of methylmethacrylate and vinylidene chloride. Since then, the apparatus was made more simple, more reliable and more accurate. It is actually monitored by an analogic computering system which keeps the ratio of the monomers constant by controlling the addition of one of them. The process based on it can be called corrected batch process because the initial value of this ratio is kept up to the end. 

The initial copolymer composition corresponds well to reactivity ratios measured 03, 7) from bulk or solution copolymerization (r =0.13 Tg = 0.34) taking into account not the whole monomer feed, but its composition within particles. So, the initial copolymer composition is practically kept constant as long as droplets remain. After their disappearance, the polymerization rate remains constant up to about 50 % conversion. 

On the other hand, it should be realized that radical copolymerization at heterogeneous conditions offers additional unique opportunities not available in homogeneous (solution) copolymerization. These include the intrinsic possibilities of exploiting the heterogeneities of the reaction system to control the chemical microstructure of the synthesized copolymers, making possible new paradigms for synthesis and production of polymeric materials. In this contribution, we discuss some new synthetic strategies, which have been developed in recent years to provide effective control of the chemical sequences. 

The relative reactivity of the macromonomer in copolymerization with a common comonomer, A, can be assessed by l/rA=kAB/kAA> i-e-> the rate constant of propagation of macromonomer B relative to that of the monomer A toward a common poly-A radical. In summarizing a number of monomer reactivity ratios in solution copolymerization systems reported so far [3,31,40], it appears reasonable to say that the reactivities of macromonomers are similar to those of the corresponding small monomers, i.e., they are largely determined by the nature of their polymerizing end-group, i.e., essentially by their chemical reactivity. 

Up to now we have not found reaction conditions permitting exclusive production of insoluble copolymer, which is the desired product in commercial copolymerization of trioxane. Conversion of a large portion of the dioxolane into soluble copolymer could not even be avoided by slow and gradual addition of the comonomer to a homopolymerization run of trioxane in methylene dichloride (9). The same result was obtained in solution copolymerization of trioxane with 8 mole % of 1,3-dioxacycloheptane (dioxepane), and even 1,3-dioxane—which is not homopolymerizable and is a very sluggish comonomer—formed a soluble copolymer in the initial phase of copolymerization (trioxane 2.5M 1,3-dioxane 0.31M SnCb 0.025M in methylene dichloride at 30°C.). 

Butadiene-Styrene Rubber occurs as a synthetic liquid latex or solid rubber produced by the emulsion polymerization of butadiene and styrene, using fatty acid soaps as emulsifiers, and a suitable catalyst, molecular weight regulator (if required), and shortstop. It also occurs as a solid rubber produced by the solution copolymerization of butadiene and styrene in a hexane solution, using butyl lithium as a catalyst. Solvents and volatiles are removed by processing with hot water or by drum drying. 

An analogous analysis of the solution copolymerization of styrene with acrylonitrile in toluene leads [283] to the same conclusion concerning the choice of the kinetic model as for the bulk copolymerization of these monomers. The applicability of the penultimate model (2.3) was also convincingly proved [283] for the given system, and the estimated values of its four parameters (2.4) (see Table 6.8) were found to be slightly different from the ones obtained in the bulk copolymerization [283], The experimental values of the fractions of all six triads, determined by means of NMR, in the solution copolymerization products, practically do fit the theoretical plots of the triad fractions vs conversion, which were calculated on the basis of the kinetic parameters presented in Table 6.8. 

To obtain amphiphilic polymers, different concepts are conceivable to introduce amphiphilic moieties into the polymer backbone. They are schematically summarized in Figure 5. Polymers of type A and B can be realized, if a polymerizable group is introduced into the hydrophobic group (type A) or hydrophilic group (type B) of a conventional surfactant, which exhibit the liquid crystalline state in solution. Copolymerization of a hydrophilic and a hydrophobic comonomer yields amphiphilic copolymers of type C. According to the convention, these polymers may be called "amphiphilic side-chain polymers"... 

Equations (7-13) and (7-14) are dimensionless all units cancel on each side of the equality sign. Thus the reactivity ratios are indicated to be independent of dilution and of the concentration units used. The reactivity ratios for a particular monomer pair should be the same in bulk and in dilute solution copolymerizations. 

This type of microheterogeneous copolymerization of DAP with vinyl monomers having long-chain alkyl groups was applied further for the bulk copolymerization systems to obtain direct evidence to support the idea of the microheterogeneity of the systems beyond the gel-point conversion [82]. Also, the solution copolymerization of DAT was explored to demonstrate the incompatibility of the initially obtained precopolymer with a high content of comonomer units with DAT-enriched polymer chains [83]. 

Fig. 15. Dependence of Mw on conversion in the solution copolymerizations of MMA with 1 mol% of ( ) EDMA, (A) PEGDMA-2, ( ) PEGDMA-3, (A) PEGDMA-9, and ( ) PEGDMA-23, along with (o) MMA homopolymerization (volume ratio total monomer/1,4-dioxane = 1/ 4, [AIBN] = 0.04 mol K at 50 °C)...

Fig. I Doublc logarithmic plots of versus Mw in MMA-EDMA solution copolymerization under various conditions volume ratio total monomer/1,4-dioxane, EDMA mol% ( ) 1/2,0.5 (a) 1/3,0.8 (o) 1/4,1 (A) 1/5,1.5 (o) 1/7, 1.5 (see Fig. 15 for other polymerization conditions)...

It has been reported that vinylferrocene is polymerized by using a radical, cationic, anionic, or Ziegler system initiator [29 — 34]. In particular, higher molecular weight products can be obtained using radical-initiated bulk polymerization [31]. Indeed, both bulk copolymerization and solution copolymerization (in benzene) of 18 with vinylferrocene by using a radical initiator (AIBN) afforded the chiral polymers 19a —e (Scheme 3-13), which were purified by reprecipitation of the benzene solution with methanol. The ratios of the two comonomers were varied in copolymerization. The composition data of the copolymers obtained revealed nearly the same reactivity between 18 and vinylferrocene, which suggests that 19a—e are random copolymers. 

Controlled and Uncontrolled Semi-batch Solution Copolymerization of Styrene with Methyl Acrylate... 

Acrylates 8, 14, and 17 were also copolymerized with n-hexyl methacrylate or n-butyl acrylate in emulsion reactions (sodium lauryl sulfate, K2S20a, 60°C) as were chain-extended acrylates 10, 13, 16 and 19. The copolymers of 17 and 19 were low molecular weight materials again due to easy chain transfer. The bulk copolymerization of 19 with n-hexyl methacrylate gave reasonably high molecular weights.1 Some solution copolymerizations were also carried out. Representative results are summarized in Table 2. 

While it is assumed that termination by coupling takes place when maleic anhydride and styrene are copolymerized in a good solvent such as acetone, insoluble macroradicals precipitate when these monomers are copolymerized in a poor solvent such as benzene (7). Insoluble macroradicals obtained by bulk polymerization of acrylonitrile (1, 11) and the solution copolymerization of maleic anhydride and styrene in benzene (7) have been used as seeds for the preparation of block copolymers. 

Assuming that the model system is a valid model for a MHAP prepolymerization solution, these results for the model system can be applied to the MHAP. The model system results suggest that the micelle solution copolymerization process can be a means of producing multiblock copolymers in which hydrophobic and hydrophilic blocks alternate. At constant monomer concentration, the number of blocks in the copolymer molecule is inversely related to the number of monomers in the block. Thus, factors that increase the sequence length of a block decrease the number of blocks. The monomer concentrations and the polymer MW are also factors governing the sequence length and number of blocks in the copolymer. Polymerization conditions (e.g., surfactant type and concentration) can be used to control the block size to some extent. 

Polymers with pendant cyclic carbonate functionality were synthesized via the free radical copolymerization of vinyl ethylene carbonate (4-ethenyl-l,3-dioxolane-2-one, VEC) with other imsaturated monomers. Both solution and emulsion free radical processes were used. In solution copolymerizations, it was found that VEC copolymerizes completely with vinyl ester monomers over a wide compositional range. Conversions of monomer to polymer are quantitative with complete incorporation of VEC into the copolymers. Cyclic carbonate functional latex polymers were prepared by the emulsion copolymerization of VEC with vinyl acetate and butyl acrylate. VEC incorporation was quantitative and did not affect the stability of the latex. When copolymerized with acrylic monomers, however, VEC is not completely incorporated into the copolymer. Sufficient levels can be incorporated to provide adequate cyclic carbonate functionality for subsequent reaction and crosslinking. The unincorporated VEC can be removed using a thin film evaporator. The Tg of VEC copolymers can be modeled over the compositional range studied using either linear or Fox models with extrapolated values of the Tg of VEC homopolymer. 

Solution Copolymerizations. Our primary objective in this preliminary study was to gain a qualitative understanding of the copolymerization behavior of VEC with various types of unsaturated monomers. Particularly, we wanted to determine if VEC could be incorporated into a variety of polymer types of interest to the coatings industry. Since VEC is used to provide cyclic carbonate functionality for subsequent reaction or crosslinking, limited amounts of VEC are used in the copolymerizations. A semi-batch process was used in the copolymerization experiments to approach starved-feed conditions. Starved-feed conditions can result in copolymers with more uniform composition since the conversion is kept high in the reactor. While there are a large number of variables to consider, we elected to focus on monomer composition, polymerization temperature, and initiator level. 

The copolymerizations in Table I were all conducted using 2,2 -azobis(2-methylbutyronitrile) as the initiator. All of the polymer solutions, while clear, had a bright yellow color. When the copolymerizations were conducted using t-amyl peroxy (2-ethylhexanoate), the polymer solutions were clear and colorless. Thus, we continued using the t-amyl peroxy (2-ethylhexanoate) for the rest of the solution copolymerizations. 

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