Polymerization conditions, effect

Various Co111 cobaioximes (90-92) have also been used as catalytic chain transfer agents.133 148"149 To be effective, the complex must be rapidly transformed into the active Co11 cobaioximes under polymerization conditions. The mechanism of catalytic chain transfer is then identical to that described above (6.2.5.1). 

Occasionally in the synthesis of the copolymers, insoluble material is produced. This results from polymer containing blocks of polyglycolide rather than the desired random structure. Obviously, such compositions would have considerable effect on the performance of controlled release formulations utilizing those polymers. This problem is particularly evident when one is seeking to utilize the 50 50 glycolide/lactide copolymer as a biodegradable excipient. However, with carefully controlled polymerization conditions, useful 50 50 polymer is readily produced. 

Figure 4. Effect of polymerization conditions on the release characteristics of the insulin/poly(acrylic acid) resin system.

Figure 3. Effect of EtsA l i-BusA l molar ratio on microstructure. Polymerization conditions monomer concentration, 11 wt % in hexane catalyst concentration, 7.5 X 10 5 mol/L molar ratio Nd(vers), Et3Al2Cls AIRS, 1 1 30 polymerization time, 2 h and 60°C.

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 VI. Effect of R m VO(OR)2Cl on catalyst activity. Polymerization conditions moiar ratio butadiene, propylene is 1.1, monomer concentration, 31 wt. % in -hexane reaction, — 50°C catalyst, 0.8 mmol VO(OR)2Cl phm, 6.0 mmol i-Bu3Al phm reaction time, 3 h. Data from Ref. 19.

Table VIII. Effect of reaction temperature on molecular weight of butadiene-propylene rubber (BPR). Polymerization conditions as in Table VII, with i-Bu3Al as alkylaluminum compound. Data from Ref. 19.

This study examines the effects of the polymerization conditions on the electro-optic performance of PSFLCs, and the influence of the LC ordering on the polymerization behavior of various monomers is discussed. Basic electro-optic proper-... 

Case 1 appears to accurately predict the observed dependence on persulfate concentration. Furthermore, as [Q]+otal approaches [KX], the polymerization rate tends to become independent of quat salt concentration, thus qualitatively explaining the relative insensitivity to [Aliquat 336]. The major problem lies in explaining the observed dependency on [MMA]. There are a number of circumstances in free radical polymerizations under which the order in monomer concentration becomes >1 (18). This may occur, for example, if the rate of initiation is dependent upon monomer concentration. A particular case of this type occurs when the initiator efficiency varies directly with [M], leading to Rp a [M]. Such a situation may exist under our polymerization conditions. In earlier studies on the decomposition of aqueous solutions of potassium persulfate in the presence of 18-crown-6 we showed (19) that the crown entered into redox reactions with persulfate (Scheme 3). Crematy (16) has postulated similar reactions with quat salts. Competition between MMA and the quat salt thus could influence the initiation rate. In addition, increases in solution polarity with increasing [MMA] are expected to exert some, although perhaps minor, effect on Rp. Further studies are obviously necessary to fully understand these polymerization systems. 

The patent and open literature were searched for examples of dye sensitized photopolymerization in which a common monomer (acrylamide), and one of several common dyes (thionine, T methylene blue, MB or rose bengal, RB) were used in combination with a stated concentration of an activator. The polymerization conditions (monomer concentration, light intensity absorbed, and extent conversion) were stated in each case chosen for inclusion. The relative photospeed of the system was calculated based on several corrections to the raw data. We here define the relative photospeed of a composition as the inverse of the exposure time t needed to effect some fixed percentage of monomer conversion. 

Effect of Polymerization Conditions on Structure. The properties and structural classification of some polymers obtained from MPP and DPP under varying reaction conditions are summarized in Table VI. 

Block copolymers were also produced by oxidizing mixtures of the two homopolymers. A summary of the effect of polymerization conditions on the structures of polymers prepared using equimolar amounts of the two monomers is presented in Table III. The preformed blocks used in these examples were a DMP homopolymer prepared with a diethylamine-cuprous bromide catalyst and a DPP polymer prepared with tetramethyl-butanediamine-cuprous bromide at 60°C. Each had an average degree of polymerization of approximately 50 units. 

To determine the effect of different polymerization conditions on the polymer endgroups produced, polymerizations were carried out using the standard bicarbonate buffer as well as other variations. Table V (13,16) shows that the use of the persulfate-bicarbonate combination with and without emulsifier gave latexes of final pH 7-8 with only sulfate groups. The addition of 10 5 silver ion gave a latex of pH 8.5, but with weak-acid groups, presumably because of oxidation of the sulfate groups. 

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