SEC/LALLS

The hydrodynamic volume separation mechanism of SEC, along with the different molecular size/weight relationships of branched and linear polymers of identical chemical composition, can be exploited with the SEC/LALLS method to gain information about polymer branching. In the studies described in this paper both conventional SEC and SEC/LALLS are used to obtain data about branching in samples of poly(vinyl acetate) (PVA) and polychloro-prene (PCP). 

The following work demonstrates the use of SEC/LALLS to study the variation of g with molecular weight for broad MkD materials. This approach gives a qualitative indication of polymer branching. 

A separate program was developed on tfie LDS-2 to correct the SEC/LALLS Rj, for band-spreading (Appendix). 

A universal calibration relation for the SEC/LALLS system was derived by fitting the seven J, Vr data pairs with a linear equation... 

Sample masses of 8.90 x 10" gm and 1.05 x lO"" gm were chromatographed for PVA 0107-066 and PVA 0106,respectively,while 1.47 X lO"" gm of PCP was injected. An estimated A2 value of 5x10" mol-cmvgm was used to process the PVA and PCP data with MOLWT. In view of the relatively small magnitude of the term containing A2 in the SEC/LALLS equations ( ), uncertainty in R from this approximation is insignificant. 

Table I shows molecular weight data obtained from SEC/LALLS measurements on the narrow MWD polystyrene standards. Bandspreading correction of the ft values generally resulted in a decrease in fl of 1% to 4% Below the value directly obtained from treatment 8f SEC/LALLS data with the MOLWT program.

Data from the SEC/LALLS Analysis of Narrow MWD Polystyrene... 

Data V(ml) Table II from SEC/LALLS and conventional SEC analysis of NBS SRM706 polystyrene /M (MJvXlO" (M )vX10-5 g ... 

Data from SEC/LALLS and conventional SEC analysis of two PVA Samples... 

The results found in this work indicate that SEC/LALLS can be used to obtain qualitative data about polymer branching. 

Since the SEC/LALLS technique always yields a weight-average molecular weight (l )y for the slightly polydisperse fraction at V, a small overestimation of the sample Rn is expected (, 1 ). As noted previously (Results) a 1% to decrease in the narrow MWD polystyrene Mp values (Table I) accompanied application of the band-spreading correction ... 

Table II shows that for SRM 706 good agreementis obtained between SEC/LALLS and conventional SEC sample My, and Rp values when the band-spreading correction was used. However, the NBS 706 polydispersity index (Ry/Rp) given by the supplier (ca. 2.1) does not agree with that 1.°) found here using the SEC/LALLS and conventional SEC techniques. Insensitivity of the LALLS detector to a small amount of low molecular weight material may account for a larger sample R however, this is not supported by the conventional SEC data. The reason for the discrepancy remains unclear.

In SEC/LALLS, the molecular weight measured at any instant is (M ). Thus the sample M can be calculated by the standard definition... 

Fig. 27. Molar mass dependence of [rj] for a fractionated comb macromolecule. The fractionation was made with a SEC/LALLS/VISC set-up. The comb macromolecule consists oi a polyimidazole backbone prepared by free radical polymerization. The imidazol side groups acted in a melt with phenylglycidylether and phthalic anhydride as multifunctional initiator for the anionic growth of polyester chains. The straight lines correspond to the behavior of unattached polyester chains and the comb polymers at low and high molar masses respectively [136]...

This section on the contraction factor may be concluded with an example of a comb macromolecule [136]. Due to the route of preparing this comb, unattached side chains also occurred in the system. Figure 27 shows the result of the molar mass dependence of [rj] which was obtained from a SEC/LALLS/VISC fractionation. One observes at low molar masses a straight line with an exponent of 11 =0 JO that coincides with the exponents of linear side chains. It follows a... 

The observations and questions raised by these workers helped stimulate the experiments which are presented here. In this work, size exclusion chromatography with low angle laser light scattering detection (SEC/LALLS) was used to probe the distribution of branching functionality in multiarm macromolecules of styrene/isoprene and styrene/buta-... 

Branching Parameter g from. SEC/LALLS. The effect of polymer branching upon the dilute solution configuration of polymers is conveniently expressed as the ratio of intrinsic viscosities of branched and linear polymers of the same chemical composition and molecular weight (35), i.e.. 

SEC System, Data Processing, and Chromatography Procedures. The SEC/LALLS system contained a Model IlOA pump (Altex), Model 7125 injector (Rheodyne), KMX-6 Low-Angle Laser Light Scattering Photometer (LDC/Milton Roy), and a Model 98.00... 

Mass recovery of MA samples was checked by using the concentration (DRl) detector response (mass/area ratio) of the corresponding LB arm it was assumed that the detector response was identical for compositionally similar samples. Corrections for 38% and 9% sample loss were applied to the "mass injected" in the SEC/LALLS data for (Sl-1) DVB and (Sl-2) DVB, respectively. 

Sample Solvent Meas. Calc. SEC/LALLS Static LALLS (mol cm3/gm2)... 

In cases where static LALLS results were obtained for the DVB-linked samples, poor agreement was found with SEC/LALLS. In both cases sh n in Table I ((Sl-4) DVB) and ((SB-1) E B), the SEC/LALLS Mw is considerably less than the off-line Mw The concentration detector (DRl) response showed no significant sample loss ("Experimental") following injection, and this discrepancy possibly results from breakup of sample aggregates during chromatography ("Discussion", below). 

Figure 1. SEC/LALLA data for K1107- Peak S is "kill" polystyrene, while peaks SI, SIIS, and (SIIS) are block copolymer, coupled block copolymer, and an unsown high molecular weight species, respectively Values of M from SEC/LALLS are 8.26 x 10 and 2.79 x 10 for SI and(sYlS). ...

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